SOLAR TRACKER, AND METHOD FOR OPERATING SAME

Abstract

The present invention relates to a solar tracker and to a method for operating same, capable of controlling the azimuth and elevation in accordance with the changing portion of the sun in the celestial sphere by the diurnal motion and annual motion so as to enable solar energy collection apparatuses to track the travel of the sun for a long period of time. The solar tracker according to the present invention is provided with two rotating shafts which are responsible for the right ascension and declination, respectively, wherein the movements of the rotating shafts are not independent from each other. One rotating shaft moves in dependence on the other rotating shaft, wherein the dependent relationship is mechanically constrained according to the correlation between the diurnal motion and annual motion of the sun. As a result, the tracker of the present invention can track the diurnal motion of the sun with a single actuator and, at the same time, compensate the annual motion which changes in the meridian altitude according to the change of seasons. The solar tracker and the method for operating same in accordance with the present invention, enables the tracking of the diurnal motion and annual motion of the sun using one actuator, thereby maximizing solar power generation efficiency and reducing initial installation costs and maintenance costs.

Description

TECHNICAL FIELD

The present invention relates to a solar tracker, and more particularly, to a solar tracker and a method of operating the solar tracker that may adjust an azimuth and an altitude based on a change in a position of the Sun by a diurnal motion and an annual motion, in order for a solar energy collector to track a path of the Sun moving on the celestial sphere for a long period of time.

BACKGROUND ART

A solar tracker is designed to adjust each rotation shaft of a mechanism to adjust an azimuth and an altitude for a light collector to be positioned perpendicularly to the Sun and maintain an optimal efficiency. Based on a degree of freedom (DOF) of the mechanism, the solar tracker may be classified into a 1-DOF solar tracker and a 2-DOF solar tracker. In general, a DOF of a mechanism is identical to the number of rotation shafts used for a solar tracker and thus, the 1-DOF and the 2-DOF solar tracker may be simply referred to as a 1-shaft system and a 2-shaft system instead of using the technical term “DOF.”

In a conventional solar tracker according to conventional technology, the 1-shaft system may track the Sun on a daily basis while rotating from east to west preferentially based on a diurnal motion of the Sun, and manually correct a meridian altitude of the Sun that changes annually. However, such a manually correcting method may be inconvenient. In addition, although the manually correcting method is quarterly performed, for example, four times a year, a maximum value of a potential tracking error may reach approximately 23.5° which corresponds to the Earth's rotational axial tilt. In terms of tracking the diurnal motion of the Sun, a maximum error angle that may occur due to an annual motion of the Sun may be greater than an error that may occur when the solar tracker fails to track the Sun for approximately one and a half hours, 90 minutes, in tracking the diurnal motion of the Sun on a daily basis while rotating from east to west.

The 2-shaft system may considerably reduce an error of the solar tracker by automatically adjusting a change in a meridian altitude occurring due to the annual motion of the Sun in addition to the diurnal motion of the Sun. However, an additional actuator and controller may be used and thus, initial equipment costs may increase, and power consumption and maintenance costs of the added actuator and controller may be required. Thus, the solar tracker may be utilized advantageously in economical terms only when a gain earned from improved generation efficiency greatly exceeds the added costs. However, in actuality, implementing the 2-shaft system which is economically advantageous and, at the same time, performs a reliable operation may not be readily achieved due to added initial costs and maintenance costs for frequent breakdowns.

DISCLOSURE OF INVENTION

Technical Goals

An aspect of the present invention provides a solar tracker and a method of operating the solar tracker to solve such issues described in the foregoing. The solar tracker is provided with two rotation shafts which are responsible for a right ascension and a declination, respectively, and do not operate independently from each other. For example, one rotation shaft may be mechanically dependent on the other rotation shaft. The two rotation shafts may have a dependent relationship and move in accordance with a correlation between a diurnal motion and an annual motion of the Sun. Thus, the solar tracker may track the diurnal motion of the Sun through a single actuator and also automatically correct the annual motion in which a meridian altitude changes depending on a solar term.

Technical Solutions

According to an aspect of the present invention, there is provided a solar tracker including a right ascension rotation shaft installed in parallel with the Earth's rotation axis and configured to track a change in a right ascension occurring due to a diurnal motion of the Sun, a right ascension rotation actuator configured to actuate the right ascension rotation shaft, a declination rotation shaft perpendicular to the right ascension rotation shaft and configured to correct a change in a declination occurring due to an annual motion of the Sun, and a declination actuation mechanism configured to transfer a portion of driving power of the right ascension rotation actuator to the declination rotation shaft to allow the declination rotation shaft to reciprocatingly rotate upwards and downwards.

The declination actuation mechanism may include additional components to be described hereinafter to enhance efficiencies.

The declination actuation mechanism may include a one-way clutch installed at a point in a power transfer path from the right ascension rotation actuator to the declination rotation shaft, and configured to selectively transfer, to the declination rotation shaft, only an amount of rotation used for the right ascension rotation shaft to track the diurnal motion of the Sun in the daytime by transferring a one-way rotation component of the driving power generated from the right ascension rotation actuator.

The declination actuation mechanism may include a reduction ratio adjuster installed at one point in the power transfer path from the right ascension rotation actuator to the declination rotation shaft, and configured to adjust a cycle of one reciprocating up and down rotational motion of the declination rotation shaft and to precisely match the cycle of the reciprocating up and down rotational motion of the declination rotation shaft to a cycle of tracking approximately 365 times of the diurnal motion by the right ascension rotation shaft.

The declination actuation mechanism may include a coupling installed at one point in the power transfer path from the right ascension rotation actuator to the declination rotation shaft, and configured to selectively connect or block a dependent relationship between the right ascension rotation shaft and the declination rotation shaft and to independently adjust the declination rotation shaft without affecting the right ascension rotation shaft.

The declination actuation mechanism may be designed to allow the declination rotation shaft to reciprocatingly rotate with a displacement of the Earth's rotational axial tilt while the right ascension rotation shaft tracks the diurnal motion approximately 365 times, based on a correlation between the diurnal motion and the annual motion of the Sun. For the designing, the declination actuation mechanism may include a declination reducer configured to receive a portion of the driving power of the right ascension rotation actuator, convert a rotation ratio, and output the converted rotation ratio, a crank attached to an output shaft of the declination reducer, a rocker fixed to the declination rotation shaft and reciprocatingly rotating upwards and downwards at the Earth's rotational axial tilt based on the change in the declination occurring due to the annual motion of the Sun, and a connecting rod connecting one end of the crank to one end of the rocker to form a four-bar linkage and configured to convert a rotational motion of the crank to the reciprocating up and down rotational motion of the rocker.

In designing the declination actuation mechanism using the four-bar linkage, the crank, the rocker, or the connecting rod may include an adjuster configured to adjust a location of a joint or a link length to change a motional displacement and a sectional speed of the reciprocating up and down rotational motion of the declination rotation shaft.

Further, to verify whether the solar tracker tracks the annual motion, the solar tracker may include a declination display device configured to convert an amount of rotation of the declination rotation shaft to an angle and display the angle, or a solar term display device configured to convert the amount of rotation to a solar term of a year and display the solar term.

Effects of Invention

According to example embodiments, a solar tracker disclosed herein may simultaneously track a diurnal motion and an annual motion of the Sun through a single actuator and thereby, maximizing solar power generation efficiency while reducing initial installation costs and maintenance costs.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates an example of a solar tracker according to an embodiment of the present invention.

FIG. 2 illustrates a diurnal motion of the Sun in the spring equinox which is observed at a point in the northern hemisphere.

FIG. 3 illustrates a change in a meridian altitude of the Sun in the spring equinox based on an observation point in the northern hemisphere.

FIG. 4 illustrates a change in a meridian altitude and in a diurnal motion of the Sun based on a season which is observed at a point in the northern hemisphere.

FIG. 5 illustrates a change in a meridian altitude based on a latitude and a season.

FIG. 6 illustrates a declination of the Sun that changes along the ecliptic in an equatorial coordinate system, and an operation principle of a solar tracker according to an embodiment of the present invention.

FIG. 7 illustrates an example of a support and a pillar capable of adjusting an altitude and an azimuth of a right ascension rotation shaft according to an embodiment of the present invention.

FIG. 8 illustrates an example of designing a frame of a solar tracker, and 2-degrees of freedom (DOF) equivalent apparatus according to an embodiment of the present invention.

FIG. 9 illustrates an example of utilization of a balance weight to equally allocate a load to rotation shafts of a solar tracker according to an embodiment of the present invention.

FIG. 10 illustrates an example of designing a right ascension rotation actuator of a solar tracker according to an embodiment of the present invention.

FIG. 11 illustrates an example of designing a declination actuation mechanism of a solar tracker according to an embodiment of the present invention.

FIG. 12 illustrates an example of a change in an angle of a light collector holder by a declination actuation mechanism of a solar tracker based on a solar term according to an embodiment of the present invention.

FIG. 13 illustrates an example of including a coupling, a one-way clutch, or a reduction ratio adjuster in a declination actuation mechanism according to an embodiment of the present invention.

FIG. 14 illustrates an example of a diurnal operation and a nocturnal operation of a solar tracker based on a solar term according to an embodiment of the present invention.

FIG. 15 illustrates an example of including a solar term display device, or a declination display device or a right ascension display device in a solar tracker according to an embodiment of the present invention.

FIG. 16 is a flowchart illustrating an example four-step method of operating a solar tracker according to an embodiment of the present invention.

FIG. 17 is a flowchart illustrating an example seven-step method of operating a solar tracker according to an embodiment of the present invention.

BEST MODE FOR CARRYING OUT INVENTION

Before describing fundamental examples and various modified examples of a solar tracker 1000 disclosed herein, a correlation between a diurnal motion and an annual motion of the Sun a01 will be described first. Reference numerals used throughout are defined as follows.

1000: Solar tracker 100: Right ascension rotation shaft

200: Right ascension rotation actuator 210: Actuator

220: Right ascension reducer 300: Declination rotation shaft

400: Declination actuation mechanism 410: Declination reducer

420: Reciprocating rotation conversion mechanism 421: Crank

422: Rocker 423: Connecting rod

424: Joint location and link length adjuster 430: Coupling

440: Reduction ratio adjuster 450: One-way clutch

460: Declination display device 470: Solar term display device

480: Right ascension display device 500: Frame

510: Support 520: Pillar

530: Right ascension rotation support 540: Declination rotation support

550: Light collector holder 560: Balance weight

600: Light collector

a01: Sun a02: Earth

a03: Sunlight a04: Diurnal motion path of the Sun

a05: Earth's rotational axial tilt (approximately 23.5°)

a10: Equatorial coordinate system

a11: Right ascension a12: Declination

a13: Celestial axis a15: North celestial pole

a16: South celestial pole a17: Equatorial plane

a18: Ecliptic a19: Celestial sphere

a20: Horizontal coordinate system a21: Azimuth

a22: Altitude a23: Meridian altitude

a24: Meridian a25: South point

a26: North point a27: East point

a28: West point a29: Horizontal plane

a30: Earth coordinate system a31: Longitude

a32: Latitude a33: Colatitude

a34: Earth's rotation axis a35: North Pole

a36: South Pole a37: Equator

a40: Solar term a41: Spring equinox (solar term)

a42: Summer solstice (solar term) a43: Autumn equinox (solar term)

a44: Winter solstice (solar term)

a45: Spring equinoctial point (position on the celestial sphere)

a46: Summer solstice point (position on the celestial sphere)

a47: Autumn equinoctial point (position on the celestial sphere)

a48: Winter solstice point (position on the celestial sphere)

a51: Earth's rotation a52: Earth's revolution

a53: Annual motion of the Sun a54: Diurnal motion of the celestial sphere

a55: Rotational motion of a right ascension rotation shaft to track a diurnal motion

a56: Reciprocating rotational motion of a declination rotation shaft to compensate for an annual motion

L0: Base link L1: First link

L2: Second link J1: First joint

J2: Second joint

A change in an azimuth a21 and an altitude a22 of the Sun a01 to be observed along a horizontal coordinate system a20 results from rotation and revolution of the Earth a02. As illustrated in FIG. 2, in a diurnal motion of the Sun 01 on the celestial sphere which is observed from a horizontal plane a29, when the Earth a02 makes one rotation for a day, an azimuth a21 of the Sun a01 changes from east to west on the horizontal plane a29, an altitude a22 of the Sun a01 gradually increases to reach a zenith around noon and gradually decreases afterwards to disappear below the horizontal plane a29 in the evening. The Sun a01 then rises in the east again after the Earth a02 revolves to an opposite side. Around noon, an angle at which an altitude a22 of the Sun a01 increases to the zenith based on a south point a25 while the Sun a01 is passing a meridian a24 is referred to as a meridian altitude a23.

As illustrated in FIG. 3, sunlight a03 is incident, almost parallel, to any points of the Earth a02 because a distance between the Sun a01 and the Earth a02 is far greater than a diameter of the Earth a02. The sunlight a03 to be horizontally incident is observed at different angles from each point of the Earth a02. Although an altitude a22 of the Sun a01 to be observed in proximity to the equator a37 moves along a high path passing adjacent to the zenith, an altitude a22 of the Sun a01 to be observed decreases as a latitude a32 increases. Thus, the Sun a01 observed in polar regions, for example, a North Pole a35 and a South Pole a36, performs the diurnal motion along a low path passing adjacent to the horizon. As described in the foregoing, the meridian altitude a23 varies depending on a latitude a32 of an observation point. Contrary to a case of the northern hemisphere, in a case of the southern hemisphere, a diurnal motion path a04 of the Sun a01 passes through the northern sky in lieu of the southern sky. In addition, when observing the meridian altitude a23 based on the south point a25, a value of the meridian altitude a23 exceeds 90° passing the zenith. Thus, in such a case, using an altitude of lower culmination based on a north point a26 may be desirable. Unless otherwise specified, example embodiments will be described based on the northern hemisphere, and the solar tracker 1000 may be identically applicable when a corresponding observed value is applied to the case of the southern hemisphere.

The diurnal motion of the Sun a01 may vary depending on a latitude a32 of an observation point, and a meridian altitude a23 may change based on a colatitude a33, which is a value obtained by subtracting a latitude a32 of an observation point from 90°. Here, a meridian altitude a23 of the Sun a01 to be observed from the Earth a02 may vary depending on where the Earth a02 is positioned in a revolution orbit in addition to a latitude a32 of an observation point. This is due to the Earth's rotation axis a34 being tilted at approximately 23.5° against a revolution axis. Although the tilted angle of the Earth's rotation axis a34 is invariant, a relative tilt direction with respect to the Sun a01 varies depending on the position of the Earth a02 while the Earth a02 revolves around the Sun a01 and thus, affects a meridian altitude a23 of the Sun a01 to be observed at an observation point of the Earth a02.

FIG. 4 illustrates a correlation between the relative tilt direction of the Earth's rotation axis a34 and a meridian altitude a23 in revolution of the Earth a02. The correlation is illustrated in detail with an example of a region in the northern hemisphere. In a region in the northern hemisphere, when a direction of the Earth's rotation axis a34 is tilted for the northern hemisphere to face the Sun a01, the diurnal motion path a04 of the Sun a01 rises and a meridian altitude a23 increases and thus, a density of solar energy arriving per unit area of the horizontal plane a29 increases. Thus, a temperature of the region is maintained to be high around the summer solstice a42 in which a meridian altitude a23 becomes a maximum. In the region, such a season is classified as summer. Conversely, on a cycle of revolution of the Earth a02, when the Earth's rotation axis a34 is tilted for the northern hemisphere to be less exposed to the Sun a01, a meridian altitude a23 decreases. Thus, a temperature of the region is maintained low around the winter solstice a44 in which a meridian altitude a23 becomes a minimum. In the region, such a season is classified as winter.

As illustrated in FIG. 4, the diurnal motion path a04 of the Sun a01 changes based on a season. Each diurnal motion path a04 is generated along a circumference of a circular disk perpendicular to the Earth's rotation axis a34 on the celestial sphere a19, and circular disks including each diurnal motion path a04 are parallel to one another. In the spring equinox a41 or the autumn equinox a43, the diurnal motion path a04 of the Sun a01 is generated along the equatorial plane a17 on the celestial sphere a19. Here, the diurnal motion path a04 is precisely divided, in half, into a path exposed above the horizontal plane a29 and a path remaining in an opposite side of the Earth a02. Thus, a period of time during which the Sun a01 remains in the sky until the Sun a01 disappears to the west after rising in the east is a half of the day. In the summer solstice a42, the path exposed above the horizontal plane a29 in the circular disk perpendicular to the Earth's rotation axis a34 is longer, and a period of time during which the Sun a01 remains in the sky until the Sun a01 disappears to the northwest after rising in the northeast is greater than or equal to 12 hours. In the winter solstice a44, the path exposed above the horizontal plane a29 in the circular disk perpendicular to the Earth's rotation axis a34 is shorter, and a period of time during which the Sun a01 remains in the sky until the Sun a01 disappears to the southwest after rising in the southeast is less than or equal to 12 hours. As a latitude a32 increases and, that is, a colatitudes a33 decreases, such a change in the diurnal motion path a04 may be further discovered. For example, in an Arctic region of the North Pole, where a colatitudes a33 is lower than the Earth's rotational axial tilt a05, a direction of the Earth's rotation axis a34 is nearly perpendicular to the horizontal plane a29 and the diurnal motion path a04 of the Sun a01 is close to a circumferential motion moving along the horizon. In the summer solstice a42, a situation in which a polar day or a white night during which the Sun a01 does not disappear from the sky and stays around the horizon all day may occur. In the winter solstice a44, a polar night that the night lasts all day while the Sun a01 rotates below the ground may occur.

FIG. 5 illustrates a change in a meridian altitude a23 by an annual motion of the Sun a01. Although the change is the same at any observation point on the Earth a02, the change occurs based on different reference values based on a latitude a32 of an observation point. A meridian altitude a23 increases starting from the spring equinox a41 and reaches a maximum in the summer solstice a42. Afterwards, the meridian altitude a23 gradually decreases and returns to the same level as in the spring equinox a41 in the autumn equinox a43, and gradually decreases again to reach at a minimum in the winter solstice a44. Afterwards, the meridian altitude a23 increases again and recovers an original level in the spring equinox a41. Although a reference value of the change in the meridian altitude a23 based on a solar term a40 varies depending on an observation point, a cycle and a displacement of the change are the same. That is, the cycle of the change in the meridian altitude a23 is approximately 365 days during which the Earth a02 revolves around the Sun a01. More accurately, the cycle is approximately 365.24219 days based on a solar time. In a case of the displacement of the change in the meridian altitude a23, a maximum displacement occurring in the summer solstice a42 and the winter solstice a44 may be equal to the Earth's rotational axial tilt a05. That is, when the Earth a02 makes one revolution around the Sun a01 as one year progresses, the diurnal motion of the Sun a01 observed from the Earth a02 occurs approximately 365 times, and a meridian altitude a23 of the Sun a01 observed from the Earth a02 gradually changes each day to pass through a maximum point and a minimum point depending on a solar term a40 and to return to an original level of the meridian altitude a23, which forms one cycle of an annual motion. Here, a difference between the maximum point and the minimum point based on the reference value is approximately 23.5°, which is the Earth's rotational axial tilt a05. The change in the meridian altitude a23 of the Sun a01 at each observation point may be expressed as Equation 1.

Change in meridian altitude=reference value+change by annual motion=90−latitude of observation point−change by annual motion  [Equation 1]

For example, at an observation point located on the equator a36, a meridian altitude a23 changes, depending on a season, from a maximum 113.5° to a minimum 66.5° based on 90° obtained by subtracting 0°, which is a latitude a32 of the equator a36, from 90°. For another example, at an observation point located at the North Pole a35, a meridian altitude a23 changes from a maximum 23.5° to a minimum −23.5° based on 0° obtained by subtracting 90° , which is a latitude a32 of the North Pole a35, from 90°. That is, a phenomenon called a polar night during which the Sun a01 is not observed may occur as the Sun a01 stays on the horizon in spring and autumn and is positioned below the ground for six months as winter progresses.

In an academic expression of a latitude a32 of an observation point, various expressions of the latitude a32 include a geodetic latitude, a geocentric latitude, and a geographic latitude. In Equation 1, an error may not be significant despite use of the geodetic latitude expressed by simplifying an ellipsoid of the Earth a02 to be a sphere. Although Equation 1 uses a latitude a32 which is generally used in a geographical coordinate system, using a colatitude a33 in lieu of a latitude a32 may be more desirable in a case of using a spherical coordinate system for mathematics. In the case of using the spherical coordinate system for mathematics, Equation 1 may be expressed as Equation 2.

Change in meridian altitude=colatitude of observation point+change by annual motion  [Equation 2]

The change occurring due to the annual motion of the Sun a01 in Equations 1 and 2 may be represented as a periodic function similar to a trigonometric function as illustrated in FIG. 5. A meridian altitude a23 passes through a reference altitude corresponding to a colatitude a33 of an observation point in the spring equinox a41 and monotonically increases to have a maximum value in the summer solstice a42. A maximum displacement of the meridian altitude a23 is equal to the Earth's rotational axial tilt a05. Afterwards, the meridian altitude a23 monotonically decreases, and returns to an original reference altitude and is inflected in the autumn equinox a43 to have a minimum value in the winter solstice a44. An angular displacement of the meridian altitude a23 is also equal to the Earth's rotational axial tilt a05. Afterwards, the meridian altitude a23 increases again and returns to an original altitude in the spring equinox a41. The annual motion of the Sun a01 may be expressed as in Equation 3 through approximation based on a trigonometric function.

Change by annual motion=Earth's rotational axial tilt×sin(360°×(observation day−spring equinox day/365 days))  [Equation 3]

The change in the meridian altitude a23 of the Sun a01 by the annual motion based on the trigonometric function, which is finally obtained by substituting Equation 3 for Equation 2, may be expressed as in Equation 4.

Change in meridian altitude=colatitude of observation point+Earth's rotational axial tilt×sin(360°×(observation day−spring equinox day/365 days))  [Equation 4]

Equation 4 expresses a macroscopic change through approximation. Thus, to express a more precise change, various variables need to be included therein. For example, a difference in a revolution speed, or an orbital speed, between a perihelion and an aphelion which occurs because a revolution orbit of the Earth a02 is not a complete circle but an ellipse may be considered. In consideration of an error of mechanical components included in a general type of the solar tracker 1000, factors that may have insignificant influence may be ignored from an engineering perspective.

For describing a position of a celestial body including the Sun a01, using an equatorial coordinate system a10 based on a right ascension a11 and a declination a12 may be more convenient than using a horizontal coordinate system a20 based on an azimuth a21 and an altitude a22. In comparison to the revolution orbit of the Earth a02, celestial bodies such as stars and galaxies astronomically observed may exist, in general, hundreds of distance further than a distance between the Sun a01 and the Earth a02. Thus, a general position of a celestial body is scarcely affected by the revolution of the Earth a02, and the position of the celestial body may be expressed as a fixed point on the celestial sphere a19 using the equatorial coordinate system a10. The Sun a01 and a planet in the solar system have a relatively shorter distance compared to the revolution orbit of the Earth a02 and thus, a position of the Sun a01 and the planet may change on the celestial sphere a19. As illustrated in FIG. 6, the Sun a01 moves along the ecliptic a18 tilted by the Earth's rotational axial tilt a05 from the equator plane a16 on the celestial sphere a19, in accordance with the revolution of the Earth a02.

Brief descriptions of an apparatus and a device used in a field of astronomy and space will be provided to assist the reader in gaining a comprehensive understanding of the solar tracker 100 described herein. Most astronomical devices used to observe stars, galaxies, nebulae, and the like adopt the equatorial coordinate system a10 to continuously track a celestial body and readily observe such a celestial body. As illustrated in FIG. 6, in the equatorial coordinate system a10 which is a method of the celestial coordinate system, positions of celestial bodies fixed on the celestial sphere a19, which is an imaginary term indicating a huge sphere fixed in space and surrounding the Earth a02, are defined through spherical coordinates. The equatorial coordinate system a10 is a method of expressing a position of a celestial body on the celestial sphere a19 based on a right ascension a11 measured in a west-east direction from a starting point, which is the spring equinoctial point a45 at which the equatorial plane a17 meets the ecliptic a18 on the celestial sphere a19, and based on a declination a12 obtained by measuring an angle in a direction of the celestial axis a13 extending the Earth's rotation axis a34 from the equatorial plane a17 of the celestial sphere a19 to the celestial sphere a19. As described in the foregoing, in observing a celestial body such as galaxies and constellations, an azimuth a21 and an altitude a22 may change depending on an observation point when using the horizontal coordinate system a20. However, a right ascension a11 and a declination a12 may be expressed as a fixed value irrespective of an observation point when using the equatorial coordinate system a10. Thus, a celestial body map arranged based on a right ascension a11 and a declination a12 is widely used in the field of astronomy, and an observer may more readily find a target celestial body within a view of a telescope by installing an astronomical telescope in an equatorial mount and adjusting a right ascension a11 and a declination a12.

The Earth a02 rotates one time each day on the celestial sphere a19 fixed in space. To eyes of an observer in the Earth a02, constellations on the celestial sphere a19 appear to gradually rotate from east to west based on a time. Such a rotation is referred to as a diurnal motion of a celestial body. A speed of the rotation corresponds to a rotation speed of the Earth a02, and the diurnal motion is performed at an angular velocity of approximately 15° per hour. Thus, although an observer finds one constellation in the wide night sky, the constellation appears to gradually flow to the west. Such a phenomenon may be more readily observed when magnifying a narrow area through an astronomical telescope. Although an observer secures a target celestial body to be observed within a view of the observer, the secured target celestial body may immediately disappear from the view when the observer fails to move a direction of the telescope from east to west. In a case of a general type telescope adjusting an azimuth a21 and an altitude a22, simultaneously adjusting two rotation shafts is required to track a celestial body performing a diurnal motion. In a case of a telescope using an equatorial mount, an observer may conveniently observe a celestial body for a long period of time while offsetting a diurnal motion of the celestial body as illustrated in FIG. 6 by gradually turning a rotation shaft for a right ascension a11 while fixing a rotation shaft for a declination a12.

When observing the Sun a01, dissimilar to other celestial bodies, a position of the Sun a01 gradually changes on the celestial sphere a19, the Sun a01 gradually moves along the ecliptic a18 and makes one revolution along the celestial sphere a19 each year. A speed of the revolution of the Sun a01 around the celestial sphere a19 is merely less than or equal to approximately 1° per day and thus, may be ignored when observing the Sun a01 for a short period of time. That is, when observing the Sun a01, the Sun a01 may be observed by ignoring a change in a declination a12 and fixing the rotation shaft for a declination a12, and gradually turning only the rotation shaft for a right ascension a11. However, when observing the Sun a01 for a long period of time, errors may be accumulated as days pass and thus, handling such an issue is necessary. Thus, offsetting the diurnal motion by turning the rotation shaft for a right ascension a11 and simultaneously offsetting the annual motion by turning the rotation shaft for a declination a12 is required without ignoring a change in the declination a12 of the Sun a01. The change in the declination a12 of the Sun a01 by the annual motion occurs while the Sun a01 travels along the ecliptic a18 titled on the celestial sphere a19. Such a change corresponds to the change in the meridian altitude a23 represented in Equation 3.

The solar tracker 1000 according to example embodiments of the present invention will be described in detail with reference to FIG. 1. The solar tracker 1000 is specially designed to daily track a change in a right ascension a11 of the Sun a01 occurring due to a diurnal motion, and also automatically correct a change in a declination a12 of the Sun a01 occurring due to an annual motion, in order to solve an error of the declination a12 accumulated for a long period of time. Based on a correlation between the right ascension a11 and the declination a12 of the Sun a01 traveling along the ecliptic a18 on the celestial sphere a19, the solar tracker 1000 includes a declination actuation mechanism 400 that may allow a right ascension rotation shaft 100 and a declination rotation shaft 300 to be in a mechanically dependant relationship to track the diurnal motion of the Sun a01 by rotating the right ascension rotation shaft 100 through a right ascension rotation actuator 200 and to automatically compensate for the change in the declination a12 of the Sun a01 by transferring a portion of rotational power of the right ascension rotation actuator 200 to the declination rotation shaft 300.

The solar tracker 1000 includes the right ascension rotation shaft 100, the right ascension rotation actuator 200, the declination rotation shaft 300, and the declination actuation mechanism 400. Hereinafter, these components will be described in detail, and an applicable method using additional components to improve convenience of example embodiments of the present invention will also be described in detail.

FIG. 1 illustrates an example of the solar tracker 1000 according to an embodiment of the present invention. Main components to be connected from the ground up to a solar light collector 600 are described as follows. A support 510 is fixed to the ground and a pillar 520 is connected thereto, and at an end thereof a right ascension rotation support 530 is installed at a suitably tilted angle. The right ascension rotation shaft 100 is installed in the right ascension rotation support 530, and a declination rotation support 540 is connected thereto for unrestricted rotation. The declination rotation support 540 and a light collector holder 550 are installed to enable the unrestricted rotation through the declination rotation shaft 300, and the light collector 600 is attached to the light collector holder 550. The right ascension rotation actuator 200 is provided to actuate the right ascension rotation shaft 100, and the declination actuation mechanism 400 is provided to transfer a portion of driving power of the right ascension rotation actuator 200 to the declination rotation shaft 300.

The example illustrated in FIG. 1 is mechanically equivalent to 2-degrees of freedom (DOF) series-type two-bar linkage, which is illustrated in (b) of FIG. 8. That is, the support 510, the pillar 520, and the right ascension rotation support 530 are formed to be a base link L0 as a single rigid body connected to the ground, and the declination rotation support 540 is formed to be a first link L1 and the light collector holder 550 functions as a second link L2. The right ascension rotation shaft 100 and the declination rotation shaft 300 operate as a first joint J1 connecting the base link L0 to the first link L1 and as a second joint J2 connecting the first link L1 to the second link L2, respectively. As described in the foregoing, a mechanical form of the solar tracker 1000 adopts a 2-DOF mechanism, and in actuality, is defined as a 1-DOF mechanism because the first joint J1 and the second joint J2 operate dependently on each other and make dependent movements. Hereinafter, a method of installing and connecting components included in the links L0, L1, and L2, and the joints J1 and J2 will be described first, and a method of dependently actuating the right ascension rotation shaft 100 and the declination rotation shaft 300 corresponding to the joint J1 and the joint J2 will be described in detail.

According to example embodiments, a frame 500 is formed to allow the right ascension rotation shaft 100 to be installed in parallel with the Earth's rotation axis a34, and allow the declination rotation shaft 300 to be installed perpendicularly to the right ascension rotation shaft 100. Thus, the frame 500 is formed to robustly support the two rotation shafts so that the two rotation shafts smoothly move in predetermined directions. The frame 500 includes the support 510, the pillar 512, the right ascension rotation support 530, the declination rotation support 540, and the light collector holder 550. The support 510 and the pillar 520 include an adjuster configured to adjust an azimuth a21 and an altitude a22 to install the right ascension rotation shaft 100 to be parallel with the Earth's rotation axis a34. An example of using one pillar 520 will be described with reference to (a) of FIG. 7. After solidifying the ground and installing the support 510 on which screw holes are processed and fixing the support 510 to the ground, the pillar 520 is set up on the support 510 fixed to the ground. Here, bolts are fastened along the screw holes on a side face of the support 510 to change an azimuth a21 for the pillar 520 to face north and to readily adjust the right ascension rotation shaft 100 to be parallel with the Earth's rotation axis a34.

The right ascension rotation support 530 is installed on the pillar 520 and the right ascension rotation shaft 100 is fixed. Here, an adjuster configured to adjust an altitude a22 of the right ascension rotation shaft 100 is provided based on a latitude a32 of an installation location. As illustrated in FIG. 7, rotation is enabled when the pillar 520 is connected to the right ascension rotation support 530, and screw holes are processed on a flange to fix the right ascension rotation support 513 to the pillar 520 with the right ascension rotation support 530 suitably tilted based on the latitude a32 of the installation location. Thus, as illustrated in FIG. 6, a direction of the Earth's rotation axis a34 and a direction of the right ascension rotation shaft 100 are formed to be parallel with each other based on the latitude a34 of the installation location by adjusting a rotation direction of the pillar 520 fixed to the support 510 and a tilt of the right ascension rotation support 530.

As illustrated in (b) of FIG. 7, the frame 500 is formed using two pillars 520, for example, a pillar 520a and a pillar 520b. The two pillars 520a and 520b are set up on the support 510, and both ends of the right ascension rotation shaft 100 are connected to the two pillars 520a and 520b. To adjust an azimuth a21 of the right ascension rotation shaft 100, the two pillars 520a and 520b are adjusted to accurately face a south-north direction while the pillar 520a or the pillar 520b moves to an east-west direction. To adjust an altitude a22 of the right ascension rotation shaft 100, a height of the pillar 520a or the pillar 520b is adjusted to suitably change an angle formed between the right ascension rotation shaft 100 and the ground. In a case of the northern hemisphere, a height of the pillar 520b in the north is installed to be higher than a height of the pillar 520a in the south based on a latitude a32. Conversely, in a case of the southern hemisphere, the height of the pillar 520b in the north is fixed to be lower than the height of the pillar 520a in the south. Here, the right ascension rotation shaft 100 may be bent while changing the height of the pillar 520a or the pillar 520b. In such a case, a deformation by the bending may be resolved by forming the pillars to be rotatable in a direction towards which the right ascension rotation shaft 100 is deflected at both ends thereof.

Examples of the support 510 and the pillar 520 are provided herein, and variously modified examples that may adjust an azimuth a21 and an altitude a22 of the right ascension rotation shaft 100 may be applicable.

According to an embodiment, the right ascension rotation shaft 100 is installed in parallel with the Earth's rotation axis a34, and is configured to offset a diurnal motion of the Sun a01 occurring due to rotation of the Earth a02 and to track a position of the Sun a01 that rises in the east and sets in the west every day while rotating in an opposite direction to a direction of the rotation of the Earth a02 at an angular velocity corresponding to the rotation of the Earth a02. In addition, the declination rotation shaft 300 is installed perpendicularly to the right ascension rotation shaft 100 and positioned in parallel with the equatorial plane a17 of the celestial sphere a19, and is configured to offset an annual motion of the Sun a01 occurring due to revolution of the Earth a02 and to compensate for a change in a meridian altitude a23 of the Sun a01 that occurs depending on a solar term a40 as illustrated in FIG. 4 while in turn rotating upwards and downwards at the Earth's rotational axial tilt a05 based on a cycle of approximately 365 days.

As illustrated in FIG. 8, the right ascension rotation shaft 100 is installed at an end of the right ascension rotation support 530 fixed to the ground through the support 510 and the pillar 520, and the declination rotation support 540 is connected for unrestricted rotation. The declination rotation shaft 300 is installed in the declination rotation support 540 to be perpendicular to the right ascension rotation shaft 100, and the declination rotation support 540 is connected to the light collector holder 550 through the declination rotation shaft 300. When the declination rotation support 540 rotates along the declination rotation shaft 300, only an angle of a declination a12 may change without a change in an angle of a right ascension a11 to which the installed light collector 600 faces. In addition, when the right ascension rotation shaft 100 is installed in parallel with the Earth's rotation axis a34, only the angle of the right ascension a11 may change independently and the angle of the declination a12 may not change although the declination rotation support 540 rotates along the right ascension rotation shaft 100 and the attached light collector holder 550 and the installed light collector 600 rotate accordingly. Thus, coordinates of the right ascension a11 and the declination a12 on the celestial sphere a19 to which the attached light collector 600 faces may be independently adjusted and, further, unrestrictedly adjusted to all directions of the celestial sphere a19 by installing the right ascension rotation shaft 100 to correspond to the Earth's rotation axis a34 based on a location at which the solar tracker 1000 is installed and by adjusting each of the right ascension rotation shaft 100 and the declination rotation shaft 300 which are perpendicularly installed with respect to each other. FIG. 6 also illustrates an example of a case in which the right ascension rotation shaft 100 is installed in parallel with the Earth's rotation axis a34, and an operation principle of tracking a position fixed to the celestial sphere a19 for a long period of time while rotating in an opposite direction to a rotation direction of the Earth a02.

According to an embodiment, a balance weight 560 is configured to allow a load to be transferred to the right ascension rotation shaft 100 or the declination rotation shaft 300 to be balanced and thus, run the solar tracker 1000 using equal rotational power at any angle. Although the balance weight 560 may not be an integral component to implement functions of the present invention, the balance weight 560 may be useful to improve efficiency of the solar tracker 1000.

A load to be applied to the right ascension rotation shaft 100 and the declination rotation shaft 200 may vary depending on forms and weights of the declination rotation support 540, the light collector holder 550, the solar light collector 600, and various attached components. When the weights of such components are not suitably distributed from a center of each rotation shaft, driving power required due to a change in an angle of a rotation shaft may change. Thus, a considerable amount of driving power may be required for movement in an opposite direction despite an easy rotation to one direction and accordingly, efficiency of an actuator used may decrease.

Thus, the weights need to be suitably distributed along each rotation shaft to be well-balanced without being inclined to one side so that a rotation shaft may smoothly operate using an equal torque at any angles. In general, a weight of the solar light collector 600 accounts for a large portion of a total weight of the solar tracker 1000 and thus, structural balance may not be readily achieved. As illustrated in FIG. 9, a counter balancing weight which counterbalances a weight of an object having a great mass is installed in an opposite side to achieve a balance and allows each rotation shaft to smoothly rotate in each rotation shaft direction. A right ascension balance weight 561 having a suitable weight is attached to suitably distribute weights in both sides from a center of the right ascension rotation shaft 100, and a declination balance weight 562 having a suitable weight is attached to suitably distribute weights in both sides from a center of the declination rotation shaft 300 as necessary. When a whole mechanism is well-balanced from a center of rotation of each rotation shaft, equal torque may be applied to rotation at any angles and thus, each rotation shaft may smoothly rotate using a lower amount of power.

To implement the solar tracker 1000, a method of constructing a 2-DOF mechanism using the right ascension rotation shaft 100 and the declination rotation shaft 300 is described above. Hereinafter, a method of operating an entire mechanism with 1-DOF through a dependent relationship between two rotation shafts will be described in detail.

According to an embodiment, the right ascension rotation actuator 200 is configured to provide rotational power to the right ascension rotation shaft 100 so that the right ascension rotation shaft 100 may track a diurnal motion of the Sun a01 traveling from east to west every day on the celestial sphere a19 while traveling at an angular velocity of 15° per hour corresponding to a rotation velocity of the Earth a02.

The right ascension rotation actuator 200 will be described in detail with reference to an example illustrated in FIG. 10. The right ascension rotation actuator 200 includes an actuator 210 and a right ascension reducer 220. The actuator 210 of a rotating type is installed in the declination rotation support 450. The right ascension reducer 220 includes a right ascension direct connection reducer 221 directly connected to the actuator 210, and a right ascension worm gear 222 and a right ascension worm wheel 223. Rotational power generated from the actuator 210 is amplified through the right ascension direct connection reducer 221 to operate the right ascension worm gear 222. The right ascension worm gear 222 is interlocked with the right ascension worm wheel 223 fixed to the right ascension rotation support 530 to operate the declination rotation support 540 and thus, the right ascension reducer 220 rotates along the right ascension rotation shaft 100. As illustrated in FIG. 10, the actuator 210 is fixed to the declination rotation support 540 to readily implement the declination actuation mechanism 400 to be described hereinafter and thus, the actuator 210 rotates along with the declination rotation support 540. As necessary, the actuator 210 and the right ascension worm gear 222 are installed in the right ascension rotation support 530 and the right ascension worm wheel 223 is fixed to the declination rotation support 540 to design the actuator 210 not to move.

The right ascension rotation actuator 200 allows the right ascension rotation shaft 100 to rotate from east to west every day. A velocity of such a rotation needs to correspond to a rotation velocity of the Earth a02, for example, one round per day which is an angular velocity of approximately 15° per hour, and to output a torque to generate a sufficient acceleration force for rapid operation. Various rotating types of actuators 210 may be used as the actuator 210, and a linear actuator 210 may be used as the actuator 210 in combination with a suitable converter such as a crank-slider. In a case of using a general electric motor, using the right ascension reducer 220 may be suitable because the electric motor has a fast rotation speed and a small torque. Here, an integral-type reducer directly connected to the electric motor may be adopted and additional reduction may be externally applied as necessary. In a case of a high reduction gear ratio, using a planetary gear and a harmonic drive may be used. Also, a spur gear may be combined to form an input shaft and an output shaft to be parallel with each other, and alternatively a bevel gear or a worm gear may be used to form the input shaft and the output shaft not to be parallel with each other. In such an alternative case, a power transfer path may be diversified and thus, a more unconstrained designing method may be applied. Gears in various sizes may be combined, and a timing belt or a cable may be used to reduce an error that may be caused by a backlash. In addition to various methods described in the foregoing, variously modified forms of reducers which are used in industrial sites may be used for the right ascension reducer 220. Alternatively, in a case of a sufficient torque of the actuator 210 used, the right ascension reducer 220 may be removed and the actuator 210 may be directly connected to the right ascension rotation shaft 100.

The declination actuation mechanism 400 is configured to allow the right ascension rotation shaft 100 and the declination rotation shaft 300 to have a mechanically dependent relationship based on a correlation between a diurnal motion and an annual motion of the Sun a01, and allow the declination rotation shaft 300 to reciprocatingly rotate upwards and downwards to compensate for the annual motion of the Sun a01 in conjunction with the right ascension rotation shaft 100 rotating to track the diurnal motion of the Sun a01.

The right ascension rotation shaft 100 moves along the diurnal motion of the Sun a01 from east to west every day, by the right ascension rotation actuator 200. Meanwhile, a portion of driving power of the right ascension rotation actuator 200 is transferred to the declination rotation shaft 300 through the declination actuation mechanism 400. Thus, the declination rotation shaft 300 moves dependently on the right ascension rotation shaft 100. Here, the declination actuation mechanism 400 is configured to allow the declination rotation shaft 300 to move similarly to the description provided with reference to Equation 4 while the right ascension rotation shaft 100 tracks the diurnal motion approximately 365 times.

As illustrated in FIG. 11, the declination actuation mechanism 400 includes a declination reducer 410 which has, as an input, one point in a path through which power is transferred from the right ascension rotation actuator 200 to the right ascension rotation shaft 100, and a reciprocating rotation conversion mechanism 420 which transfers a rotational motion of an output shaft of the declination reducer 410 and converts the rotational motion to a reciprocating rotational motion of the declination rotation shaft 300. In FIG. 11, driving power is extracted from one point in the right ascension reducer 220. In detail, rotational power of the right ascension worm gear 222 is transferred to the declination reducer 410.

In determining a reduction gear ratio of the declination reducer 410, the reciprocating rotation conversion mechanism 420 may be readily designed by allowing the output shaft of the declination reducer 410 to rotate one revolution with respect to an amount of rotation generated while the right ascension rotation shaft 100 tracks the diurnal motion of the Sun a01 approximately 365 times. As illustrated in FIG. 11, a four-bar linkage is formed by determining the reduction gear ratio at which the output shaft of the declination reducer 410 makes one rotation for approximately 365 days, fixing a crank 421 to the output shaft of the declination reducer 410, fixing a rocker 422 rotating upwards and downwards along the annual motion of the Sun a01 to the declination rotation shaft 300, and including therein a connecting rod 423 connecting one end of the crank 421 to one end of the rocker 422. In FIG. 11, a pin joint is provided on a side face of the light collector holder 550 for the light collector holder 550 to function as the rocker 422.

An operation principle of the reciprocating rotation conversion mechanism 420 formed as the four-bar linkage is as follows. The rotational motion of the crank 421 is converted to the reciprocating up and down rotational motion of the rocker 422 through the connecting rod 423. When the crank 421 makes one rotation through the declination reducer 410 while the right ascension rotation shaft 100 tracks the diurnal motion approximately 365 times, the rocker 422 in turn rotates upwards and downwards on a cycle of approximately 365 days.

FIG. 12 illustrates an example of a change in an angle of the light collector holder 550 attached to the declination rotation shaft 300 based on a solar term a40. The crank 421 rotates approximately ¼ every three months and rotates approximately 90° each solar term a40. The crank 421 adjusts the light collector holder 550 to be positioned at a top dead center and a bottom dead center in the summer solstice a42 and the winter solstice a44, respectively. Thus, the light collector holder 550 is positioned at a neutral point in the spring equinox a41. After the spring equinox a41, the crank 421 pulls the connecting rod 423, and an angle of the light collector holder 550 gradually increases and reaches a maximum angle in the summer solstice a42. When the crank 421 pushes the connecting rod 423 upwards while passing the top dead center in the summer solstice a42, an angle of the light collector holder 550 gradually decreases and returns to the neutral point in the autumn equinox a43. After approximately nine months, the crank 421 reaches the bottom dead center in the winter solstice a44 and the angle becomes a minimum angle and afterwards, the crank 421 pulls the connecting rod 423 downwards and the angle of the light collector holder 550 increases. After approximately one year, the crank 421 makes one complete rotation and the light collector holder 550 returns to the neutral point when the spring equinox a41 arrives again.

Here, a relative length of the crank 421, the connecting rod 423, and the rocker 422, and a position of each connection joint need to be suitably determined to allow a maximum angle at which the declination rotation shaft 300 reciprocatingly rotates to be an angle in an upper and lower sides corresponding to the Earth's rotational axial tilt a05. An adjuster 424 that adjusts a position of a joint and a link length may be provided to the crank 421, the rocker 422, or the connecting rod 423 to finely adjust a motional displacement and a sectional speed of the reciprocating up and down rotational motion of the rocker 422. Thus, the declination rotation shaft 300 may operate similarly to the change in the meridian altitude a23 of the Sun a01 described with reference to Equation 4.

In actual operation of the solar tracker 1000, an amount of rotation of the right ascension rotation shaft 100 varies depending on a season and accordingly, an angle accumulated in the declination rotation shaft 300 varies. For example, in the summer, an amount of rotation of the right ascension rotation shaft 100 increases and a change of the declination rotation shaft 300 is accelerated. Conversely, in the winter, an accumulated angle to be transferred to the declination rotation shaft 300 is reduced. In addition, a difference in a revolution speed of the Earth a02 between an aphelion and a perihelion occurs and thus, an error for a short period of time may become greater. To consider such a change, the adjuster 424 adjusting a position of a joint and a link length is used to finely adjust the motion of the rocker 422. In an example of a change in a rotation angle of the crank 421 and a reciprocating rotation angle of the light collector holder 550 as illustrated in FIG. 12, a section from the spring equinox a41 to the autumn equinox a43 through the summer solstice a42 is longer than a section from the autumn equinox a43 to the spring equinox a41 through the winter solstice a44. In the example of FIG. 12, the crank 421 is not simply designed to rotate ¼ rounds at each solar term a40, but specially designed to vary a sectional speed based on a change in the revolution speed at the aphelion and the perihelion and the equation of time.

Although the four-bar linkage is provided as an example of the reciprocating rotation conversion mechanism 420, various mechanism modifications, for example, a crank-slider type, a cam follower type, and a five-bar linkage, may be applied to achieve functions of the reciprocating rotation conversion mechanism 420 to simulate the correlation between the diurnal motion and the annual motion. In addition, in various methods of applying modified examples of the reciprocating rotation conversion mechanism 420, although a dependent relationship between the rotational motion of the right ascension rotation shaft 100 and the reciprocating up and down rotational motion of the declination rotation shaft 300 differs from the description provided with reference to Equation 4, the difference may not restrict an operation of the solar tracker 1000 unless a range of the difference is large.

A coupling 430 is provided to remove the dependent relationship between the right ascension rotation shaft 100 and the declination rotation shaft 300 as necessary. In an initial installation of the solar tracker 1000, adjusting an angle of the declination rotation shaft 300 to be suitable for a corresponding solar term a40 based on an installation time is necessary. In a long-term operation of the solar tracker 1000, an error may occur between an angle of the declination rotation shaft 300 and an actual declination a12 of the Sun a01 and thus, an angle of the declination rotation shaft 300 may be reset to eliminate such an error. The right ascension rotation shaft 100 and the declination rotation shaft 300 of the solar tracker 1000 have a correlation by being dependent on each other through the declination actuation mechanism 400, and such a correlation may be an inconvenience in resetting an angle of the declination rotation shaft 300. To solve such an inconvenience, a means may be provided to remove such a dependent relationship between the right ascension rotation shaft 100 and the declination rotation shaft 300 as necessary and independently adjust the declination rotation shaft 300. Driving power used to actuate the declination rotation shaft 300 is supplied from the right ascension rotation actuator 200 and transferred through a reducer or a linkage. Thus, the coupling 430 is installed at one point in a path through which power is transferred from the right ascension rotation actuator 200 to the declination rotation shaft 300, and is configured to selectively connect or block rotational power to be transferred and apply or remove the dependent relationship between the right ascension rotation shaft 100 and the declination rotation shaft 300.

Referring to FIG. 13, the coupling 430 is installed in a portion connecting a final output shaft of the declination reducer 410 to the crank 421 of the reciprocating rotation conversion mechanism 420. When releasing the coupling 430, an angle of the light collector holder 550 may be unrestrictedly changed by adjusting a rotation angle of the crank 421 without affecting the right ascension rotation shaft 100.

According to an embodiment, a one-way clutch 450 is provided to allow only one-way rotational motion of the right ascension rotation shaft 100 to interwork with the declination rotation shaft 300. In general, due to a large volume of the light collector 600 attached to the solar tracker 1000, an interference may occur in a surrounding environment. Thus, the right ascension rotation shaft 100 may perform a two-way reciprocating rotation without continuous rotations while avoiding such an interference. As illustrated in FIG. 14, in the daytime, the right ascension rotation shaft 100 makes a half rotation until the Sun a01 sets in the west after the Sun a01 rises in the east. Conversely, in the nighttime, the right ascension rotation shaft 100 returns to the east after reversely rotating in an opposite direction and tracing up a path through which the right ascension rotation shaft 100 passes in the daytime, and waits for the next morning to track the Sun a01 again. In the interworking between the declination rotation shaft 300 and the right ascension rotation shaft 100, the reverse rotational motion of the right ascension rotation shaft 100 in the nighttime needs to be ignored, and an amount of the normal rotation used to track the Sun a01 from east to west in the daytime needs to be selectively extracted and transferred to the declination rotation shaft 300 through the declination actuation mechanism 400.

Using the one-way clutch 450, such a one-way rotational power may be selectively extracted from the two-way reciprocating rotational motion. Thus, only a rotation component that tracks the diurnal motion of the Sun a01 from east to west in the daytime may be extracted, and the reverse rotational motion of the right ascension rotation shaft 100 in the nighttime may not be transferred to the declination rotation shaft 300. FIG. 13 illustrates an example of the declination actuation mechanism 400 including the one-way clutch 450. In the example of FIG. 13, the one-way clutch 450 is installed at a front end of the input shaft of the declination reducer 410 to allow only one-way rectified rotation component to be input to the declination reducer 410. In principle, the one-way clutch 450 may be installed at any point at which the driving power is transferred from the right ascension rotation actuator 200 to the declination rotation shaft 300 to achieve the same functions as described in the foregoing. In a case of the light collector 600 of a small volume and absence of the interference to the surrounding environment, using the one-way clutch 450 may be unnecessary because the right ascension rotation shaft 100 may track the Sun a01 while continuously rotating.

As illustrated in FIG. 14, in the solar tracker 1000 using the one-way clutch 450, an amount of diurnal rotation occurring while the right ascension rotation shaft 100 normally tracks the diurnal motion of the Sun a01, exclusive of the reverse rotation to return to the east in the nighttime, is approximately a half rotation per day. Here, a reduction great ratio at which the crank 421 of the declination actuation mechanism 400 rotates approximately 1/365 times needs to be set with respect to the half rotation per day. Since the half rotation varies depending on a surrounding topography, a season, a mechanical motion range of the right ascension rotation shaft 100, and the like, the declination reducer 410 or a reduction ratio adjuster 440 needs to be suitably adjusted based on an installation environment.

The reduction ratio adjuster 440 is provided to adjust a ratio of an amount of rotation of the declination rotation shaft 300 to the rotational motion of the right ascension rotation shaft 100. In the solar tracker 1000, the declination rotation shaft 300 gradually operates each day in conjunction with an amount of rotation of the right ascension rotation shaft 100 used to track the diurnal motion of the Sun a01 each day. An amount of rotation of the declination rotation shaft 300 which is gradually accumulated each day may be merely 23.5° per three months. However, when the reduction gear ratio of the declination reducer 410 is not accurately set, an error may be accumulated during the long-term use and thus, accuracy may decrease. When the right ascension rotation shaft 100 operates to perform the reciprocating rotation in opposite directions in the daytime and in the nighttime, a motional range of the right ascension rotation shaft 100 may change depending on a surrounding environment and an installation condition and also, an additional error may occur when operating the one-way clutch 450. For example, in a mountainous region dissimilar to a beach around which no obstacles are present, a period of time used to track the Sun a01 in the daytime may be considerably decrease and thus, reducing a motional range of the right ascension rotation shaft 100 may be necessary. In a case of installing multiple solar trackers 1000, an amount of rotation of the right ascension rotation shaft 100 may be restricted to dispose the multiple solar trackers 1000 not to cover sunlight to one another. Since an error may be accumulated due to the long-term operation, the reduction ratio adjuster 440 is provided to readily adjust the reduction gear ratio of the declination reducer 410.

In the example of the reduction ratio adjuster 440 illustrated in FIG. 13, rotational power is extracted from the right ascension worm gear 222 of the right ascension rotation actuator 200 and the extracted power is input to the reduction ratio adjuster 440. A pulley-belt transfer device used mainly for a continuously variable transmission and changing a rotation radius may be used as an example of the reduction ratio adjuster 440. Here, two rotation wheels having respective inclined planes are installed to face to each other to form a V-groove pulley, and a distance between the two rotation wheels is adjustable. When the distance of the V-groove pulley increases, a valid rotation radius in which a belt operates decreases. Conversely, when the distance of the V-groove pulley decreases, the valid rotation radius increases. Thus, the reduction gear ratio may be adjusted to increase and decrease. Alternatively, the reduction gear ratio may be adjusted by installing a multi-stepped pulley having different radii at both shafts and hanging a belt on a suitable position. Alternatively, various devices may be provided to adjust a radius of a pulley, and other mechanisms in addition to the pulley may be provided to adjust the reduction gear ratio.

In adjusting the reduction gear ratio, matching a one year cycle of the reciprocating up and down rotational motion may be more necessary rather than considering a short-term error of the declination rotation shaft 300. In general, an amount of rotation of the right ascension rotation shaft 100 varies depending on a season and an angle to be accumulated in the declination rotation shaft 300 may vary accordingly. For example, in the summer when an amount of rotation of the right ascension rotation shaft 100 increases, a change in the declination rotation shaft 300 may be further accelerated. Conversely, in the winter, an accumulated angle to be transferred to the declination rotation shaft 300 may decrease. Thus, although an error occurs when a short-term change in the declination rotation shaft 300 deviates from a curve provided in Equation 4, an error accumulated in the summer and the winter may be offset and the error may be autonomously removed after the one year cycle elapses.

A declination display device 460 is provided to display, as an angle, a declination a12 in a direction to which the light collector 600 attached to the solar tracker 1000 faces the celestial sphere a19. A solar term display device 470 is provided to convert, to a solar term a40, a declination a12 in the direction to which the light collector 600 attached to the solar tracker 1000 faces the celestial sphere a19, and display the solar term a40. At an initial installation of the solar tracker 1000, a direction of the light collector holder 550 and the light collector 600 attached thereto needs to match to a declination a12 of the Sun a01 by suitably adjusting an angle of the declination rotation shaft 300 based on an installation time. A difference between an angle of the declination rotation shaft 300 and an actual declination a12 of the Sun a01 currently staying in the sky may occur due to the long-term operation of the solar tracker 1000, and correcting such a difference may be necessary. FIG. 15 illustrates an example of the declination display device 460 configured to display an angle of the declination rotation shaft 300. The light collector holder 550 is in a neutral state in which the light collector holder 550 is parallel with the right ascension rotation shaft 100 in the spring equinox a41 and the autumn equinox a43 in which a declination a12 of the Sun a01 becomes 0°. In the example of the declination display device 460, a declination measuring pointer 461 is fixed to the light collector holder 550 rotating along with the light collector 600, and a declination marking 462 is attached to the declination rotation support 540 to measure an angle formed between the light collector holder 550 and the right ascension rotation shaft 100. Thus, a declination a12 on the celestial sphere a19 to which the solar tracker 1000 actually faces may be readily read through the declination display device 460.

In the long-term operation of the solar tracker 1000, verifying accurate operation of the solar tracker 1000 may be important. However, performing a comparison of an actual direction of the solar tracker 1000 measured through the declination display device 460 and a declination a12 of the Sun a01 based on a measurement time may be inconvenient. As described with reference to Equation 4, since a declination a12 of the Sun a01 and a solar term a40 have a correlation and most countries in the world use a solar calendar based on a declination a12 of the Sun a01 as a method of counting dates, a declination a12 of the Sun a01 may be readily converted to dates on the calendar. Thus, an error may be more intuitively verified by, rather than displaying an actual direction of the solar tracker 1000 as an angle through the declination display device 460, converting the angle to a solar term a40 in which the solar tracker 1000 tracks and displaying the solar term a40. FIG. 15 also illustrates an example of the solar term display device 470 configured to convert an angle of the declination rotation shaft 300 to a solar term a40 and display the solar term a40. In the example, a solar term measuring pointer 471 is installed in the crank 421 connected to the output shaft of the declination reducer 410 to rotate together, and a solar term marking 472 is provided in the declination rotation support 540 to convert an amount of rotation of the crank 421 to a corresponding solar term a40 and read the solar term a40. For example, when the crank 421 is designed to make one rotation per year, a correlation between an amount of rotation of the crank 421 and a solar term a40 is illustrated as in FIG. 15. The solar term marking 472 is broadly divided into four solar terms, for example, the spring equinox a41, the summer solstice a42, the autumn equinox a43, and the winter solstice a44, and displays the solar terms and rotates along with the crank 421. Thus, a solar term a41 corresponding to a current rotation angle of the crank 421 may be read through the solar term measuring pointer 471. More precise measurement may be enabled using more detailed markings of the solar term marking 472 by dividing the solar term marking 472 into, for example, 12 solar terms, each month, and each day, in addition to the illustrated four solar terms. In addition, intervals between the markings may be modified based on a case that an amount of rotation accumulated in the summer differs from an amount of rotation accumulated in the winter. Based on a change in an angle of the crank 421 illustrated in FIG. 12, a summer section is designed to be longer than a winter section and thus, intervals between the markings in the summer are designed to be longer than intervals in the markings in the winter.

When the solar tracker 1000 is appropriately installed and an error is suitably corrected, the right ascension rotation shaft 100 gradually moves along the diurnal motion of the Sun a01, and the solar term marking 472 through which the solar term measuring pointer 471 passes increases each day. After one year passes over the four solar terms, the solar term marking 472 makes one complete rotation and returns to an original date. Through the solar term display device 470, an angle of the declination rotation shaft 300 may be periodically converted to a temporal solar term a40, and a tracking error of the declination rotation shaft 300 may be intuitively verified based on a comparison of the solar term a40 and a current date on the calendar. In addition, an accurate tracking may be enabled by applying, to the reduction ratio adjuster 440, a trend of the tracking error which is gradually put forward or backward.

The declination display device 460 and the solar term display device 470 are identical in principle without a difference in a unit of markings. When the markings of the declination display device 460 are displayed as a solar term a40, the declination display device 460 may be used as the solar term display device 470. Alternatively, the declination display device 460 and the solar term display device 470 may be integrated into one display device by indicating both the angle and the solar term a40. In addition, since all driving shafts in a power transfer path through which driving power generated from the right ascension rotation actuator 200 is transferred to the declination rotation shaft 300 through the declination actuation mechanism 400 include information on a declination a12 to which the solar tracker 1000 faces and on a solar term a40, a rotation angle of the declination rotation shaft 300 or a corresponding solar term a40 may be verified although the markings are indicated at any point of the power transfer path. Thus, various methods may be applicable in addition to the example described in the foregoing.

For example, an additional rotation shaft may be provided for measurement at one point at which power is transferred from the right ascension rotation actuator 200 to the declination rotation shaft 300, and a rotation plate having markings at an end thereof may be installed. When the right ascension rotation shaft 100 reciprocatingly rotates and a one-way rotation component is transferred to the declination rotation shaft 300 through the one-way clutch 450, the declination display device 460 or the solar term display device 470 needs to be installed at one point of a power shaft to which a rectified rotation component is transferred through the one-way clutch 450.

Further, improper operation of the solar tracker 1000 may be readily verified in the presence of a right ascension display device 480 for the right ascension rotation shaft 100. FIG. 15 also illustrates an example of the right ascension display device 480 applying a right ascension measuring pointer 481 and a right ascension marking 482 to the declination rotation support 540 and the right ascension rotation support 530, respectively.

FIG. 18 is a flowchart illustrating an example four-step method of operating the solar tracker 1000 according to an embodiment of the present invention.

In a first step (S01), the method includes matching a direction of the right ascension rotation shaft 100 to the Earth's rotation axis a34.

In a second step (S02), the method includes matching an angle of the declination rotation shaft 300 to a declination a12 of the Sun a01.

In a third step (S03), the method includes tracking a diurnal motion of the Sun a01 by actuating the right ascension rotation shaft 100 through the right ascension rotation actuator 200.

In a fourth step (S04), the method includes tracking a change in a meridian altitude a23 of the Sun a01 occurring due to an annual motion by transferring a portion of driving power of the right ascension rotation actuator 200 to the declination rotation shaft 300 through the declination actuation mechanism 400.

The following steps may be additionally included in the method as necessary.

In a fifth step (505), when a motional displacement of the declination rotation shaft 300 is less or greater than the Earth's rotational axial tilt a05, the method includes changing the motional displacement of the declination rotation shaft 300 by adjusting the declination actuation mechanism 400.

In a sixth step (506), when a motion cycle of the declination rotation shaft 300 is longer or shorter than a revolution cycle of the Earth a02, the method includes changing the motion cycle of the declination rotation shaft 300 by adjusting the reduction ratio adjuster 440.

In a seventh step (507), when a difference between an angle of the declination rotation shaft 300 and a declination a12 of the Sun a01 is large, the method includes releasing the coupling 430 and resetting the angle of the declination rotation shaft 300.

FIG. 19 is a flowchart illustrating an example seven-step method of operating the solar tracker 1000 in which the additional steps, for example, the fifth step (S05), the sixth step (S06), and the seventh step (S07), are all included.

Hereinafter, each step of the method of operating the solar tracker 1000 will be described in detail. For an appropriate operation of the solar tracker 1000, accurate installation needs to be performed in accordance with the first step and the second step.

The method of operating the solar tracker 1000 includes the first step (S01) of adjusting and matching a direction of the right ascension rotation shaft 100 to the Earth's rotation axis a34. A first task to be performed to implement the solar tracker 1000 may include preparing robust fundamentals on the ground, and installing the solar tracker 1000 to match the right ascension rotation shaft 100 to the Earth's rotation axis using measuring apparatuses such as a horizontal level measurer configured to determine a reference of an inclination of the ground, an angle measurer configured to measure an inclination or a tilt, a distance measurer configured to measure a distance, a compass configured to measure a magnetic north, and a theodolite or a total station configured to measure a true north. Here, simultaneously matching two angles—an azimuth a21 on the horizontal plane a29 and an altitude a22 facing the sky—is necessary. A method of matching the azimuth a21 includes projecting the right ascension rotation shaft 100 to the ground to place the right ascension rotation shaft 100 on a plane through which a meridian a24 passes and to make both ends face the south and the north, respectively. In the example of using the one pillar 520 illustrated in (a) of FIG. 7, the matching of the direction may be performed by suitably rotating the pillar 520. In the example of using the two pillars 520a and 520b illustrated in (b) of FIG. 7, the matching of the direction may be performed by adjusting a relative position of each pillar.

A method of matching the altitude a22 includes adjusting an angle formed between the right ascension rotation shaft 100 and the horizontal plane a29 based on a latitude a32 of an installation location. For example, in a case of the northern hemisphere, an angle formed between the right ascension rotation shaft 100 and the ground with respect to a north point a26 is adjusted to be tilted by a latitude a32 of the installation location. In a case of the southern hemisphere, an angle formed between the right ascension rotation shaft 100 and the ground with respect to a south point a25 is adjusted to be tilted by a latitude a32 of the installation location. Thus, when the installation location is on the equator a37, the right ascension rotation shaft 100 is parallel with the horizontal plane a29. When the installation location is in the North Pole a35 or the South Pole a36, the right ascension rotation shaft 100 is set up perpendicularly to the horizontal plane a29 as shown in the pillar 520. When the installation location is in Korea, the right ascension rotation shaft 100 is installed to be tilted at approximately 37° from the north point a26, and tilted at approximately 143° from the south point a25 passing a zenith to the horizontal plane a29. In the example of using the one pillar 520, an altitude a22 of the right ascension rotation shaft 100 may be adjusted by suitably tilting the right ascension rotation support 530 fixed to the pillar 520. In the example of using the two pillars 520a and 520b, an altitude a22 of the right ascension rotation shaft 100 may be adjusted by adjusting a height of the pillar 520a or the pillar 520b which has an adjustable length.

The method of operating the solar tracker 1000 includes the second step (S02) of matching an angle of the declination rotation shaft 300 to a declination a12 of the Sun a01 based on a solar term a40. At an initial installation of the solar tracker 1000, the second step (S02) of adjusting the declination rotation shaft 300 needs to be appropriately performed in addition to the first step (S01). The second step (S02) includes adjusting an angle of the declination rotation shaft 100 based on a distance between the equatorial plane a17 and the ecliptic a18 based on a solar term a40, for example, a declination a12 of the Sun a01 based on a season, and changing an angle of the light collector holder 550 to allow the attached light collector 600 to face the Sun a01. As described with reference to Equation 4, a declination a12 of the Sun a01 monotonically increases until the declination a12 reaches an angle of the Earth's rotational axial tilt a05 in the summer solstice a44 after passing through a point at which the declination a12 is 0 in the spring equinox a41, for example, passing through the equatorial plane a17 of the celestial sphere a19. The declination a12 increases to a meridian altitude a23 at a maximum angle in the summer solstice a44 and decreases afterwards, and passes through the equatorial plane a17 of the celestial sphere a19 and stays in the southern hemisphere after the autumn equinox a43. The meridian altitude a23 of the Sun a01 has a minimum angle in the winter solstice a44. Since a change of season in the southern hemisphere of the Earth a02 occurs conversely in the northern hemisphere and a reference point for measurement and a seasonal solar term a40 changes, the solar tracker 1000 needs to operate based on such a fact.

In an example of the solar tracker 1000 without the coupling 430, an angle of the declination rotation shaft 300 needs to be adjusted to have a suitable declination a12 based on a solar term a40 in conjunction with the right ascension rotation shaft continuously rotating. Since the declination rotation shaft 300 performs only one cycle of a motion while the right ascension rotation shaft 100 rotates approximately 365 times, the right ascension rotation shaft 100 needs to greatly rotate for a small movement of the declination rotation shaft 300 and thus, an inconvenience may occur. However, in an example of the solar tracker 1000 including the coupling 430, a dependent relationship between the right ascension rotation shaft 100 and the declination rotation shaft 300 may be immediately removed, and the declination rotation shaft 300 may be independently adjusted. When the coupling 430 installed in a power transfer shaft of the declination actuation mechanism 400 is released, an angle of the declination rotation shaft 300 and the light collector holder 550 attached thereto may be unrestrictedly adjusted without affecting the right ascension rotation shaft 100.

In an example of the solar tracker 1000 including the declination display device 460, a declination a12 on the celestial sphere a19 toward which the light collector 600 faces may be readily verified through the declination marking 462 of the declination display device 460 without an additional measuring apparatus. By referring to the declination marking 462, the declination rotation shaft 300 may be adjusted. In an example of the solar tracker 1000 including the solar term display device 460, a declination a12 of the Sun a01 based on a seasonal solar term a40 may be converted and thus, an inconvenience in adjusting an angle of the declination rotation shaft 300 may be relieved. In the example of the solar tracker 1000 including the solar term display device 460, an angle of the declination rotation shaft 300 is converted to a seasonal solar term a40 and the solar term a40 is displayed. Thus, adjusting the angle of the declination rotation shaft 300 to a current solar term a40 may only be performed after reading the solar term marking 472 without performing a comparison of an angle of the declination rotation shaft 300 and a declination a12 of the Sun a01. That is, a time comparison method may be more intuitive than an angle comparison method.

The first step (S01) and the second step (S02) described in the foregoing are prerequisites for the initial installation of the solar tracker 1000. Hereinafter, the third step (S03) and the fourth step (S04) will be described in detail and theses steps may be prerequisites for a process of tracking the Sun a01 after the initial installation of the solar tracker 1000.

The method of operating the solar tracker 1000 includes the third step (S03) of tracking the diurnal motion of the Sun a01 by actuating the right ascension rotation shaft 100 through the right ascension rotation actuator 200. After completing the initial installation of the solar tracker 1000 in accordance with the first step (S01) and the second step (S02), the solar tracker 1000 is activated to allow the light collector 600 attached to the solar tracker 1000 to move along the diurnal motion of the Sun a01 occurring every day. A simplest method of tracking the diurnal motion may include operating the right ascension rotation shaft 100 at a constant angular velocity of an approximately 15° per hour at which the Earth a02 rotates, starting from a certain angle in the east at a certain time in the morning, in accordance with a predetermined program, and suspending such an operation at a certain angle in the west in a certain time in the evening and returning to the east at night. In such a manual tracking method by the time-based program, the Sun a01 may be precisely tracked without a significant error when data on a latitude a32 and a longitude a31 of a location at which the solar tracker 1000 is installed is correct and a direction of the right ascension rotation shaft 100 is accurately installed. In operating the time-based program, since a revolution orbit of the Earth a02 is not an exact circle, but an ellipse, the equation of time of a maximum eight minutes, which corresponds to a tracking error of approximately 2.5° when converted to an angular velocity, may occur due to a difference in a revolution speed at a perihelion and at an aphelion. Thus, the program may more precisely operate by correcting the equation of time from a mean solar time based on Kepler's laws. However, in such a manual tracking method based on the program, a real-time correction may be impossible when an error occurs due to an external factor such as a slip effect of an actuator. To improve the manual tracking method, a sensor-based active tracking method may be used to measure, in real time, a position of the Sun a01 through an included sensor configured to sense the Sun a01 and actuate the right ascension rotation shaft 100 based on the measured position of the Sun a01. In such an active tracking method, despite an external issue such as a breakdown, the actuation may be enabled through real-time verification of an actual position of the Sun a01. However, an operation may be temporarily suspended due to an influence of weather or a passing obstacle, and a speed may fluctuate without maintaining a constant speed due to a vulnerability to vibration. Thus, the two methods described in the foregoing may be used in combination. The solar tracker 1000 may operate based on time using data on an observation point in accordance with the predetermined program and monitor a state of tracking the Sun a01 using the sensor, and also correct an error in real time in a case of a significant error.

The method of operating the solar tracker 1000 includes the fourth step (S04) of tracking a change in a meridian altitude a23 of the Sun a01 based on a solar term a40 by transferring a portion of driving power of the right ascension rotation actuator 200 to the declination rotation shaft 300 through the declination actuation mechanism 400. The fourth step (S04) is automatically generated from the third step (S03). In the third step (S03), when the right ascension rotation shaft 100 rotates along a direction of the diurnal motion of the Sun a01, a rotation angle of the right ascension rotation shaft 100 is transferred to the declination rotation shaft 300 through the declination actuation mechanism 400 and the declination rotation shaft 300 reciprocatingly rotates upwards and downwards along the annual motion of the Sun a01. The driving power is extracted from one point in a power transfer path of the right ascension rotation actuator 200 and used to actuate the declination rotation shaft 300 through the declination actuation mechanism 400. Here, when the right ascension rotation shaft 100 does not continuously rotate in one direction, the one-way clutch 450 is used to selectively transfer a one-way rotation component that tracks only the diurnal motion of the Sun a01. The declination actuation mechanism 400 is designed to match an amount of rotation accumulated for one year during which the right ascension rotation shaft 100 tracks the diurnal motion of the Sun a01 to a cycle of the reciprocating up and down rotational motion of the declination rotation shaft 300. Here, the designing may be readily performed by adjusting a reduction gear ratio at which the output shaft of the declination reducer 410 of the declination actuation mechanism 400 makes one rotation per year. For example, the crank 421 is installed in the output shaft of the declination reducer 410, and the rocker 422 that rotates upwards and downwards along the annual motion of the Sun a01 is installed in the declination rotation shaft 300 to form the four-bar linkage. Thus, when the crank 421 makes one rotation per year, the declination rotation shaft 300 fixed with the rocker 422 reciprocatingly rotates upwards and downwards on one year cycle. Here, when relative lengths of the crank 421, the connecting rod 423, and the rocker 422, and respective positions of each connection joint are adjustable, changing a motional range of the four-bar linkage and adjusting the declination rotation shaft 300 to have an angle of the Earth's rotational axial tilt a05 in an upward and a downward side, respectively, may be readily performed. The method of operating the solar tracker 1000 may be performed only with the four steps including the first step (S01) through the fourth step (S04). However, for maintenance, the additional steps, the fifth step (S05), the sixth step (S06), or the seventh step (S07) may be added to the method.

When a motional displacement of the declination rotation shaft 300 is greater or less than the Earth's rotational axial tilt a05, the method of operating the solar tracker 1000 may include the fifth step (S05) of changing the motional displacement of the declination rotation shaft 300 by adjusting the declination actuation mechanism 400. When the motional displacement of the declination rotation shaft 300 rotating upwards and downwards on one year cycle is less or greater than the Earth's rotational axial tilt a05, an error in tracking the Sun a01 may increase. The motional displacement of the declination rotation shaft 300 is a value determined based on a mechanical configuration of the declination actuation mechanism 400, and needs to be accurately designed to have a suitable range. In an example of the declination actuation mechanism 400, the motional displacement and a sectional speed may be adjusted by adjusting a position of a joint of the crank 421, the rocker 422, or the connecting rod 423, and a link length. In addition to the motional displacement of the declination rotation shaft 300, various operation characteristics including a motional trajectory and a sectional speed may be adjusted by adjusting the link length and the position of each connection joint. However, the motional displacement of the declination rotation shaft 300 may not change depending on an installation location or a surrounding environment and thus, the declination rotation shaft 300 may operate identically anywhere on the Earth a02 and a situation in which the motional displacement of the declination rotation shaft 300 needs to be adjusted may not occur frequently.

When a motion cycle of the declination rotation shaft 300 is longer or shorter than a cycle of revolution of the Earth a02, the method of operating the solar tracker 1000 may include the sixth step (S06) of changing the motion cycle of the declination rotation shaft 300 by adjusting the reduction ratio adjuster 440. In a long-term operation of the solar tracker 1000, the motion cycle of the declination rotation shaft 300 may become gradually faster or slower than a cycle of the annual motion of the Sun a01. Here, a rotation range of the right ascension rotation shaft 100 tracking the diurnal motion per day may be adjusted based on an environmental condition such as a surrounding geographic feature of an installation location, and a reduction gear ratio of the declination actuation mechanism 400 may need to be adjusted accordingly. For example, in an open location such as a beach, the right ascension rotation shaft 100 rotates up to a maximum 180° per day. In a mountainous region around which numerous obstacles are present, a sunrise time is moved forward and a sunset time is moved backward and thus, an amount of daily rotation may be reduced. Despite an amount of rotation of the right ascension rotation shaft 100 varying depending on a region or a location, a rotation angle at which the declination rotation shaft 300 moves a day to track the annual motion of the Sun a01 is invariant as described with reference to Equation 4. Thus, adjusting the reduction gear ratio of the declination actuation mechanism 400 is required based on an operation range of the right ascension rotation shaft 100 for which an environment of the installation location is considered. In an operation of the solar tracker 1000, a lack of the reduction gear ratio of the declination actuation mechanism 400 may lead to a shortening cycle of the reciprocating up and down rotational motion of the declination rotation shaft 300 compared to an actual cycle of revolution of the Earth a02. Thus, increasing the reduction gear ratio may be necessary. Conversely, a large reduction gear ratio may lead to a prolonged motion cycle of the declination rotation shaft 300 compared to the actual cycle of revolution of the Earth a02. Thus, decreasing the reduction gear ratio may be necessary. In an example of the solar tracker 1000 including the declination display device 460 or the solar term display device 470, verifying an error in the motion cycle may be readily performed by referring to the declination display device 460 or the solar term display device 470. When the error is verified to occur after periodically verifying the motion cycle of the declination rotation shaft 300, the reduction gear ratio of the declination actuation mechanism 400 may need to be suitably adjusted to increase or decrease the reduction gear ratio to remove the error. In a case of a fixed reduction gear ratio of the declination actuation mechanism 400, changing the motion cycle of the declination rotation shaft 300 may be inconvenient and thus, attaching the reduction ratio adjuster 440 is recommended herein.

When a difference between an angle of the declination rotation shaft 300 and a declination a12 of the Sun a01 is large, the method of operating the solar tracker 1000 may include the seventh step (S07) of releasing the coupling 430 and resetting an angle of the declination rotation shaft 300. In a long-term operation of the solar tracker 1000, an error may occur in relation to the motional displacement or the motion cycle of the declination rotation shaft 300. In such a case, an error that may potentially occur may be reduced using the methods provided in the fifth step (S05) and the sixth step (S06). However, since an already accumulated error remains, an additional step to remove the error may be necessary. To remove an error accumulated while the declination rotation shaft 300 tracks a declination a12 of the Sun a01, a method similar to the method provided in the second step (S02) may be applied. The method may include releasing the coupling 430, independently rotating the declination rotation shaft 300 to remove the accumulated error, and connecting the coupling 430 again to allow the declination rotation shaft 300 to interwork with the right ascension rotation shaft 100.

Claims

1. A solar tracker 1000, comprising:

a right ascension rotation shaft 100 installed in parallel with the Earth's rotation axis a34 and configured to track a change in a right ascension a11 occurring due to a diurnal motion of the Sun a01;

a right ascension rotation actuator 200 configured to actuate the right ascension rotation shaft 100;

a declination rotation shaft 300 perpendicular to the right ascension rotation shaft 100 and configured to reciprocatingly rotate on a four season cycle to track a change in a declination a12 occurring due to an annual motion of the Sun a01; and

a declination actuation mechanism 400 configured to transfer a portion of rotational power generated when the right ascension rotation actuator 200 actuates the right ascension rotation shaft 100 to the declination rotation shaft 300 to allow the declination rotation shaft 300 to reciprocatingly rotate upwards and downwards, and comprising a one-way clutch 450 installed at one point in a power transfer path from the right ascension rotation actuator 200 to the declination rotation shaft 300 and configured to select and transfer a one-way rotation component of the rotational power to be transferred to the declination rotation shaft 300.

2. The solar tracker 1000 of claim 1, comprising:

a reduction ratio adjuster 440 installed at one point in the power transfer path from the right ascension rotation actuator 200 to the declination rotation shaft 300 and configured to increase or decrease a rotation ratio to be transferred.

3. The solar tracker 1000 of claim 1, comprising:

a coupling 430 installed at one point in the power transfer path from the right ascension rotation actuator 200 to the declination rotation shaft 300 and configured to connect or block the rotational power to be transferred.

4. The solar tracker 1000 of claim 1, wherein the declination actuation mechanism 400 comprises:

a declination reducer 410 configured to receive driving power of the right ascension rotation actuator 200, convert a rotation ratio, and output the converted rotation ratio;

a crank 421 attached to an output shaft of the declination reducer 410;

a rocker 422 fixed to the declination rotation shaft 300 and reciprocatingly rotating upwards and downwards at the Earth's rotational axial tilt a05 based on the change in the declination a12 occurring due to the annual motion of the Sun a01; and

a connecting rod 423 connecting one end of the crank 421 to one end of the rocker 422 to form a four-bar linkage 420, and configured to convert a rotational motion of the crank 421 to the reciprocating up and down rotational motion of the rocker 422.

5. The solar tracker 1000 of claim 4, wherein the crank 421, the rocker 422, or the connecting rod 423 comprises an adjuster 424 configured to adjust a location of a joint or a link length to change a motional displacement and a sectional speed of the reciprocating up and down rotational motion of the declination rotation shaft 300.

6. The solar tracker 1000 of claim 1, comprising:

a declination display device 460 configured to convert an amount of rotation of the declination rotation shaft 300 to an angle and display the angle; or

a solar term display device 470 configured to convert the amount of rotation to a solar term a40 of a year and display the solar term a40.

7. A method of operating a solar tracker 1000, comprising:

a first operation S01 to match a direction of a right ascension rotation shaft 100 to the Earth's rotation axis a34;

a second operation S02 to match an angle of a declination rotation shaft 300 to a declination a12 of the Sun a01;

a third operation S03 to track a diurnal motion of the Sun a01 by actuating the right ascension rotation shaft 100 by a right ascension rotation actuator 200; and

a fourth operation S04 to track, by the declination rotation shaft 300, a change in a meridian altitude a23 of the Sun a01 occurring due to an annual motion, by allowing a declination actuation mechanism 400 to selectively extract a one-way rotation component and allow the declination rotation shaft 300 to reciprocatingly rotate on a four season cycle when the declination actuation mechanism 400 transfers a portion of driving power of the right ascension rotation actuator 200 to the declination rotation shaft 300.

8. The method of claim 7, comprising any one of:

a fifth operation S05 to change a motional displacement of the declination rotation shaft 300 by adjusting the declination actuation mechanism 400 in response to the motional displacement of the declination rotation shaft 300 being less or greater than the Earth's rotational axial tilt a05;

a sixth operation S06 to change a motion cycle of the declination rotation shaft 300 by adjusting a reduction ratio adjuster 440 in response to the motion cycle of the declination rotation shaft 300 being longer or shorter than a cycle of revolution of the Earth a02; and

a seventh operation S07 to release a coupling 430 and reset an angle of the declination rotation shaft 300 in response to a large difference between the angle of the declination rotation shaft 300 and the declination a12 of the Sun a01.

9. The method of claim 7, wherein an angle at which the declination rotation shaft 300 reciprocatingly rotates upwards and downwards in the fourth operation S04 corresponds to the Earth's rotational axial tilt a05 in each of an upward direction and a downward direction.

10. The solar tracker 1000 of claim 1, comprising:

a balance weight 560 configured to adjust a weight and an attached location of a load to allow a centroid of the load applied to each rotation shaft to be positioned in each rotation shaft by changing the centroid of the load, in order to prevent a rotation by a self weight and minimize an amount of rotational power required for actuating a rotation shaft through a balance of the load applied to the right ascension rotation shaft 100 or the declination rotation shaft 300.