ULTRA HIGH EFFICIENCY, HIGH TEMPERATURE SOLAR COLLECTION AND STORAGE
High-temperature solar trap collectors provide near ambient temperature solar entry surfaces and negligible thermal radiation losses by counterflowing low velocity transparent gases or liquids (fluids) to nullify internal thermal diffusion and radiative heat losses at the solar entry surface. Small steradian (sr) baffling plus wavelength-selective materials trap the entire 0.35 u to 2.7 u incoming solar spectrum and heat highly absorbing internal surfaces to high temperatures; only a small solid angle of the 2π steradians—on the order of 0.01 sr—of internal thermal radiation escapes. A nearly 100% efficient flat panel solar trapping embodiment exhibits alpha (α) absorption nearing 1.0 and radiant emission losses nearing 0.0 even at solar collection temperatures in excess of 1,000° K. Ultra high collection efficiency counterflow configurations are ideal for solar hot water, space heating, cooling, energy storage, and electric power generation applications.
This application claims the benefit of U.S. Provisional Application Ser. No. 61/851,083, entitled “Ultra High Efficiency, High Temperature Solar Collection and Storage”, Filed Mar. 1, 2013, the disclosure of which is hereby incorporated herein in its entirety by reference.
BACKGROUND OF INVENTIONField of the Invention
The present application relates, in general, to a method and apparatus for achieving low-cost, renewable global energy utilizing an ultra efficient solar trap that is capable of meeting even centuries more of civilization's relentless 2% per year exponentially rising energy demands.
Discussion of Prior Art
Conventional easy-access, cheap energy is already depleted and unsustainable energy economic ceilings are being breached, but international prosperity can be restored by adopting a new abundant, dramatically lower cost energy source, such as clean solar energy. Solar energy, the world's largest energy resource, once harnessed in a useful form, such as high temperature thermal energy, can be readily stored and transformed into almost all other forms of energy, such as chemical energy, mechanical energy, electrical energy, and others. See chart 10 in
Energy costs have risen from less than 1% of the global economy and are now approaching 14% of the $70 trillion world economy. The cost of energy, not energy abundance, now limits global prosperity—including fresh water, agricultural food production, manufactured products, and almost all jobs. All products and transportation are inexorably linked to energy costs and almost all jobs are inexorably linked to manufacturing and transporting all products. An entirely new, far larger, cheaper, and cleaner prime energy source is absolutely essential, unless gross human depopulation begins to occur within about one generation. Patch-work energy alternatives cannot meet the need. There is little debate that the industrial revolution was triggered by the combustion powered steam engine invention in 1712, and our energy appetite has exponentially grown since—enabling 300 years of unparalleled global prosperity. However, underpinning this long period of prosperity was abundant very low-cost energy—typically costing less than about five percent of the global economy. Rapidly rising and unsustainable energy recovery obstacles now govern the world economy, not to mention the almost totally ignored larger costs associated with air, land, and sea pollution. Energy, per se, is essentially unlimited if energy prices could be ignored. But, prices cannot be ignored. Thus, affordable energy governs life as we know it. The world urgently needs an immediate transition to a far larger, cleaner, and considerably less expensive alternative prime source of energy. Until the present invention, the world's largest energy resource—solar energy, which is 10,000 times larger than man's present energy needs—has not been either affordable or reliable. For just one example, the well-known prior art concentrating solar mirrors and photovoltaic solar panels shown at 12 and 14 in
In essence, the subject invention is a one way solar energy valve which enables entry of the entire solar spectrum into a solar trap, wherein solar energy is cumulatively absorbed and converted to exceptionally high usable temperatures, but does not allow the usual thermal radiation to escape from within. In other words, a solar trap device is provided which simulates a high temperature blackbody absorber with little to no emissive losses, similar in some ways to an astronomical black hole which grows in temperature with little escaping energy. Solar traps efficiently concentrate very high temperature thermal energy which can be densely stored and thereafter used on demand for an unlimited number of energy applications. This new very high temperature solar trapping technology can theoretically approach 100% efficiency per acre of solar collection, which exceeds by many times the surface area collection efficiency of all prior art solar technologies.
Briefly, the present invention is directed to an exceptionally high efficiency solar energy collector which incorporates an enclosure having an outermost entrance aperture to allow incoming radiation to enter the aperture. A working fluid is supplied to the enclosure at substantially ambient temperature and flows laminarly through the enclosure in a direction of flow that is substantially perpendicular to the outermost entrance aperture, whereby the incoming radiation is absorbed within the enclosure to heat the working fluid within before it exits as a very hot working fluid. At least one optical radiation mechanical and/or fluidic baffle is positioned to allow the incoming radiation to ultimately heat the exiting fluid within the enclosure but to prevent spectral radiation which is generated within the enclosure from escaping the enclosure. This ensures that the fluid will exit the enclosure as a highly heated working fluid, containing essentially all of the incident solar energy for directly powering thermal processes or for storage and later use as thermal energy on demand.
The invention further comprises a method for collecting solar energy, the method including the steps of directing the incoming solar spectrum through an entrance surface, which may be a wide or narrow aperture, into a container, and supplying a substantially ambient temperature working fluid to the container so as to have a laminar flow within the container in a direction that is parallel to the incident solar light direction. The method includes absorbing solar energy within the container to directly or indirectly heat the flowing working fluid and also preventing thermal energy within the container from exiting the container. Finally, the method includes directing the heated fluid out of the container to provide useful high temperature thermal energy.
The subject invention meets all of the high temperature, high collection efficiency, and long term reliable solar energy storage objectives of practical solar thermal energy—all at many times lower costs than prior arts. As will be illustrated herein, high temperature solar collection nearing 100% efficiency can be achieved by the subject invention—thereby leaving negligible room for all other solar technology improvements. The subject invention advocates the use of the most abundant raw materials on earth to construct low-cost solar traps and inexpensively store unlimited solar thermal energy—thereby paving a path to the lowest possible cost solar power technology. Such a combined breakthrough leaves little impetus for others to do better than the subject invention. For the first time in history, the subject invention employs essentially all of the fundamental physics energy functions to economically satisfy almost all of man's energy needs—not just electricity, space conditioning, and hot water—for centuries of exponentially rising energy demands.
The foregoing, and additional objects, features and advantages of the present invention will be understood by those of skill in the art from the following detailed descriptions of preferred embodiments when taken with the accompanying drawings, in which:
The preferred embodiments of the subject solar trap invention that will be described below can readily exceed 1200° K collection temperatures with only one-sun applied instead of the typical 100-sun mirror concentration of the prior art, while simultaneously exhibiting exceptionally high collection efficiencies in excess of 90%. Prior solar art one-sun flat panels typically fall to near 0% collection efficiency at under 500° K (200° C.), and typical prior art mirror-concentrating solar tower receivers fall to 0% efficiencies at about 1200° K (900° C.). If the subject one-sun invention is augmented by the use of optical mirror concentration, such an embodiment would have no known upper temperature limits, even in excess of 1200° K, while still retaining high collection efficiencies, thereby illustrating more than a 10-fold to 100-fold improvement over the prior art. This latter embodiment can be better appreciated by emphasizing that radiation losses in prior art devices skyrocket by a factor of T4, which means that radiative losses normally rise by 16-fold each time the absolute collection temperature is doubled. The subject invention does not suffer from the usual prior art hot surface radiative losses. As will also be illustrated, collecting and storing just twice higher temperatures does not merely double the useful stored energy, but can surprisingly provide 10-fold or higher useful draw-down energy, which translates to an opportunity to slash storage costs by more than 10-fold.
Until the advent of the present invention, all prior art solar thermal collection technologies have suffered from huge thermal radiation losses, even at very low collection temperatures.
It is the very high temperature plus the very high efficiency distinction of the subject invention that differentiates it from all prior solar arts. This distinction is only possible by overcoming the formidable T4 infrared radiation losses from heated surfaces that are depicted by chart 30 in
Where W is the work done by the system (energy exiting the system as work),
QH is the heat put into the system (heat energy entering the system),
TC is the absolute temperature of the cold sink reservoir, and
TH is the absolute temperature of the hot source reservoir.
Clearly, the highest thermal efficiencies are achieved by employing the highest TH source temperatures (and/or the coldest TC sink temperatures such as in deep space). Exceptionally high temperatures are also a fundamental requirement of the lowest cost, highest energy-density storage technologies. Thus, prior art solar thermal collection technologies have been restricted to low Carnot efficiency devices, high cost solar collectors, and costly, short term thermal storage, and these formidable restrictions create unaffordable and unreliable solar power. As emphasized above, all of these items govern energy costs, products, jobs, and economic prosperity, not to mention the very long list of environmental consequences.
The total radiation intensities curve 32 in chart 30 of
Pnet=Aσε(T4−T04). eq 2
Where, P is the total radiation is 2π steradians and across all wavelengths, in waits;
A is area of the radiating surface in m2
σ=a constant 5.67×10−8 W m−2 K−4
ε=emissivity of the specific material (0 to 1)
T=temperature of surface
To=temperature of the environment into which the radiation is liberated.
Once energy is captured in a truly usable form, such as high temperature thermal energy, it can be directly employed as thermal energy or it can be efficiently transformed into almost any other form of energy, such as electricity or chemical energy. That fact envelopes almost 100% of civilization's energy needs such as direct conversion of high temperature thermal energy into cold refrigeration energy; direct space heating of buildings; direct high temperature industrial thermal process manufacturing; conversion of thermal energy into liquid or gaseous fuels; and direct thermoelectric power generation. Such ultra-efficient and low-cost solar energy invites the use of a wide array of thermo-chemical technologies to produce lower cost synthetic liquid or solid fuels. For example, thermal depolymerization chemical industries can mass produce lower cost synthetic liquid and solid fuels. Likewise, much lower cost hydrogen fuels, having no greenhouse footprint, can also be produced at high temperatures and saved at ambient temperatures. Of course, stored synthetic fuels often suffer gross inefficiencies when the stored energy is retrieved (usually by way of combustion processes).
The actual need for liquid fuels can be almost eliminated if the many promising superior battery technologies mature to enable 85% efficient electric vehicles instead of 20% efficient combustion based vehicles. If mass produced electric vehicles replace combustion vehicles, then the subject solar invention can also be the clean electric source for electric transportation.
Overarching man's long term energy dependence is the grim prospects of no energy wiggle room. Combustion, nuclear fission, fusion, deep geothermal, wind, tidal, and all other energy sources are simply inadequate, unsafe, polluting, environmentally destructive, and above all, too expensive. All prior solar arts have been unaffordable, despite the 10,000-fold abundance of solar energy. The present vastly improved solar technology removes all of the previous solar barriers. Sheer “abundance” of clean energy is no longer the prime objective. Cost is now the primary barrier.
Chart 40 in
The immediate need for an urgent transition to a new much larger prime energy resource is an understatement. It is widely acknowledged that conventional affordable energy resources will be largely exhausted within as little as 52 to 56 years at our current 2% per year exponential consumption rate. Some cavalierly refute the 50 year premise with disregard to exponentially rising demands; to the soaring energy recovery costs; to the dire global environmental harm; or the severely adverse economic impacts. Clearly, starting a transition away from combustion fuels 50 years from now is too late, when it's all gone. A complete transition will likely take 50 years, if started today. The small percentage of combustible fuels that will be left for posterity, after a full transition to an alternative energy, will likely not be much. Many other products that require these precious hydrocarbon commodities might be scarce. Hydrocarbons simply should never be burned. Instead, they should be used and recycled.
Many are convinced that the above worrisome energy consequences will adversely impact international peace several decades before the world's conventional energy coffers are empty. But it would likely take several decades to transition from combustion and nuclear fuels and to preserve a meaningful fraction of our versatile finite material resources for posterity. If peace is important, it is essential that other far larger and especially less expensive, alternative energy resources be introduced immediately, not later.
It is widely acknowledged that global conventional energy costs will continue to sharply rise as the world's finite and easy-access resources dwindle. Thus, man's practical options are reduced to two: 1. either do without unaffordable/unavailable energy or, 2. find a way to capture and store vastly superior solar energy far less expensively. The first sacrificial option can reverse man's ascent. The second option can accelerate the ascent with abundant food, water, jobs, shelter, productivity, and human population, like few can imagine, and like mankind has never experienced. It can be vividly shown that about 98-99% of products, services, jobs, and survival itself, are inexorably linked to energy—and now—no longer the abundance of energy, but to the sheer cost of energy.
History (
Thus, humanity itself is now 98% dependent on about 198.000 btus per capita per day of external machine energy (˜2,440 continuous watts per person per 24 hours). Human survival or extinction has subtly become inexorably linked to non-human energy. Modern life, and more importantly, man's future, depends on it.
The above per capita approximations are readily supportable. The total theoretical net output power of 7 billion healthy adult males laboring at a maximum of 50 watts for 10 hours every day equals “only” 5×1015 btus per year (5 quads). But, the fact is that 7 billion of us actually consume 520×1015 btus per year (520 quads)—104 times more energy than humans alone can provide. Thus, a mere 5 quads of manpower alone, can only supply ˜1% of humanity's real energy dependence. 99% must be supplemented by external energy from the likes of combustion fuels, nuclear, hydro, bio, wind, and, preferably, the largest of them all—solar energy. This firmly illustrates how insidiously our external energy dependence has grown from near zero, now surpassing 99%—illustrated in
To drive the above 99% energy dependence image home—envision the impacts of energy shortages. Energy-intense farming and food production, electric and water shortages, reduced transportation of people and goods, jobs, and peace, can all be decimated without energy. Human extinction is not an option, especially when there is now one hopeful solution—affordable and reliable solar energy. Emergency-scale solar energy preparations can only do good by providing massive new jobs, improving economic prosperity, saving the environment, and preserving our finite natural resources.
Cheap, easily accessible oil and gas will be the first to go.
Improved energy efficiencies are always highly recommended but those bandaids can only modestly prolong the inevitable environmental destruction and energy depletion. The need of a historic paradigm energy transition remains inescapable—unless a dramatic human depopulation somehow becomes an acceptable option. Even then, an inescapable energy transition is still required to preserve global environments. The sooner the inescapable energy transition the better for the environment, the economy, and for peace. In all cases, energy costs still need to fall, not merely be maintained.
Civilization's future energy consumption (up to 400 times our current needs; see chart 40 in
Inaccurate reports of “hundreds of years” and even some extremist reports of “a thousand years” of nuclear energy reserves are simply unsupportable by the raw facts. Study after study supports a relatively abrupt end to affordable conventional energy reserves and resources. Even optimistic nuclear physicists proclaiming a “thousand years” of energy seem to completely ignore the shocking impact of a mere 2% per year exponential increase of energy demand, which destroys such optimism [e.g. a possible 400 times our current annual consumption PER YEAR in just ˜300 years]. For vivid clarity, the above most optimistic “1000 years” of conventional nuclear fuels could be consumed in just one or two years if, in the future, mankind actually does consume “hundreds of times” more energy PER YEAR (see
Prior art solar technologies all fail on cost, efficiency, and long term storage. Typical 100-sun prior art Concentrating Solar Power (CSP) thermal solar collection technologies fail vital collection efficiency tests—roughly 60% efficient at meager 500-600° C. collection temperatures. Far worse, prior art CSP technologies typically achieve near 0% collection efficiencies (radiation losses equal to incoming solar flux) at only 900° C. (1200° K) as depicted in
In other words, if 100-suns (100,000 watts per square meter) of solar power were concentrated on a highly absorbing 900° C. (1200° K) solar receiver surface, each square meter of hot receiver surface would radiate and lose an equal amount—100,000 watts—of longer wavelength light. Unfortunately, even 900° C. is not hot enough to achieve the lowest cost energy storage. If a hypothetical state of the art high efficiency 800° C. (1472° F.) turbine were powered by a hypothetical 900° C. solar storage source, the storage source would rapidly drop only 100° C. to below the 800° C. design turbine temperature and efficiency would suffer as the storage temperature decreases. By comparison, a much higher storage temperature, of the same physical size, could supply the same turbine design temperature and it could remain efficient many times longer. Thus, higher temperatures permit higher energy densities, physically smaller units, and can be much less expensive.
The scientific community is much more familiar with thermal “conductivity” (k) than thermal “diffusion”, alpha (symbol “α”). Thermal conductivity is a measure of the steady state rate of heat flow in w/mK, whereas a is related to the time required for heat to propagate a specified distance. Thermal diffusion is a vital component of the subject invention and thus, a brief explanation is in order.
Thermal diffusion is mathematically defined:
∂T/∂t=(k/cp*ρ)(∂2T/∂x2) Eq. 3
Where: T: temperature, K
-
- t: time, s
- x: propagation distance, m
- α=k/(cp·ρ): thermal diffusivity, m2/s
- k: thermal conductivity at T, W/(m□K)
- cp: specific heat capacity at T, J/(kg□K)
- ρ: density at T, kg/m3
The thermal diffusion graphs in
The low thermal diffusion time property of materials enables the subject invention to overcome one of the most problematic barriers of prior art solar collection. If the working fluid in a solar collector is purposely flowed through the solar collector at the correct velocity to prevent heat from ever conductively or convectively reaching the solar entry surface, then the surface cannot heat or radiate (lose) energy. This diffusion phenomenon will be referenced in the invention section below, but it is not the only feature which enables the subject invention to reach extremely high temperatures and remain so energy efficient. Wavelength selectivity and angular geometric radiation directivity/selectivity are also features which greatly help to make the subject solar traps ultra efficient at extremely high operating temperatures. Each of the features and physics phenomena is expanded in the preferred embodiments below.
PREFERRED EMBODIMENTS OF THE INVENTIONAs illustrated diagrammatically in
The flowing fluid 60 retains or traps an exceptionally large proportion of the received solar energy as heat, and the resulting highly heated working fluid is directed out of solar trap 50 by way of an outlet passageway, or pipe 70 to a heat storage mass vessel 72 which may contain a porous mass 74, through which hot fluids flow from the solar trap 50 and exit at 75 near ambient temperature. A second heat extraction fluid may enter storage vessel 72 at 76 and exit as a very hot fluid at 78 so that the hot fluidic heat energy may power, on demand from storage, almost any heat engine such as powerplants or other thermal machines 80
In another aspect, the invention is directed to a method for collecting solar energy which may be briefly stated as including the steps of directing radiant energy into a container, or trap, supplying a working fluid to the container, causing the working fluid to have a laminar flow within the container in a direction perpendicular to the entrance aperture surface to nullify conductive and convective thermal losses, employing one or more baffles to nullify internal emission losses, and to convert such solar energy almost totally into thermal energy in order to ultimately heat a working fluid, while preventing almost all internal energy from conductively or radiantly escaping from within the container, and followed by directing the heated fluid out of the container for energy storage or for direct usage.
In another preferred embodiment, many of the subject solar traps may be mounted on a single central tower to be used as dramatically improved central tower receivers in a well known mirror field CSP (Concentrated Solar Power) configuration, such as that illustrated in
Prior art tower receivers attempt to increase efficiencies by employing thousands of mirrors to greatly intensify the solar flux received at a central receiver surface, and by brute force, overcome the well known thermal reradiation losses when producing temperatures of only 600° C. This was illustrated and mathematically shown in the discussion of
Note that prior art central towers are designed so that a typical 90 degree wide azimuth angle of mirrors are accepted by a single central receiver hot surface having a typical absorbance of 0.92 and an emissivity of roughly the same 0.9. As will be shown below, a preferred form of the present invention takes advantage of a very narrow solar beam, typically a solid angle of 0.01 to 0.001 steradians (less than 0.3 degrees), as indicated in
The back surface 90 of each solar trap enclosure 54 depicted in
As will be further explained below, the term “baffle” applies to more than just mechanical structures such as solid angle constrictor honeycombs (polygons), screens, fibrous wool, and the like. Such mechanical baffles can also be constructed from materials which selectively reflect and absorb solar and infrared radiation. Mechanical baffles can also be coated with selective wavelength materials such as SiO2.
To be more clear about honeycomb (triangular, square, hexagonal, polygon) mechanical “baffles” and especially “selective wavelength” baffles, equation 4 can help design exceptionally sharp multiple reflection selective wavelength baffles:
Net reflective transmission=(Rλ)n Eq. 4.
where: (Rλ) defines the decimal reflection of one surface at a given wavelength and n is the number of reflections of light on a path through a selective wavelength baffle
A selective wavelength baffle, such as the baffle 64 used in the embodiment of
Even more broadly, the term “baffle,” as employed herein, also applies to selective transmitting and absorbing gaseous or liquid fluids—water and many oils being examples of highly selective transmitters of solar spectrums and highly absorbing infrared absorbing “baffles.” See
The solar trap system 50 depicted in
The first priority of counterflowing solar traps is that of maintaining the solar entry surface 56 at non-radiative near ambient temperatures as previously computed in the emission discussion relating to
The curves 100, 102, 104 and 106 in
Another advantage of counterflowing fluids is the continuous cooling effects on the fluid-cooled baffle surfaces. Radiation, which is so T4 dependant, can be largely kept in check by the cooler counterflowing fluid. In other words, the highest temperatures nearest the bottom surface 90 and the associated extraordinarily intense radiation therefrom, is absorbed deep in the honeycomb where that heat is re-absorbed and convectively carried by the counterflowing fluid deeper into the trap 50 towards surface 90. When the correct fluid velocity is employed, the end result is a fixed thermal standing wave between the ambient entry surface 56 and the bottom hottest surface 90.
Still another advantage of counterflowing fluids in a solar trap is that they can be employed as the working fluid throughout the entire solar collector and its thermal storage container, shown at 72 in
Referring to
As is well known by those skilled in powerplant technology, river water or some other means is needed to keep powerplant turbine condensers as cool as possible in order to meet equation 1 Carnot efficiency requirements. Thus, the exiting working fluid from a powerplant (or other thermal machine) can be returned to the bottom of the thermal storage bed 72 by way of loop 77 return pipe 76 at or near ambient temperatures. The bottom of a counterflowing storage bed can be maintained at ambient temperatures while the top portion of the bed can be maintained at the highest possible temperatures from the solar trap. Should the collected solar energy be excessive and saturate the entire solar storage medium, several fail-safe features can automatically limit and protect the solar trap. For example, if the working fluid were returned to the solar entry surface at roughly 90 to 100° C., the front surface 56 of the solar trap will radiate and lose about 1000 watts/m2, an amount equal to the most intense incoming solar energy. Thus, solar trap collection can be self limiting. The counterflowing fluid 60 can also be halted or slowed, thereby also limiting the collection of solar energy. Finally, if snow starts to build on top of solar traps, the counterflowing fluid temperature can be briefly increased to melt the snow with a surprisingly small amount of stored energy, thereby preventing snow accumulation. The thermal energy to melt snow (80 calories/gram) is not a large drain on a well designed solar storage system.
The counterflowing working fluids 60 can be selected from a wide variety of gases/fluids. The preferred gases, but by no means limited to these gases, are the inert gases such as N2, Ar, Ne, CO2, SF6, Kr, Xe, or mixtures thereof, with or without selective absorbing spectral gas additives. Some would argue that SF6 gas is a potent global warming greenhouse gas and should not be industrially used. However, the very purpose of solar energy is to eliminate gigatons of CO2 greenhouse emission gases. Thus, employing a small charge of a very potent greenhouse gas has the profound effect of eliminating millions of times of combustion greenhouse gas emissions. SF6 is fully justified in all solar trap configurations proposed herein. Xenon is another controversial gas. Xenon, which has no greenhouse impacts, is a very rare and expensive gas. Nonetheless, Xe is one of the best gases to use in solar traps and the cost savings of physically smaller solar trap systems can offset the one-time cost of expensive Xe gas. Over 10 million liters of Xe gas is currently a byproduct of air separation technologies in producing mostly liquid nitrogen and oxygen. Low purity Xenon could, in principal, be practically given away while negligibly impacting LN2 and oxygen revenues. Xenon atmospheric concentrations are about 87 parts per billion (about 4.3×1011 kg in earth's atmosphere or, about 76 billion cubic meters—far more than needed to solar power civilization). Similar arguments can be made in favor of employing 10 times more abundant and 10-fold less expensive krypton or mixtures of Kr and Xe.
Solar traps used as receivers in central tower (CSP) systems offer additional indirect performance advantages. As previously stated, the first large advantage includes the possibility of more power output from a powerplant as a result of higher Carnot operating turbine temperatures. The highest turbine powerplant efficiencies (over 60%) are presently possible in state-of-the-art 760° C. (1400 F) ultra critical steam temperature powerplants. Compare that efficiency with just over 35% efficiencies of most of the world's current coal burning powerplants. Such high solar operating temperatures can almost halve the number and cost of CSP mirror fields—while providing much higher thermal storage temperatures. Recall that storage temperatures drop when called into service and thus, ideally, much higher storage temperatures can maintain full powerplant efficiencies. Very high CSP solar trap efficiencies make capturing and storing extremely high temperatures possible, which slashes the number of field mirrors by more than 50%. And the cost of thermal storage can also be reduced dramatically in surprising ways. Thus, the employment of the subject gaseous solar trap embodiment can reduce the cost of CSP electricity more than 3 to 5 fold. That helps to make solar electricity even more competitive than the least expensive electricity on earth—even before financially accounting for the far cleaner land, air, and sea environments.
Thus far, only one CSP preferred embodiment of the subject invention has been illustrated. Another, non-CSP embodiment of the invention has an even greater impact by totally eliminating heliostated concentrating mirrors. The embodiment of the invention depicted in
No sacrificial solar land is required if flat panel solar traps are located on existing rooftops and atop existing parking lot land. In just the U.S., there exist about 7,000 square miles (18 billion sq meters) of potential solar rooftops and solar parking lots. At high noon, 18 billion m2 of sunshine equates to about 18,000 gigawatts of solar power (˜30 trillion kwhrs per year of cloudless skies . . . about $3 trillion at $0.10/kwh). 30 trillion kwhrs equates to about 100 quads (100 quadrillion BTUs) per year or, the total U.S. energy demand of all electricity, liquid fuels, natural gas, and nuclear energy combined. Of course, this first approximation assumed cloudless days. But even with normal cloud coverage plus large energy storage, the total actual clean energy available on rooftops and parking lots would provide a very large fraction of the total U.S. energy demands.
With emphasis, this flat panel, one-sun embodiment illustrates the broad applications of the subject invention, inviting the use of a wide range of materials, working fluid choices, and geometric configurations, to increase temperatures and optimize solar trap performance. Estimates have shown that the retail value of solar energy which can be collected and sold from shopping center rooftops (as space heating, cooling and electricity) can exceed the typical rental revenues that can be generated by mall owners under shopping mall roofs.
The key to one-sun, flat panel solar trap performance remains similar to 100-sun CSP solar receiver operations. In other words, a one-sun solar trap can achieve the same 98% efficiency if only 20 watts/m2 of the available 1000 watts/m2 were lost (instead of 1,845 watts/m2 of 117,000 radiative watts at 900° C.). See the
One-sun flat panel solar traps can be gas filled or liquid filled for counterflow purposes. Few optically clear room temperature liquids can withstand prolonged exposure to much more than 500° C. (800° K, 932° F.), whereas many gases can withstand prolonged exposure to more than 10,000° C. One optically clear liquid which boils at about 575° C. is a common vacuum diffusion pump silicon oil known as 1,1,3,5,5-pentaphenyl-1,3,5-trimethyl-siloxane oil. Very thin (centimeters thick) flat panel solar traps of the subject invention can work with silicone oils, but even higher temperatures can be trapped using inert gases, particularly high atomic weight Xenon gas. A thin, “flat panel” solar trap is illustrated in its simplest form at 120 in
Once a thermal diffusion velocity is computed for a given fluid, and under high temperature conditions (where all of the fluid properties, such as density and thermal conductivity, change with temperature), a second calculation can be performed knowing the input solar energy per second. In the Xenon flat panel solar trap example of
The solar input power 122 to a flat solar trap receiver 120 may be assumed as 1000 watts/m2 or 1 kj/sec. To achieve the highest solar trap operating temperature a sufficiently high fluid thickness, X (Eq. 3), and a sufficiently slow counterflow velocity must be selected so as to obtain the longest possible solar exposure time in order to heat the fluid to the desired temperature before it exits the solar trap. The latter calculation simply requires knowledge of the exposure time (which is determined by the solar trap thickness; i.e., the distance between the entry surface 124 and the black porous layer 144, and the fluid velocity) and having access to the density and the specific heat values of the chosen fluid at the desired high operating temperature. These are reasonably straightforward calculations done by those skilled in these arts, using equation 3, plus the fluid thermal constant values, such as specific heat values, at elevated temperatures. The latter calculations have been performed for Xenon gas exiting at 900° C. and it was found that a Xenon solar trap must be about 15 cm thick and must counterflow inside the trap at a velocity of about 0.75 cm/second under a one-sun exposure intensity. See
Higher temperatures can be achieved if the exemplar Xenon solar trap is made thicker than 15 cm and thus, the counterflow velocity slowed considerably (by “1/X2”). As illustrated in
As illustrated in
Also shown in
High temperature commercial and industrial rooftop solar raps discussed above can be scaled down for use on residential rooftops, which represent many thousands of square miles of solar surface area in the U.S. Furthermore, residential solar traps applications offer several unexpected benefits far beyond those provided by prior art supplemental hot water rooftop technology.
A typical 150 m2 residential rooftop can collect up to 1000 watts/m for 5 or more hours per day or, about 750 kwhrs (2.55 million BTUs) per day (930 million BTUs/year). Even if such a typical residence needed 30,000 BTUs/hr (8.8 kw/hr) of winter space heating (720,000 BTUs per day), there would be 1.85 million extra BTUs per day left for hot water (typically 100,000 BTUs/day) and electricity (2 kwhrs×24 hrs=48 kwhrs, or 163,000 BTUs per day)—leaving about 1.567 million BTUs/day for sale during winter months if there were a way to sell the excess solar energy at each residence. In this example, the total 2.55 million BTUs/day or, 930 million BTUs/year, annual rooftop energy, based on a current retail energy price of about $4 per 140,000 BTUs, would be worth about $26,592 per year. Just the excess 1.567 million BTUs per hour (572 million BTUs/year) rooftop energy would be currently retail valued at about $16,118 per year, if a way to sell the excess thermal rooftop energy was available. There are at least two ways that excess residential energy can be sold. One obvious high temperature option would be to generate electricity on site and sell the electricity using the existing power lines feeding the building. If, for example, a mere 25% efficient turbine generator produced 25%×572 million BTUs per year of electricity—or 167,637 kwhrs/year—the electricity might be valued at 10 cents/kwhr, and the excess electricity alone would be worth $16,764 and the waste heat (429 million BTUs) from the 25% efficient generator, would have an additional value of $12,257—a total excess energy sale potential of $16,764 plus $12, 257 (or, $29,021/year)—again, provided a means to sell the waste heat existed.
U.S. Pat. No. 6,688,129 discloses a means to sell such waste heat. The patent describes an exceptionally low-cost method to distribute either pre-warmed or pre-cooled potable water using the existing potable water lines feeding residential buildings. And if high temperature residential rooftop units are partially used to generate on site electricity, not only can the excess electricity be sold using the existing power grid, but the inefficient waste heat from miniature residential thermoelectric power generators can be employed on site for residential heating, and the excess thermoelectric waste heat can also be sold using the nation's existing potable water infrastructure. There is possible a nearly 100% efficient use of residential solar energy. Almost all of the solar collected heat can go towards generating electricity (which can all be sold at the highest prices), and the remaining waste heat can be used for winter space heat and to provide for hot water on site in the solar residence. Solar heat beyond the needs of the on site solar residence can be sold as warm potable water to heat nearby buildings as detailed in U.S. Pat. No. 6,688,129. In summer months, super efficient, high temperature, solar traps are ideal for highly efficient heat-powered, prior art, Absorption Cooling technology. Excess ice-cold space cooling water can be sold via the existing national potable water infrastructure.
Since transparent liquid fluids greatly limit the operating temperature of the subject solar trap invention to less than about 550° C., unlimited temperature gas fluids can be employed in the serpentine counterflow solar trap to achieve the highest operating temperatures. However, gas fluids do not offer optical index matching opportunities as do transparent liquids. Fortunately, slightly absorbing, extremely broad band thin films can be coated on each transparent serpentine layer 230 to nearly eliminate all reflections within a serpentine solar trap. Such slightly infrared absorbing layers 230 and absorbing thin films offer additional benefits to trapping thermal radiation as well. Beer's law and equation 4 come into play here, as discussed previously concerning selective wavelength baffling, and as depicted in
The diagrammatic serpentine flow illustrated in the embodiment of
A serpentine counterflow solar trap offers all of the high solar spectrum entry opportunities of other solar traps detailed herein, including the elimination of thermal diffusion and entry surface thermal radiation losses; including the ability to re-absorb and recycle intense internal thermal radiation; and the opportunity to achieve exceptionally high solar trapping efficiencies at exceptionally high efficiencies. Therefore, such high temperatures at high efficiencies, offers the same opportunities to long-term densely store solar thermal energy at the lowest cost for reliable on-demand solar energy for unlimited applications.
Low velocity counterflowing liquid and gaseous working fluids in the subject solar trap invention have been illustrated to totally nullify thermal conductivity, thereby eliminating almost all front solar entry surface radiation losses in solar thermal collection technology. Wavelength selective and mechanical angular selectivity blockage of internal hot surface radiation has also been shown to prevent thermal radiation from escaping the subject thermal solar traps. The combined results of the breakthrough solar trap technology plus much lower cost energy storage enables many times less expensive solar power, thereby enabling worldwide implementation of the most abundant energy resource on earth as the least expensive and cleanest energy on earth. Quad generation, the world's most efficient use of energy for electrical power, space heating, cooling, and hot water is also disclosed.
Several very high temperature preferred embodiments of the subject invention illustrate how it can dramatically improve existing central tower CSP technology; how it can retrofit existing combustion and nuclear powerplants with clean, reliable, high temperature solar energy; and how solar energy technology can rapidly progress beyond the concept of large central power utilities by implementing small, highly profitable distributed rooftop solar energy. And it has been shown that distributed rooftop solar technology can meet the energy needs of entire nations without demanding any dedicated solar land. High temperature solar collection has been shown to economically store vastly higher useful solar energy for as long as desired, thereby making solar energy reliable without the need for extremely costly standby conventional backup power.
It has also been shown how potable water U.S. Pat. No. 6,688,129 can be an integral component in delivering vast quantities of perfectly clean and cheap solar energy to buildings, and at incredibly low delivery costs, for space heating, cooling, and hot water—over of the world's energy demand. Likewise, it has been shown how low-cost distributed solar electricity generation can employ the existing grids to power nations, especially if ultra efficient electric cars are popularized.
Solar energy not only can, but must, become the world's least expensive energy resource. There is no larger, cleaner or, better option. The subject invention can more than meet that need. It offers an unparalleled boost to prosperity. And, to the more conscientious people, the most important consequence of a rapid transition to a solar age, are the free environmental bonuses and the preservation of the world's versatile and finite hydrocarbon resources for posterity. Mankind can finally stop excavating for energy and stop burning our valuable resources.
Thus, it will be understood by those skilled in the several arts described herein that the subject invention and its many described embodiments and numerous variations may employ a wide variety of mechanical structures and numerous transparent and semi-transparent liquids and gaseous fluids to produce a counterflowing effect, wherein a working fluid opposes thermal conduction, thermal convection, and/or internal reradiation effects, to reduce energy loss to near zero, and thereby increase solar energy collection efficiency, without departing from the spirit and scope of the invention, as set forth in the following claims. It will be understood that the upper temperature limits discussed herein are by no means the maximum temperatures or the maximum solar efficiencies achievable by the subject invention and that an unlimited combination of spectrally selective solids, liquids, gases, and coatings can be employed in and with counterflowing working fluids and, in general, to “baffles” for higher performance solar traps, without departing from the spirit of the subject invention.
Claims
1. An exceptionally high efficiency, high temperature; solar energy collector, comprising:
- an enclosure having a front portion and a rear portion;
- a solar entrance at said front portion to allow incoming solar radiation to enter said enclosure;
- a fluid inlet at said front portion of said enclosure to receive a counterflowing working fluid at substantially ambient temperatures;
- at least one baffle positioned laterally across said enclosure between said front and rear portions to guide the flow of said fluid through said enclosure toward said rear portion, said at least one baffle allowing said incoming radiation to be nearly fully absorbed and converted to heat within said enclosure;
- a fluid exit at said rear portion,
- wherein said at least one baffle further preventing radiation which is generated within the enclosure from escaping, whereby the fluid is heated and exits the enclosure at said fluid exit as a highly heated working fluid.
2. The energy collector of claim 1, further comprising a solar spectrum absorption surface within the said enclosure, wherein said baffle permits an effective passage of said counterflowing fluid between said solar entrance surface and said absorption surface.
3. The energy collector of claim 2, further comprising a plurality of baffles within said enclosure, each said baffle being gradually heated by reradiated and conductive energy within said enclosure and by incoming solar energy, as said working fluid flows from said front portion of the enclosure where it is at ambient temperature, toward said rear portion, whereby said fluid exits the enclosure as a very high temperature working fluid.
4. The energy collector of claim 3, wherein said solar incoming radiation heats said fluid, said baffles, and said rear portion, wherein said heated fluid and heated baffles reradiate energy, and wherein each baffle is fabricated of, or is coated by, a material which exhibits selective wavelength absorption, whereby solar radiation passes through said baffle toward said rear portion and reradiated energy is substantially prevented from reaching said front surface.
5. The energy collector of claim 3, wherein said baffles are honeycombs which exhibit angular selectivity to impinging radiation, wherein said incoming solar radiation heats said fluid, said baffles, and said rear portion and any reradiated energy from said heated fluid, said heated baffles, or said rear portion is substantially prevented from reaching said front portion.
6. The energy collector of claim 1, wherein said at least one baffle produces substantially laminar fluid flow in said enclosure in a direction that is substantially perpendicular to the direction of said incoming solar radiation and also follows a serpentine counterflow path from said front portion to said rear portion.
7. The energy collector of claim 6, wherein said at least one baffle is nonporous and transparent to incoming radiation and exhibits an index of refraction substantially the same as the working fluid flowing through the enclosure.
8. The energy collector of claim 7, further comprising a plurality of baffles in said enclosure to produce said serpentine path, wherein said incoming radiation is solar energy to heat said fluid and said rear portion, wherein said heated fluid and said heated rear portion reradiate energy, and wherein each baffle exhibits selective wavelength absorption, whereby solar radiation passes through said baffles toward said rear portion and reradiated energy is substantially prevented from reaching said front surface.
9. The energy collector of claim 1, wherein the rear portion of said enclosure incorporates a solar spectrum absorber.
10. The energy collector of claim 8, wherein said solar entrance includes a transparent aperture for admitting said solar radiation.
11. The energy collector of claim 1, wherein said solar entrance includes a transparent aperture for admitting said solar radiation.
12. A method for collecting solar radiant energy, comprising the steps of:
- directing solar radiant energy through a front portion of an enclosure toward a solar spectral absorbing rear portion of the enclosure to trap heat in the enclosure;
- supplying a counterflowing working fluid to said enclosure at a relatively low temperature;
- causing said fluid to flow generally away from said front portion of the enclosure toward said rear portion of the enclosure to be heated by absorbed incoming solar radiant energy in said absorbing rear portion;
- preventing heat from within said enclosure from exiting said enclosure while the fluid is still within said enclosure; and
- directing heated fluid out of said enclosure.
13. The method of claim 12, further including causing the working fluid to have a substantially laminar flow within said enclosure in a direction generally perpendicularly away from said front portion.
14. The method of claim 12, wherein the step of preventing heat from within the enclosure from exiting includes wavelength-selectivity.
15. The method of claim 12, wherein the step of preventing heat from within the enclosure from exiting includes angular-selectivity.
16. The method of claim 12, further including thermally insulating the enclosure.
17. The method of claim 12, wherein causing said fluid to flow generally away from said front portion of the enclosure toward said rear portion of the enclosure includes providing a plurality of wavelength selective or angle selective baffles.
18. The method of claim 12, wherein causing said fluid to flow generally away from said front portion of the enclosure toward said rear portion of the enclosure includes a plurality of flow-direction baffles extending across said enclosure.
19. The method for making a solar energy collector, comprising the steps of:
- providing an enclosure having a front portion and a rear portion;
- providing a solar entrance at said front portion to allow incoming solar radiation to enter said enclosure;
- providing a fluid inlet at said front portion of said enclosure to receive a counterflowing working fluid at substantially ambient temperatures;
- providing at least one baffle positioned laterally across said enclosure between said front and rear portions to guide the flow of said fluid through said enclosure toward said rear portion, said at least one baffle allowing said incoming radiation to be nearly fully absorbed and converted to heat within said enclosure; and
- providing a fluid exit at said rear portion,
- wherein said at least one baffle further preventing radiation which is generated within the enclosure from escaping, whereby the fluid is heated and exits the enclosure at said fluid exit as a heated working fluid.
20. The method of claim 19, wherein said baffles are honeycombs which exhibit angular selectivity to impinging radiation.
Type: Application
Filed: Feb 25, 2014
Publication Date: Jan 19, 2017
Inventor: Ronald S. ACE (Laurel, MD)
Application Number: 15/121,594