Abstract: One or more solar cells are sandwiched by a pair of glass laminations substantially transparent to (i.e., essentially transmissive of) the impinging light, thereby avoiding output drop which may occur due to temperature increase by passing of the impinging light therethrough. A thermoplastic or thermosetting type filler, for example, polyvinylbutyral or a silicone resin is used to fill the cavity surrounded by the glass laminations for accommodating the solar cells therein, while serving as an embedding and potting compound to provide resilient environmental protection for the solar cells. Any room temperature vulcanizing type filler may be used.

Abstract: A light-emitting element and a light-responsive element are optically connected with each other through a U-shaped optical guide. An output level of the light-responsive element indicates whether the U-shaped guide is above or below the liquid-level.

Abstract: An oscillator utilizing a negative resistance light emitting semiconductor diode is connected in series with voltage booster means which in turn provides a high voltage to electrodes of a gas igniter. Discharge of the gas between the electrodes occurs with the aid of the high voltage derived from the voltage booster means to thereby effect an ignition of the gas. Light emission from the diode in the absence of gas ignition is indicative of a deficiency in the supply of gas, while the absence of light emission in the absence of gas ignition is indicative of a deficiency in the operation of the oscillator circuit.

Abstract: A metal layer made of a high heat conductivity material such as silver or aluminum is provided at the rear surface of a solar battery with the use of vacuum evaporation technology. A thermoelectric converter is attached to the metal layer in a manner to convert solar energy into electric energy by means of not only the optoelectric effect but also the thermoelectric effect. The solar battery can be maintained at its preferred operative temperature by the metal layer and the thermoelectric converter.