Unlike photovoltaic solar power, which is used to generate electricity, solar thermal power systems are specifically designed to collect, absorb, and distribute heat. Solar thermal power is primarily used to heat swimming pools, heat water for domestic use, and heat the interior of buildings.
Major thermal power technologies include power tower and parabolic troughs, grid connected electrical plants for industrial use. Smaller, standalone systems are used for domestic purposes. These systems generally utilize thermal collectors consisting of flat plates, evacuated tubes, or integral collector storage boxes.
Flat plate collectors are the most common type, used to generate hot water. These consist of rectangular boxes with transparent glazing that prevents heat from escaping while allowing sunlight in. The sun’s radiation enters a metal absorbing sheet designed with built-in pipes that transfer the heated water through the system and into a storage tank. Flat plate collectors that heat water for swimming pools typically don’t have glazing. These collectors work well in warm climates, where swimming pools are prevalent.
Evacuated tube collectors feature solar absorbers with evacuated glass tubes that can reach higher temperatures than flat plate collectors. Evacuated tube collectors perform well in colder climates. In integral collector storage systems, the water itself is the absorber. This heating system is often used to preheat water before it reaches a back-up system.
Solar space heating systems can be classified as passive or active. Flat plate and evacuated tube collectors are usually built into active heating systems, which use pumps or fans to circulate heat. Passive heating systems, such as the integral collector storage system, circulate air or water without the use of mechanical devices.
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