Solar thermal technology comprises three different methods to convert solar energy for use. The first method collects the energy of the sun to heat water or air for direct use in solar home heating. The second method is used by large power utilities to indirectly create electricity through concentrated solar heat energy. The third method, known as passive solar, leverages energy efficiency and the design of a building to regulate the amount of solar energy it receives in order to regulate it's temperature.
Solar Power Plants or Thermal Solar Farms indirectly generate electricity when heat from solar thermal collectors turns water or molten salt to steam. As in fossil-fueled power plants, this steam turns turbines that power electric generators.
1) Solar tower: When surrounded by heliostats, which are special mirrors that track the sun, a solar tower collects the sun’s energy. The central receiver at the top of the tower collects and stores heat in special liquid salts that are transported from the tower to a steam generator.
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2) Parabolic troughs: This kind of system uses the shape of a parabola to intensify heat and collect it from the sun no matter what time of day. Tubes filled with a special fluid run through this system. As the special fluid travels by, it warms up and essentially “collects” the heat. The fluid carries its heat to the water, which converts to steam and powers a generator.
3) Fresnal reflector: Instead of heating fluid, this mechanism heats water directly. It does this efficiently by increasing the atmospheric pressure. Steam is created to power turbines.
4) Solar dish: These move with the sun to collect heat all day. Using mirrors, dishes reflect sunlight onto a focal point. They convert this heat to mechanical power by heating a compressed fluid. The hot compressed fluid expands and powers a piston to create electricity.
Solar thermal is the most common form of solar energy used. The simple process of heating water with the sun is used throughout the warmer, sunnier climates of the world. Most homes have some type of water storage tank, painted black to absorb the suns heat. The water is used for showering, laundry and other household uses. It's not sophisticated, but it works. And it's free. The U.S. was a big user of solar water heating until gas water heating became popular. Solar thermal water heating is now making a big comeback because of environmental concerns and very favorable cost comparisons.
The most cost efficient way to implement solar thermal is through a solar water heater. Because most household energy is used to heat water for showers or laundry or dishwashing, having the sun heat your water for free is a great way to save money. Solar water heaters don't create electricity - they simply collect the heat from the sun and store it in a tank for later use. Solar heating works the same way the hose in your backyard works when it's exposed to a few hours of sunlight. The water gets very hot - typically rising 10 degrees per hour of sunlight. These systems are also fairly simple mechanically. The solar installer who implements these types of solar thermal energy systems has a background in plumbing.
Solar thermal water heating is also a great way to heat your pool and spa.
Another extremely simple use of solar thermal for your home is a solar hot air collector. A solar collector made out of thin metal and painted black is fastened to the side of the home and air is circulated through it with a fan. Check out the video of the professionally manufactured solar hot air collector made out of used soda cans on the DIY solar page.