The sun is the ultimate source of energy in all life on Earth. Otherwise known as solar energy, the energy from solar radiation can be harnessed and utilized in two general methods. The first method, photovoltaics, uses the LIGHT from solar radiation, while the second classification uses the solar HEAT for various applications. Light and heat are not inseparable components of solar radiation, but understanding whether which element is utilized by what method enhances the effectiveness and efficiency of operation. So how does each application work? What are the principles behind its function?
Photovoltaic is a method of generating electricity by converting sunlight into direct current using semiconductors known to exhibit photovoltaic effect. When photons from sunlight strike these materials, electrons are excited into a higher state of energy, allowing them to act as charge carriers for an electric current. Materials commonly used for photovoltaic applications include amorphous silicon, polycrystalline silicon, monocrystalline silicon, cadmium telluride, and copper indium selenide/sulfide.
The assembly of these semiconductors along with a glass cover and other coating makes up the solar cell, and a collectively, cells are electrically connected together to form photovoltaic modules or solar panels. Accordingly, a single module is enough to power a telephone, but a house or power plant needs more electricity that only wide arrays of solar panels can provide.
Photovoltaics was first used to power orbiting satellites and other spacecrafts via direct current. Since then, photovoltaic cells and modules are used for grid connected power generation which needs an inverter to convert DC to AC. Photovoltaics has also been used in buildings as rooftop installations and in transportation sector.
Solar Thermal Systems.
These applications involve harnessing the solar thermal energy, or heat, from solar radiation. Under a clear sky condition, intensity of solar radiation at the Earth’s surface is about 1 kilowatt of energy per square meter area. Electricity is not directly generated with these applications; instead, solar radiation is used for space heating or heating water.
Solar thermal collectors are generally classified as low-, medium-, or high-temperature collectors. Low-temperature collectors are typically used to heat swimming pools and even for space heating. Collectors are normally flat plates with efficiency up to 70%. Operating temperature is below 100 degrees Celsius. Medium-temperature collectors are also usually flat plates but are used for heating water or air for residential and commercial use. Collection efficiency is up to 50% with an operating temperature of 80 to 250 degrees Celsius. The system can also work for drying wood for construction and wood fuels such as wood chips for production, for solar cooking, and for solar distillation. High-temperature collectors use mirrors or lenses and are concentrating-type solar collectors. Operating temperature is above 100 degree Celsius and efficiency is much as 80%. They are generally employed in electric power production through heating water to power up steam turbines.