Solar energy is endless and the cleanest among the known sources of energy. Solar radiation contains huge amounts of energy and is responsible for almost all natural processes on earth. Until recently, the energy of the sun was barely used.
There are two categories of solar energy: thermal and photovoltaic.
Thermal energy can be used for passive heating of buildings by using particular building materials or is used directly to heat water for domestic use. Solar water heaters are now an actual alternative to appliances powered by other sources of energy in many regions. The use of solar energy and other forms of renewable energy reduces dependence on fossil fuels, which directly reduces the emission of CO2. An average household can reduce the emission of CO2 by as much as 20% by installing solar collectors. Flat collectors have been used for several decades. Vacuum collectors have been in use for over 20 years, but have always been much more expensive than flat ones. They were chosen, for example, to be used in high-temperatures. In recent years, increased production has resulted in a significant reduction in prices. Vacuum collectors are now at a price similar to flat collectors, but they have the advantage in the form of better thermal insulation. They are slowly becoming the default choice for all applications.
Photovoltaic cells (PV) using semi-conductive technologies for converting light energy into electricity can be used directly or can store energy in a battery to be used later on.
Photovoltaic panels are now becoming commonly used as they are very versatile and can be easily installed on buildings and other structures. They can provide a clean, renewable source of energy that can complement (and thus reduce) consumption of energy from the power supply network. In regions without an electricity source (for example, emergency telephones, telecommunications relays, monitoring systems), energy from panels can ensure a reliable electricity supply. The disadvantage of photovoltaic panels is their high cost and relatively low energy conversion rate (about 15-20%).