In terms of usefulness, the solar radiation has both advantages and disadvantages. Although it reaches the entire surface of the Earth, the surface is lit unevenly, depending on the latitude, season and time of day. The presence of dust and water vapour in the atmosphere, as well as clouds, prevent the effective use of this energy source. On the other hand, solar energy seems to have the least negative impact on the environment when compared with other unconventional sources. In particular, the lack of harmful emissions is of great significance.
In its direct form, solar energy is used to produce electricity using photovoltaics (photovoltaic energy), and thermal energy in the form of solar panels.
Photovoltaic cells are made of silicon-based semiconductors. They are characterized by high reliability and long life-span. However, they are rather inefficient and very expensive. Their main disadvantage is the high demand for installation space. At present, the energy produced by such cells is several times more expensive than the electricity generated by conventional means. They are used in solar power plants, small watches and calculators.
Another trend concerning use of solar energy is to convert it into heat. Currently, the most common and least expensive device that uses this characteristic is a solar collector. It absorbs radiation and then transfers the energy to water that is heated to 40-65 °C when flowing through the collector. This system is most often used in agriculture and for heating water for domestic purposes, mainly in detached houses. The properly selected solar installation, which guarantees the absorption of solar radiation at the level of 95 percent, can satisfy 50-60 percent of the heat demand.