Solar powered electricity
Traditional energy sources like coal, oil, and nuclear power have a negative environmental impact. Thus, more and more of the electricity we need for our everyday lives is provided through renewable energy sources. Because the cost of solar cells is falling, solar energy installations are becoming increasingly popular for producing electricity for everyday use.
For the last three decades or so, we have already seen solar cells built into small devices like calculators. But now, we also see them installed on roofs. We read about new solar power plants like the Blythe Solar Power Project in California (which will be the biggest solar power plant in the world) and the Desertec in northern Africa. Most large scale solar installations transform the sun's rays into heat before electricity is produced. But with photovoltaic cells, you can produce electrical power directly from light. This method exists in big scale installations (e.g. the Nellis Solar Power Plant), but it is more often used in roof top installations or in small electrical devices.
Below, I will explain the two different kinds of solar power systems: thermal and photovoltaic.
Thermal power systems
Thermal power systems usually collect the sun's rays in long mirrors which form a half tube. In the focus, where the collected rays are reflected, there is a tube through which water runs. This water will be heated up and transformed into steam by the sun's rays. The steam then drives a turbine, which is connected to a generator which produces the electrical energy.
For the production of electricity through photovoltaic systems, cells of semiconductor materials are used. In these cells, sunlight is directly transformed into electrical power. The light penetrates into the solar cell's material and eventually hits electrons. This knocks them out of their usual place, which is bound to an atom. These electrons are then free to move. Because of the special combination of n-type and p-type semiconductor materials, an electrical field exists. This field forces the free electrons to the surface of the solar cell, where they are collected by metal contacts and led into an attached electrical circuit. The electrons form an electrical flux through which the electrical energy can be used directly. The electrons return to the solar cell's material through the back of the solar cell so that the electrical circuit is closed. As long as light knocks electrons loose, a steady flux of electrons can take place and the electrical energy can be used directly.
Figur of the design and inner workings of a solar cell.