The two main solar technologies for the energy production are:
1. Photovoltaic panels
The advantage of this technology is the ability to transform directly sun rays into electricity.
Despite the decrease of its production costs and its improved efficiency, PV technology does not always appear as an optimal solution. Some unsolved issues are still remaining such as the impossibility to store electricity or the limited efficiency of the energy conversion.
2. Thermo-solar systems
a. Low temperature solar panels
These panels use the direct irradiation of the sun to heat water enabling thus to reach temperatures up to 100°C. On one side, these panels appear to be quite efficient as heat is converted into heat directly and heated water is relatively easy to store. On the other side, this technology is ideal to generate warm water for domestic and industrial use but inefficient to convert heat energy into other form of energies such as hydrogen, electricity, or other outputs. However, due to their low temperature, the conversion of the heat energy into ordered forms of energy (mechanical or electric energy) is very inefficient.
b. High temperature thermo-solar panels and systems (100-350°C)
These systems collect heat energy from the sun (mainly visible and infrared irradiation), typically to generate saturated (but not super heated) vapor at high temperature (up to 350°C) and high pressure (up to 60 bars). These high temperatures are needed to increase the efficiency of energy conversion from heat to usable electric energy. To get to these higher temperatures, the solar radiation needs to be concentrated, so that the specific irradiation surface- corresponds to “many suns”.
There are mainly two types of systems:
Trough-shaped concentrators: The sun is focused to a centrally disposed tube, in which a liquid circulates that can absorb heat. Heat absorbents are typically water or mineral oils.
Extra Flat Concentrators: The same principle can be arranged in a lower cost arrangement.
c. Thermo-solar very high temperature panels and systems (>1000°C)
There are many examples of very high temperature solar concentrators. The high temperature allows for a very efficient energy conversion, but current solutions are still by far too expensive.