Energy efficiency solar PV modules are not that high. Many different influences relate to this. For example the weather conditions, but also the material that is used and the production techniques. In practice, various internal and external loss factors reduce the return. The most crucial loss factor is the inverter. It converts approximately 90% to 97% of the direct current into alternating current. The rest of the energy is heat loss.
PV cells mainly convert visible light into electricity. However, a large part of the solar energy reaches the earth in the form of infrared light (IR) and ultraviolet radiation (UV). For that part of the sunshine spectrum, the current PV modules are not sensitive. The theoretical maximum efficiency of silicon cells is 30%.
With a “return” of 30% is meant the following:
If a certain amount of light (“irradiation”) from the sun, at a specific moment 1000W falls on 1 m2 of solar cells, then these cells together produce one electrical power of 0.3 times 1000 = 300 W. Technical imperfections in the material currently reduce this to around 19%. Improved production processes are expecting to increase the return to 22 to 25% over the years.
Highly efficient cells have stacking semiconductors with different spectral sensitivity. In this way, returns above 30% are achievable. Determination of the actual efficiency is under Standard Test Conditions (STC).
That means irradiation of 1000 W / m2 (radiant blue sky in June) at a cell temperature of 25ºC. The power that a particular panel below these circumstances, the so-called peak power, expressed in watt peak (Wp). For example, a panel with a cell area of 1 m2 and a yield of 15%, has a peak power of 0.15 x 1000 = 150 Wp.
Have a negative influence on the efficiency of solar panels because the sun is not directly on the boards but at an angle. Another effect that occurs is shadow. When on a small part of the panel is a shadow or less light received by pollution. Then it will produce less electricity.
However, this also affects the other modules that are not in the shadow. Together these panels will produce less electricity than the sum of the production of the individual modules. Mostly al the components have a serial connection with only one PV inverter ( String Inverter ). For places with shadows, a microinverter can solve those problems.
Finally, with high irradiation, the temperature of cells increases. A higher cell temperature harms the efficiency of crystalline silicon cells in particular. A 10% higher temperature reduces the yield of crystalline silicon cells with 5%.
One way to increase cell efficiency is to have a thermal solar PV collector. With liquid that goes true, the panel and taking the heat out. In that way, you can use to warm up a boiler.
These loss factors together:
Explain why the real efficiency of a system is approximately 20 to 30% lower than the STC efficiency. The ratio between the actual return and the STC return results in the
“Yield factor” or performance ratio (PR).
For a network-connected system, this factor is therefore between 0.70 and 0.80. In a solar power system with a yield factor of 0.80, for example, each panel with a peak power of 150 Wp only delivers 0.80 x 150 = 120 W (with an irradiation of 1000 W / m2).