Photovoltaic power generation
Small grid tied rooftop systems dominate the German market. Roughly 80% of the capacity is installed on rooftops and roughly 60% has a capacity between 10-100 kW. Furthermore larger scale installations (>200 kW) are also increasing. Photovoltaic efficiency can currently achieve 17% and is improving. Historically it has grown around 0.5% annually since 2004. The theoretical maximum efficiency of a silicon cell is about 21%. Using a more costly technology 31% conversion has been achieved.
The listed power of a solar cell is the power measured under ideal laboratory conditions, which prescribe a temperature of 25 °C. However, on a typical hot summer day, it is not uncommon for a solar cell to reach a temperature of 70 °C. A general rule of thumb is that the efficiency of a solar cell decreases with 0.5% for every 1 °C above 25 °C. This means that on a hot summer day, the efficiency of a solar cell could drop as much as 25%. It is therefore extremely important to keep solar panels well ventilated. An alternative option might be to implement liquid cooling, using the heat captured by the liquid for household heating purposes
The main factors impacting solar power generation are:
· Solar radiation (direct beam radiation and diffuse radiation)
· Positioning of fixed panels
· Obstructions (i.e. snow, dirt, leafs, etc.)
As solar radiation passes through the earth's atmosphere, some of it is absorbed or scattered by air molecules, water vapour, aerosols, and clouds. The solar radiation that passes through directly to the earth's surface is called direct beam radiation. Diffuse radiation solar is radiation reaching the Earth's surface after having been scattered from the direct solar beam by molecules or suspensoids in the atmosphere.
German solar PV capacity is concentrated in the south of the country, soaking up 30% of total renewable subsidies and providing around 9% of total renewable output.