Carbon dioxide (CO2) is a colourless, incombustible gas with slightly sour taste. It is present in the air on a natural level of 0.04%. CO2 is produced in the combustion of coal, oil and gas – the non-renewable energy sources. The rise of the CO2 content in the atmospere is made responsible for the greenhouse effect, because CO2 hinders the emission of heat radiation from the earth into space and thus diminishes the earth's heat losses, resulting in a higher mean temperature on earth. Using energy from PV systems instead of electricity from fossile energy sources, the CO2 savings within few years balance the complete CO2 emissions caused by production and installation of the PV system.