Solar heat generation: hot water thanks to solar energy
"Generating heat with the power of the sun – that is the principle of solar heat generation. The general public in Germany are becoming more and more aware of this. According to the Bundesverband Solarwirtschaft e.V. (BSW-Solar) [Federal Association of the Solar Industry], 2.15 million solar heat generating systems had already been installed in the Federal Republic of Germany by 2015. Private households that opt for this environmentally friendly method of energy generation are financially subsidised."
How does solar heat generation work?
In the use of solar energy we distinguish between two types: photovoltaic and solar heat generation. In photovoltaic, sunlight is converted into electricity, whereas in solar heat generation it is converted into heat for hot water and heating.
A solar collector with pipes is mounted on a surface on which the sun shines, for example the roof of a house. This is the core of a solar system. The most widely used type is the flat collector, which consists of a selectively coated absorber. This absorbs the incident sunlight and converts it into heat. A heat transfer fluid, usually a mixture of water and anti-freeze, flows through the absorber. The fluid circulates between the collector and the hot water storage tank. As soon as the temperature in the collector exceeds the temperature in the storage tank, the controller switches the solar circulation pump on. The heat transfer fluid then transports the heat absorbed by the collector through exceptionally well insulated solar pipes into the hot water storage tank. Here it passes through a heat exchanger, which transfers the heat to the drinking water without contact and with high efficiency.
In summer the solar heat generating system is often sufficient to provide the energy for the supply of heat to a private household. In winter, however, the heating system must assist with the heating of the water.
"According to BSW-Solar, more than 100,000 new solar heat generating systems were installed in Germany in 2015 - that is equivalent to a solar collector area of 0.8 million m2. In total, 2.15 million systems had been put into operation by the end of 2015. They generated a total heating power of 13.4 GW in 2015. According to calculations carried out by BSW-Solar,that saved fuel costs of €190 million."
On account of rising oil prices, stricter climate and thermal protection regulations and the state subsidies, BSW-Solar is forecasting increased demand for, and thus further growth of solar heat generating systems in Germany in 2017.
In Germany, the subsidising of a solar heat generating system is controlled by the Bundesamt für Wirtschaft und Abfuhrkontrolle (BAFA) [Federal Office of Economics and Export Control], which initiated a new subsidy programme in 2016. This is made up of different subsidy rates. A lump-sum subsidy of €500 is paid for hot water solar systems with an area of 3 to 10 m2. With a collector area of 11 to 40 m2 the subsidy amounts to €50/m2. The extension of an existing system is subsidised by the same amount.
In addition to this so-called basic subsidy, application can be made to the BAFA for additional subsidies. €500 are paid in addition if the solar system is combined with a biomass plant or heat pump, if a connection for a heating network with several consumers is installed or if the boiler is replaced by a condensing boiler.
Owners of solar systems in residential buildings of the KfW Standard Effizienthaus 55 standard (Reconstruction Loan Corporation Standard Efficiency House 55) are subsidised with the building efficiency bonus. To qualify as a KfW Efficiency House 55, the energy requirement per square metre of living space per year may only be 55% in relation to the low-energy standard according to EnEV (German Energy Saving Act) and thus has a 45% lower consumption. The bonus granted in this case amounts to 50% of the basic subsidy.