In a 100-year-old farmhouse in the district of Nienburg/Weser in the German state of Lower Saxony, a farmer has made himself largely independent of the electricity grid with photovoltaics and a solar-electric water heating system. This is because he uses the surplus from the photovoltaic installation on the roof to feed it into a hot water tank.
Wood chips heat the rooms
The actual heat supply for the house has been provided by a wood chip heating system for seven years. This is designed to operate in the winter months, when it provides enough energy to heat the spacious rooms of the 340 square metre farmhouse and also supplies hot water.
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But for the warmer months, when the room heating is switched off, this system is far too big. To solve this problem, the farmer first installed a photovoltaic system with an output of 9.7 kilowatts. This system primarily covered the electricity consumption in the building.
Surpluses despite storage
By expanding the photovoltaic output to 14.2 kilowatts, a huge surplus of solar electricity remains after all the electrical consumers in the house have been supplied. Even with a ten-kilowatt battery storage system, the farmer is not able to consume all of the sun's energy on site. To avoid having to feed it into the grid, he uses it to heat water.
Heating rod covers hot water consumption
An AC Elwa-E heating rod with a power consumption of three kilowatts was installed in the hot water tank in the basement of the house. This device provides the entire hot water supply for the building from the beginning of May to the end of October, when the room heating is switched off. It uses only surplus solar power from the roof.
Support in winter
Between November and April, the wood chip heating system runs anyway to provide the room heating. During this time, the AC Elwa-E supports the hot water heating as best it can with the reduced supply of solar power. „If surplus electricity is also available in the less sunny months, this is used to support the heating system,“ explains farmer Erich Hormann. „The wood chip heating system is switched on to provide hot water when the desired temperature has not been reached by the photovoltaic power and the intelligent heating element from My PV after 4 pm. The AC Elwa-E works perfectly, regardless of whether it's summer or winter,“ reports the farmer.
A package for an almost fully solar-powered house
65 per cent of hot water supplied by solar electricity
In the first year of operation, he was able to provide 40 cubic metres of the approximately 60 cubic metres of hot water used in the building from solar power and heating rod. This amounts to 65 per cent of the hot water requirement covered by the AC Elwa-E. As the heating rod is only used as a backup in winter, the farmer was also able to avoid having to use grid electricity to heat the water. (su)
