Cooking with solar power, showering with geothermal energy – and whatever energy is not being used is stored in batteries for later, or simply flows to a neighbour. So-called multi-energy-hub systems (MES) make it possible to supply entire districts with renewable energy – instead of individual buildings.
Depending on what energy sources are available locally, multi-energy systems can be constituted differently: whether wind power, photovoltaics or heat pumps with batteries as energy storage. Another component is electrolysis units, which convert excess wind or solar power into a fuel gas such as hydrogen. Fuel cells can then use this to produce electricity and heat when the sun is not shining or the wind is not blowing. This process is also called power-to-gas technology. Further sub-modules of a multi-energy system are natural gas-fired combined heat and power plants – plants that use their fuel twice by generating heat and electricity simultaneously.