German city of Münster to use excess grid power to heat water

Renewables International

The city of Münster plans to use excess electricity on the grid to generate heat, which can be easily stored.

The local municipal utility is investing 1.7 million euros in a hot water storage tank that will be charged with electric heaters reacting to price signals on the power market. Symbolically, the heat storage facility is located in an old coal bunker in the town’s port.

Essentially, four giant thermoses – each containing 2 million liters of water – will be installed. At times of low power demand, the water can be heated for use in the town’s district heat network. One goal is to further financially optimize the use of the municipal gas-fired cogeneration unit.

Because fluctuations on the wholesale spot market for power are quite small, the price signals used will be for ancillary services. The market for frequency response and backup generators is far more lucrative than arbitrage (when power is purchased at low prices and sold back at high prices).

The electric heaters will therefore serve as a kind of negative operating reserve, meaning that they will increase demand when power plants begin to reach there must-run level.

The approach is an integral part of Denmark’s strategy to go 100 percent renewable for all energy. In countries like Denmark and Germany, demand for heat is quite high, and it is easier to store heat than electricity.

Using excess electricity to generate heat is therefore one of the least expensive power storage options. In this case, however, power can be consumed when large amounts of wind and solar power are generated, driving conventional plants down into their must-run range.

Source: Renewables International. Reproduced with permission.