Energy, the lifeblood of a society

With refuse and regional wood, the Energiezentrale Forsthaus (EFZ) has shown how sustainable energy can be generated. Today this is 80 to 85 percent for district heating.

The target of the energy plan for the entire city of Bern is at least 70 percent for the heat supply from renewable energy sources. 80 percent is required for the power supply.

Swiss Engineering: Why does the energy guideline represent a major challenge?

Roland Hediger: The planned expansion of the district heating network will more or less double the output and energy sales. The required share of renewable energy of at least 70 percent remains. In order to achieve the specifications of the city of Bern’s energy guideline plan, the proportion of renewable energy should be as high as possible.

So we need a significant increase in the production of renewable energy. To this end, we have initiated projects such as heat recovery systems, geostorage and the construction of additional wood-fired power plants. Other technologies such as solar thermal power plants, geothermal energy and air (air heat pump power plants) are being tested.

Swiss Engineering: What do you achieve with these projects?

Roland Hediger: With the heat recovery systems from the waste incineration plants (KVA) and the wood-fired power plant (HHKW), we can recover around 8 megawatts of waste heat. This heat can be used directly for district heating in winter.

The excess heat in summer (about 16 gigawatt hours) is stored and shifted to winter. The waste heat is stored in the sandstone at a depth of 200 to 500 meters using a water circuit. In winter, the heat is taken from the geo-storage and reaches the households via the district heating network.

Swiss Engineering: How high is the share of electricity and heat from the EZF for the city of Bern?

Roland Hediger: Depending on how the gas turbine is used, up to 35 percent of the city’s electricity requirements can be covered by the EFZ. This in addition to the waste incineration and the wood-fired power plant.

In terms of heat, it’s currently around 15 percent. The gas turbine, or the gas and steam combined cycle power plant (CCPP), produces electricity and steam for additional electricity generation. This via steam turbine or for heat extraction for district heating.

Steam is also produced when waste and wood chips are burned. This is also conducted via steam turbines and on the one hand generates electricity and on the other hand heats the return water for the district heating via heat exchangers.

The gas turbine is only used depending on the electricity and gas market prices, as it is primarily intended for electricity production. If required, but also to ensure the heat supply. The operating hours of this machine and thus also the production is strongly dependent on the market.