Intelligent coupling is driving forward the heating transition

04.05.2016
The energy centre of Police Academy Biberach in Germany: Two CHP units are combined using power to heat aggregates.(Photo:Duckek)
The energy centre of Police Academy Biberach in Germany: Two CHP units are combined using power to heat aggregates. (Photo:Duckek)

Combining the power and heat market requires sophisticated overall systems that do not just consist of a single CHP unit or a heat pump. A virtual electricity storage facility in Biberach, Germany, illustrates how this can be achieved.

At the Police Academy (Hochschule für Polizei) in Biberach, Germany, Südweststrom is operating a first-of-its kind virtual electricity storage system – a combination of combined heat and power (CHP), heat pump, solar collectors and electrical boiler. The municipal utility group is pursuing hybrid heat supply systems as a promising new business area.

“Compared to conventional plants, we expect annual operating cost savings amounting to about 250,000 euros as well as reduced primary energy consumption of around 40 %,” says Daniel-Klaus Henne, CEO of Südwestdeutsche Stromhandels ­GmbH (Südweststrom). Basis of the virtual electricity storage is an intelligently controlled combination of two CHP units with an electric capacity of 400 kWe and a thermal capacity of 500 kWth each, heat pump (350 kW), an electric boiler (400 kW), two heat storage systems with 100 m3, a cold water storage for the heat pump (500 m3), a solar collector array with a surface of 500 m2 and a gas boiler with 1,700 kW. The CHP units are operated primarily to produce electricity.

Flexible response to electricity prices

“The hybrid CHP unit can be used to generate the property’s heating demand by using the natural gas-powered CHP unit, or alternatively the excess electricity from the public grid with the help of heat pump and electric boiler,” explains Eberhard Frey, Head of Technical Engineering at Landesbetrieb ­Vermögen und Bau Baden-Württemberg. This en­ables the plant to draw excess renewable electricity from the public grid at any time and, if required, feed back the power generated in the CHP unit,” says the civil engineer. In the process, electricity is stored virtually by using the excess power as well as the generated savings, while temporarily storing natural gas in the gas supply grid. “Thanks to intelligent system control we can respond flexibly to fluctuating prices on the electricity market,” says Henne, and adds that an in-house-developed ­control software computes the most economically feasible mode of operation by taking into account expected power exchange prices, demand-side ­predictions and weather forecasts, as well as up-to-date measuring values.

Payback period of eight years

Henne sees the cooperation with the Land of Baden-Württemberg as a game-changer. The Land is owner of the property in Biberach an der Riss, where up to 700 police students have been accommodated. The municipal utility group as service provider participates pro rata in the proceeds. According to Patrick Kruppa, Head of Product Development at Südweststrom, operation of the plant, which was inaugurated this March, has been off to a good start. He thinks, however, that reliable operating results will only be available in spring after the first winter period. The investment sum of € 2.5 million was funded by the Land as part of the energy refurbishment and modernization of the Land’s properties. “We are confident that we will achieve the eight-year payback target,” says Henne.

Promising new business area

The Südweststrom CEO views hybrid heat supply concepts as a promising new business area. A combination of local heating networks, operation geared towards electricity prices, central CHP unit, heat pump as well as domestic heat storage tanks equipped with heating rod, could save more than three quarters of primary energy demand. According to Henne, costs were about 35 % under those of distributed gas supply. The efficiency of a virtual electricity storage system including hybrid CHP unit, power-to-heat and utilisation of the gas network for seasonal storage of saved natural gas is clearly greater than other power storage concepts, underlines Südweststrom founder Friedrich Weng, stating that the efficiency factor of a hybrid CHP unit with heat pump is 4.3, compared to a heat pump storage (1.0), heating rod 1.2, and power to gas, which amounted to just 0.67.

Importance of intraday trading

Henne points out that especially intraday trading at the spot market provides interesting business opportunities for marketing electricity from renewable energy in combination with a hybrid CHP unit. Here, power supply deliveries are mostly traded in intervals of 15 minutes as well as in hourly intervals within the same day. He points to the fact that prices on the power exchange during intraday trading from April 2014 to April 2015 stood at over € 50/MWh for 1,100 hours. In the same period, by contrast, prices for day-ahead trading broke this mark only for 700 hours. This underscores the attractiveness of intraday trading, says Henne.

In all, Südweststrom currently has renewable ­energy systems and CHP units with a capacity of 110 MW under contract. These systems are remotely controlled from Tübingen and their electricity is ­marketed flexibly at times of peak demand. Henne announced that business in this field would ­continue to be expanded. However, price-driven load ­management is usually only cost-effective starting from an electric capacity of 300 kW, says Südweststrom’s CEO.

Hans-Christoph Neidlein

This article was originally published in Sun & Wind Energy 02/2016 - The Solar Edition.