Green electricity for a high-capacity heat pump


A flagship project: a heat pump system powered by electricity from a solar park is being added to the local heating network in the Bavarian town of Mertingen. The Fuhne project in Saxony-Anhalt is based on the same technology – only bigger.

While many municipalities – in response to new legal obligations – are only now beginning to develop municipal heating system plans, the responsible parties in Mertingen have already achieved a lot. A regeneratively operated heating network has been delivering climate-friendly heating within the community in the Donau- Ries district since 2017.

And now, in what is currently the 20th building phase, the innovative municipality is once again acting as a trailblazer: in November 2023, a high-capacity heat pump system with a thermal output of up to 900 kilowatts began operations there, powered by electricity sourced from a neighbouring photovoltaic park. Using green energy to power a heat pump at this level was previously unheard of in Germany.

Mertingen decided early on to switch its energy supply to renewable energies and carried out a feasibility study in 2014. After the positive result, ProTherm Mertingen GmbH was founded in 2016 with the aim of constructing and operating a heat grid. The municipality holds 55 percent of the shares and GP JOULE holds the other 45 percent.

A trailblazer for climate-friendly heating

The first households received heating from the new network, planned and built by GP JOULE, as early as 2017. Other consumers include municipal and commercial buildings. Most of the thermal energy comes from two biogas plants, with heat also sourced from a wood chipping facility.

Demand for connections is growing continuously. As a result, the network is being expanded gradually, and now serves an additional 60 households. However, the quantity of heat is no longer sufficient and there is a need for a new generation plant. And this is where GP JOULE broke new, innovative ground by installing an industrial-scale air source heat pump.

The system consists of a twin unit with two compressors that are connected in series, which enables a high supply temperature of 80° Celsius to be achieved. Climate-friendly ammonia is used as a natural coolant.

Heat pump runs on solar energy

The high-capacity heat pump is powered by electricity from an outdoor photovoltaic plant with an output of 750 kilowatts, which has been in operation since 2021. GP JOULE constructed the heating system directly beside it so that the solar park and the heat pump could be directly connected.

Before the heat pump was commissioned, the solar power was fed completely into the public power grid; the aim now is to use as much of it as possible for heat generation. The heat is either channelled directly into the heating network or stored temporarily in two new buffer tanks, each of which holds around 84,000 litres of water. The goal is to create as much heat as possible while the sun is shining, in order to minimise the need to purchase power from the grid. “This helps us to create additional value and offer our customers lower-priced heating,” said Felix Schwahn, Managing Director of the heating division of GP JOULE, as he explained the benefits of the new technology.

Further solar parks will be built in Mertingen in the medium term. These will then generate electricity for local industrial businesses in the face of rising demand for carbon-free electricity generation.

“The commissioning of the first heat pump of this scale for a municipal network, and which is powered using green electricity, is a flagship project that serves as a blueprint for many other heating networks that GP JOULE is currently developing,” said Schwahn. “We can use it to showcase the opportunities that present themselves when you connect the heating and electricity sectors in an intelligent manner.” Interested municipal representatives are warmly invited to attend an in-person meeting on the subject.


Renergiewerke Fuhne: all go in Quellendorf

The Fuhne is a small river in Saxony-Anhalt, from which the Renergiewerke Fuhne project takes its name – and for good reason. Because just as the Fuhne links the town of Südliches Anhalt with the integrated municipalities of Zörbig and Petersberg, so too is GP JOULE connecting the three municipalities to an integrated energy system in order to achieve the local energy transition. As part of the initiative, some 57 heating networks will be installed in the area’s 46 villages. The heat will be generated on-site by high-capacity heat pumps, which in turn will be powered by electricity from wind farms and photovoltaic plants. Ideally, the energy supply in the three municipalities will be switched to renewables within ten years.

Things are now getting under way in the town of Südliches Anhalt, after the town council concluded the urban development contract for the heating network in mid-October 2023. The urban development planning for the heating plants and solar parks began after that, prioritising Quellendorf as the first of the 24 districts of the town of Südliches Anhalt in which a heating network is to be built. Construction on the six-kilometre main heating line is set to begin in early 2024, with the first heat expected to be supplied during the 2024/25 heating season. In addition to private households, municipal buildings such as the school and kindergarten will also be connected to the system.

All of these will enjoy a ten-year guaranteed heating price of 11 cents net per kilowatt- hour and will then no longer need to worry about modernising their dated heating systems, switching to renewable energies or having a secure heat supply. Together with Renergiewerke Fuhne, GP JOULE opened an office in Radegast at the start of November to ensure that a contact person will be available locally at all times to assist the responsible parties within the municipalities as well as all business operators and citizens.