By June 2026, Stadtwerke Gießen will have built a plant in Schlachthofstraße that extracts heat from the River Lahn. It is the centrepiece of a state-funded project.
Decarbonising heat production across Germany is considered by experts to be a key component of the national energy transition and the achievement of ambitious climate targets. PowerLahn - the current large-scale project of Stadtwerke Gießen (SWG) - is paying tribute to precisely this: In Schlachthofstraße, directly on the banks of the River Lahn, a plant with lighthouse character will be built in the coming months. In future, three powerful large heat pumps will extract heat from the river water and feed it into the existing district heating network. These units form the centrepiece of a so-called iKWK plant. The project is one of the largest in the company's history.
The abbreviation iKWK stands for innovative combined heat and power generation. "In this context, innovative means that part of the heat generated by the overall system comes from renewable sources," explains Matthias Funk, Technical Director at SWG. The three heat pumps in Schlachthofstrasse fulfil precisely this role.
Three components, subsidised by the state
In order to accelerate the heat transition, the state is subsidising iKWK projects. "Such systems can only be operated economically with the help of subsidies. However, the hurdles before these government grants are available are relatively high," says Jens Schmidt, Commercial Director of SWG. But that didn't stop the energy experts from Lahnstrasse from taking an in-depth look at the matter. On the contrary. "We saw an opportunity here to take Giessen a step further in terms of climate protection," says Jens Schmidt, explaining the company's involvement. Once again, it turned out that SWG is at the forefront of technology. "Apparently, not too many competitors dare to tackle this complex topic," summarises Matthias Funk. In fact, SWG was able to win the bidding process for the attractive subsidy comparatively easily. "We are a little proud of that," adds Matthias Funk.
Subsidies from the state coffers are usually linked to strict criteria. For example, the components that make up an eligible iKWK system are clearly defined. A total of three components are required: a highly efficient CHP system, an all-electric boiler and a regenerative heat generator. For the PowerLahn project, this means that the three heat pumps powered by green electricity on the River Lahn form the regenerative part. SWG is having two highly efficient combined heat and power plants (CHP) and an efficient power-to-heat unit installed a good two kilometres to the south-west as the crow flies on the site of the combined heat and power plant in Leihgesterner Weg. A combination that is impressive in more ways than one: the engineers have designed the heat pumps in such a way that they can supply around 3,900 households with heat and hot water -CO2-neutral, of course. In addition to plenty of heat, the two CHP units produce enough electricity for 21,300 average households. The electric boiler is used for sector coupling. "The more such power-to-heat systems are connected to the grid, the better the potential of wind and solar energy can be utilised," says Matthias Funk, explaining the idea behind it. The electrical heat generators convert potential surplus solar and wind power into heat. And unlike electricity, this can be stored comparatively easily - in the existing district heating network. "This also reduces the load on the electricity grids," says Matthias Funk, citing a further advantage.
The environment benefits twice over
All of this means that significantly lessCO2 will be released into the environment in Giessen in future. Compared to gas boilers, the heat pumps alone will save around 7,767 tonnes ofCO2 per year. In total, the system will generate around 29,000 megawatt hours of emission-free heat and thus contribute around ten per cent of Giessen's district heating.
"Thanks to its outstanding environmental performance, PowerLahn is an important milestone on the way to making the city of Giessen climate-neutral by 2035," explains Jens Schmidt.
In addition to the massiveCO2 savings, PowerLahn has another positive effect on the environment: for reasons of efficiency, the plan is to run the heat pumps primarily in the warmer months. And it is precisely this that will improve the living conditions for many species native to the Lahn. This is because climate change is causing the water to heat up more frequently and more strongly, especially in summer. This is not exactly conducive to the well-being of fish, snails and other inhabitants. The higher the temperature, the less oxygen the water can bind. Heat pumps counteract this harmful development. After all, they extract heat energy from the river and thus lower the water temperature again. This makes life easier for the animals in the river.
Taking people with them
SWG is not content to simply plan, build and ultimately operate a highly efficient CHP plant. "Our aim is also to get people excited about our project, to take them with us, so to speak," summarises Jens Schmidt. For precisely this reason, SWG is not erecting a purely functional, square concrete building in Schlachthofstraße. Instead, it will be a functional building that is also aesthetically pleasing. The energy centre will also have large, round windows in the façade facing the road. Matthias Funk puts it this way: "We are providing a view of the technology and thus ensuring transparency in the truest sense of the word. Our aim with PowerLahn is to make the energy transition tangible here on site."
In order to get the necessary water from the river into the heat pump and back again, SWG is building an inlet and outlet structure directly on the banks of the Lahn. "We attach great importance to ensuring that everything blends into the riverbank in the best possible way," promises Jens Schmidt. In addition, the naturally designed return flow with a basin and various stones ensures that the returning, cooled water is enriched with oxygen.
Conclusion: With the PowerLahn project, SWG is taking the heat supply in Giessen to a completely new level and bringing it significantly closer toCO2 neutrality. In fact, the plant is setting new standards in terms of sustainable energy supply and may also serve as an example for other companies in other municipalities. SWG will of course provide regular updates on progress and explain the project in detail. SWG has also set up its own website to accompany the project: www.stadtwerke-giessen.de/powerlahn