Zero-carbon heat supply in Solingen: ENGIE Deutschland convinces in the GREEEN Quarter

Cologne - Sometimes things turn out differently than you think. This was the experience of project developer Kondor Wessels NRW during the planning of the GREEEN neighborhood project in Solingen - and thanks to the expertise of ENGIE Deutschland, it mastered unforeseen challenges in an outstanding manner. Because in 2020, preparations began for a new quarter with seven buildings and 167 rental and owner-occupied apartments on a gross floor area of 13,500 square meters on the former production site of the Breuer & Schmitz machine factory. As a partner, the team from ENGIE Deutschland accompanied the planning process from the very beginning and showed various supply options for heat and hot water. Project manager Frank Martin from ENGIE Deutschland reports: "For the GREEEN neighborhood project, we originally planned a classic supply solution with a natural gas combined heat and power plant (CHP) and condensing peak load boiler. At the time, this was undoubtedly the best option, and the contracts were about to be signed - then came the Russia-Ukraine conflict." The associated world and energy policy events led to the concept being put to the test and Kondor Wessels NRW wanting to consider regenerative alternatives - while retaining the already planned start of construction in early 2023.

Turning gas into renewables: rescheduling in record time

A challenge that the experts from ENGIE Deutschland mastered with flying colors: Within just eight months, they created a completely new technical concept for GREEEN, which also took into account the adapted interfaces to the technical building equipment. The contract was signed in December 2022, and the first excavators entered the construction site in January 2023. The new concept is completely geared to the future: "For the GREEEN district, the most important thing was that the heat supply should be as regenerative as possible and independent of fossil fuels. We are meeting this requirement with an approach that has rarely been implemented in this way in Germany: We combine heat pumps, geothermal energy and photovoltaics with a long-term contracting agreement for the heat and hot water supply," explains Frank Martin. The basis was a feasibility study conducted by ENGIE Deutschland together with its subsidiaries geoENERGIEKonzept and Solarimo - which confirmed the geothermal suitability of the site. As a result, the majority of the required heat of approximately 800 megawatt hours per year will be generated in the future by five brine-to-water heat pumps with a total capacity of 435 kilowatts. The heat source is an earth probe field with 54 boreholes, each at a depth of 160 meters. A cascade of seven air-to-water heat pumps with a total output of 104 kilowatts provides for the regeneration of the ground. As a redundancy to the brine-water heat pumps, it continues to cover possible peak loads. To ensure that the heat pumps operate as economically as possible, the system runs at a flow temperature of 45 degrees Celsius. In the residential units, instantaneous water heaters reheat the water to the temperatures required to provide hot water. This data illustrates how complex the necessary replanning process was: "Our new concept is electricity-based and requires completely different supply and return temperatures in the system than originally envisaged. Therefore, the rescheduling was highly complex and demanding, especially since it took place during the ongoing process. Nevertheless, we have shown that this is definitely possible - and have thus taken a big step in Solingen towards independence, security of supply and climate neutrality," says Frank Martin.

GREEEN: A concept with a future

In the future, around 30 percent of the electricity required to operate the heat pumps will be generated by a photovoltaic system with a capacity of 217 kilowatts peak; a photovoltaic tenant electricity project is also planned so that future owners and tenants can use the photovoltaic electricity generated on site. The remaining share will be purchased from the grid, with ENGIE Deutschland's concept relying entirely on green electricity. As the contractor, ENGIE Deutschland guarantees long-term heat supply for all residential units for a period of 20 years - at a price for consumers comparable to the current market electricity mix, but with a much more sustainable concept than usual. This is also the view of BAFA, which approved funding for the project as part of the "Bundesförderung für effiziente Wärmenetze (BEW)" (Federal funding for efficient heating networks). Thus, the neighborhood project GREEEN could not have been more appropriately named: Originally conceived as a "green" allusion to the adjacent woodland, GREEEN now scores with a heat supply that is CO₂ -neutral and thus fully "green" thanks to the expertise of ENGIE Deutschland.

A concept with a future: ENGIE Deutschland is implementing a completely CO₂ -neutral heat supply in the GREEEN neighborhood in Solingen.