Moving CHP components

16.06.2025

Source: E & M powernews

Stadtwerke Ulm/Neu-Ulm has installed a CHP plant with a renewable heat share of at least 65 percent for a new development in Wullenstetten.

A new energy center from Stadtwerke Ulm/Neu-Ulm for the new "Wohnen am Stadtpark" development in the Wullenstetten district of Senden (Bavaria) is highly flexible and can be operated with a renewable share of at least 65 percent. The system consists of pellet boilers, a combined heat and power unit, a peak load boiler and buffer storage tanks. When completed, the energy center will supply up to 350 residential units and the school center, according to the supplier.

"The energy center at Stadtpark makes an important contribution to reducing CO2 emissions and underlines the importance of modern, resource-saving technologies for a sustainable future," says Bernd Adolph, Managing Director of SWU Energie GmbH. The utility opted for a modular container construction method. On the one hand, this greatly shortened the construction time, and on the other hand, components on the plant can be dismantled more easily - which is also planned by SWU in this case.

The modular construction of the generation plant was a "central element that ensured that the extremely ambitious schedule, which aimed to commission the generation plant in October 2024, could be met. The total construction time was only around eight months," adds Bernd Adolph. Previously, there was only a mobile natural gas solution for the first buildings in the development area.

The plant components are housed in a total of ten concrete containers. At the heart of the system are two wood pellet boilers, each with a thermal output of 350 kW. The pellet stores with a total volume of 40 tons are located above the boilers, which are manufactured by Fröling. "In winter, we need up to 30 tons per week," explains Lisa Kienzle. Together with Steffen Gutte, she manages the project for the municipal utility SWU.

The system is supplemented by a Tedom combined heat and power unit with 107 kW thermal and 70 kW electrical output, a peak load boiler from Viessmann with 1,950 kW and two buffer storage tanks from BTD, each with a capacity of 25 cubic meters, which were installed next to the containers on the site of the energy center. "The buffer storage tanks are loaded by all three generators," says Kienzle. This means that the plant can be operated highly flexibly and economically.

Around 20 percent comes from the CHP and only a maximum of 10 percent comes from the natural gas boiler. "In summer, 100 percent of the heat is supplied by the pellet boiler," says Kienzle. The CHP plant is operated to optimize the electricity market. It generates around 3 million kWh of heat and around 640,000 kWh of electricity. The heat is fed into the local heating network, while the electricity flows into the public grid.

The plant currently feeds into a stand-alone grid. The flow temperature in summer is around 75 degrees Celsius, in winter it is around 90 degrees Celsius. With the "peak load boiler, 100 percent supply security is guaranteed despite the current island grid situation," says project manager Kienzle. The network is currently 4.3 kilometers long. The connection to the interconnected grid is planned for 2026/2027. SWU opted for a CHP solution for this new-build district for economic reasons. Kienzle: "Heat pumps were out of the question here because, among other things, a separate transformer station would have been necessary." This would have caused additional costs and construction time.

"The residential area and the school center are also to be connected to the Neu-Ulm/Senden district heating network in a few years' time." Individual elements of the generation systems and the system peripherals will then be adapted accordingly. As soon as the grid is connected, "we will dismantle the CHP unit and the peak load boiler," explains the project manager. The components will then no longer be necessary, as the large interconnected grid will provide the necessary security of supply. "The components will then be used again elsewhere."

In total, SWU has invested several million euros in the energy center and the grid expansion. The utility has received both a subsidy from the federal subsidy for efficient heating networks (BEW) and a subsidy for the CHP plant. The two pellet boilers were subsidized via BEW module 3. The CHP unit received an operating cost subsidy and the buffer storage tank an investment cost subsidy - both via the KWKG. In order to receive the KWKG subsidy, an energy mix is necessary that requires a minimum proportion of heat from pure CHP plants or from plants that are fed from CHP and renewable energy plants. According to SWU, this minimum proportion is achieved with this energy center.

In this context, Adolph Bernd emphasizes that a continuation of the funding programs is urgently needed for a further successful heat transition. "An expansion of district heating with a high proportion of renewable energies only works with subsidies."

Stadtwerke Ulm/Neu-Ulm has been working together with the city of Senden on the expansion of district heating since 2013. Further expansion is planned in the city center from 2026. At the official inauguration of the energy center in April for the new "Wohnen am Stadtpark" district, Mayor Claudia Schäfer-Rudolf (CSU) was particularly pleased with the high proportion of renewables and that the "plant only needs gas at peak load times".

Author: Heidi Roider