"Nationwide we are the first"

07/07/2023

Source: Energy & Management Powernews

The Stadtwerke Heidelberg have commissioned an iKWK plant with a so far unique air-water heat pump.

The Stadtwerke Heidelberg have an innovative combined heat and power plant (iKWK) in its energy park Pfaffengrund officially put into operation. A special feature is a three-part air-water heat pump, it is said in this regard from Heidelberg. The iKWK plant is a further component for the fact that the enterprise can supply its district heating customers now with to over 50 per cent with green warmth.

A iKWK plant goes beyond the simultaneous production of river and warmth. In an iKWK system, one or more CHP units are connected to a renewable heat source and an electric heat generator to form a system. In Heidelberg, the following components are used:

- Three CHP units with a total capacity of 6 MW electrical as well as thermal and a generation capacity of 21 million kWh electricity and heat each
- Three air-to-water heat pumps as renewable heat generators with a total capacity of 4.5 MW and a capacity of 7.8 million kWh of heat
- A power-to-heat plant as an electrical heat generator with an output of 1.8 MW

According to Heidelberg, the system of air-to-water heat pumps used is particularly unique in Germany. It was not at all easy to organize a corresponding system, they say. "We finally succeeded in doing so on the Scandinavian market," says project manager Tobias Enders. "Air-to-water heat pumps of this size are already being used there. Nationwide, we are the first to have built a plant of this dimension."

The three air-to-water heat pumps extract heat from the ambient air and transfer it to the medium water. "As low-temperature systems, they can even extract heat from air that is still five degrees cold." They are therefore used primarily during the transitional seasons between summer and winter, the company said.

Since 2011, the heat supply has been converted

The three CHP units are operated primarily during the winter months from mid-October to mid-March. The power-to-heat plant is used whenever there is too much electricity in the grid and produces heat with the excess electricity, which is stored for later times. "By intelligently interconnecting the various heat generators, iKWK plants can respond flexibly to fluctuations in the power grid and help stabilize it."

The municipal utility began converting its heating system back in 2011. The basis was an "Energy Concept 2020," since further developed into the Energy Concept 2030. And that was "12 years before the obligation to submit a municipal heating plan," according to the Stadtwerke. Investments have since been made in a wood-fired cogeneration plant, four biomethane cogeneration plants, waste heat recovery from thermal waste recycling in Mannheim and now in the iKWK plant.

All these efforts have resulted in the Stadtwerke now being able to supply its customers with 50 percent green heat on an annualized basis. "In summer, the district heating is already completely CO2-free". During this period, the heat demand is covered exclusively by the waste-to-energy plant in Mannheim, the wood-fired CHP plant and the biomethane CHP plants.

"Spot-on" compliance with deadlines

The German Federal Network Agency continuously invites tenders for quotas of iKWK plants, which are associated with financial support. "We are pleased that we have now been able to add the iKWK plant to our portfolio of plants for more green heat - and on time," says Michael Teigeler, managing director of Stadtwerke Heidelberg Energie.

The authority sets implementation deadlines for tenders. It was helpful that it extended the deadlines for iKWK plants by half a year due to the supply difficulties resulting from the Corona pandemic, the company says. As a result, Heidelberg was able to meet the deadlines "right on time."

Author: Stefan Sagmeister