Leipzig starts operation of Germany’s largest solar thermal district heating plant

In the western part of Leipzig, thousands of solar collectors are now being used not to generate electricity, but to produce heat. The new solar thermal plant, “Solarthermie Leipzig West”, feeds hot water directly into the city’s district heating network. After an initial testing phase, the system has now entered continuous operation. With more than 65,000 square meters of collector area, the project is considered the largest solar thermal plant of its kind in Germany and one of the largest worldwide connected to a district heating system.

Turning Sunlight into Heat for the City

Unlike photovoltaic systems, which convert sunlight into electricity, solar thermal plants capture solar energy as heat. In Leipzig, this heat is transferred into water that can reach temperatures of up to 110 degrees Celsius. The heated water is then fed into the existing district heating infrastructure and used to supply homes, businesses and public buildings. The plant consists of 13,200 collectors arranged in long rows across part of a 14-hectare site. Its peak thermal output is around 41 megawatts, with an expected annual yield of approximately 26 gigawatt hours.

For a city of around 635,000 residents, the plant will not replace conventional heat generation on its own. On average, it is expected to cover around two percent of Leipzig’s annual district heating demand. However, its role becomes much more significant during sunny summer days. When heating demand is lower and the network mainly needs energy for hot water, the plant can provide up to 20 percent of the city’s daily district heating requirement. This allows fossil-based heat generation to be reduced at times when solar energy is readily available.

How the Technology Works

The system uses vacuum tube collectors. These collectors are designed to capture solar radiation efficiently and minimize heat losses. Mirrors help concentrate sunlight onto tubes through which water flows. The vacuum inside the tubes works in a similar way to a thermos flask, keeping the collected heat inside the system. A digital control system continuously monitors solar radiation and adjusts the water flow. When sunlight is strong, the water can move faster through the collectors. When radiation is weaker, the flow slows down so that the water can still reach the required temperature before entering the heating network.

Further details about the project are available here.