The "Kleine Schwalbacher Straße local heating island" is a pilot project that was launched in 2007 by Wiesbaden and ESWE Versorgungs AG. It was completed in 2008. Today, private and commercial customers in Wiesbaden's city center can use a local heating supply with thermal water - at the usual district heating prices. This was made possible because the Environment Agency provides and operates the heat exchanger.

In the first phase, the local heating island was set up with an output of 300 kilowatts. Since 2008, the system has been supplying the buildings of Stadtentwicklungsgesellschaft Wiesbaden with around 200 kilowatts. Further customers are to follow and the output is to be increased to 3,000 kilowatts.

The heating systems in the connected buildings are designed for flow and return temperatures of 60 degrees and 40 degrees respectively. ESWE Versorgungs AG supplies and invoices the heat. The Environmental Agency is responsible for the operation and expansion of the heat exchangers.

The project contributes to climate protection as it reduces CO2 emissions. In the initial phase, it will save around 85 tons of CO2 per year. At full capacity, it could be up to 850 tons per year.

The project was supported by ESWE Versorgungs AG's climate protection and innovation fund.

Wiesbaden produces around 440,000 cubic meters of thermal water from five springs every year. This generates 16.8 gigawatt hours of heat. A further 14.6 gigawatt hours could be extracted and used.

However, the thermal water has a high salt content and is corrosive. When it comes into contact with oxygen, lime quickly forms. These properties make it difficult to use. The technical solution is to use glass-fiber reinforced pipes and titanium heat exchangers to prevent corrosion. However, high investment costs make individual building heating unattractive for individuals. Unless the heat exchanger is provided centrally.