Waste heat as a climate-neutral energy source

A challenge for the industrial sector and cities alike

In order to feed energy into a local or district heating network, suitable pipes must be available or new ones laid. However, what may appear trivial at first glance poses a massive challenge in densely populated urban areas because, in many places, every metre that has to be dug up costs several thousand euros. Checkmate for the idea of a climate-neutral energy source?

Not quite. In fact, the situation gives rise to two different possible solutions. Firstly, companies of all sizes can check to what extent their own waste heat can be used for other processes. For example, it can be converted into cooling or electricity. Secondly, short distances are the key – as in the case of a data centre belonging to Telehouse in Frankfurt am Main. It’s located directly opposite a new housing estate, which it will supply with 2,400 megawatt hours of heat by pipeline each year once construction has finished in 2025. A hugely promising figure that could cover about 60 per cent of the new housing development’s needs. Compared with conventional heat generation, these measures will save up to 400 tonnes of CO2 per year – and make the residential neighbourhood significantly more independent of the local district heating network.

In order to check whether a business might qualify as a waste heat source or whether this heat should be used to optimise its own energy supply, there are a number of factors to be taken into account. According to the Bavarian Environment Agency, these include:

• Is the temperature suitable for the heat consumer’s needs? The temperature difference between the producer and the consumer determines whether it’s worthwhile harnessing the waste heat or what adjustment measures are required.
• Calculate the amount of heat available. How much heat can be stored for future use and at what temperature, or how much can be transferred directly?
• Does the time at which the waste heat is available match the time it’s needed? Or is heat required in winter, for example, but only produced in large quantities in summer?
• Are the waste heat source and the heat consumer physically close to each other? This reduces losses through transport and keeps pipeline costs low.

Tonnes of CO2 emissions saved, lower costs for companies and a step towards independence, especially in times of possible supply bottlenecks – making use of waste heat sounds like a clear win-win situation. But to drive these plans forward, it’s not only companies that need to take action, but above all policymakers. In Germany, a partial obligation for data centres to supply waste heat is currently under discussion – it could require data centres built from January 2025 onwards to divert at least 30 per cent of the energy they generate for reuse. However, where there is no heat network in place capable of being expanded, the partial supply obligation could prevent data centres from being built because they’re unable to afford to transfer this energy. After all, the optimal proximity of the above-mentioned Telehouse data centre to the housing estate is probably the exception rather than the rule.

Close cooperation between city authorities, energy suppliers and companies would seem to be essential. For small businesses in particular, it’s well worth seeking out additional funding. Options include the federal support scheme for energy and resource efficiency in business available through the KfW promotional bank or the Klimaschutz-Plus (climate protection plus) programme offered by the state of Baden-Württemberg.

One good example can be found in Meldorf in Schleswig-Holstein. It started when waste heat generated by a printing plant located in the peaceful little town was used to heat the nearby swimming pool. Meldorf then also seized upon further energy surpluses as an opportunity to set up a large-scale heating network, which now benefits schools, a sports hall and museums. Heat that’s mainly generated in summer but needed in winter is stored temporarily in an innovative storage pit – the first of its kind in Germany.

Since 2010, the city of Karlsruhe has benefitted from the waste heat produced by a nearby oil refinery, which is enough to heat around 32,000 private and public properties. Munich, on the other hand, is making use of geothermal energy – that is to say, the Earth’s waste heat. The city sits above a molasse basin that extends across the entire foothills of the Alps. The special thing about it is that deep layers of rock in the ground store water at temperatures of up to 150°C. When it goes into operation, a large geothermal power plant will process this water and make it available to 80,000 Munich residents.

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