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The market for wasted energy

It seems ridiculous in light of industry complaints about excessive energy prices: the market value of the unused waste heat in Germany exceeds 25 billion euros a year. Researchers have calculated that the final energy consumption for industrial process heat, which amounted to 1,600 petajoules (PJ) in 2007, was equivalent to around two thirds of the final energy requirements of Germany’s industry in the same year. The waste heat is created almost everywhere, whereby the sources are diverse: machines that release heat to their surroundings, waste water from washing, dyeing and cooling processes as well as exhaust gases from ovens and engines. For temperatures greater than 140 °C, it is estimated that in economic terms German industry has a waste heat potential of 316 PJ per year or 12% of the final industrial energy consumption and a further 160 PJ per year for temperatures between 60 and 140 °C, whereby this does not even take into account the potential provided by small and medium-sized companies or new CHP plants. With domestic energy generation amounting to around 4,000 PJ each year, probably up to around 1,000 PJ or almost a quarter of the energy generated in Germany is wasted as exhaust heat.

Since the thermal utilisation of waste heat is limited in many places, a particularly attractive aspect is the ability to use the waste heat to generate electricity, which can be more diversely used. Particularly the efficiency of engines used in CHP plants operated with (bio)gas can be considerably improved by utilising their exhaust heat. The developers of new ORC modules with turbines or steam expansion engines promise to increase the  electrical power yield in addition to the engine output by up to 14 per cent. The researchers therefore want to realise the vision of decentralised engine combined cycle power plants with overall electrical efficiencies of almost 50 per cent. These “ECC” power plants enable decentralised electricity generation to approach the efficiency of modern large-scale power plants using technology that can be immediately implemented.

There would also be much to be gained in climate policy terms if the otherwise “cooled away” waste heat were to be transformed into electricity. The utilisation of a typical industrial waste heat source of 2 MW can prevent more than 4,000 tonnes of CO2 each year. In order to systematically develop such waste heat sources, public registers are being set up in increasingly more federal states in Germany. In Saxony a “waste heat atlas” is being created and in Saarland a “heat sink register”.


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