In the Future Energy Solution (FES) project, an energy storage system is to be developed, providing a low-cost enhancement to the existing storage technologies. The idea currently being investigated at the test facility in Hamburg consists of storing surplus wind power in the form of hot air amongst stones.
The approach being analysed by the project partners Siemens Wind Power GmbH, Hamburg University of Technology and the municipal utility company Hamburg Energie consists of converting surplus wind power into heat by means of electric heater fans, from where it is in turn transferred to a well-insulated bin of stones. There, low-cost natural stones are heated up to 600°C and absorb the heat for several hours up to a whole day. As soon as the energy is needed again, a heated airflow above the stones creates a steam cycle, which in turn sets a steam turbine in motion. The electricity generated from this can then be fed into the grid.
Instead of using natural stones, 13,000 similar-sized, ceramic balls were used for the Hamburg plant which was set up in a bin of stones; this makes it easier for researchers to observe the processes. In addition to the air volume flow and the loss of power, the heat transport is also being measured. To do this, around 50 temperature sensors have been incorporated in the storage site. However, ceramic balls are too expensive for the planned, large-scale technical implementation – the researchers are therefore also seeking the best kinds of stone to achieve the highest possible thermal stability.
Whilst the researchers are attempting to achieve a degree of efficiency of 25 per cent and a storage capacity of 36 MWh with a second, complete test facility, an output of over 100 MW and a degree of efficiency of up to 50 per cent is being aimed for with a large-scale plant.