There is too much on summer days and too little at night: electricity from solar energy. Wind turbines are also not very reliable: sometimes the wind blows, sometimes it is calm. To ensure that electricity from such renewable energy sources is also available on still, dark winter days, it needs to be stored. Scientists from the Professorship of Renewable Energy Carriers at the Swiss Federal Institute of Technology (ETH) Zurich have researched such an innovative storage solution as part of a joint project.
In the Ticino Alps, researchers from ETH Zurich, the EPF Lausanne, SUPSI and the Paul Scherrer Institute, together with the company ALACAES, have tested a compressed air reservoir in an old tunnel under the leadership of Andreas Haselbacher. The principle: when more electricity is generated from renewable sources than is needed, it is used to compress air, a process similar to that of inflating a bicycle tyre. If there is too little electricity at a later time, you open the tire valve, so to speak, and the compressed air escapes, driving a turbine that generates electricity in the process.
At the pilot plant, the air is pressed into a cavern 120 metres long and 5 metres in diameter – this mountain cavity is a remnant of the construction of the Gotthard Base Tunnel. The cavity is closed off by two five-metre-thick concrete plugs and steel doors. Some 400 metres of rock tower above it. The researchers have demonstrated in this project that pressure can actually be built up here and that no air leaks through the rock.