Taking the heat out of wind intermittency

Siemens, along with Technical University Hamburg Harburg (TUHH) and municipal utility company Hamburg Energie, is working on a thermal energy storage system for use in conjunction with wind turbines, employing rockfill as the storage medium. For charging, wind generated electricity is used to provide heated air to warm the rockfill. For discharge, the hot rockfill produces hot air, which is used as the heat source for a steam boiler. Steam from the boiler drives a generator via a steam turbine. The simple principle of the store promises “an extremely low-cost set-up”, says Siemens.

The project, called FES (Future Energy Solution), has received research funding from the German Federal Ministry for Economic Affairs and Energy.

The concept is currently being investigated using a test rig at Hamburg-Bergedorf. Together with colleagues from the TUHH Institute for Thermofluid Dynamics, Siemens is looking at ways to make charging and discharging of the store more efficient. The arrangement of the rock fill and the form of the surrounding insulating container are crucial, the company notes. The store is being tested at temperatures over 600°Celsius.

The current rig is confined to testing thermal aspects of the storage process, but it is hoped to test the complete energy conversion concept in spring 2017: from electricity to heat storage in the rockfill and back to electricity.

For this purpose a larger thermal store is being constructed at the Trimet aluminium smelter site in Hamburg-Altenwerder, to the south of the River Elbe close to the A7. The full size facility will be able to store around 36 MWh in a container with around 2000 m3 of rock. Via a boiler, the heat it contains will generate sufficient steam to drive a Siemens compact steam turbine, able to provide an electrical output of up to 1.5 MW for up to 24 hours. The researchers expect to achieve an efficiency of around 25% even at this early development phase. In the future, the concept has the potential to reach an efficiency of around 50%.

Partner Hamburg Energie will “investigate appropriate marketing options for the stored energy”, says Siemens.

The concept “deliberately uses mainly tried and trusted technology,” says Till Barmeier, Siemens’ project manager. “Because we are working here with tested thermal components and a series- ready steam turbine, we will be able to offer a practical solution within a few years. Our complete experimental system will be operational in just around 15 months.”