Stones to store energy

In a resource as abundant and available as stones can be the secret not to lose the wind energy captured and unused, and convert it naturally when there is demand for electricity. This is what German researchers are working on, who estimate that installing insulated containers loaded with rocks for the storage of surpluses could improve the efficiency of a factory of more than 100 megawatts by 50%.

The University of Hamburg, the company Hamburg Energie and Siemens are participating in this project funded by the German Ministry of Economy as part of the Future Energy Systems initiative, with which they seek to store excess energy captured in wind power plants for hours or even a whole day, in a natural, simple and economical way.

The system “This is the essence of simplicity”According to the promoters of this idea, which consists of converting excess energy into heat, which would pass into an insulated container in which the stones would be located, which would retain this heat by reaching temperatures above 600 degrees. As soon as there was a demand for stored energy, the rocks themselves would heat the airflow, producing a cycle of value and generating energy in the process.

The invention is tested in a five meter long container in which, in this phase, natural stones are still replaced by ceramic balls, up to 13,000 of the same size and shape, which facilitates calculations on heat transport and observation of the processes in progress. in the container.

The next step will be to replace the ceramic parts with stones, the high cost of which makes their use impractical for projects on an industrial scale. To mitigate the uncertainties that exist about the effect that different sizes and shapes of rocks can have on heat transport, Researchers are working to identify the type of stone that might provide better results. For now, if they are clear on something, it is that the candidate will have to have high thermal stability, a quality that will improve the efficiency and durability of the storage system.

As they research which stone to use in this system, the researchers attempt to solve one of their biggest unknowns: how to measure heat transport processes inside containers. So far, they have installed 50 thermocouples (sensors for temperature measurement), which will do the same at different points in this space, where they will also check the pressure and air flow.

Although this concept may already be extended, members of the research team will continue to work on it, for which the construction of a pilot plant should start in 2018 in Hamburg which integrates the storage system and the technology necessary to convert heat into electricity.

The planned pilot plant is expected to have an efficiency of 25%, although the researchers believe that a large-scale installation at a plant with an output of more than 100 megawatts could increase its efficiency by 50%, a result they trust. . that this stone-based storage system plays a decisive role in the German energy transition.

More information in Siemens.