An idealized model for a system that would store large amounts of electrical energy by heating a tank of fluid has been developed by a physicist in Germany. The model is based on the concept of pumped heat electricity storage (PHES), which is a family of energy-storage technologies being developed worldwide to store electricity generated by intermittent sources such as wind turbines or solar panels. This latest research could help boost both the energy and cost efficiencies of these storage systems.
Renewable energy sources such as wind and solar do not produce energy at a constant rate and as a result engineers are developing large-scale energy-storage methods that can hold excess energy for use when the wind is not blowing or when the Sun is not shining. However, creating efficient storage systems is proving difficult as André Thess of the Ilmenau University of Technology points out in a recent paper in Physical Review Letters. Today, two techniques are used: pumped hydro storage (PHS) and compressed-air energy storage (CAES). Both, however, can be very difficult to implement. PHS needs kilometre-sized, elevated water reservoirs containing nearly 10 million cubic metres of water, while the CAES method involves finding or creating huge underground caverns.
PHES, on the other hand, is much simpler – electricity from a source such as a solar or wind farm is used to run a heat pump. The pump heats water stored in a large tank (normally about 100,000 cubic metres in volume) and then, when needed, the heated water is sent to a heat engine and electricity is produced. A heat pump, rather than an electric heater, is used to heat the water because it makes the whole process much more efficient. Heat pumps are designed to move thermal energy in the direction opposite to that of spontaneous heat flow and so use much less energy than would be needed to generate the heat with an electrical heater.