Researchers at Lehigh University in Pennsylvania have developed a modular thermal battery – a device that can store thermal energy (heat) efficiently. The battery tested has a capacity of 150 kWhthermal and can be charged and discharged at a rate of 16.4 and 19.8 kW respectively. The battery is contained in a 5 foot diameter 15 foot tall structure.

What makes this battery novel is that it utilizes a hybrid approach to storing energy. Much of the mass is a heavy sensible heat media – storing large quantities of heat as a temperature difference. Inside the sensible heat media are thermosiphons that are two phase materials (solid-liquid or liquid-gas). The thermosiphons allow the unit to quickly move large amounts of heat since the heat transfer coefficients for phase change are very high.

The 150 kWh unit was tested using 480°C compressed air to prove feasibility. A smaller 3 kWh unit was tested at a power plant in West Virginia to show a 70% electric to heat roundtrip efficiency. The technology is being expanded to work at temperatures up to 800°C and can be used to store energy for use during on-peak periods or to supplement intermittent renewable energy sources. – Steve Terry, DTC HVAC & Refrigeration Instructor

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