US engineers have built a scalable thermal energy storage prototype system that combines the best of latent and sensible heat transfers. The technology, which is now market-ready after three years of testing, consists of engineered cement-based materials and thermosyphons in a combination that enables fast and efficient thermal performance at low costs.
The earlier thermal method uses the amount of thermal energy required for a phase change – that is, a change in physical state, such as from solid to liquid or from liquid to gas – without changing the temperature of the material. This technique is associated with high energy densities. The latter is the thermal energy needed to raise the temperature of the material without causing phase changes. A major advantage of this heat transfer method is its low cost.
Now, with the support of the US Department of Energy, engineers at Lehigh University in Pennsylvania have developed a new thermal energy system that combines the best of both technologies. The Lehigh Thermal Battery consists of engineered cement-based materials and thermosyphons in a combination that enables fast and efficient thermal performance at low cost. The technology can work with heat or electricity as a charging energy supply.
The team has announced that after three years of research and development, the Lehigh Thermal Battery is now ready for the market. The process involved testing the integrated system with 3, 10 and 150 kilowatt-hours (kWhth) of thermal energy in the relevant environment.
The 150 kWh prototype built at the Energy Research Center is a fully instrumented structure containing 22 fin thermosiphons. The 150 kWh prototype has been extensively tested with compressed air at 480 C and produces a solid media energy-to-energy charge/discharge efficiency of over 95%, uniform temperature distribution in the solid medium during charging, and smooth cycling. repeatability.
The average power rates achieved during charging and discharging were 16.4 kWth and 19.8 kWth, with a very fast energy gradient of the thermal battery of 0.51 kWh/min during the first hour of discharge.
Principal investigator Sudhakar Neti, professor emeritus in Lehigh’s Department of Mechanics and Mechanical Engineering, argued that the technology is innovative on many levels.
“It is modular, designed for independent energy input/output streams during charge/discharge, which is possible with thermosyphons, and the two-phase exchange process inside the thermosyphon tubes enables rapid isothermal heat transfer to/from the storage medium with very high heat transfer coefficients and heat rates,” Neti said.
Carlos Romero, assistant principal investigator on the project and director of Lehigh’s Energy Research Center, said the concrete plus thermosiphon concept is unique among thermal energy storage concepts.
“The technology offers adaptability to a wide range of temperatures, heat transfer medium and operating conditions,” said Romero.
These features make the Lehigh Thermal Battery suitable for reducing carbon dioxide emissions in energy-intensive industries, flexing traditional power plants, and promoting and spreading concentrated solar power.
“Another opportunity for Lehigh Thermal Battery to play an important role in reducing carbon emissions is by integrating thermal energy storage into a system that includes heat pumps and organic Rankine cycles that work with renewable surplus electricity,” Neti said.