Scientists have developed thermal photovoltaic devices with an efficiency of more than 40%.

Thermal photovoltaic cells convert heat into electricity. Image credit: FELICE FRANKEL

How can renewable resources be stored without sunlight or wind? This is one of the thorniest problems hindering the construction of green grids. Recently, researchers reported in Nature a device that converts stored heat into electrical energy.

In the new study, a team at the Massachusetts Institute of Technology and the National Renewable Energy Laboratory in the United States achieved thermal photovoltaic (TPV) conversion efficiency of more than 40%. A TPV is a semiconductor structure that converts photons emitted from a heat source into electricity, just as a solar cell converts sunlight into electricity.

Corresponding author Asegun Henry, mechanical engineer at MIT, said, “TPV batteries are the last critical step in proving that thermal batteries are a viable concept, and a crucial step on the road to promoting renewable energy and achieving a fully decarbonized grid.” ”

When the first TPVs were invented in the 1960s, they converted only a few percent of their heat into electricity. This efficiency jumped to around 30 percent in 1980 and has remained largely stagnant ever since. In the design of the new TPV, Henry and colleagues hope to capture high-energy photons from heat sources at higher temperatures to improve efficiency.

The new unit consists mainly of 3 areas: the high band gap metal alloy is located on top of the metal alloy with slightly lower band gap, and below it is a mirror-like gold layer. The top layer captures the highest energy photons of the heat source and converts them into electrical energy. Lower-energy photons passing through the top layer are captured and converted by the lower layer to increase the voltage produced. Any unrecapsulated photons that pass through the first two layers are reflected back to the heat source by the specular layer to avoid energy loss.

The researchers experimentally demonstrated the efficiency of high bandgap series TPV batteries – 41.1%. “We think there’s a clear path to 50 percent efficiency.” Henry said.

Andrej Lenert, a materials engineer at the University of Michigan in Ann Arbor, believes that “this is the first time that TPV has entered the truly promising efficiency range.” As a cheap backup for renewable energy systems, this new work, along with related advances, has greatly contributed to efforts to promote the large-scale rollout of hot batteries. ”

In the future, these new devices can be integrated into TPV systems for thermal grid storage, enabling a decarbonized grid powered by renewable energy sources with high enough efficiency and low cost. In fact, Henry recently formed a company to commercialize the team’s technology. “This technology costs $10 per kilowatt-hour of stored electrical energy, less than 10 percent of the cost of grid-scale lithium-ion batteries.” (Source: China Science Daily Wang Fang)

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