A new heat-to-energy converter has achieved a record-breaking efficiency of 44%, significantly higher than the average steam turbine’s 35%. This innovative thermophotovoltaic (TPV) cell marks a significant advancement towards sustainable, grid-scale renewable energy storage.

As renewable energy prices plummet, the challenge lies in their intermittency. Critics often point out the variability of solar and wind power, asking, “What happens at night or when the wind isn’t blowing?” The solution lies in effective energy storage systems, which can bridge the gap during periods of low renewable energy generation. Traditional options include lithium-ion batteries and emerging technologies like iron-air, water-in-salt, and flow batteries. However, one of the most promising methods involves storing energy as heat.

The new TPV system, developed by researchers at the University of Michigan, is designed to efficiently convert stored heat back into electricity. TPV cells operate similarly to solar cells but are engineered to capture photons from the infrared spectrum, utilizing heat (thermo) as an additional energy source.

In their experiments, the researchers used silicon carbide as the heat-storage material, though other materials could also be employed. This material is surrounded by a semiconductor made of indium, gallium, and arsenic, which is optimized to capture a broad range of photons emitted by the heated material.

When heated to 1,435 °C (2,615 °F), the material radiates thermal photons at various energy levels. The semiconductor captures 20 to 30% of these photons. To enhance efficiency, the TPV cell includes a thin layer of air followed by a gold reflector. This design allows some photons to bounce back to the semiconductor for conversion into electricity, while others are reflected back to the heat storage material for re-emission as usable photons.

This innovative configuration results in a total power conversion efficiency of 44%, outperforming other TPV systems operating at the same temperature, which typically achieve up to 37% efficiency. While some designs have surpassed 40% efficiency, they require much higher temperatures, making them less practical for many applications.

The TPV cell can be heated using electricity from wind or solar farms, or by absorbing excess heat from industrial processes or solar thermal systems. Although it has half the efficiency of lithium-ion batteries, its safety and lower production costs make it a viable option. Given the abundance of renewable energy, even a 50% loss in conversion efficiency can be acceptable.

Stephen Forrest, a contributing author of the study, is optimistic about further improvements. “We’re not yet at the efficiency limit of this technology,” he said. “I am confident that we will get higher than 44% and be pushing 50% in the not-too-distant future.”

This breakthrough in thermophotovoltaic technology represents a major step towards efficient and sustainable energy storage, addressing one of the key challenges of renewable energy deployment.

By Impact Lab