Green energy sources like solar and wind are generating more power as their infrastructure expands, but we need robust methods to store excess for later use.
Solar power generation peaks during the day, but usage is highest after dark. Wind generation also suffers from the intermittent nature of air flows, making storage the key to harnessing the full potential of these renewables.
Researchers at the University of Michigan have heeded that call and recently developed a cost-effective and highly efficient thermophotovoltaic cell that converts heat to energy, according to a report by New Atlas.
According to the outlet, thermophotovoltaic cells absorb photons from the infrared part of the spectrum in the form of heat, whereas normal photovoltaics absorb them from visible light. Energy generated by clean sources can be discharged as heat into these cells and extracted as electricity again later.
As the report detailed, the medium for storing heat could be anything such as sand, molten salt, or clay bricks, but the researchers' new system uses silicon carbide. It's surrounded by semiconductor materials, including indium, gallium, and arsenic, that are designed to maximize the range of photons collected from a heated source.
When the researchers subjected the cells to a temperature of 1,435 degrees Celsius (2,615 degrees Fahrenheit), semiconductors captured 20% to 30% of energy exuded. Additional layers of air and gold reflectors worked to bounce some escaped photons back to have another chance at being converted to electricity.
The team eventually reached an impressive total power conversion efficiency of 44%, which beats the 37% achieved by other projects at the same temperature, according to New Atlas.
Stephen Forrest, a contributing author of the study, said: "We're not yet at the efficiency limit of this technology. I am confident that we will get higher than 44% and be pushing 50% in the not-too-distant future."
As the U.S. Energy Information Administration reported, U.S. electricity consumption is expected to grow by 3% in 2024 and 2% in 2025, while electricity generation should grow by 3% in 2024 and 1% in 2025. Wind energy should remain around 11% of our renewable output, but solar is expected to grow to 7% of U.S. electricity generation by 2025.
To try to help keep pace, at least one solar project using stored heat in a different way is already being implemented and specifically dealing with the intermittent nature of the supply. That project will focus on solar energy as heat at a tower and use this heat to create electricity by powering a turbine. Some of the heat will be stored to power the turbine when the sun isn't shining.
While systems that store energy as heat, including thermophotovoltaic cells, may be less efficient than lithium-ion batteries, the research team believes that its tech is better in several ways. As New Atlas detailed, it's safer and cheaper to make and maintain, enough so that even losing some of the stored energy is still cost-effective.
Forrest expanded on the benefits in a statement to the Michigan News, saying: "It's a form of battery, but one that's very passive. You don't have to mine lithium as you do with electrochemical cells, which means you don't have to compete with the electric vehicle market. Unlike pumped water for hydroelectric energy storage, you can put it anywhere and don't need a water source nearby."
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