Tiny heat engine with no moving parts reaches incredible energy milestone

(ORDO NEWS) — Scientists hope that solid-state thermophotovoltaic cells (SPVs) with no moving parts can achieve higher efficiency at higher temperatures when it comes to converting heat into electricity – and pave the way for electricity grids based entirely on renewable energy.

One such TPV cell has set a new world record for efficiency of 40 percent, the researchers report. This is better than steam turbines traditionally used for heat-to-electricity conversion, which typically reach 35% and have an upper temperature limit.

TPVs convert high-energy photons from incandescent heat sources into electricity. Combined with thermal batteries, they can capture energy from the sun and store it, releasing electricity as needed.

“One of the benefits of solid-state power converters is that they can operate at higher temperatures with lower maintenance costs because they have no moving parts,” says Ashogun Henry, a mechanical engineer at the Massachusetts Institute of Technology (MIT).

“They just sit there and reliably generate electricity.”

The thermophotovoltaic cell involved in the record conversion can generate electricity from heat sources at temperatures ranging from 1900 to 2400 degrees Celsius (3452 to 4352 degrees Fahrenheit). These temperatures are too high for conventional steam turbines to operate due to the presence of moving parts.

Now the effectiveness of these elements is also growing, which makes them more viable. The previous record was 32 percent, while most TPV cells produced to date are around 20 percent efficient.

The efficiency record was measured using a heat flux sensor to measure the heat absorbed by a cell about a centimeter square. A high temperature lamp was used to change the amount of heat the cell was exposed to, showing that it was indeed suitable for installation in a larger system.

“We can get high efficiency over a wide temperature range, which is typical for thermal batteries,” Henry says.

The increase in efficiency is mainly due to the materials used, which have a so-called low bandwidth, a gap that electrons must pass through to generate electricity. In this case, the researchers used materials with higher throughput, as well as several joints (or layers of material).

Three layers are used: a high bandwidth alloy to capture high energy photons and turn them into electricity, a low bandwidth alloy to capture low energy photons that have passed through the first layer, and a gold mirror to reflect the photons that have traveled all the way back to the heat source. which minimizes heat loss.

Once a thermophotovoltaic cell has been proven to work, reliable, and efficient, scientists can begin to work on expanding it and combining it with other elements to create a complete power generation system and one that produces no carbon in use.

“Thermophotovoltaic cells were the last key step towards demonstrating that thermal batteries are a viable concept,” Henry says. “This is an absolutely important step towards the spread of renewable energy and the transition to a fully decarbonized energy system.”

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