A New Heat Engine With No Moving Parts Is As Efficient as a Steam Turbine
The novel design could someday enable a fully decarbonized power grid, researchers say.
A heat engine with no moving parts has been developed by engineers at MIT and the National Renewable Energy Laboratory (NREL). Their new demonstrations show that it converts heat to electricity with over 40% efficiency — a performance better than that of traditional steam turbines.
The heat engine is a thermophotovoltaic (TPV) cell, similar to a solar panel’s photovoltaic cells, that passively captures high-energy photons from a white-hot heat source and converts them into electricity. The team’s design can generate electricity from a heat source of between 1,900 to 2,400 degrees Celsius, or up to about 4,300 degrees Fahrenheit.
The TPV cell will be used in a grid-scale thermal battery, according to the researchers. Excess energy from renewable sources, such as the sun, would be absorbed by the system and stored in heavily insulated banks of hot graphite. When the energy is needed, such as on cloudy days, TPV cells would convert the heat into electricity and send it to the power grid.
With the new TPV cell, the team has now successfully demonstrated the main parts of the system in separate, small-scale experiments. They are working to integrate the parts to demonstrate a fully operational system. From there, they hope to scale up the system to replace fossil-fuel-driven power plants and enable a fully decarbonized power grid, supplied entirely by renewable energy.
“Thermophotovoltaic cells were the last key step toward demonstrating that thermal batteries are a viable concept,” says Asegun Henry, the Robert N. Noyce Career Development Professor in MIT’s Department of Mechanical Engineering. “This is an absolutely critical step on the path to proliferate renewable energy and get to a fully decarbonized grid.”
Henry and his collaborators have published their results on April 13, 2022, in the journal Nature. Co-authors at MIT include Alina LaPotin, Kyle Buznitsky, Colin Kelsall, Andrew Rohskopf, and Evelyn Wang, the Ford Professor of Engineering and head of the Department of Mechanical Engineering, along with Kevin Schulte and collaborators at NREL in Golden, Colorado.
Jumping the gap
More than 90 percent of the world’s electricity comes from sources of heat such as coal, natural gas, nuclear energy, and concentrated solar energy. Steam turbines have been the industry standard for converting such heat sources into electricity for over a century.
On average, steam turbines reliably convert about 35 percent of a heat source into electricity, with about 60 percent representing the highest efficiency of any heat engine to date. But the machinery depends on moving parts that are temperature-limited. Heat sources higher than 2,000 degrees Celsius (~3,600 degrees Fahrenheit), such as Henry’s proposed thermal battery system, would be too hot for turbines.
In recent years, scientists have looked into solid-state alternatives — heat engines with no moving parts, that could potentially work efficiently at higher temperatures.
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