Science and Technology Daily, Beijing, April 17 (Reporter Zhang Mengran) According to a study recently published in the British "Nature" magazine, engineers from the National Renewable Energy Laboratory and the Massachusetts Institute of Technology have designed a heat engine without moving parts.
Demonstrations show that it converts thermal energy into electricity with more than 40 percent efficiency, a performance that outperforms conventional steam turbines.
A heat engine is a thermal photovoltaic (TPV) cell, similar to the photovoltaic cells of a solar panel.
The researchers plan to integrate TPV batteries into grid-scale thermal batteries.
The system will absorb excess energy from renewable sources such as solar energy and store this energy in a highly insulated thermal graphite reservoir.
When energy is needed, such as on cloudy days, the TPV battery converts the heat into electricity and distributes the energy to the grid.
"TPV batteries are the last critical step in proving thermal batteries as a viable concept," said Arsegan Henry, a professor in MIT's Department of Mechanical Engineering, which is critical on the road to promoting renewable energy and achieving a fully decarbonized grid. important step.
In recent years, scientists have been studying solid-state energy converters.
Scientists believe one advantage of solid-state energy converters is that they can operate at higher temperatures with lower maintenance costs because they have no moving parts.
TPV cells offer an avenue to explore for solid-state heat engines.
Just like solar cells, TPV cells can be made of semiconductor materials with specific band gaps.
But so far, most TPV cells are only around 20 percent efficient, with the highest at 32 percent.
In the new TPV design, Henry and colleagues hope to capture higher-energy photons from higher-temperature heat sources, thereby converting energy more efficiently.
Compared to existing TPV designs, the team's new cell employs higher bandgap materials and multiple junctions, or layers of materials.
The cell is made of three main regions: a high-bandgap alloy on top of a slightly lower-bandgap alloy, and below it is a mirror-like layer of gold.
The first layer captures the highest energy photons of the heat source and converts them into electrical energy, while the lower energy photons that pass through the first layer are captured and converted by the second layer to increase the resulting voltage.
Any photons that pass through the second layer are reflected by the mirror and returned to the heat source, rather than being absorbed as waste heat.
The research team exposed the cells to high-temperature lamps and focused the light on the cells.
They then varied the intensity or temperature of the bulb and observed how the power efficiency of the battery changed with temperature.
The efficiency of the new TPV cells remains around 40% in the temperature range of 1900°C to 2400°C.
The experimental battery is about one square centimeter.
For a grid-scale thermal battery system, the researchers envisage that the TPV cells would have to be scaled up to about 900 square meters.
Henry said the technology is safe and environmentally friendly over its life cycle and could have a huge impact on reducing carbon dioxide emissions from electricity production.
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Is electricity clean and green?
It depends on what energy it is converted from.
Because electricity is a secondary energy source, it needs to be obtained through primary energy conversion.
For example, when we drive a pure electric car, although the car does not produce exhaust gas, if the electric energy for charging the car comes from fossil energy, it cannot be said that it is completely green and clean.
The same is true for promoting the green and low-carbon transformation of the power grid. With more and more advanced technologies, more and more clean energy can be connected to the power grid and entered into thousands of households. This is an important way for people to achieve a green and low-carbon life.