MIT and the National Renewable Energy Laboratory (NREL) developed the design of a heat engine that contains no moving parts and can convert heat to electricity with a better than 40% efficiency. According to researchers, the approach beats conventional steam turbines and could eventually allow for a decarbonized power grid.

The MIT and NREL heat engine uses thermophotovoltaic (TPV) cells like the photovoltaic cells in solar panels. It generates electricity by passively capturing high-energy photons from a white-hot heat source. Using a heat source that is between 1,900 and 2,400 degrees Celsius, or up to 4,300 degrees Fahrenheit, the team’s concept can produce energy.

It is surpassing the steam turbine‘s efficiency, which could lead to a change in how we produce and store energy. This article describes why thermophotovoltaic cells are more effective than a steam turbine.

Thermophotovoltaic Cells Produce More Than 40% Efficiency: How is it possible? 


The researchers plan to use the thermophotovoltaic cells in a grid-scale thermal battery. It aims to store excess energy from renewable sources like the sun in the well-insulated banks of heated graphite. Thermophotovoltaic cells would use heat to turn it into electricity, such as during cloudy days. They would then send the electricity to the electrical grid.

The thermophotovoltaic cells, which resemble the PV cells on a solar panel, may generate power at 40% efficiency, a performance better than standard steam turbines. Low maintenance costs would result from the absence of moving parts.

How can Thermophotovoltaic Cells assist you?

So far, the system’s essential components have been successfully proved in small-scale studies by researchers. They are now attempting to combine the parts with building a fully functional system. From there, they intend to scale up the system to take the place of thermal power plants. Researchers want to enable a fully decarbonized power grid powered entirely by renewable energy.

Companies would swap out the fossil heat for thermal batteries for complete decarbonization. They would discharge heat through thermophotovoltaic cells when the grid needed them. You can charge thermal batteries with excess energy from intermittent sources like solar.

The researchers also used the components from the thermophotovoltaic cell to build a more established “operational” system. They are planning to develop a replacement for fossil fuel-powered power plants. Scientists look forward to building an utterly carbon-free power infrastructure using renewable energy sources.

Segun Henry, an MIT’s Department of Mechanical Engineering professor, says, “Thermophotovoltaic cells were the last key step toward demonstrating that thermal batteries are a viable concept.”

 “This is an absolutely critical step on the path to proliferate renewable energy and get to a fully decarbonized grid,” he added.

The journal Nature published the results on Wednesday, Apr. 13, by Henry and his co-authors. Through Nature.com, you can access the study titled “Thermophotovoltaic efficiency of 40%.”

Comparison between thermophotovoltaic cells with steam turbines;

Using coal, natural gas, nuclear energy, and concentrated solar energy, heat-generating power plants produce over 90% of the world’s electricity. In terms of generating power through the conversion of heat to electricity, steam turbines have been widely used for a very long time.

They are typically just 35 percent efficient. It strongly depends on the moving parts while converting a heat source into electricity. These moving parts could not withstand temperatures of more than 2,000 degrees Celsius. Steam turbines couldn’t handle the heat from systems like Henry’s thermal battery system.

Thermophotovoltaic cells convert heat into energy more effectively than a steam turbine.

Solid-state heat engines have no moving parts and may function effectively at greater temperatures. They have attracted the attention of experts in recent years.

No moving parts lead to higher temperatures and less maintenance:

“One of the main advantages of solid-state energy converters is that they can operate at higher temperatures with lower maintenance costs. This is because of the reason that they contain no moving parts,” Henry claims. “They just sit there and generate electricity in a reliable way.”

Thermophotovoltaic cells offer one experimental path toward solid-state heat engines. Like solar cells, TPV can create cells through semiconducting materials with a specific bandgap or the space between a material’s valence band and conduction band. Here the electron can conduct and produce electricity without moving rotors or blades.

Because they get constructed of relatively low-bandgap materials, which convert lower-temperature, low-energy photons and less effectively convert energy. Most thermophotovoltaic cells have only achieved efficiencies of approximately 20%, with the record being 32%.

Capturing more powerful photons:

Henry and his colleagues sought to more effectively convert energy by capturing higher-energy photons from a higher-temperature heat source in their new thermophotovoltaic design. Compared to prior thermophotovoltaic cells, the team’s new cell achieves this using higher-bandgap material and many junctions, or material layers.

The cell constructs from three primary regions: a high-bandgap alloy on top of a somewhat lower-bandgap alloy and a mirror-like layer of gold. The highest energy photons from a heat source grab by the first layer, which then transforms them into electro power.

The second layer captures the lower energy photons that pass via the first layer, which converts them to contribute to the generated voltage. Any photons that do travel through this second layer are then reflected by the mirror back to the heat source rather than absorbed as wasted heat.

The scientists used a heat flux sensor, a tool that monitors the heat absorbed straight from the cell, to test the cell’s effectiveness. They focused light onto the cell from a high-temperature bulb and exposed the cell to the light.

The next modified the bulb’s intensity or temperature and watched how temperature affected the cell’s power efficiency or how much power it produces and how much heat it absorbs. The new TPV cell kept its effectiveness at roughly 40% over a temperature range of 1,900 to 2,400 degrees Celsius.

 “There’s definitely a huge net positive here regarding sustainability,” Henry says. “The technology is safe, environmentally benign in its life cycle, and can significantly impact abating carbon dioxide emissions from electricity production.”

The U.S. Department of Energy contributed in parts to this study.

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