Fourth Power’s Grid Scale Thermal Battery

Fourth Power's white-hot grid scale thermal battery uses advanced science yet aims to outcompete lithium-ion in price.
Reading Time: 3 minutes

Fourth Power’s white-hot grid scale thermal battery uses advanced science yet aims to outcompete lithium-ion in price. Image Fourth Power.

Reading Time: 3 minutes

White-hot grid scale thermal battery uses advanced science yet aims to outcompete lithium-ion in price.

Fourth Power says its ultra-high temperature “sun in a box” grid scale thermal battery tech is more than 10X cheaper than lithium-ion batteries and vastly more powerful and efficient than any other thermal battery. It’s hoping to prove it with a 1-MWh prototype.

As a grid scale thermal battery, Fourth aims to compete with big lithium battery arrays in the short-duration 5-10 hour range – basically storing excess solar energy during the heat of the day for use in the evening and at night when generation drops off. But the company says it’s also relevant up to the 100-hour stage, which would cover the “several days of bad weather and poor renewable generation” case.

Fourth Power is one of a number of grid scale thermal battery energy storage companies coming up out of Massachusetts and backed by Bill Gates’s Breakthrough Energy Ventures fund. You might remember Antora Energy from a few months ago, with its ultra-hot carbon block batteries and high-efficiency thermophotovoltaic energy converters.

Some other players in the thermal energy storage space include Swedish startup Azelio which has an interesting thermal storage concept using alumina ceramic particles that can be charged with renewable energy or waste industrial heat, maintaining high temperatures for 13 hours to be dispatched on demand.

UK-based Sunamp offers a modular, compact solution with its phase-change materials (PCM) thermal batteries. PCMs store energy by transitioning between solid and liquid states at specific temperatures, allowing for precise control of heat release and efficient integration into existing energy grids.

With multiple large corporations developing proprietary molten silicon or molten salt storage solutions, it’s clear that grid scale thermal energy storage is gaining significant momentum as an alternative to lithium batteries in long-duration, stationary energy applications. Integrating these high temperature reservoirs into concentrated solar power plants also holds great potential.

See also: Cement Energy Storage – Two Ways.

The idea is simple enough: a grid scale thermal battery uses excess renewable energy to heat something up inside a heavily insulated storage system. Both Antora and Fourth use big, super cheap, and abundant blocks of graphite for grid scale thermal battery energy storage – in Fourth’s case, heating them up as high as a white-hot 2,500 °C.

Energy is moved around Fourth’s system using liquid tin metal, which melts at a relatively low 232 °C (450 °F). This is Fourth’s secret sauce and relies on a Guinness World Record-holding pump designed by founder Dr. Asegun Henry. At high temperatures over about 1,000 °C, liquid metals can destroy metallic pumps, but Henry claims his engineered ceramic design will happily operate up to “almost half the sun’s temperature.”

These pumps move the superheated liquid tin around a graphite plumbing system, transferring heat from the heating elements to the graphite blocks and then taking it from the blocks to the energy recovery system when it’s time to send it back to the grid.

The liquid tin is pumped through lots of narrow graphite pipes inside an array of power-harvesting cells to recover the energy. These pipes become white-hot and emit intense light, which is harvested through thermophotovoltaic (TPV) cells – much like solar cells, but tuned to work optimally with this storage system.

At these temperatures, nearly all the heat transfer happens as light rather than conductive or convective heat, and these TPV systems are able to harvest energy using photovoltaic principles. Indeed, that’s the major reason behind the company name: the light emitted by an object scales with the “fourth power” of its absolute temperature.

As the energy is harvested, the liquid tin drops from around 2,400 °C to 1,900 °C, and it’s sent back to the heating elements to be “recharged” when energy is available.

The combination of that liquid tin pumping system and these high-efficiency TPV cells, says the company, combine to give you a grid scale thermal battery that’s incredibly responsive, delivering energy back to the grid within seconds of a demand spike, and with an unprecedented power density, since the system can transfer 10 to 100 times more heat than any other company with the same size equipment.

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