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To make renewable energy as reliable as fossil fuels, we need large-scale batteries to store and supply electricity to the grid when the sun isn’t shining or the wind isn’t blowing.

Utility-scale energy storage company Fourth Power has secured $19 million in Series A funding, which will be used to scale up its short- and long-duration thermal energy storage technology, the company announced Tuesday.

Fourth Power’s thermal battery system converts renewable energy from sources like windmills and solar panels into heat, which can be stored in carbon blocks until needed and then discharged as electricity.

The solution aims to offer grid operators control and flexibility at a lower cost compared to other energy storage options. It is also scalable, allowing for increased storage duration as renewable generation increases.

The funding enables the company to accelerate the development of its storage solutions. Fourth Power will initiate the construction of a prototype facility outside Boston that is expected to be completed in 2026. The capital will also help support durability tests as well as the expansion of Fourth Power’s engineering team.

Thermal energy storage is a key enabling technology for decarbonizing both industrial energy use and electric utilities, Blaine Collison, executive director of the Renewable Thermal Collaborative, said in an email. For the power sector, it is a means to manage renewables’ intermittency — instead of curtailing peak-production solar or wind, or facing low or negative pricing periods, electricity suppliers can sell the energy to industrial facilities using thermal energy storage, Collison said.

Fourth Power is looking to solve a couple of problems facing the energy sector, CEO Arvin Ganesan told Utility Dive — the significant amount of cost-effective energy storage that will be needed on the grid over the next 15 years, and the fact that all of those storage resources can’t draw from the same supply chain of rare earth materials. 

The company’s technology comprises a scalable, modular battery that address both those challenges. The technology takes grid energy — ideally curtailed wind or solar — and fuels an industrial-sized furnace that heats up liquid tin to some 2,600 degrees Celsius, Ganesan explained. That tin is moved through a series of graphite piping, transferring the heat to insulated carbon blocks that can hold on to the heat for over a month.

To convert the heat back to electricity, that piping system transfers the heat through the tin to another block, lined with tungsten and gold, which radiates a bright light that is then reconverted back to electricity, using specially crafted thermophotovoltaic cells. 

The technology is best suited for projects that are around 100 MW at commercial scale, and can store energy for a duration of five hours to 100 hours.

“The biggest advantage this whole system and approach can have is that it can grow with the grid,” Ganesan said. “Right now, the average duration that the electricity system needs is five hours [of storage] – building a 50-hour battery doesn’t solve today’s problems, it solves problems 10 years from now.”

The duration of the battery is shaped in part because while the blocks can hold on to the heat for a month, they tend to lose about 1% to 3% of the heat every day, he said. 

So “once you get past 100 hours, the heat starts to dissipate from the batteries and it’s just not economically ideal [or] as efficient as it would have been when more heat was stored,” he said. 

The funding that Fourth Power has raised will now be used to build a demonstration of the technology. The next step is to conduct pilots with utilities, Ganesan said. 

Along with the demonstration, the company is also taking a closer look at the projected cost of the technology, which it estimates to be ten times cheaper than a lithium-ion battery. 


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Arun Bhatia

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