Fourth Power’s Thermal Batteries: Revolutionizing Energy Storage Costs
Discover how Fourth Power’s thermal battery technology is reshaping energy storage with cost-effective, long-duration solutions that challenge lithium-ion and natural gas plants, unlocking new possibilities for renewable power.
Key Takeaways
- Fourth Power’s thermal batteries use molten tin and TPV cells to store and convert heat to electricity.
- The technology targets energy storage costs as low as $25 per kWh, one-tenth of lithium-ion batteries.
- Thermal batteries can provide 8+ hours of continuous power, twice lithium-ion’s typical duration.
- The system operates at extreme temperatures (up to 2,400°C) with innovative liquid metal heat transfer.
- Commercial-scale deployment is planned for 2028, aiming to replace costly natural gas peaker plants.
Imagine a battery that sounds like it belongs in a sci-fi thriller—molten tin heated to over 2,400°C, sealed argon chambers, and solar panel-like cells converting heat back into electricity. This is Fourth Power’s thermal battery technology, a breakthrough from Cambridge, Massachusetts, that’s rewriting the rules of energy storage.
Unlike traditional lithium-ion batteries, Fourth Power’s system stores energy as intense heat in carbon blocks, then uses thermophotovoltaic cells to reclaim that energy with record-setting efficiency. Backed by Bill Gates’ Breakthrough Energy Ventures and others, the startup is gearing up to build commercial-scale batteries by 2028 that promise to be dramatically cheaper and longer-lasting.
This article dives into how Fourth Power’s thermal batteries work, their economic edge over lithium-ion and natural gas plants, and what this means for the future of renewable energy storage. Buckle up for a journey into the future of power that’s as fascinating as it is practical.
Explaining Thermal Battery Technology
Fourth Power’s thermal batteries might sound like science fiction, but their core idea is elegantly simple. Electricity heats carbon blocks inside argon-filled chambers, turning them white-hot at temperatures up to 2,400°C. This heat is then converted back into electricity using thermophotovoltaic (TPV) cells, which capture the intense infrared light emitted by the glowing carbon.
The secret sauce? Molten tin circulates through graphite pipes, transferring heat efficiently at nearly half the sun’s temperature. Graphite pipes are the only cost-effective material that can survive such extreme heat, making this system uniquely durable. The entire setup operates inside a sealed warehouse filled with argon gas, protecting components and maximizing lifespan.
This approach differs from lithium-ion batteries, which store energy chemically. Instead, Fourth Power’s system stores energy kinetically—every atom in the carbon blocks participates, resulting in energy densities comparable to lithium-ion but with potentially much lower costs and longer life. It’s a fresh take on an old problem, blending physics and engineering to unlock new possibilities.
Achieving Cost Breakthroughs
Cost is king in energy storage, and Fourth Power is aiming to dethrone lithium-ion batteries with a bold target: $25 per kilowatt-hour. That’s one-tenth the cost of typical lithium-ion systems, which hover around $330 per kilowatt-hour. How? By using abundant, inexpensive materials like petroleum coke for insulation and molten tin for heat transfer, the supply chain is streamlined with fewer moving parts.
CEO Arvin Ganesan highlights that the simplicity of the system’s components makes hitting these cost targets straightforward. Unlike lithium-ion batteries, which rely on complex chemical materials and rare metals, Fourth Power’s thermal batteries sidestep those expensive inputs. This cost advantage could make renewable energy storage not just viable but obviously preferable to fossil fuel alternatives.
With $20 million raised in a Series A Plus round led by Munich Re Ventures and Breakthrough Energy Ventures, the company is well-positioned to scale production and deliver commercial systems by 2028. The financial backing underscores strong market confidence in this disruptive technology.
Delivering Long-Duration Power
One of the biggest hurdles for renewable energy is storing power long enough to cover nights and cloudy days. Fourth Power’s thermal batteries shine here, offering continuous electricity for around eight hours or more—double the duration of most lithium-ion grid-scale batteries.
The carbon blocks’ insulation, made from petroleum coke, keeps heat loss to just 1% per day, allowing stored energy to last longer and be dispatched flexibly. The system can respond within seconds, giving grid operators precise control over power delivery. This rapid dispatch capability is crucial for replacing natural gas peaker plants, which currently fill gaps during peak demand but come with high costs and emissions.
Moreover, the modular design means utilities can add storage capacity over time, scaling with the grid’s evolving needs. This “grow with the grid” feature offers a practical path for integrating more renewables without costly overhauls.
Setting Efficiency Records
Efficiency often gets lost in the hype, but Fourth Power’s thermal batteries deliver measurable breakthroughs. Their thermophotovoltaic cells have set a world record at 41% efficiency, with designs aiming for 50%. This means nearly half the stored heat converts back into usable electricity—a remarkable feat for thermal systems.
Roundtrip efficiency, the ratio of energy output to input, targets 50% for power generation alone. For co-generation applications, where heat and power are used simultaneously, efficiency approaches 100%. This contrasts with traditional batteries, where chemical reactions limit efficiency and lifespan.
These efficiency gains translate into real-world savings and reliability. The system’s ability to operate at extremely high temperatures without degradation is a testament to the innovative liquid metal heat transfer infrastructure, the first major advance in thermal fluids in nearly a century.
Paving the Path to Commercialization
Fourth Power’s journey from lab to grid is well underway. After refining their technology for multiple years, the company is building a 1-megawatt-hour demonstration battery, expected to be operational by 2026 near Boston. This prototype will validate performance and durability under real-world conditions.
With letters of interest from multiple utilities, the startup is gearing up for pilot projects in 2026 and 2027, followed by full-scale 100 MWh installations by 2028. This timeline aligns with growing demand for clean, reliable energy storage as renewable penetration accelerates.
The company’s focus on replacing peaker plants and providing flexible, long-duration storage positions it uniquely in the market. As environmental regulations tighten and carbon pricing rises, Fourth Power’s thermal batteries offer a cost-effective alternative that could reshape how grids balance supply and demand.
Long Story Short
Fourth Power’s thermal battery technology isn’t just a new gadget—it’s a game changer for how we store and use renewable energy. By harnessing molten tin and cutting-edge TPV cells, the company is pushing storage costs down to $25 per kilowatt-hour, a fraction of lithium-ion prices. This breakthrough could make solar and wind power reliable around the clock without the hefty price tag of natural gas peaker plants. The promise of longer-duration storage, rapid energy dispatch, and scalable design means utilities can plan for a cleaner, more flexible grid that grows with demand. As Fourth Power moves toward commercial deployment in 2028, the energy landscape stands on the brink of transformation. For investors, policymakers, and energy enthusiasts alike, this technology offers a fresh perspective on overcoming the myths that renewable energy can’t be affordable or dependable. The future of power storage is heating up—literally—and it’s worth watching closely.