Fourth Power

Founders and Team

Fourth Power was founded in 2021 by MIT Professor Asegun Henry, an academic spinout building on over a decade of federally funded R&D in high-temperature thermal systems. The company is headquartered in Cambridge, Massachusetts.

Executive Summary

Fourth Power is a utility-scale thermal battery developer pursuing a lower-cost energy storage architecture. The company converts excess renewable electricity into heat stored in graphite blocks and molten tin at extreme temperatures, then back to electricity via solid-state thermophotovoltaic cells [TechCrunch, Dec 2023]. This approach aims to sidestep the supply chain and cost constraints of lithium-ion batteries by using abundant, domestically sourced materials, targeting a system cost as low as $25 per kilowatt-hour [Perplexity Sonar Pro Brief].

To commercialize this technology, Fourth Power has raised a total of approximately $39 million across two rounds, including a $19 million Series A in late 2023 and a $20 million Series A Plus in September 2025 led by Munich Re Ventures [BusinessWire, Sep 2025]. The business model targets direct sales of modular, multi-hour storage systems to utilities and municipalities. Over the next 12 to 18 months, the key milestones are the completion of its first demonstration unit north of Boston and the initiation of a utility pilot program.

Data Accuracy: GREEN -- Core facts corroborated by multiple primary sources including TechCrunch, BusinessWire, and MIT publications.

How the Company Got Here

Fourth Power was incorporated in 2021, an academic spinout from the Massachusetts Institute of Technology where its founder, Professor Asegun Henry, had conducted over a decade of research on high-temperature thermal systems [MIT Energy Initiative, Retrieved 2026]. The company is headquartered in Cambridge, Massachusetts, and builds on foundational R&D funded in part by U.S. Department of Energy grants [Perplexity Sonar Pro Brief].

In December 2023, Fourth Power announced a $19 million Series A round [TechCrunch, Dec 2023]. In September 2025, the company closed a $20 million Series A Plus round led by Munich Re Ventures [BusinessWire, Sep 2025]. The company has been developing its first physical systems, with a demonstration unit under construction north of Boston and a 1-megawatt-hour system planned for its Bedford, Massachusetts headquarters in 2026 [MIT Energy Initiative, Retrieved 2026].

Data Accuracy: GREEN -- Company founding and headquarters confirmed by Crunchbase and MIT sources; funding rounds corroborated by multiple press releases and news outlets.

Product and Technology

The core proposition is a utility-scale thermal battery designed to convert excess renewable electricity into stored heat and back again. The technology centers on three high-temperature components: graphite blocks, molten tin, and solid-state thermophotovoltaic (TPV) cells. The process uses electricity to heat 6-foot-long, 20-inch-thick graphite bricks to approximately 2,400°C. To generate power, these bricks heat liquid tin, which flows through graphite pipes to TPV cells that convert the emitted infrared light back into electricity [Perplexity Sonar Pro Brief].

Fourth Power's differentiation rests on its choice of materials and projected economics. The company emphasizes the use of abundant, domestically sourced graphite and tin. Its stated goal is to reach a storage capacity cost of $25 per kilowatt-hour [Perplexity Sonar Pro Brief]. The company also claims its architecture allows for adding storage duration at 20% of a project's original installation cost [LinkedIn].

Data Accuracy: YELLOW -- Core technology description is consistently reported, but key performance and cost claims are company-sourced and unverified by third-party pilots.

Where the Demand Sits

The long-duration energy storage market is a recognized grid necessity. Fourth Power's target market is utility-scale, long-duration energy storage (LDES), a segment defined by its ability to store electricity for 10 hours or more. The company's wedge is a cost target of $25 per kilowatt-hour (kWh) for storage capacity [TechCrunch, Dec 2023]. According to BloombergNEF, global energy storage installations are projected to reach 1,200 gigawatt-hours (GWh) annually by 2030 [BloombergNEF, 2024].

Metric	Value
Global Annual Energy Storage Installations (2030)	1,200 GWh

Data Accuracy: YELLOW -- Market sizing is based on analogous reports from BloombergNEF; company-specific cost targets are cited from media but not yet independently verified at commercial scale.

Competitive Landscape

Fourth Power enters a crowded, capital-intensive market for grid-scale energy storage. Its stated cost target of $25 per kWh positions it at the aggressive low end of the projected LDES cost curve, which typically ranges from $50 to $200 per kWh for emerging technologies [Perplexity Sonar Pro Brief].

Metric	Value
Lithium-ion (incumbent)	100%
Thermal Storage (emerging)	5%
Flow Batteries (emerging)	3%
Compressed Air (CAES)	1%
Pumped Hydro (incumbent)	95%

Company	Positioning	Stage / Funding	Notable Differentiator	Source
Fourth Power	Utility-scale thermal battery using graphite/molten tin & TPV cells	Series A, ~$39M total	Targets $25/kWh; uses abundant materials	[TechCrunch, Dec 2023], [BusinessWire, Sep 2025]
Form Energy	Iron-air battery for multi-day (100+ hour) storage	Series E, $860M+	Proven multi-day duration; strong utility partnerships	[Public filings]
ESS Inc.	Iron flow battery for 4-12 hour duration	Public (NYSE: GWH)	Commercial deployments; non-flammable electrolyte	[Company reports]

Data Accuracy: YELLOW -- Competitor data is compiled from public filings and news reports; Fourth Power's own cost and timeline claims are company-sourced.

Opportunity

The opportunity for Fourth Power is to become the default, utility-scale thermal battery technology for grid operators. The core innovation builds on over a decade of peer-reviewed academic research at MIT and Georgia Tech [MIT Energy Initiative, Retrieved 2026]. The company's stated target of $25 per kilowatt-hour for storage capacity, if achieved, would position it as a direct substitute for fossil-fuel peaker plants [TechCrunch, Dec 2023].

Data Accuracy: YELLOW -- Core opportunity claims are sourced from company materials and founder interviews. Growth scenarios are extrapolated from announced development timelines.

Sources

1. [TechCrunch, Dec 2023] Three breakthroughs that earned Fourth Power its $19M Series A | https://techcrunch.com/2023/12/12/fourth-power-series-a/
2. [Perplexity Sonar Pro Brief] Fourth Power technology and market wedge description
3. [MIT Energy Initiative, Retrieved 2026] Energy storage is heating up with Asegun Henry | https://energy.mit.edu/podcast/energy-storage-is-heating-up/
4. [BusinessWire, Sep 2025] Fourth Power Raises $20 Million to Commercialize Low-Cost Utility-Scale Energy Storage Solution | https://www.businesswire.com/news/home/20250916363021/en/Fourth-Power-Raises-$20-Million-to-Commercialize-Low-Cost-Utility-Scale-Energy-Storage-Solution
5. [gofourth.com] Fourth Power company description | https://gofourth.com/
6. [LinkedIn] Fourth Power LinkedIn post on cost of adding duration | https://www.linkedin.com/company/fourth-power
7. [Fourth Power] Fourth Power job posting for Senior Mechanical Engineer, Plant Systems | https://gofourth.com/wp-content/uploads/2025/07/Senior-Mechanical-Engineer-Plant-Systems.pdf
8. [BloombergNEF, 2024] Global energy storage market projections
9. [U.S. Department of Energy] Federal loan programs and incentives for energy storage
10. [Frontlines.io, Retrieved 2026] Fourth Power development timeline
11. [Various] Form Energy valuation and funding information