Fourth Power

Cover Block

PUBLIC

Name	Fourth Power
Tagline	Utility-scale thermal battery storage converting renewable electricity into heat and back to power.
Headquarters	Cambridge, Massachusetts
Founded	2021
Stage	Series A
Business Model	B2B
Industry	Cleantech / Climatetech
Technology	Hardware
Geography	North America
Growth Profile	Venture Scale
Founding Team	Academic Spinout
Funding Label	Series A (total disclosed ~$39,000,000)

Links

PUBLIC

• Website: https://gofourth.com/
• LinkedIn: https://www.linkedin.com/company/fourth-power

Executive Summary

PUBLIC Fourth Power is a utility-scale thermal battery developer that merits attention for its pursuit of a radically lower-cost energy storage architecture, a critical bottleneck for grid decarbonization. Founded in 2021 by MIT Professor Asegun Henry, 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]. The founding team is anchored by Henry, whose decade of federally funded R&D on high-temperature thermal systems at Georgia Tech and MIT forms the core intellectual property [MIT Energy Initiative].

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 to watch are the completion of its first demonstration unit north of Boston and the initiation of a utility pilot program, which will provide the first real-world validation of its cost and performance claims at meaningful scale.

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

Taxonomy Snapshot

Axis	Classification
Stage	Series A
Business Model	B2B
Industry / Vertical	Cleantech / Climatetech
Technology Type	Hardware
Geography	North America
Growth Profile	Venture Scale
Founding Team	Academic Spinout
Funding	~$39M total disclosed

Company Overview

PUBLIC 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, Unknown]. Its core mission is to commercialize a utility-scale thermal battery, a technology path distinct from the electrochemistry of lithium-ion batteries.

The company's public timeline is anchored by two major funding events. In December 2023, Fourth Power announced a $19 million Series A round, which TechCrunch reported was raised to scale its thermal battery technology [TechCrunch, Dec 2023]. Nearly two years later, in September 2025, the company closed a $20 million Series A Plus round led by Munich Re Ventures, capital intended to fund the commercialization of its low-cost storage solution [BusinessWire, Sep 2025]. Between these financings, 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

MIXED

The core proposition is a utility-scale thermal battery, a hardware system designed to convert excess renewable electricity into stored heat and back again on demand. The technology centers on three high-temperature components: graphite blocks, molten tin, and solid-state thermophotovoltaic (TPV) cells. According to company descriptions, 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]. The system is described as modular and utility-scale, intended to provide flexible-duration storage that can "grow with the grid" as renewable capacity expands [gofourth.com].

Fourth Power's public differentiation rests on its choice of materials and projected economics. The company emphasizes the use of abundant, domestically sourced graphite and tin, avoiding the lithium, cobalt, and complex electrochemistry of conventional batteries. Its stated goal is to reach a storage capacity cost of $25 per kilowatt-hour, a figure cited as significantly cheaper than lithium-ion alternatives [Perplexity Sonar Pro Brief]. The company also claims its architecture allows for adding storage duration at just 20% of a project's original installation cost [LinkedIn]. These cost claims, while central to the company's market wedge, are not yet substantiated by commercial deployments.

Public information on the product's technical stack and development status is limited. The company has announced plans for a 1-megawatt-hour demonstration system at its headquarters in Bedford, Massachusetts, targeted for operation later in 2026 [MIT Energy Initiative]. Job postings for Senior Mechanical Engineers focused on "Plant Systems" and "R&D" suggest an ongoing build-out of engineering capabilities around mechanical design, thermal systems, and prototyping (inferred from job postings) [Fourth Power]. There is no publicly announced product roadmap or detailed specifications for commercial units beyond the flagship 100 MW/1 GWh target mentioned in company material [Fourth Power].

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

Market Research

MIXED The long-duration energy storage market is no longer a theoretical niche but a recognized grid necessity, driven by the accelerating build-out of intermittent renewables and the resulting need for dispatchable power.

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, a figure it states would be significantly cheaper than incumbent lithium-ion batteries [TechCrunch, Dec 2023]. While a specific, third-party-validated TAM for LDES is not publicly available, the broader energy storage market provides a relevant analog. According to BloombergNEF, global energy storage installations are projected to reach 1,200 gigawatt-hours (GWh) annually by 2030, representing a multi-hundred-billion-dollar cumulative investment opportunity [BloombergNEF, 2024]. Fourth Power's initial SAM is the subset of this market requiring 10+ hour duration for grid balancing, a segment where alternatives like pumped hydro are geographically constrained and new technologies like iron-air and flow batteries are competing.

The primary demand driver is the rapid, policy-accelerated deployment of wind and solar generation, which creates a growing mismatch between energy production and consumption patterns. Grid operators require firm, dispatchable capacity to maintain stability as baseload fossil fuel plants retire. This creates a direct need for storage that can shift large volumes of energy across multiple days, not just peak hours. Tailwinds include the U.S. Inflation Reduction Act's investment tax credits for standalone energy storage and Department of Energy loan programs targeting first-of-a-kind demonstrations, which de-risk capital-intensive hardware deployments [U.S. Department of Energy].

Key adjacent markets include short-duration grid services (frequency regulation, voltage support) where lithium-ion currently dominates, and industrial process heat, where high-temperature thermal storage could directly decarbonize manufacturing. Fourth Power's technology, which can provide both short- and long-duration storage from a single platform, positions it to potentially address both [Fourth Power]. The primary substitute market remains natural gas peaker plants, which are currently the default for meeting peak demand but face increasing regulatory and carbon price pressures.

Global Annual Energy Storage Installations (Projected) | 1200 | GWh (2030)

The projected scale of annual deployments underscores the magnitude of the infrastructure challenge and the corresponding opportunity for technologies that can meet duration and cost targets.

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

MIXED Fourth Power enters a crowded, capital-intensive market for grid-scale energy storage, where its primary competition is defined not by a single technology but by a spectrum of solutions, each optimized for different durations and costs.

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

The chart above illustrates the relative market maturity of various long-duration energy storage (LDES) technologies, with lithium-ion and pumped hydro dominating current deployments and thermal storage representing a small but growing segment. Fourth Power's 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].

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; single platform for short- and long-duration	[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 (e.g., Georgia Power)	[Public filings]
ESS Inc.	Iron flow battery for 4-12 hour duration	Public (NYSE: GWH)	Commercial deployments; electrolyte is non-flammable, earth-abundant	[Company reports]

Beyond these direct LDES competitors, Fourth Power's total addressable market is contested on multiple fronts. Incumbent lithium-ion batteries remain the default for short-duration (2-4 hour) storage due to plummeting costs and extensive manufacturing scale, though they face constraints on duration, safety concerns, and supply chain volatility. Pumped hydro and compressed air energy storage (CAES) are mature, geographically limited solutions for bulk, long-duration storage. A wave of emerging challengers includes flow batteries (vanadium, zinc-based), other thermal storage concepts (e.g., using molten salt or rocks), and mechanical systems like gravity storage. Fourth Power's wedge is its specific materials stack and conversion technology, aiming to undercut all of them on a levelized cost of storage basis for durations between 4 and 100 hours.

Fourth Power's defensible edge today rests on two pillars: its foundational intellectual property and its academic pedigree. The core technology builds on over a decade of U.S. Department of Energy-funded R&D in Professor Asegun Henry's labs at Georgia Tech and MIT, covering extreme-temperature materials and thermophotovoltaic cell efficiency [Perplexity Sonar Pro Brief]. This deep technical moat around high-temperature thermal management and solid-state conversion is difficult to replicate quickly. The second edge is capital efficiency and investor alignment; securing backing from Breakthrough Energy, DCVC, and Munich Re Ventures signals validation from investors with deep climate tech expertise and long time horizons. However, these edges are perishable. The IP lead must be translated into commercial-scale demonstration units without major efficiency losses. The investor confidence is contingent on hitting technical milestones; a significant delay or cost overrun in the planned 2026 demonstration system could erode it [Fourth Power].

The company's most significant exposure is to competitors with more advanced commercial traction and established utility relationships. Form Energy, for example, has announced multiple utility-scale projects and has a clearer path to near-term revenue, giving it a first-mover advantage in signing offtake agreements. Fourth Power is also exposed in the manufacturing and supply chain domain. While its materials (graphite, tin) are abundant, scaling the production of specialized, high-purity graphite blocks and high-temperature plumbing systems presents an execution risk that more modular, containerized battery systems may not face. The company does not yet own a channel; its go-to-market relies on convincing risk-averse utilities to adopt a novel, unproven-at-scale technology, a process that typically involves multi-year pilot programs.

The most plausible 18-month competitive scenario hinges on the success of Fourth Power's demonstration unit. If the company can successfully commission its 1 MWh system in Bedford, Massachusetts in 2026 and generate validated performance data matching its cost claims, it would become a winner if it secures a first utility pilot with a named partner. This would validate the technology for investors and potentially accelerate a Series B. Conversely, Fourth Power becomes a loser if its demonstration reveals unforeseen technical or cost hurdles, while competitors like Form Energy or ESS Inc. continue to announce new commercial projects. In that scenario, the narrative would shift, and the company could struggle to raise the significantly larger capital required for its first gigawatt-hour-scale system, ceding ground to rivals with more demonstrable commercial progress.

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

PUBLIC

The opportunity for Fourth Power is to become the default, utility-scale thermal battery technology for grid operators, unlocking a path to energy storage at a capital cost that could undercut lithium-ion by an order of magnitude and enable the deep decarbonization of power grids.

The headline opportunity is to establish a new standard for long-duration energy storage (LDES) by commercializing a technology that uses domestically abundant, low-cost materials. The outcome is not merely a niche player but the foundational infrastructure for a renewable-dominated grid. This is reachable because the core innovation,storing electricity as extreme heat in graphite and converting it back via thermophotovoltaic cells,builds on over a decade of peer-reviewed academic research at MIT and Georgia Tech, funded in part by U.S. Department of Energy grants [MIT Energy Initiative, Retrieved 2026]. The company's stated target of $25 per kilowatt-hour for storage capacity, if achieved, would represent a step-change in economics, positioning it not just against other LDES technologies but as a direct substitute for fossil-fuel peaker plants [TechCrunch, Dec 2023]. The recent capital infusion from Munich Re Ventures, a strategic investor with deep ties to energy and infrastructure risk, signals institutional validation of the technical roadmap [BusinessWire, Sep 2025].

Growth is likely to follow one of several concrete paths, each hinging on specific, near-term milestones.

Scenario	What happens	Catalyst	Why it's plausible
Utility Pilot to Standard	Fourth Power's first demonstration unit proves reliability and cost targets, leading to a multi-utility procurement framework.	Successful operation of the 1 MWh demonstration system in Bedford, Massachusetts, slated for 2026, followed by a utility pilot in early 2026 [Frontlines.io, Retrieved 2026].	The modular, utility-scale design is intended to "grow with the grid," and the technology addresses a critical pain point for utilities: firming intermittent renewables at a predictable cost [Fourth Power, Unknown].
Federal Policy Acceleration	National clean energy storage mandates or tax credits specifically favor non-lithium, domestic supply chain technologies.	Inclusion of thermal storage in future federal infrastructure or energy bills, similar to incentives for other LDES technologies.	The company's use of graphite and tin, materials not subject to geopolitical supply constraints like lithium and cobalt, aligns with U.S. energy security priorities, a point emphasized in its public messaging [Perplexity Sonar Pro Brief, Unknown].
Technology Licensing & Stack Integration	Fourth Power's thermal block and TPV cell technology becomes a licensed component within larger renewable energy projects or other storage systems.	Partnership with a major renewable developer or engineering firm to integrate the thermal battery as a subsystem.	The core thermal storage medium is separate from the power conversion system, creating a potential for modular licensing. The company's focus on the entire system suggests this is a later-stage scenario, but the underlying IP is a distinct asset.

What compounding looks like for Fourth Power is a cost-driven flywheel. Initial deployments generate operational data that validates lifetime and efficiency claims, reducing perceived technology risk for subsequent buyers. This lower risk profile translates into easier financing and lower cost of capital for future projects. As manufacturing scales, the unit economics of its simple material inputs,graphite and tin,are likely to improve further, reinforcing the cost advantage. Early evidence of this flywheel beginning to turn is the company's claim that it can add duration to a project at just 20% of the original install cost, a feature that improves the business case for follow-on capacity [LinkedIn, Unknown]. Each successful gigawatt-hour-scale installation would serve as a reference case, accelerating sales cycles in a conservative, reference-driven industry.

The size of the win can be framed by looking at the market it seeks to address and comparable valuations. The LDES market is projected to require hundreds of gigawatts of capacity to support high-renewable grids. A credible comparable is Form Energy, a developer of iron-air battery systems for multi-day storage, which was valued at over $1 billion following its Series D round in 2021 [Various]. If Fourth Power can capture a meaningful share of the LDES market with a superior cost structure, its enterprise value in a successful scaling scenario could reach similar, if not greater, heights. This is a scenario-based outcome, not a forecast, contingent on the company proving its technology at the promised cost and scale.

Data Accuracy: YELLOW -- Core opportunity claims (cost targets, technology lineage) are sourced from company materials and founder interviews. Growth scenarios are extrapolated from announced development timelines. Market comparable (Form Energy valuation) is widely reported but not from a single definitive source for this report.

Sources

PUBLIC

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, Unknown] 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, Unknown] Fourth Power company description | https://gofourth.com/

6. [LinkedIn, Unknown] Fourth Power LinkedIn post on cost of adding duration | https://www.linkedin.com/company/fourth-power

7. [Fourth Power, Unknown] 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 |