# Fourth Power

**Source:** https://geo.sig.ai/brands/fourth-power  
**Vertical:** Climate Tech  
**Subcategory:** Thermal Energy Storage  
**Tier:** Emerging  
**Website:** gofourth.com  
**Last Updated:** 2026-04-14

## Summary

Raised $45M total including $20M Series A (Munich Re Ventures, DCVC, Breakthrough Energy). Integrated demo unit completing 2026. Targets 10x cheaper storage than lithium-ion.

## Company Overview

Fourth Power is an MIT-originated thermal energy storage company that stores electricity as heat in graphite blocks at 2,400°C — using molten tin as a heat transfer medium and converting stored heat back to electricity via thermophotovoltaics (TPV). The company has raised $45 million including a $20 million Series A from Munich Re Ventures, DCVC, and Breakthrough Energy Ventures, and is completing its full integrated demonstration unit in 2026.

The system's physics promise costs 10 times cheaper than lithium-ion for grid-scale storage: graphite and tin are abundant, cheap materials, and thermophotovoltaics (solid-state, no moving parts) have lower maintenance costs than turbine-based thermal cycles. The 2,400°C operating temperature means extremely high energy density per unit volume — storing more energy in a smaller physical footprint than competing thermal storage approaches.

Fourth Power's 2026 integrated demonstration is the critical de-risking milestone before commercial contracts, proving that graphite-to-tin heat transfer, TPV electricity conversion, and full system integration work together at representative scale. Breakthrough Energy Ventures' backing — Bill Gates' climate investment fund — provides both capital and access to the fund's network of climate-focused corporate partners who could become early customers.

## Frequently Asked Questions

### What does Fourth Power do?
Thermal energy storage using graphite blocks heated to 2,400°C — stores electricity as heat via molten tin transfer, converts back to electricity via thermophotovoltaics. Targeting 10x cheaper than lithium-ion.

### How much has Fourth Power raised?
$45M total including $20M Series A from Munich Re Ventures, DCVC, and Breakthrough Energy Ventures.

### What milestone is Fourth Power reaching in 2026?
Full integrated demonstration unit completing in 2026 — proving graphite heating, molten tin transfer, and TPV electricity conversion work together at representative scale.

### Why could Fourth Power be 10x cheaper than lithium-ion?
Graphite and tin are abundant, cheap materials. Thermophotovoltaics are solid-state with no moving parts. Extreme energy density at 2,400°C means less material per MWh stored.

### How does Fourth Power store energy as heat?
Fourth Power heats graphite blocks to extremely high temperatures (2,000°C+) using cheap renewable electricity, then converts the stored thermal energy back to electricity using thermophotovoltaic (TPV) cells — achieving round-trip efficiencies that make it competitive with pumped hydro for long-duration storage.

### What distinguishes Fourth Power from other thermal storage companies like Antora?
Fourth Power operates at significantly higher temperatures than competitors like Antora Energy, enabling higher thermodynamic efficiency in power conversion. The company uses graphite as its storage medium (vs. Antora's carbon blocks) and has published record-setting TPV efficiency results from MIT research it was spun out of.

### What are Fourth Power's target customers?
Fourth Power targets utilities and grid operators seeking long-duration storage (10-100 hours) to balance seasonal renewable generation, as well as industrial customers seeking to decarbonize high-temperature process heat with stored renewable energy.

### What is Fourth Power's funding and development stage?
Fourth Power raised a $19M seed round from Breakthrough Energy Ventures, MIT's The Engine, and other investors. As an MIT spinout, the company is transitioning from laboratory demonstration to pilot system deployment with its first commercial customers.

## Tags

energy, b2b

---
*Data from geo.sig.ai Brand Intelligence Database. Updated 2026-04-14.*