Exowatt: A New Take on Solar Data Centers
Thermal Solar Modules Optimize for Power and Long-Duration Energy Storage
Much of the recent discussion of data center power has focused on strategies supported by natural gas, or perhaps small modular nuclear reactors. But what about renewable energy?
Exowatt is an energy startup that has raised $140 million from backers including Andreessen Horowitz, MVPVentures, MCJ Collective, Sam Altman and Leonardo DeCaprio. It has introduced a new powered land solution for data centers, hoping to provide a renewable alternative for builders seeking on-site power to accelerate their path to market.
To learn more about Exowatt, we spoke with Chief Data Center Officer Nic Bustamante, who has held data center leadership positions at several hyperscale players, as well as a wholesale developer.
We talk about the current state of data center energy, Exowatt’s thermal solar technology, and the opportunity for solar in the AI boom.
This Data Center Download guide summarizes this podcast, exploring Bustamante’s insights on the opportunity for solar data centers, details on Exowatt’s approach to thermal solar and energy storage, and the geography of inference.
📌 Key Takeaways
Thermal vs. Photovoltaic: Unlike traditional PV, thermal solar stores energy as heat in low-cost silica “batteries,” providing reliable power even when the sun isn’t shining.
Supply Chain Resilience: Exowatt utilizes a 100% U.S.-based supply chain and manufacturing process, eliminating reliance on “conflict minerals” like lithium and cobalt.
Powered Land Strategy: Through the Exorise initiative, the company is developing “powered land” campuses, including the 5-gigawatt Project Mercury vision.
Unit Economics: For renewables to win, they must be engineered for cost-competitiveness with natural gas and traditional PV, not just sustainability.
The Thermal Battery Strategy
The primary challenge with traditional solar (photovoltaics) is its intermittency; it produces massive power during the day but requires chemical batteries to function at night. Exowatt bypasses this by storing energy as heat directly, while optimizing several “old school” strategies.
Concentrating Energy: The Fresnel Lens
To reach the temperatures required for industrial-grade power, Exowatt uses high-precision Fresnel lenses. Unlike a standard thick glass lens, a Fresnel lens is composed of a series of concentric grooves that act as individual refracting surfaces.
Mechanism: This design allows for a large aperture and short focal length with a fraction of the weight and volume of a conventional lens, focusing sunlight into a pinpoint of intense heat.
History: Originally invented by French physicist Augustin-Jean Fresnel in 1823, these lenses were first used to magnify lighthouse beams so they could be seen from significantly greater distances. Exowatt has modernized this concept to concentrate solar rays into its thermal storage system.
Storing Heat: The “Box of Rocks”
The concentrated heat is stored in a thermal battery composed of fumed silica.
Heat Range: The system maintains temperatures between 500°C and 800°C.
Sustainability: Unlike chemical batteries, this “box of rocks” uses common materials that do not require environmentally damaging mining practices.
Power Conversion: The Stirling Engine
When electricity is needed—whether at noon or midnight—the system extracts the stored heat using a Stirling engine.
Mechanism: The Stirling engine is a closed-cycle regenerative heat engine. It uses a permanently gaseous working fluid (like helium or nitrogen) that moves between a hot heat exchanger and a cold heat exchanger. The expansion and contraction of this gas drive pistons that generate mechanical work, which is then converted to an electrical signal (AC or DC).
History: Patented by Robert Stirling in 1816, the engine was originally designed as a safer alternative to the steam engines of the time, which were prone to exploding. Because it is an external combustion engine, it can run on any heat source, making it the perfect partner for thermal solar storage.
💡 Key Idea: By storing energy as heat rather than electricity, Exowatt avoids the high costs and environmental baggage of rare earth minerals while utilizing two centuries of mechanical engineering.
Scaling Infrastructure for the AI Boom
With AI training requiring unprecedented levels of power, the industry is moving away from “NFL cities” (major metropolitan hubs) toward regions with high solar radiance, such as the U.S. Southwest. That aligns with the optimal setting for Exowatt’s approach.
Exorise: Delivering “Powered Land”
The Exorise initiative is a strategic land procurement program designed to offer data center developers a “solution” rather than just a “box.”
Site Selection: Identifying low-cost land in high-radiance zones with existing infrastructure intersections (fiber, water).
Modular Scalability: Using the P3 module , which can be multiplied “infinitely” to grow a campus alongside its data load.
Manufacturing Integration: Proposing large-scale factories that create thousands of regional jobs, changing the community narrative around data centers.
The Economics of Energy Security
In a market where demand outstrips supply, “time to power” has become a competitive moat. However, long-term success still relies on the fundamental unit economics of the power source.
Competitive Cost Profiles
Exowatt aims for cost-parity with traditional PV but with the added value of integrated storage.
Sustainability Premium: Unlike natural gas, which carries a $20 to $50 per megawatt-hour carbon “cleanup” cost, thermal solar has zero emissions and no noise pollution.
Supply Chain Sovereignty: By sourcing raw materials domestically, the company avoids the geopolitical volatility associated with international fuel and mineral markets.
💡 Key Opportunity: Energy security is becoming “table stakes” for investors; assets with dedicated, sustainable microgrids will likely command a premium over those relying solely on a congested utility grid.
This text companion accompanies the video “The Solar Startup Aiming to Transform Data Centers.”