6 clean energy startups to watch as the race for reliable power accelerates
The clean energy transition has spent much of the past decade becoming a story about scale. Solar modules became cheaper, wind farms grew larger and batteries moved from a relatively niche technology into an increasingly important component of electricity grids.
The next phase looks considerably more complicated.
As electricity demand rises, driven partly by data centres, manufacturing and electrification, the challenge is no longer simply generating more renewable electricity. Energy systems increasingly need technologies capable of supplying power when the sun is not shining and the wind is not blowing, storing energy for longer periods and replacing the fossil fuels still used to produce industrial heat.
For energy startups, that is opening markets well beyond conventional solar and wind.
Some are trying to extract enormous quantities of energy from heat beneath the Earth’s surface. Others are storing renewable electricity inside blocks of carbon or refractory bricks. A growing group of heavily financed companies is pursuing fusion, a technology that has promised abundant energy for decades but has yet to produce commercial electricity.
Capital is following those ambitions. Commonwealth Fusion Systems raised another $1 billion in July 2026, taking its total capital raised to $4 billion. Antora Energy announced a $550 million Series C the same month, while geothermal developer Quaise Energy secured $134 million in the first close of its Series B.
Those numbers do not guarantee commercial success. Many of the technologies being developed still face substantial engineering, economic and deployment risks. But they illustrate how the definition of a clean energy startup is expanding.
Here are six companies attempting to solve some of the energy transition’s most difficult problems.
1. Commonwealth Fusion Systems
Few clean energy technologies carry expectations as high as fusion.
The attraction is straightforward. Fusion seeks to recreate the process that powers stars, combining light atomic nuclei and releasing energy in the process. A commercially viable fusion plant could potentially provide large quantities of firm electricity without the carbon emissions associated with fossil fuel generation.
The difficulty is making the physics work inside a machine that can ultimately operate as a power station.
Commonwealth Fusion Systems, an MIT spinout based in Massachusetts, has emerged as one of the most heavily financed companies attempting to bridge that gap.
Its approach centres on high-field magnetic confinement using a tokamak, a doughnut-shaped device designed to confine extremely hot plasma. A key part of the company’s strategy is the use of high-temperature superconducting magnets, which allow it to pursue powerful magnetic fields in a comparatively compact machine.
The first major test is SPARC, the company’s demonstration fusion machine. Beyond that sits ARC, its planned commercial fusion power plant.
Investors are putting considerable capital behind the attempt. CFS announced another $1 billion equity financing round in July, bringing the total invested in the company to $4 billion. The company said it was the largest single financing round completed by a fusion company since its own $1.8 billion raise in 2021.
Commercial interest has also begun to move ahead of actual electricity production. Eni signed a power purchase agreement worth more than $1 billion with CFS in 2025, while the company’s plans have attracted partnerships across the energy and technology industries.
That creates an unusual position for the startup. CFS is simultaneously an experimental technology company and a prospective developer of major energy infrastructure.
Its biggest milestone, however, remains technical. The economics of fusion matter only if a reactor can reliably produce useful amounts of energy.
For that reason, CFS is one of the most important energy startups to watch not because commercial fusion has arrived, but because the company is approaching the point where some of its largest claims will increasingly be tested against physical infrastructure.
2. Quaise Energy
Where fusion attempts to recreate the conditions inside a star, Quaise Energy is looking in the opposite direction.
Its target is the enormous quantity of heat already beneath the Earth’s surface.
Geothermal electricity has long offered an attractive combination of characteristics. Unlike solar and wind generation, geothermal plants can operate continuously. They also occupy relatively little land and do not depend on fuel markets.
Geography has traditionally been the problem.
Conventional geothermal projects work best in locations where useful heat is relatively close to the surface. Quaise is developing technology designed to radically expand the locations where geothermal energy could be economically accessible.
The company wants to drill deeper and hotter using millimetre-wave technology. Instead of relying solely on conventional drill bits to mechanically break rock, its system uses electromagnetic waves to heat and vaporise it.
The objective is to access what Quaise calls superhot geothermal resources.
In July, the company announced the first close of a $134 million Series B financing round led by Prelude Ventures, with strategic investments from Japanese energy companies JERA and Idemitsu. Quaise said its drilling system was approaching one kilometre in depth at a field site in Central Texas.
The financing is intended to support Project Obsidian in Central Oregon, which Quaise plans to develop as a commercial superhot geothermal power plant. The company’s roadmap targets commercial operation in 2030.
Quaise says the project will eventually progress through several phases, beginning at 50 MW before potentially expanding to 250 MW and ultimately more than 1 GW. Those remain company targets rather than demonstrated commercial output.
If the drilling technology proves commercially viable, however, the consequences could extend well beyond a single geothermal plant.
One particularly interesting possibility is the reuse of skills and infrastructure from the oil and gas industry. Deep drilling expertise, geological knowledge and parts of the existing supply chain could potentially be redirected towards geothermal development.
That gives Quaise an unusual proposition among clean energy startups. Rather than replacing every component of the existing energy system, it could potentially repurpose parts of it.
3. Antora Energy
Not all energy storage needs to end with electricity coming back out of a battery.
For heavy industry, heat itself is one of the world’s most important energy products.
Factories need enormous amounts of thermal energy for processes ranging from producing chemicals to manufacturing cement, steel, food and other materials. Much of that heat is still generated by burning fossil fuels.
Antora Energy wants to replace some of that combustion with renewable electricity stored as heat.
Its thermal batteries use carbon blocks that are heated using electricity. The stored thermal energy can then be delivered to industrial users, allowing intermittent renewable power to become a more continuous source of energy.
It is an apparently simple idea aimed at a very large problem.
Antora has also developed thermophotovoltaic technology that can convert some of the stored heat back into electricity, broadening the potential applications of its storage platform.
Investors increasingly see commercial potential in the model. The California company closed an oversubscribed $550 million Series C in July, co-led by G2 Venture Partners and Eclipse. Antora said the financing would support expansion as it targets industrial customers, data centres and the grid.
The data centre opportunity is particularly significant.
Artificial intelligence infrastructure is adding another source of electricity demand at the same time that utilities and governments are attempting to decarbonise existing consumption. Technologies capable of shifting renewable electricity across time could therefore become valuable for reasons that extend beyond climate policy.
Antora’s progress is also part of a wider change in how the storage market is being defined.
Lithium-ion batteries have become central to electric vehicles and short-duration grid storage. But storing energy for industrial processes or over longer periods can require different economics and materials.
Thermal storage companies are betting that one answer may be to stop trying to make every battery resemble the electrochemical devices found in cars and phones.
4. Rondo Energy
Rondo Energy is pursuing the same broad industrial challenge as Antora with a strikingly different storage medium: bricks.
The company’s heat batteries use electrical heating elements to warm refractory brick, storing renewable electricity as thermal energy. That heat can subsequently be supplied to industrial processes as high-temperature air or steam.
The underlying materials are familiar. The business proposition is to combine them in a system capable of helping factories consume renewable electricity even when renewable generation itself fluctuates.
That matters because industrial heat remains one of the harder parts of the global economy to decarbonise.
Electrifying a passenger car is relatively straightforward compared with replacing the continuous high-temperature heat required by some industrial plants. Batteries designed primarily for electricity storage can also become expensive when the requirement shifts towards supplying heat over extended periods.
Rondo is attempting to exploit that distinction.
In January 2026, the company and materials manufacturer Covestro broke ground on a 100 MWh Rondo Heat Battery at Covestro’s Brunsbüttel site in Germany. Commissioning is planned for the end of 2026. The companies expect the installation to provide about 10 percent of the steam required at the site and potentially avoid up to 13,000 tons of carbon dioxide emissions annually.
Rondo has also moved into commercial projects elsewhere. Its technology is operating at an industrial site in Thailand, while another 100 MWh heat battery is planned for Heineken with renewable power supplied through a partnership with EDP.
The attraction of heat batteries is not technological novelty for its own sake. It is almost the opposite.
Bricks, electrical heaters and insulated enclosures are relatively conventional technologies. Rondo’s wager is that combining mature components with cheap renewable electricity can produce an economically compelling replacement for fossil fuel heat.
If that model scales, industrial decarbonisation could depend as much on better ways of storing heat as on breakthroughs in conventional batteries.
5. Base Power
Base Power approaches the storage problem from inside the home.
The Texas-founded energy startup combines electricity retail with residential battery storage. Rather than simply selling homeowners a battery, Base installs storage at participating properties and uses that network of batteries as part of its broader electricity business.
Customers gain backup power during outages. Base gains a distributed pool of energy storage that can be managed around periods of grid stress and expensive electricity.
The model points towards a larger change in the architecture of electricity systems.
Historically, grids have largely been built around centralised generation, transmission networks and consumers at the end of the system. Rooftop solar, electric vehicles and home batteries are turning millions of buildings into potential energy assets.
Coordinating those assets could allow energy startups to create something resembling a power station without building one in a single location.
Base has been expanding that proposition beyond its original Texas footprint. In June 2026, it launched in the Chicago area, offering customers in ComEd territory home battery installations alongside electricity supply. The company says it can use those batteries during periods when electricity is scarce and wholesale supply becomes more expensive.
That makes Base notable not simply as another battery company, but as an example of how storage could change the relationship between energy suppliers and households.
A residential battery can provide resilience to an individual homeowner. Thousands of connected batteries can potentially become part of the grid itself.
The challenge will be demonstrating that the economics work as the model expands into markets with different electricity regulations, pricing structures and grid conditions.
If they do, the next generation of energy companies may look increasingly different from the utilities that preceded them.
6. Type One Energy
Fusion is sufficiently difficult that even companies pursuing the same ultimate goal disagree about the best machine for achieving it.
Type One Energy is betting on the stellarator.
Like a tokamak, a stellarator uses magnetic fields to confine the extremely hot plasma required for fusion. Its geometry is considerably more complex, but stellarators offer the potential for steady-state operation, an attractive characteristic for a machine ultimately expected to behave like a power plant.
Type One is attempting to turn decades of stellarator research into commercial infrastructure.
The company is developing Infinity One at the Tennessee Valley Authority’s Bull Run Energy Complex near Oak Ridge, Tennessee. Type One describes the machine as an engineering verification platform and workforce training facility, with completion planned for 2029.
Its commercial ambition is Infinity Two, a proposed grid-scale stellarator power plant being developed in partnership with TVA.
The underlying design has been accompanied by unusually visible efforts to establish a peer-reviewed scientific basis. In 2025, Type One published a series of seven papers in the Journal of Plasma Physics setting out the physics basis behind its proposed plant.
The company has continued building the surrounding commercial and technical infrastructure. In August 2026, Oak Ridge National Laboratory announced the licensing of cryogenic pellet fuelling technologies to Type One for use in its fusion development programme.
Yet, as with CFS, timelines deserve caution.
Type One is targeting commercial fusion power in the next decade, but fusion developers still need to turn increasingly sophisticated experiments and designs into machines capable of producing reliable, economical electricity.
That uncertainty is precisely why having two fusion companies on a list of clean energy startups is instructive.
The contest is not simply between businesses. It is also between engineering philosophies.
CFS is pushing high-field tokamak technology while Type One is trying to commercialise the stellarator. Both ultimately want to provide firm electricity, but they are taking different routes towards it.
The same pattern can be seen across the wider clean energy market.
Antora and Rondo both want to transform renewable electricity into dependable industrial heat but use different storage architectures. Quaise is attempting to make geothermal resources accessible in places where conventional drilling struggles to reach them. Base is turning household batteries into distributed grid infrastructure.
What connects these companies is not one technology.
It is the problem they are trying to solve.
Solar and wind have demonstrated that enormous quantities of low-carbon electricity can be generated at increasingly competitive costs. The harder question is how an economy built around continuous access to energy can operate with much larger quantities of variable renewable generation while simultaneously electrifying transport, industry, buildings and digital infrastructure.
That requires more than generating additional clean electricity.
It requires storing energy, moving demand, producing industrial heat and finding new sources of firm power.
Some of the technologies attempting to provide those capabilities will fail. Others may work technically but struggle economically. Fusion and superhot geothermal, in particular, still face substantial engineering challenges before their advocates’ visions can be judged against operating commercial plants.
But the direction of investment is revealing.
The clean energy startup sector is moving beyond the first phase of the renewable transition. Its biggest opportunities are increasingly found in the gaps left behind by that transition: the hours without wind or sunlight, the factories that cannot easily electrify, the grids struggling with higher demand and the need for dependable power without fossil fuels.
The companies that successfully fill those gaps may ultimately prove just as important as the technologies that began the clean energy revolution.
