PJ Popovic, founder and CEO of Houston-based Rhythm Energy, which has acquired Inspire Clean Energy. Photo courtesy of Rhythm

Houston-based Rhythm Energy Inc. has acquired Inspire Clean Energy for an undisclosed amount. The deal allows Rhythm to immediately scale outside of Texas and into the Northeast, Midwest and mid-Atlantic regions, according to a release from the company.

Inspire offers subscription-based renewable electricity plans to customers in Pennsylvania, New York, New Jersey, Massachusetts, Ohio, Delaware, Illinois, Maryland, and Washington, D.C. By combining forces, Rhythm will now be one of the largest independent green-energy retailers in the country.

“Adding Inspire to the Rhythm family gives us the geographic reach to serve millions of new customers with the highly rated customer experience Texans already enjoy,” PJ Popovic, CEO of Rhythm, said in the release. “Together we become one of the largest independent green-energy retailers in the country and can roll out innovations like our PowerShift Time-of-Use plan and device-enabled demand-response programs that put customers fully in control of their energy costs.”

Rhythm was founded by Popovic in 2020 and offers 100 percent renewable energy plans using solar power, wind power and other renewable power sources.

In addition to scaling geographically, the acquisition will "(marry) Rhythm's data-driven technology with Inspire's successful subscription model." Rhythm also plans to upgrade its digital tools and provide more advanced services to help lower clean energy costs, according to the release.

Popovic spoke with EnergyCapital in 2023 about where he thinks renewables fit into Texas’s energy consumption. Read more here.

Houston's Calpine Corp. will be acquired by Baltimore-based nuclear power company Constellation Energy Corp. Photo via DOE

Houston-based Calpine Corp. to be acquired in clean energy megadeal

big deal

Baltimore-based nuclear power company Constellation Energy Corp. and Houston-based Calpine Corp. have entered into an agreement where Constellation will acquire Calpine in a cash and stock transaction with an overall net purchase price of $26.6 billion.

The companies say the agreement has the potential to create America’s “largest clean energy provider,” with what is reported to be the largest fleet of U.S. power stations servicing about 2.5 million customers.

“This is an incredible opportunity to bring together top tier generation fleets, leading retail customer businesses and the best people in our industry to help drive a stronger American economy for a cleaner, healthier and more sustainable future,” Andrew Novotny, president and CEO of Calpine, said in a news release.

Calpine is the largest U.S. producer of energy from low-emission natural gas generation and oversees the largest geothermal generation operation in the U.S. Last year it announced plans to build the Baytown Carbon Capture and Storage Project (Baytown CCS Project), a first-of-its-kind carbon capture demonstration facility, as part of a cost-sharing agreement with the U.S. Department of Energy.

Constellation is considered the top clean energy producer in the U.S., which provides 10 percent of the country’s emissions-free energy. The deal will add to Constellation’s already diverse portfolio of zero- and low-emission sources, including nuclear, natural gas, geothermal, hydro, wind, solar, cogeneration and battery storage.

“Both companies have been at the forefront of America’s transition to cleaner, more reliable and secure energy, and those shared values will guide us as we pursue investments in new and existing clean technologies to meet rising demand,” Joe Dominguez, president and CEO of Constellation, said the release. “What makes this combination even more special is it brings together two world-class teams, with the most talented women and men in the industry, who share a noble passion for safety, sustainability, operational excellence and helping America’s families, businesses and communities thrive and grow. We look forward to welcoming the Calpine team upon closing of this transaction.”

Constellation also announced that it will invest in adding more zero-emission energy to the grid to create “the most reliable generation portfolio in the U.S.” It plans to explore new advanced nuclear projects, invest in renewables and increase the output of existing nuclear plants.

“Together, we will be better positioned to bring accelerated investment in everything from zero-emission nuclear energy to battery storage that will power our economy in a way that puts people and our environment first,” Novotny said in a news release. “It’s a win for every American family and business in our newly combined footprint that wants clean and reliable energy. ECP’s commitment to these goals over the last seven years was critical to the progress we have made as a company and to laying a foundation for future growth.”

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Houston geothermal company raises $97M Series B

fresh funding

Houston-based geothermal energy startup Sage Geosystems has closed its Series B fundraising round and plans to use the money to launch its first commercial next-generation geothermal power generation facility.

Ormat Technologies and Carbon Direct Capital co-led the $97 million round, according to a press release from Sage. Existing investors Exa, Nabors, alfa8, Arch Meredith, Abilene Partners, Cubit Capital and Ignis H2 Energy also participated, as well as new investors SiteGround Capital and The UC Berkeley Foundation’s Climate Solutions Fund.

The new geothermal power generation facility will be located at one of Ormat Technologies' existing power plants. The Nevada-based company has geothermal power projects in the U.S. and numerous other countries around the world. The facility will use Sage’s proprietary pressure geothermal technology, which extracts geothermal heat energy from hot dry rock, an abundant geothermal resource.

“Pressure geothermal is designed to be commercial, scalable and deployable almost anywhere,” Cindy Taff, CEO of Sage Geosystems, said in the news release. “This Series B allows us to prove that at commercial scale, reflecting strong conviction from partners who understand both the urgency of energy demand and the criticality of firm power.”

Sage reports that partnering with the Ormat facility will allow it to market and scale up its pressure geothermal technology at a faster rate.

“This investment builds on the strong foundation we’ve established through our commercial agreement and reinforces Ormat’s commitment to accelerating geothermal development,” Doron Blachar, CEO of Ormat Technologies, added in the release. “Sage’s technical expertise and innovative approach are well aligned with Ormat’s strategy to move faster from concept to commercialization. We’re pleased to take this natural next step in a partnership we believe strongly in.”

In 2024, Sage agreed to deliver up to 150 megawatts of new geothermal baseload power to Meta, the parent company of Facebook. At the time, the companies reported that the project's first phase would aim to be operating in 2027.

The company also raised a $17 million Series A, led by Chesapeake Energy Corp., in 2024.

Houston expert discusses the clean energy founder's paradox

Guest Column

Everyone tells you to move fast and break things. In clean energy, moving fast without structural integrity means breaking the only planet we’ve got. This is the founder's paradox: you are building a company in an industry where the stakes are existential, the timelines are glacial, and the capital requires patience.

The myth of the lone genius in a garage doesn’t really apply here. Clean energy startups aren’t just fighting competitors. They are fighting physics, policy, and decades of existing infrastructure. This isn’t an app. You’re building something physical that has to work in the real world. It has to be cheaper, more reliable, and clearly better than fossil fuels. Being “green” alone isn’t enough. Scale is what matters.

Your biggest risks aren’t competitors. They’re interconnection delays, permitting timelines, supply chain fragility, and whether your first customer is willing to underwrite something that hasn’t been done before.

That reality creates a brutal filter. Successful founders in this space need deep technical knowledge and the ability to execute. You need to understand engineering, navigate regulation, and think in terms of markets and risk. You’re not just selling a product. You’re selling a future where your solution becomes the obvious choice. That means connecting short-term financial returns with long-term system change.

The capital is there, but it’s smarter and more demanding. Investors today have PhDs in electrochemistry and grid dynamics. They’ve been burned by promises of miracle materials that never left the lab. They don't fund visions; they fund pathways to impact that can scale and make financial sense. Your roadmap must show not just a brilliant invention, but a clear, believable plan to drive costs down over time.

Capital in this sector isn’t impressed by ambition alone. It wants evidence that risk is being retired in the right order — even if that means slower growth early.

Here’s the upside. The difficulty of clean energy is also its strength. If you succeed, your advantage isn’t just in software or branding. It’s in hardware, supply chains, approvals, and years of hard work that others can’t easily copy. Your real competitors aren’t other startups. They’re inertia and the existing system. Winning here isn’t zero-sum. When one solution scales, it helps the entire market grow.

So, to the founder in the lab, or running field tests at a remote site: your pace will feel slow. The validation cycles are long. But you are building in the physical world. When you succeed, you don’t have an exit. You have a foundation. You don't just have customers; you have converts. And the product you ship doesn't just generate revenue; it creates a legacy.

If your timelines feel uncomfortable compared to software, that’s because you’re operating inside a system designed to resist change. And let’s not forget you are building actual physical products that interact with a complex world. Times are tough. Don’t give up. We need you.

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Nada Ahmed is the founding partner at Houston-based Energy Tech Nexus.

Houston maritime startup raises $43M to electrify cargo vessels

A Houston-based maritime technology company that is working to reduce emissions in the cargo and shipping industry has raised VC funding and opened a new Houston headquarters.

Fleetzero announced that it closed a $43 million Series A financing round this month led by Obvious Ventures with participation from Maersk Growth, Breakthrough Energy Ventures, 8090 Industries, Y Combinator, Shorewind, Benson Capital and others. The funding will go toward expanding manufacturing of its Leviathan hybrid and electric marine propulsion system, according to a news release.

The technology is optimized for high-energy and zero-emission operation of large vessels. It uses EV technology but is built for maritime environments and can be used on new or existing ships with hybrid or all-electric functions, according to Fleetzero's website. The propulsion system was retrofitted and tested on Fleetzero’s test ship, the Pacific Joule, and has been deployed globally on commercial vessels.

Fleetzero is also developing unmanned cargo vessel technology.

"Fleetzero is making robotic ships a reality today. The team is moving us from dirty, dangerous, and expensive to clean, safe, and cost-effective. It's like watching the future today," Andrew Beebe, managing director at Obvious Ventures, said in the news release. "We backed the team because they are mariners and engineers, know the industry deeply, and are scaling with real ships and customers, not just renderings."

Fleetzero also announced that it has opened a new manufacturing and research and development facility, which will serve as the company's new headquarters. The facility features a marine robotics and autonomy lab, a marine propulsion R&D center and a production line with a capacity of 300 megawatt-hours per year. The company reports that it plans to increase production to three gigawatt-hours per year over the next five years.

"Houston has the people who know how to build and operate big hardware–ships, rigs, refineries and power systems," Mike Carter, co-founder and COO of Fleetzero, added in the release. "We're pairing that industrial DNA with modern batteries, autonomy, and software to bring back shipbuilding to the U.S."