Blossom Energy, a startup developing graphite-based thermal storage boilers and high-temperature gas reactors, announced on May 27 that it had completed a 300 million yen funding round. The round closed on May 8, 2025, amounting to roughly USD 2 million at that day’s exchange rate.
Blossom Energy was founded in 2022. Its founder is CEO Shinpei Hamamoto, who conducted research and development on high-temperature gas reactors at the Japan Atomic Energy Agency.
Graphite Thermal Storage Boiler Set to Begin Mass Production Later This Year
Storing heat is one approach to achieving carbon neutrality, and such efforts are underway around the world. Beyond Blossom Energy, the Finnish startup Polar Night Energy is advancing projects that store heat using a sand battery, supplying district heating and reconverting it back into electricity.
The product Blossom Energy is currently working to mass-produce and sell is its graphite thermal storage boiler, the “Blossom Energy G-TES.” The G-TES stores electricity derived from renewable energy as heat, using graphite as the storage medium. According to the company, the stored heat can be used as steam, warm air, and hot water, and—through an absorption chiller—as cooling or chilled water as well. Blossom Energy cites specific applications such as land-based fish farming, paint-drying ovens, hot-water bathing facilities, and air conditioning for airport facilities.
In 2025, the G-TES was successfully demonstrated in Takehara City, Hiroshima Prefecture. In the second half of 2026, the company plans to move into mass production and expanded sales.
Blossom Energy is also advancing development aimed at “generating” electricity. That approach is the high-temperature gas reactor, which CEO Hamamoto has long worked on developing. A type of nuclear power generation, it confines the nuclear fuel within graphite. The advantage of this design is that even if the coolant gas stops, the fuel cools naturally, making it structurally resistant to accidents.
Touting Stronger Hiring to Support Expanded Sales
The newly announced round drew Energy & Environment Investment as a new investor and Animal Spirits as an existing investor. Both are venture capital firms.
The funds will be used to strengthen hiring and expand the organizational structure in order to mass-produce and broaden sales of the G-TES. As part of the latter, the company also announced that Toshiyuki Abe—who spent 38 years in energy-related work at Itochu Corporation—has been appointed an adviser to Blossom Energy.
On the funding, CEO Hamamoto commented: “We are broadly seeking colleagues to take on, together with us, the challenge of transforming the very nature of energy that underpins daily life.”
