elleThermo, which is developing a technology known as the semiconductor-sensitised thermal cell (STC), announced on 26 August that it had secured ¥830m ($5m) in a Series A funding round.
The company was founded in 2023 by Sachiko Ubukata, its co-CEO and CTO, who is also an associate professor at the Institute of Science Tokyo. It is headquartered at INDEST, part of the Institute of Science Tokyo Campus Innovation Center, in central Tokyo.
A generation method adapted from the solar cell
There exists a type of photovoltaic cell, the dye-sensitised solar cell, that can generate electricity even in relatively weak light. The STC that elleThermo is developing has a structure in which the dye of a dye-sensitised solar cell is replaced by a semiconductor, and the transparent electrode by a conductive material. Doing so, the company says, makes it possible to excite electrons, and so generate electricity, using even low-temperature heat.
Unlike solar power, which keeps generating for as long as there is light, an STC stops generating at the point where the cell reaches chemical equilibrium. If the circuit is opened so that no power is drawn, however, the cell absorbs heat, shifts to a different equilibrium and is able to discharge once again. Switching the circuit on and off therefore allows generation to be repeated.
Japan is a country with limited energy resources, and yet two-thirds of the heat produced from the primary energy it imports is discarded, the company explains. Examples include heat from electronic equipment, such as that given off by data centres, waste heat from vehicles and other transport equipment, and waste heat from factories. The venture aims to put such “unused heat” to work.
In May this year the company carried out a demonstration in a KDDI test environment simulating GPU servers, announcing that it had “confirmed the possibility of power generation and of a localised drop in temperature within the rack”. If it can be scaled up, it may become one of the cooling systems for the AI data centres that are currently proving such a challenge.
“We will create a new industry”, says Ubukata
The Series A was led by the venture capital firm Spiral Innovation Partners. Among the other investors, Hulic Startup took part. It is the corporate venture capital arm of a major Japanese property group, and had backed Astroscale Holdings, the space startup that listed in June 2024.
The proceeds will go towards research and development, setting up a prototype production line, and hiring. Ubukata, elleThermo’s co-CEO, commented: “This mission cannot be achieved by our company alone. We will join forces with many who share our aspirations, and create a new industry.”
