p2h.org
Power-to-heat is one of the main routes for using surplus renewable electricity instead of curtailing it, and P2H is the shorthand district heating operators, grid balancers and industrial decarbonisation projects already use.
That gives this three-character .org a credible home where the audience reads the name correctly on sight. A research consortium, an industry association, a standards project or a nonprofit working on heat decarbonisation would find the term already in their vocabulary, and the extension is the one those bodies use.
Other readings hold up: peer to human, path to health, pledge to help. Development and health nonprofits build programme names in the X-to-Y form constantly, and three characters is a tidy fit for a campaign identity that has to survive being printed on everything.
Short, structured, and sitting inside a technical vocabulary that gets used more each year.
The name is listed for sale. Enquiries welcome.