The only really new kinds are thermocouples (mostly garbage) and solar panels (poor efficiency, but abundant fuel).
Some fusion might end up using magnet pumping, which is basically just a plasma powered piston.
Don’t skip the betavoltaic battery, (or the brand-name: Betacel), which turns beta-radiation directly into electricity. They used them in the 70s to power pacemakers, since batteries were kinda shit back then, and implanting Prometium into people is just too epic not to do.
Nowadays we have tritium-decay betavoltaic batteries, on satellites, buried or underwater sensors and probably some too secret military stuff.
The best solar panels are getting at or above the efficiency of converting nuclear heat to electricity (about 1/3) so they probably shouldn’t get that poor efficiency label.
Some cells are getting 47%, which is ridiculous for a generator! The theoretical maximum efficiency for solar cell from the sun as it appears in the sky is about 68%, so that’s pretty good!
However, how expensive is that cell going to be? How much maintenance does it need, and how fragile is the system once deployed? It’s very obvious that PV efficiency has beed skyrocketing recently, and I don’t thinks it’s stopping soon, but a commercial PV panel available today is just breaking 20% efficiency. Luckily, sunshine is quite abundant.
