The thermocouples those use are wildly inefficient and only make sense in cases where no moving parts that might break is the utmost priority (spacecraft, extremely remote lighthouses or radio relays, etc.)
Betavoltaics are another option, which actually skip the thermal step, but those are only good for very small amounts of power.
Betavoltaics are another option, which actually skip the thermal step, but those are only good for very small amounts of power.