Now, a research team at MIT has developed an all-solid device that converts 1900 to 2400°C heat back into electricity.
Their sandwich-design comprises 3 layers and uses the thermophotovoltaic principle.
Having captured high-energy photons from a white-hot heat source, the uppermost layer converts them to electricity.
Lower-energy light particles are captured by the middle layer. The bottom layer of gold, meanwhile, reflects any remaining photons back to the heat source.
The efficiency rating of 40% is higher than the 35% of steam turbines. These, however, are temperature-limited and high-maintenance because of moving parts.
Nevertheless, air can be pretty useful too.