Heat can be converted into work or electric power using some sort of heat engine, such as the steam engine. Many types and variations of heat engines exist, from the steam engine to modern and exotic novel concepts. When exploring the heat-to-power conversion, all heat engines are limited by the same laws of nature dictating the maximum amount of work or electric power that can be extracted from a heat source.
Only part of the energy in heat can be converted to electric power, the rest is rejected to ambient at low temperature. The higher the temperature of the heat, the more of the thermal energy can be extracted as work.
The H2P calculator outputs the maximum theoretical potential together with a range of feasibly obtainable net power output for a given heat source.