The article says that iron burns at up to 1800 C. I found a short list of other fuels: https://toolsowner.com/blacksmith-forge-temperature https://toolsowner.c

The article says that iron burns at up to 1800 C. I found a short list of other fuels: https://toolsowner.com/blacksmith-forge-temperature https://toolsowner.com/blacksmith-forge-temperature And we can use the Carnot formula to calculate efficiency: https://en.wikipedia.org/wiki/Carnot%27s_theorem_(thermodynamics) https://en.wikipedia.org/wiki/Carnot%27s_theorem_(thermodyna... efficiency = 1 - T_cold/T_hot = (T_hot - T_cold)/T_hot First we must convert to Kelvin by adding 273.15 to the Celsius temperature. Here is a table with Carnot efficiencies calculated, assuming that the cool end of the cycle is something like a car radiator at just below the boiling point of water at 373 K (100 C or 212 F): Material Temperature(Kelvin) Efficiency: --- Coal 2250 83% Iron 2073 82% Propane 1533 76% Wood 893 58% Im having a hard time finding efficiencies for iron oxide electrolysis because all of the papers are behind paywalls. A big portion of the energy required is in heating the iron oxide in the first place, which could be done easily by solar collectors for free: https://newenergyandfuel.com/http:/newenergyandfuel/com/2010/08/31/use-sunlight-to-smelt-iron-ore/ https://newenergyandfuel.com/http:/newenergyandfuel/com/2010... This claims about 85-96% efficiency for aluminum oxide electrolysis: https://www.tms.org/pubs/journals/JOM/9905/Welch-9905.html https://www.tms.org/pubs/journals/JOM/9905/Welch-9905.html I think a 95% efficiency might be reasonable for iron oxide if the temperature is raised by free solar thermal energy. So round trip efficiency is: efficiency = 0.95 * 0.82 = 78% This could be raised by a few percent by using a colder radiator (closer to room temperature at 300 K) and recapturing some of the waste heat with a Stirling engine. So I think that the article is accurate. If someone has a table of electrolysis efficiencies for various compounds, that would be helpful. Edit: after thinking about this for a moment, I realized that the Carnot efficiency should be calculated against room temperature if only the heat is being used and we aren't generating electricity. It only increases the efficiencies in the table above by about 3-8% from hottest to coldest, respectively. Edit 2: for anyone curious, capturing heat and converting it to electricity is usually about 70% efficient at a turbine, and 95% efficient at a generator, for about 65% total. That's why a jet engine is limited to about 0.80 * 0.70 * 0.95 = 55% efficiency (40% in practice). Stirling engines are much closer to their ideal Carnot efficiency because their losses to turbulence (friction/entropy) are much lower. If my numbers are a little off here, please correct me.