2 ms·
That analysis ignores the heat used to raise the reactant (water) temperature to 800C. On its face, the claim doesn't make much sense anyway. If you could con
by labcomputer 5y ago
That analysis ignores the heat used to raise the reactant (water) temperature to 800C.
On its face, the claim doesn't make much sense anyway. If you could convert water to 2 H2 + O2 at zero energy cost, you could make a perpetual motion machine by taking advantage of the exothermic reaction 2 H2 + O2 -> 2 H2O.
- darksaints 5y agoThat's the difference between LHV and HHV. It is possible to exceed 100% efficiency when using HHV because it is an inherently more conservative convention for energy content due to practical concerns. LHV, by contrast, is bounded by the laws of physics.
- labcomputer 5y agoWell, no, that's still wrong. The >100% efficiency comes from using two slights of hand: 1. Counting only the electrical energy input. But you also need to supply heat at the same time. That's the whole point of this product--use heat ~~instead of~~ (edit: in addition to) electricity to split water. Critically, they are assuming you get "free" (as in beer) waste heat at 800C... which is fairly silly. 800C heat is high-grade energy, not waste heat. Exhaust gas from a combined-cycle NG power plant, for example, is more like 250-300C. Thermal steam plants operate with a Th of ~550C (so the waste heat is much, much cooler). 2. Ignoring the fact that you need to heat the reactant (water) to 800C before you can have the discussion in #1. Now, the problem is that the heat capacity of water is much higher than an equal mass of H2 and O2. So, you can't even use the hot as-produced gas to heat the incoming water to anywhere near the operating temperature of the electrolyzer. The efficiency in a practical application is probably half to two-thirds of what they are claiming.