Comment by phenol

kind of. the real figure of merit here is the levelized cost of hydrogen (LCOH), which requires you to build a technoeconomic model to simulate the total cost and production of a hypothetical unit over its lifetime. focusing just on "energy efficiency" will be misleading (in favor of geoH2!) because, relative to a green H2 elyzer, this approach has relatively lower operational costs (OPEX) and relatively higher capital costs (CAPEX) because you don't need stoichiometric amounts of electrons but you do need to drill a bunch of boreholes. if you just looked at "energy efficiency" you'd fail to amortize the drilling capex which is probably a bigger cost driver than electricity opex.

and fwiw estimates of LCOH by this process are $0.50-1.50/kg compared to maybe $3-6/kg for green H2. but these are obviously pie-in-the-sky NOAK figures and a technoeconomic analysis is only as good as the assumptions you feed into it. is it actually cost effective? there is only one way to know for sure, and these guys are gonna find out it's the hard way.