Map of seafloor and formation of oceanic ridges.
Geothermal power plants operate at a constant rate, so the electrolysis is constant thus justifying the higher capital investment needed for the most efficient electrolytic cells. If the technical issues are solved economically, we can use the least-expensive electricity to produce the least-expensive hydrogen. In contrast, current proposals for electrolysis using renewable energy would occasionally use excess power from intermittent resources that have a higher electricity cost than geothermal. Since these resources only run occasionally, they will support only less-efficient electrolytic cells producing more-expensive hydrogen. The higher capital costs of highly efficient electrolysis, and the volume of hydrogen that will be needed to replace carbon-based transportation and heating fuels, will require baseload geothermal energy, not intermittent renewables.
The use of geothermal energy will not only increase the contribution of geothermal to the overall portfolio of renewable resources, it will also, by providing the capacity to balance the grid, avoid the decrease in capacity and energy values of wind and solar power. This in turn allows renewables to expand more rapidly. Because hydrogen will go into the kind of inventories that the economy has always used for transportation and heating fuels, hydrogen is a form of storage that does not impose an additional expense or burden on the economy, like batteries will.
With a foundation of baseload, high-enthalpy geothermal energy and supercritical electrolysis, all renewable resources can work together to advance, and replace fossil fuels in transportation as well as in electricity. This replacement combines of the best of both speed and efficiency.