Can Hydrogen play a major role in our path to decarbonization?
Hydrogen is exciting; it has great promise as an essential tool on our path to decarbonization.
However, there are a few things to understand about Hydrogen. The first thing is this: Hydrogen is not a Source. Like Electricity, it is a Carrier. You can’t mine hydrogen. You have to use some other energy source to produce it, and any time you convert one form of energy into another, or store it, you lose some of the original energy in the process.
There are also technical challenges. Although hydrogen is the most energy-dense chemical fuel we have (almost 3 times natural gas) per kilogram, it is a very light gas. Therefore, to have reasonable utility per unit volume, it must be compressed, or even liquified. This adds to the energy burden. Then there are difficulties in storage and transport. After compression, it requires strong, generally thick and heavy tanks to contain it. Hydrogen, the smallest molecule in nature, can actually move through hot metals. Transporting it through pipelines presents technical challenges in terms of pipeline embrittlement, as well as demands on pumps, seals, and valves. It should also be noted that the popular idea of using hydrogen in fuel cells is challenging because there is energy lost in the original conversion to hydrogen and further loss in the marginally efficient fuel cell itself.
In spite of these challenges, the potential utility of hydrogen is huge. It can be used to produce electric power, burned for high temperature heat in industry, serve as a feed stock for the chemical and agricultural industries, and – perhaps key – be the foundation of synthetic fuel production. Synthetic fuels would allow us to continue to benefit from the advantages of liquid fuels for transportation without entirely recreating a lot of existing infrastructure. Ammonia could power shipping; other products could be used in heavy trucking and aviation.
Returning to the challenge of producing hydrogen, the high quality and high temperatures available from nuclear energy are arguably the only way we can do this cost-effectively and with a reasonable infrastructure. Electrolysis from renewable sources is a non-starter. The quality of renewable energy is so poor for this purpose that we would have to carpet the earth to produce the hydrogen we are looking for.
High temperature electrolysis, combining thermal heat from natural gas with electric generation, is more efficient, but still costly, and not carbon free. High temperature Generation IV reactors can finally get us to a temperature regime where electrolysis becomes cost effective, and these reactors can do even better than that. High enough temperatures can allow direct thermal production through methods such as the sulfur-iodide process. Finally, using this high-quality high temperature heat for pyrolysis of methane is seven times more energy efficient than electrolysis, producing useful solid carbon instead of carbon dioxide as a by-product.