My earlier post, on the topic of synthesizing organic compounds from water and carbon dioxide [1], included a schematic representation of the chemical processes involved in the formation of methane from H(OH) and CO2. You might have noticed that the process involves dissociation of water to form hydrogen and oxygen, and might possibly have asked yourself why it is desirable to go further than that in producing a gaseous fuel, especially considering that burning hydrogen produces no CO2, while burning methane does. If so, you would have anticipated this post.
In implementing a sustainable, decarbonized energy infrastructure based on the Galain model from Uruguay [2] it is necessary to provide a nominally quiescent but available on demand source of electricity for times when diurnally variable sources such as solar and wind are unable to meet load demand. Choices include thermal generators fueled by sustainable biofuels or sustainable gases such as synthetic methane, in conjunction with carbon dioxide capture, or alternatively thermal generators powered by hydrogen. Nuclear fission power is not an option here because of the long times required to bring reactors on and off line.
It is fair to say that up until now, free hydrogen, that is hydrogen that is not bound in a compound like water, has been an alien concept. The atmosphere contains practically no hydrogen, because the earth's gravitational field is insufficiently strong to prevent its escape. We are accustomed to thinking that producing hydrogen entails some sort of processing such as chemically stripping it from hydrocarbons, either with or without subsequent capture of the carbon dioxide that is inevitably produced in the process, or by electrolysis of water.
In plants, a water molecule can be split into an oxygen atom and a hydrogen molecule using the energy equivalent to that of a single near ultraviolet photon having a wavelength of about 372 nm; on a macroscopic level this equates to 285.83 kJ/mole, or 4396.3 kWh/ton, assuming perfect efficiency for electrolysis. This is costly, and that's why at present most hydrogen is produced chemically from hydrocarbons without carbon dioxide capture by the fossil fuel industry, because, if one ignores the negative effects of CO2 emissions, it is cheaper. Here we will concentrate on the electrolysis process because it is both sustainable and carbon free, assuming as we will use of solar or wind power to provide the electricity. It is also true that electrolysis is becoming increasingly cost-competitive as the solar and wind power infrastructure is built out.
Hydrogen as a fuel has many critics, and the critics have a number of valid points. In the following I will enumerate and qualitatively evaluate a number of its claimed weaknesses, and summarize the implications for its use.
Although hydrogen has a very high energy per unit mass, its being the lightest of gases equates to a correspondingly low energy per unit volume in comparison to other gases such as methane, at a given pressure, and minuscule in comparison to liquids. Liquification is not a solution to this problem because of hydrogen's very low boiling point (-253C). Of course it can be pressurized to provide more energy per unit volume but it remains inferior to other, heavier gases in any event. Hydrogen is therefore a poor choice as a motor vehicle fuel. This however does not make it unsuitable for use in fixed applications such as power plants. The technology for bulk storage of hydrogen is well known and practical.
Issues are sometimes raised concerning the transport of hydrogen via pipelines. It is useful to keep in mind that a hydrogen pipeline has been in operation in Germany since 1938 [3], and that over 1,600 miles of hydrogen pipelines are currently in use in the US [4]. That said, hydrogen, particularly at very high pressures, can embrittle some forms of steel, a problem that can be avoided or mitigated in a number of ways. See also below.
As hydrogen molecules are very small, special attention has to be paid to the welding of pipes and vessels used in the transportation and storage of the gas, and to the associated valves and seals. As before, this is not a difficult problem.
It has been pointed out that electrolysis of water requires the addition of a corrosive electrolyte. While true, once again this does not engender any insoluble problems, any more than does the use of sulfuric acid as an electrolyte in automobile batteries.
Almost all large thermal power plants are located on or near the banks of rivers or lakes, because of the requirement for water as a coolant. This can be used to advantage in converting them to, or replacing them with, intermittent operating, hydrogen fueled plants, as the water needed for electrolysis is readily available on site, and very little pipeline infrastructure is needed. The repurposing would require construction of large capacity hydrogen storage tanks and possibly modification of the electricity grid to power the electrolysis facility using wind or solar power.
In conjunction with the replacement of coal, oil or gas with hydrogen in power plants, it will be necessary to expand the wind and solar capacity to a level such that it can simultaneously
Satisfy peak customer electricity demand;
Power CO2 capture and sequestration (CCS) at a level of tens of billion tons per year worldwide; and
Produce sufficient hydrogen to enable meeting of peak customer electricity demand at times of limited wind and solar energy availability.
After I wrote the foregoing, I read in a newspaper article [5] that conversion to hydrogen as the fuel of choice may be simpler than portrayed above. The article in question concerned a hydrogen drilling project near the German-French border, and linked to an article published in Science [6] which reported on hydrogen seeps and wells, primarily in Africa and Asia Minor, and raised the possibility of very substantial underground reserves of hydrogen. Apparently it is not unusual for significant percentages of hydrogen to be found in methane wells, but its presence has been ignored because nobody was looking for it. Should the reserves be as widespread and substantial as indicated, it would remove a commensurate burden on the energy grid by reducing the need for electrolysis, albeit at the cost of increased requirements for separation facilities and pipelines. The potential bad news here is that already some are suggesting the use of so-called "enhanced recovery" (aka fracking) techniques for underground hydrogen extraction. [7] Although there are known mechanisms for underground hydrogen release from water that are presently active, it is not necessarily true that underground hydrogen can be considered to be a renewable resource, and therefore for the long term we will need to rely on electrolysis.
Notes
[1] https://stephenschiff.substack.com/p/methane-from-co2
[2] https://stephenschiff.substack.com/p/sustainable-eneregy
[3] https://en.wikipedia.org/wiki/Hydrogen_pipeline_transport
[4] This report from the Congressional Research Service, also discusses the regulatory framework as pertains to hydrogen pipelines in the US: https://crsreports.congress.gov/product/pdf/R/R46700
[5] Süddeutsche Zeitung, Nr. 15 [19. Januar 2024] s. 14
[7] The Science article extends the color jargon that has arisen around hydrogen. With the inclusion of underground sources we now have the "spectrum":
GRAY: Hydrogen produced by chemical means using petrochemicals, with waste CO2 released into the atmosphere;
BLUE: As with gray except with CCS;
GREEN: Hydrogen produced by electrolysis of water, using carbon-free energy
GOLD: Hydrogen extracted from natural subsurface reserves
ORANGE: Hydrogen extracted from underground with the aid of hydraulic fracking
I must note that there are degrees of blue-ness in blue hydrogen. Very rarely if at all does the fossil fuel industry build DAC facilities and sequester supercritical CO2 in deep saline aquifers; mostly they buy "Carbon credits" or the like from others who ostensibly do something to sequester CO2, such as planting trees. But usually that is a false equivalency. Whenever someone starts talking about carbon offsets you should clutch your wallet.
Personally I think the implementation of micro grids, utilizing the geologically most efficient renewable, is the starting point of any best practice energy discussion. The last thing we need is another industrial complex. If it can’t be done by individuals or small communities, I don’t think it should be part of that equation.