Cheap, reliable electricity and heat enables efficient hydrogen electrolysis plants that split H2O to make H2 and O2. The hyrdrogen can used as fuel, as high heat in plasma arc torches, as feedstock to synfuel and ammonia production plants, and as a reducing agent to refine iron ore.
Hydrogen is used as an intermediate energy carrier. Its energy is released by burning, making H2O. One of hydrogen’s values is that it can be a portable energy source in gas or liquid form. Hydrogen an important feedstock for chemical reactions in the Heavy industry sector, for example.
The power flow lines beneath the blue hydrogen box symbolize that some of the power from fission sources is converted to intermediate hydrogen, and some is transferred directly as electricity. In an electrified economy, Heavy industry is expected to consume 1800 GW, but the trade-off between hydrogen power and electric power will evolve as technology and economics evolve.
Today hydrogen is produced from methane, CH4. The resulting release of ~1 gigatonne of CO2 per year represents about 2% of global CO2 emissions. Oil refineries use hydrogen to “crack” long hydrocarbon chains of heavy crude to become more hydrogenated, shorter molecules such as in gasoline.
Hydrogen has a high energy density per unit mass [40 kWh(t)/kg], but not per liter.
Basic electrolyzers pass DC current through water. Oxygen is a byproduct, but will become a waste product if hydrogen production increases to 3,000 GW.
In the US natural gas (methane) is cheap because of fracking technology. Today it’s difficult for hydrogen electrolysis to compete with steam methane reforming.
Simple electrolysis of water is not cost effective for hydrogen production. High temperature electrolysis uses less electric power. With temperature sources as high as 850°C, the sulfur-iodine cycle splits H2O without electric power at all.
The bottom reactions use sulfur and iodine as catalysts, which are not consumed. The dissociation reactions require high temperature heat, at the top.
The 850°C temperature is higher than can be achieved with molten salt fission reactors such as ThorCon. Future versions of high temperature gas reactors may reach this high temperature.
Electrolysis can be more efficient starting with hot steam rather than water. Heating water from 0°C to 100°C was the original definition of 100 calories. A calorie is roughly 4 joules. It takes 540 calories to transform 100°C water to 100°C gas. Thus it’s more efficient to use cheap heat to get a head start on electrolysis rather than just using more expensive electricity.
Nutritionists describe energy in kilocalories, often written as Calories, or Kalories.
SOFC means solid oxide fuel cell. Conceptually the SOFC and HTE cell are similar.
Europe is active in exploring hydrogen utility. Electrolyzers are commonly rated by their electricity input consumption, rather than output. Hydrogen energy is not yet nearly competitive with diesel energy.
Denmark’s NEL Hydrogen filling station factory can produce 300 H2Stations per year.
Hydrogen Hype has been reborn. Many media and analyst reports are very positive about the market future. Governments are flooding R&D groups with funding. Will hydrogen be boom or bust?
Much current motivation stems from excess energy produced by wind and solar generators during peak weather periods. Because wind/solar sources are not dependable, they are sometimes overbuilt to provide power from more distant sunny/windy locations when local wind/solar generators are idle or days are shorter. When good weather prevails, there is excess available power, now curtailed. Electrolyzing hydrogen provides the opportunity to utilize and save the excess, “free” power instead of curtailing it. There are two issues.
Electrolyzers are expensive pieces of capital equipment. Running them at the very low capacity factors created by running only when there is excess wind/solar reduces the time when the electrolyzers can produce hydrogen and earn money to pay back capital investment. Ramping electrolyzer equipment up and down rather than operating it steadily reduces efficiency and lifetime.
If electrolyzer power demand were to increase, then the wind/solar power will not longer be “free”.
Electrolyzer-produced hydrogen today is $10/kg, not nearly competitive with $2/kg hydrogen from steam methane reforming. Low cost hydrogen should be the most important priority.
Hydrogen interest is not new. This 2013 review is from Volume 38. PEM stands for polymer electrolyte membrane, or sometimes proton exchange membrane. Alkaline water electrolysis is a membrane-free technology. High-temperature steam electrolysis is yet another.
To electrify our world, hydrogen’s contribution depends on prioritizing low cost. Here are the important variables that directly affect costs. Engineering projects are conducting R&D to achieve low costs.
In this case, much of the electric power production of a fission power plant has been curtailed by priorities assigned to intermittent renewable energy sources, making continued operation uneconomic. The conclusion of the DOE report is that $2/kg-H2 is possible.
This analysis model for high temperature steam electrolysis of hydrogen gets closer to methane-produced hydrogen. R&D has progressed since 2014.
Here is a technical summary of the recently funded project to extract hydrogen from a nuclear reactor.
The keys to electrolytic hydrogen production competitive with methane steam reforming are:
- Electrolyzer capital costs ~ $35/kW of power input
- Electricity < 4 cents/kWh
- Heat
Lucid Catalyst published a 2020 analysis of the future potential of hydrogen production with high temperature electrolysis. The project capital costs of $250-400 per kW of electrolyzer input power, and strikingly high 95% efficiency, the ratio of kW(t)-H2 output to kW(e) input.
This seems good, but remember that a kWh(t) of heat from hydrogen for combustion has less value than a kWh(e) of electricity. However a hydrogen fuel cell in a vehicle can transform kWh(t)-H2 to kWh(e)-electricity to power the wheels with ~ 50% efficiency, which is pretty good, perhaps double that of an internal combustion engine.
Aside: The lower heating value (LHV) for hydrogen combustion does not include the energy taken away in the resulting water vapor. The higher heating value (HHV) would only be meaningful if there were some means for recovering the energy of condensation of the produced water vapor to liquid water (540 calories per gram, 540 Kalories per kg, 0.63 kWh/kg).
the point is that wind/solar electricity sources with only 30-40 % availability will double or triple depreciation cost contribution to hydrogen production, in comparison to a steady power source such as fission.
With fission power it makes sense to co-locate the power plant and the electrolyzer plant, to utilize heat as well as electricity. The combined system capital cost of the fission power plant plus electrolyzer determines capital cost contribution. Here $2/kg-H2 cost is achieved at 64% conversion efficiency. Lucid Catalyst’s report says efficiency can be 95%.
This is a similar analysis from another source. You must add Opex (left) and Capex (right) to obtain $/kg-H2.
These goals are all within reach.
So what’s that one kilogram of hydrogen worth?
- 33 kWh of heat
- energy of a gallon of gasoline
Bloomberg New Energy Finance is another sell-side financial analysis firm. They confirm the Energy Transistions Commission estimate of 3,000 GW of hydrogen, at $1/kg.
Storage and distribution of hydrogen will raise costs a bit.
We lose 11% just by compressing H2 to 200 bar.
Here’s a nice introduction to the hydrogen economy that could take an afternoon to read.
8% loss is better than 11%. Yet vehicle filling stations for fuel cell vehicles use 350 or 700 bar. More engineering is needed.
Wikipedia will provide more information about the Hydrogen Economy.
Bloomberg seems to suggest that hydrogen storage is costly, but not a roadblock. Expensive long-term storage would be needed to meet winter needs in a 100% wind/solar economy.
Here’s the role of hydrogen in world power flows in a fission-electrified economy.
Steam methane reforming uses methane (CH4) and steam (H2O) to make hyrdrogen (H2) and releases waste CO2 amounting to 1 gigatonne/year to the atmosphere. The H2 cost is only $2/kg.
Using conventional electrolyzers and buying electric power from the grid to generate hydrogen costs ~ $10/kg.
High temperature steam electrolysis can improve efficiency, using both heat and electric power from a fission power plant.
Electrolyzer thermal stress and capital expense is less if the electrolyzer runs full time, using 24×7, non-intermittent power.
Electricity is the most costly ingredient, so low $/kWh is important to be able to produce hydrogen in competition with SMR.
Projections of 3,000 GW(t) of hydrogen may be high.
At least two sources project H2 costing $2/kg by 2030 dropping further to $1/kg.
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