Hydrogen for Energy?
by David von Seggern
CONTENTS
Basic Hydrogen Fuel Use
Hydrogen for Internal Combustion Engines
Hydrogen for Fuel Cell Motors
So Why the Hype Over Powering Vehicles with Hydrogen?
Reasons Not to Develop a Hydrogen Transportation Industry
Hydrogen for Space Heating — Bad Idea
Are There Legitimate Uses for Hydrogen As an Energy Medium?
Maine Hydrogen Use
Basic Hydrogen Fuel Use
It is important to first understand that hydrogen is an energy storage device (or carrier, or medium) and is not an energy resource such as fossil fuels, solar, or wind. As such, it can be compared loosely to batteries. Free hydrogen is rare in nature, and most uses depend on it being created through chemical reactions which themselves require energy inputs to produce the hydrogen.
The International Energy Agency (IEA) published a lengthy report in 2019 on the future of hydrogen in the global energy market. This report presents a rather optimistic and biased picture of hydrogen, ignoring some of the problems and flaws of a greatly expanded role for hydrogen in the energy transition.
A factsheet was prepared by Sierra Club on hydrogen and should be consulted for further information. The Sierra Club policy on hydrogen is summed up in the first sentence of this factsheet: “The Sierra Club only supports the use of green hydrogen—hydrogen made through electrolysis that is powered by renewable energy.” There are other means of hydrogen production using different energy inputs: black (coal power), gray (methane power), blue (fossil fuel power with carbon capture), and pink (nuclear power). Only green hydrogen is acceptable. Here, I try to briefly make the case against hydrogen fuel, no matter how produced, for most uses.
Hydrogen is most commonly produced (over 50%) through “steam-methane reforming” which involves this reaction:
CH4 + H2O + energy → CO + 3H2
Note the emission of the pollutant CO. Hydrogen can also be produced by electrolysis of water (splitting the water molecule):
2H2O + energy → O2 + 2H2
Hydrogen can also be produced by methane pyrolysis, a currently developing process:
CH4 + energy → C + 2H2
where bulk carbon is the byproduct and can be captured and used or stored. All of these processes requires energy input from some source and are non-polluting only if the energy used to drive the reaction is from renewable or nuclear energy sources rather than from fossil-fuel power plants.
Regardless of the exact reaction used to produce free hydrogen, some input energy is required. Depending on the efficiency of the conversion, the resulting hydrogen gas will represent only 50% or more of the energy used to produce it, with conversions of 100% impossible due to the 2nd Law of Thermodynamics which requires that some waste heat always be generated.
Hydrogen for Internal Combustion Engines
It is well known that hydrogen, with some engine modifications, can replace gasoline or diesel or natural gas as a fuel for internal combustion engines (ICE). Hydrogen fuel combustion has this reaction:
2H2 + O2 → 2H2O + energy
Note that no carbon pollutants are released, as opposed to engines run on fossil fuels. This is what happens when an ICE is modified to burn hydrogen, and such engines are already in use in vehicles today. The efficiency of a modern vehicle’s ICE is roughly 30-35%, regardless of the type of fuel, while electrical motors are in the range of 80% efficient. This is an overwhelming argument against using hydrogen in ICEs for the transportation sector .
Hydrogen for Fuel Cell Motors
Hydrogen can also fuel a vehicle through a fuel cell which produces electricity to be used by electrical motors to propel the vehicle. This is called a fuel-cell electric vehicle (FCEV). Here the reaction is simply the reverse of the electrolysis reaction:
2H2 + O2 → 2H2O + energy
which is identical to that of hydrogen combustion above, except that there is much less heat loss.
FCEV vehicles are also in use today and can be more directly compared to battery electric vehicles (BEV) in regard to efficiency. The webpage published by Volkswagen, Inc. nicely shows the comparison of efficiencies, starting with the electricity produced by a renewable energy source. The overall efficiency rate for the BEV is 76% while that of the FCEV is 30%. Similar figures are reported by Miranda in a detailed study. The dismal figure for the FCEV is due to the several steps required in the energy flow, with losses at each step. Given that ICEs are far less efficient than electrical motors, by a factor of two or more, the 30% figure would decrease to perhaps 15% when an ICE is substituted for the fuel-cell and motor of a FCEV.
So Why the Hype Over Powering Vehicles with Hydrogen?
If clearly using electrical power directly for a vehicle is 2-4 times more efficient than powering it with hydrogen, why is there any interest in hydrogen as a fuel for transportation? Here are some reasons put forth for FCEVs:
1. FCEVs reactions produce little to no air pollutants and no CO2 emissions and are thus desirable for urban settings.
2. FCEVs refueling can take as little as 3-4 minutes.
3. FCEVs driving range is typically 300 miles or more.
4. FCEVs hydrogen fuel can be produced cleanly if renewable sources such as wind or solar are used.
5. FCEVs fuel-cell stacks are potentially more environmentally friendly than lithium batteries.
The BEV comparisons to the above are:
1. BEVs have zero pollutants and no CO2 emissions and are thus desirable for urban settings.
2. BEVs will take 30 minutes or more to fully charge at Level 3 charging stations (overnight for level 2 charging).
3. BEVs are just now offered with ranges of 300 miles or more, but there is a weight penalty with that large of an energy storage.
4. BEVs will, like FCEVs, be as clean overall as the power used from the grid for charging.
5. BEVs batteries are not economically recyclable at this time.
Ten Reasons Not to Develop a Hydrogen Transportation Industry
There are solid reasons why BEVs are a better option than FCEVs for our transportation industry in general.
1. Currently, the automobile industry has embraced the BEV, with only two multinational companies offering a FCEV — Toyota and Hyundai.
2. The cost of refueling a FCEV may be as much as five times more than a BEV.
3. Hydrogen must be pressurized greatly to fit in an acceptably sized tank of a passenger vehicle, and there are safety concerns for handling these high pressures.
4. The FCEV refueling network is now dwarfed by the BEV charging network, with California having a few dozen stations and only a very few outside California.
5. The cost to society of building a separate hydrogen-vehicle infrastructure seems unlikely to bring any compensatory benefits.
6. The ranges of BEVs are increasing and likely to match those of FCEVs in the near future.
7. The extension of hydrogen as fuel to ICEs brings even less efficiency and more complications to the drivetrain of a vehicle.
8. FCEVs do not perform as well as BEVs in cold climates.
9. New renewable energy sources should be utilized in a manner that maximizes efficient use of that renewable energy, and hydrogen vehicles are so demonstrably less efficient that they should not be mass-produced for the US transportation market.
10. With the nearly complete transition of the auto industry to BEVs, the societal pressure to make batteries more recyclable will increase with time while the infrastructure to actually recycle them will grow and mature.
Hydrogen for Space Heating — Bad Idea
Recently, there has been some media coverage given to hydrogen for space heating. The fact that hydrogen combustion does not give off CO2 as do fossil fuels (see combustion equation above) might make it attractive for replacing these dirty fuels in residential and commercial space heating. Given that space heating amounts to about 40% of the energy consumption of a US home, it is imperative to lessen the carbon emissions from heating appliances.
It is noteworthy that the IEA report cited above does not mention space heating as an application of hydrogen. The hype on hydrogen for space heating likely comes from those not familiar with the basic chemistry outlined above as compared to the efficiency of today’s electrical heat pumps. A leading energy expert’s review of literature on the viability of hydrogen for space heating showed that all relevant, non-commercial studies of such indicated that hydrogen heating was plainly inferior in several aspects:
“The evidence assessment shows that the widespread use of hydrogen for heating is not supported by any of the 32 studies identified in this review. Instead, existing independent research so far suggests that, compared to other alternatives such as heat pumps, solar thermal, and district heating, hydrogen use for domestic heating is less economic, less efficient, more resource intensive, and associated with larger environmental impacts.”
Are There Legitimate Uses for Hydrogen As an Energy Medium?
There are some situations in which hydrogen, as an energy carrier or storage medium, is useful and could be employed. Remember that hydrogen must be created, and the first requirement in an environmental sense is that the energy source for creating hydrogen should be “green”. The IEA’s Global Hydrogen Review 2021 suggests hydrogen supplies are becoming greener and that there are notable applications for hydrogen as a supplier of energy.
One beneficial use of hydrogen may be in remote power plants to generate electricity where solar or wind structures are not feasible and a power line hookup to renewable energy sources would be very expensive due to distance and terrain. In such situations, compressed hydrogen could be stored onsite to produce electricity through ICEs or, preferably, through fuel cells.
Hydrogen is used intensely in some industrial applications today. According to an IEA report, the top four industrial uses of hydrogen are: oil refining (33%), ammonia production (27%), methanol production (11%) and steel production (3%).
It is not altogether clear that these industrial uses will persist. Oil refining will certainly diminish with the energy transition. Ammonia fertilizer production, depending also on methane, involves large CO2 emissions; and alternative agricultural methods may lessen the need for ammonia fertilizers. Methanol is used in miscellaneous applications and may be replaceable in some. Steel production may find methods that can replace hydrogen as a high-temperature reducer.
Maine Hydrogen Use
Maine, with a large component of energy usage in the space heating sector and a large transportation sector, is seeking to decarbonize its economy. Recognizing that hydrogen may have a role in that, Maine has joined other New England states in a consortium to seek funding to advance hydrogen technology. The Governor’s Energy Office is now in a fact-finding mode to collect information and ideas on what role hydrogen does play, or will play, in Maine’s economy. The Ninth Biennial Report on Progress toward Greenhouse Gas Reduction Goals (published in July 2022) has no mention of hydrogen at all.
In January 2021, SP 16 was introduced into the Maine Senate with the title: “An Act To Promote Renewable Energy by Authorizing a Power-to-fuel Pilot Program” by Senator Lawrence of York. The legislation died in committee. The intent of the legislation was to establish, but not yet fund, one or two alternative fuel projects which met this definition: “‘Power-to-fuel project’ means a facility that converts renewable energy to hydrogen gas, methane gas or other fuel.” Sierra Club Maine should object to “methane gas or other fuel”. Moreover, the use of “renewable” is subject to interpretation — one would like it to mean truly renewable, such as solar or wind power.
Sierra Club Maine cannot support any hydrogen project that is not “green” hydrogen under Sierra Club policy, nor should it support hydrogen projects that are wasteful of energy such as powering ICEs. This leaves it open to use the energy from Maine’s now numerous solar and wind farms to produce hydrogen fuel for some applications. In fact, the off-shore wind development proposed for the Gulf of Maine could provide some electrical power for hydrogen production that would have acceptable end uses. Placing production facilities near the landing points of the cables carrying electricity from the installed wind turbines would offload a given part of the power from the onshore transmission system.