The Generation Professionals Group is for utility professionals who work in biomass, coal, gas/oil, hydro, natural gas, or nuclear power generation fields. 


Show me the Electrolyzer to deliver Hydrogen and Decarbonize our Energy System

Paul Hobcraft's picture
Innovation & Energy Knowledge Provider Agility Innovation

I work as a transition advocate for innovation, ecosystems, within IIoT, and the energy system as my points of focus. I relate content to context to give greater knowledge and build the...

  • Member since 2020
  • 129 items added with 60,844 views
  • Sep 8, 2020


There are an awful lot of different Electrolyzers already in the market. The different parts of the industry will need to come together and establish some standards and common definitions and measurements to allow the focus to return to technology, resolving the basics of the Electrolyzer and bring it into a robust Industrial solution on a higher level of automation and scale.

I have referred to several technical documents offered by the Hydrogen Council, the Hydrogen Europe, and specifically, a white paper by Dr. Philipp Lettenmeir of Siemens called “Efficiency- Electrolysis,” written in January 2019.

So, getting into the different choices of Electrolyzer first, drawing from the different papers.

Currently, there are two commercially relevant electrolysis technologies on the market for products in the MW range. These are the PEM and alkaline electrolysis. Both of their underlying technologies differ primarily in the ionic charge carrier that electrically closes the electrochemical process, as well as in the actual electrolytes.

The efficiency of the electrolysis systems is critical both technically and economically for electrochemical hydrogen generation using renewable energy.

Hydrogen generation costs are primarily dominated by the relatively high-power costs in addition to operating hours and amortization of the plant. From a technical standpoint, these costs can only be reduced by increasing overall efficiency.

The Different Electrolyzers currently available

Electrolyzers consist of individual cells and central system units. By combining electrolytic cells and stacks, hydrogen production is presently adapted to individual needs. Electrolyzers are differentiated by the electrolyte materials and the temperature at which they are operated.

Water electrolyzers needed for the Green Hydrogen solutions are classified into three main categories: alkaline, polymer-electrolyte membrane (PEM) and solid oxide electrolyzers (SOE).

Polymer electrolyte membrane (PEM) or proton exchange membrane technology, as the name indicates, includes a solid electrolyte that electronically isolates the anode from the cathode but electrically closes the electric circuit through its selective conductivity for cations. This nearly gas-tight solid electrolyte offers several specific advantages. On the one hand, it serves as a physical divider between the anode (oxygen side) and the cathode (hydrogen side) and prevents the mixing of the generated gases. This divider enables operations with differential pressure. The concern for the PEM electrolyzers it presently needs significant amounts of platinum for their catalyst layers.

The alkaline electrolyzer has a porous separator to physically separate the hydrogen and oxygen gases while still enabling the transport of the liquid electrolyte. This porous separator increases the requirements for alkaline electrolyzers in dynamic operation. Differential pressures that can result in hazardous mixing of oxygen and hydrogen need to be absolutely prevented in the alkaline electrolyzer due to its porous separator.

The question of comparing the efficiency of both technologies is therefore not easy to answer.

The fact is that the selection of the operating point and the associated voltage is decisive for efficiency. The generally low overall resistances in PEM technology result in a broader range of operating modes.

Solid oxide electrolyzers hold the potential of improved energy efficiency but are still in the demonstration and development phase. They work on high temperatures and mainly require ceramics and a few rare materials for their catalyst layers. The need for high-temperature might limit their long term viability as they require renewable sources of concentrated solar power and high-temperature geothermal power. Where it might become a game-changer is its conversion efficiencies of possibly producing synthetic gas or liquid fuels directly from steam and Co2, potentially attractive to aviation, etc.

There is a fourth Electrolyzer called the anion exchange membrane (AEM) electrolysis (also known as alkaline PEM). I need to find out more about this one.

To sum up, the efficiency of electrolysis is mostly determined by the amount of electricity used to produce an amount of hydrogen. Depending on the method used, the efficiency of the water electrolyzer and is currently in the region of 60 to 80 % (based on the calorific value).

While electrolyzers are already operating in many locations, research continues to improve them further to be more reliable, robust, and efficient.

Research priorities concerning electrolyzers are currently including the following;  increasing the efficiency of the electrolyzer system as a whole, along with its operating life, looking at improving power density and stack size, reducing costs (primarily material costs), introducing pressurized systems to avoid the need for subsequent compression of the H2 produced, and not least, developing flexible systems adapted to an intermittent and fluctuating power supply.

All have slightly different operating principles.

The most established and well-matured technique is alkaline electrolysis, whose main advantages are low costs (not using noble electrodes) and long-term stability.

On the other hand, PEMs and SOEs offer a more compact design and make operation at differential pressures feasible and favorable. Due to the solid form of the electrolyte, the systems are more dynamic with a faster response rate upon application of variable power load. It seems that PEM electrolyzers are the most suitable to deal with high current densities, variable partial pressure load, overload, and on-off conditions.

Technology needs radically improving for all Electrolyzers.

To achieve this improvement in Electrolyzers, we will need some remarkable technological enhancements and advancement. The list is long but includes; achieving higher efficiencies, less degradation, higher availability of the number of units, larger cell sizes, higher operating pressures, less reduced critical materials together with this need for reduced material size.

Getting to this ramping up needs the plants will require a significant plant capacity ramping up. Plants need to ramp up their volume produced, and they will be a need for more automation production of the Electrolyzer cell components, the cells, and stacks. A radical redesign of the plant assembly to build GW scale electrolyzer plants and then the final component assembly and engineering finishing work will be radically different from today’s plants.

Researchers and Engineers will be exploring and exploiting new design and innovation.

The issues on the researchers and engineers’ plate in the next few years are many;

They include looking at all levels of efficiency, determine if substitute critical raw materials can be substituted or reduced due to cost and rarity concerns.

The research and technology solutions have system boundaries to work within. This useful visual gives you some understanding, courtesy of Siemens.

Technicians need to look at solutions to reduce the degradation of the polymer membrane, so it is reliable over an average accepted industrial lifetime of 10 to 20 years in varying conditions.

They need to look to reduce the electricity consumption, improve the system hydrogen finished yield, concern themselves with varying contaminants that can affect performance and efficiencies, and find more robust ways to control the temperature of the electrochemical reaction at differing loads and conditions.

Then there are challenges at the installation site to resolve.

At the installed location of any Electrolyzer, the cost of the compressors, gas cleaning, demineralized water, the transformers, the cost of electricity and water, and the installation costs all need addressing and adaptive solutions depending on the operating conditions found.

The real dominant part of establishing Electrolyzers will be the electricity costs, suggested as 60-80% of the finished hydrogen cost. It is renewable energy, coupled with Electrolyzers, makes them viable. The operating conditions and variances the Electrolyzers work within will determine its performance and the demand loads placed on it.

Mastering the technology variables is key to the speed of progression of the Electrolyzer.

So as we all look to Electrolyzers as the solution towards offering a power source of Hydrogen, it is the technology developments that will need to be mastered.

The need to build out capacity volumes to bring down the unit price, we need to see the GW scale to make them industrially attractive, a low renewable integrated electricity- hydrogen partnership, and integrated project development.

The need for construction and installation approaches to make electrolyzers competitive. All variables will need to come together and be resolved.

From my perspective, this indicates a long hard road to travel between now and 2030 to get the Electrolyzer the Real alternative to other power generation options.

Moving to Industrial Ready is the current step to achieve

Today, the Electrolyzer is not Industrial Ready in it is asset readiness, system design, and value chain development. All three aspects will need to be all worked upon to offer solutions that will give underlying confidence in accelerating the  Industrial shift to green Hydrogen through the deployment of Electrolyzers fit for each industry, transport, and buildings.

The problem today is the Electrolyzer has only recently moved from a KW to an MW in design. Today the 1 to 10 MW PEM Electrolyzer is a market norm, and 10MW scale systems built-in stack or modular design with developments of 100 MW single scale solutions about three to four years away. To get to a GW scale will possibly be hit by 2030 (Sources Hydrogen Europe Roadmap).

There is an excellent time to provide the research and development needs to this in this period 2020 to 2025 and then into a further “wave” of technology advancements by 2030. The belief is that technology principles, technology understanding, and validations are determined to build a road map of Electrolyzer advancement in the next ten years. It becomes one where the shift is into large scale Industrial solutions needs to make multiple advances across the Electrolyzer board.

In Summary

There is a lot of hard work to ramp up Electrolyzers to make them commercially viable (and subsidy-free). The need is to make them energy-efficient in their use of water and electricity and the conversion process as possible. The ability to generate large volumes of Hydrogen needed in any primary energy change will be demanding, challenging, but rewarding. The Electrolyzer delivering Hydrogen is necessary if we want to decarbonize the current energy system.



***Thanks to the various reference points provided by the Hydrogen Council, as well as  Hydrogen Europe, and specifically, a white paper by Dr. Philipp Lettenmeir of Siemens called “Efficiency- Electrolysis,” written in January 2019. Several other articles were also referred too for my research and understanding.

*** A “triggering” post “From MW to GW’s of Renewable Hydrogen using Electrolyzers” can be found on my other posting site,, focused more on innovation development.

Paul Hobcraft's picture
Thank Paul for the Post!
Energy Central contributors share their experience and insights for the benefit of other Members (like you). Please show them your appreciation by leaving a comment, 'liking' this post, or following this Member.
More posts from this member
Spell checking: Press the CTRL or COMMAND key then click on the underlined misspelled word.
Jim Baird's picture
Jim Baird on Sep 8, 2020
Paul Hobcraft's picture
Paul Hobcraft on Sep 13, 2020

Thanks Jim

just downloaded the paper and will work through it

Winners and losers in your opinion on the choices?

Roger Arnold's picture
Roger Arnold on Sep 9, 2020

That's a pretty good summary of the currently available electrolyzer technologies.

A quibble about SOECs, however:

The need for high-temperature might limit their long term viability as they require renewable sources of concentrated solar power and high-temperature geothermal power.

I don't think that's right. High temperature SOECs, once they've been heated to operating temperature, shouldn't require any further heat input to continue in operation. All they require is good thermal insulation to keep the waste heat from steam electrolysis from leaking away too fast, along with a cell voltage overpotential to generate enough waste heat to supply enough heat for the endothermic electrolysis reaction. 

You're certainly right, however, that "technology needs radically improving for all electrolyzers". That's my biggest reservation about the rush to green hydrogen. It's premature. The technologies aren't yet good enough to meet the requirements of the vision. It's not just a matter of reducing costs; efficiencies need to be drastically improved.

It makes a lot more sense to me to deploy blue hydrogen as a bridge technology. Blue hydrogen could support zero-carbon backing generation for renewables and delay the need to overbuild the grid with variable renewables. 


Bob Meinetz's picture
Bob Meinetz on Sep 9, 2020

"That's my biggest reservation about the rush to green hydrogen. It's premature. The technologies aren't yet good enough to meet the requirements of the vision."

Agree Roger, and I'll take it one step further: as a preliminary exercise, let's assume an electrolyzer that's perfectly efficient - that the theoretical minimum energy for splitting water (40kWh/kg) will be all that's required to get the job done.

Now add any reasonable approximation of system losses: electricity transmission and pumping fresh water to the electrolyzer, pumping hydrogen from the electrolyzer to storage, compression/refrigeration, transport to point of use, pumping to a vehicle or local storage, and finally, PEM fuel cell conversion back to water + electrical energy.

With a high degree of confidence I'll predict there is no practical application of "green" hydrogen that won't be hopelessly more expensive, wasteful, and carbon-intensive than using electricity stored in batteries as the source of energy for the same application.

With slightly less confidence, I'll argue green hydrogen is a decoy for introduction of hydrogen from steam-reformed methane - brown hydrogen - into the supply chain. And what about ardent environmentalists who will demand all hydrogen come from renewable sources? Any suitably-impressive assemblage of pipes, tubes, bottles, pumps, compressors, and empty tanks onsite at the unveiling ceremony should be sufficient to put them at ease.

This bottle is filled with hydrogen generated from electricity generated by wind farms in the North Sea. No, really.

Paul Hobcraft's picture
Paul Hobcraft on Sep 13, 2020

Bob, I like your comments and observations. All to be done maybe all not to be done as the economics or alternative solutions make it uncompetitive. Good point. Thanks, taken on board

Nathan Wilson's picture
Nathan Wilson on Sep 12, 2020

"... blue hydrogen as a bridge technology ... delay the need to overbuild the grid with variable renewables."

As an implementation of fossil fuel with CC&S, given the cost of transporting hydrogen and efficiency loss in its production, it seems unlikely to me that it would be cost effective to burn hydrogen in a power plant rather than simply burning the fossil fuel and capturing the CO2 (e.g. oxy-combustion or a retro-fit post-combustion solution).

I think a better compromise would be to over-build the central plains grid with renewables, and build-out the coastal grids with 80% nuclear (perhaps with some thermal storage).  That way the total amount of over-building is much less, and a much smaller hydrogen economy is needed (maybe only somewhat larger than the existing fertilizer industry).

Paul Hobcraft's picture
Paul Hobcraft on Sep 13, 2020

The political debates on where Nuclear fits seem highly sensitive, especially over here in Europe. It needs to be a critical part of any solution to decarbonize but the headwinds seem tough to fight against at the moment. Am I right? The idea of modular nuclear plants might be the place to settle but I do not see the discussions opening up in the public domain yet, do you? What would change that? Failure of the other solutions perhaps to be commercially realized at the level of promise all are presently making?

I have real doubts on CCUS, I just cant relate to this. Cost, Salt Caverns, Returns etc, it does not stack up yet in my mind. What do you feel?

The answer of many who can't get there heads around a complex problme is "well let's have a carbon tax" then all these issues get magically resolved. Is it going to happen?

Nathan Wilson's picture
Nathan Wilson on Sep 14, 2020

Correction, nuclear is a critical part of a minimal cost climate solution.  I doubt that green hydrogen as a pipeline gas can economically replace fossil methane gas.  But, if wealthy European countries want to use their wealth to chose a non-nuclear renewables+hydrogen solution, they are free to do so.  The US and the developing nations will choose a low cost path, or continue with no solution.

My personal feelings pull me away from carbon capture; however the geologists say it will work fine.  So I put my feelings aside and side with science in saying that it is technically an option.  Whether such a policy can be enforced is a country specific question.  As the skeptics point out, in many places widespread cheating on environmental rules make it non-viable.  For example, in much of the US, recycling plastics has been a failure, because our free market allows foreign companies to bid on recycling contracts, and some foreign companies get paid to recycle plastics, but lax local enforcement allow them to simply dump it in a land-fill instead.

I don't think we'll get a climate solution until activists start demanding one, instead of simply demanding renewables.  Having the public or the government tell scientists and engineers how to do their jobs (by choosing answers for them) is a recipe for failure.  I'm reminded of the Flint Michigan contaminated water scandal (in which politicians chose a low cost provider for municipal water, but did not let the scientists test the water for compatibility with their pipes; it turned out their lead pipes were not compatible, and their drinking water was contaminated with lead for a year a two before doctors noticed a problem with their children's health).  Another example is the US manned space program; the government lawmakers have dictated that NASA stick with proven 1970s technology for their SLS rocket, and as a result, NASA has been struggling to comply with the law while much of the public laughs at them for under-utilizing SpaceX's more advanced technology.

Bob Meinetz's picture
Bob Meinetz on Sep 14, 2020

"My personal feelings pull me away from carbon capture; however the geologists say it will work fine.  So I put my feelings aside and side with science in saying that it is technically an option. "

Trust your personal feelings, Nathan. Because CCS, or CCUS, or whatever they're calling it now is 100% unverifiable, there's no money in it.

My challenge to CCS advocates: "Over the past month I've stored one million tons of CO2 in a salt deposit 4,000 ft. below this impressive array of gauges, pipes, digital displays, valves, stopcocks, pumpjacks, and other oil field knick-knacks. Either pay me $80/ton, or prove me wrong." No one has been able to do either.

Paul Hobcraft's picture
Paul Hobcraft on Sep 16, 2020

Hi Nathan,

Your words would send chills down any energy providers back "technically an option". So right. I just can't get into being convinced of CCS or CCUS, it is not (commercially) viable.....yet or scalable.

I like your shift in activism- not fixating on renewables but on solving climate degradation with solutions.

Roger Arnold's picture
Roger Arnold on Sep 14, 2020

If thermo-electrochemical production of hydrogen from methane [q.v.] is ever successfully commercialized, we'll have a process where one megajoule's worth of natural gas plus about 0.25 megajoules of surplus electricity produce some 1.15 megajoules worth of compressed hydrogen. It will yield a pure CO2 waste stream.

If that doesn't work out, we'll still have other reforming processes that produce hydrogen from natural gas with about 80% efficiency, Those also have nearly pure CO2 waste streams ready for sequestration. 

In general, efficiency of conversion isn't as critical when producing hydrogen from fossil fuels or biomass as it is when producing it by electrolysis. In the first case, wasted energy is from the raw fuel. In the latter, it's from electricity -- a much more valuable resource. 

The rationale for using hydrogen to supply backing power for variable renewables is the lack of carbon emissions. If we weren't concerned about carbon emissions, it would certainly be more efficient to use natural gas directly for backing generation rather than hydrogen derived from natural gas. But if we want to curb carbon emissions to the atmosphere, it's much easier to "capture" a pure CO2 waste stream from a blue hydrogen production facility than it is to extract the CO2 from the flue gas stream of a gas-fired power. plant.

Perhaps more to the point, there *will* come a day when natural gas runs out or becomes more expensive for backing power generation than green hydrogen from storage. When that day arrives, it will be helpful to have the necessary hydrogen infrastructure already in place. The only thing that will have to change will be the source of the hydrogen. The distribution and. power generation infrastructure will have been built, making use of cheap blue hydrogen.

Paul Hobcraft's picture
Paul Hobcraft on Sep 13, 2020

The view as I understand it Roger is if Hydrogen is there to support VRE the ability to ramp up to meet sudden demand might play a part and the PEM I gather does that better. You I am sure are right keep the SOEC in a ready state but what is the cost of that? I do not know above my pay grade that.

It seems each type of Electrolyzer can be located in different needs, specific to do the job. Any thoughts ?

Roger Arnold's picture
Roger Arnold on Sep 14, 2020

Support for VRE would never involve ramping up electrolysis in response to sudden demand. Electrolysis is a load, not a supply. You probably meant ramping down in response to sudden load.

That could indeed be a factor in favor of PEM electrolysis over alkaline. But I doubt it would be a significant issue. An electrolysis facility would be a natural. place to integrate grid-scale battery storage. Integrated batteries would enable a lower capacity of electrolysis cells to produce the same amount of hydrogen, by operating at a higher capacity factor. 

The real issue remains efficiency. If electrolytic hydrogen is really going to be used for multi-day and longer energy storage, its miserable 40% round trip efficiency really has to improved. Otherwise the economic penalty is too severe. But the inefficiency is a tough nut to crack.

Almost all of the applied R&D on low temperature electrolysis cells is aimed at capital cost reductions, in most cases by developing new catalysts that work "as well as platinum" but at lower cost. But even with platinum catalysts, low temperature electrolysis cells are inefficient. The inefficiency is mostly due to the large overpotential needed to drive the 4-electron oxygen evolution reaction at practical rates. There is some ongoing work aiming to address that, but it's still early stages. 


Nathan Wilson's picture
Nathan Wilson on Sep 13, 2020

My favorite electrolyzer used to be the PCC, which is proton-conducting-ceramic, because it has the useful feature of being able to make not only hydrogen, but also ammonia (when nitrogen is put in one electrode and steam in the other, ammonia, NH3 comes out of the nitrogen electrode).  That's helpful, since ammonia is much more valuable than hydrogen, both as a fertilizer, and a potential transportation fuel, since between the factory and the end-user, ammonia has much lower transportation and storage cost than hydrogen.

Unfortunately, PCC materials have been hard to develop beyond the lab demo stage.

However, the solid-oxide electrolyzers actually do have some application for ammonia synthesis, thus are my current favorites.  The Danish electrolyzer company Haldor Topsoe says that you can put steam and air into one electrode and use the 2nd electrode as the oxygen output. With proper feed levels, the steam electrode will produce the right mixture of hydrogen and nitrogen to feed a standard ammonia synthesis loop (Haber-Bosch).  In other words, the solid oxide separates the hydrogen from water as well as the nitrogen from air.

Part of the old PCC enthusiasm came from the "small is beautiful" bias for 10kW residential scale systems which don't need large grids, for which Haber-Bosch is a poor fit (because it uses a high-temp, high-pressure multi-pass synthesis and separation loops).  Haber-Bosch works fine at 500 MW scale however, and long distance GW-scale electrical grids continue to be the chosen solution for electricity.

Solid oxide electrolyzer (and PCC types) are also reversable, and can consume ammonia to make electricity.  Of course, for grid use, that's as expensive as burning diesel fuel.  However if you are building the electrolyzer anyway, you can use it as a source of emergency generation capacity, for use only a few days a year.  That lets you close more fossil fuel fired plants (and shrink the fuel supply chain), rather than keeping them around as reserves.

Paul Hobcraft's picture
Paul Hobcraft on Sep 13, 2020

Often what is the favorite in the research lab just does not "fly" in the world. Will PCC and Solid Oxide scale as would be needed? From what I understand they will miss any "hydrogen train" if they cant move into commercial piloting. Do you know if that is happening?

Get Published - Build a Following

The Energy Central Power Industry Network is based on one core idea - power industry professionals helping each other and advancing the industry by sharing and learning from each other.

If you have an experience or insight to share or have learned something from a conference or seminar, your peers and colleagues on Energy Central want to hear about it. It's also easy to share a link to an article you've liked or an industry resource that you think would be helpful.

                 Learn more about posting on Energy Central »