There has been a tendency for the automotive sector to view batteries and hydrogen as competing technologies when they are in fact highly complementary, says Dr Gareth Hinds, Science Area Leader in Electrochemistry at the National Physical Laboratory (NPL).
With the UK government’s aspiration to end the sale of new diesel and petrol vehicles by 2035, it’s hard at the moment to escape the ongoing debate: Battery electric vehicles (BEVs) or fuel cell electric vehicles (FCEVs)?
While the choice of technology to power their vehicles ultimately comes down to individual manufacturers, the fact that this change is being driven primarily by environmental imperatives rather than purely market forces makes this a very interesting debate. My view is that the response should be informed by the science.
Growing a green gas giant: innovations in hydrogen production
Sodium-ion batteries can get ahead in the power game
Electrochemical energy storage involves the interconversion of electrical energy and chemical energy. Electricity generated from renewable sources, such as solar and wind, can be stored for later consumption by using the electrons to transform more stable materials into less stable materials containing higher amounts of energy. Examples include the electrolysis of water to form hydrogen and oxygen, or the insertion of lithium ions into the graphite electrode in a lithium ion battery (known as intercalation). Such a chemical store can then be raided when required by reversing the process and allowing the material to revert to its more stable form, with the release of low carbon electricity. In a FCEV, this is achieved by combining the hydrogen with air in a fuel cell.
Thermodynamics dictates that each time we convert energy between any of its forms we lose a fraction of this energy through irreversible heating of the system and its surroundings. Fortunately, the process of intercalation in a lithium ion battery is incredibly efficient (> 99%). This translates into a round-trip efficiency of around 70% for BEVs. Hydrogen fuel cells, on the other hand, have much lower efficiencies of around 60%, mainly due to losses associated with the oxygen reaction. When this is combined with the losses in producing the hydrogen from electrolysis in the first place, the round-trip efficiency of a FCEV drops to around 30%.
So why do we need hydrogen at all, given its much lower efficiency?
Firstly, there is an inherent weight limitation for BEVs because all of the energy in a battery is stored within its electrodes. If we want to power a bigger vehicle or drive a longer distance, we need to add more electrodes to store the additional charge. Battery electrodes are relatively heavy and the extra battery weight rapidly becomes impractical. In contrast, in a FCEV the fuel cell itself is inert and all of the energy is stored in the hydrogen tank. Since hydrogen is so light, the incremental mass associated with increasing the size or range of the vehicle is much lower than for a BEV.
Hybridisation of battery and fuel cell technologies is…likely to be explored more widely
So, for heavy duty applications such as vans, trucks, trains, ships and aircraft, it makes far more sense to power them with hydrogen. Vehicles that regularly travel long distances or that need to refuel quickly are also more suited to hydrogen. But for light duty passenger vehicles regularly travelling short distances, the superior efficiency of BEVs makes them ideal for this purpose.
Fast charging of BEVs may sound attractive but it carries several challenges, including the power demand on the electricity grid and the tendency to curtail the lifetime of the battery. Hybridisation of battery and fuel cell technologies is a potential solution that is likely to be explored more widely in the coming years.
Another important factor is that hydrogen is more suited to longer term storage of energy since it is a gas and can be easily stored in tanks, containers and underground caverns. Batteries tend to lose their charge over time due to side reactions within the cell and their lifetime suffers when they are not charged and discharged regularly.
Hydrogen can also be burned in boilers and cookers, which makes it an attractive candidate to replace methane in the gas grid. This would effectively create a country-scale storage facility that could be continuously topped up by electrolysis using renewable electricity. Efficiency losses would then be less of an issue.
Finally, hydrogen technologies are almost 100% recyclable and are much easier to handle at end-of-life than batteries, for which significant sustainability concerns exist. Another key role for hydrogen may be to limit the scale on which it is necessary to deploy battery technology in order to avoid major waste disposal issues in the longer term.
Hydrogen has a number of advantages that allow it to fill gaps in our decarbonisation strategy that batteries cannot address effectively on their own. Most of these benefits are associated with the fact that the energy in a fuel cell is not stored in the device itself but in the hydrogen gas.
It should also be noted that the requirement for decarbonisation of energy goes well beyond the transport sector, which comprises only a third of global CO2 emissions. There are many complex interdependencies between the different sectors, all of which need to be taken into account.
As the UK’s National Metrology Institute, the National Physical Laboratory (NPL) is working closely with academia and industry to develop more reliable standard test methods, novel diagnostic techniques and advanced modelling tools to support improvements in cost, performance, lifetime and safety of batteries and hydrogen cells, plus electrolysers. This important underpinning work will help to build a greener and more sustainable infrastructure to power industry and society in the future.
Dr Gareth Hinds is Science Area Leader in Electrochemistry at the National Physical Laboratory (NPL)
Yes, batteries and hydrogen should be partners since they complement each other. Yet the Tesla folks feel threatened by fuel cells and are still busy demonizing hydrogen. But here is the irony. They’ll need a hydrogen network to power-up their high demand battery chargers — our anemic electric grid just won’t do. The obvious question then is, if we’re going to need a hydrogen infrastructure to power-up battery chargers in remote locations, why not use that same infrastructure to bring hydrogen to stations to fill-up fuel cell trucks and cars to use the hydrogen directly.
Hydrogen will protect the environment far better than batteries
From every thermodynamic and economical viewpoint both battery power and hydrogen power are foolish and squander primary energy purely to support unreliable renewable sources. Would not a better solution be to sequester the CO2 at the hydrocarbon use point, such as central heating boilers and engine exhausts?
Similarly to catalytic converters on cars we could use CO2 absorbers such as activated-lime that remove the fearful gas and then can be used as road-fill etc. Would need a fairly small change to gas central heating systems, compared with supplying and using hydrogen. Hydrogen was widely considered in the 1960s and ruled out then; the same thermodynamic laws apply now.
Yes, exactly. The both fill an appropriate niche and functionality. While hydrogen can run a fuel cell and hence potentially the same EV, the cells are not without issues themselves. But hydrogen can be burnt as we do with LPG using (adapted) existing IC technology. Battery electric is fine for urban or constrained route use, but in rural areas far more flexibility will be required in fuelling. Hence some form of liquid fuel is by far the most practical and usable. Hydrogen infrastructure supply will not need anything like the grid and generation requirements for pure electric and will therefore not need so much investment, which would be a better use of the money to be wasted on HS2. The primary energy from renewables is effectively free and we either use it or it does nothing, it is not squandered so while it may not be particularly efficient to turn it into liquid hydrogen or instantaneous grid supply, and liquid hydrogen solves the storage problem associated with random renewable electricity, it can do the job. Petrol and diesel are not particularly efficient but with technology improvements it is much better than it was 100 years ago and the same will apply to both hydrogen and electricity storage.
Adapted piston engines can run on hydrogen. Wouldn’t that be a better way to ‘reinvent the wheel’ ?
Yet another hydrogen is good article from someone professionally predisposed to like hydrogen.
Much like the IMechE who’s chief campaigner did a Phd in it.
The round trip efficiency quoted is selectively quoted to narrow the difference leaving out distribution & compression losses for hydrogen.
Hydrogen market for transportation will tend towards zero. The issues are the aforementioned round trip losses and the difficulty of storing and distribution of hydrogen Vs electricity which available everywhere already.
EVs have won cars, the EV models and production facilities already in the build/planning phase mean all new cars will be EVs before 2030.
Given that all light vehicles will be EVs, so will all road haulage, Tesla is releasing a 500 mile truck next year and even Nikola is planning to release a BEV truck first and then follow up with hydrogen at a later date or more probably never.
The issues with charging and battery degradation have mostly been solved in the last 5 years and the billions poured into battery research every year are solving the residual issues for EVs at scale commercially whereas hydrogen isn’t getting beyond pleading for government funding for pilots.
Sounds great until you look at where lime comes from. and the vast quantities of CO2 released in its production.
It’s really no contest (and if you don’t like my off-the-top-of-my-head figures substitute your own) :
Electricity to hydrogen via electrolysis ~80%; hydrogen to mechanical power (IC engine) ~30%: overall efficiency 24%
Electricity to hydrogen via electrolysis ~80%; hydrogen to mechanical power (fuel cell = £££) ~50%: overall efficiency 40%
Electricity to charge battery ~80%; electric motor to mechanical power ~90%: overall efficiency 72%
Not that small …
Assume a typical household heating demand of 12,000 kW-h per year
The CO2 generated by burning natural gas is 0.185 kg / kWh https://www.carbonindependent.org/15.html
Annual production 2,220 kg CO2
CO2 is 44 kg/kmol
Hydrated lime Ca(OH)2 is 72 kg/kmol
Calcium carbonate CaCO3 is 100 kg/kmol
Absorption reaction equation:
Ca(OH)2 + CO2 → CaCO3 + H2O
i.e. 2220*72/44 kg (3.6 tonnes) lime reagent consumed and 2220*100/44 kg (5 tonnes) calcium carbonate for disposal
From every sane, sensible scientific viewpoint, prevention is better than treating symptoms. i.e. Leave fossil hydrocarbons where they are – the sooner the better. We know how this can be done:-
The planet receives sufficient energy from the (Moon and) Sun to generate all the electric power we’ll ever need, using NO (fossil) fuel. We can retire nuclear fission and forget fusion. ALL thermal generation is last century tech. All we need to liberate the RE bonanza is energy storage. KISS.
As the American author H.L. Mencken said; “For every complex problem there is an answer that is clear, simple, and wrong.” Really? Then prove it!!! The “transition from 100% brown hydrogen to 100% green hydrogen” is where we need to focus all our scientific/economic attention. . .
https://www.riversimple.com/batteries-hydrogen-wrong-question/
“It’s time to put the batteries or hydrogen question to rest. The challenge now is to use both clean technologies appropriately so that we can cut carbon emissions as quickly as possible.”
[1] Well to Wheel (WtW) efficiency is the critical measure of energy consumption; it is broken down into two key stages, Well to Tank (WtT), covering extraction of energy, refinement and distribution to cars, and Tank to Wheel (TtW), covering fuel consumption in the car.
[2] This is true to a small degree for any vehicle – the longer the range, the more energy must be carried – but it is very acute for BEVs, as batteries are much heavier than petrol or hydrogen, including the tank, per unit of energy stored.
Battery charging has not been solved! This is a critical issue and closely linked to the implications for infrastructure to facilitate that charging. A typical fossil fuel pump can service a small to medium vehicle in around 5 minutes, and for a large one 10 to 15 minutes. In that time a car will take on around 600KWH of stored energy, a large lorry with 1000l tank wil take on 10MWH. Over the space of that 15 minutes that equates to 40MWh. Just for one pump! The local grid has to be capable of supporting that. It isn’t batteries or lack of EVs that constrains take up it is the stark practical reality of charging. Unless people limit themselves to using a vehicle range that can be completed in a round trip within reach of its home/base charger battery EVs are not a practicable universal replacement for IC engines. A car carries around half a tonne of batteries that give it less range than 100kg of a full fuel tank. Yes there are chemical and engineering issues with storing and trnsporting hydrogen but they can be resolved as they are simply a mechanical engineering problem. Battery technology is dependant on sophisticated chemical engineering which is a different type or problem. It is not possible to charge a battery at the equivalent rate of a liquid fuel pump. Battery EVs have their niche, but will never achieve the flexibility and adaptability of liquid fuels. Exhorting the public to buy battery cars will never achieve anything until the charging infrastructure has matured sufficiently to make them universally viable. What do you do with a tractor in the middle of a remote field with a flat motive battery, or several hundred vehicles stranded on a frozen motorway after hours of discharging? While the various theoretical arguments above are all correct, practicality has to be considered. We receive ample power from the sun. We need ways of collecting it in a usable and practical fashion and then facilitate making use of it. Theoretical efficiency arguments are in the context of which is best a waste of time and a diversion from what we really need to do. Store hydrogen and it can be used as a primary fuel source for about anything, can power our EVs via fuel cells or be burnt in an IC engine. It can be transported and produces when used no toxic waste. Instead of arguing for one or the other we need a mix of systems to suit specific market needs.
Thanks to Trevor for putting some fairly accurate numbers to my proposal for lime usage. It was just an idle thought given that we are heading for an exergy-wasteful future, but maybe it has some merit. A generation or so ago, we used to have coal-fires and produce substantial quantities of ash that were used for fillers and were far more awkward than adding to the flue of a gas fired boiler.
6 tonnes per year lime would be over about 30 weeks of heating season, so 200 kg/week of useful / regenerable material. I guess that the big question is would people prefer to pay for expensive fuel or suffer a little inconvenience?
I would note that Trevor has omitted a large factor in his case for batteries, the power is generated either at high cost using “renewables” (£140 / MWh at present) or at about £ 40/MWh using fossil fuels, however this is at about 40% efficiency; thus, the battery storage route’s real efficiency is about 28%
I’m beginning to think that CCS at source is the best answer for both domestic and car use, however it lacks the excitement of hydrogen.
Jack Broughton – I too am from the coal fire generation. I remember the ‘coal man’ bent almost double, lugging sacks of coal, a hundredweight at a time, from lorry to our coal bunker. As kids it was our chore to go out, come rain or snow, fill a bucket from the bunker and hand it to Dad to throw coal onto the fire. Coal ash generally went straight into the galvanised steel dustbin (a literal description) to be collected on the back of the ‘dustbin man’ – no wheelie bins or kerbside collection
Later on when we got our first gas fire I was amazed that a tiny copper pipe the thickness of a finger could displace all that backbreaking labour. Well – maybe we will have to go back to something similar, but it seems regressive to me
It beggars belief that anybody, let alone ‘engineers’, would even be discussing coal, oil or gas in the 21st century, especially when truly green replacements can be 100% home-grown and owned.
@ Jack: You know that “£140/MWh at present” is untrue for most renewables, whereas £92.50 is a well established fact for nuclear power, and still not yet delivered. Using that for electrolysis would be uneconomic, but CCS would be worse still. and it’s totally unproductive.
“Engineering issues with hydrogen can be resolved.” Likewise, battery-charging logistics can be easily resolved through design. Legislation to mandate that new BEVs conform to one standard of demountable battery pack. Service stations can gradually convert from FF to battery swap and/or hydrogen refuel – simples. Political ideology, driven by vested interests, stymies progress.
“Just like a conventional power plant, a fusion power plant uses heat to produce steam and then electricity by way of turbines and generators.” Electricity generation using steam turbines wastes 65% of all prime energy as heat. The wrong R&I – how dumb can we be?
The right R&I, for harvesting RE, would easily facilitate novel energy storage engineering.
“Prof. Mazzucato will discuss why economic theory needs to rethink the role of policy, away from fixing market failures, towards actively co-creating markets to DELIVER outcomes for the public GOOD.” R&I that is primarily for the public good (infrastructure) reduces an incumbent’s profit margins, so it won’t attract investment, and government policy only ‘lures’ the private sector into investing in projects (a state-backed Hinkley Point C!) with revenue (CfD) guarantees.
“When Softbank bought the firm for £24bn soon after the referendum to leave the EU in 2016, it was hailed by the government as a vote of confidence in a post-Brexit Britain.” – A prime example of the self-deluding ideology that destroys the economic health and wealth of the UK!
http://www.bbc.co.uk/news/technology-53637463
But where does this lime come from?
Most of it is made from cacination of limestone or chalk, heating the mineral to red heat and driving off the carbon and some of the oxygen. You dig up 100 tons of rock to get 56 tons of lime releasing 44 tons of CO2 – and that’s ignoring any CO2 released from the energy needed to get your mineral up to red heat.
Unless you can come up with a carbon-free way of deriving lime from somewhere other than limestone/chalk/crushed seashells, using lime to capture CO2 is a non-starter.
Reply to Steve Boyd. My lime suggestion was originally just a conversation-piece. However, when one looks at the idea that batteries and hydrogen could become the future maybe it is not so daft.
The lime has to be manufactured thermally and CO2 would be released at high concentrations where it can be captured and stored . However, I have no idea as to the economics of this concept and it remains at the back-of-envelope stage. It seems unlikely that it would be any less cost effective than hydrogen and battery storage!
Replying to Jack Broughton – if the energy is truly carbon-free then some waste isn’t an issue. It will all have derived from sunlight and will all finish up warming the planet whether by direct sunlight or by being diverted for our use by solar or wind power. I worry about CO2 storage. People are freaked out by storage of nuclear waste which, by and large, is solid and needs storing for hundreds or thousands of years until it is safe. CO2 is a gas and needs to be stored for all eternity to be safe. Which of those two problems is the easier to solve?
Batteries do not address sea level rise. Electrolytic H2 and O production and use from desalinated seawater can help to usefully sequester/manage ocean water. Ocean renewable energy provides the electrons. Oxygen can be pumped down to revigorate dead zones.
Exactly what #riversimple preach –
http://www.riversimple.com/batteries-hydrogen-wrong-question/
Demonising one over another leads to market confusion and polarised debate just as we see average emissions from new vehicles rise due to demonisation of diesel since #vwgate 2015.
We need multiple solutions including improving existing fleets whilst H2Ev adn BEVs improve. One way is #HVO instead of fossil diesel which is also a potential JetA1 replacement. Higher MPG, much lower NOx, PMs and all other emissions for all ;legacy and current generation CI existing engines. See Helsinki buses and NESTE
A short reply to David Smart on electricity prices. Current CfDs are costed at average £ 162.1 / MWh for offshore winds. There are as yet unfounded claims that in the future this will fall, but this is what it costs. To put this into context, offshore wind generated 31.9 TWh at a subsidy of £ 3,588 m. last year. When the wholesale price for this would have been about £ 1200m. Biomass subsidies are even more ludicrous at £1,650m last year for no true reduction in CO2!
The cost of renewables subsidies to the UK is about £ 10b / year, for no measurable reduction in CO2; this money could be much better used.
Hi
No doubt we need both hydrogen and batteries. A point though: the hydrogen generation efficiency could be improved be positioning it close to needs of central heating off homes. The heat is energy we need in many regions, and also result in CO2.
Taking this argument further why not produce
Methane or even methanol. Less energy efficient seen from a simple viewpoint, but if heat is reused?
Methane and methanole is much easier handled, stored and used.
Regarding cost of electricity; already we see peaks, where the RE cannot be used. This will increase, and electrolysis might be the answer.
NO ‘unfounded claims’ Jack. It’s very ‘old’ news of known facts:-
“That price is 30% lower than the lowest strike price seen in the second CfD auction in 2017, when projects came forward at £57.50/MWh.”
http://www.current-news.co.uk/news/offshore-wind-smashes-price-records-in-third-cfd-auction-round
Onshore wind and solar PV were excluded from the last two rounds as “mature technologies”; i.e. not ‘nascent’ enough to warrant the inherent support of a government-backed contract.
The truth is; privatisation and private equity claim the right to profit off national infrastructure investment. Blame politicians, not the technology per se. e.g. The price of ‘mature’ nuclear:-
“If the building of Sizewell C were financed in the way that transmission lines are financed – the terms of the regulated asset base (RAB) deal from which Scottish and Southern Electricity benefits – then Sizewell C would cost consumers somewhere around GBP40/MWh.”
http://www.world-nuclear-news.org/Articles/Speech-Cutting-costs-with-the-fleet-approach
Sci-fi can be more realistic than today’s political reality! From: “The Day The Earth Stood Still.”
Professor Karl Barnhardt, a Nobel Prize-winning physicist who specialises in the evolutionary basis of altruism: “You must have some technology that could solve our problem.”
Klaatu: “Your problem is not technology. The problem is you. You lack the will to change.”
It’s an entirely political decision to force the consumer to pay for new infrastructure.
Why the assumption that hydrogen is used in a fuel cell, the pollution caused by the production of batteries is horrendous and only a fraction of it can be recycled, by comparison, a petrol engine can be modified to run on hydrogen and cost mothing like the pollution emitted by battery production.
With a standard IC engine you know it can be very efficiently recycled and reused, and all without shipping tonnes of waste to third world countries.
To reply to David Smart: it is true that low prices have been offered for future projects on as yet unstarted projects. None of the existing wing farms are “earning” less than £ 120/MWh. The future projects are backing the fact that power prices are linked to energy prices and will rise substantially before the projects proceed. The main inflationary factor which will guarantee these “financial-engineers” large returns is the entirely arbitrary carbon tax that penalises sensible generation in the name of political dogma and ensures the ridiculous rate of price rise of electricity will continue. The poorest people pay most for this profligacy unfortunately to satisfy the “chattering classes”.