Monday, July 28, 2008

london's hydrogen buses

London was one of nine European cities to take part in the Clean Urban Transport for Europe (CUTE) trial of hydrogen fuel-cell buses.

Because the buses emit nothing but water vapour, they were called ‘zero emission’. This is seriously misleading, because whilst they have no exhaust gas except steam, they are responsible for an increase in carbon emissions.

The front page of CUTE's website declares ‘This public transport system will contribute to the reduction of overall CO2 emissions’(1). It will do nothing of the sort. I am no professional on these matters, but I have endeavoured to use credible, published sources for my figures, including damning ones from CUTE themselves.

The London trial showed fuel consumption of 23.9kg per 100km(2). That’s 4.2km/kg.

There are several ways to make the hydrogen required.

Hydrogen from natural gas

The cheapest and most common way of making hydrogen is from natural gas. This hydrogen is actually as much of a fossil fuel as diesel.

Manufacturing hydrogen from natural gas emits 9.1 kg CO2 per kg of hydrogen(3).

9,100g divided by 4.2 km = 2167g/km to make hydrogen gas from natural gas.

But it's not over, because at this stage all we've got is hydrogen gas. This has about one three-thousandth of the energy density of petrol. Assuming you're not going to have a fuel tank far bigger than the bus itself, you have to shrink it. It has to be either cooled to a liquid, or else it has to be compressed.

CUTE’s fuel cell buses used hydrogen compressed to a pressure of 350 bar(4), or 5,000psi.

It takes 2.6-3.6 kilowatt-hours of electricity to compress 1kg of hydrogen to 5,000psi(5). That electricity is made from a variety of sources, predominantly fossils. The UK grid CO2 emissions are 480g/kWh(6) .

2.6-3.6kWh x 480g/kWh = 1248g-1728g CO2 emissions per kg hydrogen compressed.

1248-1728g divided by 4.2km = 297-411g/km for compression.

This gives us an emissions total of 2167 + 297-411 = 2464-2578g/km for compressed hydrogen from natural gas.

A normal diesel bus emits around 640g/km(7). According to the US government's Argonne National Laboratory, exhaust emissions are only 78% of petrol's greenhouse gas emissions - 22% are emitted in the manufacturing process.

Assuming it's a similar figure for diesel as petrol, to be fair we should bump up that bus figure accordingly so that, as with the hydrogen, we're comparing total emissions for making and using the fuel.

That would make the emissions from a diesel bus - and this is the figure to keep bearing in mind - 821g/km.

CUTE’s own report on their trial says that when the hydrogen was made from natural gas, the buses had around two and a half times the climate impact of using normal diesel buses(8), which would make it around 1650g/km. This is somewhat different to the figures I’ve arrived at, but the thing that CUTE and I are both clear on is that the buses powered from hydrogen derived from fossil sources had a far worse climate impact than if they had been driving diesel buses.

CUTE hope that future efficiencies could save 25% of the fuel or more(9). Even if this were achieved it would be, even by their own figures, almost twice the CO2 emissions of a diesel bus.

The emissions for hydrogen from natural gas can only get worse with time. As we try to reduce our reliance on Russian gas, we have begun importing natural gas from the Middle East, liquefied so that it can be shipped. To be liquefied, gas must be cooled to –162 degrees and kept at or below that temperature for its entire journey, with the colossal energy consumption that implies. This means that emissions from using gas effectively increase.

Hydrogen from water using renewable electricity

Hydrogen needn’t be derived from fossil fuels. It can be made by electrolysis of water, using an electric current to split its hydrogen and oxygen components. CUTE say there was far less climate impact from the buses that used hydrogen made by electrolysis of water, using electricity from hydroelectric sources(10).

Firstly, I’m not sure if they’ve made the common error of assuming hydroelectricity is zero-emission. Hydroelectric dams are not the clean, green zero-emission sources they are often portrayed as. Submerged vegetation decays without oxygen, releasing methane, a greenhouse gas 25 times as potent as carbon dioxide(11). The amount released varies widely, from many times worse than burning coal to substantially less. At best it appears a dam gives one-tenth of the greenhouse effect of generating the same power thermally(12).

The World Commission on Dams – despite being paid by the largest funder of dams, the World Bank – said, ‘greenhouse gases are emitted for decades from all dam reservoirs in the boreal and tropical regions for which measurements have been made. This is in contrast to the widespread assumption that such emissions are zero. There is no justification for claiming that hydroelectricity does not contribute significantly to global warming.’(13)

But whether CUTE allowed for hydroelectricity’s climate impact or not is a side issue. The important thing is that there is still an enormous climate impact from making hydrogen from any sort of renewable electricity.

Our vehicles are currently powered by oil products. If we start making our vehicle fuel from electricity, we add to the total electricity demand. If the electricity we’re getting from renewables is taken for hydrogen production, it means the shortfall would have to be made up by more fossil electricity being generated elsewhere.

It’s rather like the way a biofuel company can proudly claim not to be cutting down forest for their plantations, yet their use of farmland displaces food production creating a knock-on effect and because of this someone somewhere is having to cut down a forest to grow food.

It could only stop having such a displacement effect if the whole grid were powered by renewables with enough spare capacity to start powering our vehicles. That would be a hell of lot of spare capacity; electrolysis is tremendously energy intensive. To replace our vehicle fuels with electrolysis hydrogen would take more than our entire present electricity consumption(14).

Do we think we can double electricity generation whilst doing away with fossil burning? Or should we stop considering hydrogen as a vehicle fuel?

Hydrogen from water using national grid electricity

As the vehicle fuel is creating additional demand for electricity and thereby displacing consumption, we should look at the emissions as if it were made from grid electricity.

A CUTE report says that it takes 5.1kWh of electricity to produce 1Nm3 of hydrogen(15), which weighs 0.09kg. This means that it takes just over 56kWh to make 1kg. (This is higher than I thought; I’ve seen 39kWh reliably quoted(16)). The UK grid CO2 emissions are 480g/kWh(17).

480g x 56kWh = 26,880g/CO2 per kg hydrogen.

26,880g divided by 4.2 km = 6400g/km to make the hydrogen gas from electrolysis.

That’s eight times the emissions from a normal bus.

(If we go with that 39kWh figure, it’s 4457g/km - still way above hydrogen from natural gas, let alone diesel, let alone any actual carbon savings).

CUTE did their own maths and calculated that grid electrolysis generates 4.71 times the emissions of a diesel bus(18), making it somewhere around 3,900g/km. There are several possible reasons for the discrepancy. Perhaps my figures aren’t reliable, perhaps theirs aren’t, perhaps the figure they have for grid emissions aren’t the same as the UK’s.

But despite there being a difference in precise figures, once again the principle is the same - the hydrogen bus is undoubtedly many times worse than the diesel models it is portrayed as being cleaner than.

The only scenario for sourcing in which CUTE don’t agree with this on is in their ‘hydrogen from renewable electricity’ example which, as I’ve already explained, ignores that fact of adding to electricity demand and so causing the same amount of electricity to be added to the grid.

If we aren’t going to use fossil-derived hydrogen but are only going to make it from electricity then the hydrogen is effectively just a way to store electricity. We take power from the grid, convert it to hydrogen, then on board the bus it’s used to make an electric charge to drive a motor. The hydrogen is effectively just a battery. That being so, surely there are more efficient and lower-carbon batteries available.

This would suggest that electric buses might well be worth looking in to. I know very little about these, although I have come across a report saying ‘fuel cell vehicles that operate on hydrogen made with electrolysis consume four times as much electricity per mile as similarly-sized battery electric vehicles’(19).

That claim comes from an avowed electric vehicle advocate, but still, it suggests that serious investigation of electric vehicles is merited. If we agree with CUTE’s figure of electrolysis hydrogen being 4.71 times worse than a diesel bus, then a system that uses a quarter of the electricity would be roughly comparable to a diesel bus.

This isn’t an immediate improvement in carbon terms, but at least it’s not significantly worse, whilst still delivering the localised air quality improvements of ‘zero-emission’ vehicles. Also, a slight increase in the amount of renewable electricity feeding into the grid would make such a bus lower carbon than diesel, whereas we’ll be waiting a long time for that to be true of electrolysis hydrogen.

Additionally, many of the problems of hydrogen as a vehicle fuel – lack of drive range, the need for specialised refuelling staff, etc – that the CUTE trial surmounted also apply to electric vehicles but would be solved by CUTE’s approach.

Impacts of making the technology

The average operating time for a bus in the CUTE trial was 2,300 hours(20). I understand that this is nearing the limits of a fuel cell’s life. The industry wants to get fuel cells up to around 4,000 hours of use, but seems to be struggling to get far beyond 2,000 hours(21). So, as well as the great expense of manufacturing the buses – both financially and environmentally (they have twice the impact of making a diesel bus(22)) – there is the cost and environmental impact of frequently replacing the fuel cells.

The London bus operated for an average of 7.952 hours a day(23). To keep the maths simple, let’s call that eight hours. Let’s say it only runs five days a week. Let’s also assume that the fuel cells meet the industry aim of 4,000 hours of life. Forty hours a week means a hundred weeks. So, even with these very generous assumptions, that’s less than two years of service.

Again, I’m ignorant of matters concerning electric buses, but I imagine they’d last longer than a year or two before needing inevitable major work doing on them.

Liquid hydrogen as a combustion fuel

The forthcoming second London hydrogen bus trial is not only to use fuel cells, but also buses run on liquid hydrogen as a combustion fuel. This is probably the least efficient and highest carbon fuel you could find.

If they're going to go down the same route as BMW - and it seems the only way to have enough drive-range with such an inefficient use of fuel - then compressed hydrogen doesn't contain enough energy and it will be liquefied. Not only do liquid combustion vehicles use more hydrogen than fuel cells, but the liquefaction process is incredibly energy intensive.

To be liquefied, hydrogen must be cooled to minus 253 degrees centigrade. It takes 12.5-15kWh of electricity to liquefy 1kg of hydrogen(24).

12.5-15 x 480g/kWh = 6-7.2kg CO2 emissions per kg hydrogen.

Let’s be generous and assume the bus will achieve the same consumption figures as its fuel cell cousin, 4.2km/kg.

6-7.2 divided by 4.2 = 1429-1714g/km for liquefaction.

So, even if the hydrogen itself were made of thin air and utterly carbon-free, a bus using liquid hydrogen is responsible for nearly three times the emissions of a diesel bus simply for the liquefaction process.

I note that, incredibly, the hydrogen used in London’s part of the CUTE trial had been liquefied and then returned to its gaseous state(25). This was a massive waste of energy and a serious contribution to climate change.

Add the liquefaction to the emissions from manufacturing hydrogen and we get this;

2167 + 1429-1714 = 3596-3881g/km for liquid hydrogen from natural gas.
6400 + 1429-1714 = 7829-8114g/km for liquid hydrogen from national grid electrolysis.

The actual amount of hydrogen consumed is even greater that that, though. Keeping hydrogen at minus 253 degrees between manufacture and dispensing is very energy intensive, and the figures above don’t include anything for that.

When it’s on a small vehicle there isn’t an energy source that can do that sort of refrigeration, so it’s in a highly insulated tank. This cannot stop it warming, only reduce the rate. As the hydrogen warms it returns to gas, increasing pressure in the tank. To avoid explosion there is a valve, rather like the one on petrol tanks to prevent explosion if you’ve left your car parked in blazing sunshine.

The problem is, liquid hydrogen regards anywhere above minus 253 degrees as blazing sunshine. It would continuously be jettisoning this high-carbon fuel. A report on BMW’s liquid hydrogen car found it ‘begins to boil after 17 hours if the car remains parked. The tank empties completely after 10 to 12 days’(26).

The EU’s encouragement

The CUTE Project is co-financed by the EU, and is so integral to the EU’s transport vision that the European Commission’s Director General for Energy and Transport, Matthias Ruente, wrote a glowing preface to one of the major reports on the outcomes of the trial.

He criticises oil-based fuels ‘that provoke climate change’ yet – at the front of a report proving the opposite - he tells us hydrogen is ‘at the heart of a zero emissions transport system that would de-couple mobility from climate change’. This, he qualifies, is once we’ve overcome the ‘challenge’ of producing hydrogen ‘with minimal or no negative environmental impact’(27).

I would reiterate that I am not a professional in researching this subject, but nonetheless from all the figures I can find, including those from CUTE, it seems to me beyond doubt that hydrogen buses lead to a massive increase in carbon emissions. To instigate a switch to hydrogen in the hope that an as yet unthought-of method of making it with minimal environmental impact will turn up soon is an act of grossly irresponsible blind faith. If what we’re proposing doesn’t improve on what we’ve got, it’s not a solution in any sense of the word.

It is surely absurd that, in the same project that grasps the nettle and legislates to reduce carbon emissions from cars, the European Commission is also pushing for an increase in vehicle emissions by promoting hydrogen(28).

The lesson is clear

A bus that is responsible for many times the carbon emissions of a diesel bus clearly has no part in any sustainable or responsible policy. This would have been clear about hydrogen before the CUTE trial, but is now proven by it. As these data show that it vastly increases carbon emissions, the forthcoming London trial of hydrogen buses should be cancelled. How can it make sense for the EU to fine car manufacturers for not decreasing emissions whilst paying bus operators to increase them?

Repeatedly portraying hydrogen buses as environmentally beneficial - the bus trials are referred to as one of Transport for London’s ‘key environmental achievements’(29) - is a fraud. Even if you were to dismiss me and my figures as a load of nonsense and judge the CUTE trial solely by its own published results, you would surely reach the same conclusion.




2- CUTE A Hydrogen Fuel Cell Bus Project in Europe 2001-2006: Vision, Teamwork and Technology. Detailed Summary of Achievements, May 2006, figure 3.3.8, p67

3- IPCC Special Report on Carbon Dioxide Capture and Storage, Cambridge University Press, 2005, p 13

4- CUTE, Project No.NNE5-2000-00113 Deliverable No.8 Final Report, 30 May 2006, p55, Table 5.1.

5- Raymond Drnevich of major American hydrogen supplier Praxair, Hydrogen Delivery: Liquefaction & Compression, Strategic Initiatives for Hydrogen Delivery Workshop, US Department of Energy Office of Energy Efficiency, May 2003, p14

6- DBERR, Fuel Mix Disclosure Data Table, 2006-07, table 3.

7- National Atmospheric Emission Inventory, Vehicle Speed Emission Factors (Version 02/3). These are the figures used by government, as cited by transport minister David Jamieson in a parliamentary answer, 8 July 2004.

8- CUTE, Project No.NNE5-2000-00113 Deliverable No.8 Final Report, 30 May 2006, p60, Fig 5-17.

9- CUTE, Project No.NNE5-2000-00113 Deliverable No.8 Final Report, 30 May 2006, p58.

10- CUTE, Project No.NNE5-2000-00113 Deliverable No.8 Final Report, 30 May 2006, p60, Fig 5-17.

11- IPCC figure: Changes in Atmospheric Constituents and in Radiative Forcing, Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, p.212, Table 2.14

12- Dams And Development, p75, World Commission on Dams, November 2000

13- Raising a Stink, New Scientist issue 2241, 3 June 2000
(paywalled: reproduced in full on World Commission on Dams’ site

14- Decarbonising the UK – Energy for a Climate Conscious Future, Tyndall Centre for Climate Change Research, 2005, p74

15- CUTE, A Hydrogen Fuel Cell Bus Project in Europe 2001-2006: Vision, Teamwork and Technology. Detailed Summary of Achievements, May 2006, p.24

16- Wind Energy and Production of Hydrogen and Electricity — Opportunities for Renewable Hydrogen, US National Renewable Energy Laboratory, March 2006, p2

17- DBERR, op cit

18- CUTE, Project No.NNE5-2000-00113 Deliverable No.8 Final Report, 30 May 2006, p60, Fig 5-17.

19- Alec Brooks, CARB's Fuel Cell Detour on the Road to Zero Emission Vehicles, Electric Vehicle World, 7 May 2004

20- CUTE, Project No.NNE5-2000-00113 Deliverable No.8 Final Report, 30 May 2006, p57.

21- Dr Sukhvinder Badwal, Fuel cells, Science on the way to the hydrogen economy, Australian Academy of Science, 5 May 2006

22- CUTE, Project No.NNE5-2000-00113 Deliverable No.8 Final Report, 30 May 2006, p61.

23- CUTE, A Hydrogen Fuel Cell Bus Project in Europe 2001-2006: Vision, Teamwork and Technology. Detailed Summary of Achievements, May 2006, figure 3.3.9, p67

24- Drnevich, op cit, p8

25- CUTE, Project No.NNE5-2000-00113 Deliverable No.8 Final Report, 30 May 2006, p40.

26- Bruce Gain, Road Testing BMW's Hydrogen 7, Wired, 13 Nov 2006

27- CUTE, A Hydrogen Fuel Cell Bus Project in Europe 2001-2006: Vision, Teamwork and Technology. Detailed Summary of Achievements, May 2006, p.3-7

28- European Commission, Competitive Automotive Regulatory Framework for the 21st Century, 7 Feb 2007

29- Transport for London is helping the Capital to tackle climate change, TfL press release, 13 March 2008


Owen said...

For the avoidance of doubt, can you confirm whether or not the standard diesel bus figures include the effect of getting the diesel into a usable state? As far as I can see, you are comparing two different things: running costs for diesel vs running and production costs for hydrogen.

This may not make much, or any, difference to the conclusion, but I'd prefer to know that rather than assume it.

merrick said...

Owen, you're right. What a glaring omission.

As is probably clear, I'm no scientist and have no expertise in this area. However, I can't find anyone who's publishing a g/km comparison. Worse, there's a ton of stuff from industry and news media saying hydrogen is 'zero-emission'.

So I'm trying to get reliable numbers and do a back-of-an-envelope sum to at least give us a rough idea.

I'll look into refining emissions and post again here.

Given that CUTE and others concede that there's a greater climate impact from most methods of making hydrogen, I suspect it'll change the numbers but not the conclusion.

The thing they all point to is the 'but we can make it by electrolysis from renewable electricity' thing.

The Tyndall Centre's figure is utterly damning on that.

What renewables we have are better off displacing coal-fired power stations.

And given the remarkable inefficiency of hydrogen as a way to store electricity, even if the grid were magically instantly 100% renewable, I can't think of any reason to make vehicle-hydrogen that isn't a stronger reason to make battery vehicles.

merrick said...

Owen, I asked a friend who knows about oil resources who said

The trouble is, energy accounting within the energy industry is a dark art, akin to voodoo I sometimes think. And often for good reason... the number of variables involved can often be unmanageable.

For instance, there can be a big energy expenditure involved in extracting the stuff from wells and transporting it to the refinery. With some wells (especially off-shore wells, or those employing enhanced-recovery techniques like gas injection) this energy might be quite large. With others, like some of the 'gushers' in the gulf, the stuff damn near pumps itself straight to the refinery.

So even before you fire up the oil refinery, you've got a potentially massive proportional variation in emissions.

All numbers on this stuff, even the sexy official stuff, can only ever be rough comparisons. But that'll do me in preference to no answer at all.

Argonne National Laboratory is a US government Department of Energy project. They've done a lot of stuff on full cycle 'well to wheels' calculations for energy use and greenhouse gas emissions of various technologies.

I've also turned up stuff from the EU's Institute of Environment and Sustainability. At first glance, their figures don't seem to match Argonne's. I'll do a big print-off and see what's what.

But in the meantime, the answer to our question is in the graph on page 3 of this Argonne PDF. It says that 78% of gasoline emissions are pump-to-wheels and 22% well-to-pump. I've assumed those from diesel will be the same and amended the maths in the above post accordingly.

Thankyou for pointing that out. With these bits of pencil-chewing, it's often a team process to make it come clear. I'm glad to have any errors of fact or reasoning flagged up, it brings us closer to the truth.

Owen said...

Thanks for the clarification.

I was pleased that your references and the transparency of your workings let me spot the incongruity in the first place.

punkscience said...

Just posted a comment and a link to your headheritage article on this: