From: Eur Ing Irvine Bell BSc CEng MIMechE CDipAF PGCE
irvine_bell@msn.com
A member of the Electric Bus Group[ www.tbus.org.uk/ ].
I refer to the Daily Telegraph, Saturday 10th February 2001, Motoring Supplement pages 1 and 5, article entitled "The Balance of Power" by Charles Clover and Andrew English, concerning the possibilities of running cars [and other vehicles] on hydrogen.
The main theme of the article seems to be that the future of cars will be to run on hydrogen obtained from renewable energy resources such as wind or hydroelectricity or from hydrogen 'grown' in places like the current oil producing states in the Middle East.
Unfortunately this scenario ignores a fundamental energy efficiency problem. It takes about four units of energy e.g. from hydroelectric or wind power, to produce about one unit of deliverable e.g. compressed hydrogen. A vehicle fuel cell is around 50% efficient which means it takes around eight units of energy to produce one useful unit of energy to propel a vehicle, if hydrogen is used as the means of 'transmitting' the energy to the vehicle. Compare this with a ratio of more like one to one if the energy is transmitted directly to the vehicle, as with for example a tram or a trolleybus.
The article mentioned the possibility of [liquid] hydrogen 'eventually' being produced for as little as 60p a litre - which is around ten times the price before tax of petrol or derv. Either Chancellors of the Exchequer are going to have to give up most of their current massive tax take on vehicle fuel, or each of us will have to take out a mortgage each time we fill up our cars with hydrogen!
Since clearly we are going to have to grow fuels in the future, instead of 'growing' hydrogen in the Middle East or wherever, the question really should be what fuels should we grow and how and where, and how should we then burn them? My money would be more on growing vegetable oils [or alcohol fuels] to run compression ignition engined / electric hybrids as these seem to be more efficient i.e. burn less fuel than vehicles with conventional transmissions.
Ideally perhaps, the energy would be transmitted with minimum losses directly to the vehicles by some sort of conductor system. Currently, this is only practicable for electric trolleybuses but maybe something could be devised of more general applicability?
Irvine Bell
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Think of a liquid hydrogen fueled car in a collision! Most unsafe if the tank goes up. The safest fuel is diesel as it takes much more energy to react with oxygen than does petrol or methanol. I doubt the fuel will run out - it is more likely we will run out of room on the roads!
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That is all very true. However the idea is that it is a renewable fuel source obtained from a renewable source of energy. Does it really matter if we actually make use of some of the energy incident on this planet (i.e. solar) or of the wind/hydro energy? It will all end up going back into the system eventually. If you remember your science energy can not be created or destroyed. You can only change the form the energy is in.
I am quite for Hydrogen powered cars. And all I can say is **** the government if they want to place a large "environmental" tax on hydrogen fuels! Seeing as the only by-product of hydrogen combustion is water (unless of course you manage to start nuclear fusion, in which case you're dead anyway...!) I think nobody could complain of the environmental impact of it.
Yes, they could be rather deadly in a collision (as demonstrated well by the early air balloons). But if the containers were designed well (or even better, people learnt to drive much more carefully, myself included) there hopefully shouldn't be a problem. LPG seems to manage to quite well.
Anyway, they're quite a few years off so it'll be interesting to see how the technology progresses.
Oh, unfortunately energy isn't delivered at a ratio of 1:1 to electric vehicles such as trams. To produce the electricity in the first place the power stations are only about 40% efficient so that ratio is more like 5:2. Still better than the ratio for hydrogen powered vehicles admittedly. But not perfect in any way.
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The main issue here is one of sustainability, and an inevitable move away from finite fossil fuels. The proposal to move to a 'hydrogen economy' using renewable energy to extract hydrogen from sea water does hold out the hope of achieving that goal, whilst removing the questions that exist about fossil fuel emissions.
Hydrogen, like any fuel, will require energy to be expended in getting it from source to vehicle. With coal and oil energy is expended in extraction, processing and transport to the point of use eg the vehicle. It's totally misleading to concentrate on the transmission system alone and say that electricity reaches the vehicles without loss (and it's untrue anyway, as transmission lines are not loss free).
The efficiency of electricity generation varies between 35 - 40% in a conventional power station to 55% in a new CCGT, and a further few percentage points are lost in transmission. Given that the efficiency of a conventional internal combustion engine is around 30 - 35%, there's no huge benefit on efficiency grounds in generating electricity and using it in vehicles, and certainly not by batteries. Battery powered vehicles are barely worth considering given that energy recovery from the battery charge/discharge cycle is well below 100% (that is, you can only recover a proportion of the energy used to charge the batteries). This produces further loss from the electricity used for recharging, and there is also self-discharge of the battery pack when the vehicle is not used. Environmentally, therefore, there is no good reason to use batteries. The arguments for battery vehicles only stack up at present because of inequalities on tax rates for petrol and household electricity.
The other big snag with batteries is their inability to 'refuel' at any acceptable rate. The energy transfer rate when a tank is filled with petrol is staggering, and is unlikely to be matched by a battery charge rate.
It's always been considered that hydrogen powered vehicles would only be environmentally acceptable if the hydrogen was produced by using renewable sources of energy. If the infrastructure for the fuel is established, then it will be transported as any other conventional fuel is today. As for estimates of fuel cost, surely it's far to early to speculate, and any governments taxation policies are impossible to guess a year in advance, never mind the timescales we are discussing here. Renewable energy (especially photovoltaic) is typically currently more expensive than fossil fuels, but surely has a long way to fall. In suitable areas, wind power is now comparable in cost to conventional electricity. As we've seen so often, development and mass production will have a significant effect on these issues. Also, as reserves dwindle and become more expensive to extract, increasing fossil fuel prices are inevitable, narrowing the gap with the cost of hydrogen fuel. It's intriguing that the current Middle East oil producers are in an ideal position to capitalise on this market - and they'll have oil revenue income with which to do it.
I don't think hydrogen is a big safety issue either. Hydrogen tanks will inevitably need to be built much stronger than petrol tanks. Every car is currently transporting safely a potential bomb in the shape of a large container part filled with flammable liquid and topped with explosive vapour, and it's not considered a big safety issue - plastic fuel tanks have even been used!
There is no question - the car manufacturers are right to be looking to hydrogen as the new fuel.
Regards
John
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Predictions that fuel reserves will run out, not enough food to feed the world, etc regularly get promoted. However even if the pumpable oil in the middle east runs out there is 10 times the oil in oil shales uneconomic to extract at present.
I like the idea of farmers growing the sunflower oil to power the new diesels. The farmers need a lifeline to keep them going. The balance of payments will improve so the government will be happy!
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