Ulf Bossel put the cat among the pigeons a while ago, by suggesting that the establishment of a Hydrogen Economy is a non-starter, compared with simply using the electrons directly that would be employed to split water into its constituent elements, oxygen and hydrogen. The European Cell Forum, which is committed to the creation of a future based on sustainable and safe sources of energy, has decided to carry on its promotion of fuel cells for sustainably produced fuels, but that it will no longer support the development of fuel cells that require "hypothetical" supplies of fuel such as hydrogen.
This may appear odd, since we hear about hydrogen all the time and to the degree that it is easy to think that when the oil "runs-out" hydrogen will simply be tapped into as a substitute for it. The problem is that hydrogen does not occur free in nature but must be freed from other elements, such as oxygen in water, with which it is naturally combined, and the separation of elements requires other forms of energy. Almost all the hydrogen used currently in the world - as a chemical feedstock e.g. for oil refining and making artificial fertilizers - is made by steam-reforming natural gas, and there is a CO2 budget that must be costed-in, hence hydrogen from this source is not clean but contributes to CO2 emissions. Furthermore, it consumes natural gas, and so there is a pressure placed on another resource in accord with the indisputable fact that it takes resources to extract resources. Ideally therefore, that hydrogen should be produced by e.g. water electrolysis using electricity made from renewable sources.
However, Bossel's argument is that the electrons produced from e.g. wind, hydro, wave or whatever sources could be used directly say to charge batteries or to make hydrocarbon fuels, even methanol, as George Olah is promulgating, at an efficiency of about three times that which would be obtained by converting them into hydrogen and processing and distributing the material to "burn" it in fuel cells. Bossel's argument goes along the lines that there are energy losses incurred at each step in the necessary chain of actions, in accord with the incontrovertible Second Law of Thermodynamics - basically, entropy.
He points-out that there are three principal loss-makers in the chain, namely production, storage and distribution. There is obviously a loss of 50 - 60% incurred when the material is burned in the fuel cell, but in its favour is the fact that an efficiency of even 40 - 50% is substantially above the Carnot-cycle limit (Thermodynamics again) of around 35% for a typical internal combustion engine. The losses may be summarised as follows: 90% efficiency for rectifying alternating current to DC to run the electrolyzer; 75% overall efficiency (ideal) for the electrolyzer itself; and then the storage of the bulky hydrogen gas either as a highly compressed gas, which takes about 20% of the energy content of the hydrogen to compress it (or as a cryogenic liquid, which takes 30 - 40% to produce); 10% for distribution and say 50% efficiency for the fuel cell itself, which amounts to about a 25% efficiency overall.
There are electrolyzer units that can produce high pressure hydrogen and if each gas-station were to make its own hydrogen by electrolysis, much of the distribution losses (probably 30%) might be recovered. A report has been published by a firm of independent analysts in Germany which is critical of some of Bossel's figures especially in regard to storage and transmission, particularly across large distances say from sunny north Africa (if the hydrogen were produced using PV technology which would be much more efficient there) by pipeline to Europe. However, an in-situ arrangement as I allude to would surely get around that, presuming we could make enough renewable electricity, or if there were a grid of electrons (rather than of hydrogen) including north African PV, European wind-power, North Sea wave energy and so on, such power might be supplied to run local electrolysis equipment, which would avoid actual hydrogen transmission. But if Bossel is right, why not use these electrons in a more direct manner?
On a tit-for tat basis, we can make the following calculation:
The heat of combustion of hydrogen is -285 kJ/mol, and so 1 kg of hydrogen = 1000 g/2 g/mol x -285 kJ= -142,500 kJ = 1.425 x 10^8 J.
We get through 82 million tonnes of oil altogether annually in the UK and we use 60 million tonnes of that for fuel. The energy content of oil is rated at 42 GJ/tonne and so that 60 million tonnes "contains" 60 x 10^6 x 42 x 10^9 Joules = 2.52 x 10^18 J of energy.
Hydrogen can be produced at a pressure of up to 10,000 psi by electrolysis at a rate of 60.5 kW/kg of H2. Hence the equivalent H2 to match that amount of oil is:
2.52 x 10^18 J/1.425 x 10^8 J/kg = 1.768 x 10^10 kg H2. Bossel has used the conversion factor of 1.5, i.e. that H2 can be used with 1.5 times the recoverable energy efficiency of gasoline. Since gasoline gives an approximately 14% well-to-wheel efficiency that would make about 21% overall for hydrogen, which seems a bit low and I would think that say 59% for the electrolysis system x 90% for rectification x 50% for the fuel cell = 26.6% is more like it.
However, let's consider the generating capacity the whole enterprise would need. To make 1.768 x 10^10 kg of H2 over a year, i.e. 8760 hours, would require:
1.768 x 10^10 kg x 60.5 x 10^3 (W/kg H2)/8760 = 122.1 GW. But this figure is mitigated according to the efficiency with which hydrogen may be used. If Bossel is right, this becomes 81.4 GW or let's call it a factor of two (which seems more reasonable), making it 61.0 GW.
Either way, we would need a colossal installation of renewables, e.g. 2 MW wind-turbines, with a rated capacity of 2 MW - but an actual output of say 30% if placed offshore, which amounts to 0.6 MW per unit. Hence we would need 61 GW/0.6 MW = 100,000 of them. Probably these could be accommodated in the North Sea in a square of turbines 316 x 316 and at an average spacing of 0.5 km we are talking about an area of 160 km^2, which doesn't sound too bad, albeit that the weather in the North Sea is some of the roughest in the world, and so maintenance might prove a problem.
As an alternative, around 60 new nuclear reactors could be installed to make the electricity for hydrogen, and on top of the new generation required to replace the decommissioned current 31 reactors, actually equal in output to about 14 1 GW reactors, and so it would be necessary to quadruple this capacity by which means to install a "Hydrogen Economy" in the UK. I have been told that hydrogen could be made more efficiently using the thermal power from a nuclear reactor to run the iodine-sulphur cycle, rather than by electrolyzing water (50% compared to 35%) , but the installation capacity needed remains huge. If Bossel is right and electrons can be used with three times the efficiency than will be recovered (hydrogen actually re-generates electrons in the fuel cell, to turn wheels, in a chemically-fuelled electric car) by turning them into hydrogen, the installation capacity immediately falls to 20 new nuclear power stations, or about 33,000 turbines, which is still enormous but appears more achievable.
I am not ruling out hydrogen altogether but simply making the point that when oil supplies begin to wane, it is not a simple matter of switching from oil to hydrogen, but a new and vast infrastructure must be implemented first, to both produce and use hydrogen. The question looms: is it worth it, or might there not be better ways to deal with our impending transportation problems, such as relocalising society to use less transport? Even those who are profound advocates of the "Hydrogen Economy" need to address the problem that the PEM (Proton Exchange Membrane) cell relies on an electrode consisting partly of platinum (about 50 - 100 g worth), which is a metal so rare than only 150 tonnes of new platinum are produced each year, and well below the current and growing demand for it.
Admittedly, the 40% of world platinum that is presently put into catalytic converters could be fabricated into PEM cells, were the putative conversion from oil-power to H2-power to be made, but this is only sufficient to put around:
150 tonnes x 1000 kg/tonne x 1000 g/kg x 0.4/50 g/cell = 1.2 million new "vehicles" on the road each year, out of a world total of about 700 million. Hence in 15 years we could replace just 3% of the current number. Thus, unless more platinum is recovered on a huge scale (from sources as yet unknown to geology), or some alternative fuel cell technology is brought to a commercial level of development on some similarly immediate timescale, the enterprise looks set to fall at the last fence, in this, the last race that humankind will ever have to place bets on.
(2) NREL National Renewable Energy Technology Laboratory, "Technology Brief: Analysis of Current-Day Commercial Electrolyzers."
(3) Ulf Bossel, Proceedings of the IEEE, Vol. 94, 2006, 1826.
(4) W.Weindorf, U.Buenger and J.Schindler, LBST, "Comments on the paper by Eliasson and Bossel 'The Future of the Hydrogen economy: Bright or Bleak. July 2003. www.efec.com/reports