In a previous listing ("A Hydrogen Economy - Is it Economic?") I calculated that we would need around 720,000 land based wind turbines, rated at 0.5 MW capacity, or 180,000 sited offshore and rated at 2 MW, in order to generate sufficient hydrogen to substitute for the quantity of liquid petroleum fuel that is currently used for transportation in the U.K. To place these totals in context, as a further assessment of the feasibility of the enterprise, I will now calculate the physical dimensions of the required "wind farms" to accommodate these numbers of turbines. In making my original estimate, I deliberately used the raw data, without taking account of energy losses, which are always incurred when converting one form of energy to another; a consequence of the Second Law of Thermodynamics. The overall loss from electricity to hydrogen to wheel (or wing, since 22% of the budget is taken by the aviation industry), I estimate to be around 50%; assuming a 70% loss in the electrolysis step, and the same in "burning" hydrogen in fuel cells to power vehicles: i.e. 70% of 70% = 49%. This is also the conclusion of Ulf Bossel, the founder and organiser of the European Fuel Cell Forum, based in Switzerland. (His article "The Hydrogen Illusion" is most illuminating).
Therefore, I must revise my original numbers upwards by a factor of two, and hence we actually need to find room for 1,440,000 0.5 MW turbines on land, or 360,000 2 MW turbines on offshore sites. Now, wind turbines can't be simply stacked together side by side, back to back. This is because, in effect, each turbine obstructs the wind flow in reaching the one behind it, unless they are placed something like 0.3 to 0.5 kilometers apart, depending on the diameter of the turbine blade. Placed on land 0.5 km apart (the arithmetic becomes a bit more complex if some other distance is chosen), 1,440,000 0.5 MW turbines would occupy an area of 360,000 square kilometers. Since the entire land area of the U.K. mainland is only 244,000 square kilometers, we are already of course 50% short of anywhere to put them, even if we covered the entire country with wind turbines, which I doubt would be a popular option with estate agents and the tourism industry!
So, let us consider the alternative option of a potential "offshore investment". As a rough calculation of the coastal periphery of the U.K. mainland, I will take the straight line distance from north to south as 680 miles and that from east to west as 200 miles = 1760 miles in total = 2800 km. We now need only to accommodate 360,000 turbines each metered at 2 MW capacity, since they are offshore and hence out of sight (and hearing) and hence out of mind. A single band spaced 0.5 km apart would accommodate 5,600 turbines, and so a depth of them of 64 around the entire country would accommodate 360,000 turbines as we require it to, which equates to a thickness of 32 km. If we set the location of the wind farm at 5 km out to sea in order to avoid offending the locals (coast dwellers around the entire country) this would stretch over onto the French coast at the English Channel, the point of closest approach between the two countries, and would surely comprise a severe obstruction to shipping!
My point is that renewable energy is dispersed not concentrated, unlike, oil, coal, gas or uranium, and will therefore never replace these other fuels at our current rate of usage of them. We have to live differently (less energy intensively) if we are to survive.