October 15, 2004

The Arithmetic of Renewable Energy

A recent paper has calculated how much new generating capacity would be required to convert the U.K.'s transport sector -- responsible for a third of the country's energy use -- to hydrogen manufactured from non-carbon fuel sources. Their conclusion is startling: 100,000 wind towers or 100 nuclear plants.

The wind towers if sited off shore would completely encircle the country in a 10-km-deep band. On shore, they would require a land area larger than that of Wales.

Their calculations assume the use of 3-MW turbines and a capacity factor of 50%. In fact, 30% is a generous figure for the capacity factor (it is what the British and American Wind Energy Associations use), and on-shore turbines are typically 1-1.5 MW in size, in rare cases approaching 2 MW. Larger turbines would be intolerable in most locations.

Further, they calculate from a density of 12 MW rated capacity per square kilometer, which is the figure from a pro-wind study prepared for Greenpeace. The giant installation proposed for the western Scottish island of Lewis has a density of 5 MW/km2, and the huge facility proposed between Cape Cod and Nantucket island in the U.S. has a density of 6.7 MW/km2.

So, roughly, we need to double these authors' conclusions to account for more realistic performance, double them again on shore for more typical turbine size, and double once more for actual installation density: over 800,000 towers, covering fully 80% of the land in the U.K., or 400,000 off-shore towers completely encircling the country in a band 36 km deep.

(The original paper, by Andrew Oswald, Professor of Economics, University of Warwick, and Jim Oswald, Energy Consultant, Coventry, is available as a 20-KB PDF by clicking the title of this post.)