http://www.zerocarbonbritain.org/ says that Britain can eliminate emissions from fossil fuels in 20 years… by halving energy demand and installing massive renewable energy generation. This contradicts my memories of a talk by David MacKay which (I recall) said that no plausible amount of UK renewables could generate 50% (or even that much) of our energy.
Could someone check their and his numbers to save me the trouble, please?
Thursday: it would seem not :-). So I’ll make a start. Looking at the ZC stuff (p94) the vast bulk of the power is coming from offshore wind and wave. In fact the contribution from these is so huge (90% by eye at least) that the obvious conclusion from that is to not bother with anything else).
Wave: they assume 250 TW/y (“out of a technical potential of 600-750 TWh annually”). DMK (p58 ff) says 4 kWh/d as a max (this max assumes wave machines over 50% of the coastline at 50% efficiency), 2 more likely, and “I’d be amazed if waves ever contribute more
than 0.1 kWh/d per person.” Happily DMK has a nice conversion chart to save us the need for thinking, so we find that 250 TW/y maps to about 11 kWh/d, and 750 to about 33. So ZC’s estimates are about a factor of 10 higher than DMK’s optimistic ones, and 100 times his practical ones. Oops. ZC’s estimates are in turn sourced to http://www.bwea.com/marine/resource.html which are in turn rather vague about where theirs come from.
Friday: talking to DMK, he really doesn’t believe their estimates. Looking closer, the BWEA quotes the DTI for 50 TW, with no clear explanation of why this differs from 700. There is a possibility that they are doing an area-integral rather than a line integral. At any event, scaling up from essentially-zero to 250 looks very unreasonable.
Wot about the other 1/2? Offshore wind. They (fig 15.1 again) get ~40/month, ie about 450 TW/y. DMK gets 16 kWh/d, which is about 350 TWh/y, so thats in the right ballpark. But he says “I want to emphasize the audaciously large area that would be required to deliver this 16 kWh/d per person. If we take the total coastline of Britain (length: 3000 km), and put a strip of turbines 4 km wide all the way round, that strip would have an area of 13 000 km2. That is the area we must fill with turbines to deliver 16 kWh/d per person.” Thats shallow offshore (up to 25m). Deep offshore could get you more. The ZC stuff uses http://www.dti.gov.uk/files/file22791.pdf as its source, and while I can’t find their (very large) 3,212 TWh/y in that, there is a figure of 100 TWh/y at under £45/MWh, which seems about the right price range.
Conclusion: their wave numbers don’t add up, so they are short about half their power. The wind numbers might, but would require truely stupendous offshore wind farms. They are being deceptive by not pointing out clearly that (offshore) wind+wave is doing 90+% of their generation and the rest is window dressing.