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.
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In a cynical mood, I'd say no - only David MacKay actually *has* numbers..
[Um. I didn't read the ZC stuff - are you saying they don't actually bother justify their values? -W]
There's a fairly simple formula for environmental organisations doing studies to prove that Wind+Solar+Other renewables can run the economy:
(a) Assume large savings (~50 of all energy use) can easily be made. Put amy resulting lifestyle changes in the small print.
(b) Assume that the costs of renewables will come down dramatically and capacity for building renewables expands equally dramatically.
(c) Assume that renewables can be built out to near the technical resource possible without major problems.
(d) Gloss over problems of intermittancy by suggesting a large range of possible solutions without detailed examination of any of them.
(e) Pad the resulting document from 20 to 114 pages with repeated diagrams, unnessiuciary sections on climate change and over presentation, but print it on recycled paper to keep your green credentials.
(f) Bask in a glow of appreciation from people whose beliefs you have just confirmed.
I'm wondering whether burying one of these:
http://en.wikipedia.org/wiki/Radioisotope_thermoelectric_generator
under my house might do the trick. 4kw of heat and 300W of electricity from the best of them... 8kg of Pu-238 is going to be expensive though.
Ian: I am reminded of an old rumor that I heard in grad school where a hunter in Russia came across one of these from an old space program and thought the heat source was an ideal place to set up camp. He dies a few days later from radiation!
Best,
John
John - I reckon I'm well supplied with heat but the electrical output is a bit marginal. Thanks for the advice, I will take care with the shielding ;-)
David Mackay's book is rather interesting - very heavily referenced and supplying much useful information.
John: that rumour's repeated on the wiki article, but it's two hunters. The Russians used(d) Str-90 apparently, which requires more shielding than the Pu-238 according to that article.
There is also an implicit assumption that some sort of cheap, reliable energy storage system can be developed to smooth out the intermittent nature of wind power (wave being a tad less intermittent, though I believe it can still be affected by unusually calm days). The last thing we want is a period of calm causing blackouts. Shame energy storage is currently so expensive...
You're mixing units, you should have TWh/y, and not TW/y, otherwise it doesn't make sense.
4 km gets you about 10 3 megawatt turbines. They produce about third of the 3 megawatts on average so per year it's 260 GWh from a 4 km string. To reach 450 TWh you'd need less than 2000 of such strings or rows. Placing a perpendicular string (a row) every half kilometer, you'd need less than 1000 kilometers.
In a favourable reality you could have perhaps ten wind parks each with 160 5 megawatt mills meaning 0.3*160*5MW*8760h/y = 2 TWh/y per park and 20 TWh total. I don't know how reasonable my estimates are. It is possible that higher usage than 0.3 can be reached offshore in the atlantic. The cost of these plants is usually roughly around 1 million euros per megawatt.
Rats, forgot the 0.3 in my first calculation.
Yeah, you'd need in the order of 3000 km, filling up the coasts.