Friday, August 5, 2016

More on nuclear versus renewables

My last posting was about the late Professor Sir David MacKay's opinion that the UK could not manage on renewable energy alone and that if we had enough nuclear and carbon capture and storage to get us through the winter (when solar power is very weak) we would have enough for the rest of the year and renewables would be superfluous. After that posting, I looked at the contrary view offered by the Centre for Alternative Technology in their 2013 publication Zero Carbon Britain (ZCB).

ZCB envisages heavy reliance on offshore wind but with 17% of the UK's land area given over to energy production - some of it through on-shore wind but a substantial amount through growing biomass such as miscanthus (elephant grass) and coppiced willow and poplar. Surplus renewable energy from wind etc. in the summer months would be used to produce hydrogen from water by hydrolysis. The hydrogen would be combined, using the Sabatier reaction, with CO2 from burning biomass (eg in conventional power stations or combined heat and power plants) to yield methane, which would be used as fuel in the winter, particularly for gas-fired electricity generation. The gas-fired generators would be switched off for most of the year and used only when there was insufficient renewable energy available, such as on windless days. If the sums add up, and I would guess that they do, this would appear to answer MacKay's point about the difficulty of getting through the winter on renewables.

The land taken up for energy crops would not be available for food production. Most agricultural land in the UK is currently used for grazing livestock and half of the the arable land is used for growing animal feed. At present we produce about 60% of our own food. To allow us to be self-sufficient in food, with land available for energy crops, ZCB assumes that we adopt a predominantly (but not totally) vegan diet. Furthermore, our overall energy use is assumed to decline by 60% through improved energy efficiency and behaviour change. It envisages, for instance, that flying would have to reduce to a third of its present level.

ZCB does not pretend to take into account financial or political constraints. Perhaps the economic cost is no greater than for a nuclear-based strategy - that's something I need to do more work on. However the political difficulties look more formidable, particularly given the massive assumed reduction in meat and dairy consumption.  MacKay, on the other hand, takes a view on what he regards as politically feasible and this leads him to the conclusion that we can't do without nuclear energy. To over-simplify things, perhaps if want to carry on eating meat we need to go nuclear so we don't have to sacrifice precious grazing land for energy crops. It's actually more complicated than that because ZCB also assumes that we become largely self-sufficient in food.

Given MacKay's premises on political feasibility, I can't fault his conclusions. I hope his premises are wrong but I fear they may be right. I don't object in principle to nuclear energy but in my heart I much prefer the idea of renewables. Unfortunately, my head isn't yet in full agreement with my heart.

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