Thursday, 16 June 2011

Save the world - with 2.5 million wind turbines

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The Intergovernmental Panel on Climate Change’s Working Group III specialises in mitigation of climate change. On 9th May, they made a startling announcement.

Abu Dhabi, 9 May 2011 – Close to 80 percent of the world‘s energy supply could be met by renewables by mid-century if backed by the right enabling public policies a new report shows.”

From the press release

The report on which this assertion is based was recently released, and considers 164 scenarios (of development of renewables, changes in energy use, etc). The relevant chapter can be found here.

The headline-grabbing figure was derived from a scenario in an article by Teske et al. in Energy Efficiency (2011) 4:409433. Energy [R]evolution 2010—a sustainable world energy outlook.

The Climate Auditor, Steve McIntyre, noticed that the lead author of the important article, a Greenpeace activist, was also involved in writing the IPCC’s report, calling into question their neutrality.

I was interested to know where the figure of “close to 80 percent” came from. Well, as you might expect, a large chunk of the energy comes from wind.

Now, based on Teske et al’s table 7 (p.422), they reckon wind (on- and off-shore) will have an installed generating capacity of 3754 GW by 2050. The number for 2008 was 120.3 GW, and this has of course increased since then.

The generating capacity in 2008 had a potential energy production of 1055 TWh and generated 219 TWh, for a capacity factor of about 21%. The modelled generating capacity in 2050 would have the potential to generate nearly 33,000 TWh if it could generate at nameplate level. If the present capacity factor was maintained, this would actually generate 6,800 TWh, or 24.6 EJ per year, which on their own figures would be <1/6th of demand. They assume that 39 EJ will be generated at a capacity factor of about 33%, and cover c.25% of total demand.

I was interested to know how many turbines these figures represented. A common nameplate capacity onshore is 1.5 MW, and most capacity is presently onshore (I think the scenario here assumes greater use of offshore, which has a higher capacity factor). Anyway, the 2008 capacity of 120.3 GW would therefore mean we had c. 80,000 turbines in 2008 (I don’t know how accurate this is). The 3754 GW in the 2050 prediction would, at the same nameplate capacity per turbine, require c. 2,500,000 turbines.

At a typical spacing of 10 turbines per hectare, that would require 2500km-sq of land, or a square 50 km on a side, which doesn’t sound too traumatic.

There are other questions to be asked about this article – about the contributions of solar power and biomass burning, for example... and the smart grid necessary for distributing the electricity. The big question is, though: how realistic is this scenario? Is it more like a fantasy?