Physical Insights

An independent scientist’s observations on society, technology, energy, science and the environment. “Modern science has been a voyage into the unknown, with a lesson in humility waiting at every stop. Many passengers would rather have stayed home.” – Carl Sagan

Wind turbines: Running some numbers.

with one comment

I recently came across the website of EcoTricity, a firm in the UK who are quite proud of a number of wind turbines they’re building. (Thanks to Atomic Insights for the tip on this story.)

If we look at some of their construction photos, we are reminded that in practice, every construction project of this sort involves vehicles powered by fossil fuels, raw materials such as concrete, Aluminium and steel, all produced using various energy inputs, many of which come from fossil fuels.

In fact, wind turbine energy is associated with whole-of-life-cycle greenhouse gas emissions of around 20g CO2 equivalent per kWh of electrical output – this is not zero, but like the other clean alternatives, it’s clearly far better than coal-fired electricity, for example, which is the most common and the most polluting electrical energy source, with a whole-of-life-cycle greenhouse gas emissions profile of about 1000g CO2-eq./kWh.

This latest turbine installation – the company’s biggest to date – was built in August this year, and consists of three massive turbines with a nameplate capacity of 2 MW a piece. We are told that this corresponds to 15 million units of actual generated capacity, but unfortunately, they seem to have neglected to tell us exactly what this unit is.

These 2MW nameplate turbines have a hub height of 78 m and a rotor diameter of 82 m.

It is claimed that this project will save the emissions of 15,408 tons of potentially dangerous CO2 annually. Sounds good.

However, if we assume that this wind energy can directly displace the same amount of coal-generated electricity, that these energy systems have whole-of-life-cycle emissions characteristics as I noted above, and assume that the wind turbines have a capacity factor of say 20%, then a simple calculation of the generating capacity required to displace that amount of GHG emissions seems to indicate that 6MW of installed capacity just isn’t enough, and that 9MW of capacity is actually required.

I’m not an expert on engineering wind energy, and finding the best site, and so forth, but I think a capacity factor reaching 30% – which is what they’d need to have, unless the coal capacity they’re displacing is really, really inefficient, would be extremely difficult to attain.

I wonder where the discrepancy arises?

To further put the scale of such a project in context, these three turbines, operating with say a 20% capacity factor, generate around 1.2MW of electricity – three thousand such turbines will generate 1.2 GW. This sort of power output can be achieved by one single modern nuclear power reactor, with a capacity factor of say 92%, with a nameplate capacity of 1.3 GW. Today’s nuclear generating plants, with two or more units on site, typically generate far in excess of that.

Written by Luke Weston

October 8, 2007 at 12:39 pm

One Response

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  1. Yeah, it seems we’re all coming to the same conclusion. There seems to be a lot of people out there who are just really bad at maths.

    Nuclear Australia

    October 8, 2007 at 1:08 pm

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