The (questionable) benefits of wind energy

I first read in Private Eye, over Christmas, that national grid balancing data are available on the internet, detailing the demand for electricity at any given time, and how it is being met by the different sources of supply. The Eye article was mainly about the poor showing of Britain's wind farms during the cold spell in December. I read it, then forgot about it, then couldn't find it. Google to the rescue - and I was soon led to a gold-mine of information provided by the incomparable Bill O' the Wisp, a Dorset based Neanderthaler with a keen interest in wind power (among other topics) - not to mention his keen intellect! This is his blog:

http://billothewisp.blogspot.com/

Here is his picture:



He has many posts on the push for wind-turbines, all worth reading. For now I want to draw your attention to this one (dated 9/1/11):

http://billothewisp.blogspot.com/2011/01/wind-power-damning-results.html

One of the highlights is this figure:

Figure 1

illustrating the power supplied by the UK wind-sector (or half of it, to be precise - not sure why) during 3 months from 3rd October 2010 to 3rd January 2011. The raw data give the figure in MW for each half-hour period during those 3 months. The x-axis of the graph is time, measured in units of half an hour (48 of those per day, 1440 odd per month, 4320 per quarter). The y-axis is the power in megawatts (MW)produced by about half of the installed wind-turbines in the UK, with a nominal rating of 2430MW (the other half isn't included in the data, unfortunately).

The raw average output is 608MW, equating to 25% of the nominal rating.

This is the figure that is much used by the turbine camp. 'We admit, the wind doesn't blow all the time at optimum strength. But on average, the turbine will produce 30% of its rated output.' Well, it was actually 25%, nationwide, during these 3 months - but let's not quibble about that.

Far more important is the extreme unevenness of the output. As Billothewisp puts it: 'Half the 3 months' energy arrived in less than 25% of the time leaving the other half to cover the remaining 75% of the period'. At times, as some of us already knew, the covering was extremely thin. For example, during the 21st December, the maximum output was 78MW (most of the time during that day it was considerably less), equating to 3% of the rated output.

Now, while bearing the output graph in mind, consider this statement from the Financial Times on 20/1/11:

'Capacity [of the wind sector] is set to increase from 5GW to 37GW during the next decade.'

(ref - best way to see it: put hull 37 gigawatt into google)

- that is, by a factor of more than 7. What will the output from this army of turbines look like? There are some who insist that the combination of large numbers of turbines will somehow smooth the output curve. But consider this: there are already thousands of turbines, dispersed through the UK contributing to Figure 1 above. If it were true that 'the wind is always blowing somewhere', those violent ups and downs would simply not be there. But they are.

Maybe some of the coming turbines will be spread more widely over the North Sea. Maybe that will improve the output graph. Maybe the ups and downs won't actually be 7 times as large as they are at present. Maybe they'll only be 5 times as large. But essentially we'll have a source of power whose output oscillates between say 30GW and 2GW on a permanent basis.

Links with other parts of the world could improve the situation. At present we can exchange 2 GW with France,and there is a link with Ireland (not much used during these three months).

A means of storing electrical energy could help to smooth the graph. As the BWEA website helpfully suggests, the National Grid can already cope with the famous 'TV pickup' when almost every Brit turns on his electric kettle at the end of Eastenders. This is a surge of demand of some 2.4 MB lasting for about 5 minutes. It can be managed by 'throwing water at it' i.e. by switching on the reversible hydroelectric plants in Wales and Scotland.

But when 10GW is missing for 2 or 3 days (because the wind has dropped)? There certainly won't be enough water to throw at that one.

The trouble seems to be this: just as wind energy becomes big enough to eat significantly into our carbon output, it becomes seriously unmanageable. The National Grid spokespeople seem to think they can cope with what is coming, but one always wonders, Have they just been told to say that everything's in hand, that there's nothing to worry about?

Imagine for a moment you're controlling the grid in ten years time. You have this giant resource of wind power, nominally rated at 37GW; but what is it really worth to you? How do you rate its contribution to the electricity supply? What point between 2GW (output on a calm day) and 37GW do you pick? Suppose you say, well, we all know the wind is somewhat intermittent, let's pick the level that we know the wind sector can deliver 75% of the time (by then our mindset has changed so that we don't always expect electricity to come down the pipe when we flick the switch). Another one of Billothewisp's graphs shows us what level this will be:

Figure 2

What Bill O' the Wisp has done here: he's taken the 4400 half-hour periods and arranged them in order accorrding to the wind-power output during each half-hour, with the less productive periods on the left, and the more productive periods on the right. Looking above the middle half-hour period (in this arrangement), we see that the power was about 500MW.

This implies that half the time, the power was more than 500MW, half the time it was less (a statistician would call this the 'median' power production). So an output of 500MW could only be guaranteed 50% of the time. To obtain 75% certainty one would have to move to the left, and to a power level of about 250MW. (For 90% certainty the level would be about 100MW; but let's stick with 75% certainty for now.) Now 250MW is about 10% of the nominal rating. Extrapolating to the situation in 10 years time, the 'guaranteed' level of output would be 3.7GW.

That much could be 'relied on' (75% of the time).

But quite often the output would jump up to 25GW, sometimes even to 30GW. That's a hell of a lot of surplus power to lose. There seems little doubt that the cheapest way to lose it (possibly even in terms of carbon emissions - but that's another story) would be to turn the majority of the wind-turbines off. Fortunately, this seems to be a strong point of wind-turbines, that they are easy to turn off (by altering the pitch of the blades - I think). The only snag - that you (the end-user) have to keep paying the wind-turbine owner an exorbitant price for the electricity that is not being generated.

It may be that in the fullness of time, we will learn how to make use of these great surges of power, coming at times set not by us but by the gods of the weather. Until that time comes, it would seem (for the reasons given above) that a realistic estimate of the productive capacity of a wind-turbine might be 10% (or less) of its nominal rated capacity - rather than the 30% quoted at present by the promoters of wind-schemes.

Am I missing some basic facts here? If so, I would be glad to be told what they are. Meanwhile, if you want to look at the raw data, this is the place to start:

http://www.bmreports.com/bsp/bsp_home.htm, scroll down to 'Generation by fuel type (graph)', click on the button just below the graph, labelled Current/Historic; on the page that comes up, click on one or the other red buttons at top right 'Historic Data XML' or 'Historic data CSV'. These will download for you the 3-months raw data in either XML or CSV format. The latter sort can be opened in Excel. Good luck!