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Wind power: not always there when you need it

By Mark S. Lawson - posted Monday, 18 July 2011

The government's recent announcement on the carbon tax contained lots of information about how the government planned to encourage the use of renewable energy. However, the large amount of material produced for the announcement neglected some inconvenient truths about renewable, particularly wind energy system.

As is now becoming apparent, although wind energy may reduce carbon use in electricity grids (this point was previously unclear) they are strictly additions to the existing generators. Detailed figures from the wind farms spread over large areas are now available and preliminary analysis of the figures in both Australia and the UK show that no grid operator in their right mind would rely on wind for base load power.

The results clearly show that wind networks over large areas generate little or no energy for hours at a time. The networks may generate enough to take over from fossil fuel plants for varying periods, but grid operators will always have to plan to have enough capacity on hand to meet peak loads as if the wind farms did not exist at all. Spreading the wind towers over a large distance helps a little, but not enough to make a difference.


In other words, wind energy will not replace one bolt of one conventional power station, despite most attempts at costing this form of energy assuming that they will replace conventional plants….

One piece of evidence in this grim assessment is an analysis of the actual output of wind farms in the UK between November 2008 and December 2010 by Stuart Young Consulting. The report 'Analysis of UK Wind Power Generation' was paid for by a conservation body, the John Muir Trust. The trust's site doesn't say much about wind, but as its main focus is on preserving wild land and wild places, the report must be the result of concern about the effect of wind towers on the landscape.

The analysis found that on 124 separate occasions in the period, the output of wind farms taken onto the national grid fell below 20 megawatts – which is effectively nothing – from installed capacity of 1600 megawatts. Those nil power contributions lasted on average (note the word average) of just under five hours. Further, at each of the major power peaks during the year (such as half time during the FA cup, when everyone puts their kettle on), wind output was just a few per cent of installed capacity. In fact, although the average output of the various wind farms in the UK network was around 27 per cent for the study period, it was below 10 per cent capacity for more than one third of the time, and below 1.25 per cent for the equivalent of just under one day a month.

All this is different from more hopeful analyses conducted in previous years, but the report says "the nature of wind output has been obscured by reliance on 'average output' figures. Analysis of hard data from National Grid shows that wind behaves in a quite different manner from that suggested by study of average output derived from the Renewable Obligation Certificates (ROCs) record, or from wind speeds that are in themselves averaged." (The ROC reference is part of the UK method of tracking carbon reduction.) The report also notes that the existing UK pumped hydro capacity (hydroelectricity from dams) cannot possibly handle those blank periods.

Denmark, which uses wind extensively, routinely exports its excess wind generated electricity across the Baltic to Sweden and Norway, where it is used to pump water uphill into dams. The water can later be released as hydro electricity. The UK system does not have as many dams with hydro potential to hand, and Australia has very few.

The Australian electricity grids, and wind farms attached to it, are spread over a much larger area, so surely that can work to the advantage of wind farms? The problem is electricity can be transmitted only so far. A wind farm in Queensland cannot fill the gap if the wind in South Australia stops blowing. So then to have any real idea of the effectiveness of wind farms, as a first step we would need to know just how meteorology interacts with transmission distances.


Despite all the screaming and shouting about wind farms, very little work has been done on assessing this point. About the only piece of evidence, one way or another in this debate in Australia, of which I am aware, is a paper by weather analyst Andrew Miskelly and Tom Quirk, a former deputy chairman of VENCorp, which used to manage Victoria's transmission network. The paper, Wind Farming in South East Australia (Energy & Environment, 2010), looked at the generation figures for wind farms in South Australia and Victoria at five minute intervals for one month, June 2009. The figures are available for researchers from the website of the Australian Market Energy Operator (AMEO), which now operates the connected grids for Eastern and South Australia. The pair found that when the wind died, it did so right across the two states. Adding in wind from Tasmania helped a little, but not enough to make a difference.

The paper found that collective average output of the farms was about 30 per cent of installed capacity  (somewhat better than the UK experience) and, thanks to the spread of wind farms over two states, about 10 per cent of their capacity could be relied on for 90 per cent of the time. That's not bad for a bunch of wind farms, but it's still nowhere near good enough for a grid.

Electricity grids are run very conservatively and designed to cope with worst case scenarios. Grid managers cannot ignore the remaining 10 per cent of the time when the wind farms are producing nothing or very little, particularly if they do not know which 10 per cent. Nor can they brush aside the worst case involving wind generation – a hot, calm day – on the assurance that it does not happen all that often. They must plan for the worst, and have a generating reserve on top of that.

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About the Author

Mark Lawson is a senior journalist at the Australian Financial Review. He has written The Zen of Being Grumpy (Connor Court).

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