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Wind power reliability

by Dave Elliott

Earlier this year (26/6/13) Daily Telegraph columnist Geoffrey Lean said that ‘it has become an article of popular faith that building wind farms also involves constructing fossil-fuelled power stations for back‑up when the weather is calm. As a result, some opponents go on to say, wind turbines do little or nothing to cut carbon dioxide emissions’.  But he reported that the National Grid says that, although between April 2011 and September 2012 wind produced some 23,700 gigawatt hours of electricity, only 22GWh of power from fossil fuels was needed to fill the gaps when the wind didn’t blow- under 0.1%. Moreover this standby burning of fossil fuels only reduced the emission saving from having wind on the grid by 0.081%. He commented ‘not surprisingly, given these figures, no new fossil‑fuel power station has been built to provide back‑up for wind farms, and none is in prospect’.

Sadly it’s a bit more complicated than that. As Gizzmag noted, this is just the extra power needed  when the wind was less than expected  i.e. due to poor wind forecasting, and that will, it’s true, be small.  But it pointed out that, depending on demand levels, the fossil plants will also have to be run whenever  there is no or little wind. However whether the emissions they produce then should be subtracted from the savings from having wind on the grid is a moot point. These fossil plants would have run anyway- wind just reduces their total running time. That still also means we would not need any extra/new fossil plants, regardless of how much wind was on the grid. We already have them, enough to meet peak demand, although some may need replacing over time and we would need more if demand rose.

Some say though, that since statistically, there will usually be some wind input to the grid  at all times, we could actually shut some fossil plants down, maybe 20% of them, and still cope. That’s debatable. There may be times when then is no wind at all across the UK. But in terms of balancing, this may only matter if we assume a basically unchanged supply and demand system. If we move to one in which there is a range of renewable supplies, some storage, interactive demand side management and supergrid imports, then there may be no need for much fossil backup. Indeed the Pugwash 2050 High Renewables study found that, given the development of smart grids and supergrid links for imports, its 80% renewables mix did not need any fossil backup from peaking plant, even when UK wind etc was very low for 5 days.

However, the UK is a long way off from having a system like this.For example, the UK lags behind most other EU states in failing to commit in law to priority access for green electricity to the national grid, according to a review of progress on the EU’s 2009 Renewables Directive.  While a majority of EU members, including Germany, Italy, Spain and Poland have all enacted laws explicitly prioritising access for renewables over fossil and nuclear generated power, the UK, along with Bulgaria, Croatia, Sweden and France, are among 12 yet to send a similar legislative signal of intent.  The Coalition’s Electricity Market Reform bill does nothing to remedy this. Instead, currently effort is being expended on a campaign to get the EU to allow nuclear to be exempted from the EU state aid rules governing subsidies.

Ofgem instituted a ‘Connect & Manage’ system in 2009 to accelerate lower cost links for new utility-scale suppliers. However, as Alban Thurston has noted in a Projekt Sonnenschein briefing paper, ‘connection’, a single event of specifying, building and commissioning a link to the national grid, is not the same as ‘dispatch’. He says that, so far, no statement in UK energy law mandates priority access for, or dispatch of, green electricity.

That’s not to say the need for better grid links and grid balancing are not clear, and as renewables expand, the UK government and power companies are making some adjustments. However some may seem, at first glance, a little provocative and short term.   ‘Thousands of dirty diesel generators are being secretly prepared all over Britain to provide emergency back-up to prevent the National Grid collapsing when wind power fails’. So said the Daily Mail on July 14th, adding that ‘the scheme is expected to cost £1billion a year by 2015, adding five per cent to energy bills’.  Though they did admit that diesel is cleaner than coal and say that this is part of the Short Term Operational Reserve, or STOR, which aims to be able to ‘generate a reserve capacity of eight gigawatts (GW) by 2020, the equivalent of about five nuclear plants’.

Well they got that bit more or less right, but rather missed the point that we have to have back-up whatever supply system we use, and that, if more is needed, rather than building new plants to run occasionally, it’s clever to make use of the standby plants that already exists, often off grid, in various institutions, including hospitals. There is about 20GW worth scattered around the UK, some of which could be grid linked and most of which would benefit from running more often than their occasional annual test runs. But under the current proposals, only about 2.4 GW of diesel sets are to be included in STOR, costing perhaps £90m/p.a by 2025 (not £1bn by 2015), though the market for the full 8GW STOR, with many other types of backup, might reach  £565-£945m p.a by then.

Using plants like this can be seen as part of the wider ‘smart grid’ idea, which is actually far from new- for example a range of standby gas plants as well as pumped hydro plants, already offer balancing services to meet demand peaks or supply shortfalls. As Alastair Martin from Flexitricity noted in a paper on Demand side electricity grid management at the recent Global Energy System Conference in Edinburgh ( on one occasion in 2009, when a nuclear plant failed at peak demand  time, the STOR system fired up and within 5 minutes filled the gap until demand fell an hour or so later. Smaller dropouts, can lead to a brief fall in mains frequency, but, as he also shows, this can be rectified within seconds using STOR. However, as these examples illustrate, STOR is mainly for backing up fossil and nuclear, rather than wind, with, in any case, diesel units only playing a small role, and then only briefly:,-despite-critics%E2%80%99-claims

STOR is, as its name suggests, for short time balancing, and, for that, in addition to existing gas plants and pumped hydro, demand side management can increasingly be  used- delaying demand peaks. For longer-term shortfalls (e.g. long wind lulls), we would also have to call on more of the existing range of plants- that’s why we have a strategic reserve, a plant margin. Some worry that, with some plants closing, what we have will not be enough. Interestingly however there is currently around 4GW of gas plants mothballed:  So if we did need more, it’s there. But then as the Pugwash study found, longer term, with multiple renewables, smart/supergrid links and some storage, we might not need it for balancing wind.

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