Saturday, December 17, 2011

The Scientific Alliance: The Limits to Renewable Energy

"<Although the report>  focuses on the UK,  the essential messages are relevant anywhere.

Our main conclusion is that wind power (which is the only technology which could be deployed on a large enough scale to have a chance of meeting the UK government’s ambitious targets) cannot fulfil the expectations which policymakers have for it. The primary objective of the present UK and EU energy policy is to reduce fossil fuel use, and hence also carbon dioxide emissions.... The challenge is immense.

In principle, the use of ‘free’ wind energy is a good idea, but in practice it can deliver less than we might think. The primary problem with wind, as with other renewable energy sources, is that it is intermittent. Although windy and calm days can be forecast reasonably reliably, the wind rarely blows steadily. Since wind turbine output follows a cube law, a doubling of wind speed leads to an eight-fold increase in electricity output (and vice versa). Even when these variations are smoothed out across large arrays of turbines and wind farms spread across wide areas, the power delivered to the grid varies considerably over short timescales.

To an extent, the electricity grid can cope with that, although the problem gets more difficult as penetration of renewables increases. However, there are periods when the wind hardly blows, and each year we experience some of these at times of high demand, particularly in winter evenings. The worst situation is to have a stable area of high pressure over the country. In winter, this leads to calm, very cold conditions, while in summer it is equally calm, but very hot. In the UK, peak demand comes in winter but, in countries further south, there will also be increased demand for air-conditioning during summer heat waves. In both cases, power would have to come from sources other than wind.

The opposite problem can also occur. If the wind is blowing too strongly (above about 50mph), turbines must be shut down to avoid damage. This is exactly what happened last week in Scotland and northern England. According to a Sunday Times report (Storm shutdown is blow to future of wind turbines), wind farm output on Thursday 8 December fell from 2GW to 708MW between 9am and noon."

Unless consumers are prepared to tolerate an intermittent supply of electricity, fossil fuel generating plant – largely relatively inefficient open-cycle gas turbines – has to be left idling in order to ramp up its output quickly and balance the grid. The result is that wind farms save less fossil fuel overall than their output would suggest. Experience from Ireland, which already has a higher proportion of wind energy capacity than the UK, shows that installing new capacity produces diminishing returns in terms of fuel savings; beyond a certain point, erecting more wind turbines saves no more gas or coal and merely adds cost and insecurity to the system.

But despite the additional costs and inefficiencies which wind energy brings, there are moves afoot to install still more.

Full article at

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