Are wind turbines efficient?

It is sometimes alleged that wind turbines are inefficient or that they ‘only work 30% of the time’.

These figures, based on the ‘load factor’ for onshore wind farms, are wrongly used to imply wind power is inefficient.

Load factor and efficiency are not the same: efficiency measures how well a plant produces power when it is running, not how much of the time it is working.

Wind farms generate electricity 80-85% of the time with an average output of around 30% of peak rated power.  This makes them just as efficient as nuclear, gas, oil and coal fired power stations.

Wind farms efficiently turn a free resource (wind) into large amounts of electricity at low capital cost.

The 30% figure is known as the “load factor” but often called efficiency. At 30% efficiency winds farms are just as good or better the traditional methods of electricity production. Many opponents of wind farms will say wind farms are inefficient but they forget to point out just how inefficient other forms of power generation are in the table below.

Load Factor Thermal Efficiency Overall “Efficiency”
Gas 47.8% 48.5% 23.0%
Coal 40.8% 35.7% 14.6%
Nuclear 66.4% 38.0% 25.2%

These figures come from the 2012 Digest of UK Energy Statistics (DUKES) published by Department of Energy and Climate Change.

Put simply it means that on average a coal fired power station in the UK (which is the most common form of power station in the UK) only produces electricity for 40.8% of the time (as opposed to 80% for a wind farm).

The nextcolumn show how efficient a coal fired power station is at turning fossil fuels into electricity.  In the UK our coal fired power stations are only 35.7% efficient.  This means that 64.4% of all the energy we put into a coal fired power station is wasted as heat.  Broadly this heat goes up the chimney or is released in the cooling towers.

The last column gives an indication of the overall efficiency of fossil fuelled power plants. As you can see it is not very good.

So wind farms are 30% efficient.  But a coal fired power plant only works 40.8% of the time and even then is wastes nearly two thirds of the energy used.  Nuclear and gas powered have the same problems.  They don’t work all the time; and when they do they are very inefficient.

Winds farms are modern and efficient. And they don’t need expensive, dirty and imported fossil fuel.

 

Intermittency of wind turbines: how to cope with calm days

There is no denying that wind power is an intermittent source of energy when focusing on isolated sites.  But does this matter?   The grid is already set up to cope with constantly changing demand; large unpredictable swings in the system are already balanced on a daily basis; and the grid is prone to critical failures (of large scale plant) for which significant reserve capability already exists.

The uncertainty of supply when considering wind means that it does require careful integration with the grid. But for the wind segment, which is highly distributed, any large scale reduction will be gradual.   Such incremental changes in supply are relatively easy for the grid to absorb.  Taking account of other initiatives taken to spread the load of the grid, there appears little need to expand overall generation reserve in response to increased wind capacity.

Whilst wind is intermittent, falling wind speeds can usually be predicted several days ahead.  This means back-up power can be brought on line as required and an “always-on” spinning reserve is not required. However spinning reserve is required for nuclear, coal and gas fuelled plants alike to deal with unexpected breakdowns.

If allocated to wind, the estimated cost of planned extra distribution infrastructure and maintaining spinning reserv

 

Can we just push all wind farms offshore?

It is argued that, because there is a superior wind resource off the coast of the United Kingdom, all efforts should go into offshore wind power where it is “less visible”, rather than onshore.

While offshore wind is forecast to be a major component of our future renewable capacity, it is in its early stages compared to onshore.  Both the capital cost and the ongoing operational and management costs of offshore wind are up to twice that of onshore. Despite the higher energy generation per MW installed, offshore wind will remain significantly more expensive than onshore.

Onshore wind is already cost competitive with conventional electricity generation without subsidies (see section 2) and will become overall the cheapest way to generate electricity by 2020. It will remain a crucial component of the UK’s renewable strategy.

Do wind farms produce more energy than is used in their construction?

Over its lifetime the average wind farm is expected to generate at least 20–25 times the energy required in its manufacture and installation: the average payback time in terms of energy is 3–6 months.

This figure takes account of manufacture of materials; transportation of the parts to the site; construction of turbines, cables and foundations; site operations over the life; and, finally, decommissioning the site at the end.

In comparison, coal-fired and nuclear power stations have an energy payback of eight and nine times respectively.

You can learn more by looking at the report “Common Concerns about Wind Farms” which has been produced by the Centre for Sustainable Energy (CSE), an independent national charity that gives advice and undertakes research and policy analysis. You can find a full copy of the report here.

If you want to read some of the orginal research these are useful sources;

1 Kubiszewski, I., Clevelan, C.J., Endres, P.K. (2010). Meta-analysis of net energy return for wind power systems. Renewable Energy, 35, pp.218-2252 Milborrow, D. (1998). Dispelling the Myths of Energy Payback Time. Wind Stats Newsletter, vol. 11, no. 2 (Spring 1998).3 Kubiszewski, I., Clevelan, C.J., Endres, P.K. (2010). Meta-analysis of net energy return for wind power systems. Renewable Energy, 35, pp.218-225, [Figure 6].4 Sustainable Development Commission, (2005). Wind Power in the UK. A guide to the key issues surrounding onshore wind power development in the UK. Available at: www.sd-commission.org.uk/publications/downloads/Wind_Energy-NovRev2005.pdf

One thought on “Wind Energy

  1. Personally I quite like the look of them and I wonder if people moaned as much about the building of the beautiful windmills of old that we now lovingly restoreand treasure? Recently I visited the only working windmill in Hampshire http://www.fatgirlslimblog.co.uk/?p=12371 I tooks lots of photos, it was quite lovely. What’s the difference, aesthetically? Surely we can’t afford to ignore the power of the wind.

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