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Renewable Energy

Blowing Hot and Cold

By 2nd January 2013 No Comments

The UK is the windiest country in Europe and generates more power from offshore wind than the rest of Europe combined.  On December 13th 2012 the last of 175 turbines was installed at the largest offshore wind farm in the world, the ‘London Array’ in the Thames estuary.  In the decade following the UK’s first offshore turbine this technology has grown to generate 1.5% of UK electricity.  The government has plans to increase this contribution to 8% by 2017 and 20% by 2020, making it central to achieving our carbon reduction targets.  This growth will require £50-£100 billion of investment.

In the next 10 years a quarter of our existing power stations will close as they reach the end of their useful life.  The 3,400 onshore wind turbines already in place have attracted considerable public outcry with several councils utilising planning laws to ban new turbines within 2km of homes.  This is currently the subject of a judicial review as, if replicated nationwide, it could render 99% of the UK unavailable to terrestrial turbines.

Offshore wind generation is therefore vital if the UK is to achieve its legal obligation to source 15% of our energy from renewable sources by 2020.  ‘RenewableUK’ contend that full utilisation of the 4% of our maritime exclusive economic zone already approved for offshore wind farms could produce 40% of our electricity requirements1.  Unfortunately, offshore wind is currently expensive at £160-£190 per Megawatt hour (‘MWh’) against £105 for coal, £100 for nuclear and £80 for gas.  DECC’s Renewable Energy Roadmap incorporates plans to reduce the cost of offshore wind energy to £100 per MWh by 2020.

The true output of a wind turbine is also subject to debate.  The ‘rated capacity’ of a wind turbine defines its maximum output in ideal conditions i.e. consistent, non-turbulent 30mph-50mph wind speeds.  Halving the wind speed below this minimum reduces power output by a factor of eight, and at sub-9mph wind speeds most large turbines cannot function.  As the wind speed rises again an on-board motor will actually consume power as it spins the blades to re-start.  Possibly a more realistic measure of output is the ‘capacity factor’, the percentage of rated capacity produced in real-world conditions at a given site.  First generation wind turbines typically produced capacity factors of 15%-30% but more recent examples achieve 40%.  However even this can be misleading – large rotors driving a small generator will deliver an impressive capacity factor at the expense of total annual output.

The variability of wind power (‘intermittency’) is also a factor.  The UK’s electrical consumption is independent of wind speed and therefore wind turbines require backup from non-wind sources when becalmed.  Maintaining duplicate power sources on permanent standby is expensive, wasteful, and rather defeats the purpose.  Other solutions include a pan-European supergrid on the basis that, at any given time, it will be windy somewhere.

In October 2012 John Hayes, a junior Tory minister, voiced the concerns of many Conservative voters by criticising the proliferation of onshore wind farms.  Although hastily contradicted by both his LibDem boss and David Cameron, renewable energy investors are highly sensitive to any indication that the government’s commitment is faltering.  The mixed messages continue – the government has announced 15 year ‘Contracts for Difference’ (‘CFDs’) to give investors guaranteed future electricity prices – yet postponed a decision to impose a decarbonisation target on electricity producers.

The waters have become even more muddied by the lure of cheap gas from ‘fracking’.  The exploitation of shale gas in the US has slashed prices whilst offering the promise of ‘energy security’.  Estimates as to the quantity of shale gas beneath the UK range from 2 years supply to 200 years supply, a tempting prospect as the UK currently imports 50% of its gas – 40% of UK electricity generation depends on it.  George Osborne recently announced plans to build 30 new gas power stations by 2030, his so-called “dash to gas”.  Hopefully this will be accompanied by substantial investment in gas storage (current facilities only hold 50 days supply).  More worrying to the green lobby is, without sizeable accompanying investment in carbon capture technology alongside these gas power stations, it seems unlikely that carbon reduction targets will be met.

1Offshore Wind Energy: A UK Success Story’ DTI publications  www.ukti.gov.uk

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