USANews版 - Wind power: Even worse than you thought |
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发帖数: 29846 | 1 But your 'leccy bill will keep going up to buy more of it
By Lewis Page
Posted in Environment, 7th April 2011 09:36 GMT
A new analysis of wind energy supplied to the UK National Grid in recent
years has shown that wind farms produce significantly less electricity than
had been thought, and that they cause more problems for the Grid than had
been believed.
The report (28-page PDF/944 KB) was commissioned by conservation charity the
John Muir Trust and carried out by consulting engineer Stuart Young. It
measured electricity actually metered as being delivered to the National
Grid.
In general it tends to be assumed that a wind farm will generate an average
of 30 per cent of its maximum capacity over time. However the new study
shows that this is actually untrue, with the turbines measured by the Grid
turning in performances which were significantly worse:
Average output from wind was 27.18% of metered capacity in 2009, 21.14%
in 2010, and 24.08% between November 2008 and December 2010 inclusive.
In general, then, one should assume that a wind farm will generate no more
than 25 per cent of maximum capacity over time (and indeed this seems set to
get worse as new super-large turbines come into service). Even over a year
this will be up or down by a few per cent, making planning more difficult.
It gets worse, too, as wind power frequently drops to almost nothing. It
tends to do this quite often just when demand is at its early-evening peak:
At each of the four highest peak demands of 2010 wind output was low
being respectively 4.72%, 5.51%, 2.59% and 2.51% of capacity at peak demand.
And unfortunately the average capacity over time is pulled up significantly
by brief windy periods. Wind output is actually below 20 per cent of maximum
most of the time; it is below 10 per cent fully one-third of the time. Wind
power needs a lot of thermal backup running most of the time to keep the
lights on, but it also needs that backup to go away rapidly whenever the
wind blows hard, or it won't deliver even 25 per cent of capacity.
Quite often windy periods come when demand is low, as in the middle of the
night. Wind power nonetheless forces its way onto the grid, as wind-farm
operators make most of their money not from selling electricity but from
selling the renewables obligation certificates (ROCs) which they obtain for
putting power onto the grid. Companies supplying power to end users in the
UK must obtain a certain amount of ROCs by law or pay a "buy-out" fine: as a
result ROCs can be sold for money to end-use suppliers.
Thus when wind farmers have a lot of power they will actually pay to get it
onto the grid if necessary in order to obtain the lucrative ROCs which
provide most of their revenue, forcing all non-renewable providers out of
the market. If the wind is blowing hard and demand is low, there may
nonetheless be just too much wind electricity for the grid to use, and this
may happen quite often:
The incidence of high wind and low demand can occur at any time of year.
As connected wind capacity increases there will come a point when no more
thermal plant can be constrained off to accommodate wind power. In the
illustrated 30GW connected wind capacity model [as planned for by the UK
government at the moment] this scenario occurs 78 times, or three times a
month on average. This indicates the requirement for a major reassessment of
how much wind capacity can be tolerated by the Grid. |
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