POWER March 2013 - 66

EMISSIONS
total investment needed to achieve environmental
goals, particularly in the UK and Europe.
A December 2012 report, published by the
UK-based Renewable Energy Foundation and
written by Gordon Hughes of the University
of Edinburgh, scrutinized wind farm lifecycle
emission benefits. The foundation in the past
has criticized the UK government's Renewables
Obligation policy, saying the subsidy distorts
markets as well as the generation mix.
The Hughes study examined wind farm
performance in the UK and Denmark and concluded
that, after allowing for variations in wind
speed and site characteristics, the average load
factor of wind farms declines as they age, probably
due to wear and tear. By 10 years of age,
the contribution of an average UK wind farm
to meeting electricity demand was said to have
fallen by as much as one-third.
The report said this performance decline
means that it is " rarely economic to operate
wind farms for more than 12 to 15 years. "
Investors who expect a return on their investment
over 20 to 25 years will be " disappointed, "
the report said. What's more,
policymakers who expected wind farms built
before 2010 to contribute toward CO2
targets
in 2020 or later should allow for the possibility
that the total investment required to meet
those targets will be much larger than previous
forecasts suggested.
The study based its findings on data reflectContent
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ing the monthly output of wind farms in the
UK and Denmark. Normalized age-performance
curves were estimated using statistical
techniques that allowed for differences between
sites and over time in wind resources,
and other factors. The normalized load factor
for UK onshore wind farms was found to decline
from a peak of about 24% at age one to
15% at age 10 and 11% at age 15. The decline
in the normalized load factor for Danish onshore
wind farms showed a fall from a peak
of 22% to 18% at age 15. For offshore Danish
wind farms, the normalized load factor was
shown to fall from 39% at the start of commercial
operation to 15% at age 10.
Hughes said that the reasons for the observed
declines in normalized load factors
could not be fully assessed using the data
available, but he speculated that " outages due
to mechanical breakdowns " appeared to be a
contributing factor.
Hughes said that analysis of site-specific performance
showed that the average normalized
load factor of new UK onshore wind farms at
age one " declined significantly " between 2000
and 2011. In addition, he found that larger wind
farms had worse performance than smaller wind
farms. Adjusted for age and wind availability,
the overall performance of wind farms in the
UK has " deteriorated markedly " since the beginning
of the century, he found.
According to Hughes, these findings have
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implications for policy toward wind generation
in the UK. First, they suggest that the current
government subsidy is " extremely generous "
if investment in new wind farms remains profitable
despite the decline in performance due
to age and over time. Second, meeting the UK
government's targets for wind generation will
require a much higher level of wind capacity
and capital investment than current projections
imply. Third, the structure of contracts offered
to wind generators may require modifications,
because few wind farms will operate for more
than 12 to 15 years.
In releasing the report, the Renewable Energy
Foundation said that policymakers who
were expecting wind farms built before 2010
to contribute toward CO2
targets in 2020 or
later " must allow for the likelihood that the
total investment required to meet these targets
will be much larger " than previous forecasts
suggested. ■
-David Wagman is executive editor
of POWER.
66
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POWER March 2013

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