The Case against Wind 'Farms'
2006 edition. Copyright © Dr J. R.
Etherington
Country
Guardian's document "The Case Against Windfarms" was
last updated in May 2000 but a great deal has happened in the intervening five
years. This update printed can be downloaded from http://www.countryguardian.net/ (about 370 kB). It is freely offered for
reproduction or other use providing it is acknowledged. The views expressed are
those of the author, who is a professional environmental scientist, formerly
Reader in Ecology in the
“Dr
Etherington writes with no affiliation to any campaigning organisation and is
not a member of one. Neither does he receive payment from any part of the energy
industry. He provides consultancy advice in the battle against
unnecessary wind power on a pro bono
basis” (Ninnau, The North American Welsh
Newspaper,
The author
will welcome and incorporate corrections and suggestions eth.pbont@virgin.net
Contents
1.
Introduction: Why wind ‘farms’ and why now?
2.
Government policy, costs and 'subsidy'
3. The
scale of development required by government 'targets' and overall saving of
carbon dioxide emission
4. The
problem of intermittency and need for backup
5.
Calculating CO2 emissions and saving
6. Homes supplied by a wind
'farm'
7.
Technical aspects of wind turbines
8. Landscape quality of wind
'farm' sites' and value of landscape
9. Wind
'farms' and the planning system
10.
Public opinion - Beauties or beasts?
11. House
prices, tourism and jobs
12. Birds
and bats
13. Noise
14.
Quality of life and safety
15.
Television interference, radar and aviation
16. Some comparisons - odious and
otherwise
17. How
can the need for electricity be met?
18.
Conclusion
Appendix 1. Climatic change,
Appendix 2. Calculations
for Section 16.
Comparisons
References and
notes
1. Introduction: Why wind ‘farms’
and why now?
Those who
advocate wind ‘farms’ base their arguments on three propositions:
i. They
produce electricity without harmful emissions - carbon dioxide (C02),
sulphur dioxide (SO2) and nitrogen oxides (NOx) - gases
associated with either global warming, acid rain or nutrient-enrichment
(eutrophication);
ii) They
do not deplete finite supplies of fossil fuels;
iii) They
produce electricity without the problems associated with nuclear power - such as waste
storage, risk of accident, and possibility of military use.
For these
arguments to be valid it is clear that wind ‘farms’, if developed in sufficient
numbers, must significantly reduce CO2 and other emissions,
measurably slow the depletion of other fuels which will eventually be exhausted
and produce a reliable and sufficient
amount of electricity to replace nuclear power stations,
The
burning of fossil fuels is a major source of CO2 emissions. Since the
Industrial Revolution atmospheric CO2 has increased by about a third
(from less then 280 parts per million by volume to 373 ppmv in 2002). The rate
of emission has risen dramatically over the last twenty five years and
increasing CO2 concentration has been linked by many scientists to
global warming.
'Global
warming' is simplistically explained by the differing transparency of carbon
dioxide to incoming solar radiation and outgoing long wave infra red radiation
(radiant heat). Extra CO2 in the atmosphere acts like a blanket
preventing the escape of the heat energy which arrived on earth as solar
radiation. There is scientific argument about the degree to which CO2
will cause 'global warming' and what, if anything, to do about it. Indeed
the House of Lords (2005) report on economics of climate change suggests that
the so-called 'consensus' on the science is a politically created myth. A
discussion of the arguments is presented in Appendix 1.
However,
few would argue against reducing CO2 emission. Release of CO2
by human activity is, after all, an open ended experiment with our one and
only atmosphere! Furthermore it is apparent that 'one day' we shall run out of
fossil fuel though there is serious dissent about the time period
involved.
Nuclear
fission power was hailed 50 years ago as the solution to all our energy
problems. Since then, for many years it has provided a quarter of British
electricity - and even now a fifth. During its developmental period it was
expensive but now it is running competitively with other generating technologies
and without subsidy (since 1995-6). Across the Channel,
Why then
do we need an alternative? Essentially because fears have grown that radioactive
materials pose an unacceptable accident risk, because the problem of storage and
reprocessing of fission by-products has not been fully resolved and because
military use may be made of such materials (see Section 16. How can the need for
electricity be met?).
Why have wind turbines arrived so suddenly? This is more a matter
of perception than fact. The first windmills date from at least the 10th century
in
All that
was needed was the perception of need and the ability to link to the AC grid,
with its problem of frequency control. This happened in the 1980s driven by the
wide acceptance of belief in CO2 -driven climatic warming. The
'switch' was thrown when various subsidies on ‘green’ electricity became
available world-wide. Nothing attracts entrepreneurs more than a free
handout!
The first
grid-connected wind turbine (more correctly aerogenerator) in the UK was
installed at the former CEGB test facility on Carmarthen Bay, southern Wales, c.
25 years ago. We have gone a long way since then.
What 'they'
say
"Clean, renewable forms of energy,
such as wind power, are essential if we are to tackle climate change. They are
also vital in ending the threat of nuclear power, which would leave a legacy of
nuclear waste that will remain a threat to our health and the environment for
hundreds of thousands of years." Yes2Wind website
Untrue. The variable nature of wind power
prevents it from displacing nuclear generation which provides continuous peak
output and is best suited to ‘base-load’ supply. Wind power is irrelevant to any
discussion of nuclear as it cannot provide such uninterrupted
generation.
2. Government policy, costs and
'subsidy'
"The aim
of government policy for renewable energy is that it should make an increasing
contribution to
The
'Energy White Paper (2003) announced that: -
"We have introduced a Renewables Obligation
for
Note –
before reading this section it may help to familiarise yourself with the units
and terminology of electricity (see References and notes: ‘Units and
terminology’ and ‘Prices’).
Government’s action has ensured
that renewable power generation is now ‘subsidised’ by the mechanisms of the
Renewables Obligation (RO), the Climate Change Levy exemption (CCLe) and the
marketing of RO Certificates (ROCs).
The
Renewables Obligation as its name suggests places an obligation on electricity
suppliers to purchase a percentage of qualifying renewably generated electricity
but it also forces a consumer-sourced 'subsidy' to be paid to the renewable
generator. During the year 2004-5 the obligation stood at 4.9% of qualifying
electricity, rising to 10% by 2010.
The
mechanism of payment results in an increase in electricity price to all
consumers, whether or not they subscribe to a 'green tariff'. Few consumers are
aware of this fact and neither government nor wind power developers apprise them
of it. The complexity of this system is deliberately obscure in an attempt to
conceal the fact that the RO is effectively a hidden tax on all electricity
consumers and a huge hidden 'subsidy' to providers of renewable energy - larger
indeed than any subsidy in history.
This
obscurity and lack of democracy has been acknowledged by the House of Commons
Committee of Public Accounts report on the DTI (CPA 2005) which says:
-
"Requiring users to source
supplies from uneconomic providers has the same affect as taxing users to
subsidise the providers, but is not as transparent or amenable to parliamentary
control... [and the DTI] has not consulted consumers, or their representative
groups, about their willingness to contribute to the cost of renewable
energy"
The net
effect of the RO and CCLe mechanism is to pay three premiums on top of the
wholesale price of wind generated electricity (and other renewable generation).
In summary: -
1. The
Renewables Obligation Certificate ‘buyout’ price which is currently £32.33.
The ROC
was set at £30/MWh in 2002 and increases each year, Retail Price Indexed. The
current period 05/06 known as Compliance Period 4, has a price of £32.33).
2. A
trading increment from marketing Renewables Obligation Certificates currently
worth about £10/MWh.
This
tradable value grew steadily after 2002 when the RO system replaced the former
Non-fossil Fuel Obligation. The price of ROCs reached about £47/MWh in 2004 but
very recently the increment has dropped back to c. £10/MWh with total ROC value
c. £40-£45/MWh.
3. The
Climate Change Levy exemption, worth £4.30/MWh.
In
addition to the consumer-sourced RO, another small advantage is given to the
renewable generator. Non-renewable generating fuels pay a tax of £4.30/MWh, but
renewables are exempt and so the electricity is effectively given an extra
£4.30/MWh.
The ROC
buy-out price, its market increment and the CCLe thus total a premium of £32.33
+ c. £10 + £4.30 = c. £ 46 - £47 per MWh, which is added to the wholesale value
of the electricity generated from renewable sources - in our context wind
power.
Electricity has increased
enormously in price since the RO was introduced and is now around £40 - £45/MWh
for wholesale base-load generation (DTI 2005) but the trading system of NETA
involves short term bidding by National Grid Transco and the price fluctuates
wildly, controlled by supply and demand. Thus we have an approximate total, at
the moment, of about £90+/MWh paid for wind power compared with c. £40-£45/MWh
for conventional generation.
The net
outcome of the ‘subsidy’ system is that wind electricity receives about twice
the price of wholesale base-load thermal generation per MWh. An 'effective
subsidy' which doubles unit-value is gigantic, historically unprecedented and I
believe unsustainable. Coal currently receives less than one twenty-fifth of
this subsidy per MWh whilst gas and nuclear get none (personal communication
DTI).
The RO
and CCLe provide the huge financial incentive which has brought multinational
power companies flocking to our shores and has been responsible for the
distortion of our planning system which the Committee of Public Accounts
virtually branded as undemocratic (CPA 2005).
A single
2 MW wind turbine operating at 30% load factor would, on the basis of the above
figures, receive an annual subsidy of over £235,000
It is a
salutary thought that it is only this cleverly sourced covert ‘subsidy’ which
allows wind turbines to be built at all. Paul Golby, the chief executive of Eon
UK (formerly Powergen), said: "Without the renewable obligation certificates
nobody would be building wind farms." (Daily Telegraph
Capital subsidies
In
addition to the huge ‘for-life’ subsidy on electricity income, substantial
capital subsidy is available for some wind power projects.
A recent question in the
Commons revealed that the public pocket supported a total capital subsidy to
offshore wind farms of £34.7 million pounds in 2004-2005 (Hansard
The Moel
Maelogan onshore windfarm in the
Capital
subsidy has also been made available for small scale renewable projects through
the Clear Skies scheme, funded by the DTI. This gave householders and
communities a chance to install renewable energy systems by providing grants and
advice. Domestic grants were from £400 to £5000 whilst ‘not-for-profit’
community organisations could receive up to £100,000 (£50,000 from April 2005).
Funding for this project is now exhausted and it will be replaced by DTI’s ‘Low
Carbon Buildings Programme’ scheme in c. April 2006 (http://www.clear-skies.org/).
As if
this was not enough public money being funnelled into the pockets of wind
developers, the Lottery fund has also been raided to provide yet more. The Burbo
Bank 90 MW offshore station due to be completed in 2010 has been awarded a ‘Big
Lottery’ grant of £10.4 million – not yet paid-out as of March 2005 – with a
completion date of 2010 (http://www.biglotteryfund.org.uk/).
Impact of
subsidy
So much
money is being channelled covertly into onshore windpower development that
development companies can offer irresistible sums in rental to landowners or as
‘sweeteners’ to local communities. Struggling farmers on poor hill land are
offered rental sums far exceeding any possible agricultural income from the
land. “If it wasn’t for the windmills I’d
have thrown in the towel a long time ago” (farmer, Guto Jones, landowner at
Blaen Bowi, Carmarthenshire – reported in the Tivyside Advertiser (2002).
A current
proposal (2006) by Dutch firm, Nuon, typifies the use of larger scale community
'sweetening' even before a planning submission is made. The publicity material
for the 26 MW Nant Bach (Mwdal Eithin) wind ‘farm’ in Conwy, N. Wales, states
that the project "will make available
£60,000 a year as a community funding" A most tempting offer even though the
sum is but 2% of the likely subsidy payment to Nuon! It is interesting to note
that the Welsh renewable energy planning document TAN 8 comments on such
community benefits that "It must be clear
that the provision of benefits is on a purely voluntary basis with no connection
to the planning application process" (Annex B. 2.4),
3. The scale of development
required by government 'targets' and overall saving of carbon dioxide emission
Targets
In
January 2000 government announced its aim for renewables to supply 10% of UK
electricity in 2010, "subject to the costs being acceptable to the consumer"
(Energy White Paper 2003).
The
target figure is 39 TWh/y which is 10% of predicted generation based on current
forecasts of total energy production of 371–390 TWh/y for 2010 (http://www.dti.gov.uk/renewables/renew_2.1.1.htm ).
About 75%
will have to be wind power so this will need 29.3 TWh/y or an average running
wind power generation of 3,339 MW.
Assuming
a load factor or 25% this would require at least 13,356 MW installed capacity of
wind power (a 30% load factor would require 11,130 MW) See section 7. Technical aspects… for the explanation of load
factor.
An
installed capacity of wind power of 13,356 MW would equate to 8,904 turbines of
1.5 MW, each c.100 m (327 ft) in height or 6678 turbines of 2.0 MW each, c. 120
m (394 ft).
It is
also fairly certain, on the basis of existing planning applications, that a
large number of much smaller turbines will also be proposed (for example Green
Amps' current attack on the Cotswolds with 60 or more 0.3 MW refurbished Carter
turbines).
What 'they'
say
"There are now some 1,120 turbines
in 90 locations. Generating 10 per cent of
“Pigs
might fly!”
Saving of CO2 emission
- country wide target
Government's own figure for saving
of the UK's CO2 emission by renewable power generation , mainly wind,
is just 9.2 million tonnes per year by 2010 (DEFRA 2004 and DTI Myths).
This is
less than the emission from a medium sized coal fired power station and more to
the point is less than four ten-thousandths (0.0004) of global total CO2 emission
(OECD 2005) and stands no chance of altering atmospheric CO2
concentration, still less deflecting climate change as suggested in DTI
Myths.
4. The problem of intermittency
and need for backup
What 'they'
say
“What happens when the wind stops
blowing?
When the wind stops blowing,
electricity continues to be provided by other forms of generation, such as gas
etc. Our electricity system is mostly made up of large power stations, and the
system has to be able to cope if one of these large plants goes out of action.
It is possible to have up to 10% of the country's needs met by intermittent
energy sources such as wind energy, without having to make any significant
changes to the way the system operates.” (BWEA FAQs)
A likely story.
In 2003
the BBC 2 programme If….. The Lights Go
Out' (10 March) included a contribution from Dr Dieter Helm, Energy
Economist and Fellow in Economics,
He
commented on wind power: -
“What we know, is the wind blows
sufficient for these windmills to be producing about 35%, perhaps 40% of the
time. So the paradox of building windmills is that you have to build a lot of
ordinary power stations to back them up and those are going to be almost
certainly gas in the short to medium term and that’s what’s required. If you ask
the question who’s making sure that there’s enough gas
stations out there to back up the windmills the answer is
nobody.”
This was
one of the first official acknowledgments of a point which Country Guardian and
many campaigners had made for years. Because of the unpredictable intermittency
of wind, and the very long time required to bring 'cold' generating capacity
into production, it is necessary to keep a substantial reserve of spinning
backup. This is usually arranged by keeping turbo-alternators at less than peak
output so that an instant increase of generation is possible. This causes a
significant amount of extra CO2 emission from such
plant.
E.ON Netz
(2004) admitted that every megawatt of installed wind power required 0.8 MW of
backup from ‘shadow power stations’,
thus, even when not generating, wind turbines are still causing some
CO2 emission. The following year E.ON Netz (2005) went further:
-
"... Dependence on the prevailing
wind conditions means that wind power has a limited load factor even when
technically available. It is not possible to guarantee its use for the continual
cover of electricity consumption. Consequently, traditional power stations with
capacities equal to 90% of the installed wind power capacity must be permanently
online in order to guarantee power supply at all times."
In the
words of ESB, the Irish National Grid (2004): -
“As wind contribution increases, the effectiveness of adding additional wind to reduce
emissions diminishes [and] the cost will be very substantial because of
the back up need”.
Using
wind power to reduce CO2 emission seems akin to emptying the
A very recent report, commissioned
by the DTI, edited by Graham Sinden (Oxford Environmental Change Institute,
2005) purported to demolish this argument by claiming that the wind always blows
somewhere in the UK and led Energy Minister, Malcolm Wicks to say "This new research is a nail in the coffin of
some of the exaggerated myths peddled by opponents of wind power."
(Independent
One could retort "So what? - 200 turbines
generating feebly on Stornoway and the rest of the country’s wind fleet
becalmed". However it is worse. Sinden simply compared the incidence of 'no
generation' versus 'some generation' but this is not the point. Had Sinden’s
group compared incidence of generation above a sensible threshold (say 20%) with
incidence of maximum generation it would have been apparent that in anticyclonic
weather there are many occasions per year when the whole
This was
indeed realised by the House of Lords Science and Technology Committee in Feb
2004 when Baroness Platt of Writtle questioned Mr Sinden on his research. He
replied: -
“There will be times when you have quite
low speeds and consequently you have low electricity output from it. The
analysis that I ran was of wind speeds being so low that electricity would not
be generated, that was the criteria for it. As I said, the single worse case in
the last 21 years was 11 hours over summer when that did happen. If you raise
the bar higher and say "We want 20 per cent output or 30 per cent output" then
it may look a little bit different but we have not carried out that
analysis.” (House
of Lords Science and Technology - Minutes of Evidence Session
2003-04)
This
weakness in the argument is such an Achilles heel that it has led the DTI and
wind industry to clutch at the straws of electricity storage and/or hydrogen
generation by electrolysis. These are expensive technologies to prop up a wind
power industry whose electricity is already over twice the price of
'conventional' generation!
A recent
report from UKERC (2006) seems to be directed at downplaying the problem of
intermittency but it fails to convince. One of its conclusions is that:
-
"Wind generation does mean that the output
of fossil fuel-plant needs to be adjusted more frequently, to cope with
fluctuations in output. Some power stations will be operated below their maximum
output to facilitate this, and extra system balancing reserves will be needed.
Efficiency may be reduced as a result."
UKERC
suggests that this will happen only with substantial wind penetration but the
document also reports “that a study of the "... transmission network-constrained
Swedish system concludes that energy spill levels would reach 16.7% at an 11%
penetration level" “
Energy
spill” is a euphemism for shutting down turbines as a consequence of
over-generation.
The
“As a retired grid control
engineer my instincts react against all thought of unpredictable renewable power
on the scale proposed, sloshing around the system... Wind resource does not
provide any governor response to assist the automatic correction of system
frequency deviations. Its exploitation on any scale would deter the introduction
of new replacement capacity by soaking up available demand, the basis of payment
within a market driven structure. At minimum levels of system demand with fixed
base load operation of nuclear plant, in turbulent conditions, the control of
system frequency would become a nightmare.”
Thus
wind-power must call upon conventional reserve generation to smooth its short
term vagaries and it is dishonest of the wind power industry and DTI (2005) to
claim "The reserves needed to guard
against loss of a large power station will readily cope with the small
perturbations due to the wind". This may be true at the moment, with wind
power providing less than one percent of average generation from an installed
capacity of just 1500 MW but if the contribution of wind power should rise to
(say) 10% of average generation i.e. 4,500 MW we would need a wind installed
capacity of up to 18,000 MW to provide it (load factor 25%).
Thus
within a period of just a few hours, wind output could swing by a substantial
fraction of 18,000 MW, balanced against the Grid’s peak load ‘insurance’ of c. 20% (which represents about 11,000 MW
– see notes on ‘Reserve capacity’). It can't be done. We shall in due course
need a bigger insurance policy and as Dr Helm said, for the DTI (above) "the paradox of building windmills is that
you have to build a lot of ordinary power stations to back them
up..."
It is my
view that the BWEA and the DTI are misleading us over this matter. There is
certainly no consensus that intermittent wind power can be fed into our
electricity network in large quantities without action being taken soon to
ensure stability. Such action will add cost to an already very expensive
technology which needs a 100% ‘subsidy’ to survive and will substantially erode
any saving of CO2 emission.
5. Calculating CO2
emissions and saving
Saving of CO2 emission
by individual onshore wind turbines
One
megawatt of wind power installed capacity generates 0.3 MW assuming a generous
load factor of 30%.
The
annual electricity yield of this would be 0.3 x 365 x 24 = 2,628 MWh/y
According
to BWEA, if this electricity displaces 'dirty coal' generation it will save 0.86
tonne CO2 /MWh (http://www.bwea.com/edu/calcs.html
) so the 1.0 MW of installed capacity would save: -
2628 x 0.86 = 2,260 tonne CO2
/year.
Both DTI
and the Sustainable Development Commission utilise a much lower factor for
CO2 emission per MWh – also upheld by a recent Advertising Standards
Authority (ASA) adjudication.
The more
truthful value for saving of CO2 emission is based on the current
generating mixture of fuel used to produce electricity (gas firing is much less
CO2-dirty than coal and nuclear power emits no CO2)
(Etherington 2003).
DTI
In a
letter to an MP representing Humberhead Against
Turbines (2005), Mike O’Brien (Energy Minister at time) agreed that: “it would be appropriate to use an average
generating mix when calculating CO2 savings from a wind turbine. This
is consistent with DTI Wind Energy fact sheet 14.” Mike O’Brien’s letter and
notes were presented in evidence at the Whinash Inquiry (2005) and are thus in
the public domain.
The
current “average generating mix” gives about 0.43 tonne CO2 /MWh,
just half of the saving claimed by BWEA (DEFRA Fuel Conversion Factors http://www.defra.gov.uk/environment/business/envrp/gas/05.htm).
ASA
An
adjudication of 21 December 2005 against Renewable Energy Systems (RES) concluded “although an emissions factor of
860g CO2/kWh might have been a reasonable figure for RES to use to
calculate the reduction of CO2 emissions at the present time, it was
not a reasonable figure to use for calculating the reduction over a period of as
long as 25 years without some qualification to indicate the uncertainties about
future fuel generating mix.”
Sustainable Development Commission
(SDC)
The SDC’s
report Windpower in the UK (see
November 2005 corrected edition) also suggest that future projections of saving
must be based on a lower figure than BWEA’s 0.86 tonne CO2 /MWh
“There
are large differences between the CO2 emissions associated with coal (243 t
C/GWh) compared to natural gas (97 t C/GWh), with none associated to nuclear
power.” [these two factors convert to 0.89 t CO2
/MWh and 0.36 t CO2 /MWh ]
SDC
continues: - for the purpose of this report, it has been assumed that wind
output will displace the average emissions resulting from gas-fired plant… it is
the figure that the DTI use and is used here so that the carbon benefits of wind
power are not overestimated."
“The
figure that the DTI uses” is currently 0.43 t CO2 /MWh (see
above)
Thus,
calculated on current generating-mix, 1.0 MW of installed windpower capacity
displaces no more than: -
2,628 x
0.43 = 1,130 tonne CO2 /MWh
Because
of the rather ‘reserved’ wording of the ASA adjudication it is wise only to use
the 0.43 tonne CO2 /MWh to estimate saving over the whole life of the
'farm' (20 to 25 years).
Payback time for energy and
CO2
Generally
speaking the wind power industry has correctly observed that a wind turbine pays
back the energy consumption of its construction and the accompanying CO2
emission within a few months (DWTMO 1997).
The cash
cost of a wind turbine is a very different matter and arguably without enormous
subsidy a wind turbine cannot pay back its financial cost in a reasonable
time-frame. This is because a large proportion of the cost derives from value
additive operations such as the complex engineering of the drive train and
generator and the specialist fabrication of blades which are expensive but do
not consume much energy – which is largely absorbed in the smelting of iron and
its conversion to steel and to a lesser extent, manufacture of other
metals..
In the
case of wind ‘farms’ on deep peat, especially if site operations such as road
construction cause drying of previously waterlogged peat, there may be
substantial CO2 emission from its oxidation. This has been
specifically observed by the Environmental Management Committee at Cefn Croes
which wrote: - “… oxidation of exposed peat was leading to a huge loss of carbon
to the atmosphere, and mitigating the impacts of the Wind Farm from a Global
Warming perspective.” Despite this,
even if serious peat oxidation occurs, the displacement of fossil fuel
electricity by wind turbines will outweigh the construction energy and carbon
emission within a year or two.
Extra CO2 from
backup
It is
remarkably difficult to calculate the amount of CO2 which is
liberated from power stations which backing-up renewable electricity generation.
This amount must be subtracted from the theoretical saving of CO2
emission.
Wind
power is supported by thermal generation which is operating below peak
generation and can be ramped up to cover losses of generation when the wind.
This causes fuel inefficiency and emission of extra CO2 per unit of
electricity generated by the backup.
At the
present the backup is taken from the existing reserve capacity used as insurance
against plant and transmission failure. The wind power industry, unfairly, has
argued that because the backup is pre-existing, there are no CO2
costs.
Be that as it may, it is
not a situation which will persist. Once the demands of wind power for cover for
its full installed capacity are sufficient to call upon a large proportion of
existing reserve it will be necessary to build dedicated backup and it is this
requirement that prompted the Irish National Grid, ESB (2004) to conclude, as
previously quoted, that:
-
“As wind contribution increases,
the effectiveness of adding additional wind to reduce emissions diminishes…The
cost will be very substantial because of the back up
need.”
At least
some power engineers have attempted to calculate CO2 costs in these
circumstances (Bass & Wilmott 2004). They claim, for a worst-case scenario,
that their analysis “suggests that the
current ‘Dash for Wind’ could actually make the situation
worse.”
6. Homes supplied by a wind
'farm'
What 'they' say: -
"4700 is the average
Most wind
‘farm’ planning applications or advertising fliers cite the number of homes
supplied and the electricity industry has always done this - it is not a new
tack on the part of wind developers. However the method of calculation is not
well understood and for an unpredictably intermittent source such as wind,
causes much controversy
For it to
be correct, given these terms of reference, it must be based on the actual
electricity supply from the wind ‘farm’ – i.e. (installed capacity x load
factor)
The
"domestic" consumption is based on a DTI estimate in the Annual Abstract of Statistics which
subdivides
For 2003
(A.A.S. 141 Table 22.8): -
Industrial 115
TWh
Domestic
116 TWh
Other 108 TWh
The
number of
Thus the
annual average domestic consumption is (116 TWh)/(24.5
million) which is 4,735 kWh per home and dividing by (24 x 365 h) is equivalent
to 0.54 kW continuous consumption per home.
This is
the source of the BWEA figure 4,700 kWh per home http://%20www.bwea.com/edu/calcs.html
and it rounds-down to a memorable 0.5 kW continuous consumption per home
allowing easy mental arithmetic.
How does
this work for wind and other intermittent sources? If a home subscribes to a
'green' tariff with a wind power company, the company guarantees to supply the
electricity grid with the same amount of wind electricity as the customer's
annual consumption. On average this will be 4770 kWh supplied to the customer
from the grid.
There is
no implication that it is the 'same' electricity in the sense that it would be
if the wind turbine were cabled to the home.
If a wind
developer or campaigning group claims that a wind ‘farm’ supplies the entire
need of an area, this may or may not be correct in terms of total amount of
electricity. It is only correct if the whole consumption of a town or county has
been accounted for - in other words almost three times the 'domestic
consumption'.
The claim
may also be made that the supply is “up to” X,000 homes
– a maximum value. In this case the calculation will have been based on
installed capacity and will be three to four times the average number of homes
supplied.
Some
campaigners get very excited about this 'homes' matter and point out (quite
truthfully) that wind power cannot 'support' ANY homes as it has to feed
indirectly via the network to iron out intermittence. Hayden (2004) consequently
describes claims such as “this windmill
farm will provide enough power for 25,000 homes” as “misleading garbage.”
However there is an advantage to fighting
them on their own ground: -
A 1.0 MW
wind turbine at 30% load factor will support 600 homes
A 1,000
MW 'proper' power station at 80% load factor will support 1,600,000
homes
No real
contest is there? - given that it would require 2667 1.0 MW wind turbines to
make as much electricity and that they would occupy over 500
km2, not to mention the
constant fluctuation of supply, with all its
disadvantages.
7. Technical aspects of wind
turbines
A typical wind
turbine
Industry
standard is now a 2.0 MW installed capacity machine, or often larger.
An
example is the Danish manufactured Vestas V 80
Rotor
Diameter: 80 m
Swept
area: 5,027 m2
Speed
revolution: 16.7 rpm
Operational interval: 9 - 19 rpm
Tower Hub
height (optional approx.): 60 - 100 m
Total
height (blade vertical) 100 - 140 m (depending on tower) i.e. 305 to 427
feet
Generator: Asynchronous
Nominal
output: 2.0 MW at 50 Hz 690 V
Weight
100 m
Tower: 220 t
Nacelle:
61 t
Rotor: 34
t
Total:
315 t
Installed capacity and load factor
(capacity factor)
The
nominal maximum output is referred to as the "installed capacity". If the
machine generated at maximum rate, continuously for a year, it would yield, per
installed MW: - 1.0 MW x (365 x 24) hours = 8760 MWh. The actual yield is much
less, mainly because there is insufficient wind to maintain full
generation.
Onshore
in the
In 2003,
Lord Sainsbury told the House of Lords that load factor was about 30% onshore
and 35% offshore (Hansard 18 November
2003: Column 1851)
During
the past two years of DTI records the average UK figures have been much less
than this onshore: 24.1% in 2003 and 26.6% in 2004 (DUKES
2005).
Calculation of load
factor –
Example for a 1.0 MW turbine:
-
(Achieved generation/(Maximum possible generation)/ x 100 = Load
factor
Maximum
possible is 1.0 MW x 8760 h/y = 8760 MWh
Achieved
generation is (say) 2190 MWh
Load
factor thus = 2190 MWh / 8760 MWh = 0.25 i.e. 25%
The
calculation should be based on yield over a stated time (the Ofgem period is
January to December.
Windspeed
A wind
turbine cannot generate until there is sufficient wind, usually about 4 m/s,
called the 'cut-in' speed. The machine does not reach peak generation until
about 15 m/s. It then maintains a constant output with increasing speed (see Physics of windpower, below) up to a
safety 'cut-out' speed of 25 m/s.
A rotor
can be allowed to idle (generator declutched) at wind speeds well below cut-in
speed to take instant advantage of periods of stronger wind (a 30 tonne rotor
otherwise takes time to come to speed).
Above
cut-out wind speed the turbine is shut down for safety, with blades 'furled'
(feathered), i.e. edge-on to the wind and with generator de-clutched and the
wind-shaft locking brake on.
Some
examples are given below, from manufacturers'
specifications.
Vestas V 66 1.75 MW
turbine. Rotor
d. 66 m cut-in 4 peak 16 cut-out 25
(metres/second)
Vestas V 80 2.0 MW
turbine. Rotor
d. 80 m cut-in 4 peak 15 cut-out 25
(m/s)
General Electric 3.6
turbine. 3.6 MW Rotor d.104 m cut-in
3.5 peak 14 cut-out 25
(m/s)
Conversion of speed units: 4 m/s =
8 knots = 14 km/h = 9 mph = B3 : 15 m/s = 29 kt = 54
km/h = 34-mph = B7 : 25 m/s = 49 kt
= 90 = km/h = 56 mph = B10.
Beaufort
wind scale (B): 3 = Gentle Breeze;
7 = Moderate or Near Gale; 10 = Whole Gale or Storm
Prediction of the performance of a
wind turbine may be obtained by previous anemometric recording of wind speed on
the site but an approximate prediction of generating output may be made from
maps of the distribution of wind speed in the
This map
shows that average wind speeds in lowland Britain are 5-6 m/s, coastal and
upland areas 6-7 m/s and exposed uplands 7-8 m/s. Only a few extreme sites in
the uplands, west and north lie between 8-10 m/s average speeds. Note that the
average wind speed, even in the windiest sites is below peak generating speed,
suggesting that a wind turbine anywhere in the UK, exposed to a variable wind
regime will spend much of its time well below maximum generation thus explaining
the low load factor of about 26% (average for 2003 and
2004)
It is
also this distribution of windspeed which makes high ground and coast the
preferred target for wind developers.
Physics of wind
power
i)
Theoretical output is proportional to the square of the blade-length
(radius).
A wind
turbine converts the kinetic energy of moving air into mechanical work. The
theoretical electrical output is thus related to the mass of air passing through
the rotor. Doubling the area of the rotor doubles the amount of power available
and, because the area of the swept circle is pi x radius squared, the output is
proportional to the blade-length squared.
ii)
Theoretical output is proportional to wind speed cubed so even a small increase
in average wind speed should give substantially more electricity over the course
of time.
Real wind
turbines follow the first rule closely hence any increase in height allowing
increase in rotor radius gives substantially more power. The practical
consequence is that machines originally designed for offshore installation (both
V80 and GE 3.6) have quickly migrated onshore.
The
second rule is not followed closely by real wind turbines. At first as wind
rises above cut-in speed the power output increases dramatically with speed
(because of the cubic relationship a doubling gives 2 x 2 x 2 increase in
power). However the output then becomes more or less proportional to wind speed
up to peak generation (i.e. x 2 increment doubles power) and then between peak
and cut-out wind speed the output remains almost constant (because the generator
is running at maximum output).
This lack
of conformity to the cubic relationship is a result of aerodynamic (stall)
regulation, or pitch regulation of power conversion by the blades, of
'electrical-braking' and of the alternator reaching its peak capacity. In the
first case the shape of the blades allows wind-flow to become turbulent over an
increasing part of the blade as the speed rises, reducing theoretical power
conversion. In the second case the whole blade pitch is varied, or control
surfaces (ailerons) are moved to 'spill' wind with the same effect. The load
imposed by the generator also controls rotor speed (just as an idling car engine
slows if the headlights are switched on) - this loading, like pitch regulation,
is under operator or computer control. Such modification of the aerodynamic and
electrical-braking characteristics allows a modern wind turbine to harvest
maximum power from fairly low wind speeds but also safely to continue operation
in high winds up to gusts of almost 60 mph.
Rotor speed (and see section 9. The effect on birds)
Wind
turbines are so gigantic that the rotor appears to be travelling quite slowly
but this is illusory. A big turbine like a Vestas V 80 2.0 MW machine rotates at
16 rpm and so, with a blade radius of 40 m, the blade tip velocity is 241 km/h
(149 mph), over twice the motorway speed limit. The GE 3.6 turbine at its
maximum 15.3 rpm has a blade tip velocity of 300 km/h (186mph), approaching the
average speed of a Formula 1 racing car and its blade-swept area is
substantially larger than that of the V80, at 8,495 m² [larger than a football
pitch which is 7392 m²]
A bird
which just avoids a GE 3.6 blade tip has only 1.3 seconds to dodge the next
blade, approaching from about 93 yards away on a strongly curved path! Further discussion of this in section 9. The effect on birds.
Spacing of turbine: area of land
needed
To avoid
“taking the wind out of each others sails”, wind turbines require spacing at 8
to 10 rotor diameters (downwind) and across-wind at c. 5 diameters (Manwell et
al; 2002). Some authors suggest even greater spacing.
An
example is Horns Rev off the Danish coast where 80 turbines (2.0 MW) are in a
square array of 20 km2, thus 0.25 km2 per 2 MW turbine (or 0.125 km2 per MW installed). This is
rather more closely packed than the counsel of perfection
above.
The
biggest onshore windfarm in the
For
comparison a 1500 MW fossil fuel station with a load factor of 80% would occupy
no more than about 2 km2 and generates 1500 x 0.8 = 1200 MW. With
wind load factor of 25% a 2MW turbine yields 0.5 MW - so we need 2400 turbines
to equal this electricity and occupying 2400 x 0.25 = 600 km2 of
land.
Foundations
Onshore
wind turbines, according to size and site conditions may require a wide range of
different foundation types and sizes. The commonest is the gravity base
comprising a ferro-concrete slab loaded with aggregate. Other options might be
rock-anchors on a hard rock site, piled foundations or an embedded concrete
cylinder in soft conditions (Civil
Engineering, November 2005).The hole excavated for a turbine's foundation
has a volume of 200 - 800 m3 depending on site conditions. This would need a
maximum of about 1700 tonnes of concrete and aggregate for a gravity base. Only
a quarter or less of the concrete will be cement - the energy intensive
component which emits CO2 in manufacture.
An
average gravity base for a 2.5 MW turbine requires about 40 truckloads of
concrete - up to about 250 m3 compared with only 40 m3 for
the smaller 250 kW turbines, common a few years ago (Civil Engineering, November
2005).
Myths of our own
making
Olympic swimming
pool.
Opponents of wind power have created a myth of their own, by suggesting that
foundations are of "Olympic swimming pool size". That would be 50 x 25 x 2 or 3
m = 2500 to 3750 m3. This is an average 12-fold exaggeration!
Failure to payback energy and
CO2. It is
often said that wind turbines fail to pay back the energy and CO2
cost of their manufacture and erection, or even that the CO2 emission
from cement manufacture alone is enough to offset the lifetime saving of
CO2 by a turbine. All of these assertions are untrue. Don't repeat them - there is enough to
complain about in wind power without resorting to easily exposed misinformation
but for more detail see Roads (below)
and Payback time for energy and
CO2 (section 5).
Wind
turbines only operate 30% of the time. In fact the industry is quite correct in
saying that wind turbines generate for near 80% of the time – but what they fail
to say is that for a large proportion of that 80% the amount of generation is
very small.
Wind
turbines need back up so they don’t save any CO2. It is certainly
true that the more wind power we install, the more backup will be necessary when
wind speeds are low but there is a high demand for electricity. That backup will
cost some of the saved CO2 emission but it will certainly not negate
all of it. Thus wind power undeniably displaces some fossil fuel burning and
saves some CO2 emission.
Roads and site
clearance
Importing
the turbine components requires access for very large low-loader trucks and a
large mobile crane able to move 50 tonne or larger components. This is achieved
by construction of a network of access toads which themselves require excavation
of overburden and infill with large quantities of crushed rock aggregate. This
work and borrow-pit sourcing of aggregate can do an enormous amount of
ecological damage in vulnerable habitats of semi-natural vegetation especially
on deep peat soils. The photo gallery accessible on the Cefn Croes website is a
remarkable illustration of this literal holocaust: - http://www.users.globalnet.co.uk/~hills/cc/gallery/index.htm
Further
discussion is posted at http://www.users.globalnet.co.uk/~hills/cc/scoutmoor.pdf
Transmission
lines
One gigawatt of generation by a large power station is a very different matter from a gigawatt’s worth electricity from 1666 two-megawatt turbines spread over perhaps