## The capacity factor of wind power

A wind turbine’s ‘rated’ capacity is its maximum power at an optimum wind speed. This is the value commonly quoted for a wind farm’s ‘installed capacity’. How does this compare with the wind farm’s average power output? That is, what is the capacity factor of wind power?

BWEA

The capacity factor of a power plant is the ratio of the electrical energy produced in a given period of time to the electrical energy that could have been produced at continuous maximum power operation during the same period. For a conventional fossil-fuel power station, the capacity factor is determined by planned maintenance downtime, unplanned equipment failure, and by shutdowns when the station’s electricity is not needed. For wind and solar energy, power output is also determined by the availability of wind and sunlight. The maximum power output, or ‘installed capacity’, is a rather theoretical value that is rarely reached. It would be clearer to quote the mean power for solar and wind energy, but because peak power is more commonly quoted, it’s important to know the capacity factor as well, to make sense of the peak numbers.

In an earlier post I looked at the difference between peak power and mean power for solar panels. Here I’ll repeat that process for wind energy.

A wind turbine’s power output depends on the wind speed:

Most wind turbines start generating electricity at wind speeds of around 3–4 metres per second (m/s), (8 miles per hour); generate maximum ‘rated’ power at around 15 m/s (30mph); and shut down to prevent storm damage at 25 m/s or above (50mph).

The turbine’s power output varies as the third power of the wind velocity. That is, if the wind velocity doubles, the power output rises eight-fold [1].

Power output depends critically on the location of the wind farm. A site with a steady 30 mph wind would be ideal. The ratio between the ideal maximum power output and the average power output achieved under real operating conditions is the capacity factor.

Table 1 shows installed capacity, mean power and capacity factor for wind energy in several countries, and it shows the global average. All the data are from key primary sources.

Table 1. Installed capacity and capacity factor for wind energy installed capacity mean power capacity factor MWe MWe Morocco Amogdoul wind farm [2] 60 23 38.1% U.S. (total) [3] (a) 6740 1941 28.8% U.K. (off-shore) [4] (b) 304 74 28.7% U.K. (on-shore) [4] 1651 408 27.2% Denmark (total) [2] [6] (c) 3128 755 24.1% Spain (total) [2] 11615 2534 21.8% Portugal (total) [2] [7] (d) 1022 202 19.8% Netherlands (total) [2] [8] (e) 1219 236 19.3% Germany (total) [5] 20622 3482 16.9% India (total) [2] [9] (f) 4430 704 15.9% Italy (total) [2] [10] (g) 1718 268 15.6% Poland (total) [2] 153 22 14.6% France (total) [2] [11] (h) 757 109 14.5% World (total) [2] [12] (i) 59051 11559 19.6% Table is sorted by decreasing load factor, with World figures at the bottom; Data are for 2006 except where noted. Notes: (a) U.S. data are for 2004; (b) U.K. load factor is for average installed capacity for 2006, not the end-of-year capacity; (c) Denmark data are for 2005; installed capacity from ref [2]; mean power from ref [6]; (d) Portugal data are for 2005; installed capacity from ref [2]; mean power from ref [7]; (e) Netherlands data are for 2005; installed capacity from ref [2]; mean power from ref [8]; (f) India data are for 2005; installed capacity from ref [2]; mean power from ref [9]; (g) Italy data are for 2005; installed capacity from ref [2]; mean power from ref [10]; (h) France data are for 2005; installed capacity from ref [2]; mean power from ref [11]; (i) World data are for 2005; installed capacity from ref [2]; mean power from ref [12]. Some Conclusions

The global average capacity factor for wind farms is just under 20%. Wind farms on the very best sites, such as those in the North African desert, can achieve capacity factors approaching 40%. France has an exceptionally poor wind resource.

The countries with well exploited wind resources, such as Germany and Spain, tend to have lower capacity factors. That’s because the best sites get developed first, and subsequent wind farm development goes onto progressively poorer sites, thus reducing the average capacity factor. The U.S. has a large installed capacity, yet it has a high capacity factor too, indicating that it has used only the very best sites so far, and still has a very large wind resource left to exploit.

The European Wind Energy Association has set a target for European wind energy for 2010 of 180 GW installed capacity and 500 TWh/yr (57.1 GW) output [13], corresponding to a 31.7% capacity factor. This is greater than the capacity factor of Europe’s existing installed capacity, and much greater than the global average. Unless they’ve saved the best sites till later, this seems to be a rather optimistic assumption about the future capacity factor.

The total energy contribution from wind power remains very small. The total global wind power output in 2005 was 11.6 GW [12]. This is only as much as four large coal-fired power stations. For example, the UK’s Drax coal-fired power station delivered 2.9 GW of average power in 2006 [14].

Related Posts

• The capacity credit of wind power

References

1. Wind Turbine Technology, BWEA Briefing Sheet, British Wind Energy Association (2005) (WebCite cache)
2. Global Wind 2006 Report, Global Wind Energy Council (2007) (WebCite cache)
3. Wind Web Tutorial, American Wind Energy Association
4. Capacity of, and electricity generated from, renewable sources, Annual tables: Digest of UK Energy Statistics (DUKES), BERR (2007) (WebCite cache)
5. Wind Power, Federal Ministry of Economics and Technology, Germany
6. Renewables and Waste in Denmark in 2005, International Energy Agency
7. Renewables and Waste in Portugal in 2005, International Energy Agency
8. Renewables and Waste in Netherlands in 2005, International Energy Agency
9. Renewables and Waste in India in 2005, International Energy Agency
10. Renewables and Waste in Italy in 2005, International Energy Agency
11. Renewables and Waste in France in 2005, International Energy Agency
12. Renewables and Waste in World in 2005, International Energy Agency
13. EWEC 2007 Review, European Wind Energy Association, (page 25) (2007) (WebCite cache)
14. Principal performance indicators of 2006, 2006 Annual Report and Accounts, Drax Group plc (2007) (WebCite cache)

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## 26 Responses to “The capacity factor of wind power”

• Angela Taylor:

A question about India came up before. The Global Wind Report
mentioned in my reply to Kolappan has a short section on India, but
I don’t have any detailed region-by-region data.

• Terry Engle:

What I need is PC+DATA CARD with unlimited internet access.This
may not cost Rs.50k(1000 US\$) as one time investment and another
Rs.100k for the whole work done(2000 US\$).

• Carolyn Ferguson:

The low capacity factor may be linked to the limited
geographical extent of the early installations, but that’s
really speculation on my part.

• Kellie Shorey:

The newest trend is to produce low and medium wind speed wind
turbines such as Vestas V112 where full production is in case of 10
m/s. Also this will contribute to increase the capability
level.

• Robert Lowe:

It therefore could be usefull to highlight some capacity factors
of recent wind parks with 2MW or better turbines.

• Susannah Chaney:

Capacity Factor Calculation for potential locations in India is
a challenging task,which I have taken up like Vivek requested and
would like to know if anybody can support this work
financially.

• William Flores:

You’re looking in the wrong place, that’s not what
this post was about.

• Danny Cleland:

Let all of those who are interested please let know,so as I can
take it forward.I have already started my work in this regard.

To get individual product pricing and service contract costs,
your best bet is to contact the turbine manufacturers
themselves.

• Tyrone Mckenney:

Hello Vivek,> I was just wondering if there was a site that put up the
capacity factor of individual regions in India. Thank you.

• David Robertson:

1) Capacity factor is very useful, but is often mistaken for the
total amount of time a wind turbine operates (that is, if the CF is
25%, people think the turbine is only producing electricity 25% of
the time). In reality, at most sites, it will be generating a much
higher percentage of the time, but at less than its peak output
level.

• Maria Doss:

2) The Euro projection assuming higher CF likely includes
offshore sites, which have higher average wind speeds. North Europe
has an excellent offshore wind resource.

• Mary Reese:

3) You mention that wind’s contribution is still very
small and cite generation of 11.6 GW in 2005. However, generation
is measured in watt-hours (watts delivered over time), not in
watts. This month, global wind energy should pass 100 GW pf
installed capacity.

• James Feldman:

One important remark though:
the capacity factor will increase despity the fact that the best
sites are taken. The current capacity factor includes facts and
figures about many older and smaller wind turbines. Modern turbines
deliver power over a broader range of wind conditions and are often
placed on higher sockets. These two factors allow to obtain better
capacity factors, even at less ideal sites on land. This fact may
also explain the lower capacity factor for India; maybe the average
size of the wind turbines is smaller?

• Susan Compton:

>>How about giving me an understandable one? Two? What
would they cost? Please do this in line item form. For S.W.
minnesota. cost of unit annual repairs &service transmission
lines

• Robin Flemming:

hello,
I was just wondering if there was a site that put up the capacity
factor of individual regions in India. Thank you.

• Melvin Dickerson:

The technology in the wind industry is not only developed only
within this branch. As an example power electronic devices can be
taken in consideration. Power converters used in wind turbines are
commonly used in other branches of industry.

• Angela Harris:

In my opinion because of mentioned remarks and other advantages
the wind power industry will be rapidly developed in the nearest
future. I am wondering what will happen when HVDC systems will be
applied in the industry and China would build few 1GW wind farms on
the northern part of the country?

• Jeanette Taylor:

The situation in the wind power marked changes rapidly and
numbers tips the scale to the wind power industry advantage. Of
course it is strongly dependent on the current political situation
and trends. As it was mentioned the wind and the physical lows are
the same.

• Beatrice Denton:

“The countries with well exploited wind resources, such as
Germany and Spain, tend to have lower capacity factors.
That’s because the best sites get developed first, and
subsequent wind farm development goes onto progressively poorer
sites, thus reducing the average capacity factor.”

• William Hamby:

It was not mentioned that installing wind turbines capacity all
over the word is purposeful due to fact that wind energy is for
free. It should be also emphasized that obtaining a power system
with many dispersed renewable sources of electricity increases
reliability.

• Ayesha Dawson:

Thats a lot of impresive numbers.
How about giving me an understandable one? Two?
If you had a developement of 100 -2 megawatt state of the art wind
towers.
What would they cost? Please do this in line item form. For S.W.
minnesota.
cost of unit
annual repairs &service
transmission lines
actual number ofKWH produced in a year.

• Harold Ball:

Hello Mr. Gray,
Thank you for taking the time to comment.
Re your point (3), I’m quoting average power (total
energy over total time) for the year.
The world-total numbers are taken from the IEA data linked to in
the references (ref 12), the US numbers are from your own web-site.
I guess these are among the most authoritative sources available,
so I’m reasonably confident I’ve got the numbers about
right (barring transcription errors).

• Laura Freeman:

I’m not familiar with India’s installations in any
detail, but in general site selection is crucial, and as installed
capacity grows, progressively poorer sites get used, hence lowering
the average.

• Bill Burns:

Hmmm, sorry, was thinking about this some more. Generation IS
sometimes reported in AVERAGE megawatts, which is what is probably
going on with the IEA report you cite. 11.6 average GW (GWa)
equates to just over 100 billion kWh, which sounds about right. In
that case, global wind generation this year should be roughly
double what it was in 2005.–Tom Gray, AWEA

• Albert Lytle:

In our area we are blessed with steady trade winds, largelly
unidirectional,day
and night,all year long ,in specific areas it is concentrated by
mountains and after measuring we believe we will reach around 50%
capacity factor,as more developers
explore the trade wind belt capacity factors should rise