Are there limits to large scale wind power?

A new paper has been published which raises questions about the amount of electricity that can be generated by large scale wind farms. You can get a free copy of it here, as well as watch a video by the lead author David Keith. The conventional view is that, on average, you can generate between 2 and 3 Watts per square metre in wind farms (note this is electricity generated not capacity of wind farm per square metre). Adams and Keith provide references in their paper that can be checked, but for a quicker (and paywall free) explanation you may want to read this blog post by David MacKay.

What Adams and Keith suggest is that for wind farms greater than 100 square kilometres the power density appears to saturate at about 1 watt per square metre, essentially the turbines have a slowing effect on the wind. They use mesocale modelling for this, however I am not a climate scientist so will not embarrass myself by either trying to explain the model or criticize it.

For some context energy use in a densely populated country such as the UK is just over 1 watt per square metre. A lower power density of large scale wind will mean a large chunk of land must be covered in wind turbines to meet a significant portion of energy demand. Simple back of the envelope calculations show that this could lead to problems in some countries. Take Japan, which is 60% forested. If large scale wind does saturate at 1 watt per square metre, then there probably is not enough land in Japan for onshore wind to provide half of its energy.

Let’s however consider what this could possibly mean in practical terms. 100 square kilometres is in fact the exact size of the soon to be opened first phase of the London Array offshore wind farm, which is currently the world’s largest offshore wind farm. The total capacity of the wind farm is 630 MW. If the power density only turns out to be 1 watt per square metre then it will have a load factor of 16%. This is about half of what I expect the wind farm is hoping for, and much less than the current average of about 27% for UK wind farms. The London Array will be operational in a couple of months according to its website, so we can probably know for sure within a year if the model of Adams and Keith is something we should be immediately concerned with.

What about existing and operating windfarms, can they tell us anything? Europe’s largest operational windfarm is Whitelee Windfarm, just outside Glasgow, and I can see it every day on my walk in to work. The operational part of it has a capacity of 332 MW, and covers 55 square kilometres. Its current load factor is 28.7% (taken from the anti-renewables lobby group REF’s website, though their data seems reliable). So the energy density is about 1.7 watts per square metre, and if we considered the 100 square kilometre region it is contained within it works out at 0.92 watts per square metre. The wind farm is currently expanding from 332 to 539 MW, with the full 539 MW expected to be fully operational next month. Again, we should know in a year if the density will be much higher than 1 watt per square metre, but it would be surprising if it was not. And certainly the finances of the wind farm will not be in good shape if it is not.

Whitelee Wind Farm
Whitelee Wind Farm

There are a few wind farms in America with total capacities greater than 500 MW. Most of them appear to wind farms split over multiple sites, so aren’t particularly useful for testing Adams and Keith’s results. However Shepards Flat Wind Farm is more or less perfect. It covers 78 square kilometres and has a total capacity of 845 MW. A power density of 1 watt per square metre would give a load factor of about 12% for this wind farm, when something like 30% might be expected. Shepards Flat opened in September 2012, so again we should know quite soon if Adams and Keith’s result holds for functioning wind farms.

About these ads

17 thoughts on “Are there limits to large scale wind power?”

  1. Robert, good post as usual. Before I comment on why I think the entire issue is a distraction, here is some data from Baltic 1: roughly 7 square kilometers, 48.3 MW, estimated 44 percent capacity utilization (word is that power production was 20 percent above that already astonishing level in 2012, but we’ll take the more conservative figure), which according to my math comes out to be three watts per meter.

    Having said that, I’ve never seen this kind of discussion in Germany. The researchers are talking about the “wake effect,” which is important for wind farm planners, but does anyone care about watts per meter? The bigger issue is what the potential will be given land constraints. If the wake effect is a problem, you spread the turbines out further, which requires more space. Where is this a problem? Tiny Denmark gets 40 percent of its electricity from the wind already.

    I’d say the real issue is grid integration (accommodating for fluctuating wind power production), not any lack of space.

    1. Craig

      Before describing the paper as a distraction you might want to understand what it is saying first. It is talking about the reduction of power density in large scale wind farms. What happens in a 7 square kilometre wind farm is neither here nor there.

      I also don’t think your “no lack of space argument” has much merit for densely populated. The UK and Germany both have energy use at over 1 watt per square metre. Clearly if the power density of large scale wind is lower than expected then the problem of opposition to wind due to its visual impact will be much bigger than expected. The basic arithmetic indicates that there is a land use problem for wind in densely populated countries, whether we like it or not.

  2. If we stick with electricity (as opposed to energy – because wind turbines produce electricity, not generally heat or motor fuel), then Germany has an average consumption of between 40 and 80 MW, so let’s say 60. The country apparently has 357,021 km2. Unless I made some mistake in my math (which would be nothing new), that looks like 0.168 watts per m2.
    Germany roughly gets 20 percent of its energy as electricity, so even taking energy as a whole only puts us at 5 x 0.168 = 0,84 watts per m2.
    You are certainly right that energy density makes a difference, and I’m glad to see the discussion focus on acreage without assuming that that land cannot be used for other purposes (wind turbines can be on farms or along highways; solar, on roofs). But I mainly find it intriguing that the discussion in German is so different than the discussion in English at times. The Germans mainly stress that we only need a small percentage of our land to produce a net surplus of renewable energy – exactly the opposite of what the paper seems concerned about. See for example: http://www.renewableenergyworld.com/rea/news/article/2012/12/schleswig-holstein-will-double-wind-capacity-on-land

  3. Thanks Craig

    To be more precise, Germany’s total energy use is 307159811 tonnes of oil equivalent (according to the World Bank http://www.gapminder.org/data/). Converting that gives just over 1.1 W/m^2.

    Using the same data source the value for electricity is 0.19 W/m^2.

    The key issue here is that you need to do something about the other 80%. There is no plausible way to decarbonize without electrifying a lot of things, so only talking about the land needed for current electricity needs is misleading.

  4. Robert, how can you translate tons of oil equivalent into watts? I think those are watt-hours.
    Above, the study talks about watts from wind farms as a part of the capacity factor – we are not talking about watt-hours.
    That’s why I took the average electric load (my ballpark figure of six BMW) instead of taking the roughly 600 TWh of electricity that Germany consumes. Do that, and you do indeed get a different number – but also expressed in watt-hours, not watts.

    1. Craig

      If you know the number of watt hours for a year it is very easy to calculate the average number of watts that will supply that. After all a watt hour is just 1 watt times 1 hour.

      Robert

  5. “For some context energy use in a densely populated country such as the UK is just over 1 watt per square metre. ”
    I presume that is average annual power use. A watt is a unit of power, not energy. A kilowatt-hour, or a watt-second, is a unit of energy. One Watt is one Joule per second, so the Joule is a watt.second. A kilowatt-hour is therefore 3.6 mega-Joules. But the kWh is what your electric bill probably shows.
    My average power consumption is no guide to the amount of wattage that my connection to the power company has to handle. The pumped storage facility at Dinorwig in Snowdonia, on which my young brother was Chief Biologist before Thatcher demolished the CEGB, kept two turbines spinning in air when demand was below maximum, ready to release the water from the upper pond to take up sudden increases in that demand, as when popular TV programs inflicted a commercial upon their audiences, and large numbers switched on their electric kettles. simultaneously.

    If you add up the average power demands, you will not have capacity to meet those peaks. WIth wind turbines it is worse, because the demand you’ve been serving becomes a peak load when the wind driving the turbines drops. Let’s not forget that our strongest winds are usually “gusty”.

    1. Albert

      What on earth does UK pumped storage possibly have to do with this blog post?

      And I provided a link to back up my claim about energy density. Please read it instead if writing a lengthy off topic comment.

    2. And Albert

      If you continue to make off topic criticisms of wind power I will have no choice but to delete your comments. You posted a bunch in the last hour and it is a complete joke. I have no problem with you making anti wind remarks, but of topic comments like these are a total waste of my time.

  6. Consider a motor car that gets 30 mpg (US or Imperial gallons -oh hell!) and is driven 15,000 miles per year. That works out at 1.7 kilowatt-years of energy consumption. But if you translate horsepower, even the average that you use while at cruising speed, into kilowatts, you’ll find that it’s a lot more than 1.7 . A nuclear power plant, producing electricity, can very well offer you stored energy in the form of charged batteries, or according to the hydrogen enthusiasts, hydrogen. If Terawatt-hours are still numbers too big to grasp. I recommend Gigawatt-years. A typical coal burning electric plant produces about a gigawatt-year (GW-yr) of energy in a year. A typical nuclear power plant, when it consumes a kilogram (2.2lbs.) of the fissile uranium, or the plutonium that the neutron flux generates from the non-fissile, generates ten million kWh, or ten GWh. SO a GW-yr requires 24×365 kilograms of the fissile part of the fuel,and that’s the real nuclear waste. It is nothing compared with the carbon dioxed, or even the oxides of nitrogen and sulphur, for the same amount of coal or gas power production.

    1. Albert

      How about considering the issue of whether large scale may have less than expects power output? Currently your comments are as relevant as a comment about the relative qualities of cappuccino or latte as a morning beverage.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s