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Large Wind Turbines

June 28, 2016
Paul Gipe

Fleet-Wide Typical Wind Energy Yields in California and the USA

Finally, after years of absence, California is again reporting on the performance of its wind farms. This is a remarkable, if not embarrassing, turnaround.

That California is doing so should not be newsworthy. All developed countries report on their wind turbine performance, and often in great detail. After all, you can’t gauge your progress toward renewable energy and climate goals if you don’t measure the results. But there’s been a dearth of reporting on California wind energy for many years.

We’ve had statewide totals, but we haven’t had the data by region or by wind farm. (You can see statewide generation on Thanks to digging by renewable energy analyst extraordinaire Robert Freehling, we now have access to data from 2014 for each wind farm.

What summary data tells us is that California wind farms generated 13.7 TWh from 6,200 MW of installed capacity in 2014. This results in a fleet-wide yield of 2,200 kWh/kW/yr. This is an important statistic for wind geeks.

In my new book, Wind Energy for the Rest of Us, I describe methods for estimating how much electricity typical wind turbines will generate. I also offer a simple method for energy planners and policymakers to use when estimating how much they can expect from a fleet of wind turbines. The number I use is 2,000 kWh/kW/yr. It’s conservative, but represents a good approximation. Modern wind turbines in windy regions will generate much more.

Here is a passage from the book.

“Like hydroelectricity that varies from one year to the next depending upon the amount of rainfall, so to does the average yield of wind turbines vary from on year to the next. While the 2,000 kWh/kW/yr is a good rule of thumb for the Danish fleet in the late 1990s and early 2000s, the yield from one year to the next varies from 2,000 to 2,500 kWh/kW/yr.

In windy countries, such as Ireland, average annual yields of 2,600 kWh/kW/yr have been reached. As the new IEC Class III wind turbines become an ever larger part of the existing mix of wind turbines, average annual yields will gradually increase as the turbines will generate more electricity per kW of installed capacity than older turbines installed in the 1980s and 1990s. This is a revolutionary development that will make wind energy easier to integrate with existing electrical grids.”

In Table 11-7 of the book, I present a range of fleet-wide typical yields for several different countries based on data I collected in 2012.

So the data for California in 2014 falls within the range I would expect.

However, as I note in chapter 11 and earlier in chapter 8, the introduction of new wind turbines with high specific area will gradually increase fleet-wide yields. We’ll get more electricity relative to installed wind-generating capacity and this is a very good thing. You can see this in the increasing yield of the wind turbine fleet in the United States, particularly in more recent years.

The fleet-wide average yield in the United States has grown from 1,600 kWh/kW/yr in the early 2000s to 2,400-2,800 kWh/kW/yr since 2010.

What this means is it will take less wind-generating capacity to meet renewable energy targets than once thought. This has far-reaching repercussions on renewable energy policy. The turbines will be bigger and will sweep more area, but there may be fewer of them and they will put fewer demands on transmission capacity. This is a revolutionary development.


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