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A Wind Farm the Size of South Carolina?

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To satisfy demand for energy in the United States with wind power would require a wind farm the size of South Carolina.


My brother asked whether I had any idea how much ground would have to be covered with wind or solar farms to cover the energy consumption of the USA.

In reply, I produced the following analysis. This is obviously “back of the envelope” analysis, so be cautious how far you run with it. Still, I think it is interesting. Because some of the facts seem a bit counterintuitive, after each fact I’ve cited the source from which I got it. As you read, be sure to notice that wind power produces only electricity, yet I am comparing it to total energy consumption, which includes petroleum used in transportation.

According to Wikipedia, as of 2013 the largest wind farm in the world was the Alta Wind Energy Center, located on the eastern side of the Tehachapi Pass in the Mojave Desert. It is sited on 3,200 acres, has a rated capacity of 1,547 MW, and has a capacity factor of 30%.

https://en.wikipedia.org/wiki/Alta_Wind_Energy_Center.

A word here is needed to explain capacity factor. The rated capacity of a wind farm is its theoretical maximum generating power. However, because the wind doesn’t always blow, and turbines sometimes need maintenance, wind farms never generate their rated capacity. The average percentage of rated capacity that they actually generate is called their capacity factor. The Wikipedia article cites Alta’s capacity factor as 30%. The National Renewable Energy Laboratory says that the average capacity factor of onshore wind farms is 30-40%, with the best guess at about 37%. Capacity factor has been increasing due to improvements in turbine technology. I will use NREL’s figure.

http://www.nrel.gov/analysis/tech_cap_factor.html.

Thus, the actual capacity of Alta would be 1,547MW * 37% = 572 MW.

There are 8,760 hours in a year. Thus, the yearly production at Alta would be 572MW * 8,760 hours = 5,010,720 MWh.

Thus, production per acre would be 5,010,720 / 3,200 = 1,567 MWh per year per acre.

In 2014, total energy consumption in the United States was 98,385.2 trillion Btu. = 28,833,750,564 MWh.

http://www.eia.gov/state/seds/data.cfm?incfile=/state/seds/sep_sum/html/rank_use.html&sid=US.

Thus, the number of acres required to meet that consumption would be 28,833,750,564 / 1,567 = 18,401,574 acres = 28,752 square miles.

How to put that in context? It is a square 170 miles on each side, or approximately 40% the size of Missouri, or roughly equal to the size of West Virginia or South Carolina. You wouldn’t want to build one contiguous wind farm, but even if you did, it would fit in West Texas, the deserts of California, or the eastern plains of Montana with ease.

Now, Alta is located in the Tehachapi Pass, which has the strongest wind resource in the nation. Wind farms located elsewhere would be located in weaker wind resources. Further, because the wind does not always blow in a given location, you would have to build excess capacity elsewhere and power storage to cover those occasions, meaning that the actual land required would be somewhat larger than my estimate. Still, it is a starting point, and it gives some sense of the size of the task involved.

Before you boggle at the size of the task, think of our current power generating infrastructure and how long it took us to create it. In 2014 there were an estimated 7,644 power plants in the USA.

https://www.eia.gov/tools/faqs/faq.cfm?id=65&t=2.

The first generating stations supplying power to the public were built in 1882, meaning that it took us 132 years to get to where we are now.

https://en.wikipedia.org/wiki/Power_station.

We have a big job in front of us, but if we give it our best effort, what might we be able to accomplish?

In the next post, I will construct a similar analysis for solar photovoltaic.

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