Wind power by the numbers

We are constantly being told that wind is now a large-scale producer of electrical power, with much talk in the green press about the thousands of homes it is often said to light and heat. Well, a little knowledge is a dangerous thing and such praise for wind turbines demonstrates that precise point.

Let me explain: The power that a wind turbine might produce under ideal circumstances is known as “nameplate capacity”, and to understand that, let’s consider a notional wind farm with, say, 150 towers, each topped by 2.5MW generator. That would give us a theoretical total output of 375MW.

Seldom mentioned is the fact that wind generators produce, on average, barely 30% of that nameplate total. This much lower number is referred to as the “capacity factor” (CF). The difference between nameplate and capacity is due to the fact that, as you may have noticed, wind is variable and does not always blow at the required speed to keep the blades turning, the turbine spinning and all those homes supplied with electricity. With no wind, the blades fall still; similarly, when the wind is too strong, they “feather” and also stop rotating. Let us now look at some actual figures, which will demonstrate just how little electrical power wind plants make available for actual consumption. For reasons of simplicity and access I will use Wikipedia as a reference for total wind power plants in the U.S.

This link quotes the total installed nameplate capacity for all wind power in the US as 51,630MW, which may seem a very impressive number. Compare that with a large nuclear plant (or coal-fired power station, for that matter), where a typical nameplate capacity is 2000MW. Wind turbines come in many sizes, with the current generation of individual units typically capable of 2.5MW to 3MW, substantially larger than earlier models. I will use an average generator size of 2MW, and with that overall nameplate capacity of 51,360MW we get a ballpark figure of 26,000 wind towers. In fact, since earlier generators were smaller, the actual number of US wind towers is more than 40,000 as shown at this link.

So, because this comparison is with nuclear plants, let’s then look for a total nameplate capacity, and for this I will use the US Energy Information Administration (EIA) site and the chart, provided at this link, detailing the nameplate capacity for all electrical power generation in the U.S. This reveals total nameplate capacity for nuclear power in the US is 106,731 MW. What we also see is that wind is listed as having almost half the nameplate capacity of nuclear. (51,630 MW). So wind is large contributor, right?

Not so fast! While you are inspecting that same chart, look at the total listed for Overall Nameplate Capacity (ONC), which is stated as 1,138,638 MW. From this we can work out the percentages of the total nameplate capacity for both wind and nuclear.Wind comes in at 4.53% of the total and nuclear represents 9.37% of ONC. Again, those figures make it look like wind power is making major inroads into total U.S. power generation.

And, once again, a little knowledge deceives. Remember, this is nameplate capacity, not the real-world power being generated for consumption — the power actually delivered to the grid. However, we do have accurate data for that, drawn from the EIA’s huge database, and as of December, 2012, the available information was only three months old.

Let us now compare the actual power delivered for consumption from both wind and nuclear.

This is the link for the page that shows the overall data and at that page I will point you to the figures for nuclear, and also the total overall power figure. This is the link for the page that shows the data for renewable power, and at that page we find the figures for wind power.

At that first page look at the figures for the actual total generation (power delivered to the grid) from nuclear plants (scroll to the bottom of the chart and they are the figures along the line headed Rolling 12 Months Ending in September). The nuclear figures are the sixth from the left, shown as 783,940 GWH (GigaWattHours), each GWH being the equivalent of 1000 MWH.

Look next at the far right and you’ll see the total power delivered to grids for consumption from every power source in the U.S. That figure is 4,051,044 GWH.

Now, from those figures, we can work out the percentage of actual power  delivered by nuclear, and it comes to 19.35%. Compare that with the percentage mentioned earlier for nameplate capacity, which was 9.37%, and the discrepancy demands an explanation. After all, how could nuclear be supplying more than twice the power of its listed theoretical maximum?

The answer isn’t too hard to nut out: Nuclear’s actual contribution is so much higher because other, less consistently productive sources – like wind, for example — fall short. According to the EIA’s numbers, nuclear plants are producing reliable power almost 90% of the time, pretty much the only interruptions coming when they are offline for fuelling and maintenance.

See how using the nameplate capacity figure is misleading, vastly understating the actual level of power generated by nuclear? Use that smaller nameplate figure and it gives the impression that nuclear is not much of a contributor, when the fact of the matter is that it is the third-largest electrical power delivery source in the U.S. after coal- and gas-fired generation.

Now, do the same exercise for wind. At that second link, you will see the rolling, 12-month figure for wind is 135,506 GWH. After comparing that to the total power delivered, the percentage for wind comes in at only 3.34%, vs. the nameplate total of 4.53%.

What is interesting here is to compare both overall nameplate figures with power-delivered figures: nuclear delivers almost six times the power while being only twice the size in terms of nameplate capacity.

I mentioned earlier the variability of wind power, and cite again the capacity factor (CF). Wind’s CF, going on this data, is currently running at almost 30%. (29.9%)  Over 12 months, and bearing in mind the total number of wind generators, that means a rule-of-thumb average per unit of just seven and a quarter productive hours per day.

And it gets worse – or just plain silly, depending on your capacity to be amused by human folly. Because of that inherent variability, wind power cannot be counted on to be available when needed, so conventional generating plants cannot be turned off if blackouts are to be avoided. What green advocates never seem capable of remembering is that conventional power plants are not wall switches; rather, they take hours to power up and power down. To be ready to make up for wind’s variability, they must be kept operating pretty much all the time.

Bottom line: wind plants provide power that isn’t needed and can never replace traditional methods of generation. As to the power they do provide, 40,000 turbines equal just nine nuclear plants.

Wind-power advocates may be inclined to accuse me of writing this in order to besmirch their favourite technology. They would be mistaken. I have no need to make wind generation look bad. It does that all by itself

Anton Lang was an electrical and electronics specialist and instructor with the RAAF. He blogs often on energy issues and green myths at PA Pundits