On a perfectly windy day…

Another thing I’ve leaned about wind energy: when the output of a wind farm is expressed as, say, “30 MW,” that means that the combined output of the turbines has a theoretical maximum of 30 megawatts. Which is to say that on a perfectly windy day with all the turbines operating at perfect efficiency a 30 MW wind farm would be generating 30 MW of electricity. Of course perfectly windy days are few and far between, so the output of a 30 MW wind farm is more often than not less than 30 MW.

Setting that aside, here’s how the economics of the publicly-owned Eastern Kings Wind Farm work: Maritime Electric has a contract to purchase all of the energy the wind farm produces at a fixed price indexed to the consumer price index. Currently they pay $78 per megawatt hour (a megawatt hour being 1 MW of energy for one hour). So on a hypothetical perfect day the return to the public purse (not accounting for paying down the capital costs of the wind farm) would be:

30 MW x $78 x 24 hours = $56,160

And in a hypothetical perfect year – all wind, all the time – the farm would return $20,498,400. In reality, because reality is less than perfect, the return is less than that – electricity sales were last reported at $8.2 million/year. Here’s the summary of the Eastern Kings Wind Farm from the last annual report of the PEI Energy Corporation:

An objective for this year was to improve turbine availability at the East Point Wind Plant, and thus increase electricity production from the facility. This was accomplished. Despite replacing all ten gearboxes, machine availability improved to 89.4% as compared to 81.0% in the previous year. This increase in availability resulted in a 10% rise in energy sales, from 78,738 Megawatt-hours in 2008-09 to 86,779 Megawatt-hours. The only other major disruptions were the repair of switch gear in a turbine and the replacement of all three blades on another turbine.

A 30 MW wind farm has 262,800 (30 MW x 24 hours x 365 days) theoretical megawatt hours of energy it can generate, meaning that in 2008-2009 the farm was operating at 33% of “perfection.”


Martin C's picture
Martin C on April 6, 2011 - 14:13

33% is pretty good, I seem to remember reading somewhere when I was researching my article that 30% is what most farms hope to achieve in a good year.

My rough estimates figure that a large wind farm would pay for itself in 6 or so years, after that the 20+ year lifespan of them would be profit (and cheaper energy for us). I really wish we’d have invested more heavily in wind in the past. Sure we were in a recession and the cost of oil was low, but that is all temporary. Typical short thinking in long term projects…

oliver's picture
oliver on April 7, 2011 - 23:10

I’m not so sure what has to be perfect or how realizable that 30MW is. It may be the mechanical power that the rotors deliver to their turbines under the wind conditions at which the system measurably peaks. Then the electric power that turbines put out is certain to be somewhat less, and the amount that gets to the grid to be tallied less again. Even then you might want to theorize more than the 30 MW theoretical maximum: Given the same system of towers, better turbines would generate more power from the same rotors under the same wind conditions; better rotors would transfer more power to the turbines from the same wind; and better rotors might even transfer it with more equal efficiency across the spectrum of wind speeds. But if 30MW is a number the company likes to toss around, then perhaps it’s not the mechanical power harnessed from the wind, because it’s against that measurement that their actual performance or yield would look the worst. I’d say to the extent the numbers make the performance look efficient, then the losses and inefficiencies of the system are being obscured/externalized.

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