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Wind Energy: Curtailment by Any Other Name Would Be Ordinary

Meredith Angwin's picture
Carnot Communications

Former project manager at Electric Power Research Institute. Chemist, writer, grandmother, and proponent of nuclear energy.

  • Member since 2018
  • 81 items added with 27,591 views
  • Aug 7, 2013

Time for an opinionated blog post about framing and word usage. Today’s weasel-word: curtailment.

Lowell Mountain Curtailment

Wind Turbines in New Zealand

During the recent heat wave, Lowell Mountain wind farm was “curtailed” by ISO-NE, the grid operator.  In other words, although there was wind available, ISO-NE did not allow Lowell Mountain to send its power to the grid.

After this event, Vermont Governor Peter Shumlin sent a complaining letter to ISO-NE. Fossil plants were putting power on the grid but the wind farm had to stop operating temporarily.  Shumlin asked ISO: Doesn’t the grid operator understand the importance of Vermont’s move to renewables? NoteAndrew Stein has an article about Shumlin’s letter at Vermont Digger.  There are close to 100 comments.

Many people realize that the grid operator had good reasons not to dispatch the wind power during the heat wave.  For example, you might want to read the Burlington Free Press editorial: Not Ready for Prime Time. ( The idea is that renewables are not ready for prime time.) The Burlington Free Press is generally in favor of renewable energy.

Curtailment Means Dispatch

In the meantime— What the heck is curtailment? It means that wind was available, but the grid operator did not allow the wind farm to put power on the grid.  In other words, the wind farm was not “dispatched.”  Dispatch is the fate of most plants on the grid.

The rules for dispatch include physical imperatives:

  • matching load
  • not over-loading transmission lines
  • taking into account how quickly various plants can come on-line.

Secondary rules for dispatch include economics and other non-physical issues:

  • dispatching the least expensive plants first
  • giving renewables a favored position in the line-up.

To keep the grid in balance, the physical imperatives take precedence.

However, the non-physical issues are also part of dispatch.  For example, coal is now more expensive than natural gas.  Five years ago, our local coal plant, Merrimack Station,  ran 75% of the time. Today it runs about 30% of the time. Merrimack Station is no longer one of the least expensive power plants.  It’s almost a peaking plant, nowadays.  (Jeremy Blackman, Concord Monitor, Extreme Weather a Testament to Bow’s Plant Relevance?)

Yes, even coal plants only run when dispatched.

Wind Turbines and the Weasel Word

Wind turbines have been high on the list for  dispatch, because they are renewables. However, dispatching renewables is a secondary issue, not a physical imperative. Despite this fact, in my opinion, the turbine owners have developed a serious case of entitlement.   If the wind turbine doesn’t get dispatched, someone is going to hear about it from the Governor.

What an attitude!  This attitude isn’t good for the future, either.  The Vermont Comprehensive Energy Plan says that 90% of all our energy is supposed to come from renewables.  Does this mean that people will use the power whenever the renewables can send it?  Perhaps we will have alarms in our house: “It’s 2 a.m. and the turbines are spinning.  Time to do your wash and bake some goodies.” Or are the wind turbines willing to be dispatched, just like a power plant?

In my opinion, the first thing we can do to encourage the wind farm owners to understand their place on the grid is is—we can stop using the weasel word, curtailment.  We can call the situation what it is. “Due to inadequate transmission capabilities in the area of Lowell Mountain, the wind turbines were not dispatched.”

There.  Doesn’t that sound better?

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Nathan Wilson's picture
Nathan Wilson on Aug 8, 2013

There is a downside to low curtailment too.  The DOE NREL modelling suggests that there will not be sufficient economic incentive to add energy storage to the grid until there is significant curtailment.

Scott Shugarts's picture
Scott Shugarts on Aug 8, 2013

During times of peak demand the grid (wiring infrastructure) has to carry as much electricity as it physically can.  The problem with wind and other renewables is that they are not constant.  A sudden drop in wind or failing of the sun (clouds or nighttime, not a supernova) can cause fluctuations, dropping the energy flowing through the grid to below capacity, and disrupting power availability through the grid (and other grids too, depending on interconnectivity).

I think renewables should be the first choice when we have the luxury of alternating between sources to avoid fluctuations.  


As far as the problem with producing wind energy (changing the landscape, noise for the residents, &etc), whenever energy is produced there will always be pollution.  Be it the land pollution associated with gas and oil drilling, the air pollution from burning coal, the radioactive material from nuclear fusion, or even the noise pollution of wind turbines.  It’s a matter of picking your poison.

Jean-Marc D's picture
Jean-Marc D on Aug 8, 2013

“It’s 2 a.m. and the turbines are spinning.  Time to do your wash and bake some goodie”

There’s a very old traditional song in France, “Meunieur tu dors, ton moulin va trop vite” => “Miller, you fell asleep, your mill is going too fast”.

That’s exactly reflective of that, the millers could never get a good sleep as they couldn’t control when the wind would start blowing and they could have to get to work any time of the day or night.

Meredith Angwin's picture
Meredith Angwin on Aug 19, 2013

Thank you for the link and the comment.

Curtailment is a word used within the industry for one stage of the dispatching and un-dispatching (making up a word here) of power plants.  However, when it is used by a politicians as part of an attack on ISO for following the rules of dispatch, THEN it is a weasel-word, in my opinion.  

Governor Shumlin’s whole point was that ISO should be nicer to wind energy, despite the problems on the grid.  He was grandstanding. HIs use of the word “curtailment” was part of his rhetoric. 


Meredith Angwin's picture
Meredith Angwin on Aug 19, 2013

Thank you for the link. I didn’t know that song, and I found several cute versions on YouTube!

Yes, you are right. Many of the problems with wind are not exactly “breaking news.”  

Meredith Angwin's picture
Meredith Angwin on Aug 19, 2013


Thank you, as ALWAYS, for your fact-filled reply! Lowell has claimed twice as much power as they have produced. 

As they say: everyone is entitled to their own opinion, but not to their own facts.  You supply the facts that we all need. Thank you.


Meredith Angwin's picture
Meredith Angwin on Aug 19, 2013

Thank you for the comment.

I agree that all forms of energy have their drawbacks.  However, one criteria could  be whether the energy is useful to the grid.  If it isn’t useful, then why tolerate the drawbacks?

On the other hand, in this case, upgrading the grid could take care of at least some of the problems with Lowell Mountain.


Bas Gresnigt's picture
Bas Gresnigt on Jan 22, 2015

Such unnecessary row shows the primitive state of the New England rules and ISO.

Seems to me that New England’s policy makers and ISO should spend a visit to German regulator dena, and a grid operator (e.g. Tennant) in Germany.
Denmark, with 40% wind produced electricity, is also advicable.
They can learn a lot.

In Germany renewable have priority, a.o. because that avoids GHG.
But the grid operator can directly remote (partial) curtail / adapt production if necessary for grid (e.g. stabilitiy) reasons.*)
The grid operator has to compensate all revenue loss to the wind/solar operator above 3% of the uncurtailed revenue.
If the grid doesn’t have enough capacity to transport the wind power, than of course the grid operator has to compensate assuming the grid operator was noticed in time with the correct info. Because the grid operator is defaulting.

*) Production adaptation (incl. curtailment and bringing in) of solar and wind, has the benefit that it is fast (though wind somewhat less) and extremely easy. The operator or computer at the grid control center just turns a switch.
So grid operators are inclined to do that first. 

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