Monday, June 22, 2009

Electricity in NH - Merrimack Scrubber (addendum)

In my earlier post about the Merrimack Station scrubber project, I mentioned that PSNH generally runs Merrimack at full capacity, since at any given time it can usually produce power for less cost than the other options.

I meant to include a neat graphic from PSNH's 2007 Least Cost Integrated Resources Plan that drives home the economics of electricity production, especially for PSNH, and helps explain why PSNH feels that Merrimack Station is too important to shut down.  

The graphic above shows how PSNH satisfies demand for electricity during a typical summer day.  MK1 and MK2 are the two coal units at Merrimack Station.  You can learn more about Newington and Schiller from this earlier post.  Next, VTY  stands for the Vermont Yankee Nuclear plant, which PSNH has a 3.3% stake in.  Finally, IPP stands for Independent Power Producers and represents long term contracts that guarantee power delivery to PSNH at fixed rates. 

The graph clearly shows the roles that various electricity sources play in providing the power needed on  a hot summer day.  Hydro, nuclear, coal, and wood plants provide the baseload generating capability.  Then, as demand increases during the day, plants with more expensive fuel sources, like Newington Station,  kick in.  

For the next 200MW of peak demand, PSNH turns to independent power producers, like Granite Ridge, LLC or Newington Energy.  Generally, it will already have contracts in place to make these purchases at pre-negotiated rates.  Finally, if demand increases beyond those contractual arrangements, PSNH may be forced to buy power on  the spot electricity market and pay whatever the market rates happen to be at the time.

So, if you're a utility like PSNH, it's best to know ahead of time how you're going to get the power to satisfy your customers' electricity demand.   Opponents of the scrubber project suggest that PSNH could just enter into more long-term contracts with Independent Power Producers to make up the difference, while PSNH believes that doing so would result in higher electricity rates.


  1. Fascinating. This doesn't show the "jet engines" - a couple of combustion turbines located (I think) at Merrimack Station that PSNH can crank up for short bursts of power. When talking to the Telegraph as part of their editorial tour during the scrubber debate, they made much of having to use those turbines occasionally, as evidence that Merrimack Station was vital.

  2. Hmmm. Good point. I wonder why the jet turbines aren't listed in that chart. I checked the Energy Information Database and it indicates that there are 4 Jet engine generators in the state. Two at Merrimack, 1 at Schiller, and 1 at White Lake. Each one can produce roughly 18 megawatts of electricity.

    As you indicated, because jet fuel is so costly, they're only used to satistfy peak demand for short bursts. I wonder if all the recent NG capability that's been added to the state in the past 5-10 years has made these turbines less economical than just buying on the spot market.


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