Commentary: When Location Rules the Grid

by Meredith AngwinMeredith Angwin

The Vermont Comprehensive Energy Plan calls for a great expansion of renewable electricity. Can we achieve it? Some of the difficulties the state may encounter came to light this summer in the Northeast Kingdom.

The biggest renewable project to come online recently is the Kingdom Community Wind Project — commonly known as Lowell Mountain — which is owned by Green Mountain Power. During the mid-July heat wave, the regional grid operator, ISO-NE, did not allow Lowell Mountain to put all of its power on the grid. The wind was blowing, but the transmission lines were running at full capacity, and the grid operator told Lowell Mountain that the grid could not accept all of its power. The wind farm had to back off and not generate as much electricity as it could. It was “curtailed” by the grid operator.

As you can imagine, this incident led to quite an outcry. First off, it didn’t look good for the future of renewables. While Lowell Mountain has been controversial, it has also been a showcase for major new renewables being built in Vermont. If Lowell can’t send all of its power to the grid, it doesn’t bode well for the future growth of renewables.

In response, Vermont Gov. Peter Shumlin wrote a letter to ISO-NE, asking why the grid operator had called upon the generating capacity of fossil-fuel plants but not that of Vermont renewables, pointing out that Vermont is very committed to renewables, etc., etc. Shumlin was clearly grandstanding. On a hot day, ISO-NE did what it is supposed to do: keep the grid functioning. To understand why that overriding concern led ISO-NE to shun power from Lowell Mountain, it’s helpful to realize that, in one regard, the grid is like the real estate market: It’s all about location, location, location.

ISO-NE’s first responsibility is to keep the grid meeting its physical and reliability requirements. It matches power generation with power use and avoids overloading lines. ISO-NE’s secondary responsibility is to dispatch power from generators according to various economic and contractual priority rules. These rules tend toward priority dispatch for renewables. (Though the grid operator is strictly fuel-agnostic, the rules tend to favor renewables.) However, such priority rules come second, after the grid’s physical constraints are met.

Those physical constraints are often about location, location, location.

Wind farms are usually located in rural areas, which generally do not have transmission lines capable of handling large amounts of power. In the case of Lowell Mountain, the nearest high-voltage lines also carry Hydro-Quebec and power from other sources. On a high-electricity-use day, these power sources fill the transmission capacity.

Transmission capacity in that area would have to be upgraded significantly to accommodate all the power generated by the wind turbines on a high-use day. At the time the Lowell turbines were built, it apparently was known that the turbine power sometimes would have to be “curtailed.” However, “curtailment” has happened more often than some expected. (That’s the simple version; it’s always more complicated on the grid.) There are other factors. Depending on the type of generator, its location and the transmission lines, additional equipment may be needed to match a generator to the grid. Lowell Mountain needs something called a synchronous condenser to “tune up” its output and match it to the grid. The Lowell Mountain developers persuaded the Public Service Board to let them connect to the grid without this expensive piece of equipment, but now the grid operator says that it will have to be installed. The condenser is now being built, and it will cost $10 million. With it, Lowell will be able to put power on the grid more often.

However, without additional upgrades of local transmission lines, Lowell may still be kept off the grid when power use is high. So, two upgrades would be needed for Lowell Mountain to have reliable access to the grid. Electricity consumers ultimately will pay for the work, but which consumers?

Green Mountain Power consumers will pay for the synchronous condenser, because GMP owns the plant. Determining payment for transmission line upgrades is more complicated because transmission lines are shared across states. If a transmission upgrade makes the entire New England system more reliable, Vermont ratepayers will pay about 4 percent of its cost. If an upgrade is considered to be only of local benefit, local ratepayers pay its entire cost. ISO-NE decides whether transmission lines are needed for grid reliability as part of its reliability planning process. At this point, it is unclear which group of ratepayers would pay.

Another question: Why is the system dealing with these problems now? Why did the Public Service Board authorize turbines without also requiring an adequate connection? For whatever it is worth, many other wind farms in other parts of the world have the same problem.

Which gets us back to location, location, location. Wind farms face some unique transmission challenges. Throughout the world, wind turbines are located in rural areas, often far from large transmission lines or large-scale users of electricity. Wind turbines also have highly variable outputs. If you build a transmission line in a rural area and build a line that is capable of taking a considerable amount of wind energy on a day when the grid is almost full, you are going to have to build an expensive line.

Building a transmission line that can always accept wind energy can be like building a freeway that is big enough to avoid congestion if a football game lets out at rush hour. We don’t do that. It would just be too expensive to build all roads big enough to avoid congestion for the infrequent occasions of abnormally high use. As a partial solution to this problem, the grid has location-dependent congestion fees.

Meanwhile, ISO-NE officials responded to Shumlin’s accusation with their own strongly worded letter. They said that Green Mountain Power knew full well that the Kingdom Community Wind Project did not meet all of ISO-NE criteria for full grid connection.

I am sure that Green Mountain Power (and others, such as the Public Service Board) must have known that the new wind farm wasn’t meeting ISO-NE connection criteria. Though such grid issues as congestion fees and synchronous condensers are arcane to most of us, there are many competent electrical system engineers who could have foreseen these problems. They almost certainly did foresee them.

What should we do now to put wind on the grid? Since Kingdom Community Wind is built, I think Green Mountain Power should take the steps necessary to be sure its energy gets on the grid more reliably. It will be expensive, but that is the only option.

However, the costs and whatever environmental impact those upgrades entail should be ascribed to the wind project. More important, these costs should be considered when other projects are proposed. That does not mean that other projects should not be built. However, Vermont now has experience with a large wind farm, and it should learn from this experience.

Meredith Angwin is a physical chemist who worked for electric utilities for more than 25 years and now heads the Energy Education Project of the Ethan Allen Institute.

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