WESTBOROUGH, Mass. — Increasing the export limits at a substation in eastern Maine’s wind country could save millions in power costs and reduce emissions, according to a draft report presented to the ISO-NE Planning Advisory Committee last week.
The study was requested by SunEdison, owner of two wind farms totaling 147 MW, Stetson and Rollins, that are served by the Keene Road substation.
The area around the substation has a peak load of 38 MW, which has dropped in recent years because of the closure of nearby paper mills.
The study found that increasing the export limit from the current 175 MW to 225 MW could save $1.4 million to $5.7 million in production costs annually by allowing additional wind development in the area and displacing more expensive hydropower. The savings are based on production costs of $0/MWh for wind, $5/MWh for hydro and $10/MWh for thermal energy imported from New Brunswick.
CO2 emissions reductions could range as high as 35 kilotons with the displacement of fossil fuel-fired generation, the draft says.
“The transmission investment could be worthwhile then, as these market efficiencies could be met,” said John Keene, senior counsel at SunEdison.
ISO-NE spokeswoman Marcia Blomberg said the analysis was an economic study of hypothetical system changes. The RTO has not developed cost estimates for the transmission upgrades that would be required to increase the export limits, she said.
Transmission Assumptions
ISO-NE is proposing changes in the way it makes transmission planning assumptions to reduce subjectivity and better reflect the likelihood of transmission constraints and generator outages.
In a presentation to the PAC, ISO-NE identified potential changes, noting that the current base case assumption that two generators are out of service “may be too pessimistic in some cases, too optimistic in others.”
The proposed changes are in response to a 2013 problem statement by the New England States Committee on Electricity (NESCOE), which said the current planning procedure allowed too much subjectivity in base case development.
“The degree of latitude in the current transmission planning procedure can create inconsistency within the region and between the development plans of various transmission owners,” NESCOE said.
The group proposed the use of statistical parameters to narrow the range of assumptions, which it said could increase the uniformity of transmission planning analyses among utilities and expedite state siting proceedings.
ISO-NE proposes using cumulative probability — the aggregation of the probabilities of specific conditions — to determine a “region of reasonable test conditions.”
Under current practice, disturbances are typically studied at peak load levels in steady-state analysis, which usually results in more pronounced thermal and voltage responses. The RTO uses 100% of the projected 90/10 summer peak load for the New England Control Area.
Going forward, the RTO proposes identifying the load and key resources that can stress transmission constraints and determine the likelihood of exceeding various combinations of load and unavailable generation. “This is similar to the installed capacity requirement, but not exactly the same way load is treated,” said Richard Kowalski, technical director of system planning for ISO-NE.
The RTO said its next steps include identifying the most appropriate weeks of the year and hours of the day to use in setting study periods and how to best model intermittent and distributed resources.
— William Opalka