Certain activities, such as improvements to the elective transmission expansion process, could help reduce the amount of wind power curtailments, Eric Wilkinson, external affairs with ISO New England (ISO-NE), told New England stakeholders in a June 28 memo.
Such improvements could help by allowing more efficient identification of marginal interconnections and transmission constraints. A more efficient elective expansion process would better complement the existing generator interconnection process, he said, adding that the possibility and nature of potential changes to interconnection studies is under consideration at ISO-NE.
While ISO-NE does not collect specific data related to the amount of time that any particular resource is curtailed, it has begun a process to collect indicators of curtailments related to wind generators. That data collection effort is part of ISO-NE’s enhanced wind power forecasting project, which, when fully operational, is expected to provide a better understanding of the magnitude of curtailments, Wilkinson added.
ISO-NE is also undertaking an initiative that will incorporate wind forecasting and wind resources into its processes, scheduling and dispatch services. The project will acquire external wind power forecasting services, create operator situational awareness displays, partially integrate wind into the real-time dispatch and maintain historical wind data for future use of the forecast service, auditing and other analysis. That project, Wilkinson added, is scheduled for implementation in the second half of this year.
After the wind power forecast integration project becomes operational, all wind resources will be required to provide real-time telemetry indicating current output and additional meteorological data, which will support ISO-NE’s short-term wind power forecast system and improve the system operators’ situational awareness during changing weather conditions.
Wilkinson also noted that when system operators need to communicate dispatch instructions or other information related to the operation of a wind resource, it is done by placing a telephone call to the resource, which is in contrast to the fully automated system that ISO-NE employs with such dispatchable resources as natural gas plants.
ISO-NE is also developing enhancements to the dispatch algorithm that will determine and communicate to each wind resource an output limit about every five minutes, which will be defined in ISO-NE’s tariff as a “do not exceed dispatch point.”
A wind resource will be able to operate at any output level between 0 MW and its output limit, Wilkinson added, noting that when design details are complete, ISO-NE plans to continue working with stakeholders to incorporate the dispatch enhancements for wind resources into the market rules.
Barring unforeseen difficulties, he said, implementation is expected in the first half of 2015.
At the start of 2013, there were about 700 MW of nameplate wind capacity installed in the six New England states, up from about 2 MW in 2005.
In 2012, wind provided about 1%, or 1,172 GWh, of the energy produced in the region, and more wind resources are on the interconnection horizon. As of April 1, Wilkinson added, 28 wind projects were in ISO-NE’s generator interconnection study queue totaling about 2,053 MW, or nearly half of the nameplate capacity in the queue.
In the region, most of the commercially operating wind resources are located in Maine, New Hampshire and Vermont, and tend to be located in rural areas. The transmission resources in those parts of the region were built to serve the native load, but not designed to accommodate the addition of generation sources or the movement of large amounts of power, Wilkinson added.
Wind resources have low operating costs and, therefore, it is nearly always economic for the region to have them operate to the maximum extent that wind conditions allow. Wilkinson also said that is true, expect when that maximum output level would jeopardize reliable operation of the system.
“Resources are less susceptible to curtailment if they interconnect in areas with particularly strong transmission infrastructure (generally closer to the load), or elect to install upgrades to the grid,” he said.
When the output from any resource, such as wind, jeopardizes reliability, curtailment may be needed, and ISO-NE, at times, needs to curtail wind resources to ensure that the bulk power system and/or sections of the system are not overloaded, and service to customers is maintained, he said.
Such factors as transmission constraints, interconnection choices and the technologies associated with wind generators can contribute to the need to curtail wind resources.
Transmission constraints, at the regional and local levels are the most significant cause of curtailments, he added.
Many wind resources elect to connect to the weaker parts of the New England bulk power system that were not originally designed to integrate large amounts of additional power supply. Wilkinson also said that those sites often have the best potential for wind power, but are usually found on portions of the transmission system with long stretches of 115-kV lines, or on lower voltage transmission facilities. Adding wind farms in those areas can result in transmission constraints.
Under FERC orders, wind resources generally are not required to provide the same basic voltage support capability that is required of other types of resources, unless studies determine that the capability is needed. Often, Wilkinson added, wind resources interconnect with a bare minimum of voltage support capability, therefore providing no additional strength or improved reliability margins to the transmission system.
He also noted that ISO-NE operates real-time and day-ahead energy markets, with the main purpose of the day-ahead market (DAM) being to serve as a hedge against potentially volatile real-time prices. Since wind resources are often unsure of their ability to produce specific amounts of power the next operating day, they tend to “self- schedule” and not participate in the DAM, he said.
Traditional resources typically participate in the DAM, have binding offers to sell energy and can be dispatched by ISO-NE in real-time. As a result, there may be times when, despite a wind resource’s availability to produce power, ISO-NE does not call on it since other resources that are already committed through the DAM will be sufficient to meet demand, Wilkinson said.