ISO Makes Highly Nuanced Prediction of "Adequate" Power for Summer


New England is expected to have sufficient resources to meet consumer demand for electricity this summer under typical weather conditions, according to ISO New England Inc., the operator of the region’s bulk power system and wholesale electricity markets. Tight supply margins could develop if forecasted peak system conditions associated with above average hot and humid weather occur. If this happens, ISO New England will take steps to manage New England’s electricity supply and demand and maintain power system reliability.

This summer, under typical weather conditions, electricity demand is forecasted to reach 24,605 megawatts (MW). Above-average summer weather, such as an extended heat wave, could push demand up to 26,421 MW.

Planning for the summer

ISO New England prepares short-term forecasts for the summer and winter seasons, taking into account estimated contributions from all resources, including those with and without an obligation through the capacity market to supply electricity; unplanned resource outages; imports from neighboring regions; and resource additions and retirements. These estimates help inform ISO New England’s planning on how to operate the grid during the upcoming summer season.

These forecasts also estimate consumer demand under a variety of weather conditions. Average summer weather is used to develop what is known as the 50-50 forecast, meaning there is a 50 percent chance that peak demand will be above or below the forecast. Above-average heat and humidity are used to generate what is known as the 90-10 forecast, which means there is a 10 percent chance that peak demand will surpass the forecast.

Tools in place to maintain reliability

Though ISO New England expects the region to have adequate supplies of electricity this summer, conditions could force system operators to take action to maintain system reliability. ISO New England operators have many tools at their disposal to maintain the overall reliability of the power system. These well-established procedures protect the region in the event of an unexpected power plant or transmission line outage, an extended heat wave that results in increased consumer demand, fuel supply issues, or emissions limitations that affect the amount of electric generation available, or a combination of these factors.

Procedures to deal with such issues include importing emergency power from neighboring regions, calling on power system reserves, and asking businesses and residents to voluntarily conserve energy. In severe events, system operators may be forced to call for controlled power outages to protect the overall grid. Climate change has caused weather to become more volatile and less predictable, increasing the potential for system operators to resort to these actions.

How the region will meet this summer’s electricity demand

More than 30,000 MW of capacity is expected to be available to meet New England consumer demand for electricity and required reserves. ISO New England employs a variety of resources to meet demand: generators that produce electricity, using fuels such as natural gas, nuclear, oil, coal, hydro, biomass, wind, and sun; demand-response resources that reduce their energy use; and power imported into New England from New York and Canada.

This summer’s forecasts incorporate the demand-reducing effects of more than 1,900 MW of energy efficiency measures. This decrease is made up of resources that are designed to save electricity across many hours, but cannot change the amount saved in response to instructions from system operators. Examples include the use of energy-efficient appliances and lighting, and advanced cooling and heating technologies.

The forecasts also include a reduction of just more than 980 MW during the peak hour that can be expected from the region’s behind-the-meter solar photovoltaic (BTM PV) installations. Though New England has over 5,400 MW of BTM solar PV installed, these systems produce their highest output in the early afternoon hours. The increase of solar power in New England has, in effect, pushed the peak hour of grid demand later in the day, when the sun is lower in the sky and production from solar PV systems is also lower. Rather than peaking during the mid-afternoon, as was customary during the summer before PV installations became more widespread, demand for grid power now tops off in the early evening hours.

Last summer’s demand peak was 24,780 MW and occurred on August 4, 2022. The all-time record for electricity demand was set on August 2, 2006, when demand reached 28,130 MW after a prolonged heat wave. In New England, consumer demand for electricity is highest during the summer because of air conditioning use.

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