Beating the heat: How ISO-NE prepares for summer peak demand
Thursday, May 26, 2016 at 11:19AM
ISO New England in Industry News & Developments, forecast, peak demand, summer, system operations

As the region gears up for a season of fun in the sun, ISO New England prepares for conditions unique to the hot, humid summer months. Peak demand brought on by warmer weather and an increased reliance on energy-intensive technologies, such as air conditioning, can create complex challenges for the grid operator.

To maintain a reliable supply of electricity to New England’s residents and businesses, the ISO’s System Operations team must rely on carefully planned procedures to increase power generation and curb consumption during periods when demand for electricity threatens to exceed available capacity and reserves. High consumer demand or unplanned resource outages—when a transmission line or generator suddenly goes offline—are typically the reasons for these procedures to be enacted.

Thermal buildup
and electricity use

On an ordinary summer day, a hot afternoon will give way to a cooler evening and some of the heat absorbed by houses and other structures will dissipate. But when temperatures are high for several days in a row and don’t cool off that much at night, houses and other structures start to retain the heat in a phenomenon called thermal buildup. That’s when people’s tolerance for heat tends to wane. As air conditioning use rises, so does demand for electricity.

Factors that affect the grid

Temperature and dew point both play pivotal roles in determining demand on the system. The difference between a normal summer temperature of 90°F and heat wave conditions of 94°F can result in more than 2,000 additional megawatts (MW) of demand. While the colder winter weather also creates a dramatic rise in electricity usage, the summer peak is different because it extends throughout much of the day—when the ramp up begins by midday and stretches well into the evening. Instead of a typical two- or three-hour peak that occurs on a winter day, the hot summer weather usually creates six hours of consistently high demand. When this pattern of prolonged peaks extends over several days, the demand for electricity builds, and that often leads to stress on the system.

A comparison of hourly load on summer and winter days reveals two very different peaks.

Pre-summer checklist

Each year, the transmission and generation resources on the system conduct maintenance and repairs that will ensure readiness for the high loads that hotter weather brings. Heading into the summer months, ISO New England closely monitors weather forecasts, fuel source availability, and other factors that may affect the grid to get a sense of what conditions system operators will be facing. A summary of expected demand and conditions of the grid is compiled into a summer outlook press release.

Actions before and during a capacity deficiency

As hot summer weather sets in, the grid operator keeps a watchful eye on changing conditions. The ISO issues a Morning Report and a Seven-Day Forecast that list expected demand, capacity, and reserves on a daily and weekly basis, respectively. These reports give stakeholders and the public an understanding of the grid’s available resources and advance notice of any possible challenges on the horizon.

Sometimes the grid experiences issues due to weather-related factors or unexpected maintenance. In the event of abnormal system conditions, the ISO issues Master/Local Control Center Procedure No. 2 (M/LCC2). This notification alerts applicable power system operations, maintenance, construction, and test personnel, as well as market participants, that an abnormal condition has occurred or is expected to occur, and that they should cease any testing or maintenance that could affect reliability. While an M/LCC2 event is not an indication of a shortage of supply and reserves, many deficiencies are preceded by an M/LCC2 notification.

The grid can enter a “capacity deficiency” when available resources are insufficient to meet anticipated demand plus the required level of reserves. This can be due to a number of factors, such as the loss of a source of supply, issues with transmission facilities, abnormal system conditions, or even responding to requests from neighboring grids for assistance that would reduce New England’s reserves below the required margin. Because electricity cannot easily be stored, procedures are in place to maintain a certain level of reserves for reliability purposes. ISO New England maintains both 10-minute and 30-minute reserves—named for the capability of generating resources to deliver electric energy within 10 or 30 minutes.

If grid reliability is jeopardized, the ISO has a series of long-established procedures it can employ. System operators can request assistance from neighboring power grids, draw upon 30-minute reserves, ask companies participating in demand-side resource programs to temporarily reduce electricity consumption, and ask the public to conserve electricity voluntarily. These actions are among the measures in ISO Operating Procedure No. 4, Action During a Capacity Deficiency (OP 4). Implemented in any order, the actions can be applied New England-wide, by state, or targeted to specific areas in order to maintain system reliability and preserve New England’s 10-minute reserves by providing generation and load relief on the system. While it’s always a good idea to use electricity sensibly, many of these steps do not call for conservation by the public. (See the Power System Alert Descriptions web page for an explanation of all the various alerts.)

Information when you need it most

In addition to the open lines of communication between system operators and the region’s power plants, demand-side resources, and transmission owners, ISO New England posts information and frequent updates on power system conditions to its website. In the event of a capacity deficiency, the ISO provides OP-4 details in a number of places, including:

Readiness and reliability

While life in New England involves a certain amount of unpredictability when it comes to the weather, the ISO is prepared to address the challenges of seasonal extremes. By closely monitoring grid conditions, communicating information about the impact of weather and fuel availability, and coordinating with pipeline companies to ensure adequate natural gas supply, the ISO can direct efforts to maintain efficient operation of the system. The ISO is capable of dealing with a wide variety of situations that could come up when demand for power is peaking, and has the procedures, processes, and expertise in place to effectively resolve issues and ensure reliability of the bulk power grid.

For summer 2016, electricity supplies in the six-state region are expected to be sufficient to meet consumer demand and under normal weather conditions, demand is forecasted to peak at 26,704 MW. Extreme summer weather, such as an extended heat wave of about 94°F, could push demand up to 29,042 MW. Last summer, demand for power peaked on July 20, 2015, at 24,398 MW. The all-time record for peak demand was set on August 2, 2006, when demand reached 28,130 MW after a prolonged heat wave.

New England’s businesses and residents can also take steps to help keep demand in check, especially when consumer demand is expected to be high. Simple measures such as raising air conditioner settings a few degrees, installing energy-efficient light bulbs, and turning off unnecessary lights, TVs, and other home and office equipment can have an impact.

Article originally appeared on ISO Newswire (
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