ISONE reports on electric reliability and the future of a hybrid system

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ISONE reports on electric reliability and the future of a hybrid system

Thu, 03/21/2019 - 1:27pm -- tim

Vermont Business Magazine ISO New England has published its 2019 Regional Electricity Outlook (REO), an annual report looking at the trends and challenges affecting New England’s power system, as well as the work being done by the ISO to ensure the region’s homes and business have reliable electricity. ISO New England Inc is the operator of the region’s bulk power system and wholesale electricity markets.

The report explores how:

  • New England’s traditional power grid is rapidly becoming a hybrid system of conventional resources, significant amounts of large-scale wind resources, and thousands of small distributed solar and storage resources.
  • Weather will continue to play a pivotal role in power system operations, both affecting consumer demand for electricity and generation from renewable energy resources.
  • Wind power dominates proposals for new generators looking to build and interconnect to the regional power grid.
  • Energy security will remain a dominant issue in New England during the years ahead, with the potential to worsen as the region continues to shift towards resources that rely on just-in-time fuel. The ISO will continue to work with stakeholders to find long-term, market-based solutions to this challenge.
  • Electricity demand on the region’s bulk power grid is trending downward over the next decade, but may trend upward in the long term as state decarbonization efforts convert the transportation and heating sectors to electricity.
  • Transmission projects have provided the region benefits beyond reliability, including lower prices and cleaner energy; additional investment in transmission infrastructure will be fundamental to reliably decarbonizing millions of vehicles, households, and businesses.

The 2019 REO is available at

Also available online are the New England Power Grid 2018–2019 Profile and New England Power Grid 2018–2019 State Profiles, a pair of documents summarizing key facts on demand growth, resource mix, transmission development, and wholesale electricity prices in the region and in individual states.

Below is the discussion found in the report on solar energy:

Energy efficiency and solar power are driving down annual energy use

Electricity consumers in New England used over 121,000 gigawatt-hours (GWh) of electricity from the grid in 2018, down from the record 136,355 GWh consumed in 2005. Nearly 3,000 megawatts (MW) of energy-efficiency (EE) measures can reduce electricity demand from New England’s power grid. And more than 150,000 behind-the-meter (BTM) solar photovoltaic (PV) installations span the six states, with a combined nameplate generating capability of nearly 2,900 MW (they typically don’t generate at maximum capacity at the same time). Almost all solar installations are connected to local distribution utilities or provide power directly to homes and businesses. The ISO doesn’t dispatch the electricity these resources produce but has to manage their impact as a reduction in demand on the grid.

New England states continue to invest billions of dollars on making solar energy affordable for consumers and on EE programs (projected $10.5 billion on EE between 2019 and 2027) that promote the use of energy-efficient appliances and lighting, and advanced cooling and heating technologies. Massachusetts, Rhode Island, Connecticut, and Vermont rank among the top five states in energy efficiency in the US, according to the American Council for an Energy-Efficient Economy’s 2018 rankings.

Future demand-reducing effects of EE and BTM PV are projected in the graph below. To enhance its planning for the future grid, the ISO improved its innovative EE forecast methodology in 2018 to more accurately forecast the amount of EE installed on the distribution systems operated by local utilities across the region. EE measures are estimated to save an average of 2,059 GWh each year and will reduce peak demand by 281 MW annually.

Solar power is changing historical grid demand patterns

When conditions are right, the ISO sees a significant reduction in regional electricity demand from BTM PV. During a heatwave in July 2018, BTM solar generation peaked each day at around 1:00 p.m., reducing demand from the regional power system by approximately 2,000 MW.

Springtime conditions are ripe for high solar output. On a cool, sunny day in April 2018, BTM solar output reached an estimated record high at 1:00 p.m. and drove down electricity demand on the regional power system by 2,300 MW. The result was a regional first: New Englanders used more grid electricity while they slept that night than during the middle of the day.

For the first time since at least 2000, and possibly ever, grid electricity demand on Thanksgiving Day did not peak in the morning as New Englanders turned on their ovens; solar pushed the peak to after sunset.

The ISO’s grid operators traditionally rely on historical patterns of electricity use to accurately predict how much electricity must be generated to meet second-to-second demand. But as distributed solar resources dramatically change electricity demand patterns, producing accurate forecasts becomes more challenging.

Weather still drives spikes in demand

Weather has always been the biggest factor in determining how much electricity New England consumers will use every hour of every day. For example, when the dew point is above 70°◦ Fahrenheit, every one-degree increase can cause demand to rise by about 500 MW—the amount produced by a medium-sized power plant.

With an increasing amount of electricity produced by resources that use sun or wind, ISO grid operators can no longer rely exclusively on traditional weather forecasts. The actual output from solar power installations can vary widely depending on a number of weather variables that vary widely across the six New England states. These include the amount and location of cloud cover, haze, humidity, and rain and snow. New England has erratic weather conditions, and New Englander know how hit or miss weather forecasts can be—even from town to town.

Summer 2018 was marked by spells of hot and humid weather that drove electricity demand on the power grid to peaks not seen in five years. Despite significant declines in grid energy use on an annual basis, spikes in electricity demand on the power grid still occur, and the region’s power system must remain prepared to meet these peaks even if they aren’t historically high. New England also reached its highest Labor Day peak ever recorded as people cranked up air conditioning to deal with the swampy air blanketing the region. Overall, consumer demand for grid electricity was up 5.3% in summer 2018 compared with the previous summer.

Solar output is especially variable in winter

In New England, winter imposes the most variation in solar output because of snow, clouds, and shortened daylight hours. Cloud and snow cover prevented solar panels from reaching their seasonal potential during last year’s historic 16-day cold spell (December 24, 2017, through January 8, 2018) and particularly during Winter Storm Grayson, which occurred during that period. In time, battery storage systems will be able to help manage through day-to-day variation but may not help when unfavorable solar conditions last for multiple days. In addition, shortened winter days means consumers use the most electricity after sunset. So whereas solar helps reduce grid demand during sunny days without significant snow cover and can help conserve other fuels for use later in the day, it doesn’t reduce winter peak demand.

Predicting the unpredictable: continuous forecasting enhancements

The ISO is working with industry experts to build a method of predicting PV output regionally that will be integrated into its existing day-ahead and seven-day operational load forecasts beginning in early 2019. Given that it’s infeasible for the ISO to collect performance data directly from all 150,000 individual PV systems, these efforts will enhance visibility and help the ISO grid operators forecast variations in system demand with the higher degree of accuracy needed to operate the grid reliably and efficiently. The ISO also now has a full-time meteorologist on staff to help with more precise weather forecasting. Looking out longer term, the ISO has incorporated improved modeling of BTM solar power in the calculations that help determine the amount of capacity to procure through the Forward Capacity Market.

Operating the grid reliably with volatile changes in electricity demand

Solar shuts off quickly as the sun sets or clouds roll in: Ensuring enough fast-start resources

The ISO launched improved real-time fast-start pricing in 2017 to help incentivize power resources that can quickly ramp up their output to bridge the steep increase in grid demand that occurs when the sun sets.

More solar will mean more extreme dips in demand: Preventing excess energy

In 2014, the ISO began allowing negative pricing in the energy market to create a disincentive for grid resources to operate when there’s surplus power. Negative pricing also provides a market-based way to manage resources such as wind that may choose to continue producing electricity at prices below zero because they receive other sources of income, such as the federal production tax credit.

Solar needs to ride through voltage or frequency changes: Strengthening interconnection standards

If a large amount of solar power were to shut down suddenly when a transmission line or generator trips off line, net demand on the regional grid would spike, potentially introducing instability. Four states so far—including Massachusetts, with over 60% of the region’s solar power—have agreed to adopt the ISO’s interim ride-through requirements for future solar interconnections.

Lower-emitting resources supply most of the region’s electricity

The region’s energy, capacity, and ancillary (regulation and reserves) markets have attracted more than 500 companies that compete to sell, buy, and transport wholesale electricity and other grid-related services. In 2018, natural-gas-fired generation, nuclear, other low- or no-emission sources, and imported electricity (mostly hydropower) provided roughly 99% of the region’s electricity.

With low-cost fuel from domestic shale deposits, advances in technology, and smaller generators that are easier to site, natural gas-fueled power plants have proliferated in New England over the past two decades. Market participants have invested billions into new, efficient (meaning they use less fuel), relatively low-emitting natural-gas-fired generation. Nearly half of the region’s electric generating capacity uses natural gas as its primary fuel (about 15,000 MW), and natural-gas-fired power plants produce about 40% of the grid electricity consumed in a year.

Until electric storage or other technologies have the ability to supply quick energy for longer periods and in greater quantities, flexible natural-gas resources are a necessary element of the hybrid grid, not only to help supply the “missing energy” when the weather is uncooperative for wind and solar resources, but also to provide the precise grid-stability and reliability services that renewables generally cannot. However, natural gas delivery constraints in winter caused by high demand for this fuel from both the heating and electric power sectors can prevent these resources from filling this need during cold weather. The need to meet environmental requirements can also restrict the amount of time natural gas plants that use oil as backup can run.


Created in 1997, ISO New England is the independent, not-for-profit corporation responsible for the reliable operation of 
New England's electric power generation and transmission system, overseeing and ensuring the fair administration of the region's wholesale electricity markets, and managing comprehensive regional electric power planning.

Source: Holyoke, MA—March 20, 2019—ISO New England