US Grid Operators, Utilities Getting to Know their Duck Curves
A phenomenon first observed in California around 2013, electricity supply-demand “duck curves” are emerging on grid systems elsewhere in the US. Utility grid customers across the New England region used more grid energy in the evening than they did during the daytime for the first time in history April 21, according to a local news report.
n other words, a grid energy duck curve has emerged in New England for the first time. Mild temperatures and “behind the meter” solar energy generation by utility customers were the primary agents that led to a historic record low in daytime grid demand, according to ISO New England, the independent systems operator (ISO) responsible for managing power markets, grid operations and grid energy resource planning across six US states.
Needless to say, weather patterns and climate in California differ greatly from that experienced across the New England region. Nonetheless, regional grid operator ISO-New England said it expects the pattern will occur more frequently as “behind the meter” solar energy and other, variable, or intermittent, sources of emissions-free electricity generation, e.g. wind power, continues to rise across New England.
Solar Magazine spoke with Paul Denholm, a principal energy analyst working as a member of the US National Renewable Energy Laboratory’s (NREL) Grid Systems Analysis Group, who, along with colleagues, developed new computer models that predicted that electricity grid duck curves could very well appear way back in 2008, long before anyone seriously considered that distributed solar power generation would grow to the degree that it would significantly impact entire power grids.
Energy, climate and policy
ISO New England is responsible for power markets and grid operations that extend across Connecticut, Maine, Massachusetts, New Hampshire, Rhode Island and Vermont. As is true everywhere, climate and geography strongly influence the nature and composition of electricity generation, transmission and distribution (T&D), and usage patterns across the region.
Energy policy and regulations also serve as fundamental, determining factors, setting the goals and ground rules that govern sources and management of generation, power markets, consumer prices and grid operations. These vary widely across the US as, by and large, they are set at the state level. The result can be seen in the varying rates of growth and varying amounts of distributed, solar, wind and other renewable energy generation capacity installed across the nation.
Massachusetts and Vermont have set the pace and emerged as leaders among New England states in terms of fostering investment in and deployment of distributed solar, wind and other emissions-free, renewable energy resources. Connecticut is doing similarly, though not as wholeheartedly. Legislators and regulators in Maine have been more reluctant.
New England power generation: A bird’s eye view
From a bird’s eye view, ISO New England hydroelectric, natural gas and nuclear power generation continue to meet the large bulk of regional electricity demand. In 2016, natural gas-fired power generation accounted for 49 percent of region-wide power generation and nuclear power 31 percent.
About 17 percent of ISO New England’s annual energy needs are met by imports via inter-regional, interconnection agreements with Canada’s TransEnergie (Quebec), Canada’s New Brunswick System Operator and New York ISO.
When it comes to planning ahead, ISO New England conducts annual Forward Capacity Auctions (FCA) for both generator and demand resources three years in advance of the period for which capacity is to be supplied. As the US Federal Electricity Regulatory Commission (FERC) explains: “The three-year lead time is intended to encourage participation by new resources and allow the market to adapt to resources leaving the market.”
Looking forward, as of late 2017 ISO New England ISO-NE expected that ongoing growth in “behind-the-meter” solar generation and energy efficiency improvements would more than offset load growth over the next 10 years.
Getting to know your duck curves
California was the first US state to enact legislation and regulations, including setting hard targets, to reduce greenhouse gas emissions and spur deployment of the solar power generation, both in front of and behind the utility meter. It should come as no surprise then that the California Independent Systems Operator (CAISO) was the first regional grid operator to notice the emergence and begin to plan ahead for the duck curve.
