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Energy Currents
A Blog by Enerdynamics

The Electric Load Curve – Once Predictable, Now Fickle

by Bob Shively, Enerdynamics President and Lead Facilitator

The electric load curve is a graph that shows system demand by hour. It once was predictable with a steady summer curve with a peak in late afternoon and with a winter curve showing two peaks – one during morning wake-up time and a second in the evening.

The load curve is used by system operators to develop hourly dispatch plans for power plants. With the traditional curves, use of power plants was predictable with baseload units running all day, intermediate load units starting in the morning, and peaking units dispatched to meet the seasonal load peaks. 

But now, three key factors are rapidly changing load curves and dispatch stacks. 

1. Growth of utility-scale renewables
With the growth of utility-scale renewables, system operators move from just looking at the load curve to studying the net load curve – the amount of load that will served by traditional generating units after variable renewable supply has been subtracted:

Net load curves have been rapidly changing with the growth of wind and solar power. Here are a few examples:

       California ISO curve for October 16, 2019:

Source: CAISO Renewables Energy Watch

       ISO New England curve for April 21, 2018:

Source: ISO New England State of the Grid: 2019

       ERCOT (Texas) curve for Summer 2019:

Source: ERCOT Summer 2019 Operational and Market Review

It is interesting to note that while California and New England net load peaks have been pushed into late in the evening, Texas is experiencing summer net load peaks prior to 4 p.m. In California and New England solar output is the driving force, while in Texas wind is the key factor.

2. Growth of Distributed Energy Resources (DERs)
In most regions, growth of DERs has yet to show a significant impact on load curves. But it is just a matter of time in regions with fast growth in rooftop solar.  Hawaii is the case study, demonstrated by the following load curve for a circuit in Oahu with significant penetration of customer-owned solar:

       Distribution Net Loading on a Circuit on Hawaiian Island of Oahu

Source: Transmission and Distribution World, Visibility Enables PV Integration, August 18, 2016

Such patterns will soon be observed in places like California where all new homes will be required to install solar panels starting next year.

3. Growth of Price Responsive Flexible Loads
Throughout the electric industry’s history, planners have assumed that loads are not flexible since consumers use energy when they want. But proliferation of controllable load devices coupled with pricing that reflects system conditions could change the assumption. Today most consumers see either flat rates that do not change with time, or time-of-day pricing with two or at most three different price levels. The rates do not change to reflect days with more or less renewable output or other changing system conditions. But this could quickly change. A recent study of vehicle-to-grid integration in Southern California by Jackson Associates suggested that a 10% penetration of EVs coupled with economic incentives and vehicle-to-grid technologies could effectively flatten load curves:

Source: Jackson Associates, SCE Electric Vehicle (EV) Virtual Power Plant Analysis Shows $5,600 10-Year Savings Per EV Customer

As we look to the future of electric grids, it is clear that load curves will remain a moving target. Planners must realize that whatever we think we know, we probably don’t know. Variables such as penetrations of DERs, growth of EVs, electrification of heating loads, and willingness of consumers to use energy flexibly in response to price signals represent large unknowns. The more uncertainty, the less value there will be associated with large centralized capital projects. The electric industry must learn to operate effectively on much shorter planning horizons than it has done in the past and developing flexible infrastructure plans.

Want to learn more about the changing electric grid and the challenges/opportunities for grid operators? Enerdynamics' Advanced Grid live seminar is available for groups as small as 8 employees. Don't forget to browse all our other online energy training resources to see what else you can advance your knowledge on. Contact us at or 866-765-5432 ext. 700 for details.

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