Net demand ramping variability




California ISO


The California Independent System Operator (CAISO) developed a more precise data calculation and control performance approach regarding the net demand variability and its influence on the reliability of the grid. This allows them to quickly analyse and respond to challenges associated with the increased volume of renewables while simultaneously adhering to existing reliability requirements.



  • Provide CAISO with accurate projections for system ramping capability needs, as increasing amounts of renewables are added to the resource mix
  • Make better-informed planning decisions and recommendations to the state regulator CPUC (California Public Utilities Commission)
  • Ensure sufficient net demand ramping capability, which assists the ISO in maintaining power balance, frequency, and reliability


Main information:

The California power grid has to cope with the integration of substantial amounts of renewable energy. Due to the fluctuation of renewables, there are times of the day when generation drops and conventional power plants have to ramp up quickly to meet the demand.

To approach this challenge, CAISO developed a measurement for net demand ramping variability that allows them to quickly analyse the issue and respond to it. The measurement also enables balancing authorities to ensure on-going electricity system reliability and compliance with mandatory operating standards.

The ISO now calculates its “net-load” on a minute-by-minute basis by subtracting forecast renewable production for the same time. The ISO then determines the net demand ramping variability over a three-hour period, which is needed to maintain reliability. Prior to the development of the new measure, performance data was measured on a monthly basis and averaged over a 12-month rolling average basis. By evaluating its performance each minute, and averaged across an hour, CAISO gained a much clearer view of actual operating conditions. In addition, this more granular evaluation revealed deficiencies in the existing information flow and allowed CAISO to put in place initiatives that will support higher levels of renewable integration. All in all, the practice contributed to better grid reliability and better compliance with mandatory operating standards.

Additional information:

The California ISO manages the flow of electricity across the high-voltage, long-distance power lines that make up 80% of California’s and a small part of Nevada’s power grid. As the only independent grid operator in the Western US, CAISO grants equal access to 26,000 circuit miles of power lines and reduces barriers to diverse resources competing to bring power to customers.


RGI gratefully acknowledges the EU LIFE funding support:

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Funded by the European Union. Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or the LIFE Programme. Neither the European Union nor the granting authority can be held responsible for them.