Participant overrides can halve the reliability value of direct load control programs

Residential air conditioning (AC) direct load control (DLC) is a common demand response (DR) strategy for maintaining grid reliability. During DLC events, consumers cede control of their thermostat to the utility, but participants can often override settings. Existing literature has not quantified the impact of overrides on the reliability contributions of DLC programs. We combine empirical override behavior from a DLC program with household- and power-system-level models to quantify the impact of overrides on the system reliability contributions of alternative DLC program designs in California. We find overrides would have little impact on the reliability value of a DLC program that calls events for 1 hour. But for DLC programs that call events that last 3 or 4 hours, overrides can lead to a 60% reduction in their reliability value. Our results guide DLC design and indicate that ignoring behavior can significantly undermine DR interventions. Policymakers must consider tradeoffs between override flexibility and electricity savings when designing and approving DLC initiatives.