The time at which renewable energy resources (e.g., solar or wind) produce electricity cannot generally be controlled. However, in many settings, consumers have some flexibility in their energy consumption, and there is growing interest in demand-response programs that leverage this flexibility to shift energy consumption to better match renewable production—thus enabling more efficient utilization of these resources. We study demand response in a setting where consumers use home energy management systems (HEMS) to autonomously adjust their electricity consumption. Our core assumption is that HEMS operationalize flexibility by querying consumers for their preferences and computing the "indifference set"—the set of all energy consumption profiles that can satisfy these preferences. Given an indifference set, HEMS can then respond to grid signals while ensuring user-defined comfort and functionality. For example, if a consumer sets a temperature range, a HEMS can precool and preheat to align with peak renewable production, thus improving efficiency without sacrificing comfort.