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REopt Optimizes Residential Solar-Plus Technologies Behind The Meter

Two charts show how standalone solar compares to solar-plus smart AC and smart domestic water heater technologies. Solar-plus technologies better utilize excess solar PV output in regions where no energy export is allowed.

REopt compares solar PV and “solar-plus” customer load profiles, grid net load, and solar PV output. Illustration from NREL

The REopt™ platform can determine the optimal mix and size of solar photovoltaics (PV) and “solar-plus” technologies to lower the life cycle cost of energy for a number of post-net metering residential utility tariffs (including time-of-use [TOU] and demand tariffs). “Solar-plus” uses solar PV in combination with energy storage and controllable devices—such as smart domestic water heaters, smart air conditioning (AC) units, and electric vehicles—to help customers increase solar self-consumption and realize value from a larger share of their system’s output behind the meter.

For Hawaii’s TOU residential tariff—where no energy export is allowed—the solar-plus approach increases net present value by a factor of three relative to the stand-alone solar PV approach. The smart AC unit and smart domestic water heater are dispatched each day to pre-cool the home and pre-heat water with solar PV output. Any excess output remaining after pre-cooling and water heating is delivered to a battery, which is dispatched to further reduce TOU rates. Customers can use solar-plus technologies to take advantage of excess solar PV output, increasing their cost-optimal system size, reducing system curtailment, and increasing the value of their solar PV system.

The results indicate that the solar-plus approach improves the customer economics of solar PV for tariffs that include demand or TOU components, or for less-than-retail rate net metering. The solar-plus approach may become an increasingly viable model for optimizing solar PV customer economics in a post-net metering environment.


A home produces solar PV energy that can be self-consumed, delivered to the grid, or stored in a battery. Residential self-consumption technologies include smart AC (an AC unit that can be configured to pre-cool the home with solar output, then allow the home temperature to drift up to a set maximum temperature before drawing from the grid), a battery (solar energy may be stored in an electrical battery for later use), smart domestic hot water (a water heater can be set to pre-heat water with solar output and store hot water for later use), and electric vehicle charging (excess solar output can be delivered to an electric vehicle and used for transportation or stored for home use).

"Solar-plus" technologies combine to increase solar self-consumption. Illustration from NREL