Effect of off-peak electrical storage on the annual cost of conventional and solar water heating and space heating/cooling at three US locations

Novel control systems and strategies were developed which reduce electric utility load peaks resulting from back-up demands of solar systems. Annual costs of residential conventional and solar water heating and space heating/cooling systems with and without off-peak thermal storage in Philadelphia, PA, Daytona Beach, FL, and San Diego, CA were compared for 1985 and 1995. Hourly simulation, best available cost data for supplying electrical service and updated contractor cost estimates were used. Utility costs and homeowner costs were added in order to determine the lowest total cost systems which are optimum from the societal point of view. The addition of off-peak electrical storage to a solar water heater decreases utility costs but increases total cost. Solar heating systems are not cost effective at any of the locations investigated, but the addition of electrically charged off-peak storage reduces total costs though increasing the electrical energy consumption 9% to 27%.