The design guide focuses on off-grid solar PV water heating, where solar energy is delivered directly to the lower heating element of a standard electric water heater through a dedicated off-grid solar inverter. By intentionally setting the lower thermostat higher than the upper thermostat, solar energy is used as the primary heat source, while grid electricity is only consumed during short periods of unusually high hot water demand. In effect, the water heater becomes a solar energy storage system, storing energy in the form of hot water.