Quick Answer
Running an electric water heater off-grid is feasible, but it requires careful planning and sizing of the solar array and battery bank to meet the water heater's energy demands.
Understanding Electric Water Heater Power Consumption
To determine if an electric water heater can run off-grid, calculate its daily power consumption in kilowatt-hours (kWh). A typical 40-gallon residential electric water heater uses around 4.5-5.5 kWh of energy per day. For example, a 4.5 kWh/day water heater requires a 2.6 kW solar array (assuming 10 hours of peak sunlight per day and an inverter efficiency of 90%).
Sizing the Solar Array and Battery Bank
To accommodate the water heater’s energy demands, the solar array should be sized to produce at least 4.5 kWh of energy per day. Assuming a 2.5 kW solar array with an inverter efficiency of 90%, and considering the system losses, the actual array size required is around 3.2 kW. The battery bank should be sized to store excess energy generated by the solar array during the day for use at night or during periods of low sunlight. A 12V, 400Ah battery bank would provide approximately 5 kWh of usable energy, which is more than enough to support the 4.5 kWh/day water heater.
Off-Grid Water Heater System Design Considerations
When designing an off-grid water heater system, consider the water heater’s efficiency, the solar array’s size, and the battery bank’s depth of discharge. A high-efficiency water heater (such as a heat pump water heater) can reduce energy consumption and increase system efficiency. Additionally, a smart inverter can optimize energy production and storage by adjusting the solar array’s power output and battery charging/discharging schedules accordingly.
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