What Size Solar System Needed for Electric Water Heating?

System Size and Efficiency

When calculating the required solar array size for electric water heating, several factors must be considered. The efficiency of the water heater is crucial, as it directly impacts the amount of energy required to heat the water. For example, a 50% efficient system would need a larger array to produce the same amount of heat as a 70% efficient system. Additionally, the desired charge time and daily hot water needs must be factored into the calculation. A general rule of thumb is to assume 4-6 hours of charge time to cover daily hot water needs for a small to medium-sized household.

Array Sizing Example

To illustrate this concept, let’s consider a household with a 50-gallon electric water heater and a desired charge time of 5 hours. Assuming a 60% efficient system (a reasonable estimate for a well-insulated tank), the daily energy requirement would be approximately 1.5-2 kWh per day. To meet this demand, a 5-7 kW solar array would be required, depending on the local insolation levels and other system losses. This array size would provide a safe buffer to account for cloudy days and other variables that may impact the system’s performance.

Cost Analysis

The cost of a solar array for electric water heating can vary widely depending on the system size, efficiency, and local installation costs. However, as a rough estimate, a 5-10 kW solar array could range from $10,000 to $30,000 or more, depending on the specific components and installation costs. This cost can be offset by the savings on utility bills and potential rebates or incentives for renewable energy installations. It’s essential to consult with a qualified solar professional to determine the most suitable and cost-effective system design for a specific household’s needs.