Quick Answer
To identify the right size for your solar hot water system, consider the household's daily hot water usage, number of occupants, and climate. You can estimate the system's capacity by calculating the gallons per day (GPD) required. A general rule of thumb is to allow 25 gallons per day for each person.
Assessing Daily Hot Water Demand
To determine the required system size, calculate the household’s daily hot water demand in gallons per day (GPD). The average person uses 25-30 gallons of hot water per day, but this can vary based on factors like water temperature, washing machine usage, and shower duration. Consider the number of occupants, their hot water usage habits, and climate conditions to estimate the total daily demand.
Determining System Capacity
A solar hot water system’s capacity is often measured in terms of its ability to raise the water temperature to a certain level, typically 104°F (40°C) or higher. To determine the system size, you’ll need to know the household’s total daily hot water demand, the water temperature, and the system’s efficiency. A common approach is to use the system’s thermal capacity in BTUs (British Thermal Units) or kilowatt-hours (kWh).
Choosing the Right System Size
When selecting a solar hot water system, consider factors like system efficiency, tank size, and collector area. A general rule of thumb is to choose a system that produces 20-25% more hot water than the household’s daily demand, to account for variations in usage and potential system inefficiencies. This can help ensure that the system meets the household’s hot water needs, even on cloudy days or during periods of low solar radiation.
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