Quick Answer
When sizing a solar panel system for off-grid, key factors include the desired energy output, sun hours per day, system voltage, and equipment efficiency, requiring a comprehensive assessment of the site and energy needs.
Understanding Sun Hours
Sun hours per day, also known as peak sun hours, are a critical factor in solar system sizing. This metric measures the amount of sunlight a location receives on a daily basis, typically expressed in hours. For example, California averages around 7 hours of peak sun hours per day, while states in the Northeast average around 4 hours. To size a solar panel system, we must first determine the site’s annual sun hours, which can be calculated by multiplying the daily peak sun hours by 365.
System Sizing Formulas
To calculate the required solar panel array size, we use the following formula: (Total System Load in kWh/day) / (Solar Panel Efficiency x Peak Sun Hours per Day) = Required Array Size in Watts. For example, a system requiring 5 kWh of electricity per day, with a 15% efficient solar panel, and 6 hours of peak sun hours per day, would require an array size of 5 / (0.15 x 6) = 58.3 kW. This calculation assumes a 1 kW system efficiency and does not account for system losses.
Considering System Efficiency
System efficiency plays a crucial role in solar panel system sizing. This includes inverter efficiency, wiring losses, and other system components. To account for these losses, we must apply a derating factor to the calculated array size. A typical derating factor ranges from 10% to 20%, depending on the system configuration and quality of components. Using the previous example, applying a 15% derating factor would result in a final array size of 58.3 kW x 0.85 = 49.5 kW, providing a more accurate estimate of the required solar panel array size.
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