Quick Answer
For a 200W solar array with a PWM charge controller, an optimal battery size is between 400-600Ah, considering a 12V system and a daily energy demand of 4-6 kWh.
Battery Selection Criteria
When choosing a battery for a 200W solar array, consider the depth of discharge (DOD), charge/discharge cycle life, and the overall system efficiency. A suitable battery bank should allow for a DOD of 50% to ensure its longevity. This translates to a minimum of 400Ah capacity for a 12V system.
System Efficiency and Charge Controller Characteristics
A PWM charge controller operates at 80-90% efficiency, which means it can convert up to 90% of the solar array’s energy into usable power. In a 200W solar array, this translates to 180-180W of usable power per day. To account for inefficiencies, it is recommended to oversize the battery bank by 10-20%. This ensures the system can function seamlessly during periods of low sunlight or high energy demand.
Battery Sizing Formulas and Considerations
To calculate the optimal battery size, use the following formula: Battery Capacity (Ah) = Daily Energy Demand (Wh) / System Efficiency (Wh/Wh) x Charge/Discharge Cycles. For a 12V system with a daily energy demand of 4-6 kWh, the calculated battery capacity would be between 400-600Ah. When sizing the battery bank, also consider the charge controller’s maximum power point tracking (MPPT) efficiency and any other system losses, such as wire resistance and inverter efficiency.
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