MPPT Solar Charge Controller Sizing: Why Choosing the Right Solar Charge Controller is Important

An MPPT Charge Controller Can Maximize Your System’s Efficiency

If you’re using solar power, a charge controller is a crucial component for regulating the charging of your batteries. An MPPT (Maximum Power Point Tracking) Charge Controller is a type of charge controller that can deliver optimal performance by converting the high voltage produced by your solar panel array to a lower voltage that your batteries can accept. Investing in a high-quality charge controller, such as the one sold by Victron Energy, can make a big difference in the efficiency of your solar system.

MPPT Solar Charge Controller Sizing: The Three Primary Ratings of an MPPT Charge Controller

When selecting a charge controller for your solar setup, it’s important to consider the following three primary ratings:

Rating #1: Battery Bank Voltage (V)

The voltage of your battery bank is the first rating to consider when selecting a charge controller. It’s important to ensure that your controller can support the voltage of your bank, whether it’s 12V, 24V, or 48V.

Rating #2: Solar Panel Input Voltage (V)

The second rating of a charge controller is the maximum input voltage that it can accept from the solar array. This rating is crucial, under-sizing your charge controller’s input voltage could damage it and void its warranty. The maximum input voltage is typically given as a single maximum voltage, such as 100V or 200V. When using a 12 volt system It’s recommended to use a solar array with at least 18V to ensure proper operation of your charge controller. The voltage from your solar panels needs to be at least several volts higher than your system voltage. However, it’s important to be aware of external factors, such as weather, which can affect the input voltage of your array. For example, cold sunny weather can increase the voltage of your array. Make sure to base your calculations on the coldest temperature that may occur during daylight hours.

Correction Factors for Below 25°C (77°F) Solar Panels

If your solar panels are rated in Voc based on standard test weather conditions of 25°C (77°F), you need to apply a correction factor for colder temperatures. For example, if the Voc of your solar panel is 26.1V and there are three connected in series, and it’s 4°C on the coldest day, you would use the equation 26.1Voc x 3 in series x 1.10= 86.13V temperature compensated. This may be too high for a 75V rated charge controller but would work for a 100V rated charge controller.

Rating #3: Output Current (A)

The third rating is the charge controller’s output current, typically given in Amps. To check if the charge controller works for your system, divide the total wattage of your solar array by the voltage of your battery bank. For example, a 2000W solar array ÷ 36V battery bank = 55.6A. The charge controller’s rating should be at least 55.6A. It’s best to make sure that the total wattage of your solar arrangement is not more than 85% of this rating. This will allow the array to charge the batteries for longer during the day while ensuring that the controller is not working at full capacity all day.