Best voltage for charging 12V batteries with a solar array — what’s ideal?

Understanding Solar Charge Controller Sizing

When sizing a solar charge controller, it’s essential to consider the voltage and current requirements of your solar array and battery bank. A general rule of thumb is to select a controller that can handle the maximum power point of your solar array, which is typically in the range of 17-20V. This ensures that the controller can efficiently charge your batteries without wasting excess energy as heat.

Calculating Maximum Power Point Voltage

To calculate the maximum power point voltage, you can use the following formula: MPPT_V = V_oc x (1 - I_sc / I_mp) where V_oc is the open-circuit voltage, I_sc is the short-circuit current, and I_mp is the maximum power current. For example, if your solar panel has a V_oc of 22V, I_sc of 5A, and I_mp of 2.5A, the MPPT_V would be 22V x (1 - 5A / 2.5A) = 17.6V. This means that your solar charge controller should be capable of handling at least 17.6V to ensure efficient charging.

Choosing the Right Charge Controller

When selecting a solar charge controller, look for a model that can handle the maximum power point voltage of your solar array, as well as the maximum current output of your solar panels. It’s also essential to consider the controller’s efficiency, which should be as high as possible to minimize power loss. A good rule of thumb is to choose a controller with an efficiency of at least 95%. Finally, make sure to select a controller that is compatible with your battery type and has a suitable level of overcharge protection to prevent damage to your batteries.