Charge Controllers

    Some controls can also be used in special situations to divert excess power for things like limited water heating; or as lighting controls; low-battery voltage disconnects; etc.  Another important feature is the ability to connect a higher voltage solar array to a lower voltage battery (48V array to 12V battery, for example).  This voltage matching capability allows the use of smaller gauge wire from the array to the control, which is especially important for large arrays with a long wire run.  Usually, the choice of which control to buy depends on system size and budget.   Never connect your batteries to a solar array without having a charge control installed.

Charge controls come in many versions, from simple to sophisticated, but they all have one basic function in common; they regulate the power from solar panels into your batteries to charge them efficiently without overcharging.  The simple ones work fine for very small systems, but generally it is truly worth the expense to buy a maximum power point tracking (MPPT) controller.  MPPT controllers actually put more energy into your batteries from the same-size solar array- up to 20-30% more.  The extra charging energy is like having more solar panels, which easily pays for the extra expense of the controller.  This effect is especially pronounced in the winter months when days are short and more power is needed.  These controls often have deluxe features like data logging, which is useful for troubleshooting, and the ability to control a fan to ventilate your battery compartment.  Most charge controllers can interface with a battery temperature sensor, and it is a very good idea to use one to ensure proper charging in changing temperature conditions.  Many controls are available with optional remote displays, so PV array performance can be monitored from a separate location.