Diversion-load controllers work very differently than standard PV controllers, though some of those can be programmed to work in diversion mode. Instead of controlling how much power is coming into the battery bank from the PV array, they always let maximum power in while charging. When the battery bank is at 100% SOC, incoming power is diverted to “diversion” or “dump” loads, usually special air or water heating elements. In certain situations, this can be very effective, providing supplemental heating for a cold cabin or a tank of hot water when you arrive back at the cabin in warmer climates. However, you can’t rely on diversion loads all of the time, as their efficacy is entirely weather-dependent.
Diversion-load controllers don’t provide electronic maximum power point tracking (MPPT) to maximize PV-generated charging. By adding ganged circuit breakers to a system, it’s possible to switch between two different controllers for occupied and unoccupied times of use, so the system can use diversion when you are away and MPPT when the cabin is in use. The question is whether the extra equipment is worth the amount of heat gained.
Pictured Above: A resistance air-heater element (shown with its safety cover removed) turns diverted excess energy into hot air.
Below: This charge controller can be used for diversion load control, allowing excess solar energy (once batteries are full) to be diverted to other tasks, such as space or water heating.