Xantrex C-35 contoller

Assuming the factory defaults are OK, or that someone has already set them for your system, there is no reconfiguration needed. The difference is in the wiring. Wired between the PV and the battery it is a PV charge controller. Wired between the battery and a dump load, it is a shunt regulator or diversion/dump controller.

In this mode, it monitors the voltage on the battery terminals. When the voltage exceeds the charge settings, it diverts excess wattage to the dump load, lowering the voltage on the battery terminals to the appropriate bulk or float charge voltage.
Assuming an active source (wind,hydro) the PWM should function in diversion mode, when there is excess wattage.