Combo GT/battery charge controller

RCinFLA
RCinFLA Solar Expert Posts: 1,484 ✭✭✭✭
I had this thought about how to accomplish both GT inverter feed during normal grid present operation and revert to battery based charge controller for power outage using the same panels. (using a regular MPPT charge controller, not the high voltage Xantrex XW-MPPT80-600).

Using per panel GTI like Enphase or PowerOne units for normal grid tie feed. In addition a low voltage (90 to 130 vdc) string connection for panels with feed down to a standard MPPT charge controller.

The switching would be a regular required AC disconnect to GT inverter array and DC disconnects for each parallel wired panel string for battery charge controller. You must have disconnect on every parallel string to avoid panel string interaction during normal grid tie operation.

During normal GT operation the AC disconnect would be closed and the DC disconnects to parallel string would be open. During grid outage the AC disconnect would be open and the DC disconnects would be closed and feeding the battery charge controller.

The key is using the individual per panel GT inverters. When their AC grid connection is loss they become pretty much inert allowing a battery charge controller to take over.

The only unknown factor that may 'put a fly in the ointment' would be if the module GT inverter would have a problem with the concurrent panel string wiring, (even though it is open circuited). If the GT inverters are truely isolated between panel output and their AC output sides there should not be a problem.

Comments

  • TheBackRoads
    TheBackRoads Solar Expert Posts: 274 ✭✭
    Re: Combo GT/battery charge controller

    Care to share a diagram?
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Combo GT/battery charge controller

    If I were to do it, I'd use a central inverter with the array split in two and rewire to feed a MidNite Classic 250 for battery charging. You'd need to switch three lines simultaneously: positive/negative at the mid string point from connected to respective positive & negative input of the Classic; and positive string output from GTI to positive input on the Classic. Much simpler and 100% certain to work providing you wire it right and make sure the array is within spec for both configurations (not exceeding the Classic 250 Voc limit or power handling requirements. This means the string would need to be about 480 Volts max for the GTI).