PV backfeed on a double throw safety switch

[ggunn]

It's not backfeeding it is running in parallel. It works the same way it does when only the PV and utility are involved.

No, it doesn't. The grid can accept backfeed from the PV system when the PV production exceeds the load, but a generator cannot. Batteries, generators, and the grid are voltage sources, which means that their output current is dependent on the resistance of the load. A PV system is a current source, not a voltage source; the output current of a PV system does not depend on the magnitude of the load. In an islanded (closed) system of just a generator and a grid tied PV system with some loads, when the load is not sufficient to absorb all the output of the PV, what is left over has to go somewhere, which means that it will try to backfeed the generator, which is bad news for virtually all generators.

 

[BackCountry]

It’s all done. I tapped ahead of the main breaker with a fused disconnect into an IQ combiner. Lucked out, the original electrician left an empty 3/4” flex into the attic from that panel. Since we used Enphase, no problem running the roof PV circuits through the flex into the main panel and into the IQ combiner.

Then I had our other electrician install an Eaton interlock kit because it didn’t come in time when we did the install. The generator is the top breaker interlocked to the main breaker, and the main breaker has a line side tap to the PV. All good.