Thanks for the reply. I got a few years of experience doing power systems in 1980, which came in handy when I did the CA PV system in 2003. (My embedded/web d

Thanks for the reply. I got a few years of experience doing power systems in 1980, which came in handy when I did the CA PV system in 2003. (My embedded/web development skills also came in handy when designing/deploying the solar M&C subsystem, because no such products existed at the time.) I'm somewhat skeptical that GPS synchronization is the real answer here. The problem is synchronizing the phase of the PV system to the grid so they can work together to power the load, allowing excess PV power to be sold back into the grid when not needed locally. To synchronize, one needs to control the phase of the PV system so it always slightly leads the phase of the grid. Determining the phase of the grid is the challenge. With two or more locally grid-tied PV systems, you cannot know the phase of the grid with much certainty because each PV's take on the grid phase is the aggregate of the actual grid phase and the phase of the other PV systems. Positive feedback and phase oscillation are likely. Using GPS to synchronize with the grid assumes that the grid's phase is stable, but my observations over the past few years have revealed that today's grid has much less short-term stability than the grid of old. I'm assuming that the lower phase stability today is caused by the recent massive adoption of grid-tied PV arrays. So instead of using GPS time to guess the current grid phase, you really need to know what it is (locally). Aside from placing grid phase monitors on nearby houses, I don't know how to do this.