excess power to grid sensor
 

When my solar grid tied power is more than I use I would like to sense this.
I can divert it to my golf cart charger. I have almost 10kw/hours worth of batteries for storage. I could have an inverter as supplement to prevent using grid power.
I could get free nights from the utility, charge the golf cart at night, use it during the day during peak power prices?
I could use it to excite the grid tie inverters during grid outages. or during the spring and fall low power needs.
I need a sensor!

Thanks for all thoughts, errors in my thinking
how do I save drafts while developing my posts?

UL 1741 makes exciting a grid-tied inverter challenging without a grid. It also saves the lives of linemen working on your grid. If you have a UL 1741 approved with stand alone production capability, that's different. Read up on UL 1741, and let us know what type of inverters you have.

There are devices out there that can sense when your PV array is producing in excess of your home's present consumption. I ran across one not too long ago that was using a Raspberry Pi (small linux PC) to do the processing. EmonPi I haven't used it, but it looked entertaining, maybe someone else has used one?

If you want to do this correctly and use the Golf cart battery’s for load shifting and battery back up you would need a hybrid battery inverter. it can be set to turn on a smart load (sol-ark has a cool set up for this). My Schnider xw+ can be set to output a 12v signal at battery full level or high battery alarm (or low battery) that can be used for a contractor. You could use this set up to detect full battery’s and turn on a smart load like you golf cart charger to use up the power. It will also fake out the grid tie inverter to run when the grid is down (this is called AC coupling). The thing about hybrid inverters is that they contain a transfer relay that disconnects the load (or home) from the grid when the grid goes down and islands itself so that the solar can still run.