Where/How to find an engineer to design AC-coupled system

[inetdog]

@niel
It's just that if the utility finds my backup system connected they will request the repayment of the rather large rebate I got for the grid-tied system. So, I was just wondering whether a simple, but very visible, connect/disconnect could be in my system circuit to satisfy the utility that I wasn't violating the spirit of the agreement about not having a battery backup.

This has the feel of a philosophical dispute. If you connect a totally separate battery backup system to your house, then you will have a situation where you sell all of your excess AC production from PV back to the grid, but part of your load on the GTI and grid will be going to a battery charger. No problem there, and none of POCOs business as long as you use an NEC compliant transfer switch setup to go to battery during a power outage.
Now compare that to the situation in which some of your solar PV goes directly to charge your batteries. From the POCO point of view, in letter and in spirit, the result is just the same.

What could be different is that POCO does not want you to collect any rebate or incentive based on that part of the system cost which is attributable to the backup function. In that case, if you still use exactly the same components for which the rebate was paid and do not try to collect a rebate on new equipment you add to get the battery backup, you should still be OK.
The question of what happens if you stop using the equipment that you got the rebate for is one I will leave to the lawyers.

[Robin Gudgel]

MidNite does offer a few systems to accomplish the AC coupling, but as you mentioned, they are not cheap. Then again, neither was your GT system. There just ain't no free lunch when it comes to AC coupling. The MAgnum system we offer is about the least expensive system possible. The Xantrex XW inverter is also good and does not require a solid state relay to knock the GT inverter off line. The problem is that you cannot buy an E-Bay inverter and AC couple it. You need a real inverter. Magnum, XW, OutBack or Sunny Island. The inverter is only one part of the expense though. You still need batteries, switchgear and over current protection, solid state relays and don't forget to make it all code compliant. Yup, not cheap. Most installers are not yet up to speed on AC coupling. It is pretty new and not so obvious.