Grid-tie passive system with an external cut-off yet still allows grid power to MB

[bcompton1]

The owner wants to install a grid-tied passive solar system into the electrical system of a new building. Grid power is 240v/600a. The power company is fine with the grid-tie system but requires a cut-off outside ? so THEY can control it - next to the meter box to prevent passive power backflowing to the grid when they don?t want it to. But when the cut-off is thrown, the customer still needs to have grid power to the MB panel. I?ve looked at auto and manual 600amp transfer switches and double throw disconnects but when you jump up to 600amps, the prices go over $4k. Anyone know of a less expensive device or way to meet the cut-off requirement but still feed grid power to the MB panel?

 

[jaggedben]

Why would a cutoff switch for the solar cut power from the grid?

The term 'grid-tie passive' is not common and you should probably explain what exactly you mean by it. The one sensible example I found with google is not a system that I would call 'grid-tied' at all. Either there is something you aren't explaining about the setup and the customer's or utility's requirements, or there is something your not understanding about how grid-tie systems and inverters work. Maybe the utility is also misunderstanding the system.

As far as the expense, yeah, 600A equipment is expensive. My only question is if you really need 600A equipment to switch off the solar. You only mentioned that the service is 600A, and not what the solar output is.

 

[don_resqcapt19]

The utility does not normally open the solar power disconnect unless they are working on the transformer that feeds the building, or on their conductors that feed the building. It is very very unlikely that the utility would open the solar power disconnect and not also have the grid power to the building disconnected.

 

[ggunn]

The owner wants to install a grid-tied passive solar system into the electrical system of a new building. Grid power is 240v/600a. The power company is fine with the grid-tie system but requires a cut-off outside ? so THEY can control it - next to the meter box to prevent passive power backflowing to the grid when they don?t want it to. But when the cut-off is thrown, the customer still needs to have grid power to the MB panel. I?ve looked at auto and manual 600amp transfer switches and double throw disconnects but when you jump up to 600amps, the prices go over $4k. Anyone know of a less expensive device or way to meet the cut-off requirement but still feed grid power to the MB panel?

I guess I am confused. It is typical for a utility to want a lockable AC disco between the inverter and the interconnect, but the power to the building doesn't go through it. It just needs to be sized for the maximum rated output current of the inverter; the size of the service is irrelevant. What you need isn't a transfer switch, just a simple AC disco.

I have no clue what you mean by a "passive" grid tied PV system.