Tying Solar to a Main Panel with 2 Service Disconnects

[gridsolar]

I'm working on a residential solar project where the main service panel has one meter but 2 main service disconnects. One disconnect is a 200A that feeds a bus with some loads in that panel, while the other one is a 100A that feeds a separate subpanel in the garage. That 100A is NOT on the bus that the 200A feeds. It's like on its separate corner inside the main panel. If I were to do a load-side tap onto the feeders of the 100A service disconnect, would solar only supply the subpanel loads and not the loads connected to the bus in the main where the 200A breaker feeds?

 

[wwhitney]

Yes, as the bus in the main would still have only one source of supply, via the 200A breaker. The utility and PV sources combine on the utility side of that 200A breaker.

Cheers, Wayne

 

[gridsolar]

Yes, as the bus in the main would still have only one source of supply, via the 200A breaker. The utility and PV sources combine on the utility side of that 200A breaker.

Cheers, Wayne

Thanks for the response! What connection would you suggest to do so that both loads from the main bus and the subpanel can be supplied by solar?

 

[winnie]

What exactly do you mean by 'supplied by solar'?

If the solar is downstream of the meter, then solar production will offset usage on either bus.

But for conductor sizing purposes the solar will impact only the bus it is connected to.

The PV source is electrically parallel to the grid, so there is no way of saying where a particular watt second of energy is going.

Jon

 

[jaggedben]

I think Wayne answered the question from the point of view of whether the 200A disconnect is subject to any code rules when you interconnect on the 100A feeder. His answer was correct from that point of view. However from the point of view of energy flow for net-metering, then the answer to the original question is yes. Electrons don't know if a breaker is a service disconnect.

 

[gridsolar]

What exactly do you mean by 'supplied by solar'?

If the solar is downstream of the meter, then solar production will offset usage on either bus.

But for conductor sizing purposes the solar will impact only the bus it is connected to.

The PV source is electrically parallel to the grid, so there is no way of saying where a particular watt second of energy is going.

Jon

If we follow the circuit of the system, since the two buses are isolated, wouldn't excess solar power (power not used by the subpanel loads) be sent back to the grid before reaching to the loads on the 200A bus - thereby not supplying these loads?

 

[jaggedben]

They are not isolated. Their feeds are paralleled between the meter and the disconnects.

 

[gridsolar]

Ah that makes sense since there is only one meter. Thanks so much!

 

[Carultch]

If we follow the circuit of the system, since the two buses are isolated, wouldn't excess solar power (power not used by the subpanel loads) be sent back to the grid before reaching to the loads on the 200A bus - thereby not supplying these loads?

The only power that a meter can measure, is the net flow of power at that point in the circuit at any instant. It cannot tell the difference between 4kW consumption-only, and production of 6 kW at the same time as consumption of 10 kW.

A meter can be built for different configurations of how it accumulates imported and exported energy in its kW-hr register(s), but the data available to it at any given instant, is only the net flow of power. E.g. net metering, bidirectional metering with two separate registers, secure-forward metering.