Line side tap with battery.

[steachj]

I have a 10kwh system being installed later this month. Installation company want me to derate my 200 amp box to 175 so they can at 50 amp system.
I asked them to get GMA line side tap from SCE and they said sure. They also said down the road I can not install a battery back up without getting rid of my line side.
My question is :: Can I have a line side hook up and a battery backup at the same time. Thanks

[Mike90250]

> My question is :: Can I have a line side hook up and a battery backup at the same time. Thanks

No. They said either one or the other

What I expect they meant was, battery cannot be on the system that the Tap is on.

[PVAndy]

> My question is :: Can I have a line side hook up and a battery backup at the same time. Thanks

No. They said either one or the other

What I expect they meant was, battery cannot be on the system that the Tap is on.

That seems strange to me. We have many back up systems with PV that use line side taps. Very rarely do we downsize mains.

Andy

[heimdm]

Not an electrician's perspective.. so take that for what it is worth.

Line side taps can create a challenge on the battery side. Essentially there are 2 challenges
1) When the power down you need to cut off the grid to prevent backfeeding.
2) You need a path to get the power from the batteries to the house, without go to the grid.

There are devices like the Powerwall gateway that pretty much does all of that in one fell swoop, and generate the sine wave to keep your inverters going. Solar Edge has a similar device as well.

In my eventual setup, my challenge is we have 320amp service and most of the islanding/gateways only give you 200 amps.

[Ampster]

......

In my eventual setup, my challenge is we have 320amp service and most of the islanding/gateways only give you 200 amps.

Is 200 Amps not enough to get you through a power outage? My apologies if that was answered somewhere else.
I have seen some large battery systems approaching 100 kWhs but even one of those would not last very long at 200 Amps (48kWs). Batteries are expensive compared to the cost of load management during an outage.

[heimdm]

In the setup of the Tesla Gateway or other islanding devices, it also becomes you service disconnect. So if you dropped that down to 200 amps, it would be for your whole house, not just during battery time. However, when I have pulled my real time electrical monitoring worst case scenario draw is probably 125 amp. The question is do you want to downsize the mains coming into your house. I have thought about when having my line side tap done, to have them swap the existing service disconnects for an ATS. If I wanted to feed a gen set or batteries down the road it would be there.. since the meter and everything would be open to do the tap.

[Ampster]

I will defer to the experts on whether the gateway is or has to become your service disconnect.
Conceptually I think it would be possible, with the right design, to distribute 150 Amps around multiple subpanels during a grid down situation. Obviously the cost of that design and those transfer switches would have to be weighed against the cost of more batteries and inverters.
Anecdotally, I was discussing the recent power outages with an electrician friend in Texas. He had recently worked on a Google data center there and I asked him how that center did during the freeze. He said that it did not lose a beat because it had so many redundancies built in. Those redundancies were both batteries and generators.

My only point is that there is a system design out there that can meet your goals. Whether that design uses multiple 100 Amp gateways/transfer switches or one 400 Amp device should not matter, as long as it is cost effective.