A few n00b questions regarding how batteries actually work with a grid-tied system.

So I'm planning my solar system and I believe I've sized it correctly. The plan is for a 18kw panel array, and a 30kwh battery and an all-in-one charger/inverter with grid features. Right now I'm planning on the EG4 18kpv with either the EG4 server rack batteries or a pair of the EG4 Powerpro 14.3kwh batteries. I'm pretty confident about sizing the system and picking out those parts.

What I don't get is how I can use the battery on a daily basis and use my power instead of the grid's power. By that I mean powering my house with the solar panels during the day and then using the battery at night and only using the grid when necessary. I can see how it would work if I somehow put the all-in-one (18Kpv) between the grid and my breaker box, but I'm trying to keep the breaker box as-is and add a sub-panel in my garage (about 30' from the panel) for all the solar/battery stuff.

Is there something I'm missing? Will simply wiring the all-in-one to the main breaker box accomplish my goal?

You can do a forced discharge at certain intervals throughout the day when you know you're using power. This is great for hot climates with predictable air conditioning. Or set the 18kpv in net zero or zero export mode to offset loads on your panel. Do you have a net metering agreement with your utility?

It is designed to go between your meter and panel. Why not do it that way?

Quite a few options

Will Prowse said:

You can do a forced discharge at certain intervals throughout the day when you know you're using power. This is great for hot climates with predictable air conditioning. Or set the 18kpv in net zero or zero export mode to offset loads on your panel. Do you have a net metering agreement with your utility?

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In California where net metering got pretty bad recently, so I want to use as little external power as possible. So, if I set it to zero export, and it's wired into the main panel but not between the grid and the panel, will it be able to tell if there's an increased load coming from something else wired into the main panel? Like if the AC turns on or the jacuzzi filter turns on.

Will Prowse said:

It is designed to go between your meter and panel. Why not do it that way?

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The meter and panel are a single unit and about 30' away from my garage where battery and the 18Kpv is going to be (to keep it all indoors). Maybe somehow I route the grid wire to the garage first and then back to the breaker? I'm not sure what that would look like to keep it up to code. The other idea was to keep everything out by the main panel but I think it would be better to keep it out of the elements which would mean some type of outdoor cabinet which would get crazy hot in the summer.

Hey Wilde - I am planning something similar. I already have a grid-tied system using micro-inverters, so I will do AC coupling on the 18kpv at the gen input. My output will go to a critical loads panel and the meter at the solar disconnect (main panel). I haven't quite finished my blueprint yet, but I will try to remember to add an update after I get this installed and working properly. Cheers,

Wilde said:

What I don't get is how I can use the battery on a daily basis and use my power instead of the grid's power. By that I mean powering my house with the solar panels during the day and then using the battery at night and only using the grid when necessary. I can see how it would work if I somehow put the all-in-one (18Kpv) between the grid and my breaker box, but I'm trying to keep the breaker box as-is and add a sub-panel in my garage (about 30' from the panel) for all the solar/battery stuff.

Is there something I'm missing? Will simply wiring the all-in-one to the main breaker box accomplish my goal?

Click to expand...

Put CT's between the main panel and the meter. You can set a sol-ark to Limit to Home, and it will backfeed the grid input to your main panel until the CT reads 0. I assume there is something similar for the eg4.

If you can't get between the meter and main panel, then before the meter, or anywhere you can.

Yes you absolutely can put the inverter between your meter and your circuit breaker panel, you can set the EG4 18K to only charge the batteries or feed power through from the grid if necessary based on state of charge / voltage of your batteries. It will maximize your power from the solar panels, then battery and finally grid.
TOU (time of use) is a fantastic feature that you can use in areas with utility has different rates during the day.

Okay, now I get it. Just learned what a CT was and that I can connect one remotely to the 18Kpv. That's how it can tell when to send power to cover any usage I have at the time.