Adding Battery Storage to a Grid Tied System?

[Walleye Hunter]

Forgive me for my ignorance but I am a retired working man and have little knowledge of these things. I have a grid tied array on my roof and I want to know if it would be feasible to add at least some battery storage capabilities to it. I have 72 panels on two Solar Edge inverters. The array seems to be divided into quadrants.
Specs are:
Panels:
72 270W, 8.69 Amp, 38 VOC, Pmax (whatever that is) 31.1V

Inverter(s):
Solar Edge SE7600A-US
Max DC Power 9300W
Max DC Volts 500 V
Max Input Current 23.5 Amps

One quadrant would be 18 panels and I did this math:

18 Panels in series at 38V/ea would equal 684V, more than the inverters are rated for. At 31.1V it comes to 559.8. I'm guessing that the inverters are underrated because max voltage will never be produced. Am I on the right track?

I have four (4) sets of wires coming into the inverter(s). Is there any reason I can't tap into those leads and feed a charge controller then a battery setup? Can I just put a switch inline to facilitate just switching it over to charge the batteries?

Thanks for any and all help,
Mark

 

[MisterB1959]

It might make a difference depending on where you are, which country/state etc as they all have their own rules ...

 

[400bird]

Solar Edge requires optimizers on each panel. These are proprietary and will only work the Solar Edge inverters. They provide RSD (required for roof mounts), panel level monitoring and MPPT, and a DCDC allowing odd strings, like yours.

So, unless you are willing to get on the roof, remove/replace the optimizers, and completely remove some portion the panels from the Solar Edge inverter, no, your idea doesn't work.

What does work is called AC coupling. You'd add a battery inverter that can charge from AC. This would be able to charge from the AC output of your solar. If set up right it can also provide back up power if the grid goes down.

 

[Walleye Hunter]

Solar Edge requires optimizers on each panel. These are proprietary and will only work the Solar Edge inverters. They provide RSD (required for roof mounts), panel level monitoring and MPPT, and a DCDC allowing odd strings, like yours.

So, unless you are willing to get on the roof, remove/replace the optimizers, and completely remove some portion the panels from the Solar Edge inverter, no, your idea doesn't work.

What does work is called AC coupling. You'd add a battery inverter that can charge from AC. This would be able to charge from the AC output of your solar. If set up right it can also provide back up power if the grid goes down.

Thanks for the information. That takes the wind out of my sails. I was also hoping to use it for long term in the event of a loss of the grid for long periods of time. So if that were to happen, I'd need to go up there and remove the optimizers.

 

[Solar Guppy]

You can replace the SolarEdge with Storedge inverters and keep the array side components as is. You still have to have a critical loads panel and other work, for more information look here

 

[400bird]

Thanks for the information. That takes the wind out of my sails. I was also hoping to use it for long term in the event of a loss of the grid for long periods of time. So if that were to happen, I'd need to go up there and remove the optimizers.

You don't need to remove anything, you can use a grid forming inverter to AC couple with your current Solar Edge inverters (maybe only one, depending on how large of a grid forming inverter)

I am doing exactly that with my Solar Edge grid tie 6k inverter and a Schneider XW pro 6848

Something like an Outback Radian, Sol-ark, Schneider XW would do the job. Or any number of cheap import inverters from the likes of EG4, Growatt, etc. I just don't know anything about those to recommend any specific inverter.

 

[MurphyGuy]

You want to look into something called AC Coupling.

 

[Walleye Hunter]

Thanks for that information. It's all above my paygrade but now I have a direction to look and some things to learn.

 

[MurphyGuy]

Thanks for that information. It's all above my paygrade but now I have a direction to look and some things to learn.

AC coupling is pretty difficult and complex in function, but stupidly easy in practical application on your side.

You just hook up a specific type of inverter (one capable of AC coupling) to a battery and connect the output of the inverter to your home's breaker panel.. (after isolating from the grid of course)

When you turn the battery system on, the battery inverter (that is capable of AC coupling ) starts making power for the home just like any other battery inverter. Shortly after, the inverter(s) on your solar array see this "grid quality power" and they think the grid is back up and running so they start making power.

If the solar array makes more power than your home needs, then the battery inverter will use that extra power to charge the battery.. If the solar array doesn't make enough, the battery inverter will add to it.

So during a sunny day, if your 5kW solar array is pumping out 4.5kW but your home is only using 1 kW of energy, then you'll have 3.5 kW going into your battery.. If you're using a 48 volt battery, then 3.5kW / 48 volts = about 73 amps of battery charge current.

As the extra 120/240 juice is coming from the solar array, the battery inverter will convert it to DC to charge the batteries as needed.

The operation is pretty complex, but wiring it up (your side of making it work) is ridiculously easy. Its just a 4 wire connection with a ground, neutral, hot and hot. No different than a sub panel in a garage.

 

[Walleye Hunter]

Thanks for everything, I watched one video on it and am starting to understand it. A question that I have on my existing system...it looks to me like the panels have a combined VOC of 684V but my inverters are only rated for 500 DCV input. I do have a friend who is more knowledgeable than I am on this and he tells me that that that's the makings of a disaster. But after 7 years, no disaster for over voltage. I'm thinking that the panels just don't make the full VOC. Any advice on what gives on all of that?

 

[MisterSandals]

One quadrant would be 18 panels and I did this math:

18 Panels in series at 38V/ea would equal 684V

it looks to me like the panels have a combined VOC of 684V but my inverters are only rated for 500 DCV input.

Are you sure each quadrant has all 18 panels in series? Maybe you have 9 in series, twice, connected in parallel (9S2P) which would be 9x single panel voltage and 2x amperage.

If you can tell the voltage of your strings in any of your readings, it would be fairly easy to make a good guess at the config. Otherwise examining the wiring of a quadrant would be definitive.

 

[Walleye Hunter]

Are you sure each quadrant has all 18 panels in series? Maybe you have 9 in series, twice, connected in parallel (9S2P) which would be 9x single panel voltage and 2x amperage.

If you can tell the voltage of your strings in any of your readings, it would be fairly easy to make a good guess at the config. Otherwise examining the wiring of a quadrant would be definitive.

I was just digging in the depths of my monitoring system and it looks like voltage tops out short of 400 VDC. I have four pairs of wires coming off of the roof into the inverters, which leads me to believe that it's just four quads. And when I open up the inverter stats, it shows two strings on each inverter.

 

[MisterSandals]

Pmax (whatever that is) 31.1V

voltage tops out short of 400 VDC.

400V / 31.1V = 12.86 panels in series (theoretical at 100% efficiency)

I dunno, seems odd.

 

[Walleye Hunter]

400V / 31.1V = 12.86 panels in series (theoretical at 100% efficiency)

I dunno, seems odd.

Well...how's 400/560=80% sound?

 

[MisterSandals]

Well...how's 400/560=80% sound?

If your SCC is 500V max input then its a piss poor installation. I cannot believe anybody would make such an egregious mistake. And thats with Vmp. If using Voc as one is supposed to for sizing, this puts it into the insane range.

 

[Walleye Hunter]

If your SCC is 500V max input then its a piss poor installation. I cannot believe anybody would make such an egregious mistake. And thats with Vmp. If using Voc as one is supposed to for sizing, this puts it into the insane range.

Like I say, I am clueless and all I can do is tell you what the specs are on my system.

 

[DIYrich]

One possible option is to get an eg4 18kpv or sol-ark; put output of Solar Edge into the Gen Input; put grid into grid line; and put main panel on Load line.

Tell the inverter there is AC PV on the Gen Input.

Add whatever batteries you want.

 

[MisterSandals]

Like I say, I am clueless and all I can do is tell you what the specs are on my system.

I think you are doing just fine and appear open to learning.

We really need to figure your array out though. It’s almost certainly not 4x 18S quadrants. But before one can make a plan or buy equipment we need to know exactly what you have up on your roof.

 

[400bird]

400V / 31.1V = 12.86 panels in series (theoretical at 100% efficiency)

I dunno, seems odd.

You guys with your math ??

Solar Edge optimizers do two things, MPPT for the panels, but also adjust output voltage to try and hold the string to about 370-400 volts (I think this varies depending on AC voltage).

Ok, prob other stuff too, like RSD, but two things related to this "math" ?

I had a 12s and 8s array of identical panels in parallel and this meets Solar Edge's recommendation because it can buck/boost voltage on each panel to get the string voltages to the ideal 380 ish volts for max efficiency. All the panels output nearly identical (and good) wattage in the monitoring platform.

 

[MisterSandals]

Solar Edge optimizers do two things, MPPT for the panels, but also adjust output voltage to try and hold the string to about 370-400 volts

Interesting! So the optimizers can prevent the SolarEdge from getting lethal voltage?
If so, is there some communication or how does it know not to deliver more than 400 volts?