Adding Battery Storage to a Grid Tied System?

[Hedges]

Not sure about communication to limit max, but I think they support up to 24s.
Output 1V while shut down, so 24V seen by inverter would mean 24 in series.

 

[400bird]

Interesting! So the optimizers can prevent the SolarEdge from getting lethal voltage?

Voc on my panels is 44.5
12 in series is something over 500 volts before temp compens.
So, yup

If so, is there some communication or how does it know not to deliver more than 400 volts?

Communication, yes
No idea how or what is communicated between the inverter and optimizers ?‍
Must be magic! ?

Not sure about communication to limit max, but I think they support up to 24s.
Output 1V while shut down, so 24V seen by inverter would mean 24 in series.

Right, there are limits to how far the things can buck/boost. I don't know what that is.
It doesn't use the shut down voltage to determine the number of optimizers. I have had two different length strings connected to the same inverter input.

 

[Walleye Hunter]

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.

Wow, I wished I was as smart as you.

 

[Walleye Hunter]

Voc on my panels is 44.5
12 in series is something over 500 volts before temp compens.
So, yup

OOOO you and your math.
I'm so glad you stepped in here with all your knowledge to help me out.

 

[Solar Guppy]

Solar/Store Edge systems are unique in that it is a small window targeting a fixed voltage from the optimizers, and there is communication between the inverter and per panel optimizers, so there is no typical VOC calculation to be made. There are limits to how little or many can be in series due to the boost limit of the optimizers.

 

[JBertok]

Solar Edge optimizers are each an MPPT DC-DC converter, with communication back to the inverter, but they even work with a non-SolarEdge inverters since they function autonomously. The optimizer emulates a solar panel in the string. The number of amps that passes through each optimizer in series will always be the same, as with the panels. The optimizers boost the voltage pressure like a panel would.

The SE7600A-US inverters each have input maximums of 500V DC and 23.5A
There are two power output level maximum for the different models of Optimizer- 60V or 85V DC. And then there are different models specific to the panel cell count and the silicon type, but all optimizer models are limited to 15A maximum output.
SolarEdge Inverters control the total string voltage and the voltage output of the optimizers.
The only Voc from the Optimizers is 1V which they default to when disconnected from the the inverter MPPT. So, they prevent higher than operating voltage from hitting the DC feeds into the inverter - only the optimizer itself has to be exposed to Voc of the unloaded panels, and those ratings are from 48, 60, 80, 87, or 125V DC maximum depending on the model of the optimizer.

The panels are probably strings of 18. This could be confirmed by opening the disconnect at the inverter and seeing 18V. While running, if you're seeing 440V DC at the MPPT inputs that would mean 24.4V from each optimizer average. Assuming the inverter is running at 100% output of 7600W and 97.5% efficiency, plus a 98.8% optimizer efficiency, that would mean a harvest of about 220W per panel, and you should be seeing about 8.85A on each of the two MPPT inputs per inverter if the string voltage is holding at 440V.

 

[Hedges]

If solar edge optimizers work with other inverters, that opens up more/easier backup options.
What about the keep-alive signal? Is it SunSpec same as Tigo and others?
That is, what switches them between 1V output and MPPT mode?

 

[Walleye Hunter]

Can the sinewave to activate the inverters.

Solar Edge optimizers are each an MPPT DC-DC converter, with communication back to the inverter, but they even work with a non-SolarEdge inverters since they function autonomously. The optimizer emulates a solar panel in the string. The number of amps that passes through each optimizer in series will always be the same, as with the panels. The optimizers boost the voltage pressure like a panel would.

The SE7600A-US inverters each have input maximums of 500V DC and 23.5A
There are two power output level maximum for the different models of Optimizer- 60V or 85V DC. And then there are different models specific to the panel cell count and the silicon type, but all optimizer models are limited to 15A maximum output.
SolarEdge Inverters control the total string voltage and the voltage output of the optimizers.
The only Voc from the Optimizers is 1V which they default to when disconnected from the the inverter MPPT. So, they prevent higher than operating voltage from hitting the DC feeds into the inverter - only the optimizer itself has to be exposed to Voc of the unloaded panels, and those ratings are from 48, 60, 80, 87, or 125V DC maximum depending on the model of the optimizer.

The panels are probably strings of 18. This could be confirmed by opening the disconnect at the inverter and seeing 18V. While running, if you're seeing 440V DC at the MPPT inputs that would mean 24.4V from each optimizer average. Assuming the inverter is running at 100% output of 7600W and 97.5% efficiency, plus a 98.8% optimizer efficiency, that would mean a harvest of about 220W per panel, and you should be seeing about 8.85A on each of the two MPPT inputs per inverter if the string voltage is holding at 440V.

Can the sinewave to activate the inverters come from something like a generator or another battery with an inverter on it? Would it be possible to bring the system up that way and disconnect it when the batteries get close to full charge without damaging anything?

 

[Walleye Hunter]

I am looking into adding a Tesla Powerwall 2 to my system and have a meeting scheduled with one of their guys this week. I'm curious to hear what he has to say.

 

[bhbaker220]

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.

So what happens when the battery becomes iompletely charged, the PV array is generating peak power, but the load is minimal? Would you have to change settings for no export control and have a smart meter installed?

 

[Hedges]

A grid-forming battery inverter like Sunny Island can be configured for zero export. If PV generation exceeds loads, it draws current into the battery, preventing export. If it can't draw down enough power to prevent export, then it disconnects from grid and raises frequency until GT PV inverter reduces PV generation so it is just enough for loads plus battery charging.

With AC coupling, the battery inverter can't tell GT PV to reduce output so long as grid is passing through, setting frequency.

Alternatively, without needing battery inverter, current transformer can be used to monitor grid current. Some inverters take CT input directly, others can be commanded over Ethernet to adjust their power output. (zero export). This doesn't require smart meter (just a utility measurement thing), but might use a separate meter. SMA makes use of 3rd party meter and Ethernet.

There might be issues trying to use zero-export GT PV and AC coupled battery inverter, because they might have a slightly different measurement of "zero". I would think one or the other would be implemented; if GT PV was zero export to the the utility meter, let grid-forming battery inverter think export was OK (but not export its own battery power to grid.)