AC Coupling query with a solar edge system & batteries

elrao

Hi

Am looking at a 6.2Kw array using a Solar Edge 6Kw inverter and an 18KwH array of batteries that will allow me to charge during the off-peak period (4 hours) and use that electricity the next day.

The installer I have been working with is proposing Growatt, with a single GroWatt SPA3000 AC coupler and 3x 6.5KwH batteries.  I am not an electrician but I do understand electricity and physics.  If I understand it correctly a single SPA3000 would limit me to charging at 3Kw or discharging at 3Kw; meaning a max charge capacity of 12KwH during a 4 hour window (i.e. i couldn't charge all my batteries every night) and would also mean I can't store my own peak solar output (6.2Kw) if I were not using any of it?

So I would need at least two AC couplers (or one larger 6Kw coupler) and have one battery on one and two batteries on the other (not sure if you can make a loop with two couplers and 3 batteries or not!!).  

To be fair to him, we started with a string inverter and then the option of Solar Edge + Tesla ... and then moved to Solar Edge with other batteries (which introduced the need for the AC coupler) - so it wasn't a system he built up in one go and hence may not have considered the above.

Meatballs

The solar isn't installed yet? Why aren't you considering a hybrid 6kW inverter? You can get Tigo optimisers that work with any inverter afaik if the reason you were looking at SE was that. 

There's plenty of 5kW AC battery inverters available which would charge 18kWh in a 4 hour Octopus Go period if you still wanted seperate inverters though.

Waywardmike

I have an SPA3000 Growatt AC inverter with a single 6.5kWh battery.  I was under the impression that you could only have two on one inverter anyway but I may be wrong?

Also, from use, it appears that it charges the battery at ~2.8kW, and discharges at ~3.2kW, max.

Coastalwatch

Hi elrao, I have a Solaredge PV array installed four years ago and just added 2 x 8.2 storage batts served by a single 3kW AC inverter. I believe the AC Inverter is capable of serving upto 40 kWh's of batts but only at that limited 3 kW rate.

I've subsequently added a third battery and second inverter, in order to be able to completely charge all three during the Octopus Go window. I'm planning to fit a fourth battery when one becomes available. Not because three are insufficient just that a fourth would maximise the second inverter together with the additional storage capacity for those occasions when surplus PV is going begging..

elrao

Coastalwatch said:

Hi elrao, I have a Solaredge PV array installed four years ago and just added 2 x 8.2 storage batts served by a single 3kW AC inverter. I believe the AC Inverter is capable of serving upto 40 kWh's of batts but only at that limited 3 kW rate.

I've subsequently added a third battery and second inverter, in order to be able to completely charge all three during the Octopus Go window. I'm planning to fit a fourth battery when one becomes available. Not because three are insufficient just that a fourth would maximise the second inverter together with the additional storage capacity for those occasions when surplus PV is going begging..

Sounds similar to my plan.  Yes, logically the 3kw ac coupler could have virtually unlimited batteries behind it, but can only convert 3kw either way, so you can charge at a collective total of 3kw...so 12kwh per 4 hour period per coupler.  Hence why most people would have one or two batteries!

elrao

Meatballs said:

The solar isn't installed yet? Why aren't you considering a hybrid 6kW inverter? You can get Tigo optimisers that work with any inverter afaik if the reason you were looking at SE was that. 

There's plenty of 5kW AC battery inverters available which would charge 18kWh in a 4 hour Octopus Go period if you still wanted seperate inverters though.

Not yet. Struggling to get an installer to actually quote for what I want (and something that will work as I want).

Originally started with a hybrid inverter.  Was going SE due to some partial shading (would rather spend a little more to not worry about it).

He's not offered a workable solution that combines SE and 18kwh battery.  Have a quote for the hybrid and SE with Tesla.  Both would work, was trying to find a good middle ground?

Meatballs

The SE only supports a limited number of batteries and they are all 400V models which are more expensive in general for limit benefit (imo).

6kW Solis hybrid  5G (max charge capacity 5kW), Pylontech batteries, tigo optimisers would do what you want without having unnecessary inverters/inflating size of your g99 application.

elrao

Meatballs said:

The SE only supports a limited number of batteries and they are all 400V models which are more expensive in general for limit benefit (imo).

6kW Solis hybrid  5G (max charge capacity 5kW), Pylontech batteries, tigo optimisers would do what you want without having unnecessary inverters/inflating size of your g99 application.

Not sure I understand about SE?  It converts DC to AC, you then need a separate "AC Coupler" to convert AC back to DC - which can be solar you've generated or electricity from the grid surely?

Limiting factor on the SE is how much solar it can convert to AC, which impacts your entire solar array (I.e. No point having an 8 kwp array and a 5kw SE)...but nothing else?

The limit is the coupler (which was the issue I had with what he proposed, as it was a single 3kw coupler).

QrizB

elrao said:

Meatballs said:

The SE only supports a limited number of batteries and they are all 400V models which are more expensive in general for limit benefit (imo).

Not sure I understand about SE?  It converts DC to AC, you then need a separate "AC Coupler" to convert AC back to DC - which can be solar you've generated or electricity from the grid surely?

The majority of battery storage inverters were designed to use 48V batteries. This harks back to the days of 12V lead-acid batteries, where you would use four of those in parallel to make 48V. 63A at 48V is 3kW. When lithium batteries came onto the scene, battery packs were developed to mimic 48V lead-acid packs and work interchangeably with them.

There are lots of suppliers of 48V batteries, including the well-respected Pylontech range.

Meatballs is saying that the SE inverters have been designed to us 400V batteries. This results in much lower currents - 7.5A at 400V is 3kW - which saves money with wiring and switchgear, and might be slightly more efficient. But it limits you to 400V batteries, and there aren't many (any?) alternatives to SE.

elrao

OK, but I am talking about SE to convert the DC from the panel to AC.  Not for DC to AC to charge the batteries.

elrao

Meatballs said:

The solar isn't installed yet? Why aren't you considering a hybrid 6kW inverter? You can get Tigo optimisers that work with any inverter afaik if the reason you were looking at SE was that. 

There's plenty of 5kW AC battery inverters available which would charge 18kWh in a 4 hour Octopus Go period if you still wanted seperate inverters though.

Need to find a suitable Hybrid that can convert 6.2kwp of solar and also charge batteries at at least 5kw (ideally 6kw as I may go to 24kwh of batteries).

The Growatt 6000 can deal with the solar, but appears to max out at 3kw for DC charging (solar or from grid), so that is a non starter.  The Solis maxes out at 5kw on solar, so would mean I'd be wasting some of my sunshine.

Need to find something 6kw rated for both!