SMA & Powerwall

[Yinn]

Does anyone have experience with a SMA system with the new powerwalls?

I currently have 10kw of solar going through 2 SMA inverters, which then go into 2 SMA Sunny Islands. At the time I bought it, it allowed me to create an "island" to do what a powerwall would be able to do as well. The limitations though was that I needed a dedicated subpanel and I couldn't exceed 5kw of backup storage (good for ~4-6 hours of my critical load panel) It's never been good enough and I have been contemplating a generator purchase, but now I'm wondering if I could hook the powerwall as the whole house backup and either rip and replace the sunny island (expensive and seems wasteful) or have it in addition to the existing system.

Anyone have any ideas?

 

[miimura]

1. Getting the PowerWalls and Sunny Islands to work together well may be challenging.
2. The Sunny Island can accommodate a generator much more elegantly than PowerWall.

Did you really mean 5kW of power or did you mean 5kWh of energy storage? What kind of batteries are connected to the Sunny Islands? Can that battery bank be expanded? If not, why not?

 

[Yinn]

1. Getting the PowerWalls and Sunny Islands to work together well may be challenging.
2. The Sunny Island can accommodate a generator much more elegantly than PowerWall.

Did you really mean 5kW of power or did you mean 5kWh of energy storage? What kind of batteries are connected to the Sunny Islands? Can that battery bank be expanded? If not, why not?

5kwh of energy storage. 12v sealed lead acid batteries wired to 48v is connected to the Sunny Islands. From what I was told the Sunny Islands have a max of 50amps & 5kwh storage per unit. Which means if I wanted to add another 5kwh of battiers, I would need to purchase another Sunny Island. The cost to do that + add batteries would be significantly more than a generator or a powerwall. I'm also going to be getting a free powerwall (due to referrals....one day) but I'm not even sure if I'd be able to install that to work with the existing system.

Optimally if I could, I would like the powerwall to act as a whole house backup. Upon depletion for a generator to kick in to provide standby power to the whole house and charge the powerwall up with any excess. Upon top off, switch back to the powerwall. If I'm still out, then switch to the existing Sunny Island on critical loads only. But I'm pretty sure I'm dreaming there and would need to custom build software for that to work.

 

[miimura]

As far as I know, there is no good reason that you can't put larger capacity batteries on a Sunny Island. Of course, each inverter will only pull a certain number of amps due to its AC power rating. However, if you want to put double or triple the Amp-hours (and resulting kWh) of batteries on it, there's not much to stop you besides practical ways to parallel the batteries. Of course, using a single string of batteries is better. You could more than triple your capacity (18kWh) by using 8 of these batteries.
Crown 6CRV390, 390Ah 6V L16 Battery - Wholesale Solar

This guy in Norway built a system with a Sunny Island and salvaged Nissan Leaf battery cells in a server rack cabinet. Proper BMS communicating with the Sunny Island and everything.
Use of Nissan Leaf battery in Solar installation. - My Nissan Leaf Forum

 

[Yinn]

As far as I know, there is no good reason that you can't put larger capacity batteries on a Sunny Island. Of course, each inverter will only pull a certain number of amps due to its AC power rating. However, if you want to put double or triple the Amp-hours (and resulting kWh) of batteries on it, there's not much to stop you besides practical ways to parallel the batteries. Of course, using a single string of batteries is better. You could more than triple your capacity (18kWh) by using 8 of these batteries.
Crown 6CRV390, 390Ah 6V L16 Battery - Wholesale Solar

This guy in Norway built a system with a Sunny Island and salvaged Nissan Leaf battery cells in a server rack cabinet. Proper BMS communicating with the Sunny Island and everything.
Use of Nissan Leaf battery in Solar installation. - My Nissan Leaf Forum

That would only be part of the solution though as I would prefer a whole house backup. I believe it's the amp/sunny island that would be the limiting factor. To supply the 200amp service I would need 4 Sunny Islands but I think the max is 3 units for 150amps and I would need to purchase more Sunny Islands. Between the cost of additional SI's and the batteries, it gets close to the powerwall cost

 

[wwhitney]

To supply the 200amp service I would need 4 Sunny Islands

Most houses with 200 amp services never draw more than 100 amps, so sizing your inverter off of your service size is inefficient. At the very least you need to do an NEC load calculation; even that is overly conservative, so somebody like a generator manufacturer might have an algorithm for a more accurate load estimate.

Cheers, Wayne

 

[miimura]

That would only be part of the solution though as I would prefer a whole house backup. I believe it's the amp/sunny island that would be the limiting factor. To supply the 200amp service I would need 4 Sunny Islands but I think the max is 3 units for 150amps and I would need to purchase more Sunny Islands. Between the cost of additional SI's and the batteries, it gets close to the powerwall cost

I have a 400 amp main panel on my house. That is mostly irrelevant. Two 5.75kW Sunny Island inverters could easily run my whole house except EV charging. I have natural gas heat and hot water and no air conditioning. You really need to look at the real simultaneous loads to know what you can or cannot run in a grid outage situation. For example, Tesla will not allow any load more than 240V 30A on the backed up side of their Energy Gateway.

Also, according to the information I found, you can install 4 SI's in "Double Split Phase" with no special hardware. With their Multi-Cluster system, you can gang up to 12 Sunny Islands for a 100kW system, so they are not the limitation. I think if someone who really knew what they were doing took a more detailed look at your system and your needs, you could get a lot more out of the system you already have. We don't know where you're located, so we can't even make an educated guess at your needs.

 

[nwdiver]

5kwh of energy storage. 12v sealed lead acid batteries wired to 48v is connected to the Sunny Islands. From what I was told the Sunny Islands have a max of 50amps & 5kwh storage per unit. Which means if I wanted to add another 5kwh of battiers, I would need to purchase another Sunny Island.

I agree with @miimura... that don't make sense. Can't think of a reason would can't increase the capacity of your battery bank. 5kWh is awfully small... I've got ~20kWh comprised of Golf Cart Batteries.

How often do you use your backup system? If it's only a few times a year upgrading to a larger PbS04 bank is certainly the best option...

 

[Yinn]

I agree with @miimura... that don't make sense. Can't think of a reason would can't increase the capacity of your battery bank. 5kWh is awfully small... I've got ~20kWh comprised of Golf Cart Batteries.

How often do you use your backup system? If it's only a few times a year upgrading to a larger PbS04 bank is certainly the best option...

That’s kind of what I figured too. And based on what I find it seems I should be able to, but this is what my installer keeps telling me

The worst part is that my house is wired in a way that my critical loads are spread out. (Dedicated Sub panel per floor - on the actual floor) so if I wanted to backup my fridge, I need to pull the wiring from the first floor subpanel in my kitchen. Well pump is basement subpanel. Bedroom upstairs subpanel in the closet hall. Even the garage has its own panel. So I’m not sure if that’s why and I need a sunny island per subpanel.

So right now only my basement loads are protected. Our sump pump, well pumps work but we sit in the dark, freeze and still have spoiled food which is silly. Hence why I’m looking for a whole house alternative. Even if I just upped my batteries, I would need to rewire the house to backup my true critical.

My house runs on well, septic, electric stoves, heating oil and all my vehicles are fully electric. Generator people recommended a 10-15kw whole house backup. My usage is roughly 70kwh/day under normal use. The grid by us is terrible, we experience several power outages per month. Most last an hour or two but about once every two months we go 6+ hours without power, but it’s usually restored within a day.

 

[idoco]

Whoever told you about the battery limit on the SI's is incorrect. We have two SI's with 16 batteries(US RE L16 XC2). Each battery is 6V rated at 400 Ah(20C) and configured as two parallel strings of 48V. So 800aH = ~40kWh of storage. According to the manual the upper limit of the settings for the battery backup is 10,000Ah...~500kWh@48V!!!

We have a 100A load center. SI's provide 240V AC @48A max continuous (peak 180A for 60secs). On the AC side you can multicluster up to 100kW power!

As for powerwalls, the older SI's don't have the ability to charge lithium. So you need to check which SW revision you have.

Slightly OT. I personally think if you have the room for lead acid they are a better choice than powerwalls for stationary home backup applications. For the price of one powerwall you can get approximately four times as much capacity in lead acid.

http://files.sma.de/dl/15216/SI4548-6048-US-BE-en-21W.pdf

 

[Yinn]

Ok so this is all very helpful. And thank you for being patient with me here. It's helping me formulate the right questions to find an appropriate installer. I have a couple more though..

@idoco - I have an older version that doesn't support lithium, but that doesn't matter too much to me. AGMs aren't all that bad. How are you wired up? Do you have your SI's backing up the entire house? Who did your install? I'm on the NJ/PA border about 45 min from Philly.

My heaviest load time will be in the evenings when I'm pulling ~70 amps to charge both cars and another ~20 amps around the house for the electric stove, lights ,etc. So I think you're right that with proper load shedding and wiring I should be able to setup a whole house backup with my SI's. I have 2 right now, a 6048 and a 4048 wired up as Master and Slave, but both support the dedicated panel.

 

[idoco]

@Yinn Sent you a DM.