Can a 7kWh and a 10kWh PowerWall be used together in a single installation?

I haven't seen this addressed either, but I'd guess that it would be possible if there were two separate paths. I doubt you could hook them up in series. It would probably be less expensive to just have more of the 7 kWh modules (unless you're planning to max out the 7 kWh and then you should probably look at a PowerPack.)

Look's like you can only get this system if get the Solar City Solar pannel's
and do not think you can get off the grid.:scared:

I think a lot of these types of questions can only be answered when the manufacturers release their Powerwall compatible inverter/chargers.

Maybe the extra type is just like an extra "string" to the inverter

Inverter
Powerwall 7 kwh x3
Powerwall 10 kWh x2
Solar Panel String 1
Solar Panel String 2

So you modularly add each of the same type into one configuration then separately add one or more of the other configuration.

Meaning so long as your inverter or cabling setup can accept another logical branch you can mix and match as you like.

but hey I'm no electrician and I don't do Solar PV for a living either.

I'm just thinking that it'd make sense that there ought to be some way to configure the overall system to use multiple types of batteries.

I was told here on the forums that the 7 kWh version may be used as backup. It's just that the 10 kWh is restricted to backup and cannot supply on demand power otherwise. Why not just get a 7 kWh or two if necessary? I see no reason to mix and match.

apacheguy said:

I was told here on the forums that the 7 kWh version may be used as backup. It's just that the 10 kWh is restricted to backup and cannot supply on demand power otherwise. Why not just get a 7 kWh or two if necessary? I see no reason to mix and match.

Click to expand...

I agree that if you are going to get the 7kWh for daily cycling it would most likely be better for both batteries to just get two 7kWh packs. That being said until all of the details on each pack is released it is kinda hard to say.

ecarfan said:

.......

Can a 7kWh and a 10kWh Powerwall be used together in a single installation? On a single inverter? Does the Powerwall BMS support them being used together?
.......

Click to expand...

Yes, anything is possible with the right inverter logic and some relays or contactors. As Jerry33 has suggested I would buy two of the 7kWh units and program my inverter to leave more room at the bottom of the daily cycle. As others have said it will be interesting to see the new inverters that will be offered in response to this less expensive battery solution. I know at least one hybrid inverter that can be programed that way but it is a 48v model but the logic is already there in the electronics.

That is kind of a "down in the weeds" question to be asking a CEO. He is the guy responsible for implementing a strategic vision for the company. Your question has no relevance to other shareholders who want to hear how the vision will be implemented. The people to ask are the inverter guys from Solar Edge. It is in the inverter where the decision about which pack, or conversely how much of a dual pack to use for daily cycling. The battery management system only manages the charging and cell balancng functions.

Ampster said:

That is kind of a "down in the weeds" question to be asking a CEO.

Click to expand...

Perhaps.... but perfectly appropriate for the 'Product Architect' :wink:

....and the answer is?

Frankly, I don't think Elon really knew the answer. He said "no", but then he backed off that a bit. I think the capability is still being developed right now, and part of the engineering is being done at the inverter manufacturers. It is the inverter that tells the Powerwall that a grid failure has occurred.

Just thinking out loud here. Assuming a SolarEdge inverter and architecture. The backup Powerwall battery is full as it must be all the time for it to be a backup battery. The grid goes down. The automatic transfer switch trips isolating the house electrical system from the grid. The inverter notices the grid has gone down, and must now somehow match power loads from the DC side to the AC side. Ie. The AC side needs 5kw of power and the inverter tries to grab 5kw of power from the DC side. Since the Powerwall and the solar panels are on the same power bus, somehow the inverter must try to grab the 5kw just from the solar panels if they are producing enough power, but then grab the rest of the power from the Powerwall should a cloud pass by. This might be as easy as telling the Powerwall that it is now in power distribution mode and for the Powerwall to supplement power as needed to the DC bus.

Anyways, in such a system, I don't see any difficulty in having mixed daily cycle batteries and backup batteries, except that the inverter software needs to know which batteries are which and be able to communicate individually with them. Perhaps their architecture isn't robust enough for individual battery addressing. If so, that's an unfortunate limitation. Or it could be that v1.0 of the inverter software for the Powerwall just doesn't support mixed battery types.

We will just have to wait and read the actual product technical manuals when the products are finished...

Here's Elon's answer about combining the 7 kwh and 10 kwh Powerwalls:

"Well, combining them actually wouldn’t be super, super great. It’s going to be -- I mean actually we could make the software do that but it doesn’t currently do that. It would treat them both -- it’s simply going to treat it, if you had a 7 and a 10 like a 17 kilowatt hour system and depending upon what your draw is, it would currently I believe draw equally from both. Maybe JB should join me on the stage and answer some of these questions."

"Can a 7kWh and a 10kWh PowerWall be used together in a single installation?"
You would probably need separate inverters. The powerwalls are designed to be connected in parallel. All the powerwalls in a circuit need to be on or off. You probably couldn't have the 10kWh being optional in that circuit.
How a group of powerwalls will balance the batteries is an interesting question. Its the balancing that is the tricky part. Musk knows this of course. But his engineering brain was flashing to how it could work.

electracity said:

"You would probably need separate inverters. The powerwalls are designed to be connected in parallel. All the powerwalls in a circuit need to be on or off.

Click to expand...

I don't think any of those three statements is true. The Powerwalls work very much like the SolarEdge optimizers: they connect in series, but the total voltage of the string is constant. And so it's perfectly possible to control the voltage and power delivered by each unit. My interpretation of Musk's comments is that he is saying it is possible, can be done with software, but isn't a use case they have considered and so is not currently supported.

I have to say I do not understand the use case for combining the units. The 10 kWh supports backup uses, the 7 kWh supports backup and time-of-day shifting use cases. If you need/want to support both use cases, buy the 7 kWh units.

How could powerwalls be connected in series?