Powerwall 2 plus Powerwall 3? possible?

Powerwall 2 plus Powerwall 3? possible?

Florida house, I have had my solar 16.38 kW solar panel system for about a month now.
We only got two of the Powerwall 2 units installed with them. Now I wish I had ordered 3 powerwalls.
So a total of 27 kwh of Powerwall storage.

I have taken the two Powerwalls down to 5% to see how long it takes to recharge.
No problem, with the 16.38 kW system, it recharges to 97% by noon or 1 pm, even on a partly cloudy day during December.
I suspect it could even recharge a Tesla for 5-6 hours at 240v/24 amps and still refill the two Powerwalls before sunset.
During the summer, probably at a much higher amp setting.

It seems like the 27 kwh are enough to get through the night, but not with a huge safety margin.

Yeah, if I turn off both ACs (Florida, we have two AC units, 3,500 sq ft house) and the water heater, then it is easy to get through the night and have plenty to spare.
But what if I don't want to worry about it? We don't have natural gas for heating. This house is 100% electric.

So I am fine with the 27 kwh of backup storage for now.
In the event of a hurricane, I am sure I can manage to get through the night with most of my first world lifestyle intact.
That is assuming the roof survives the hurricane and we are then just off the grid for a week while the region recovers.

I am not planning on adding another Powerwall for now. However, I wish I had done a 3rd one, looking back on it, while the tax credit is 30%.

But in the future, in a few years once my storage capacity declines, I suspect I will want a Powerwall 3 added to the existing system.

Is Tesla making these things to be backwards compatible? Any word on if they are making Powerwall 2 and 3 compatible with older versions?
Will we be able to just add a Powerwall 3 into the garage next to existing Powerwall 2?

Thanks for reading and considering my horrible first world problems.

Passion2Fly | 15 December, 2019

Forget about Powerwalls. I’m interested in Tesla allowing the cars to connect to the house. These are huge 80-100 kWh batteries sitting in your driveway.
I know that the Cybertruck will come with 240V outlets. Maybe this is the way to go...

PapaSmurf | 15 December, 2019

Vehicle to Grid is unlikely anytime soon. I think the battery packs of a car are configured differently than a stationary system like the Powerwall 2. Totally different software for different applications. And do you really want extra deep cycles on your expensive car battery pack?

I agree that it would be great for an emergency. But I don't think Tesla wants the cars being used for everyday Powerwall type usage.

Perhaps Tesla designs the functionality where the car could be used Vehicle to Grid in an emergency, but limit a Tesla Model S to perhaps 100 hours in "Home Powerwall Mode" before a reset is required to be sent by Tesla in order to continue. That way people wouldn't use it every day like that. It would truly be for emergency use only. It would probably be an expensive option to add on to your Tesla.

Passion2Fly | 16 December, 2019

If it’s just software, it can be done...

gregbrew | 16 December, 2019

I can backup my refrigerator, a couple of LED lights, a cell phone charger and a laptop with my Chevrolet Bolt for about a week. I put a 150A fused 120A Anderson connector on its 12V auxiliary battery. With the Bolt "on", I can hook up a 1500W pure sine wave inverter to the Anderson connector and draw 1kW continuous from the inverter, as the Bolt's DC-DC converter can convert 1600W of power from the 60kWh traction battery to the 12V auxiliary battery. I used large gauge welding cable to get the high current 12V DC to the external inverter. It isn't terribly efficient, but it does the job. The loads described above take nowhere near the 1.6kW max that the DC-DC can provide. I've tested it overnight. I made a similar modification to my Chevy Volt, and with 10 gallons of gas and a full tank, it should provide a similar backup capability as a "mobile generator" for a couple of weeks more. Each gallon of gas translates into roughly 10kWh of power in this application.

Using your EV as an emergency backup power source can be done today. It just requires a little skill and a few hundred dollars.

gregbrew | 16 December, 2019

I should also note that almost any ICE vehicle with an adequate alternator can also be used as a generator for emergency power off the 12V battery. You just need to be careful to size the alternator properly. Stock alternators are typically barely adequate to keep the 12V PbA battery happy.

The vehicle mods I noted above became moot, as I added two Powerwalls to my 5kW PV installation earlier this year. Now, they're just backup for the backup.

Patrick | 16 December, 2019

Papa - its probably a little too soon to know if a Powerwall 3 in the future will be compatible with the currents PW2s but I’d wager the answer will be yes. As you may know, this was not the case with PW1s and very early PW2s as they were DC-coupled, but I understand this was due to a major strategy shift to AC-coupled products going forward. Current PW2s are all AC-coupled - a little less efficient but much simpler, more practical and more interoperable.

We shall see, but IMHO it sounds like Powerwalls are flying off the shelf now that they have finally become readily available. I’m thinking their broad adoption over just the next year or two will pretty much ensure compatibility with future models.

That said, we went with 3 PW2s for many of the same reasons you mention in a similar sized home. We went even further by installing dual-fuel HVAC systems to eliminate those thirsty electric heat strips in the colder NC winters when solar generation is lower... I suspect three may be a bit of overkill in our case - we’ll see what happens. Would rather have a little more juice available if needed.

Patrick | 16 December, 2019

Gregbrew - love the creative VTG solutions. Have been watching others doing the same thing - simple and effective.

One would assume Tesla is studying this market opportunity carefully and will elegantly integrate their fixed and mobile battery products at some point in the future. Hope so anyway as now we have both...

reed_lewis | 21 December, 2019

The difference between all of these solutions involving using your bolt or car with a 12v to a/c inverter versus a PowerWall is that the PowerWall basically just works automatically. I just got two installed and when they did a test, the switchover was immediate, and nothing in my house even knew the power had dropped.

With any other solution I need to plug stuff in, and am without power for that period of time.

Patrick | 22 December, 2019

Yes - and there is no question that seamlessly integrating a large Tesla EV battery with a Powerwall microgrid would open up some really interesting and useful capabilities for both the vehicle and the microgrid.

I’m guessing one of the design challenges (using current technology anyway) is adding 240 VAC inverter output functions to the vehicle, which one would assume impacts basic vehicle weight, range, cost, etc. Once added, however, it seems like the EV could have a single integrated AC-coupled connection to the microgrid generation panel to handle both its charging and discharging functions.

Maybe it’s as simple as designing a new two-way battery “charger” in the EV to replace the current charging-only setup, but it’s likely more complex as the current EV battery output is high-voltage DC.

Knowing Tesla they will ultimately solve the challenges and bring us yet another something elegant and amazing....

Passion2Fly | 22 December, 2019

The future cybertrack comes with a 240V outlet. They will need an additional plug/outlet to interconnect the EV and the TEG. The standard 14-50R outlet doesn’t allow bidirectional power flow per electrical code. Also, the TEG has a wired communications link with the PowerWall; probably the same will be required with the EV but via WIFI... I do expect the EV to be managed as an “add on” (temporary) to the micro grid due to its mobile nature... A primary PowerWall will still be required. The Solar PV and the EV will probably be managed similarly, as ON/OFF systems. The PV via frequency shifting and the EV via WIFI. If the WIFI link drops, the EV will automatically get disconnected...
Can you imagine driving to a Supercharger (with solar and Power Packs) to charge your car and come back home to supply your house until the next morning when you go to work again?... no more need for the grid!

Passion2Fly | 22 December, 2019

Needless to say that Tesla will control the World. Maybe not a good thing...

Patrick | 22 December, 2019

@Passion - all good points - and something along those lines seems practical and doable. Perhaps we’ll see their first VTG solution rolled out with the CT and maybe even the Semi given their massive battery capacity.

Our energy future is so bright I think we need shades.... :-)

PapaSmurf | 22 December, 2019

"Can you imagine driving to a Supercharger (with solar and Power Packs) to charge your car and come back home to supply your house until the next morning when you go to work again?... no more need for the grid!"

That is likely the fear Tesla has and will require VTG to prevent people abusing Superchargers in that manner. Some people have free Supercharger use grandfathered in.

If Tesla does create a VTG option, I am sure they will charge for it because there is extra hardware likely required.

Not everyone with a Tesla car will want or need a VTG option. So there is no need to provide the hardware for everyone. I suspect Tesla will also want to limit this option to people that already have a Powerwall 2 or later installed in their garage with the TEG for easy Tesla power management, updates, etc.

One suggestion I think that makes sense is some sort of limit, perhaps 100 hours, so that a Tesla car is not part of the everyday home power system. Using your car battery pack really should be for emergency use only. Putting those types of cycles on your car battery pack should not be a daily event.

Just my opinion.
As always, everyone is welcome to my opinion.