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Tesla DC PowerWall

Tesla DC PowerWall

How would this DC home battery work with ever growing solar panels using micro-inverters? So DC from solar panel is converted to AC at each panel by micro-inverters. Then reconverted to DC by second inverter for DC PowerWall? Would Tesla ever make AC home battery?

windex | 1 maj 2015

You're pushing electrons either way. AC is what is called a transmission technology. Transformers with AC power allow you to step the voltage trivially, while decreasing or increasing amperage to suit. Higher amperage loads require larger cables, which are more expensive and more lossy under load. Higher voltage loads are more likely to kill you if you come into contact with them, which is why your house runs at 120V/230V (most likely), while the utilities are running at 35,000V.

You convert DC to AC using an inverter. You convert AC to DC using a rectifier. Inverters and rectifiers are cheap, with inverters being slightly more complex and rectifiers being a bit easier to understand.

Every device in your home, save a few special cases, likely contains a rectifier / power supply to convert AC to DC. Every one of those power supplies wastes heat in the process.

Batteries output DC because it wouldn't be cost effective to integrate an inverter to introduce switched polarity into each battery, and even if it were, all of your batteries would have to be in phase for this to work when they reached your electrical panels.

Googling any of this stuff will give you tons of resources.

Brian H | 2 maj 2015

There is no such thing as an AC battery.

ken | 2 maj 2015

@limfamily, I too have micro-inverters but that makes no difference it simply means that the conversion takes place on the roof-top and feeds AC into your home system. The Powerwall should work the same for us as for those that do the inversion down at the main breaker panel. This can easily be sorted out by a licensed electrician like Solar City, just make sure you use someone that is licensed.

scanner2 | 2 maj 2015

I currently have leased solar panels with Solar City. I would like to reserve the PowerWall for my house but can I use it or am I allowed to use it with my Solar City Lease? I would then be able to store the electricity and not have to sell it back and use it as a power back-up in the event of a power outage. Will the installation connect directly to my current panels?

USCRXDR | 2 maj 2015

I currently have 54 solar panels and have 2 inverters connected to them. I also have a sig reservation for the modelX and am planning to have the power installed in the garage, i would like someone to call and figure out how to weave it all together in one service call.

Blueskies | 2 maj 2015

Can anyone tell me why we can't just use the Tesla we paid for with it's huge battery to power our homes instead of the little Powerwall battery? I'd think many of us would happily pay more than the price of the Powerwall for that privilege of accessing the power in our cars; if you must, charge us a monthly fee in addition to our cost of the inverter and all the hardware.

windex | 2 maj 2015

@Blueskie

The only direct access you would have would be to the same terminals the superchargers use.

The superchargers are over 135kW in. Which means the continuous (not peak) discharge rate is similar. You'd need an absolutely massive conversion system and wiring system on the order of the same class as a supercharger to access that stored energy, at least to the point it was regulated to a lower voltage/amperage.

Not going to be trivial. Financially not worth it by an order of magnitude relative to even the complexities of integrating Powerwall itself vs a lower voltage battery.

modelx2015 | 2 maj 2015

scanner2: I also have Solarcity Panels and called them about the Powerwall. They said it will only be available to new customers right now. Thanks Solarcity for caring about and offering it to their current customers. I might buy it elsewhere now.

Blueskies | 2 maj 2015

@windex, I'm not interested in using anything close to that peak discharge output; if I have a charged tesla battery, whatever the voltage, I should be able to discharge however little I like over a long period of time, no?

windex | 2 maj 2015

@Blueskies

It's my understanding that the regulator in the DC charging setup is on the supercharger, not on the car. The car communicates SoC data over a bus interface passed along the same connector, but the SC does the work.

If there were a regulator on the car, they wouldn't be able to increase supercharger output over time like they do (at least, not as easily).

Because there's no regulator, the step has to be done externally, so the cable running to the DC-DC converter (for safety) has to be able to carry the full load plus a safety margin.

Either that or your adapter plugged into the car would need a very combustible fuse in-line.

You are right in that low output levels would be cheaper to convert, but the front end of the system still has to survive 135kW of discharge capacity, even with a fuse (they take time to burn), and that side of the system will cost more than the rest of the DC-DC converter/DC-AC inverter.

Grinnin'.VA | 2 maj 2015

@ windex | May 2, 2015

@The superchargers are over 135kW

The last time I checked, the SCs were limited to a maximum power of 120 kW for any single charging MS. Each SC charger can only deliver 135 kW when it's charging two MSes at the same time.

Walid.rhannou | 2 maj 2015

Hi,
I work in a country where power is very unstable (insufficient input voltage half of the time) plus we have in average 4h outages per day.
The typical 4 room home (plus kitchen, laundry room and outdoor lighting) usually runs with a 20kva generator for the outages and is equipped with elevators and stabilizers for the power stability.
Can the powerwall help with those issues? How many powewalls are needed for one house?
Best regards

tina.h.le | 2 maj 2015

@ Walid,

The next question would be it depends on how often you plan to recharge the battery.

Looking at my own electricity bill, for two people who live with laundry room, dishwasher, water heater, AC, etc. , we don't use enough kW in a day to drain the whole 10,000 kW in a day. So 1-2 sounds feasible for a 2 person household, if you recharge the battery during daylight.

windex | 2 maj 2015

@ Grinnin'.VA

There are several screenshots clearly showing Model S' charge at well over 120 and occasionally over 130 kW.

I almost never use superchargers.

Requires a B or C version battery apparently. Plan is to move to 150kW at a later date.

You can go look around for yourself, you can determine kW rate of a supercharge from the Tesla charge screen by taking volts * amps / 1000. You particularly want to look for charges ongoing with a SoC between 20% and 60% complete.

Grinnin'.VA | 3 maj 2015

@ windex | May 2, 2015 new

@ Grinnin'.VA

There are several screenshots clearly showing Model S' charge at well over 120 and occasionally over 130 kW.

If so, I missed the announcement. Can you please provide a link to it?

Plan is to move to 150kW at a later date.

Ditto, my response above.

windex | 4 maj 2015

@ Grinnin'.VA

I am sorry you can't use google or do math.

I will refrain from indulging you in the future.

Red Sage ca us | 4 maj 2015

Blueskies: You can't do it because JB Straubel thinks it is a bad idea. Tesla Motors has shown no interest in V2H or V2G technologies. That's fine by me. I'd rather keep the energy in my car so I can drive a couple of states away during a disaster, rather than sit in the wreckage of my home heating hotdogs in the microwave.

dennis.calderone | 2 marts 2020

Does anyone know if the Powerwall II has any DC outputs (12, 24 or 48VDC) that can be used for dedicated DC lines? I want to wire a new house with DC circuits for 12VDC LED's or USB outlet, etc.

reed_lewis | 2 marts 2020

The powerwall only has 240V power lines. You would need a step down transformer. It is designed to be wired into your house's panel only.

andy.connor.e | 2 marts 2020

+1 reed. The power wall does not have connectors like that. Its designed to be hard wired into your main panel.