Powerwall for Planned Power Outages

[Freakyguy666]

1) At a minimum, I imagine 4 would be required. Six power walls may not be needed if you are able to shed power usage during a power outage. Pool equipment, EV charging, and power for secondary structures could be moved to a non-backup electric panel. Use of an electric cloths dryer can be mitigated by hanging clothes under sun.

Consider average winter use (with an added margin) as your metric for 24 hour backup use. Summer use is higher (with AC loads) and can be mitigated with great summer production.

Note, the extra money spent on two more Powerwalls may be better spent connecting a natural gas backup generator for maximum flexibility. The Powerwall can control the backup generator as needed.

2) Mokuzai has the best answer. As a reminder, the Tesla Powerwall support page states, "To ensure reliable operation during power outages, at least one Powerwall is required for each 7.6 kW AC of solar included in the backup circuit." Three is the minimum for a 15.2 kW-DC system, though four makes better sense.

3) Without knowing how your home is wired, I assume Tesla will install your gateway and Powerwalls based on the below sample layout from the Tesla Powewall Installation guide.

View attachment 544543

Non-critical loads would remain in the 400 A main panel. All your critical loads would be moved to a 200 A "backup-load" panel. A 200-400 A "generation" panel would include your Powerwalls, solar, and generator (if applicable).

So theoretically, if a 400A gateway becomes available, would there be any need to add sub panel(s)?

 

[Janus]

So theoretically, if a 400A gateway becomes available, would there be any need to add sub panel(s)?

If you wanted to do whole-house backup, then you probably won't not need a sub panel. That being said, I wonder how many customers need 400A gateways, and does it make business sense to develop a device for a (possibly) very small market.

One other option to note. Other folks on this forum have talked about splitting their 400A service into two 200A sub panels. Then each sub panel would have it's own gateways, solar, and powerwalls. Basically, it'd be like have two totally independent systems (i.e. there would not be any way to transfer energy generated/stored between the two 200A panels during an outage).

 

[GenSao]

So theoretically, if a 400A gateway becomes available, would there be any need to add sub panel(s)?

If your 400 A main panel is directly connected to your electrical meter, than yes, sub panel(s) are required.
If there is a way for Tesla to intercept the conductors from the meter to the 400 A main panel, then no, sub panel(s) are not required.

One other option to note. Other folks on this forum have talked about splitting their 400A service into two 200A sub panels. Then each sub panel would have it's own gateways, solar, and powerwalls. Basically, it'd be like have two totally independent systems (i.e. there would not be any way to transfer energy generated/stored between the two 200A panels during an outage).

Although this is possible, it is not as efficient. In the case of an extended power outage, there is no way to share power between the two separate systems in the case of a load imbalance. I believe you may not need more than a 200 A backup load panel.

A crude check is to compare what your "average" peak load is. Add a factor of safety of say 150%. With the below sample, my peak usage was 5.87 kWh (excluding solar) in an hour period. Adding a 50% factor of safety results in 8.81 kWh/h (or kW). As I have 2 Powerwalls, this fits within the 10 kW continuous power and 14 kW peak power of the Powerwalls.

Alternatively, consider increasing the efficiency of high load devices. I recently upgraded from a 1990's 4 ton single stage AC unit (SEER 9?) to a 4 ton two stage AC unit (SEER 17).

 

[Owner]

Official nice response to why non-profits don't want old solar systems

"What I learned from my team is that right now we cannot accept the equipment because there have been challenges in the past from donations, e.g. liabilities, designs, production. We also offer equipment warranties for all of our clients, and with donated systems we cannot provide that. Sorry we cannot accept your donation."

 

[Janus]

Although this is possible, it is not as efficient. In the case of an extended power outage, there is no way to share power between the two separate systems in the case of a load imbalance. I believe you may not need more than a 200 A backup load panel.

Agreed, the best option here would be for Tesla to offer a 400A gateway. My point was simply that with the current limitations, that's one way to offer whole-house backup with a 400A service.

 

[Owner]

I just got a second response for my solar. They can likely use it. Sounds like the non-profit will avoid their warranty issues by using it on their own building.

The longer haul is trying to figure out how to replace the gas boiler with something electrical.... working on that slowly....will report back if I find something suitable.

 

[StealthP3D]

Yeah... mini-splits are AWESOME for off-grid use since they're inverter driven so there's no starting surge. My lights flicker more when my fridge cycles than when my HVAC cycles. How old are your mini-splits? The newer ones seem to have better specs for cold weather operation.

I installed a 1-ton mini-split in my ski cabin a couple years ago and it's amazing! The electric bill from my baseboards was killing me and now it's about 1/4 the cost!

But the point I wanted to make is that some mini-splits are optimized for heating in cold weather and some are a bit better at cooling in warm weather. I'm not sure if it's a difference in the sizing of the heat exchangers or the pressures the various valves run at but if you live in a cold climate it's something to keep in mind. Mine puts out it's rated capacity down to 5 degrees F! But it still cools well too. I could have saved a small amount (around $400) by just buying the Mitsubishi but I got a Daikin instead and very pleased!

Specific info can be hard to come by in the US and many dealers/installers don't even know the details, just that you charge them up, connect the wires and they work! It would be nice if there was a non-profit resource that was brand agnostic and could direct consumers to the best brand/model for their application!