Help me understand my options for backing up circuits using a single Powerwall.

[spooky981]

I'm running out of time to make final decisions to lock on Tesla's commitment of the 2020 tax credit value.

With a single Powerwall what can I back up on this breaker box?

I know all the 15/20 amp outlets and lights aren't an issue. It's the 30amp and higher circuits that I'll have to make some decisions on. By my count that's five: Two AC units, the car charger, the stove, and the dryer.

The LRA of my AC units is 37 so soft start kits should bring that down to a usable level. I'd probably only need one of the AC units but two would be nice.

I don't need the car charger at all. If the power is out I've got a gas vehicle that will do just fine. Could probably live without a stove during an outage.

I also don't much care how long the battery lasts in an outage. I'm going for coverage not duration.

What are my options with the remaining circuits?

IMG_20201122_202847

• spooky981
• Nov 22, 2020

Breaker Box

 

[h2ofun]

1 powerwall, basically just lights, refrig. what good is coverage if it only lasts an hour?

 

[BrettS]

You are definitely looking at backing up a subset of your circuits with a single powerwall. Tesla will not allow anything with more than a 30A breaker to be installed on a single powerwall system. Up to a 60A breaker can be connected to a two powerwall system.

 

[power.saver]

Everything except the dryer, oven and car charger.

 

[bob_p]

We have 4 PowerWalls, which should provide 20KW of continuous power.

Based on our "full load" testing, with the start upgrades added to our 3 air conditioners, we are able to run everything in our house off grid with the PowerWalls, except for our double electric ovens and the 50A EV charging outlet connected to PowerWalls. And we could use the ovens or EV charging, if we don't have all 3 air conditioners running and/or turn off the pool pumps.

A single PowerWall may be challenged in powering an air conditioner along with other loads from the house. Plus with a single PowerWall, an air conditioner is going to draw down the power pretty quickly.

We're confident that if our PowerWalls have at least 50-60% charge, we can run our house off grid during unplanned power outages for several hours. If we anticipate an extended power outage (hurricane), we plan to manually turn off devices (2 of the 3 air conditioners, pool pumps, no electric ovens, unnecessary lights, ...) to reduce power consumption enough to allow us to operate for days without grid power (as long as there is sun during the days).

 

[jlv1]

I struggled between ordering 2 or 3 PowerWalls. We have 2x HVAC systems (2 furnaces, 2 A/C). In the ordering process it stressed that I needed 3 to have a whole house backup; with just 2, they would only put critical loads on the PowerWalls (e.g., everything except the 50A EVSE and the two A/C).

But when they came to do the actual install, the installers just put the whole 200A panel behind the 2 PowerWalls. Most of my outages have been in the winter (we get 2-3 a year) so I'm alright with just not running the A/C if we were in an outage. When the zombie apocalypse comes and the electrical grid fails, I'll probably regret that decision.

 

[SMAlset]

@spooky981 I would also plan ahead in the event you want to add any additional storage at a future date. Where and how you place the PW would be important. If you mention the possibility to the installers when they arrive and discuss your set up, they might suggest some alternatives to you and run things to make upgrading easier.

We originally ordered 2 PWs but midway decided to go with 3. We were able to floor mount a stack of 2 on the floor and add the 3rd as a nearby floor mounted one, leaving us an easy route to add a 4th to that single floor guy. You can’t stack mount on the wall. We were lucky to have enough wall/floor space in the garage to run PWs next to each other and stacked.

 

[gpez]

Your panel looks a lot like mine, though we only have one AC unit. You mentioned stove but I don't see a breaker for that.

I backed up all but the high watt appliances so no oven, AC, car charger, or dryer. We have gas everything else, including water, heat, and stove. Given the fairly low wattage of your AC units you could probably get 1 of those on the backup circuit. But running, say, the oven on the Powerwall is "like powering a hairdryer with AA batteries" according to my installer.

 

[JeremyWhaling]

15A for an A/C seems pretty low, unless it's a wall mounted unit for a single room. Seems somewhat reasonable to be able to back that up, at least in theory.

I was also considering a single powerwall setup, and trying to shoehorn a 25A 4 head mini split on the backed up side. In theory it could work (it's under the 30A breaker requirement), but now that we have lived with both the mini splits and 4 kW of solar without powerwall for a summer and some cooler weather in heat mode, we'd basically be out of power in 5-8 hours without solar (or a poor producing day). Or to put more practically - you don't know how long an outage lasts until the power comes back on!

Do you have access to green button data with your utility or otherwise have a sense or TED or some other metering device to see what your actual consumption is? While you may be successful in convincing Tesla or a third party installer into backing up an A/C unit, you should probably take a look at your consumption just to see how viable one powerwall truly is for your needs. I mean, I have a nearly all gas appliance townhouse, and one powerwall is a bit "iffy" for durations longer than a day (which, to be fair, is extremely rare here) when combined with only 4 kW of solar. 13.5 kWh isn't a whole heck of a lot of storage, and may require some management/rationing of essentials depending on time of year.

 

[jrweiss98020]

Back up as much as they will let you! Just because it is connected, doesn't mean you will use it all the time.

I have my whole house (200 A service) backed up with 2 Powerwalls. I might choose to NOT use the dryer in the cold of winter, but I HAVE used the oven in the summer!