Nope, nothing special - just a short gap. From the UPS' perspective it doesn't know better if there is grid power or coming from the Powerwall. The UPS is just simply a bridge for that short switchover time.
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How long does a Powerwall support a home during a power outage?
- Thread starter jboy210
- Start date
Nope, nothing special - just a short gap. From the UPS' perspective it doesn't know better if there is grid power or coming from the Powerwall. The UPS is just simply a bridge for that short switchover time.
We already have UPS for all of our sensitive devices - which require periodic battery replacements as the usable capacity of those batteries degrade.
Once we get onto our solar/PowerWall system - even if the UPS batteries degrade - it looks like we'll only need them to run for a few seconds at a time - probably eliminating the need to replace batteries unless they fail completely.
Once we get onto our solar/PowerWall system - even if the UPS batteries degrade - it looks like we'll only need them to run for a few seconds at a time - probably eliminating the need to replace batteries unless they fail completely.
My PW can run my house for about 24 hours if I'm super careful about what's left on. Having said that, the solar charges it up again so I don't need that long. Also in northern cal but was never shut off in my small neighborhood.
We unfortunately couldn’t use Tesla PW (their gateway is limited to 200A and it would have required a few hundred feet of trenching), so we installed two Sonnen batteries (2x16kw). Switchover time seems to be longer than PW, as digital clocks go to flashing 00:00. I was home once during an outage, and it seemed to take a couple of minutes.
Since we are 99% electrical (still have propane for hot tub heater and generator (which only kicks in if no sun for solar and grid out), it is reassuring that we can we can survive almost indefinitely (although our garage is not backed up).
Since we are 99% electrical (still have propane for hot tub heater and generator (which only kicks in if no sun for solar and grid out), it is reassuring that we can we can survive almost indefinitely (although our garage is not backed up).
When you set up the PW they will add a second breaker box and you decide what circuits will get backed up. I excluded my A/C and pool and reserve only 20% for power outages as I have regular outages but seldom for more than a 10 minutes, max 2 hrs. I added solar primarily to always have a charge source in case of long periods and then f course to offset the grid
CounsellorTroy
Member
Agreed. The cost of UPS's are so cheap these days, and they are typically good for 3+ years before needing battery replacement, that it is a relatively small investment -vs- having to replace a computer, a big television, or any other major sensitive electronics, let alone the time lost having to deal with a fried motherboard or other power spike issue. Anxiously awaiting the installation of my (2) PW2's later this month to complement my two solar arrays.@jboy210 the Powerwall is fast to switch over, much faster than a generator that needs spin up time, but it is not the single-digit millisecond response times that even your cheap your under-the-desk UPS provides. In ideal conditions the Powerwall can take at least 100ms-200ms to switch over, I've experienced single digit seconds delay during high PV production. Even a 100ms blip can cause sensitive electronics, like your PC, to have issues. I have all of my home electronics (PC, TVs, servers, Xbox, etc) behind a UPS for this reason. Probably overkill but I'd rather have happy electronics
SoundDaTrumpet
Member
Hmm. I am considering eliminating the UPS (use surge protector instead) for my networking closet for the reason they are unneeded. Desktop computer didn't blink and no clocks didn't need to be reset. Anyone else fortunate as me or am I being too optimistic?
I live in Southwest PA and have a 10.5 kW solar system with 2 powerwalls (27.5 Kw). My home is a 4 bedroom and 2,800 sq ft. 5 years old with high efficiency appliances, gas furnace and AC and all LED lights. There are several variables when it comes to how long a system can power a home. My electric bill shows an average monthly use of approximately 800 kW. I record my usage and solar generation from the Tesla app (and previously MySolarCity) daily so I have a good idea of what drives the usage.
One thing to remember is the Powerwalls only charge off of the Solar Panel generated electricity not the grid (unless it is in Storm Mode) so how fast they charge depends on how much is excess generation you have during the day. Another is while you are off the grid the length of time the Powerwalls will last depends on how much generation you get during the days you are off the grid.
Based my average daily use (26.3 kW) my two Powerwalls should last about 43.5 hours or just under 2 days. However if I look at my average daily solar generation of 37.4 kWhrs which is greater than my average daily use I theoretically would never run out assuming I ALWAYS have nice sunny days (not gonna happen in southwest PA). I installed a system that should (theoretically) generate 150% of my usage but solar is highly dependent on SUNNY days and this year to date I am generating 127% which I expect to go up some since in the winter months (Sept - April) I have been generating greater than 150%.
I have only had two outages so far that were greater than a few days. The first was in the winter (Feb) last year and the Powerwall lasted just over 48 hours for 2 reasons, first those days were cloudy and it snowed so no sun and snow covered solar panels meant very little solar generation and I did not go to minimum house usage. The second time was in the spring and I never lost full power because we had partially sunny days and the Powerwalls basically only had to power the evenings when we have minimum electric usage.
Not sure this answers your specific needs, and I do not think anyone really can given the number of variables but my advice is get the largest solar system you can afford and a sufficient number of power walls to cover at least your average daily usage.
One thing to remember is the Powerwalls only charge off of the Solar Panel generated electricity not the grid (unless it is in Storm Mode) so how fast they charge depends on how much is excess generation you have during the day. Another is while you are off the grid the length of time the Powerwalls will last depends on how much generation you get during the days you are off the grid.
Based my average daily use (26.3 kW) my two Powerwalls should last about 43.5 hours or just under 2 days. However if I look at my average daily solar generation of 37.4 kWhrs which is greater than my average daily use I theoretically would never run out assuming I ALWAYS have nice sunny days (not gonna happen in southwest PA). I installed a system that should (theoretically) generate 150% of my usage but solar is highly dependent on SUNNY days and this year to date I am generating 127% which I expect to go up some since in the winter months (Sept - April) I have been generating greater than 150%.
I have only had two outages so far that were greater than a few days. The first was in the winter (Feb) last year and the Powerwall lasted just over 48 hours for 2 reasons, first those days were cloudy and it snowed so no sun and snow covered solar panels meant very little solar generation and I did not go to minimum house usage. The second time was in the spring and I never lost full power because we had partially sunny days and the Powerwalls basically only had to power the evenings when we have minimum electric usage.
Not sure this answers your specific needs, and I do not think anyone really can given the number of variables but my advice is get the largest solar system you can afford and a sufficient number of power walls to cover at least your average daily usage.
I'm getting solar and powerwall from Tesla. They are surely pushing me to get 2 powerwalls as each one is limited to 30A and for AC and I need more than that.
I'm wondering if (not during power outage) the system is capable of drawing current from partially the grid and partially from the powerwall in case I turn on the AC while drawing from the PW? For example if I set my power wall to kick in during super peak time (4 pm-9 pm where I live).
I'm wondering if (not during power outage) the system is capable of drawing current from partially the grid and partially from the powerwall in case I turn on the AC while drawing from the PW? For example if I set my power wall to kick in during super peak time (4 pm-9 pm where I live).
SoundDaTrumpet
Member
In often cases, the A/C is not compatible with soft start devices. In the sales phase, they are speaking generalization without know more about the particulars of your AC. 2 powerwalls can easily offset your A/C loads during peak periods. I have two BASIC A/C units that peak 8-9kW, and a single one does 4.8kW. In theory if you have one powerwall you can offset one A/C unit. Keep in mind both A/C are not backed but ARE monitored by the powerwall system... in other words, they don't operate when grid is out, but when grid is on... between 4-9pm, nothing draws from grid (until powerwalls reach the powerwall user's specified-reserve limit). In fact when the sun is out, solar is sent to grid while A/C + home loads are powered by Powerwall. (while in Time Base Control: either flavors). I am biased towards 3 powerwalls after coming out of 6mo of ownership during the summer, but see that 2 powerwalls are a happy medium, while 1 powerwall is essential for fire season power shutoffs in NorCal.
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If you run in Self-Powerered Mode you might be ok. However, I run in TBC and I have found that when the power goes out and the Powerwalls are in Standby, there is always a delay long enough that computers reboot and clocks go blinky-blinky. So, my computers, networking, and DVR remain on UPS.
SoundDaTrumpet
Member
@miimura you convinced me to leave the UPS where they are! Clearly, I have not run enough 'regression' testing. UPSes are tried and true!
Sounds like a great setup — but what was the final outlay to get everything installed, and how many years to recoup it?
this seems to be the largest barrier in my view. If you’re young(er) and plan to stick around for a while, it’s probably a great investment. But if you’re older and closer to retirement age, the investment seems not to make as much sense. You’ll be paying a significant bill, while perhaps not saving as much as you need to offset that bill.
just curious as to the thoughts of folks who either made the decision to purchase, or went the other way and could not justify for some reason.
this seems to be the largest barrier in my view. If you’re young(er) and plan to stick around for a while, it’s probably a great investment. But if you’re older and closer to retirement age, the investment seems not to make as much sense. You’ll be paying a significant bill, while perhaps not saving as much as you need to offset that bill.
just curious as to the thoughts of folks who either made the decision to purchase, or went the other way and could not justify for some reason.
I'm not familiar with customers connecting and disconnecting from the grid. that might have safety issues for the Utility workers if they are working on the same circuit. The procedure to connect and disconnect from the grid must not be as easy and simple as you implied.
cusman
Member
I live in south of Fort Worth, TX. My full home has 48 Solar Panels and 2x Powerwalls supporting 4000 sq feet of living space across two floors. There are two central AC units with an open floor plan. We got our Solar System installed in February and got PTO (permission to operate) in March.
During March & April, allowing my Powerwalls to deplete down to 40%, I was 99% self-powered. Most nights the 2x Powerwalls even running 2x AC units sporadically didn't deplete more than 60%.
As the months got hotter May-June, I found that they started depleting up to 40% and start drawing from grid before sun is back the next day to start powering home and recharging the Powerwalls.
Jul-Aug-Sep, I was lucky if the Powerwalls wouldn't get depleted to 40% even before midnight.
In Oct, things are finally getting cooler and now Powerwalls are back to being able to last night without even using up 50%.
All of this while we also charge one Tesla Model 3, mostly during day between 11am-3pm (peak sun hours). If we ever have to charge Tesla in evening / night, the Powerwalls get depleted super fast (within 1-2 hours). Sometime I think it would have been good to isolate the Tesla Wall Connector circuit as not being supported by Powerwalls and always pull from Grid or Solar only, but I didn't think of it to ask during install design / implementation or know if that is even possible.
Long story short, it basically depends on the load. The faster you are drawing power from them, the faster they deplete. If you can exclude your AC or you don't have high heat to combat, like you might have in CA year round, you can leave full home supported by the PowerWalls for days on end if you also have Solar during day to keep your home running plus re-charge your Powerwalls.
I think my situation would be better if I had 3x Powerwalls for my home size and the amount of heat we get in Summer to cool for even during night, but 2x is all that was minimally required to support both my AC units along with everything else. We have net metering and produce more during day than we are pulling at night so our electric bill is basically $0 and earning credits for future.
The only days we pull more from grid than we produce during day are hot days that are also cloudy.
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As @miimura points out, it's pretty easy to flip the main breaker. That effectively takes the house "off-grid". We weren't cutting power lines or anything. The house solar and Powerwalls are isolated and don't pose any danger to utility workers.
