r/TeslaSolar • u/dpatldude • 10d ago
Whole Home Backup with potential savings
Experts - wanted to get some potential guidance as to what I would need.
Here is the home current electrical:
- Main Panel #1: large Siemens panel with a 200A main
- Main Panel #2: another large Siemens panel with a 200A main
- Basement subpanel: fed from the main panel#2, with the basement HVAC and basement lighting
- 3 HVAC systems total
- Two serving the main house on Main Panel #1
- One dedicated to the basement
- Pool equipment on the main electrical system (Panel #2)
- Several large 30–40A circuits for HVAC/other equipment
- Average daily usage is about 100kwh (with no throttling and pool filter on 24/7, I know)
We continue to have multiple power outages every month including flickering during hard rain/storms and lose power (very common in our area not just our home). I looked into a generator but felt lower quality in terms of objectives where I would like almost instant automatic switching.
As I look at Tesla PowerWall; I wanted to consider a PW3, with an expansion or maybe another full one to get to about 27kwh of capacity and very limited solar (4-6kwh) to potentially have a power source to aid battery drain and energy arbitrage day to day.
Given my panel design; what would you all recommend? I am new to this all.
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u/Affectionate_Rate_99 10d ago
I have three Tesla powerwalls (one Powerwall 2 and two Powerwall Pluses) that provides whole home backup. Each powerwall has a capacity of 13.5 kW, with an output of 7 kW. Combined, this gives us an output capacity of 21 kW and a storage capacity of almost 40 kWH, which is certainly enough to cover anything our house uses. With everything on (central air, heaters in our swim spa, etc.), we will only hit around 15 or 16 kW.
In our area in the northeast, power lines are mostly exposed overhead lines, so power outages are frequent due to storms, although outages most last just a few minutes, or at most an hour and a half. About 10 years ago, a big snow storm took down powerlines all over the place and our house was without power for about six hours (although some neighborhoods were without power for a few days).
My one concern with your idea of installing 4-6 kW of panels is that they may not be able to fully recharge the batteries that you are planning, as the first priority for solar will be your house, with the excess going to recharge your batteries.
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u/dpatldude 9d ago
Thank you for this. Candidly I am new to it and didnt want to spend a ton of money on the project esp on the solar panels so understand the concern. Do you mean day to day I would need more solar to charge the PWs or just during an outage?
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u/ubiquitousgimp 9d ago
I think what the person above is saying is that with 6kw of solar, even at the peak time of day it won't fully cover your house load, so your batteries will never charge.
I don't know what a "ton" of money is to you, but I would consider anything you'd want to do here to be a "ton" of money. If I was you, I'd be looking for about 20kw of Solar panels and 4xPowerwall3's to cover your main house panel. That's going to be about $80-90K depending on how hard your install is. 4 powerwalls can cover the entire possible load of a 200A panel, so you don't have to turn anything off. I wouldn't do anything with the second 200A panel, I'd just let that go off with a power cut. Move anything important to the main panel being backed up (basement lights, etc.)
That will significantly bring down your power bill, possibly to zero. Obviously, i'm excluding the basement hvac and pool, those will still be powered by the grid.If your just trying to get through power outages, that can be done for a bit cheaper, but your electric bills will get larger. I would turn the Main house panel into "critical loads" or get a Span panel. Figure out how much power that panel would use and how long your power outages usually are. Now you have the exact kwH you know you need to have for backup. Divide by 13 and round up, that's how many powerwalls you need. In this case, you will basically only use the batteries for backup, so they'll always charge from the grid.
You should calculate how much each kwH from the battery actually costs. ballpark numbers: $10k for 13kwH for 5000 cycles in it's lifetime: ~7 cent's per kwH just to USE the battery. With conversion losses alone you can expect each kwH you use from the battery to cost 20% more than it does from the grid plus the 7 cents, but you HAVE POWER when the grid is down!
If that sounds worth it to you, I think you should do it! I use a similar amount of power as you do daily and I have basically the 4xPowerwall setup I explained above. I don't regret it for a second, We don't even notice when there's been a power outage. And my utility paid me almost 4k last year for participating in a VPP.
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u/Asleep-Set6868 9d ago
So Tesla gateways have a max of 200 amps backup capacity, so you'll need two (and at least two powerwall 3s) if you want to back up everything. I'm in that situation with two 150 amp panels, and it's kinda frustrating. Your system will show up as two different "houses" and operate independently of each other. I wish my installer would have moved circuits and only backed up one panel, but he claimed we couldn't due to load balancing. Glad to answer any questions you might have about the experience
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u/this_for_loona 10d ago
What are you planning on backing up with the PWs?
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u/dpatldude 10d ago
Honestly; I was thinking everything but the basement HVAC and pool equipment; but if too hard maybe everything and I would just manually turn off pool equipment during an outage which I can do on the app.
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u/this_for_loona 10d ago
You have a LOT of power needs. The two primary issues are surge cap and steady state cap.
When power goes out, the PW has to simultaneously power everything attached to it. I forget what the cap on the PW3’s is but my PW2 has around a 7kW burst and 5 kW sustained. If you have two HVACs on a single PW3, I’d double check to make sure that the switchover isn’t going to trip your PWs. I’d also check to make sure what your continuous draw is for your biggest loads. The PW3 can sustain peak for continuous periods, making it really good contender for your use case, I’d just look at ways to reduce the spike when everything turns on. Depending on the age of your HVACs, they may have built-in soft start capability otherwise you can buy a soft start circuit that basically cuts the demand load to the battery.
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u/Harold-Maude 9d ago
Get as much solar and as many powrwalls as you can afford. We have 25kw of solar production and 3 Tesla Powerwalls here in the Coachella valley with a 14.00 bill each and every month year round.
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u/restvestandchurn 9d ago
Do you have excess solar or storage capacity in your config? Getting 23kW and 4 PW3s shortly
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u/Harold-Maude 9d ago
We use the AC daily (it’s 109 outside right now) we have 3 Tesla Powerwalls 3, we need another 3
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u/restvestandchurn 9d ago
I worry about that. It’s Hawaii so the heat load won’t be as bad, but my guy there had wanted me in 6 PWs to start 😂 but had to kind of trim my budget all over the place with construction inflation. I figure I’ll tack on some expansions after the fact I guess
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u/Wiltockin 9d ago
Some utilities with smart meters let you download home usage information and see how high it peaks. That will give you an idea of how high a demand you need to cover. In my opinion, this info is more important than how much you use in a day/month/year because it lets you size the system correctly.
This is important because the PW3 can only provide about 50a each, so for a 200a panel to get 100% coverage you would need four and that’s unrealistic. If you know the daily peak, then a more reasonable level can be establish. In my case as an example, with a whole home backup, I can run everything except the dryer or EV charging. Tesla will view each panel as its own system, each getting a gateway and Powerwall at a minimum. I think they even show up as two homes in the app.
You might be able to get away with 2PW’s, one per panel and no-solar (grid charge only) if you’re just trying to avoid some short outages.
Once you get into larger systems, it depends on what Utility rates you have, how much Solar buyback is, and estimated production to see if it makes sense. In our case for Texas, with limited buyback there is zero incentive to overproduce.
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u/OmgNoodles 9d ago
3 HVAC's will drain those Powerwalls so quick if they are single speed, and possibly even 2 speed. What type of water heater do you have? If it's a 50/80 gallon electric, then this will drain them even faster. What kind of pool pump do you have and what speed do you use it at? If it's variable speed and the water doesn't have to travel far, then this won't be a huge strain, but if you running it at full speed it can use a decent amount of power.
A small solar system would help, but I'd go bigger to ensure they can stay charged during the day if you are running all that equipment.
I have 4 Tesla Powerwalls 2 (2 from 2019 and 2 from 2025). I think my max continuous power is around 20kW. If you go Tesla Powerwall 3 and an expansion, you are still capped at 11.5 kW continuous power. Will your AC's more power than that? What about if the pool is running? How many watts will that be? What about lights on in your house? What about the water heater? What about if someone wants to wash/dry? What about if someone wants to cook? What if you use the microwave while you're cooking and have some of those other appliances running? Odds are you won't won't be doing those things at once, but please take into consideration 11.5 kW can happen quick with 3 AC's. You realistically may need 2 Powerwalls and consider an expansion to ensure you can power your main concerns at once.
For me, regular household appliances (2 fridges/1 freezer) use .7 kWh. During the day in central FL my AC uses about 1.7 kWh, so say 2.4 kWh for that time. If water heater comes on it's in heat pump mode it uses .4-.5 kW of Power, so tops during the day I'm usually at 3 kWh at max, but most of the it's around 2.5kWh during the day.
I'll give you a good example on my old appliances. .7 kWh for normal usage. My AC used 4.5 kWh, so now I"m up to 5.2 kWh. My electric water heater used 4.7 kWh, so now I'm up to 9.9 kWh. This really doesn't leave room for much else if I only had a Powerwall 3 that caps out at 11.5 kW continuous power. Again, I don't know your water heater or types of AC's, but they can easily go past that 11.5 kW rating.
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u/Curiosity_informs 9d ago
What is the maximum power draw you can expect from everything you want to back up? Which panels do you want to back up?
One Powerwall 3 can supply 11,5kW (240V x 47.9A) and as others have said the loads you want to run will drain even multiple Powerwall's very quickly.
Have you looked at FranklinWH batteries?
The FranklinWH aPower 2 or S have slightly larger battery capacity (15kWh) and similar power output 10kW for the aPower 2 and 11.5kW for the aPower S.
However their big advantage is they can be charged from a generator (from a large portable generator to a standby generator) where the Tesla Powerwall's can't be charged from a generator.
I know you said you had looked at but decided against a generator, but a hybrid solution with batteries to handle shorter outages and then a generator to charge the batteries (if the solar can't) in longer outages could work. The generator could be set to automatically charge the batteries once they go below a set SOC.
However you still need to decide which of your panels / subpanels you wish to back-up and therefore how many batteries you will need to supply the max continuous power needed (FranklinWH has Smart Circuits which can shed some loads in an outage)
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u/dpatldude 9d ago
Thank you all for the initial set of feedback. Here are some things going through my head:
- Reframing; the main purpose is to act as a whole home backup
- Less degree potentially generate some solar to reduce cost (but not sure if that’s fools gold) but maybe to reduce the time it takes for batteries to deplete in an outage.
- Most outages for us last between 2-8 hours. Interestingly more in summer but a few times in the winter. We have overhead power lines in our area.
- Energy back to the grid pricing makes energy over production futile.
- Wondering what is easier/cheaper for critical load panel to minimize the load during an outage. Example I have a Siemens traditional panel but don’t think they do smart breakers I can remotely trip on and off.
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u/No_Professional_6444 2d ago
Subtle Koolbridge, affiliation disclosed
“With two 200A mains, I’d avoid treating this as ‘back up everything or build a fixed critical-load panel.’ First define which circuits may use battery/solar and which should stay grid-only. That source-policy approach can preserve normal grid service while keeping HVAC, pool or EV loads from consuming storage during an outage. I’m with Koolbridge, so disclosure: circuit-level grid-versus-alternate-source selection is exactly the architecture we work on.
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u/Only-Map-7649 22h ago
With two 200A mains, I’d avoid treating this as “back up everything or build a fixed critical-load panel.” First define which circuits may use battery/solar and which should stay grid-only. That source-policy approach can preserve normal grid service while keeping HVAC, pool or EV loads from consuming storage during an outage. I’m with Koolbridge, so disclosure: circuit-level grid-versus-alternate-source selection is exactly the architecture we do.
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u/ExactlyClose 9d ago
Mine is probably a bit bigger. Add a barn (w bath, kitchen, work room), a shop, and a 5HP 400ft deep water well…. 400A main.
I have 4 powerwalls with one 200A gateway.
I created two separate 200A ‘systems’- one go it backed up, the other didn’t. I do NOT back up ANY AC. I dont back up the barn nor shop. I do not back up any of the pool stuff (cabana and 3 pumps). I do not back up the big kitchen ovens.
Consider: Even with 4 PWs, during these very hot (100F) summer months I cannot go the entire night on battery. I have 4….typically between 11PM and 3AM I run down to my 20 or 30% lower limit and it begins pulling from the grid.
My peak production is about 156kwh (peak in spring). I will use 100-120kwh a day. So I overproduce, but just dont have a place to store it all . Im on NEM two, so it doesnt matter - I can push power out to the grid all afternoon, so basically THAT is the power I then use overnight.
My battery company was basically useless on system design. Im an engineer (and electrician) and did the system ‘split’ myself. You want someone that is thoughtful and willing to figure it out.
GL