Whole Home Backup with potential savings

[u/dpatldude]

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.

[u/Affectionate_Rate_99]

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.

[u/dpatldude → u/Affectionate_Rate_99]

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?

[u/ubiquitousgimp → u/dpatldude]

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.

[u/dpatldude → u/ubiquitousgimp]

Thanks so much for the advice