The Tesla Powerwall is an inverter and battery storage all in one. You can use it with or without solar panels. without panels just think of it as a whole home battery backup with the brains to automatically switch on and off when needed. The grid charges the batteries, and the batteries are ready to be used when needed. You can also use them to take advantage of different electricity plans, for example, if you had a plan that was free electricity at night, you would use the grid at night and the Powerwall during the day as long as it would last, and then at night while you are using the free electricity it would also charge the batteries for free. That's an extreme example, but there are plans with different rates depending on demand and the Powerwall has the brains to automatically find all that stuff and optimize your grid usage to reduce your bill while also serving as an emergency backup. Obviously using it with solar panels is the best bang for your buck, but Tesla's AI brains and Apps and all that stuff is where they lead. Combining the inverter and batteries into one package, and combine that with their Apps, it makes it extremely easy for the installers.

MRB10 said:

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-What are they telling you about the useful life of the equipment?
-What literature did they provide to prove their number?
-How long do they warranty the panels and batteries?
-When should you reasonably expect output to start being reduced due to age or normal wear of the equipment ?

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The industry seems like it has gravitated to 30 years as being the expected lifetime. They have all the literature you could ever want to try and hammer that point home, but who knows?

My installer has a 25 year product, labor, and performance warranty (signed contract). But installers go out of business so I default to the manufacturer of the components. I'm using REC panels, they have a 20 year product warranty and a 25 year linear performance warranty. The linear performance warranty just means that the expected degradation will be linear through the entire 25 years. In my case with the REC panels, the warranty states a .25% annual degradation is allowable (each panel is individually monitored) and at the end of 25 years I should still be producing 92% power. I'm using Pytes batteries, they have a 6000 cycle warranty that states it will be above 90% depth of discharge (when installed by a certified installer). I'm planning to be using my batteries at night so a nightly discharge is expected, that's about 15 years. The inverters have a 10 year warranty, this would be the only one where I really hope my installer is still around for their 25 year warranty. I'm getting two inverters and they are $7500 each.

Batteries are currently expensive, I'm hoping that by the end of the warranty battery technology has jumped enough that to get a direct replacement won't be too expensive

someone once made this comment about solar and its stuck with me.....if it was worth it every company that owns a building would have panels on every square inch.

ought1ag said:

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someone once made this comment about solar and its stuck with me.....if it was worth it every company that owns a building would have panels on every square inch.

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If you look at it strictly from a financial perspective, it isn't worth it in most cases for a business. They already have business interruption insurance that will cover them if the power goes out and they have to send everybody home for a week. But how much is it worth to not spend a week in August sweating your balls off after a hurricane knocks out all the power to your area? How much is it worth to not spend a week freezing your ass off in February after an ice storm knocks out the power? How much is it worth to not have a freezer full of wild game you paid good money to hunt go bad because you can't get enough gas for your generator to keep it running or the natural gas supply gets cut off/slowed down by a power outage and your generator won't run?

Those unlikely scenarios have all happened in Texas for thousands of people within the last 5 years. What is the value of having the peace of mind to be able to withstand those kinds of things without having to scramble for gas, ice, get propane delivered, etc.? When you add that value on top of the lack of an electric bill, for some people it makes sense.

I am in the large-scale (1000+ acres) solar business. I would not do rooftop solar, but I will be very interested in a system like OP's when I finally find some land to buy. Ground mounted systems > rooftop.

Well, I own a business and that business owns the building, and while I think it makes sense for my residence, when you start talking about commercial, the motivation starts to wain. First of all, the scale of economies is vastly different. The percentage of our operating budget spent on the companies electricity usage is so small, it doesn't even register in the reports. For one, people are only there for 8-10 hours a day, 5 days a week, and no weekend usage. Another issue, we only occupy about 1/3 of the building, the other areas are leased out with NNN leases. When you start trying to bring tenants along on the ride it can get a little hairy, especially when talking about roof penetrations, and the liability associated if something happens.

Not to mention, if you've looked at commercial prices on anything, there is a big difference between residential and commercial. And as another poster stated, while backup power is a big motivator for me on the residential side, I have no need (or very little) for backup power for my business, my business is right across the street from a major hospital and the grid power has always been a priority.

My guess is companies that are high energy users, like crypto miners, are probably doing it. And for better or worse, when I look at ROI for my company, I have much higher expectations with shorter break even timeframes.

You don't need solar for those problems. You need a massive battery backup.

EMY92 said:

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My big fear with solar is needed to get a new roof after the panels are in place. It's not cheap to have a contractor remove then reinstall the panels. My guess is that the cost of that alone would exceed any savings that you expect.

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If the roof is being replaced as part of a covered storm (hail) claim, then the d&r is covered.

Good info, thanks. The payoff math still doesn't make sense for my situation and my $1,700 portable Nat gas generator is good enough in a pinch that I have little incentive to try and justify solar.

My assumption was that useful life was closer to 10-15 years but it sounds like that belief is outdated.

If you can sell excess lower back at the retail rate why pay for storage. Your payback has to be better by doing solar only and scrapping the batteries and getting a gas gen backup. You can use a portable gas generator for a fraction of the cost of batteries.

The case for batteries is really for locations without net metering to offset more costs. For you, there is no additional costs savings of using batteries.

You can't really financially justify the batteries if you're getting 1:1 from your power provider. The grid is essentially your battery. I'm just doing it because I want to and its a bit of redundancy for power back-up.

The technology that is in the Tesla wall system is pretty awesome, especially if you're in a location that has sliding rates like California. Its smart enough to know when power is cheap and to pull fro the grid for the house and to recharge. I expect we will start seeing more variable rate structures in the residential market but I also use to push solar panels and energy saving measures expecting we would be paying $0.25/kWh by now.

h_town_ags said:

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If you can sell excess lower back at the retail rate why pay for storage. Your payback has to be better by doing solar only and scrapping the batteries and getting a gas gen backup. You can use a portable gas generator for a fraction of the cost of batteries.

The case for batteries is really for locations without net metering to offset more costs. For you, there is no additional costs savings of using batteries.

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There are relatively few places that are buying back power at the retail rate. Most are buying back at the wholesale rate, which is generally fairly low in the middle of the day when solar generation is at its peak. The case for batteries is not made just by savings on electric bills using battery power overnight, it is made by not having to have a generator to cover minor outages and having sustainable power for longer outages.

txags92 said:

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h_town_ags said:

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If you can sell excess lower back at the retail rate why pay for storage. Your payback has to be better by doing solar only and scrapping the batteries and getting a gas gen backup. You can use a portable gas generator for a fraction of the cost of batteries.

The case for batteries is really for locations without net metering to offset more costs. For you, there is no additional costs savings of using batteries.

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There are relatively few places that are buying back power at the retail rate. Most are buying back at the wholesale rate, which is generally fairly low in the middle of the day when solar generation is at its peak. The case for batteries is not made just by savings on electric bills using battery power overnight, it is made by not having to have a generator to cover minor outages and having sustainable power for longer outages.

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You are missing my point or mistaking my questions/comments to OP as general question about solar.

The point is he lives in a unique are of Texas where he actually gets full retail rate net metering. Battery storage adds zero value to the FINANCIAL proposition of resi Solar which was what he was asking about.

If he wants backup generation I would go with a generac gas unit. Basically the same cost as a powerball and doesn't have to be replaced 2-3 times over the life of the panels. It will also run for as long as it's needed vs batteries which can only last so long (and building up excess supply only hurts ROI)

Unless he is buying from SunRun (which isn't a great credit) the solar company he is buying from is not going to be around for 25 years. Generac is a much safer bet in that regard.