I have an estimate for a 17.3K solar roof (~$75K). Three powerwalls increase the price to $99k. I live in the Bay Area CA where we have PGE netmeetering (and they pay almost nothing for extra electricity produced). Is there any financial justification for adding the powerwalls? It looks like a lot of people do include powerwalls with their installs. Is this just for covering blackouts?
-
Want to remove ads? Register an account and login to see fewer ads, and become a Supporting Member to remove almost all ads.
Justifying Powerwalls with Solar Roof
- Thread starter gottlie
- Start date
SoCal Dave
Member
You will need to be moved to a Time-of-Use plan which means you will be charged more for electricity in the evenings. This can be addressed by over-sizing the system so you generate more electricity during the day to offset the additional cost in the evenings (but the power company will potentially limit how much you can do). Or you can install Powerwalls to store the electricity during the day and provide power during the evening so you don't have to buy it from the power company. Or you can eat the higher cost of the evening power usage.
Personally, I think Powerwalls are too expensive and I can't cost justify them. I'm with SCE and I'll be going with their TOU-D-5-8 plan. This means normally I'll be paying/receiving $0.25/kWh but it will cost/pay $0.50/kWh from 5 pm to 8 pm. My solar is over-sized (normal panels are cheap) and I'll be shifting my usage outside 5 pm to 8 pm as much as reasonably possible (having the AC pre-cool the house before 5 pm for example).
Solar roofs are not as cheap as solar panels, so over-sizing might not be as economically viable. This may lend itself to Powerwalls.
Personally, I think Powerwalls are too expensive and I can't cost justify them. I'm with SCE and I'll be going with their TOU-D-5-8 plan. This means normally I'll be paying/receiving $0.25/kWh but it will cost/pay $0.50/kWh from 5 pm to 8 pm. My solar is over-sized (normal panels are cheap) and I'll be shifting my usage outside 5 pm to 8 pm as much as reasonably possible (having the AC pre-cool the house before 5 pm for example).
Solar roofs are not as cheap as solar panels, so over-sizing might not be as economically viable. This may lend itself to Powerwalls.
SoCal Dave
Member
1. You will be moved to another plan, which has time of use and either 4-9 or 5-9 peak charges in the 50c range, while your solar will only net meter credit at tier one rates (whatever off peak is on that plan) which could be around 15 cents). Having powerwalls helps you not use peak power at all, if you buy enough of them (and you would need a minimum of 3 for a system that size.
2. It depends on how much you value "having power". one thing I can tell you from personal experience, you spend 75k on a brand new solar roof, then find out that during a PSPS or any other power outage when there is sun in the sky, you have no power and WONT have any power even though there is sun in the sky (and you spent 75k to get solar) you will be at a minimum "frustrated".
Nothing like having a power outage, having solar on your roof, and KNOWING your solar could power your home but isnt setup to do that because you have no battery storage. Let that happen a few times, or have a multi day outage when you are throwing food away etc, and having your significant other say "I thought we had solar???? why dont we have power?" to really drive that point home.
Everyone always says "we dont have many power outages where I live so...." it usually doesnt take "many" for someone to see the value in it, especially someone who can afford to spend 75k on a solar roof.
PSPS are the new normal in california, from the utilities, and just look at what is going on right now as I type this with the heat wave in Nor Cal (and southern california.. it was about 105 at my home today with some clouds and stuff, crazy weather).
Knowing that I should have power, or can manage it as such (I put myself in backup only mode "just in case" as I dont have TOU energy usage charges because I am on a grandfathered plan), means that, if power is out, I dont have to worry (much).
The financial payback tends to be long, so it has to be more than the finances, but in PGE territory when you will be forced on TOU, and pay 50+ cent a kw between 4-9 pm or so, and get base credit of like 15-18 cents for your solar, having battery storage means you can use your own power at least during peak and not pay 50c a kWh during that time.
For the most part, I've owned and operated my solar connected powerwalls for 3 years... I have 3 of them and was eligible for SGIP 3rd tier (because they think it's commercial). Even with the "help" from SGIP, it was more of an ego/backup thing than savings. I'm on legacy SCE TOU-D-A which has peak from 2-8pm and legacy NEM. So, I do send all the battery use on a daily basis from 2-8pm, but during these rolling blackouts, I can add another hour or two of outage without much of a challenge. If it happens to be between 2-8pm, it's not an extra hour or two.
However, if you're checking this post before August 16, 2020, 11am. I also run the Tesla Owners Club of Orange County and we're having our Meet rEVolutionaries #2 with Kyle Field, Sr. Editor, CleanTechnica, and we're covering Tesla Solar Roof and PowerWall2 from an Owner's Perspective. We have some space available for folks from the Tesla Community.
If you're interested in joining us at 1pm tomorrow (August 16, 2020), email us and find the contact information at http://www.octeslaclub.com/ or PM me here (though not sure if I'll get these in time).
https://twitter.com/OCTeslaClub/status/1294369367795277824
If you don't want to participate fully, but interested in the information, I am going to try to live stream it on YouTube and possible leave it recorded. However, this is the SECOND stream we're doing, so I hope I don't screw it up... -
However, if you're checking this post before August 16, 2020, 11am. I also run the Tesla Owners Club of Orange County and we're having our Meet rEVolutionaries #2 with Kyle Field, Sr. Editor, CleanTechnica, and we're covering Tesla Solar Roof and PowerWall2 from an Owner's Perspective. We have some space available for folks from the Tesla Community.
If you're interested in joining us at 1pm tomorrow (August 16, 2020), email us and find the contact information at http://www.octeslaclub.com/ or PM me here (though not sure if I'll get these in time).
https://twitter.com/OCTeslaClub/status/1294369367795277824
If you don't want to participate fully, but interested in the information, I am going to try to live stream it on YouTube and possible leave it recorded. However, this is the SECOND stream we're doing, so I hope I don't screw it up... -
For use the combination of solar roof and power walls can cover almost all our usage, especially during the peak time of our plan. That saves around 500/mo. Second, there is the PSPS impact. We were out for 4 days last year. Since we work from home an outage can cost several hundred/hour in billables.
A non financial, but equally important factor is it ensures you can use the energy produced by your roof during an outage. I call this the “I would be pissed if I could not power my house from my solar roof during an outage”.factor.
Last edited:
Yes, their estimate of the size of the system was much higher than I expected. We use around 900Kwh / mo. I was thinking they would have said our system should be around 10kW.
Thanks for the replies and education on PGE (all of you). Sounds like my first step is to check with Tesla as to how they decided to size my system.
SoCal Dave
Member
That is odd.
My usage averages slightly higher than you and most non-Tesla quotes were in the 8kW-10kW range. I debated going 8kW or 12kW with Tesla and finally decided on the 12kW to overproduce a bit giving us some room to grow and to help with the TOU as I mentioned. It also was only $23.5K vs $16K (pre-incentive) since it is panels. A pretty negligible difference over 20-30 years.
I don't know why they would suggest such a large system for you. PG&E would possibly have an issue with it being so oversized.
Good luck with you install. I'm curious what Tesla tells you.
They use your previous electrical usage as a base. The gave us 2 options. We took the larger 12.75 kW option. It will be hard to expand the roof so I figured more was better.
That sounds like a "max solar" quote.. something isnt adding up. A system sized at 17.3kW in california is likely going to produce more than that, even though solar roof seems to be less efficient than panels. My 8.7kW sized system produces between 12,000 and 13,000 kWh a year, for example.
That system is over double your usage, IF your usage is actually 900 kWh a month. With that being said, if I was getting a solar roof I would want to get as much as I could, regardless of usage, because its not like you are coming back and adding onto it later. It sort of "is what it is" until you replace the roof again.
Maybe your home is just situated perfectly for solar (angle, roof type etc)? Thats a very large system for someone who has fairly minimal usage. I go from 800-900 kWh in the winter to 1700 ish in the summer when I am using AC.
The YouTube livestream weirdly crashed 15 minutes in.
So, uploaded the discussion from a backup recording:
Hope it’s helpful...
Solar roof is less efficient than solar panels, but that is accounted for in the nameplate rating of 17.3 kW. But solar roof may also be less optimally oriented, since most roofs are across 2-4 different roof plane orientations. So estimated production could be quite a bit less than 17.3 kW of solar panels that might be able to pick the best of the roof plane orientations
