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365 days of Solar Roof

It's been 365 days since I received PTO on my 10.52kW solar roof. Here's some stats on how the roof has performed. I'm quite happy with this, especially considering how much the California wildfires impacted production.

Production estimate: 12,494 kWh
Production actual: 13,995 kWh (12% over estimate)
Home usage: 12,453 kWh (way up this year with covid)
Bill savings: ~$3,783

solar_summary.png
 
Nice numbers - better than our roof is currently trending relative to Tesla's prediction (8 months in,) but it seemed for us that the winter was unexpectedly bad, possibly due to worse weather than typical, so I am hoping the numbers will improve for spring. Right now, it looks like we are about 1%-2% above Tesla's numbers (using PVWatts to estimate the monthly breakdown.) In any case, we definitely won't hit those types of savings numbers with the lower electric rates out here.
 

jboy210

Well-Known Member
Supporting Member
Dec 2, 2016
6,507
4,452
Northern California
When I try to check out the cost of installing the solar roof on Tesla’s website, it is indicating a 6.1kW system. Is that system size fixed since it is solar roof and not solar panels?
The system size is based on what they can fit on your roof. You can ask them to try to fit more on the roof. Also, solar Roof systems will generate less for the same amount of roof coverage because active solar tiles are less efficient than solar panels.
 
When I try to check out the cost of installing the solar roof on Tesla’s website, it is indicating a 6.1kW system. Is that system size fixed since it is solar roof and not solar panels?
It is not fixed - it is an estimate based on the information you provide. It might be sized based what on it can estimate will fit on your roof or based on your reported electric usage. Once you place a deposit, a human will produce a layout that is more exact, and you can potentially request they add more capacity if the limitation was not due to the available roof space being used up.
 
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When I try to check out the cost of installing the solar roof on Tesla’s website, it is indicating a 6.1kW system. Is that system size fixed since it is solar roof and not solar panels?
If you have not submitted your order by placing a deposit yet, then the estimated 6.1 kW system is probably due to the dollar amount of electricity you put on the web form. I would suggest to get your annual electricity usage in kWh from you utility bills for the last 12 months, place the order, as soon as you have a project advisor assigned, call the advisor to tell them your annual electricity usage and ask to size that + 10% to 20% more. Depending on placement of active tiles and shading, you may need to upsize the active tiles to compensate.

If you plan to install your roof this year, you should place your order now. I am in the San Francisco Bay Area and would be considered prime Tesla location, i placed my order in Aug 2020, just only got installed in Feb 2021 and still waiting for PTO. BTW, the system + 2 PWs that I ordered has gone up by 8,500.00 if I order today.
 
I do not believe, IMO, that there is a ROI cost savings for powerwalls. Now adding more solar, yep
There just isn't a blanket statement that can cover either of these. It is dependent on the individual and the rate structure. For many cases, adding solar tends to make the most sense up to the point where any net metering maxes out, at which point the returns tend to diminish. PWs make sense in cases where there is some combination of big differences in the rates at different times of day and/or the utility offers no or less-than-full net metering. The math for PWs certainly doesn't work out for everybody (and maybe not for a majority) but it does work out for some.

(And I am, of course, speaking strictly about one aspect of PWs here - it does not take into account any benefits related to grid issues.)
 

h2ofun

Active Member
Aug 11, 2020
3,606
867
auburn, ca
There just isn't a blanket statement that can cover either of these. It is dependent on the individual and the rate structure. For many cases, adding solar tends to make the most sense up to the point where any net metering maxes out, at which point the returns tend to diminish. PWs make sense in cases where there is some combination of big differences in the rates at different times of day and/or the utility offers no or less-than-full net metering. The math for PWs certainly doesn't work out for everybody (and maybe not for a majority) but it does work out for some.

(And I am, of course, speaking strictly about one aspect of PWs here - it does not take into account any benefits related to grid issues.)
I agree. When I was writing, I tried to say IMO, since I know a few believe they are saving tons using EV2-a and batteries.

But for the average person, I have yet to see any analysis that works out.

Yep, I agree if one could predict NM running out. But what I am seeing, the more I have, the warmer, or cooler, I have a choice to consider. I have yet to hear a person who said they put in too much solar, just like I have yet to hear a person say they bought too large a TV.

Now, if you have an EV, not the average person. If you like to try and play the back and forth TOU grid stuff, not the average person.

So again, I agree. For some, math may play out.
 
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I agree. When I was writing, I tried to say IMO, since I know a few believe they are saving tons using EV2-a and batteries.

But for the average person, I have yet to see any analysis that works out.

Yep, I agree if one could predict NM running out. But what I am seeing, the more I have, the warmer, or cooler, I have a choice to consider. I have yet to hear a person who said they put in too much solar, just like I have yet to hear a person say they bought too large a TV.

Now, if you have an EV, not the average person. If you like to try and play the back and forth TOU grid stuff, not the average person.

So again, I agree. For some, math may play out.
I don't think it really makes sense to talk of an "average person" in this context since there are so many variables involved in solar, and particularly solar + PW. Indeed, an "average person" in CA has, as I have learned, a very different profile than one in MD, and it seems clear that even within CA there are a lot of differences based on location and the utility company. The point being that each person needs to run their own numbers to see what makes sense for them financially (and then also apply other considerations they may have, including goals like grid independence, supporting the environment, backup protection, etc.) That is the case even if PWs don't pencil out for 50% or more of people.
 

h2ofun

Active Member
Aug 11, 2020
3,606
867
auburn, ca
I don't think it really makes sense to talk of an "average person" in this context since there are so many variables involved in solar, and particularly solar + PW. Indeed, an "average person" in CA has, as I have learned, a very different profile than one in MD, and it seems clear that even within CA there are a lot of differences based on location and the utility company. The point being that each person needs to run their own numbers to see what makes sense for them financially (and then also apply other considerations they may have, including goals like grid independence, supporting the environment, backup protection, etc.) That is the case even if PWs don't pencil out for 50% or more of people.
Agreed
 
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Everyone needs to look at what they want out of PW, I never gave consideration to ROI on PWs the same way as I never considered ROI on my Model S, I will never save enough gas money to justify the cost of it. Personally, my primary objective is grid independence and environment, secondary objective is backup protection, I had 1 PSPS outage in the last 2 years and in the SF Peninsula it is almost never really hot, I however have a collection of wine that I would not want to go to waste. So do what is right for yourself for whatever reason.
 
PWs make sense in cases where there is some combination of big differences in the rates at different times of day and/or the utility offers no or less-than-full net metering. The math for PWs certainly doesn't work out for everybody (and maybe not for a majority) but it does work out for some.
I would be interested in seeing any calculation/use case that would show that PWs would pay for themselves or even 50% of their cost without the SGIP incentive which is very limited.
 

miimura

Well-Known Member
Aug 21, 2013
7,174
7,124
Los Altos, CA
I would be interested in seeing any calculation/use case that would show that PWs would pay for themselves or even 50% of their cost without the SGIP incentive which is very limited.
I think this really depends on how much of the cost you attribute to the value of backup power. There is certainly a limit to how much you can save with TOU arbitrage. Personally, I calculated a 5 year ROI from arbitrage after I deducted what I would have spent installing a generator, the tax credit, and the Step 1 SGIP rebate. Keep in mind that in order to actually save money with TOU arbitrage, you have to actually owe money at true up that you can reduce with the arbitrage. In my case, it's very easy because my solar system is small and I owe a lot each year.
 
I would be interested in seeing any calculation/use case that would show that PWs would pay for themselves or even 50% of their cost without the SGIP incentive which is very limited.
Our Powerwalls were $7500 each when we signed our contract last summer. With the federal tax credit this took the cost down to $5,550 each. Here in the northeast our utility has a virtual power plant program with Tesla called connected solutions that earns about $1000 per year per Powerwall. In addition our utility credit is about $.04 per kWh generated by solar if we have battery storage. That’s every kWh even if it’s never stored. So on our system generating about 12Mwh a year that is another $480 per year. So our Powerwalls each pay themselves off in just under four years.

And as others have said, the ROI is only one of a few reasons Powerwalls made sense for us.
 
I’m afraid I can’t get the math / cost savings to work for powerwalls. I may have to give up powerwalls for now as much as I would like it to complete the system. I’ve seen the price of powerwalls creep up
Yes, PWs make no sense in terms of ROI unless...
You get into a situation like what happened in Texas and some people are being charged thousands of dollars for their electricity.
In that rare scenario, the PW becomes cheap.

On the other hand, if you think of it as insurance and protection, like a stand by generator, how much is that worth to you?
I, sadly, do not have a PW setup as I also went the ROI route.
Every time the power goes out, I am reminded of that decision.
or worse, when the power goes out mid day and it's always on a nice bright sunny day and I know my panels are providing ZERO power because of the grid shut off switch. Can't even use it for my house! If only I had a PW.
 
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holeydonut

Active Member
Supporting Member
Jun 27, 2020
3,070
2,419
East Bay NorCal
The ROI on Powerwalls comes from all the mental happiness you get by living your life the way you want, when you want.

If you are solar only, then the time of use rates are a dagger that PG&E holds over your head to manipulate you. If you're driving on 101 or anywhere near the local broadcast TV channels, you'll see the utilities are paying for a "power down 4 to 9" ad campaign right now. This is to encourage people to push using energy consumption out of peak time.

If you put batteries in, then you're turning on your lights and cooking your meals when you want. Your AC is running just fine whenever you are hot. You're cranking on that dishwasher or dryer to do some chores when you want.

You may not be charging your EV when you want (depends how you sized your system), but that one is easier to manage since the Tesla app is pretty good.

Even if TOU rates aren't "that bad" right now between Peak and Off-Peak (some people think a 20% difference isn't all that bad), you can be confident PG&E is going to keep widening the costs between peak and off-peak in the coming years to manipulate consumption patterns. Not being manipulated is a very valuable part of the ROI for ESS.

My entire job involves finance and numbers on a daily basis. I'm literally a finance person telling you that for the ESS application, take your normal abacus and maths and throw them out the window. Simply getting away from PG&E's absolute bullshit is priceless and worth the investment. I know this is a strange value proposition, but keep in mind what I'm saying if you ever encounter the situation where someone turns on the AC at 5pm and you're thinking "but what is the the TOU rate right now?"
 
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