Tesla says to pick 1,2,3,4 size systems. I was looking at 8k and 12k (2,3). 8k is too little and 12k is too much. My guess is 10k is about right. But in the long run would 12k be too much? I will be getting 2 Powerwalls as well.
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Can you buy too much Solar?
- Thread starter d21mike
- Start date
Akikiki
A'-Lo-HA ! y'all
Can you buy to much range? I don't think so Tim. No such thing as to my solar. You should not even ask this question. 
If you produce more than you use and are not paid by the utility, you've installed (and paid for) too much.Can you buy to much range? I don't think so Tim. No such thing as to my solar. You should not even ask this question.
Akikiki
A'-Lo-HA ! y'all
You have perfectly described me and my situation. I upgraded my system from a 5.7 to 11.8 kw system. As of last week, I am generating about 40-50% more than I am using. I had "just enough" for a one person household and my Tesla. The tax credits are falling this year. I want to future proof my house by making Too-Much, so when I sell it, a family of 4-5 can have a zero utility bill. So, I will make more than I need and use as much as I can/wish to use. In Hawaii, the state grants us a 35% tax credit and the feds still have the 30% tax credit. So it costs me 35 cents on the dollar. Power cost us 30-32 cents a kWh. Breakeven will be about 6 years again. (Same as last time.) To me, its a no brainer.
It kinda depends on what your goals are. For max economic payback (assuming net metering of some kind) size your panels so solar production equals 100% of your annual energy usage.
For maximum environmental impact reduction, size your panels for 100% of your December usage. This means you’ll run zero emissions, even during the worst production months. But this means you’ll have something like 2X as much solar as you need during June/July. But hey, it’s fun to think of creative uses of energy. Bitcoin mining maybe?
For maximum environmental impact reduction, size your panels for 100% of your December usage. This means you’ll run zero emissions, even during the worst production months. But this means you’ll have something like 2X as much solar as you need during June/July. But hey, it’s fun to think of creative uses of energy. Bitcoin mining maybe?
Akikiki
A'-Lo-HA ! y'all
Yes, we have Net Metering. And we have something new called Net Metering Plus. It allows us to add to a full grid without violating our NEM Agreement. Its not as hot here in the summer as it is TX or AZ, but its nice that I can run the A/C all day every day if I wish. I still break even in a half dozen years or so. The plan is to live that long.
Yes, you can buy too much solar.
However, you will probably not have much regret over too much solar.
It just means you need more EVs and fewer fossil cars and fewer fossil fueled appliances.
However, you will probably not have much regret over too much solar.
It just means you need more EVs and fewer fossil cars and fewer fossil fueled appliances.
How large is your house? Can all of the panels produce 90%-100% all day based on location? 10k seems like quite a bit with 2 Powerwalls.
No, Jevon's Paradox. Also, you're not factoring in cloudy days which cuts 2/3rds of your production.
200%+ or live under range-anxiety.
200%+ or live under range-anxiety.
This... Cover your roof if you can if you are serious about zero grid usage year around. I’ve got a dollar for dollar net metering plan here in Texas that covers my cloudy days but I wish I had more room on my roof. 70 panels works fine for most days but my 24kw system can produce as little as 11kwh on cloudy rainy days... Peak output can push 140kwh. That said, on a cloudy day all your panels will produce about that same amount, doesn’t matter what orientation they are...
This may be closest to my question. How accurate are the "estimates" from Tesla. Does the 8.19kw system produce "Est. Annual Production: 13214" only on the best days? Or does the estimate take in consideration my weather here in Southern California? I know it seems like we have all sun but we do have rainy and cloudy days part of the year. I also have 2 tall palm trees in the front yard close to the front of the house. The solar is east of them so I expect all good until Sun passes past them in the early afternoon and they could shade some. I think if they put on 12k panels it would have to have some in front of the palm trees so will get some late afternoon sun but really hard with my roof line. I did see the engineering for the 8k system but still waiting for the 12k. There was some confusion I guess. They sent pricing documents for the 12k but sent engineering for the 8k. After I order I told the sales guy the 8k was probably too little but 12k might be too big. He said he could do the engineering on the 12k and then based on the how many they could put on that is what I would be charged which sounded good. But then got docs as I said.
8.19kw System - "Est. Annual Production: 13,214"
12.28kw System - "Est. Annual Production: 20,095"
More details based on another question above.
There is only 2 of us living in a 3100' home.
We use our AC maybe 4 or 5 months and our gas heater maybe 4 months. Not sure about other months.
Last year I only had 1 Tesla Model S.
My usage last year was 13,412 kWh
My usage during Super Off Peak was 6,495 - so almost 1/2 was my Tesla - more then I was expecting.
We just bought a second Tesla Model 3 for the wife. We are estimating that the will drive about 2-3,000 miles because we normally drive together on the weekends so that could be high. But not sure.
So, 13,412 + 2,500 = 15,912 kWh of usage seems to be a pretty good estimate. This is why I was think a 10k system with Est. Production of about 16,000 would be about what I need to match 100% unless assuming the Tesla Estimate is conservative. I know they get less over the years so that is a consideration. I also only have AC in the upstairs because that is where we spend most of the time and I live not that far from the beach. That works fine except when the kids come for a visit then at bit warm downstairs bedroom during the hot months.
My Grandfathered TOU-D-B will expire 2022 unless then force me to switch early because of Solar. So Super Off Peak is only about $.11 from 10pm - 8am. The new rate plan will be $.13 for all hours except 4-9pm Peak. Which is not that much more for my past charging time. So, not like Hawaii.
We do have NEM 2.0 so the amount of extra production to the grid goes in at the cost at the time of day. I take it out at the cost of time of day. With the new 2010 TOU-PRIME the cost is the same except for 4-9pm peak. For my current plan it is different with peak from 2-8 so could add some extra production between 2-4pm. I expect most production to be between 11-2pm. This is a great deal except that at the end of the year is the "True up" time (I think that is the name) where they pay me wholesale for all current excess at $.03 per Kw. So, best to use what I produce but better to have a little extra than not.
AND... Things could change in the future. Rates could change or my usage could change. Who knows maybe my Teslas will start earning my money in the Tesla Network once FSD is here. Or my car's can run my family around town like a private UBER.
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SoundDaTrumpet
Member
I have not encountered any solar installer large or small (6 bids) back in 2016 who inaccurately calculated annual production. Unless you have trees! Everyone uses NREL's PVWatts calculator that has been validated with test data. I have ultra premium panels so my annual generation beat PVWatts' premium panel estimate by 3%. Wet years vs. drought years amounted to 8% annual production differences.
2500kWh amounts to 10,000 miles of EV driving. You stated your wife drives 2-3k miles per year.
Recommend 105% per this article, page 23: https://www.ourenergypolicy.org/wp-content/uploads/2017/07/Aurora_NEM2_Whitepaper_v1.01__1_.pdf
2500kWh amounts to 10,000 miles of EV driving. You stated your wife drives 2-3k miles per year.
Recommend 105% per this article, page 23: https://www.ourenergypolicy.org/wp-content/uploads/2017/07/Aurora_NEM2_Whitepaper_v1.01__1_.pdf
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In my experience,Tesla’s estimate has been pretty good, if just a tad conservative (5% difference maybe).
I think they are running the design through a tool like PVWatts (PVWatts Calculator), which you can also do if you know the particulars of the design.
Ever since we installed Solar last year, our electricity usage has been up. We keep the cars more charged, use the hot tub more, and our AC died so we converted it to a heat pump to move our home heat off natural gas. So personally I’d go bigger if you anticipate any changes in electricity use in the next 5 years or so.
If you have shading issues, you might want to request SolarEdge with DC optimizers, or Enphase micro inverters. We have some shade and the stock Delta do just OK with it.
I think they are running the design through a tool like PVWatts (PVWatts Calculator), which you can also do if you know the particulars of the design.
Ever since we installed Solar last year, our electricity usage has been up. We keep the cars more charged, use the hot tub more, and our AC died so we converted it to a heat pump to move our home heat off natural gas. So personally I’d go bigger if you anticipate any changes in electricity use in the next 5 years or so.
If you have shading issues, you might want to request SolarEdge with DC optimizers, or Enphase micro inverters. We have some shade and the stock Delta do just OK with it.
This may be closest to my question. How accurate are the "estimates" from Tesla. Does the 8.19kw system produce "Est. Annual Production: 13214" only on the best days? Or does the estimate take in consideration my weather here in Southern California? I know it seems like we have all sun but we do have rainy and cloudy days part of the year. I also have 2 tall palm trees in the front yard close to the front of the house. The solar is east of them so I expect all good until Sun passes past them in the early afternoon and they could shade some. I think if they put on 12k panels it would have to have some in front of the palm trees so will get some late afternoon sun but really hard with my roof line. I did see the engineering for the 8k system but still waiting for the 12k. There was some confusion I guess. They sent pricing documents for the 12k but sent engineering for the 8k. After I order I told the sales guy the 8k was probably too little but 12k might be too big. He said he could do the engineering on the 12k and then based on the how many they could put on that is what I would be charged which sounded good. But then got docs as I said.
8.19kw System - "Est. Annual Production: 13,214"
12.28kw System - "Est. Annual Production: 20,095"
More details based on another question above.
There is only 2 of us living in a 3100' home.
We use our AC maybe 4 or 5 months and our gas heater maybe 4 months. Not sure about other months.
Last year I only had 1 Tesla Model S.
My usage last year was 13,412 kWh
My usage during Super Off Peak was 6,495 - so almost 1/2 was my Tesla - more then I was expecting.
We just bought a second Tesla Model 3 for the wife. We are estimating that the will drive about 2-3,000 miles because we normally drive together on the weekends so that could be high. But not sure.
So, 13,412 + 2,500 = 15,912 kWh of usage seems to be a pretty good estimate. This is why I was think a 10k system with Est. Production of about 16,000 would be about what I need to match 100% unless assuming the Tesla Estimate is conservative. I know they get less over the years so that is a consideration. I also only have AC in the upstairs because that is where we spend most of the time and I live not that far from the beach. That works fine except when the kids come for a visit then at bit warm downstairs bedroom during the hot months.
My Grandfathered TOU-D-B will expire 2022 unless then force me to switch early because of Solar. So Super Off Peak is only about $.11 from 10pm - 8am. The new rate plan will be $.13 for all hours except 4-9pm Peak. Which is not that much more for my past charging time. So, not like Hawaii.
We do have NEM 2.0 so the amount of extra production to the grid goes in at the cost at the time of day. I take it out at the cost of time of day. With the new 2010 TOU-PRIME the cost is the same except for 4-9pm peak. For my current plan it is different with peak from 2-8 so could add some extra production between 2-4pm. I expect most production to be between 11-2pm. This is a great deal except that at the end of the year is the "True up" time (I think that is the name) where they pay me wholesale for all current excess at $.03 per Kw. So, best to use what I produce but better to have a little extra than not.
AND... Things could change in the future. Rates could change or my usage could change. Who knows maybe my Teslas will start earning my money in the Tesla Network once FSD is here. Or my car's can run my family around town like a private UBER.
Chancellor32
Member
In AZ unfortunately yes you can buy too much solar. SRP charges demand fees and the payout on what you sell back is $.028. Here is makes sense to offset about 40% and thats it
Can you buy too much? No
Can you spend money with absolutely no return? Absolutely.
Seeing that a lot of solar is sold on long term loan, you can make your loan payments more than your previous electric bill and any buyback.
Or spend $50k upfront with payback being a lot longer than the cell's lifetime.
Can you spend money with absolutely no return? Absolutely.
Seeing that a lot of solar is sold on long term loan, you can make your loan payments more than your previous electric bill and any buyback.
Or spend $50k upfront with payback being a lot longer than the cell's lifetime.
Thanks for all the feedback. I really enjoy these forums.
We decided to go big then to have less then we need. Also, Tesla does not sell custom sizes with Panels. So maybe that is ok. We are also considering a pool and if we do and can get electric motor would do that.
Part of my decision was that as the Tax Credit goes away it is better to buy more then I need now then later at maybe more money without the tax credit. And I really can use the Tax Credit now more than maybe later.
Also, I am getting 2 power walls but I do not consider that as part of my ROI of solar because I do not really need them for ROI Solar with the SCE Credits. But I have thought of battery backup for some time and it is simply a personal thing for my wife and I. Also, with 2 Tesla's I just like the idea of it.
Oh, and the lead time to install is short now. No lack of Power Walls so I am being told < 30 days to start constructions so easy to have done this year with the 30% Tax Credit. Of course I will believe it when I activate the system.
We decided to go big then to have less then we need. Also, Tesla does not sell custom sizes with Panels. So maybe that is ok. We are also considering a pool and if we do and can get electric motor would do that.
Part of my decision was that as the Tax Credit goes away it is better to buy more then I need now then later at maybe more money without the tax credit. And I really can use the Tax Credit now more than maybe later.
Also, I am getting 2 power walls but I do not consider that as part of my ROI of solar because I do not really need them for ROI Solar with the SCE Credits. But I have thought of battery backup for some time and it is simply a personal thing for my wife and I. Also, with 2 Tesla's I just like the idea of it.
Oh, and the lead time to install is short now. No lack of Power Walls so I am being told < 30 days to start constructions so easy to have done this year with the 30% Tax Credit. Of course I will believe it when I activate the system.
Annually, the estimates are pretty much on the mark. I also look at daily as that actually matters, vs yearly which is very squishy.
For a baseline, a 10 kW system will produce ~60 kWh on an average summer day in SoCal, ~40 kWh on an average winter day, and about 15-30 kWh on an average cloudy day. Rescale for bigger, smaller system.
So, If this fits your daily-power envelope, and/or you can vary your power-consumption, then you'll be fine.
If SCE will let you switch to TOU-A, the ROI is better than -B, otherwise, you should be able to stay on TOU-B until at least Aug, 2020.
The ROI on 4-8pm TOU throws everything out the window.
If the system can cover A/C usage at noon-time (depending on your RLA/FLA of ~4 kW), the PowerWalls can help cover sunset times. As of yesterday, 10 kW of SSW-facing panels still generates ~4 kW at 5:30pm.
I believe you can not change from -B to -A since both are grandfathered. Pretty sure I read that on SCE. I picked -B when I got my Tesla 2 years ago but not sure why. Maybe because of the very low rate of currently $.10 from 10pm-8am. -B is 2-8pm peak. The new TOU are either 4-9 or 5-8. I forgot what -A was. Is it 2-8 like -B. Anyway, hope to stay on -B instead of the new TOU-Prime which is my next option which is 4-9. Lastly, I think 10k system would have worked but Tesla would not sell it.
groovidad
Living the Dream!
Net Metering here. Anything left in your "solar bank", with your provider, at the end of the year not utilized, becomes theirs. So, yes, you can overproduce. Your installer should be able to take a years worth electric bills and average your usage and provide you a system that won't allow for over production that will benefit the provider. Yet, weather is different year to year so, bear that in mind.
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