What size inverter?So, Tesla just finished the site survey. I was surprised that the surveyor came with a panels max out design. They have added 4 additional panels, this brings 20 panels to 24 panels and 8.5kw to 10.2 kw.
I was told by the advisor that placing additional panels in area B is not possible, somehow now it's possibleNow I have to decide if I should proceed with the new design.
Here is the design that he just showed me:
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I checked with him whether a service panel upgrade (100 amp) is needed, he doesn't think so but it's up to the engineering team. Then I asked if I need to install EV charger later, he said in that case, it might be needed to be upgraded.
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Solar Panels Design
- Thread starter KHYE
- Start date
They haven't share this info yet. I have to wait till the site survey data is shared with the engineering team and then they will update the design.
Tesla updated the design with 4 additional panels in the NE, N roof and bring total to 26 panels (10.2 kw). The estimated generation is 14,900 kwh/yr. Just talked to Tesla, they said one 7.6 kwh Tesla inverter.
Now I'm in dilemma to finalize the system sizing. I gave it some more thought. Financially (payback period, ROI wise), it might not be a good idea since SCE will only pays me 3 cents per kwh for the true up credit. My current usage is about 7900 kwh/yr (for higher est).
System Size Est Prod Est Over Production
10.2 kwh (24) 14,900 kwh/yr 88% (7000kwh/yr)
8.5 kwh (20) 12,757 kwh/yr 61% (4857kwh/yr)
I won't get much for true up with big oversize, also I'm not sure if my solar production might be capped by the 1 X 7.6 kwh Tesla inverter. I don't have any immediate plan when I will get EV yet and won't be able to use up all the over production power. My appliances are mainly gas.
I'm wondering if I should instead scale back the # of panels to only 18 panels and get rid of all the N, NE facing panels in the front of the house. I will save about $5K. Also, my house is sitting on lower grade than the street level, might look better aesthetically by excluding the 6 front facing panels.
System Size Est Prod Est Over Production
7.65kwh (18) 11675 kwh/yr 48% (3775kwh/yr)
Just looking at your last post, not reviewing the whole thread:
For a ballpark, assume your 6 N/NE panels are worth 2/3 of the other panels. So 24 equivalent panels make ~15,000 kWh/yr, or each equivalent panel makes ~625 kWh/year.
If you expect your future usage to be under 625*20 = 12,500 kWh/year for the next 5-10 years, sounds to me like the marginal benefit of the 6 N/NE panels is low and likely not worth the cost.
Conversely, if you know you'll be using over 12,500 kWh/year in 5 years, you might as well put those panels in now, I think. At least economically; it's a close enough call that if aesthetically or for some other reason you'd prefer to omit them, that would also make sense.
Cheers, Wayne
For a ballpark, assume your 6 N/NE panels are worth 2/3 of the other panels. So 24 equivalent panels make ~15,000 kWh/yr, or each equivalent panel makes ~625 kWh/year.
If you expect your future usage to be under 625*20 = 12,500 kWh/year for the next 5-10 years, sounds to me like the marginal benefit of the 6 N/NE panels is low and likely not worth the cost.
Conversely, if you know you'll be using over 12,500 kWh/year in 5 years, you might as well put those panels in now, I think. At least economically; it's a close enough call that if aesthetically or for some other reason you'd prefer to omit them, that would also make sense.
Cheers, Wayne
GenSao
Member
Do keep in mind that a Powerwall will consume energy (0.5 to 1.0 kWh/day) and there is a 10% round trip penalty for Powerwall. Say you use 10% of your usage by the Powerwall (I use about 20% with two Powerwalls), that is 790 kWh. Say your one Powerwall will consume 300 kWh. Combined, with your current usage that is 8,990 kWh/year (7,900+790+300).
Also consider that solar panels will degrade over time, conservative assume a 20% degradation over 30 years. So for year 30, 11675 x 80% = 9,340 kWh/year
If you do not plan on adding any additional loads, then I think you are ok to go down to 18 panels.
Thanks for informing me about this. I didn't think about this, so much to learn
The additional load that I might add is getting EV but has no immediate plan. I might have to replace the gas water heater in 5 yrs with a hybrid one, that's about it that I can think of. So, with the biggest system size, in the next 3-5 yrs, not sure what to do with the surplus
Not suggesting, but, I have never heard a person saying they put on too many. BUT, I hear ALL the time, folks saying they wish they would have put on more. You do get 26% backI won't be able to match yours
GenSao
Member
Indeed. I started with a 5.7 Kw system and added a 3.8 Kw system later.
GenSao
Member
I am not a fan of Tesla downsizing your breaker capacity from 100A (meter) to 80A to you backup load center. Assuming you have no more loads in the old load center, see if you can get them to install 100A circuit breaker instead.So, I asked Tesla to send me the detailed plan before I sign and accept. Here are the diagrams. To be honest, I don't know what I should be looking for, especially for the electrical
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Thank you! I saw that on the diagram but didn't understand what it meant.
They did some calculations on the load, according to them, i have about 71.8 A, probably that's where the 80A comes from. I asked them how they came up with the calculated loads, did they go into my SCE account to get the info. They said no, just looking at different resources but it's kind of vague. I have 100A and would rather not being downsized so I can't add more in the future.
Sometimes it seems they do this for no obvious reason while other times it is a limitation of the current service panel in terms of the max allowed breaker size.
See this thread for an example:
'whole home backup' confusion
Also, they insisted that I remove one 60 A unused breaker from my subpanel before they come. I asked why can't they remove it on the installation day, they said I have to remove it myself, very strange. From the instructions on how to remove circuit breakers, I think I can handle it and survive
This is the response from Tesla when I questioned them about the 80A:
The changes in the main panel won't affect the main breaker and are based on the branch rating.
I hope this is ok?
If "are based on the branch rating" means that the service panel is only rated for a maximum 80A breaker (other than the main), then there's basically nothing that can be easily done. You can confirm this by reading the fine print on the label in your service panel. You could still ask for the feeder from the panel to be #3 Cu, good for 100A, in case you ever upgrade the service panel.
But a side effect will absolutely be that the maximum load you can draw (when there's no solar and the PW isn't discharging) is going to be reduced from 100A to 80A. In practice not likely to matter.
With an 80A feeder to the gateway, a 20A breaker could be left in the service panel for some non-backed up load, if that would be helpful for some reason.
Cheers, Wayne
But a side effect will absolutely be that the maximum load you can draw (when there's no solar and the PW isn't discharging) is going to be reduced from 100A to 80A. In practice not likely to matter.
With an 80A feeder to the gateway, a 20A breaker could be left in the service panel for some non-backed up load, if that would be helpful for some reason.
Cheers, Wayne
Thanks so much Wayne for your explanations.
I checked my panel, looked like its rated for 125 A? Attached is the label but rather hard to see clearly due to the age and dirt.
If it's rated at 125A, should I ask Tesla to at least keep it at 100 A instead of 80A?
Thanks.
Attachments
That's an old panel. I would think if there were an 80A branch breaker limit for a panel like that, the label would explicitly say so. Perhaps @Vines would know. Maybe at the time that that label was printed, the breaker types listed only went up to 80A, so there's an implicit 80A limit.
Otherwise, I don't see why Tesla wouldn't use a 100A branch breaker and a 100A feeder.
Cheers, Wayne
Otherwise, I don't see why Tesla wouldn't use a 100A branch breaker and a 100A feeder.
Cheers, Wayne
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