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11.6kw Solar Roof, but only one Inverter?

tdawg67

Member
Sep 21, 2021
5
0
colorado
No overdrive.... They would need to increase your wiring awg size and breaker size to handle the higher output, if they never did that during install....

Where are you located? All your panels face the same direction and which direction?
i'm in colorado at 5k feet, mostly bright sunny days here. My panels are not all in the exact same direction but close, all my panels are mostly facing south, i have relatively direct exposure to all panels for significant portion of the day. I hit 7.6kw at 10:30am and stayed there till 2:30pm.. Summers will be significantly better as sun is pretty low in the sky right now. I had to increase my home coverage to support >10kW, but if my system is truely limited to 7.6kw due to hardware this seems like a money saving ploy on tesla's part if my solar system can indeed generate >7.6kw for sig. portions of time. Non-tesla installer who installed system at my neighbor said the solar inverter should be sized similar(maybe a little lower) than my true solar capacity. Friends down the street with 8kw tesla system peak at 7.6kw daily. Yes, i understand when my system is running below max capacity my extra solar arrays give me extra power, but i paid for a 12kw system. I have a friend in California that has a 12kw system, he has a 7.6 and a 3.8 inverter. Need to go thru inspection tomorrow, get PTO, but this seems a bit odd to me.
 

Vines

Active Member
Jul 20, 2018
2,078
2,495
Silicon Valley, CA
i'm in colorado at 5k feet, mostly bright sunny days here. My panels are not all in the exact same direction but close, all my panels are mostly facing south, i have relatively direct exposure to all panels for significant portion of the day. I hit 7.6kw at 10:30am and stayed there till 2:30pm.. Summers will be significantly better as sun is pretty low in the sky right now. I had to increase my home coverage to support >10kW, but if my system is truely limited to 7.6kw due to hardware this seems like a money saving ploy on tesla's part if my solar system can indeed generate >7.6kw for sig. portions of time. Non-tesla installer who installed system at my neighbor said the solar inverter should be sized similar(maybe a little lower) than my true solar capacity. Friends down the street with 8kw tesla system peak at 7.6kw daily. Yes, i understand when my system is running below max capacity my extra solar arrays give me extra power, but i paid for a 12kw system. I have a friend in California that has a 12kw system, he has a 7.6 and a 3.8 inverter. Need to go thru inspection tomorrow, get PTO, but this seems a bit odd to me.
Your 7.6 kW inverter will likely never see more than about 7.8 kW. It is constrained by its rating, the wire and breaker size, and cannot "overdrive" beyond 32A for any significant length of time.

The 32A rating is as much as you will ever see, so if the grid is perfectly at 240vac, that is exactly 7.68 kW. If your grid voltage is over or under that then the inverter output will be a bit over or under its rating. In some crazy part of the world with a grid that was just at the upper edge of the UL allowable voltage range, you might see 8.32 kW at 260 vac. I know of no such place, and most likely you are going to get within a few percent of the rated power, which is 7.68kW at 240 volts.
 
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tdawg67

Member
Sep 21, 2021
5
0
colorado
i'm in colorado at 5k feet, mostly bright sunny days here. My panels are not all in the exact same direction but close, all my panels are mostly facing south, i have relatively direct exposure to all panels for significant portion of the day. I hit 7.6kw at 10:30am and stayed there till 2:30pm.. Summers will be significantly better as sun is pretty low in the sky right now. I had to increase my home coverage to support >10kW, but if my system is truely limited to 7.6kw due to hardware this seems like a money saving ploy on tesla's part if my solar system can indeed generate >7.6kw for sig. portions of time. Non-tesla installer who installed system at my neighbor said the solar inverter should be sized similar(maybe a little lower) than my true solar capacity. Friends down the street with 8kw tesla system peak at 7.6kw daily. Yes, i understand when my system is running below max capacity my extra solar arrays give me extra power, but i paid for a 12kw system. I have a friend in California that has a 12kw system, he has a 7.6 and a 3.8 inverter. Need to go thru inspection tomorrow, get PTO, but this seems a bit odd to me.

Your 7.6 kW inverter will likely never see more than about 7.8 kW. It is constrained by its rating, the wire and breaker size, and cannot "overdrive" beyond 32A for any significant length of time.

The 32A rating is as much as you will ever see, so if the grid is perfectly at 240vac, that is exactly 7.68 kW. If your grid voltage is over or under that then the inverter output will be a bit over or under its rating. In some crazy part of the world with a grid that was just at the upper edge of the UL allowable voltage range, you might see 8.32 kW at 260 vac. I know of no such place, and most likely you are going to get within a few percent of the rated power, which is 7.68kW at 240 volts.
Thanks Vines, a brief conversation with someone at tesla today seems to indicate they likely underestimated my peak solar output. I know other folks that have 12kw arrays have 2 inverters, 7.6 and a 3.8. Not sure how tesla is going to respond.. Will see..
 

Rccarps2

Member
Mar 30, 2021
12
12
19311
Thanks Vines, a brief conversation with someone at tesla today seems to indicate they likely underestimated my peak solar output. I know other folks that have 12kw arrays have 2 inverters, 7.6 and a 3.8. Not sure how tesla is going to respond.. Will see..
FWIW, I have a 11.9kW system. 3 strings (11, 11, and 12). All are on the same plane/direction. Tesla has me on 2 inverters, the 7.6 and 3.8. I have seen my system peak out at 11.6kW a few times (and even 11.7kW, very rarely) throuhgout the summer (Southeastern PA).
 

Vines

Active Member
Jul 20, 2018
2,078
2,495
Silicon Valley, CA
Thanks Vines, a brief conversation with someone at tesla today seems to indicate they likely underestimated my peak solar output. I know other folks that have 12kw arrays have 2 inverters, 7.6 and a 3.8. Not sure how tesla is going to respond.. Will see..
Nobody at Tesla underestimated it, they decided it was ok to run a 7.6 kW inverter with 11-12 kW worth of solar roof panels. Especially in the high elevations of Colorado, solar irradiation can be as good as it is in the Bay Area.

I'll assume Tesla tells you it's working as intended, based on my rough calculation of energy lost due to the design of the Solar Roof.

Solar roofs are somewhere between 10-30% less efficient than comparable discrete PV modules from what I have gathered so far, so comparing apples to oranges only leads to juice.
 
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dareed1

Member
Jan 15, 2021
110
103
Belmont, CA
Thanks Vines, a brief conversation with someone at tesla today seems to indicate they likely underestimated my peak solar output. I know other folks that have 12kw arrays have 2 inverters, 7.6 and a 3.8. Not sure how tesla is going to respond.. Will see..
If this were my installation, I would want to get a fairly good estimation of how much energy is being lost compared to having an additional inverter. That way, I would know if it is worth pursuing the issue with Tesla. Secondly it would, I believe, help in demonstrating to Tesla that the system needs to be improved if that is what the estimate shows.

To estimate expected production, one needs to know the inclination of your roof, and the actual azimuthal angles of the panels (not just "mostly south"). The drawings I received from Tesla had this information, and I expect yours would also have the info. If not, Google maps can show you the orientation of your house, and most any smartphone can function as an inclinometer.

With that information in hand, one can use PVWatts to get an estimate of annual production. PVWatts tries to take historical weather patterns into account and that makes estimating production on a cloudless day more difficult, but you can probably find some periods in a given month where the sky is assumed to be cloudless. Or post the data about the orientation of your arrays here, and one or more of us will weigh in on how much is being lost with your relatively high DC/AC ratio.
 

wjgjr

Active Member
May 11, 2020
1,331
1,051
Silver Spring, MD
If this were my installation, I would want to get a fairly good estimation of how much energy is being lost compared to having an additional inverter. That way, I would know if it is worth pursuing the issue with Tesla. Secondly it would, I believe, help in demonstrating to Tesla that the system needs to be improved if that is what the estimate shows.
While I generally agree with this approach, the other piece that needs to be addressed is what was contracted. In particular, what (if any) specs were provided that indicated the number/size of inverters and what was the estimate for annual production? It does all get a bit murky, because the contract itself may not list the inverter specifics, and the annual estimate is not a contract guarantee, but my general point would be that Tesla arguably provided what was contracted for if they did not deviate from any inverter specs and if the system meets the estimates provided by Tesla. Put another way, if a solar install hypothetically could generate 25 MWh annually based on the panels but will only generate something like 20 MWh due to the inverters, that is certainly a big loss, but if the customer was told to expect 20 MWh, then they got what they were promised.

Especially as they move to using their own inverters, I wish Tesla would be more explicit about the hardware being installed in the contract than they have been in the past (unless it has changed) but as long as their annual production estimates take into account what they are planning to install, it does not seem like Tesla is in the wrong.
 

SageBrush

REJECT Fascism
May 7, 2015
12,563
16,587
New Mexico
With that information in hand, one can use PVWatts to get an estimate of annual production. PVWatts tries to take historical weather patterns into account

PVwatts has an advanced parameter setting to change the DC:AC setting. For Albuquerque at 6300 feet elevation, 180 degree azimuth and 20 degree panel incline, about 25 kWh a YEAR per kW DC is lost by having a 1.4:1 AC to DC ratio instead of 1:0

Works out to 0.8 kWh a day average missed collection over a year. Average daily collection will be around 53.5 kWh instead of 54.3 kWh
Call it 1.5% missed collection
 
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ericl

Member
Aug 19, 2021
68
25
florida
Nobody at Tesla underestimated it, they decided it was ok to run a 7.6 kW inverter with 11-12 kW worth of solar roof panels. Especially in the high elevations of Colorado, solar irradiation can be as good as it is in the Bay Area.

I'll assume Tesla tells you it's working as intended, based on my rough calculation of energy lost due to the design of the Solar Roof.

Solar roofs are somewhere between 10-30% less efficient than comparable discrete PV modules from what I have gathered so far, so comparing apples to oranges only leads to juice.
10-30% less efficient is true. Comparing to Solar Panels at a nearby site with the same array size but are panels instead, I generally lag 20% less efficient comparing non peak times. That array gets max of around 10kw/h so the 7.6 I have currently now is pretty close. I'm probably only clipping maybe at most 5kw on a perfect day. It's very cloudy here in Florida and for the last month of data, there has only been only one day where there's a consistent plateau at 7.6.

Factor in solar roof degradation + getting dirty; I think the oversize is guarantee me consistent production vs. getting disappointed because production drops over time.

That being said 1 month after installation, they are finally coming to inspect tomorrow!!!!
 

SageBrush

REJECT Fascism
May 7, 2015
12,563
16,587
New Mexico
10-30% less efficient is true.

There is something there I am not following. I understand that your peak production is less for what you think is a comparable STC and panel installation, but then what is different ? PTC ?

I'd be very interested to hear from Tesla whether the PTC derating is different between Tesla tiles and standard panels
 

tdawg67

Member
Sep 21, 2021
5
0
colorado
Here's day 1, flat top is 4 hours wide, last week, system hasn't been on since then. This is a normal, representative weather day, since may with exception of sun angle is lower of course. Anyone see this type of clipping as a typical day? An unofficial conversation with a tesla electrician said he'd never seen a discrepecy between solar/inverter as large.. 12.2kw/7.6kw(powerwall plus).. Most of the points above are valid, however i haven't found a single person that experiences this amount of clipping. Seems to be relatively rare, but i'm still looking.

solarday1.jpg
 

h2ofun

Active Member
Aug 11, 2020
3,028
658
auburn, ca
Here's day 1, flat top is 4 hours wide, last week, system hasn't been on since then. This is a normal, representative weather day, since may with exception of sun angle is lower of course. Anyone see this type of clipping as a typical day? An unofficial conversation with a tesla electrician said he'd never seen a discrepecy between solar/inverter as large.. 12.2kw/7.6kw(powerwall plus).. Most of the points above are valid, however i haven't found a single person that experiences this amount of clipping. Seems to be relatively rare, but i'm still looking.

View attachment 712915
That seems to be excessive clipping!!
 

nwdiver

Well-Known Member
Feb 17, 2013
8,341
11,392
United States
That seems to be excessive clipping!!

Nah... it's fine :cool:

Screen Shot 2021-09-22 at 7.31.18 PM.png


It looks worse than it is. Annual loss is < 5%. And keep in mind that as solar becomes more prevalent clipping will increasing occur when there's likely to be curtailment anyway so you're losing the least valuable energy.
 
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ericl

Member
Aug 19, 2021
68
25
florida
so many clouds here in Florida - tried to find the worst "plateau" days.
 

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