Please help me understand my production rate vs my system size.....???? Confused...

[Yet another Yeti]

East-West or SE-SW situation ?

[bcroe]

I do not know how bad your angle/shade situation is, but 30KWH a year is so far down
in the dirt it might as well be zero. On the face of it, the number is ridiculous. Bruce Roe

[J.P.M.]

I read this thread and I have a similar question.I'm in the process of getting a system and just had the sire survey last week.
It's a 320watt 21 panel with optimizers 6.7kw system. They have me down for a Solaredge SE6000H-US sine wave inverter.
The designer said it pulls 25 amps. I was not sure if that was large enough. When I had an inverter before with my electric powered food truck, I went with a larger inverter so it ran cooler and would last longer. I asked for the 7.6 inverter and they can do it but for a $300 charge. I would have thought they'd use that in the first place so it runs more efficiently than running at peak during the sunny times. I also have zero shade on my flat roof and in Arizona so there's plenty of sun. Doesn't the SE7600H-US make more sense.
Also, I inquired about installing the meter/inverter in the garage and keeping the disconnect out by the panel and they said no problem, but for $500. I would just think that if it were in the garage, it wouldn't get as hot in the summertime and it would last longer and also not have to worry about vandalism. The panel is on the opposite side of the garage, so I wouldn't think I'd get quoted $500.
Is that something I shouldn't even worry about ?

As a first approx., an inverter ought to put out close to or slightly more than the max. likely instantaneous output of the array it's attached to. After that, if it'll cost $300 more for an inverter that eliminates 20-30 kWh/yr. of clipping, it might make more economic sense to use the smaller and $300 less expensive inverter.

The key is to have some idea of how much the average annual system output will perhaps be over many years and how much of that will be lost to clipping with any inverter. If it's going to cost $300 more to knock $5.00/yr. off your bill, the larger inverter might not be as cost effective and tolerating a bit of clipping might be the more cost effective choice.

Run PVWatts w/correct array orientation and location and model the system w/10 % system losses. Get the hourly output option and sort by max. hourly output. Then size up an inverter and see how much loss of output, or output reduction results for each inverter.

[Jasper7821]

I read this thread and I have a similar question.I'm in the process of getting a system and just had the sire survey last week.
It's a 320watt 21 panel with optimizers 6.7kw system. They have me down for a Solaredge SE6000H-US sine wave inverter.
The designer said it pulls 25 amps. I was not sure if that was large enough. When I had an inverter before with my electric powered food truck, I went with a larger inverter so it ran cooler and would last longer. I asked for the 7.6 inverter and they can do it but for a $300 charge. I would have thought they'd use that in the first place so it runs more efficiently than running at peak during the sunny times. I also have zero shade on my flat roof and in Arizona so there's plenty of sun. Doesn't the SE7600H-US make more sense.
Also, I inquired about installing the meter/inverter in the garage and keeping the disconnect out by the panel and they said no problem, but for $500. I would just think that if it were in the garage, it wouldn't get as hot in the summertime and it would last longer and also not have to worry about vandalism. The panel is on the opposite side of the garage, so I wouldn't think I'd get quoted $500.
Is that something I shouldn't even worry about ?

[bcroe]

If your output under good sun goes up and then flattens to a straight line for any
significant time, your inverter is clipping. You could prove this by checking string
output voltage to the inverter. Voltage will be around 80% of open circuit rating,
then begin to rise as the curve flattens, maybe to 85 or 90% of open circuit. Same
thing in reverse later.

I would expect 3KW is a pretty poor best peak for a 4.3KW system.

My inverters clip at about 101% of inverter rating, you should see a similar thing.
Bruce Roe

[J.P.M.]

I'm hoping I could open this thread again as I found it very useful. I understand the original posting and the following replies but I'd like to propose a slightly different angle that I've been fighting for some time now. I have 20 Canadian panels 230w with an ABB inverter (installed Jan '19) that is rated at 3.6kw (stated by Tesla(solarcity). For every sunny day I've encountered the inverter shows production shoot up to 2971kw then flattens there. Occasionally it'll drop due to clouds and of course there's a ramp up in the morning and ramp down in the afternoon as the sun moves across the sky but for a few hours mid day it's plateau's.

When I called Tesla, their support team was surprised to hear that. They indicated it should only produce at any one time a maximum of 3.6kw but felt the inverter had some head room (clearly I spoke with a level 1 person). My question is less what it's capable of producing in a day or in a month, I think I'm clearing seeing the inverter limiting what my panels can produce at any one point. I'm aware that they won't each procude 230 in reality on a roof but the graph really shows a flat ______ roof limit.

I think they undersized my inverter but half say yes, most say it was purposeful to not over utilize the panels (what??!) I'm wondering what this community thinks and how you think I should approach Tesla. I may be only seeing a gap of 20watts per panel but no way of me knowing what's above that plateau. They won't even look at my graphs ...from THEIR dashboard...

1.) Run PVWatts for your location and array orientation w/a 10 % system loose factor rather than the 14 % default value.
2.) Then, get the hourly output option. Then find the max. hourly output. That will give you some ballpark # for likely max. hourly output.
3.) If you have a production curve with a very flat top on (some) sunny days, that usually, but not always indicates a condition called "clipping". That is, the panels are putting out more power than the inverter can take in. If your output is flat @ 2,971 W ( not kW BTW) for a period of time > say, ~ .5 hour or more, chances are the inverter is clipping.

For how long, under what conditions and about what time(s) of day and/or seasons of the year does the output flatten out ?

4.) I'd guess, without knowing your location, array orientation or shading that a reasonably oriented (that is generally equator facing and at some tilt to the horizontal) 4.6 kW array that's mostly shade free ought to have a max. output maybe a bit less than 4 kW or so. Without being there, and only going by what you've written, I wouldn't be surprised if you have a 3 kW inverter that's clipping in sunny weather and at times when the solar incidence angle on the array is small (that is, the angle between the sun vector and the array normal).

[Homer]

I'm hoping I could open this thread again as I found it very useful. I understand the original posting and the following replies but I'd like to propose a slightly different angle that I've been fighting for some time now. I have 20 Canadian panels 230w with an ABB inverter (installed Jan '19) that is rated at 3.6kw (stated by Tesla(solarcity). For every sunny day I've encountered the inverter shows production shoot up to 2971kw then flattens there. Occasionally it'll drop due to clouds and of course there's a ramp up in the morning and ramp down in the afternoon as the sun moves across the sky but for a few hours mid day it's plateau's.

When I called Tesla, their support team was surprised to hear that. They indicated it should only produce at any one time a maximum of 3.6kw but felt the inverter had some head room (clearly I spoke with a level 1 person). My question is less what it's capable of producing in a day or in a month, I think I'm clearing seeing the inverter limiting what my panels can produce at any one point. I'm aware that they won't each procude 230 in reality on a roof but the graph really shows a flat ______ roof limit.

I think they undersized my inverter but half say yes, most say it was purposeful to not over utilize the panels (what??!) I'm wondering what this community thinks and how you think I should approach Tesla. I may be only seeing a gap of 20watts per panel but no way of me knowing what's above that plateau. They won't even look at my graphs ...from THEIR dashboard...

[camilo]

ok I just reread and saw where you said you were kidding about that. Phew

[camilo]

I'm having a hard time understanding whether or not the "shading the panels during the daytime" comment was serious or a sarcastic response.

One thing I haven't seen covered (i skipped around a lot on this topic though) is pitch. Depending on where you live and the pitch in which you have the panels installed, that could also take away from your production, but being that you have a 7.6 kW inverter and you are sometimes seeing 8kW worth of production, then you are good.

Overall though, your location, and the pitch and azimuth of where the panels are installed all determine overall power production. They should have done a shade analysis as that would have shown you what the panels will produce throughout the year.

Again, if you have a 7.6 kW inverter, and they loaded it at about 130% of that with panels, your system is producing as should if you are seeing 7-8 kW peak production throughout the day.

[DanS26]

Sorry I used an acronym.....in the electrical sense it only has one meaning:

https://www.allacronyms.com/POCO/electrical

[ButchDeal]

POCO? (yes, i did try googling it...

Power Company

[sharpd1]

There is a conversion loss, sometimes referred as inverter efficiency to convert DC watts as generated by your panels to AC watts that sent to the home or grid. Your POCO has nothing to do with this.

POCO? (yes, i did try googling it...

[DanS26]

There is a conversion loss, sometimes referred as inverter efficiency to convert DC watts as generated by your panels to AC watts that sent to the home or grid. Your POCO has nothing to do with this.

One of your panels outputs 305 DC watts under ideal conditions.....but your inverter only outputs say 290 watts AC. Your original question was mixing apples and oranges.

[sharpd1]

This entire thread has ignored the conversion of DC watts to AC watts. It almost totally explains the OP's original question.

hmm....could you elaborate?
I believe there was some discussions i had with my rep early on about the limit that Dominion Energy puts on residential installations before imposing fees/penalties. i believe he said as long as the system is below 10kW "DC", we're ok......we can generate 12,000 kwh 'AC" given my roof's position.

Did i get that remotely correct?
btw, how does that answer my original question? curious what you meant.

[DanS26]

This entire thread has ignored the conversion loss of DC watts to AC watts. It goes a long way to explain the OP's original question.