New install yesterday but they gave me a smaller inverter than quoted.

[SunnyInVegas]

My 12.24kw system got installed yesterday and everything went well. I’m in Las Vegas.

I ordered in late August and got installed Dec. 1.

My spec sheets indicated I would receive the SE11400, but they installed the 10000 unit instead. They installer said it didn’t matter and don’t worry.

Should I insist they change it to the SE11400 unit, or does it really not make a difference?

 

[wwhitney]

More information about your install would be needed to know if it would make a difference. It may make 0 difference (in which case one wonders why the designers specified the larger inverter) or it may make a small difference. It's very unlikely the economic value of the difference exceeds the labor cost of swapping out to a larger inverter. So if you determine that it does make a difference, the optimal solution would be ask for a small rebate on the cost of the system because of the equipment substitution.

Cheers, Wayne

 

[Vines]

Only issue to note is your DC/AC ratio is now near 1.23, instead of 1.07 or so. There will be some clipping of maximum power, whether that leads to a lower total energy harvest is a more complicated question. I know SE systems are tolerant of relatively high stacking ratios, and others have pointed out @nwdiver that there is a very small total energy harvest loss even with clipping up to higher stacking ratios.

 

[SunnyInVegas]

Thanks for the quick reply.

My system is a 36 panel 12.24kW system with 1 inverter. 200A main breaker panel. I have 31 panels on the south facing roof maxing out my available space there. The remaining 5 panels are on the north facing roof but they still have very good sun exposure. I have 2x powerwalls. Is there more info I can provide to help?

 

[getakey]

what is your panel config? Are all the panels facing same direction?

 

[getakey]

Thanks for the quick reply.

My system is a 36 panel 12.24kW system with 1 inverter. 200A main breaker panel. I have 31 panels on the south facing roof maxing out my available space there. The remaining 5 panels are on the north facing roof but they still have very good sun exposure. I have 2x powerwalls. Is there more info I can provide to help?

you beat my post

 

[adspguy]

my 36 panel 12.24kw system has a 10000 solaredge inverter which is what was specified as well. 3 powerwalls in my system. It was recently installed so I haven't got to see what the full summer performance is.

 

[wwhitney]

My system is a 36 panel 12.24kW system with 1 inverter. 200A main breaker panel. I have 31 panels on the south facing roof maxing out my available space there. The remaining 5 panels are on the north facing roof but they still have very good sun exposure.

What is your roof slope on the north and south?

If your roof slope is 12:12, then when the sun is perpendicular to your south panels (maximum irradiance), there's no sun on your north panels. So your maximum DC power is effectively 31/36 * 12.24 = 10.54 kW DC. Very reasonable to have on a 10 kW AC inverter, you'll have little or no clipping.

While if your roof "slope" were 0:12, then there'd be no difference, and you have the possible worst case clipping of the DC/AC ratio of 1.23. Even that wouldn't be too bad, and of course that would only be if your house was in the tropics so the sun was sometimes directly overhead.

In between, you get a blend of the two extreme cases. If you provide the roof slope, and the azimuth (how far off true south your "south" roof faces), then if I get a chance I'll do a little vector math to see if your panels could every actually produce enough power at STC to cause your inverter to clip.

Cheers, Wayne

 

[h2ofun]

My 12.24kw system got installed yesterday and everything went well. I’m in Las Vegas.

I ordered in late August and got installed Dec. 1.

My spec sheets indicated I would receive the SE11400, but they installed the 10000 unit instead. They installer said it didn’t matter and don’t worry.

Should I insist they change it to the SE11400 unit, or does it really not make a difference?

Two reasons I have always had the largest inverter put in. First, with my 47 panels and a 11400, I do see some clipping during the summer. at 133% spec, 47 is the most panels I can have, 14.5K, on a 11400.

Second, is what if you want to put more panels on? So if the contract said 11400, I would insist on the 11400, even if you do not need it now. They can easily say you do not.

If I split my system, technologically, I could get away with a 3800 and 7600. But I have insisted I want 2 11400's, one I have now, and a new one, which I have also asked I want the EV port, even though I would have zero plans to use.

 

[jedmo]

What is your roof slope on the north and south?

If your roof slope is 12:12, then when the sun is perpendicular to your south panels (maximum irradiance), there's no sun on your north panels. So your maximum DC power is effectively 31/36 * 12.24 = 10.54 kW DC. Very reasonable to have on a 10 kW AC inverter, you'll have little or no clipping.

While if your roof "slope" were 0:12, then there'd be no difference, and you have the possible worst case clipping of the DC/AC ratio of 1.23. Even that wouldn't be too bad, and of course that would only be if your house was in the tropics so the sun was sometimes directly overhead.

In between, you get a blend of the two extreme cases. If you provide the roof slope, and the azimuth (how far off true south your "south" roof faces), then if I get a chance I'll do a little vector math to see if your panels could every actually produce enough power at STC to cause your inverter to clip.

Cheers, Wayne

Just wanted to note, there are a lot of smart and helpful people on these forums...me not being one of the smart ones. cheers!

 

[SunnyInVegas]

What is your roof slope on the north and south?

If your roof slope is 12:12, then when the sun is perpendicular to your south panels (maximum irradiance), there's no sun on your north panels. So your maximum DC power is effectively 31/36 * 12.24 = 10.54 kW DC. Very reasonable to have on a 10 kW AC inverter, you'll have little or no clipping.

While if your roof "slope" were 0:12, then there'd be no difference, and you have the possible worst case clipping of the DC/AC ratio of 1.23. Even that wouldn't be too bad, and of course that would only be if your house was in the tropics so the sun was sometimes directly overhead.

In between, you get a blend of the two extreme cases. If you provide the roof slope, and the azimuth (how far off true south your "south" roof faces), then if I get a chance I'll do a little vector math to see if your panels could every actually produce enough power at STC to cause your inverter to clip.

Cheers, Wayne

How can I find these details for my roof?

 

[wwhitney]

How can I find these details for my roof?

If you have access to the approved plan set for the permit that was issued, then they should be printed on there somewhere. If you don't have the plan set, ask the contractor for it. When the permit is finaled, it should remain with you.

Cheers, Wayne

 

[SunnyInVegas]

If you have access to the approved plan set for the permit that was issued, then they should be printed on there somewhere. If you don't have the plan set, ask the contractor for it. When the permit is finaled, it should remain with you.

Cheers, Wayne

I think I found it on the spec sheet for my hoa.

South facing— pitch 17, azimuth 181
North facing — pitch 18, azimuth 1

 

[getakey]

could probably estimate. Most roofs are between 4/12 and 9/12 with 9/12 being steep

 

[wwhitney]

South facing— pitch 17, azimuth 181
North facing — pitch 18, azimuth 1

OK, here's a quick first look. I'm going to simplify to 31 panels, pitch 18 degrees, azimuth 180 degrees, and 5 panels, pitch 18, azimuth 0 degrees.

I'll call Las Vegas's latitude 36.2 degrees. The earth's tilt is 23.5 degrees. So the sun will occasionally be directly perpendicular to your panels (18 > 36.2 - 23.5). Then when that's true, it will be 36 degrees off perpendicular from the 5 panels on the north. cos(36 deg) = 0.81, so effectively your 5 north panels are like 4 south panels.

That means on those occasions, your DC/AC ratio is 35/36 * (12.24 / 10) = 1.19. That's a bit worse than I expected, but your roof slope is pretty low.

A better analysis would consider how often it's true that the sun's angle is close enough to the panel normal to cause clipping. But that would require more time/interest/knowledge than I have right now. I don't think PVWatts supports multiple arrays, otherwise that would be a good solution. Not sure if there's a free multiple array PV simulator that would model the clipping issue with a common inverter.

Cheers, Wayne

 

[sorka]

Don't forget clouds. On partly cloudy days, I've seen my output go way higher than it can with 100% blue sky due to the extra reflected sunlight off the clouds.

 

[arnolddeleon]

I'm sure @nwdiver has good thoughts on this.

My thoughts on clipping:

• How often will it occur? If a larger inverter will cost more money will you recover that cost in extra production? Assuming you had the space on the roof, are the dollars better spent on additional panels?
• What's the efficiency curve look like? It looks like the smaller inverter gets to peak efficiency sooner than the larger inverter. It is possible that the total energy output will work out the same. E.g. the smaller inverter captures more energy earlier and would lose some on the rare times it would clip. It might be work out the other way, the smaller inverter will capture more energy.
• The panels will degrade and get dirty
• Vegas is presumably hot (which lowers panel efficiency) when the sun is high and closer to the optimal angle.

 

[nwdiver]

I'm sure @nwdiver has good thoughts on this.

My thoughts on clipping:

• How often will it occur?

NREL says ~never. Oversize ratio of 1 (12.24kW inverter (math was easier)) vs Oversize ratio of 1.22 (10kW inverter)

 

[wwhitney]

NREL says ~never. Oversize ratio of 1 (12.24kW inverter (math was easier)) vs Oversize ratio of 1.22 (10kW inverter)

Nice. Did you enter it as a single array of 36 panels on the south exposure? Or is there a way to enter a system with two different array orientations?

Cheers, Wayne

 

[SunnyInVegas]

OK, here's a quick first look. I'm going to simplify to 31 panels, pitch 18 degrees, azimuth 180 degrees, and 5 panels, pitch 18, azimuth 0 degrees.
...

Cheers, Wayne

Looking at my ‘optimizer map’ with the panels scan codes, I see the drawing shows ‘pitch 4/12’ on both roof tops.