Max reported output vs system size

[farokhboston]

Ok, so just had my new 8.2 KW system "commissioned" last week, and am monitoring it with the Enphase Envoy system.

One of the things the Enlighten Manager shows me is "peak" output (usually around 1230pm), and its always (so far) showing as 6.5 KW.

I get that I'm not going to get "peak" output all the time, but if I have a 8.2KW system, is the peak of 6.5KW now/today "normal" or is there something wrong?

The panels are Suniva 280 Watt Panels, with Enphase S-250 Micro-invertors.

I understand that the total efficiency of the system is "only" 80%, since I have some shading issues on one side of the house, but that shouldnt affect "peak" output, right?

[J.P.M.]

Ok, so just had my new 8.2 KW system "commissioned" last week, and am monitoring it with the Enphase Envoy system.

One of the things the Enlighten Manager shows me is "peak" output (usually around 1230pm), and its always (so far) showing as 6.5 KW.

I get that I'm not going to get "peak" output all the time, but if I have a 8.2KW system, is the peak of 6.5KW now/today "normal" or is there something wrong?

The panels are Suniva 280 Watt Panels, with Enphase S-250 Micro-invertors.

I understand that the total efficiency of the system is "only" 80%, since I have some shading issues on one side of the house, but that shouldnt affect "peak" output, right?

What's your orientation and what does PVWatts say for an hourly output on a clear day this time of year ?

[Mike90250]

amazing and awesome

2 spammy posts and you are now banned. Amazing and good bye

[ButchDeal]

Ok, so just had my new 8.2 KW system "commissioned" last week, and am monitoring it with the Enphase Envoy system.

One of the things the Enlighten Manager shows me is "peak" output (usually around 1230pm), and its always (so far) showing as 6.5 KW.

I get that I'm not going to get "peak" output all the time, but if I have a 8.2KW system, is the peak of 6.5KW now/today "normal" or is there something wrong?

The panels are Suniva 280 Watt Panels, with Enphase S-250 Micro-invertors.

I understand that the total efficiency of the system is "only" 80%, since I have some shading issues on one side of the house, but that shouldnt affect "peak" output, right?

PV modules are measured at STC (standard test conditions) your roof is not STC.
you stated the size is 8.2kw but I think it is 8.12kw system of 29 Suniva 280w modules, or 30 suniva modules would be 8.4kw

You also mentioned that you have Enphase S-250 micro inverters but they do not make an S-250 There is the older M250 and the new S230 and S280

So is the size 8.12kw or 8.4kw
are the inverters M250 or S230, or S280?

Yes shadow and orientation can easily cut the peak

[farokhboston]

PV modules are measured at STC (standard test conditions) your roof is not STC.
you stated the size is 8.2kw but I think it is 8.12kw system of 29 Suniva 280w modules, or 30 suniva modules would be 8.4kw

You also mentioned that you have Enphase S-250 micro inverters but they do not make an S-250 There is the older M250 and the new S230 and S280

So is the size 8.12kw or 8.4kw
are the inverters M250 or S230, or S280?

Yes shadow and orientation can easily cut the peak

Butch,

You are right. <grin>

It is 8.12 Kw, w/M250 inverters.

I've got my panels divided onto two parts of my roof:

20 @ Azimuth 215 w/a 15 degree tilt
9 @ Azimuth 135 w/a 15 degree tilt

So neither set of panels is directly facing south, which I guess can affect the peak..

[gbynum]

Ok, so just had my new 8.2 KW system "commissioned" last week, and am monitoring it with the Enphase Envoy system.

One of the things the Enlighten Manager shows me is "peak" output (usually around 12:30pm), and its always (so far) showing as 6.5 KW.

My 4.25kW DC gives me, at best, 3.8kW AC which is about what I expected. Based on that, I'd expect you to see ABOUT 90% of DC as your AC generation. Following up on what others have said, what does PVWatts predict for your installation. What components present production.jpg do you really have? Aside, I bought the Enphase optional reporting capability with panel level data; assuming you didn't, your installer can use theirs and look at that for you to see if there is something unusual.

[farokhboston]

My 4.25kW DC gives me, at best, 3.8kW AC which is about what I expected. Based on that, I'd expect you to see ABOUT 90% of DC as your AC generation. Following up on what others have said, what does PVWatts predict for your installation. What components [ATTACH=CONFIG]n313138[/ATTACH] do you really have? Aside, I bought the Enphase optional reporting capability with panel level data; assuming you didn't, your installer can use theirs and look at that for you to see if there is something unusual.

Hmm. So using your 90% rule, I should be seeing a peak of about 7.3 Kw AC.

I did get the panel level monitoring, and so far, all seem to be "ok". (I can see the individual output of each panel).

I'll check with my installer, to see what they think might be going on.

[J.P.M.]

Butch,

You are right. <grin>

It is 8.12 Kw, w/M250 inverters.

I've got my panels divided onto two parts of my roof:

20 @ Azimuth 215 w/a 15 degree tilt
9 @ Azimuth 135 w/a 15 degree tilt

So neither set of panels is directly facing south, which I guess can affect the peak..

Given those orientations, that 6.5 kW max. output doesn't look too out of line to me.

[sensij]

I've got my panels divided onto two parts of my roof:

20 @ Azimuth 215 w/a 15 degree tilt
9 @ Azimuth 135 w/a 15 degree tilt

So neither set of panels is directly facing south, which I guess can affect the peak..

It isn't just that they aren't facing south, it is also that each roof face will hit its peak at a different time of day. That will necessarily reduce the measured total peak relative to a system of the same size with all the panels facing the same direction.

Do the daily playback.. what is the peak that a panel in each subarray hits, relative to the individual panel rating?

[DanKegel]

Sounds fine to me. I have 8.9kW split between south and west.
Peak power for whole array is usually between 7.1 and 7.6 kW, see http://pvoutput.org/list.jsp?id=38786&sid=44908
Daily playback http://kegel.com/energy/solar/retrofit2/screencast.ogv shows south peaks an hour before west.

[farokhboston]

It isn't just that they aren't facing south, it is also that each roof face will hit its peak at a different time of day. That will necessarily reduce the measured total peak relative to a system of the same size with all the panels facing the same direction.

Ok. Now THAT makes perfect sense. Thanks for explaining it that way.

[ButchDeal]

Butch,

You are right. <grin>

It is 8.12 Kw, w/M250 inverters.

I've got my panels divided onto two parts of my roof:

20 @ Azimuth 215 w/a 15 degree tilt
9 @ Azimuth 135 w/a 15 degree tilt

So neither set of panels is directly facing south, which I guess can affect the peak..

you have 29 individual systems. each will have its own peak but that peak is not likely to ever be 280W except on cold windy days.

[Amy@altE]

Your tilt angle is also very low for this time of year. You should see some improvement in the summer, although the voltage drop from the heat may offset that angle gain. Best year round tilt is latitude, which is about 42 degrees here.

[farokhboston]

Your tilt angle is also very low for this time of year. You should see some improvement in the summer, although the voltage drop from the heat may offset that angle gain. Best year round tilt is latitude, which is about 42 degrees here.

Ok, so what should my "ideal" tilt have been, and why? Isnt "the flatter, the better"? (Max surface area, at peak).

[ButchDeal]

She isn't suggesting that the tilt should be altered since you have a roof mount. On the roof and at the roof tilt is best.
She is indicating why your performance at this time of year is unlikely to get as close to max as it could be. The modules are rated for STC ( standard test conditions). Your roof is not STC, even at optimal tilt it isn't, but would be slightly closer...

[sensij]

Ok, so what should my "ideal" tilt have been, and why? Isnt "the flatter, the better"? (Max surface area, at peak).

No, the general rule is you want the panels directly facing the sun at solar noon for maximum production. A decent write up on it is here, if you are unfamiliar with how the sun's path through the sky changes throughout the year:

http://www.solarpaneltilt.com/