How to evaluate health of a new system?

[insaneoctane]

Now that my system has been operational for just over a month, I'm disappointed with my 6kW system's first month production. From Nov 1 to Nov 30 my 6kW system producted 488kWh. The only thing I have to compare to that is my PVWatts prediction of 730 kWh. Since the system is new and I don't have a lot of data, how do I identify a "problem"? If I had a bad panel, for example, what would my overall system output look like? I see that the first week of running my system was, by far, my best. Then it's gone down hill since then. This last week weather has been poor, but I just am not sure. By the way, my installer doesn't guarantee production. If there is something wrong, they will fix it, but how would I prove something is wrong? Here is my data. I've manually added the weather "condition" per www.wunderground.com for a zipcode that is 7-8 miles away (my zipcode wasn't available). That might help, but it shows sunny days where my production was low. Any advice? I know I'm only 1 month into this, but if I have an equipment issue, I'd rather ID that sooner than later. Thanks for your input/thoughts....

DATE	GENERATED (kWh)	PEAK(kWh) PEAK_TIME CONDITION
12/4/2014	10.577	3.63	12:35	Hazy Fog
12/3/2014	4.468	1.11	11:00	Showers
12/2/2014	0.958	0.224	12:20	Showers
12/1/2014	8.356	1.508	12:20	Partly Cloudy
11/30/2014	4.517	1.59	11:30	Showers
11/29/2014	13.78	3.242	10:35	Partly Cloudy
11/28/2014	13.87	3.295	10:35	Sunny Clear
11/27/2014	13.371	3.347	10:35	Sunny Clear
11/26/2014	13.958	3.294	10:30	Sunny Clear
11/25/2014	14.539	3.49	10:40	Sunny Clear
11/24/2014	16.313	4.015	11:30	Sunny Clear
11/23/2014	16.775	3.97	11:25	Sunny Clear
11/22/2014	15.253	3.512	11:35	Sunny Clear
11/21/2014	15.562	3.57	10:45	Sunny Clear
11/20/2014	11.149	3.525	11:40	Showers
11/19/2014	12.865	4.675	11:00	Partly Cloudy
11/18/2014	14.337	4.425	12:45	Sunny Clear
11/17/2014	18.652	4.114	12:00	Sunny Clear
11/16/2014	19.193	4.609	11:00	Sunny Clear
11/15/2014	16.989	4.337	12:00	Partly Cloudy
11/14/2014	16.269	4.531	10:35	Partly Cloudy
11/13/2014	13.154	3.264	12:20	Showers
11/12/2014	14.42	5.126	11:00	Partly Cloudy
11/11/2014	7.516	3.582	10:30	Cloudy
11/10/2014	15.104	4.584	12:15	Mostly Cloudy
11/9/2014	19.88	4.344	12:00	Hazy Fog
11/8/2014	19.622	4.278	12:00	Sunny Clear
11/7/2014	20.255	4.324	11:45	Sunny Clear
11/6/2014	20.461	4.26	12:00	Sunny Clear
11/5/2014	21.88	4.634	11:30	Sunny Clear
11/4/2014	23.436	4.838	11:30	Sunny Clear
11/3/2014	23.104	4.868	11:45	Sunny Clear
11/2/2014	23.101	4.646	11:15	Sunny Clear
11/1/2014	18.703	6.112	13:30	Showers
10/31/2014	4.9	0.994	12:00	Showers

You can look at my output yourself on pvoutput.org:

http://pvoutput.org/list.jsp?id=36410&sid=33299

TNTArray2014.12.05.jpg

[Ben25]

Where are you located? My 10.92kw system made 424kWh in November. There were only a few sunny days, and the panels were covered with snow for 4-5 days. I'm in Vermont though. All in all, your numbers sound pretty good for this time of year.


Ben

[Bikerscum]

As said, it depends on where you live. I'm east of the SF Bay, my 6kw system put out 591 kwh. There were cloudy & rainy days, I consider that to be a good output.

[myfriendSUN]

Every System is Different!!!

There is no way we can compare system to system to tell about the performance.
The only way we can tell about the performance of each panel would be by using the micro inverters.
My 8.2kW system produced 420kWH in November. I am in Staten Island NY.

[control4userguy]

850kWh in Nov. from a 7.9kW system. It was a so-so month due to climate here. Going downhill from now until probably March.

[J.P.M.]

Since PVWatts is an estimator of long term performance and not a predictor of short term performance, it may not be of much help. FWIW (not much), I ran PVWatts from your PVOutput info on size, equip. and orientation, and 93021 zip 26 deg. tilt, 171 deg. az. and got 637 kWh for Nov., different than your 730 kWh.

Still, 488 kWh seems a bit on the low side. How does it compare to other PVoutput mapped systems near you on a kWh output per installed kW basis ?

As to what to do, assuming you've checked the elec. meter, POCO billing and monitoring equip. for correct operation, I'd call the installer and advise them of your findings/concerns and request a resolution or at least some believable explanation.

[thejq]

A drop of 10 KWh for Sunny days within the same month does sound suspicious. If you have two strings (MPPTs), you can compare the relative outputs from each to see if they're proportional. If not, it would be quite difficult to pin-point without per panel monitoring. Is there's any shading problem? snow covering? leafs? dirt?

[Sunking]

It will continue to go down until February.

[insaneoctane]

... How does it compare to other PVoutput mapped systems near you on a kWh output per installed kW basis ?

I found a 7kW system in a neighboring city (6 mi away) that tracks quite well with my efficiency...Makes me feel more like bad conditions than bad equipment. It's just hard to swallow 488 kWh for a month from a 6kW system in Southern California!

The system is called "Miles Away" if you are familiar with picking comparisons in pvoutput and want to see the data yourself.

For those who asked, I'm in Southern California, zipcode 93021

TNTArray2014.12.05compare.jpg

[Ian S]

It will continue to go down until February.

Not likely in S. Cali. Probably same as here in Arizona: our worst month is December by far.

[gregvet]

You need more time to see what your "normals" should be. After about 6 months, if my 7.755 kW DC did not produce between 32-45 kWh on a sunny winter day, i would be worried. On rainy days, I'll get maybe 5-10 kWh. Likewise on cloudy days, if I do not see a 7-7.5 kW instantaneous peak value, particularly if I get almost exactly 1/3 or 2/3 of that value, I know I have a faulty string since I have 3 strings. You can see my PV Output here:

http://www.pvoutput.org/list.jsp?userid=28753

[J.P.M.]

Not likely in S. Cali. Probably same as here in Arizona: our worst month is December by far.

Worst month is Dec. Nov. & Jan. are about 8% or so higher.

[silversaver]

By looking at the graph of your system vs. the 7kW in your area, I don't see any difference to worry about.....

My 7.1kW SW 245 with 23 deg tilt only produced 701kWh during Nov 2014. I bet lots smaller system outperform me but I think I'm on the track comparing with few system in my area.

[MGE]

Im in San Diego and have a 7.6kw AC system that generated 699kw hrs for this past month of November. Last year I generated only 643kw hrs. I think the PV watt estimate was 738kw hrs. Had a lot of cloudy days here on the coast so I'm not surprised on the output. I overproduced from April through Sept of this year so I guess I can't complain. My first year generating I was 238kw hrs under the PVwatt estimate, we'll see how the second year add's up when April 15 of 2015 comes around. So far so good.

[bcroe]

Now that my system has been operational for just over a month, I'm disappointed with my 6kW system's first month production. From Nov 1 to Nov 30 my 6kW system producted 488kWh. The only thing I have to compare to that is my PVWatts prediction of 730 kWh. Since the system is new and I don't have a lot of data, how do I identify a "problem"? If I had a bad panel, for example, what would my overall system output look like? I see that the first week of running my system was, by far, my best. Then it's gone down hill since then. This last week weather has been poor, but I just am not sure. By the way, my installer doesn't guarantee production. If there is something wrong, they will fix it, but how would I prove something is wrong? Here is my data. I've manually added the weather "condition" per www.wunderground.com for a zipcode that is 7-8 miles away (my zipcode wasn't available). That might help, but it shows sunny days where my production was low. Any advice? I know I'm only 1 month into this, but if I have an equipment issue, I'd rather ID that sooner than later. Thanks for your input/thoughts....

Days with very good sun are best for troubleshooting. I use a clamp on DC ammeter to compare
identical strings, which should have nearly identical output. A bad string shows up immediately;
finding the exact fault takes longer. How are your panels connected? Bruce Roe