new member here - looking to learn

[ajonestx]

Have had solar for a few years, but admittedly, do not understand how to read all the published literature on module output and expectations. System appears to be underperforming and attempts to ask those smarter than me for help have left me with more questions than answers. I do not wish to bad mouth anyone or any company... just want to understand and put my expectations in line with the capabilities of the system installed on my roof. If there is a particular forum here to have a conversation, I would like to start there. Any help would be a appreciated.

[SunEagle]

Hello ajonestx and welcome to Solar Panel Talk

If you provide some details on your system (hardware and arrangement) we might be able to assist you with any issues you are running into.

[RichardCullip]

I’m curious about what leads you to think your system is under performing? Pvwatts is a great online tool to get an estimate on what your specific system should be producing.

[ajonestx]

Hello ajonestx and welcome to Solar Panel Talk

If you provide some details on your system (hardware and arrangement) we might be able to assist you with any issues you are running into.

Hello SunEagle and thank you for allowing me to add some additional data from the installer.

• total panel area: 409 SF
• proposed System Peak Power: 5.767 kW DC (5.761 kW AC)
• Proposed annual production: 7,250 kWh (supplying 83% of annual electric use).
• 18 panels - STC DC Power: 327W with micro inverters
• array is south facing (with some shade) that feed into two strings to a combiner box, then into main electrical panel

[ajonestx]

I’m curious about what leads you to think your system is under performing? Pvwatts is a great online tool to get an estimate on what your specific system should be producing.

Hello Richard: I guess that is the part that I do not understand... my four indicators that influence my thoughts about underperformance are below. I might qualify that while I "think" there might be a problem, I do not know due to lack of education and officially, I still recommend solar to everyone!

kWh: installer suggested I might see 7,250 kWh per year (taking into consideration a shade analysis). In year one, I saw 6,300 kWh, but the most I have seen over the last three years (after 18 inverter replacements) is about 5,500 kWh per year. I know we have some shade that affects some panels at different times of the year, so I discount this one some.

kW at micro inverter level: In February of 2017 (two months after install), I obtained a screen shot where some of the panels were generating 318 Watts (pretty close to name plate at 327 W / AC Max continuous output power at 320 W). I recently read that it might be a good idea to clean the panels. After cleaning, I obtained a recent report (March of this year) that suggested the panels were maxing out over a one week period at around 270 watts each. Some of the panels were much lower due to shade that affects a few panels at different times of the day.

kW at system level: In 2017, we saw one maximum of 5,410 watts in April. Maximum that I am seeing now is about 4,400 watts (even after cleaning).

Electric bills: I know, not a good indicator due to usage, but in year one, we saw lots of negative electric bills (mostly in the spring). In last three years, we have only seen one negative electric bill.

I have been researching how to test the panels, but the recommendations vary from using volt meters, amp meters, irradiance meters, insolation meters and the like, but not really sure what kind of questions to ask.

[Ampster]

.........

Electric bills: I know, not a good indicator due to usage, but in year one, we saw lots of negative electric bills (mostly in the spring). In last three years, we have only seen one negative electric bill.
.......

I keep track of my monthly electric bills and compare that to my NET usage. I track dollars and kWhs from the bills. I have two EVs so i have a lot of control when I charge my EVs and how much I charge them. I expect some degradation and occasionally think about cleaning the panels. I am on a TOU rate and my conclusion is that I have more control over my consumption than I do over the factors that influence production. The biggest return on my investment of time is the energy conservation measures that I can take. That includes shifting usage to lower TOU rate periods. After 10 years with solar panels on 3 different homes I have seen the rate changes take more out of my economics than any degradation of the system output.

[scrambler]

What kind of monitoring does your system provide both in terms of time interval (hours or only days), and system details (only the full array, or also individual panels).
Also do you have the ability to download that data for any given period, so you could potentially bring it into a spreadsheet like Excel?

Based on that, we can devise an approach to try and narrow down what has been happening over the last few years.

For example, assume you have access to everything I mentioned above. You could start by downloading the full array daily interval production for the last few years, and graph that in the same graph, to see how the graph changes from year to year on a daily basis.

Based on the results, you can then dig deeper with similar graph for each panel, or if the above shows specific periods with wide variations, you can create the graph for these specific periods using the hourly data.

[J.P.M.]

Hello Richard: I guess that is the part that I do not understand... my four indicators that influence my thoughts about underperformance are below. I might qualify that while I "think" there might be a problem, I do not know due to lack of education and officially, I still recommend solar to everyone!

kWh: installer suggested I might see 7,250 kWh per year (taking into consideration a shade analysis). In year one, I saw 6,300 kWh, but the most I have seen over the last three years (after 18 inverter replacements) is about 5,500 kWh per year. I know we have some shade that affects some panels at different times of the year, so I discount this one some.

kW at micro inverter level: In February of 2017 (two months after install), I obtained a screen shot where some of the panels were generating 318 Watts (pretty close to name plate at 327 W / AC Max continuous output power at 320 W). I recently read that it might be a good idea to clean the panels. After cleaning, I obtained a recent report (March of this year) that suggested the panels were maxing out over a one week period at around 270 watts each. Some of the panels were much lower due to shade that affects a few panels at different times of the day.

kW at system level: In 2017, we saw one maximum of 5,410 watts in April. Maximum that I am seeing now is about 4,400 watts (even after cleaning).

Electric bills: I know, not a good indicator due to usage, but in year one, we saw lots of negative electric bills (mostly in the spring). In last three years, we have only seen one negative electric bill.

I have been researching how to test the panels, but the recommendations vary from using volt meters, amp meters, irradiance meters, insolation meters and the like, but not really sure what kind of questions to ask.

What's your zip and what did PVWatts suggest you might see in a year ?

[ajonestx]

I keep track of my monthly electric bills and compare that to my NET usage. I track dollars and kWhs from the bills. I have two EVs so i have a lot of control when I charge my EVs and how much I charge them. I expect some degradation and occasionally think about cleaning the panels. I am on a TOU rate and my conclusion is that I have more control over my consumption than I do over the factors that influence production. The biggest return on my investment of time is the energy conservation measures that I can take. That includes shifting usage to lower TOU rate periods. After 10 years with solar panels on 3 different homes I have seen the rate changes take more out of my economics than any degradation of the system output.

absolutely... we have been tracking kWh from electric bills for 25 years and have implemented energy reduction strategies like adding insulation, replacing windows, changing out lamps with LEDs and the like. Nice to see your consumption numbers go down over the years... work in progress - only 8 fluorescents and 6 incandescent to go! We also have an EV, so that hits the electric bill pretty hard sometimes (less in COVID times). I think I will look into the TOU rate plan - right now, we are the same rate coming in and going out.

[ajonestx]

What's your zip and what did PVWatts suggest you might see in a year ?

Hello J.P.M - 77008. I ran the numbers in PVWatts and they suggested the following: 7,053 kWh/Year (System output may range from 6,823 to 7,243 kWh per year near this location).

[ajonestx]

What kind of monitoring does your system provide both in terms of time interval (hours or only days), and system details (only the full array, or also individual panels).
Also do you have the ability to download that data for any given period, so you could potentially bring it into a spreadsheet like Excel?

Based on that, we can devise an approach to try and narrow down what has been happening over the last few years.

For example, assume you have access to everything I mentioned above. You could start by downloading the full array daily interval production for the last few years, and graph that in the same graph, to see how the graph changes from year to year on a daily basis.

Based on the results, you can then dig deeper with similar graph for each panel, or if the above shows specific periods with wide variations, you can create the graph for these specific periods using the hourly data.

Hello Scrambler - My monitoring only provides the full array (no individual panels). Time interval available is hourly. Occasionally, I am able to obtain a snap shot of panel level data from the manufacturer, but they do not like to do that very often. We have downloaded daily data for the entire ownership period and input into excel. Not really sure what it is telling me other than in 2017, we produced 6316.8 kWh (average daily was 17.259 kWh), in 2019 (I will skip 2018 due to inverter replacement that year), we produced 5570 kWh (average daily was 15.22 kWh) and in 2020, we produced 5532 kWh (average daily was 15.11 kWh). I do have an excel file of daily production and graphed it but do not know how to post an image here.

[ajonestx]

30 DAY MOVING AVERAGES. BLUE IS 2017, RED IS 2019 AND GREEN IS 2020 (skipped 2018 due to inverter replacements that year).


Capture.JPG

[Ampster]

........... We also have an EV, so that hits the electric bill pretty hard sometimes (less in COVID times). I think I will look into the TOU rate plan - right now, we are the same rate coming in and going out.

I did not have a choice about a TOU rate when I went with an EV rate. The super off peak rate used to be $0.11 per kWh but now it is up to $0.15. The tradeoff is the peak rate of up to 0.51 per kWh in summer. That high rate is a two edge sword because that is the rate I get credited at when I send solar to the grid but it is also the rate I pay when the sun goes down. I am in California with PGE.

[scrambler]

From looking at the daily graphs (day interval), it looks like the second half of the year track fairly well, and that the bulk of the difference is in the first half ( I assume day # goes from January first (1) till December 31st (365)

The difference between the 2017 (blue) and 2020 (green) could probably be seasonal weather difference.

The fact that during the second half of the year, the production tracks better would indicate that if there was an actual HW problem, it would have fixed itself which is rare, and so also comfort weather as the more likely source.

The fact that each year at times crosses over to be the top production is also encouraging and pointing to seasonal weather rather than HW failure

That said, 2019 (red) looks way low in April May June, So I would make a separate hourly graph of the three years for each of these month.
April only with the 3 years, May only with the three years, and June only with the three years, to see if the offset is uniform or crosses over.

But the next step would really require to have access to the panel level data, first with daily interval during these three month.
If the difference is weather related, all panels will pretty much track, but if the panels do not track it may point to panels or micro inverter failures.
It may also reveal if your shade is evolving for the worst. Trees grow taller each year and could play a big factor.

Troubleshooting is where having panel monitoring is worth it. You have micro inverters, you may want to request or pay for full panel level monitoring.

[ajonestx]

I did not have a choice about a TOU rate when I went with an EV rate. The super off peak rate used to be $0.11 per kWh but now it is up to $0.15. The tradeoff is the peak rate of up to 0.51 per kWh in summer. That high rate is a two edge sword because that is the rate I get credited at when I send solar to the grid but it is also the rate I pay when the sun goes down. I am in California with PGE.

I fully understand how you might consider TOU rate plans with those drastic swings in pricing!