Reasons why my system is underperforming

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  • System2
    System2 Posts: 6,290 admin
    #32
    Re: Reasons why my system is underperforming

    I am in Tucson and have a 4.92KW array with Enphase micro inverters. I have some early morning shading from my chimney and also from a neighbors trees.

    So far this year production has been 8729KWh. Enphase rocks!

    See at http://enlighten.enphaseenergy.com/public/systems/tL4K292

    Run the "movie" for the past seven days and observe the shading on the top left frame of panels.
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  • Grandpaclark61
    Grandpaclark61 Registered Users Posts: 5 ✭
    #33
    Re: Reasons why my system is underperforming

    That's a good question, and I wish I could help you out with all of the technicals, but I would just say that often times manufacturers overestimate (or estimate for absolutely perfect conditions, and that's not always going to happen), and I am not really sure what to do about it. For example the EPA on cars is often too high, etc. Sorry I couldn't be of more help, but I sure hope some other people give you some good questions because I am interested to hear what they are! Is there a San Jose electrician that would be able to install solar panels in my home? I think I could do most of it, but I would definitely not want to mess that up. :)
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  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    #34
    Re: Reasons why my system is underperforming
    Grandpaclark61 wrote: »
    That's a good question, and I wish I could help you out with all of the technicals, but I would just say that often times manufacturers overestimate (or estimate for absolutely perfect conditions, and that's not always going to happen), and I am not really sure what to do about it. For example the EPA on cars is often too high, etc. Sorry I couldn't be of more help, but I sure hope some other people give you some good questions because I am interested to hear what they are! :)

    From what I can tell, that's pretty much what happened, and it seems to happen a lot. It really gives our industry a black eye when system sellers overpromise what a system will produce and the customer doesn't find out until the money is spent. It behooves every customer to do their homework before they plunk down on a system. PVWatts is extremely easy to run and will give a pretty good idea (if a little pessimistic using the default derate) of what a system will produce. Shading issues cannot be ignored, either.

    Caveat emptor.
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  • lesyl
    lesyl Solar Expert Posts: 40 ✭
    #35
    Re: Reasons why my system is underperforming

    I sure appreciate the response and help everyone. There are several things I have hard time believing at this point.

    1. I’m all about buyer beware. I did a lot of careful research to make sure I got estimates from the most reputable companies in town. As I mentioned before, their systems and estimated projection figures were are all essentially the same. Given their reputations it’s hard for me to believe that all of them would have purposely overestimated.

    I’m a deeply skeptical person and never trust anyone trying to sell me something. I double checked the companies, their systems and estimates with two people who know a lot about solar, but had no vested interest in who we went with and all the systems and estimates checked out with them. I also doubled checked the estimates with online calculators and they confirmed the estimates. Admittedly I didn’t use PVWatts, but that’s only because I didn’t know about it.

    So far at least, the company I’ve been working with has been responsive and concerned. They’ve admitted the problem. The contract has them on the hook, and I’ve been told flatly that if the system doesn’t meet their estimates then, “we owe you.”

    They want more data before they offer us options, but at this point seem ready to move panels or add more to resolve the problem.

    Any suggestions on what more I could have done, ggun?

    2. It’s hard for me to believe that they could have missed the shading issue, especially given the extensive experience of the people I was dealing with, many of whom including the main installer have been doing this for well over 20 years. All I can think of is that there may have been some sort of miscommunication between us, but I know I was extremely clear that we wanted the best possible placement for maximum production.

    Shoot, even the power company double checks the plans before and the system after it’s installed to make sure it’ll produced what it’s supposed to. They provide rebates based on production estimates that, in our case, paid for 40 percent of the system. According to the people I talked to, they are quick to reduce the rebate after the system is installed if they suspect they’ll be any shading issues. But they didn't.

    So, I don’t get it…And yeah, we’re annoyed, but we’ll see how things turn out.
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  • solarix
    solarix Solar Expert Posts: 713 ✭✭
    #36
    Re: Reasons why my system is underperforming

    My experience is that many of my local competitors and the industry in general, tend to overestimate yearly production. It is just human nature I guess. And they get away with it because few homeowners understand let alone pay attention to their kwh numbers.

    Maybe I missed it, but what angle is your array oriented at?

    I've come to the conclusion that most people have poor spatial visualization. They look up at the sky and only visualize where the sun will be at noon and just not realize where the shading will kill their solar gain at other times. I've seen arrays installed on either side of a 4 foot furnace flue etc. Works good at noon I guess, but what where they thinking?
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  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    #37
    Re: Reasons why my system is underperforming
    lesyl wrote: »
    I sure appreciate the response and help everyone. There are several things I have hard time believing at this point.

    1. I’m all about buyer beware. I did a lot of careful research to make sure I got estimates from the most reputable companies in town. As I mentioned before, their systems and estimated projection figures were are all essentially the same. Given their reputations it’s hard for me to believe that all of them would have purposely overestimated.

    I’m a deeply skeptical person and never trust anyone trying to sell me something. I double checked the companies, their systems and estimates with two people who know a lot about solar, but had no vested interest in who we went with and all the systems and estimates checked out with them. I also doubled checked the estimates with online calculators and they confirmed the estimates. Admittedly I didn’t use PVWatts, but that’s only because I didn’t know about it.

    So far at least, the company I’ve been working with has been responsive and concerned. They’ve admitted the problem. The contract has them on the hook, and I’ve been told flatly that if the system doesn’t meet their estimates then, “we owe you.”

    They want more data before they offer us options, but at this point seem ready to move panels or add more to resolve the problem.

    Any suggestions on what more I could have done, ggun?

    2. It’s hard for me to believe that they could have missed the shading issue, especially given the extensive experience of the people I was dealing with, many of whom including the main installer have been doing this for well over 20 years. All I can think of is that there may have been some sort of miscommunication between us, but I know I was extremely clear that we wanted the best possible placement for maximum production.

    Shoot, even the power company double checks the plans before and the system after it’s installed to make sure it’ll produced what it’s supposed to. They provide rebates based on production estimates that, in our case, paid for 40 percent of the system. According to the people I talked to, they are quick to reduce the rebate after the system is installed if they suspect they’ll be any shading issues. But they didn't.

    So, I don’t get it…And yeah, we’re annoyed, but we’ll see how things turn out.

    If your installer is being stand up about it, then it may get resolved painlessly. Do you have roof area they could move modules to that doesn't have a shading issue? Do they plan to address the deficiency in production that you have experienced since the system was commissioned? Is (re)moving the pole that is shading the array a possibility?

    Did you run your system's configuration through PVWatts to see how the projections it makes compares with the numbers your installer used to pitch the system to you? All you need to do that is your location, the size of the system (the DC rating), and the orientation (azimuth and tilt angles).
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  • bmet
    bmet Solar Expert Posts: 630 ✭✭
    #38
    Re: Reasons why my system is underperforming

    When ever I adjust my panel, I look up "solar noon calculator"on google to find the right time of day for the shadow stick. Yes, one panel is not the same beast as a fixed installation but at least you get a clear visual of the "ideal" vs actual . More than +/- 13 degrees off (according to iCarpenter) and the production falls.
    solarix wrote: »
    My experience is that many of my local competitors and the industry in general, tend to overestimate yearly production. It is just human nature I guess. And they get away with it because few homeowners understand let alone pay attention to their kwh numbers.

    Maybe I missed it, but what angle is your array oriented at?

    I've come to the conclusion that most people have poor spatial visualization. They look up at the sky and only visualize where the sun will be at noon and just not realize where the shading will kill their solar gain at other times. I've seen arrays installed on either side of a 4 foot furnace flue etc. Works good at noon I guess, but what where they thinking?
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  • lesyl
    lesyl Solar Expert Posts: 40 ✭
    #39
    Re: Reasons why my system is underperforming

    So far, dealings with the installer have been painless. I can't complain. They seem genuinely willing to address the problem. They aren't making excuses or telling me, "Sorry, that's just the way it is." We do have an area on the roof where the panels could be placed without shading issues. The pole cannot be moved or lowered per the electric company. The PVWatts estimate is less than the installer's estimate, but more than the system produced in a year. We only had electric bills for two months this summer, but we were expecting just one and both were higher than we were expecting. Although one those can be partially explained by a housesitter we had for two weeks while were on vacation that kept the A/C 8 degrees cooler than we normally do. Not sure yet what they'll cover. I believe the panels are oriented at 32 degrees.

    As always, I appreciate the feedback.
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  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    #40
    Re: Reasons why my system is underperforming
    lesyl wrote: »
    The PVWatts estimate is less than the installer's estimate, but more than the system produced in a year.
    Did the installer provide any rationale as to why the estimate they gave you was more than what PVWatts predicted?
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  • lesyl
    lesyl Solar Expert Posts: 40 ✭
    #41
    Re: Reasons why my system is underperforming
    ggunn wrote: »
    Did the installer provide any rationale as to why the estimate they gave you was more than what PVWatts predicted?

    No. But I haven't asked that question yet either. As I mentioned before, other solar calculators I used supported their estimate.

    In the earlier back and forth between you and a0128959 over PVWatts calculations, you seemed to be suggesting that PVWatts estimates were not that accurate. But I admit some of that went over my head -- or maybe I'm just not that smart.
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  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    #42
    Re: Reasons why my system is underperforming
    lesyl wrote: »
    No. But I haven't asked that question yet either. As I mentioned before, other solar calculators I used supported their estimate.

    In the earlier back and forth between you and a0128959 over PVWatts calculations, you seemed to be suggesting that PVWatts estimates were not that accurate. But I admit some of that went over my head -- or maybe I'm just not that smart.

    No; actually, I think they are pretty good. I had a chance to survey an installation that had been in place for a while for which there was two year's worth of monitoring data. I entered the parameters of the system into PVWatts and it agreed with the monitoring data on the yearly system output to within about 5%. The only thing is that the default derate value of 0.77 is a little pessimistic; for our system projections we use PVWatts with a derate of 0.8.

    One caveat with any estimating system that uses NREL insolation data (I'm pretty sure they all do) is that the data is statistically derived and of course cannot predict what tomorrow's weather will be. The day to day differences tend to average out over time, but still, a year can have more (or fewer) sunny days than the data shows, which will be reflected in the monitoring data.
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  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    #43
    Re: Reasons why my system is underperforming
    lesyl wrote: »
    No. But I haven't asked that question yet either. As I mentioned before, other solar calculators I used supported their estimate.

    In the earlier back and forth between you and a0128959 over PVWatts calculations, you seemed to be suggesting that PVWatts estimates were not that accurate. But I admit some of that went over my head -- or maybe I'm just not that smart.

    I agree the derate is pretty conservative, my system is running at a derate most of the time @ 0.82 or better. Lots depends on the weather variations on how PVwatts calculates the derate. The last 2 months I have been over the PVwatts by 10% with even 0.82 but the 2 months previous were about right on the money. You can look at the factors for the derate by clicking the box next to the derate.
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