X
 
  • Time
  • Show
Clear All
new posts
  • JSchnee21
    Solar Fanatic
    • May 2017
    • 522

    #31
    Yes, perhaps I was generalizing a bit too much. The HD series of inverters is not more "prone" to clipping, per se. But there are two important differences which can lead to more clipping depending on the characteristics of individual installs:

    1) Increase in supported DC to AC ratio. Yes, SE permits higher DC to AC ratios on the HD units without voiding the warranty. This has led some novice installers to "oversubscribe" more generously than they should be for some installs.

    2) Name plate versus actual DC inverter capacity. Some models in the older A-series actually have a higher DC inverter capacity than their name plate suggests. In contrast, the new HD's series strictly curtails inverter capacity to match the nameplate.

    See these comparison spec sheets. Most notably the 7600 which is one of the most popular sizes.

    HD (7600VA for the 7600 A-Series)


    A-Series (8350VA for the 7600 A-Series)


    While some minor clipping is generally acceptable -- in some cases even preferable to the added costs of replacing load centers, etc. if a line side tap is not permitted -- the reality is that the differential cost between models of the SE inverter line is pretty small. Usually only a few hundred dollars -- sometimes less. Which in the grand scheme of a $30k or $40k project is insignificant.

    While upgrading inverters from ROI perspective may not always make fiscal sense, running electronics at 50-80% load versus 70-105% load, particularly passively cooled electronics, makes sense to me from a longevity perspective. But others may disagree.

    Customers will complain when they see clipping, even if the amount of power lost is insignificant and not cost effective to remediate.

    For example, the cost differential between the 7600HD and 10000HD on Alt-E for example is $429. ($1579 versus $1999)


    And only $404 on Renvu (you need a log on to see pricing) $1,451.30 versus $1,855.02


    Similarly price differentials between the 6000 and 7600 and 10000 and 11400 are even less.

    All I'm saying is that installers should be more transparent about these types of choices and discuss the pros and cons.

    Comment

    • flowing
      Member
      • Feb 2019
      • 40

      #32
      @macaddict I see that yous install was done via GPE. How close was their estimate to the actual production you have been getting?

      Thanks!

      Comment

      • flowing
        Member
        • Feb 2019
        • 40

        #33
        Are you guys south-facing?

        Comment

        • flowing
          Member
          • Feb 2019
          • 40

          #34
          I received an updated estimate. This is with srecs at 175 and 10k down. I still think the yearly production sends too optimistic. How much do the estimates differ from real production?

          SmartSelect_20190218-191250_Drive.jpg
          Thanks

          Comment

          • J.P.M.
            Solar Fanatic
            • Aug 2013
            • 14926

            #35
            Originally posted by flowing
            I received an updated estimate. This is with srecs at 175 and 10k down. I still think the yearly production sends too optimistic. How much do the estimates differ from real production?

            SmartSelect_20190218-191250_Drive.jpg
            Thanks
            First, how much has been estimated for annual production in kWh? And by who ? What's your zip, your planned array size and array orientation (tilt and azimuth). Vendors commonly use models and often/commonly (at least the ones I've seen in CA) overestimate production by something like 10 % or more.


            Run PV Watts and get your own unshaded estimate. Yearly unshaded output will vary by ~ +/- 10% or so, mostly due to weather. Can't be helped.

            Comment

            • Ampster
              Solar Fanatic
              • Jun 2017
              • 3650

              #36
              Originally posted by JSchnee21
              Yes, perhaps I was generalizing a bit too much. The HD series of inverters is not more "prone" to clipping, per se..............

              All I'm saying is that installers should be more transparent about these types of choices and discuss the pros and cons.
              I agree. In my case the difference between the 3800kW and the 5800kW was $150. If my installer had communicated to me that we were going to be at 150% I probably would have said let's go with a 6kW system instead of a 5.7kW. At 2.50 a Watt that would have been $750 more cost to me (and revenue to them) but their equipment costs would have increased maybe $500 and incremental labor and overhead very little.
              9 kW solar, 42kWh LFP storage. EV owner since 2012

              Comment

              • JSchnee21
                Solar Fanatic
                • May 2017
                • 522

                #37
                My array faces 175 degrees (almost due South -- very good) but my pitch is only 20 degrees (not good). Ideally it would be ~33.5 degrees. I haven't measured it, but the gap between my panels and the roof is also fairly small, probably 4 inches or so.

                See this website:
                www.solarpaneltilt.com/

                Additionally I have shade on both sides of my house and across the street. And because I live in a raised ranch, my array is very wide and not very tall. As a result, I see a significant impact as the sun moves across the sky. Array is ~ 4 panels high (landscape) and 10 panels wide. Solar production is only optimal under full sun conditions when the angle of incidence is nearly orthogonal to the plane of panel.

                GPE didn't do a lot of production estimates for me. I did most of them myself. My original GPE proposal was for a 12.775kW array with an estimated annual production of 15.3MWh. But this array size didn't fit on my roof. From my estimates of the array which ended up fitting (12.21kW 37x330W). I forecasted ~12 to 14 MWh. But, I know now that I failed to accurately estimate the how much shading I had, and how severely it would impact my production. I ended up with just under 12 MWh (11.8) last year.

                If you look at the efficiency of arrays near you in NJ, you can get a rough impact of weather conditions in your local area and compare "efficiencies" of similar systems
                pvoutput.org/ladder.jsp

                E.g KWh (produced) per kW (DC):
                Name Location Size Generation Efficiency Average Outputs Last Seen

                For MacAddict
                Mario' System - Sunnyside NJ United States 08833 8.960kW 19.251MWh 3.499kWh/kW 31.353kWh 614 days Today

                For Me
                Panasonic12kW_SolarEdge_GPE United States 08831 12.210kW 18.294MWh 2.477kWh/kW 30.239kWh 605 days Today

                As you can see the productivity of MacAddict's system is much better than mine mainly due to the differences in our designs. I think MacAddict also gets more sun than I do (less clouds).

                But a word of caution, no two installations are ever really the same. The efficiency parameter is an all encompassing comparator which is influenced by all system variable (equipment quality, installer quality, orientation, pitch, shade, age, soling, differences in micro-climate, etc.).

                -Jonathan
                Last edited by JSchnee21; 02-19-2019, 11:52 AM.

                Comment

                • hiya
                  Junior Member
                  • Feb 2019
                  • 5

                  #38
                  I hate to interrupt this thread but not sure what else to do. I am a new member and for some reason cant start a new thread, i can only reply to a thread. Sorry for butting in to this conversation.

                  Comment

                  • flowing
                    Member
                    • Feb 2019
                    • 40

                    #39
                    J.P.M.

                    They estimate 20,670 kWh a year.
                    I'm on 07059
                    Thanks for the link to PV Watts this is what they estimated: 22,944 kWh/Year*

                    I'm unsure of the angles. Once they do the survey I should have a better idea.

                    Thanks again for all the help.

                    Comment

                    • flowing
                      Member
                      • Feb 2019
                      • 40

                      #40
                      JSchnee21 You can see I'm definitely not oriented the best for solar. Its hard to tell from this image. There's a 6' roof that runs on the side on the home that I'm hoping to fit 7 panels along with that roof next to the driveway.


                      Capture.JPG

                      Comment

                      • J.P.M.
                        Solar Fanatic
                        • Aug 2013
                        • 14926

                        #41
                        Originally posted by flowing
                        J.P.M.

                        They estimate 20,670 kWh a year.
                        I'm on 07059
                        Thanks for the link to PV Watts this is what they estimated: 22,944 kWh/Year*

                        I'm unsure of the angles. Once they do the survey I should have a better idea.

                        Thanks again for all the help.
                        You're welcome. Two points:

                        1.) PVWatts is not an estimator of annual performance. It's a design tool whose output is representative of a long term average output. It's no better than the inputs used (GIGO). Any actual year is most likely to be no better than +/- 10 % of the model's output, mostly due to weather variation. Folks think that if they have a month or a year that's very different from PVWatts, they either got screwed or made out like a bandit.

                        2.) Note 20,670/22,944 = 0.901. Looks about like that 10 % I wrote about in my last post, huh ? maybe just coincidence.

                        Peddlers who (mis)use PVWatts or other models to provide "estimates" routinely manipulate the input or simply lie about the output to underestimate the output of the system they're peddling by about 10% or more. A couple of reasons:

                        - To give some false but authoritative looking backup for their low performance performance estimates. That makes their estimate more believable and makes it easier to sell larger a larger system than needed.

                        - Keep in mind that no peddler ever got fired for selling the customer more than was needed, especially if the customer is clueless and will only think that the system is outperforming the estimate by 10 % or so which is what it can look like to the solar ignorant buyer. Bigger system with more profit and a happy customer who thinks their system is doing 10 % better than expected. Win/win - for the peddler ( the customer just got screwed and lied to).

                        One trick of many.

                        Just sayin'

                        Comment

                        • Ampster
                          Solar Fanatic
                          • Jun 2017
                          • 3650

                          #42
                          I reread this thread and it looks like you may be evolving to a roof mount system. If I understand your site your main roof surfaces may face south west and north east. I also understand that you have two EVs.

                          If your goal is to generate as much power as possible, or at least up to your consumption of 2,000 Watts per day then you may want to look at what bcroe did with multiple orientations. That could include roof mount and ground (carport or pergola). While others my suggest you would want to optimize panel productivity only, my opinion is that you may want to optimize site productivity. That may mean a higher DC to AC ratio overall. With proper design of strings that high ratio may not have to penalize you with any mid day clipping. Essentially you might be able to capture more morning and afternoon light without losing the best mid day light.

                          Bruce had the advantage of doing some of his install himself and with a ground mount that may be easier to adjust during the build. The key will be your site survey and how innovative the designer is. Of course if you do get an innovative design that looks too aggressive you may want to ask for a production guarantee.
                          Last edited by Ampster; 02-19-2019, 11:17 PM.
                          9 kW solar, 42kWh LFP storage. EV owner since 2012

                          Comment

                          • JSchnee21
                            Solar Fanatic
                            • May 2017
                            • 522

                            #43
                            Hi flowing

                            Based on your image above, am I correct to assume that North is up? So you essentially have three possible faces. ENE (which you would prefer not to use), WSW (preferred face), and SSE (possible/preferred face). Is that correct?

                            It's always hard to judge scale in these satellite images, but I'm doubtful you will fit ~40 panels using just the WSW and SSE faces, Additionally, production from the WSW face will not be very good. I'm having some doubts about a 20 MWh estimate given a mostly WSW array.

                            I know you would rather not, but using all 3 faces would be ideal. Not quite a good as all facing South, but having a large East and West contingent would enable you to capture a lot of sun in the morning and afternoon. and the SSE would be a nice bonus. Given the different orientations, using two 7600H inverters would likely be fine, even with 18kW to 20kW of panels (per SE's requirements) as production is spread out throughout the day.

                            Shade may also be an issue. You seem to have a lot of trees (as do I). They can cast surprising long shadows 9 months of the year, and, they grow

                            Comment

                            • flowing
                              Member
                              • Feb 2019
                              • 40

                              #44
                              JSchnee21

                              Yeah North is up.

                              I would be placing panels on the "red" squiggly lines. I definitely will not be placing them on the east/front of the home. I too doubt the amount of panels they think they can fit on my roof. Lets see when they do the survey.

                              The trees dont cast shadows on my home. The angle of that shot is weird. The trees to the left are very far from the home. The willow at the bottom of the screen is gone due to lasts years storms.

                              What is this "clipping" I heard you mention.

                              Thanks again!

                              Comment

                              • Ampster
                                Solar Fanatic
                                • Jun 2017
                                • 3650

                                #45
                                Is it a two story house? I am asking because there is a great opportunity for a lot of south facing panels above the cars parked in the driveway. I know that has probably been ruled out earlier and maybe you keep it for future expansion.
                                9 kW solar, 42kWh LFP storage. EV owner since 2012

                                Comment

                                Working...