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  • adding panels: two separate inverters or one new big inverter

    Hi,

    I have an existing PV system of 15 Canadian Solar 260 panels together with SolarEdge P300 Inverters and a Solaredge 3800 inverter. I want to add 11 Sunpower E19 320 watt panels with Solaredge P400 optimizers. I could do that buy adding a separate inverter the smallest 3KW Solaredge inverter or buy buying one big new inverter, maybe the 6 kw one or 7.8 KW one and run all panels on one inverter. The new system will get significant shading for some panels at all time of the day, since the panels are oriented south, west, east and two north. So I thought all on one might be better, because it would make it easier to reach the minimum voltage for the inverter to kick in. Does it matter which way I go? Two separate inverters or one unified one? There would be only two strings altogether: one from the existing system and one from the new system . Thanks for any suggestions ! Matthias

  • #2
    Using Sunpower panels is almost never cost effective. Putting them in partial shade just makes them less cost effective than they already are.

    Are you writing that the new 11 panel array will face south with significant shading, or all 26 panels will be all over the place, or what ?

    Every application is a bit different from others, and it's your property/money/choice, but it sounds like you're somewhat unfamiliar with PV. What are your goals in adding to the existing array ?

    Comment


    • #3
      Thanks for the reply. Yes, sunpower is typically expensive, but thanks to a group purchase agreement, they are actually no more expensive than others I have gotten quotes for. I cannot give a price here, but I can say that the quote is very competitive. The existing 15 panels are largely south facing. The additional 11 other panels will be put on the garage. 3 south, 3 east, 3 west, 2 north on a hipped roof of the detached garage. I understand that north facing panels produce probably only about 50 percent of south facing panels, but keep in mind that in my area ( washington dc), the solar energy renewable credits (SRECs) sell for about $400 per MWh, so the payback is via SRECs, not save electric bill. My question is merely as to whether to go with one inverter vs 2 . Maybe it makes little difference? You asked for my goals: produce electricity at a relatively low level of CO2 emissions compared to my local grid ( which is 50% coal).
      Last edited by matrose; 04-26-2018, 11:37 AM.

      Comment


      • #4
        Originally posted by matrose View Post
        Thanks for the reply. Yes, sunpower is typically expensive, but thanks to a group purchase agreement, they are actually no more expensive than others I have gotten quotes for. I cannot give a price here, but I can say that the quote is very competitive. The existing 15 panels are largely south facing. The additional 11 other panels will be put on the garage. 3 south, 3 east, 3 west, 2 north on a hipped roof of the detached garage. I understand that north facing panels produce probably only about 50 percent of south facing panels, but keep in mind that in my area ( washington dc), the solar energy renewable credits (SRECs) sell for about $400 per MWh, so the payback is via SRECs, not save electric bill. My question is merely as to whether to go with one inverter vs 2 . Maybe it makes little difference? You asked for my goals: produce electricity at a relatively low level of CO2 emissions compared to my local grid ( which is 50% coal).
        Why can't you give a price here ? Most everyone else does.

        If you did not have access to a SREC market, would you have the PV at all ?

        The whole idea of mixing panels, multiple orientations, partial shading and uncertainty about inverter arrangements all sounds a bit disjointed to me, but I'm only one opinion.

        As for group pricing, everything is negotiable. I'd see what other vendors might be able to do.

        Comment


        • #5
          Members of the group are not allowed to post price. I think the idea is that no one wants the winning bid to become public knowledge so that there is no collusion by bidders in future rounds of other group purchases. Whether this makes sense ( I doubt it) is another question, but I joined the group under those terms and will stick to it. But I can say that the quote I got was almost a full dollar per watt installed below what I got as a lonely individual customer from sunpower installer when they tried to sell me there premium product individually earlier in the yeaer. As I said, I have gotten quotes from many other vendors and they were not any cheaper. As for the question at hand, other than pointing out that is dis-jointed, could you point me to any references on the issue I am asking about or clarify what information I am lacking to provide to maybe give a better answer? Recall, I have optimizers so the partial shade is less of an issue for the system as a whole ... The production estimate overalll suggest only a 20 percent drop relative to best orientation for all panels .... Thanks for your time !

          Comment


          • #6
            Originally posted by matrose View Post
            Members of the group are not allowed to post price. I think the idea is that no one wants the winning bid to become public knowledge so that there is no collusion by bidders in future rounds of other group purchases. Whether this makes sense ( I doubt it) is another question, but I joined the group under those terms and will stick to it. But I can say that the quote I got was almost a full dollar per watt installed below what I got as a lonely individual customer from sunpower installer when they tried to sell me there premium product individually earlier in the yeaer. As I said, I have gotten quotes from many other vendors and they were not any cheaper. As for the question at hand, other than pointing out that is dis-jointed, could you point me to any references on the issue I am asking about or clarify what information I am lacking to provide to maybe give a better answer? Recall, I have optimizers so the partial shade is less of an issue for the system as a whole ... The production estimate overalll suggest only a 20 percent drop relative to best orientation for all panels .... Thanks for your time !
            I'm with you in that the secrecy you describe makes no sense - sounds like a B.S. reason to me.

            FWIW, As a lonely, individual customer, I got about a buck lower than the average bear/STC Watt in my system pricing, and lower than any other price for a Sunpower system in CA at that time by knowing what others were paying - see CSI reservation # SD-CSI-17646 and check other sunpower systems sold before/around the same time for comparison prices - (thanks to the CSI database that's full of information that vendors don't want customers to know - like what everyone pays for a system, and other reliable sources of info), and some sharp negotiating. I did nothing anyone else couldn't do, and I did it with several vendors of different panels and inverters. Everything is negotiable.

            As for pointing out where to go for information, I don't know where to start. Maybe if you mentioned your goals for having PV in the first place and what you want to accomplish by increasing output in what sounds (to me anyway) like less than cost effective ways, I'd have some opinions. Basically, without knowing more about the application, and no disrespect meant, but it sounds, to me only, like you're running pell mell away from high energy bills more than you're searching for a cost effective way to use less electricity.

            Take what you want of the above. Scrap the rest.

            Comment


            • #7
              Nice Wash. D.C. solution.
              Game the SREC system with unproductive north facing panels to get the savings from artificial credits instead of real savings from producing clean, renewable power from the sun.... And make sure you don't violate any terms of your interconnect agreement with your Utility by adding on or modifying your existing solar system.
              BSEE, R11, NABCEP, Chevy BoltEV, >3000kW installed

              Comment


              • #8
                Originally posted by matrose View Post
                Thanks for the reply. Yes, sunpower is typically expensive, but thanks to a group purchase agreement, they are actually no more expensive than others I have gotten quotes for. I cannot give a price here, but I can say that the quote is very competitive. The existing 15 panels are largely south facing. The additional 11 other panels will be put on the garage. 3 south, 3 east, 3 west, 2 north on a hipped roof of the detached garage. I understand that north facing panels produce probably only about 50 percent of south facing panels, but keep in mind that in my area ( washington dc), the solar energy renewable credits (SRECs) sell for about $400 per MWh, so the payback is via SRECs, not save electric bill. My question is merely as to whether to go with one inverter vs 2 . Maybe it makes little difference? You asked for my goals: produce electricity at a relatively low level of CO2 emissions compared to my local grid ( which is 50% coal).
                A single inverter would be best. I would if I were you move the older canadian solar 260W modules to the other roofs and use the new sunpower on the prime locations. Even better sell the Candian solar 260W modules or give them away and install all sunpower modules.

                I think like others that your reason is BS on the price of the modules would do a single inverter of the SE7600H or SE6000H

                Note that the P300 are optimizers not inverters.
                OutBack FP1 w/ CS6P-250P http://bit.ly/1Sg5VNH

                Comment


                • #9
                  Thanks for all the responses. First of all, I will not game any system. I will apply for addition to the interconnetion agreement, getting the utility to agree to the additional panels. Second, no gaming on the SRECS either. My two north facing panels (out of a total of 27 after adding to the existing system) will get SRECS credits only for actual production, not for the nominal installed wattage. Butch Deal, I appreciate you answering my question directly and that a single inverter would be best (with best meaning it would have the best bottom line conversion of solar radiation to actual power. I thought as much, my reasoning was that maybe the single big inverter would " kick in " early in the day when two separate inverters may not have reached the minimum input voltage to start producing. Is that about right or is your reasoning based on a different logic? ( maybe just that one inverter is "cleaner" and less clunky than two units on the wall?). In any case, I appreciate all the input from this forum. Somewhere in the thread someone asked for my goals in installing additional panels. The goal is to produce electricity in a manner that involves less CO2 than the local grid, which has a CO2 content of about 900 grams per KWh produced. Most solar panels produce at about 40 grams per KwH produced ( not nominal, but actual production) once one takes into account production and installation embodied CO2 emissions ...

                  Comment


                  • #10
                    IMHO two or more inverters is always better than one large inverter. Why? Because a problem anywhere in your system is more easily diagnosed.

                    You will develope a relationship between inverters and when a difference is detected in production you can more easily notice and thus focus on the problem.

                    Comment


                    • #11
                      Originally posted by matrose View Post
                      Butch Deal, I appreciate you answering my question directly and that a single inverter would be best (with best meaning it would have the best bottom line conversion of solar radiation to actual power. I thought as much, my reasoning was that maybe the single big inverter would " kick in " early in the day when two separate inverters may not have reached the minimum input voltage to start producing. Is that about right or is your reasoning based on a different logic? ( maybe just that one inverter is "cleaner" and less clunky than two units on the wall?).
                      The single inverter will kick on earlier , stay on later as well as in low light situations like cloudy days, particularly since you will have solar on many different azimuths.
                      on top of that you can upgrade the existing inverter to the new more efficient hdwave model adding more efficiency as well.
                      OutBack FP1 w/ CS6P-250P http://bit.ly/1Sg5VNH

                      Comment


                      • #12
                        Originally posted by ButchDeal

                        This is a highly monitored SolarEdge system. It can be much more easily diagnosed using the monitoring
                        True, but if that one big inverter goes down you're totally down as opposed to only being partially down with a multiple inverter system.

                        Comment


                        • #13
                          Originally posted by ButchDeal

                          So do you only drive cars with two engine, and two transmissions?
                          Have two refrigerators, two water pumps, two heat pumps, two service panels,

                          i have ave to say I have only ever seen one car with two completely independent systems, some guy had shoe horned a front engine trans, drive system in a Corvair and left the original system in the car. Resulted in the strangest (poorest handling ) 4 wheel drive Frankenstein drag car....
                          Klingons have lots of redundant organs, they're hard to kill and they kick ass.

                          Comment


                          • #14
                            Originally posted by ButchDeal

                            So do you only drive cars with two engine, and two transmissions?
                            Have two refrigerators, two water pumps, two heat pumps, two service panels,

                            i have to say I have only ever seen one car with two completely independent systems, some guy had shoe horned a front engine trans, drive system in a Corvair and left the original system in the car. Resulted in the strangest (poorest handling ) 14 cylinder, 4 wheel drive Frankenstein drag car....
                            Butch, its funny that you say that......I have redundant systems all over the place.....

                            Two furnaces with two humidifier systems and four heat systems
                            Two propane tanks
                            Two AC units
                            Two water wells with two pumps with two water purification systems
                            Two solar arrays with two inverters
                            Two trucks and two automobiles
                            Two generators
                            Two service panels
                            Two workshops (his and hers)
                            Two dishwashers
                            Two refrigerators and two freezers
                            Two washing machings
                            Two water heater systems
                            Two broadband data systems
                            Two banking systems
                            Two investment advisers
                            Two independent computer systems
                            Two lawn mowers
                            Two tractors
                            Two barns
                            Two cats....Two donkeys....but only one dog.



                            Comment


                            • #15
                              Originally posted by DanS26 View Post

                              Butch, its funny that you say that......I have redundant systems all over the place.....

                              Two furnaces with two humidifier systems and four heat systems
                              Two propane tanks
                              Two AC units
                              Two water wells with two pumps with two water purification systems
                              Two solar arrays with two inverters
                              Two trucks and two automobiles
                              Two generators
                              Two service panels
                              Two workshops (his and hers)
                              Two dishwashers
                              Two refrigerators and two freezers
                              Two washing machings
                              Two water heater systems
                              Two broadband data systems
                              Two banking systems
                              Two investment advisers
                              Two independent computer systems
                              Two lawn mowers
                              Two tractors
                              Two barns
                              Two cats....Two donkeys....but only one dog.


                              And sometimes 2X the maint./hassle ?

                              And on the outside of your body, two of everything except for what's in the middle.

                              My bride claims she has 2 buttholes - one of which she says regales SPT all too much.

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