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East+West roof may now be "better" than southern exposure ?

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  • East+West roof may now be "better" than southern exposure ?

    I have a house with an east/west facing roof. PVWatts predicted 20% less production due to facing east (versus south). I had an 8.4kw array installed on the east roof, and it is working decently, considering the orientation (18.1 mW-hrs over 36 months in Minnesota, or 6 mW-hrs/year). When I had the array installed, I was wishing I'd bought a house with a south-facing roof.

    I started driving an electric car, so my power use went up by about 3 mW-hrs last year (but my gasoline bill went down $100/month). Now I'm looking at the west roof of my house, and realizing that I could install a second array, and it would pay for itself. Despite the penalty for not facing south, I could produce 60% more power than if I had a north-south facing roof.

    Obviously, the payoff for east/west is slower than south-facing, but if it means that you can produce 60% more, then having an east-west roof could be an asset, and not a liability. It depends on your needs and priorities. (for example, in my case, east/west facing payoff is still faster than a solar garden membership).

  • #2
    An East / West array will always be much better then any array with North facing panels (if you live above the Equator).

    The % difference between which way the panels face is dependent on not only the Sun's path but also the type of weather you get in the morning or afternoon.

    Clouds and Fog will reduce the % production even if they face South.

    Comment


    • #3
      Be careful. If you have super off peak rates available (say from 0000 hrs. until 0500 hrs. for example) and you charge an EV between those times, and at what may be very low rates, adding PV for the purpose of offsetting what might be a very low cost to fuel an EV may not be cost effective.

      As an example only, @ $0.05/kWh for an examp[le super off peak rate, and at 3 miles/kWh for EV mileage and 12,000 miles/yr., ~ $200/yr. "fuel cost". Back of envelope: 6,000 kWh/yr./8 kW array ~ 750 kWh/yr./STC kW --->>> 4,000/750 = 5.33 STC kW array will be needed for saving $200/yr. At, say, $3.00*.7/installed STC W ~ $11,200 for a 5.33 STC kW array that will offset $200 in EV "fuel cost"/yr. 11,200/200 ~17.9 yrs. using the moron payback method.

      Moral of the story: Check what you'll be paying to charge the EV.

      Comment


      • #4
        Originally posted by J.P.M. View Post
        Be careful. If you have super off peak rates available (say from 0000 hrs. until 0500 hrs. for example) and you charge an EV between those times, and at what may be very low rates, adding PV for the purpose of offsetting what might be a very low cost to fuel an EV may not be cost effective.

        As an example only, @ $0.05/kWh for an examp[le super off peak rate, and at 3 miles/kWh for EV mileage and 12,000 miles/yr., ~ $200/yr. "fuel cost". Back of envelope: 6,000 kWh/yr./8 kW array ~ 750 kWh/yr./STC kW --->>> 4,000/750 = 5.33 STC kW array will be needed for saving $200/yr. At, say, $3.00*.7/installed STC W ~ $11,200 for a 5.33 STC kW array that will offset $200 in EV "fuel cost"/yr. 11,200/200 ~17.9 yrs. using the moron payback method.

        Moral of the story: Check what you'll be paying to charge the EV.
        Too bad the sun doesn't shine at night when you can charge an EV from solar at your home.

        Comment


        • #5
          Originally posted by SunEagle View Post

          Too bad the sun doesn't shine at night when you can charge an EV from solar at your home.
          Yea, but the Almighty compensated for that by giving some of humanity a fairly reliable and infinite storage facility called the grid.

          Comment


          • #6
            Originally posted by specialgreen View Post
            I have a house with an east/west facing roof. PVWatts predicted 20% less production due to facing east (versus south). I had an 8.4kw array installed on the east roof, and it is working decently, considering the orientation (18.1 mW-hrs over 36 months in Minnesota, or 6 mW-hrs/year).

            I started driving an electric car, so my power use went up by about 3 mW-hrs last year (but my gasoline bill went down $100/month). Now I'm looking at the west roof of my house, and realizing that I could install a second array, and it would pay for itself. Despite the penalty for not facing south, I could produce 60% more power than if I had a north-south facing roof.

            Obviously, the payoff for east/west is slower than south-facing, but if it means that you can produce 60% more, then having an east-west roof could be an asset, and not a liability. It depends on your needs and priorities. (for example, in my case, east/west facing payoff is still faster than a solar garden membership).
            I don't know the configuration, AC and DC ratings of your system. But with a string system, a string or 2
            on the west side could be tied directly in parallel (with fuses) to the existing inverter. That, because the 2
            sides will peak at different times, and avoid clipping by the inverter. How many can be added in parallel
            depends on peak separation, controlled by the angle towards E and W (probably limited by the roof).
            Bruce Roe
            Last edited by bcroe; 11-11-2018, 04:28 PM.

            Comment


            • #7
              E/W let's you cram more daily kwh production into a smaller inverter too, keeping it running near peak longer. Less of a curve and more of a wide plateau. It's a valid strategy when the needs call for it.

              Comment


              • #8
                Originally posted by ImInPhxAZ View Post
                E/W let's you cram more daily kwh production into a smaller inverter too, keeping it running near peak longer. Less of a curve and more of a wide plateau. It's a valid strategy when the needs call for it.
                It's also a waste of money if it's unnecessary. In any event, for most every application, an E-W split will result in a more costly system than a more southerly orientation and a longer ROI. Smaller inverters do not save as much as smaller, more southerly arrays will save in initial costs.

                Comment


                • #9
                  I have recently modified my panels from south facing to east west and I am at present very pleased with the results.
                  I started with a very small setup 4 years ago and progressively increased. After buying an MPPT charge controller of 40amps ( biggest i could find with limited budget) and increasing panel wattage to 600 I had no problems to keep 1,000 amps batterie bank fully charged all summer and well into the fall. Winter is obviously a different matter. By increasing my panels to 1,000 watts with 300 east 400 south and 300 west I have considerably increased the length of time that I have maximum power for the charge controller. It took a while to find optimum angles to keep production just under the 40amps. For my set up I find that 400 watts of panels is cheaper and more effective than buying and running a tracker. The ambient light of 1,000 is more than the ambient light of 600 when there is no or limited sun which is the only time that I worry for the health of my batterys.
                  Early days yet, and I'm sure I will be playing with number of panels and angles through the different seasons before I can find the correct set up for all year round or two angle changes a year.
                  If I'm not happy with end result I'll just upgrade controller I'll allready have the panels. Only time will tell but at present I find it very promoising.
                  James

                  Comment


                  • #10
                    There are a few reasons that an array might be set up as east-west. As James says it can lengthen
                    hours available to charge batteries. It can eliminate the problems of a tracker, by matching its output
                    under best sun, and out performing it under clouds. It could be the lack of a south facing mounting.
                    It could be about squeezing more energy through a limited AC facility.

                    Here, it is about clouds. Very poor output under clouds can be boosted by adding a lot of panels. At
                    this moment we are overcast, no clear shadows. Despite that, my reserve meter shows enough
                    energy is being collected to just balance the energy being consumed by heating the house in 30
                    degree F weather. Then the issue becomes what should be done with panel orientation when the
                    sun is good. Spreading the peak power over much of the day gathers more energy while minimizing
                    mid day clipping. Here are some curves from Sun Danzer and my yard. Bruce Roe

                    SunDazer10Oct17.png

                    NScurJn17.jpgPVm17Jn16.jpg

                    Comment


                    • #11
                      Bruce,
                      Your first graph is very representative of my set up. the other two clearly show the huge differences in our set ups. I should image that the principal stays the same regardless of the scale. I do have two questions that maybe you can clarify.
                      I think that the angles that you have stipulated 61 / 30 / 61 are the vertical inclination,could you give me an idea of the rough angle of east and west? As in how much they are turned from south torwards the east and west. Do you need to move them in the course of the year or have you found an optimal setup for all year round.
                      I cheated there, that was actually two questions.
                      My second question, what you call "mid day clipping" if I understand correctly is when my panels are producing more electricity than my controller will allow into the battery therefore 40amps at 12 to 14.8 V depending on batterie charge status. Is mid day clipping something that should be avoided to reduce premature wear of controller or should I not worry at all about it all the time I stay well within the 1.5 x rated charge current /power?
                      James

                      Comment


                      • #12
                        Originally posted by J.P.M. View Post
                        It's also a waste of money if it's unnecessary. In any event, for most every application, an E-W split will result in a more costly system than a more southerly orientation and a longer ROI. Smaller inverters do not save as much as smaller, more southerly arrays will save in initial costs.
                        I don't think that's true.
                        Assuming you're targeting a specific amount of kwh, I think an EW array can sometimes be more cost effective than a straight south array that produces the same kwh.
                        I would agree if you said south is *usually* more cost effective - especially if you have to pay labor for installation of modules.

                        A 5kW S pointing system gives 8,316 kwH/year for my location (Northern CA, 4/12 roof, 10% system losses)
                        An EW system would need to be 14% more DC watts to give equivalent kwh.
                        The EW system *might* save you $200 by being able to use smaller inverter. But it'd require 14% more in modules - assuming ~$0.54/W for modules, that's $2700 vs. $3038.
                        So still ~$138 more for an EW system producing same kwh.


                        So....
                        after doing the calculations on what I thought would be a counterexample, I have changed my mind and have to agree with you.
                        The exception would be where there's a bigger cost for a larger inverter (like having to upgrade the panel because of the larger inverter)

                        Comment


                        • #13
                          I think that J.P.M is absolutely right when being connected to the grid. It's only when offgrid that there is an advantage. By increasing the length of the day for the charger you are decreasing the length of the night. The battery is being correctly charged earlier and later as with an expensive tracker. The increased number of panels is a considerable advantage when cloudy as shown by bruce. All of the advantages are only valid for bad weather conditions. Everybody with an offgrid system is only interested in the crappy weather conditions. In the middle of the summer the majority of sites are on float mode well before solar noon ( if it's not the case you have little hope of making it through the winter). For grid connections the bottom end of production is negligable when you consider annuel production, for off grid the bottom end of production is what decides how many years your battery pack will last.and for many people if they can play on the computer or not. I would very much like to hear other peoples thoughts and experiences with east west setups when offgrid. James

                          Comment


                          • #14
                            Originally posted by Robinhood-46 View Post
                            Bruce,
                            Your first graph is very representative of my set up. the other two clearly show the huge differences in our
                            set ups. I should image that the principal stays the same regardless of the scale. I do have two questions
                            that maybe you can clarify.
                            I think that the angles that you have stipulated 61 / 30 / 61 are the vertical inclination,could you give me an
                            idea of the rough angle of east and west? As in how much they are turned from south torwards the east
                            and west. Do you need to move them in the course of the year or have you found an optimal setup for all
                            year round. I cheated there, that was actually two questions.
                            My second question, what you call "mid day clipping" if I understand correctly is when my panels are
                            producing more electricity than my controller will allow into the battery therefore 40amps at 12 to 14.8 V
                            depending on batterie charge status. Is mid day clipping something that should be avoided to reduce
                            premature wear of controller or should I not worry at all about it all the time I stay well within the 1.5 x
                            rated charge current /power? James
                            I am doing net metering, so some things will not directly compare to an off grid.

                            Here is the arrangement of 3 panels used for measurements a couple years ago. Each single
                            panel was oriented directly east, south, or west, with means to read power output.


                            Test3dir.jpg

                            The angle listed is tilt up from flat on the ground. The facing direction is straight east, south,
                            or west. That brings up the question if the E/W should somewhat favor the rising/setting
                            sun, south in the winter, or north in the summer. After looking at my Solar Pathfinder chart,
                            I decided to leave them straight. For off grid you might want to favor sun in the south, to
                            get the most at poor winter time. For net metering, I might favor north, for when the most
                            summer energy may be collected. However, If the panels put me into clipping,
                            I would go more south. That is where I am, centered.

                            Several tilt angles were tried, and from June through Dec. The objective was to create the
                            flattest day long output, then bring up panel count to put the inverters at maximum. A couple
                            other tilt curves here.

                            PVm16Jn16.jpg

                            PV23Aug.jpg
                            PVm13Jn16.jpg



                            I expect your equipment indicates a maximum input level, mine does. However I regard
                            that as the level of the composite peak, not the actual equipage which can never all
                            approach rating at the same time. Not much written on this, be careful. Bruce Roe
                            Last edited by bcroe; 11-13-2018, 04:31 PM.

                            Comment


                            • #15
                              Originally posted by Robinhood-46 View Post
                              I think that J.P.M is absolutely right when being connected to the grid. It's only when offgrid that there is an advantage. By increasing the length of the day for the charger you are decreasing the length of the night. The battery is being correctly charged earlier and later as with an expensive tracker. The increased number of panels is a considerable advantage when cloudy as shown by bruce. James
                              Its more complicated than that, and each situation needs individual evaluation. In my case a 600 foot
                              loop of 4 gauge AC wire was already buried out to the inverters, and I didn't want to re bury a lot heavier.
                              That wire causes me a just tolerable 3% loss even at my high line voltage, and some 9V of rise at the
                              inverters, close to tripping out. Besides the physical plant, my contract limits me to 15 KW. So to get
                              any more energy a higher peak is not doable, it must be spread over the day. And of course so much
                              energy is being used to heat the house, something not generally recommended here. It all is needed.
                              Bruce Roe

                              Comment

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