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facing PV arrays: East/West, North or South

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  • #31
    Originally posted by ButchDeal View Post

    That is in Australia so it would be for you E/W vs S
    Bcroe has already given you the benefits of E/W which would be more for an off grid system or one with some limitation. Your PoCo doesn't have a limitation so you are better off with south.
    thanks. duh, aussies, south of the equator.

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    • #32
      Originally posted by SunEagle View Post

      Based on an earlier post you mentioned "florida/florida" so should I presume you are in Florida and it is one of their POCO's you are talking about?

      Based on FPL solar net metering process they indicate a max of 115% of the AC kWh used in a year. Once you have determined your average AC kWh yearly usage you multiply that by 115%. Now divide that number by 0.85 to get the max DC wattage of the system.
      let me clarify what the poco rep said: take the annual kwhac; multiply it by 1.15 (i had a typo in the post); divide by 1135 and this yields the 'allowable system scaling'. so, this results in (8269 * 1.15) / 1135 = 7.1kwdc. i can't believe this is the correct scaling value?

      if i took the (8269 * 1.15) * .85 = 8082 or 8.1kwdc, which is a better number than 7.1kwdc.

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      • #33
        Originally posted by Jest Waitn View Post

        let me clarify what the poco rep said: take the annual kwhac; multiply it by 1.15 (i had a typo in the post); divide by 1135 and this yields the 'allowable system scaling'. so, this results in (8269 * 1.15) / 1135 = 7.1kwdc. i can't believe this is the correct scaling value?

        if i took the (8269 * 1.15) * .85 = 8082 or 8.1kwdc, which is a better number than 7.1kwdc.
        So, that's the max. allowable array size. Any thoughts as to what might be the most cost effective size ? Given your rates, a smaller system might be more long term cost effective. No one's got a gun to your head saying you must max. out to some allowable size and no less.

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        • #34
          Originally posted by J.P.M. View Post

          So, that's the max. allowable array size. Any thoughts as to what might be the most cost effective size ? Given your rates, a smaller system might be more long term cost effective. No one's got a gun to your head saying you must max. out to some allowable size and no less.
          i want to max it out & i already have the inverters and most of the panels. one panel was damaged when assembling the first array, so 1 or 2 more need to be purchased.

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          • #35
            Originally posted by Jest Waitn View Post

            what i said is the following: "a method is actually used, that's not a %, but that arrives at a %. florida/florida power. the calculation used was based on 8269 kwhac. so the result is 7.1 kwdc = (85.9% * 8269). but for this to be 'true' it has to be stated and i can't find it, so i have asked to see this in print.

            the method is to take annual kwh, multiply it by 115 and then divide the result by 1135. which yields 7.1kwdc for the maximum array. the present array size is 3460wdc.
            "

            i live in florida and florida power is the poco. the rep said to multiply annual usage by 115 and divide the result by 1135. these are stated in the post.

            btw, dividing the result by .85 would result in an enormous number!

            anyway, where have you found max 115% stated by florida power?
            Ok maybe I explained it poorly.

            FPL states your solar pv system can't generate more than 115% of your yearly kWh AC usage. It then says that your gross power output of your AC system can be calculated by multiplying the DC wattage by 0.85.

            Here is the link to the Net Metering Guidelines for FPL.

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            • #36
              Originally posted by SunEagle View Post

              Ok maybe I explained it poorly.

              FPL states your solar pv system can't generate more than 115% of your yearly kWh AC usage. It then says that your gross power output of your AC system can be calculated by multiplying the DC wattage by 0.85.

              Here is the link to the Net Metering Guidelines for FPL.
              ok, thanks.

              this is what i have found. i sent an e-mail last friday to the rep asking for documentation substantiating the method he used to calculate 'scaling'. he is on vacation until next week.

              the 115% is not a statement from florida power, it is from the PSC and is in the FAC, state statutes. so florida power has to abide by the FAC; it has no choice.

              http://www.psc.state.fl.us/Files/PDF...nd%20Light.pdf

              https://www.flrules.org/gateway/RuleNo.asp?ID=25-6.065

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              • #37
                Originally posted by SunEagle View Post

                Ok maybe I explained it poorly.

                FPL states your solar pv system can't generate more than 115% of your yearly kWh AC usage. It then says that your gross power output of your AC system can be calculated by multiplying the DC wattage by 0.85.

                Here is the link to the Net Metering Guidelines for FPL.
                thanks. the rep i spoke with last week is now on vacation, so he will contact me next week. it is unclear why he doesn't know this; it's his job.

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                • #38
                  So here in the UK we get 6.5p per generated kWh.
                  But our grid power costs are 10-20p per kWh.
                  This means if I use 1 kWh thats worth not generating up 4kWh that i send back to the grid.
                  taking 56% used from southern panels vs 75% west stats i seen from a study in Austin. TX:-

                  100kWh from south produces 56kWh of usable power(the other 46kWh goes back into the grid)
                  that same array facing west would produce 90kWh but 68kWh is usable. cost wise thats equivalent to producing an extra 46% more power.

                  With West facing panels aligning with afternoon/evening usage It could be worth a lot more than south.

                  Of course austin would produce more in total, more in the winter. and distrubuted over less hours per day in summer than the UK. So im looking for some stats for UK installations to see how S vs W works out.
                  My hunch is West facing panels are even better in the UK than Austin.

                  Comment


                  • #39
                    Originally posted by Marli View Post
                    So here in the UK we get 6.5p per generated kWh.
                    But our grid power costs are 10-20p per kWh.
                    This means if I use 1 kWh thats worth not generating up 4kWh that i send back to the grid.
                    taking 56% used from southern panels vs 75% west stats i seen from a study in Austin. TX:-

                    100kWh from south produces 56kWh of usable power(the other 46kWh goes back into the grid)
                    that same array facing west would produce 90kWh but 68kWh is usable. cost wise thats equivalent to producing an extra 46% more power.

                    With West facing panels aligning with afternoon/evening usage It could be worth a lot more than south.

                    Of course austin would produce more in total, more in the winter. and distrubuted over less hours per day in summer than the UK. So im looking for some stats for UK installations to see how S vs W works out.
                    My hunch is West facing panels are even better in the UK than Austin.
                    According to PVWatts for Austin, TX, USA:

                    South facing, 20 deg. tilt, TMY2 data, annual production = 1,533 kWh per installed STC. kW.
                    West facing, 20 deg. tilt, TMY2 data, annual production = 1,385 kWh per installed STC kW.

                    Tariffs and use patterns will influence the cost effectiveness of an array's orientation, or, if possible, an array can be oriented for the highest probability of maximum annual electric bill offset as
                    f(tariff, solar temporal patterns, shading). But make no mistake, all other things being equal, equator facing arrays will usually and almost always produce more electricity per installed STC Watt than west facing arrays, or any other orientation for that matter.

                    The information cited in the above post looks to be a bit deceptive to the uninformed.

                    The trick is to first and foremost, use less electricity. Then, be aware of the tariff in place and how it works. Third, use the knowledge of the tariff to game the system by adjusting use patterns and then, using that knowledge of the tariff and reduced/time altered use patterns, size (and optimally orient if possible) an array that provides a LOCE (Levelized Cost of Energy) <= other or the current LOCE.

                    FWIW, PVWatts has several UK data.

                    Comment


                    • #40
                      Originally posted by Marli View Post
                      100kWh from south produces 56kWh of usable power(the other 46kWh goes
                      back into the grid) that same array facing west would produce 90kWh but 68kWh is usable. cost wise
                      thats equivalent to producing an extra 46% more power.

                      With West facing panels aligning with afternoon/evening usage It could be worth a lot more than south.

                      Of course austin would produce more in total, more in the winter. and distrubuted over less hours per
                      day in summer than the UK. So im looking for some stats for UK installations to see how S vs W works
                      out.My hunch is West facing panels are even better in the UK than Austin.
                      No doubt S facing panels could produce the most KWH per day (north of the equator). But the real
                      world is more complex than that. People charging batteries may prefer a longer production day. Size
                      of existing equipment, distance power must be sent, hourly tariffs, line voltage, and stock on hand
                      all matter and influence in the real world. Timing of clouds. Each app needs to evaluate overall.

                      Conservation always works. Spent decades on that here, more recently
                      to the extreme of redesigning much of the electrical equipment. Bruce Roe

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                      • #41
                        FWIW, PVWatts has several UK data.
                        Thanks just pulled the HOURLY data.

                        TMI!!!!!!!!!!!!!

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