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  • What way to face the panels

    I'm new to this so be gental its my first time so im in the South west UK and ready to fit up my first solar system on my workshop roof What way to face the panels on this then its a shallow pitched tin sheet roof 25 degrees facing East in the sun 13 -14 hours mid summer winter about 5 - 6 hours do I just put them flat on the roof. Or build a frame lift the back up on the panels how much ?. Or spin the lot on the roof round to South and lift the back up how pitch ? but they will still be falling 25 degrees down hill east. Its 4 panels of 120w. help please
    Pug

  • #2
    Pug,
    Welcome. The general rule of thumb is 30 degrees from horizontal and pointing true south. But the good news is that it isn't that critical which way you point. If you're too far east, you get lots of morning sun and less afternoon sun. If you're too far west, you get lots of afternoon sun. Low is good in winter, high in summer, etc.
    That said, if you want to try some angles, this tool is superb:
    https://pvwatts.nrel.gov

    Comment


    • #3
      Originally posted by bob-n View Post
      Pug,
      Low is good in winter, high in summer, etc.
      :
      https://pvwatts.nrel.gov
      Other way around, High in winter, low in Summer.
      2.2kw Suntech mono, Classic 200, NEW Trace SW4024

      Comment


      • #4
        Originally posted by bob-n View Post
        Pug,
        Welcome. The general rule of thumb is 30 degrees from horizontal and pointing true south. But the good news is that it isn't that critical which way you point. If you're too far east, you get lots of morning sun and less afternoon sun. If you're too far west, you get lots of afternoon sun. Low is good in winter, high in summer, etc.
        That said, if you want to try some angles, this tool is superb:
        https://pvwatts.nrel.gov
        The general rule of thumb as I learned it: Without more detailed site information, and to a reasonable first approximation, the highest probability of the greatest irradiance on an array and so the greatest annual solar energy utilization is with a tilt at approximately the latitude of the location and an azimuth of approximately equator facing (south in the northern hemisphere) or maybe 0-15 deg. west of south.

        As Pug notes, the actual orientation penalties for being off such an ideal orientation is actually rather small until those orientations get more than 20 - 30 degrees or so degrees off on azimuth and maybe 10 -15 deg. off on tilt.

        Lots of site or local factors will modify that optimum orientation such as lots of winter clouds, or predominant morning fog for example. If you have solar models available such as PVWatts, such things will be largely accounted for, making the task of finding a good array orientation lot easier. Another factor affecting system output and orientation is any shading from local objects such as trees, buildings or things like roof vents or chimneys.

        If you're near Plymouth or thereabouts:

        Some guesses from PVWatts for long term (probably > 10 yrs. or so) annual average system output :

        Best orientation: Az,: 180, tilt 45 deg., annual output ~ 1,127 kWh/installed STC kW.
        Your orientation: Az, 90 deg, tilt 25 deg., annual output ~ 917 kWh/installed STC kW.

        Output will be less for any orientation if any shading on the array. How much is a guess you'll need to make or do some shade modeling. Small amounts of shading can have a large effect on output - probably causing a much larger production drop than it may appear from the size of the shade produced on the array.

        Use a multiplier of ~ 0.48 for those roughly modeled annual output numbers ( ((4*120)/1000 ) for your stated system size.

        Welcome to the neighborhood.

        Cheers.
        Last edited by J.P.M.; 11-30-2019, 10:59 AM.

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        • #5
          Originally posted by pug View Post
          I'm new to this so be gental its my first time so im in the South west UK and ready to fit up my first solar system on my workshop roof What way to face the panels on this then its a shallow pitched tin sheet roof 25 degrees facing East in the sun 13 -14 hours mid summer winter about 5 - 6 hours do I just put them flat on the roof. Or build a frame lift the back up on the panels how much ?. Or spin the lot on the roof round to South and lift the back up how pitch ? but they will still be falling 25 degrees down hill east. Its 4 panels of 120w. help please
          Pug
          Add to my other post: Do as you wish, but don't fool yourself. Make sure you account for any likely imposed wind loads when you attach the panels to the roof. Solar arrays act like large sails and can impose serious loads on a structure of a type that may well not have been anticipated and so not accounted for when the structure was designed and erected.

          Comment


          • #6
            Thanks for every ones input just for now as its winter and not nice up on the roof I'm going to put them orientation: Az, 90 deg, tilt 25 deg., annual output ~ 917 kWh/installed STC kW. as it will only take a hour ot two on a frame i have made and have a 2nd look at it in mid summer when i can swing them round and redo to Best orientation: Az,: 180, tilt 45 deg., annual output ~ 1,127 kWh/installed STC kW. And test over two clear days each way thanks for everyones help if anyone has anything to add please do its going to be next weekend before i get to it on the roof
            Pug

            Comment


            • #7
              Originally posted by pug View Post
              Thanks for every ones input just for now as its winter and not nice up on the roof I'm going to put them orientation: Az, 90 deg, tilt 25 deg., annual output ~ 917 kWh/installed STC kW. as it will only take a hour ot two on a frame i have made and have a 2nd look at it in mid summer when i can swing them round and redo to Best orientation: Az,: 180, tilt 45 deg., annual output ~ 1,127 kWh/installed STC kW. And test over two clear days each way thanks for everyones help if anyone has anything to add please do its going to be next weekend before i get to it on the roof
              Pug
              The optimum orientation that rule of that thumb is for maximizing annual output of a fixed orientation flat solar array, not for any particular day(s) or time of year.

              Keep in mind that since the sun's orientation with respect to day long clear sky irradiance changes as the sun "moves" from more a more southerly orientation in the winter to more northerly in the summer and then back again to more southerly for winter, while comparing 2 orientations' outputs on consecutive clear days' will give different results of each orientation's day long production, whatever those ratios might be they won't tell you much quantitatively about the likely annual output of either orientation.

              Subject to shading reductions, I'd SWAG the ratio of annual output of one orientation to the other will be something like 917/1127 ~ = 0.81 favoring the 180 deg. az., 45 deg. tilt orientation.

              By way of a brief example of how comparing two clear day's outputs can be less than trustworthy as a means of guessing which one might yield the greatest annual production:
              Comparing the 2 orientation's approx. outputs on clear days around the summer solstice results in a ratio of ~ 1.0 or so.
              Comparing the 2 orientation's approx. outputs on clear days around the winter solstice results in a ratio of ~ 0.39 favoring the 180 deg. az., 45 deg. tilt orientation.

              In all likelihood, unless you've got some substantial shading going on that's been brought on by objects/trees/whatever that are located to the south of the array, I'd wager the more southern orientation with greater tilt will result in greater annual array output.

              Whether or not that additional annual production is worth the effort in terms of time, toil and money is a separate question, particularly with respect to any design considerations for wind loads on the supports or building structure as a result of higher tilts and also any visual considerations, although those visual aspects seem to have less importance at higher latitudes.

              If you're interested in a bit more information, download and read a PDF of a tome entitled "Solar Power Your Home for Dummies". IMO, it's a decent primer on residential PV. The PDF is a bit dated but the price is right.

              Good luck.

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              • #8
                Thanks JPM have wired up the battery bank and inverter today took a minute or two to work out a good way to crimp the heavy wires for the battery's but lots of helpful videos on the tube I will build a frame to hold the panels and get it on the roof next weekend and mount the panels on it and mount the charge controller and wire it to the battery's so i should be good to go will post up some pic's when finished

                Comment


                • #9
                  Originally posted by pug View Post
                  Thanks JPM have wired up the battery bank and inverter today took a minute or two to work out a good way to crimp the heavy wires for the battery's but lots of helpful videos on the tube I will build a frame to hold the panels and get it on the roof next weekend and mount the panels on it and mount the charge controller and wire it to the battery's so i should be good to go will post up some pic's when finished
                  You're welcome.

                  All the best, but I'd put less than full faith in what I found on the tube or on U-tube (the new idiots' bible) when it comes to technical stuff as it's mostly unvetted, harmless or not with a lot of it from wrench heads who think they know what they're doing.

                  Comment


                  • #10
                    I know what you say with you tube and the idiots I run a Channel on Koi keeping and some of the Koi fish keeping channels I would not let them look after a gold fish in a tank let alone a koi pond. Some of the so called experts on most things have a subscriber count that makes you wonder how come so many idiots get taken in and follow them. yet good creators on you tube with good sound content in the videos on how to and doing this things cant get off the ground. This is my channel should you want a look see the old man you been talking too.
                    About 9 min into the video for the start of the solar bit
                    https://www.youtube.com/watch?v=vGDodDbxog4&t=203s
                    Martyn

                    Comment


                    • #11
                      Originally posted by pug View Post
                      I know what you say with you tube and the idiots I run a Channel on Koi keeping and some of the Koi fish keeping channels I would not let them look after a gold fish in a tank let alone a koi pond. Some of the so called experts on most things have a subscriber count that makes you wonder how come so many idiots get taken in and follow them. yet good creators on you tube with good sound content in the videos on how to and doing this things cant get off the ground. This is my channel should you want a look see the old man you been talking too.
                      About 9 min into the video for the start of the solar bit
                      https://www.youtube.com/watch?v=vGDodDbxog4&t=203s
                      Martyn
                      Understood.
                      Rant mode on.

                      Off thread topic but with respect to u-tube, and for me, anyway and only, the big problem with u-tube is that any bonehead and/or shyster who thinks because he knows which way to turn a nut or get others to buy the B.S. gets to spew just about any imaginable crap without someone checking to see if what's shown is, first of all safe, much less useful or practical. The great unwashed masses get to pay the price.

                      Looks to me, and maybe me only, that most of what I see is unvetted and unverified as either safe or workable. To the degree it is unvetted makes the content of the information on U-tube, de facto unreliable until verified, and I don't see a lot or any verification going on.

                      A lot of the U-tube stuff I've seen is, in my opinion only, little more than the display of the fruit of mental masturbation from wannabes with way too much time on their hands and too little in the way of critical thinking skills, or plain old conmen with a new platform to screw people from.

                      My apologies to U-tube posters who are not boneheads, shysters, or conmen.

                      Rant mode off.

                      Comment


                      • #12
                        JPM
                        As you know what you are on about solar wise I'm only just getting my head round this sun power thing if I put my hands on a grid tie inverter and wire that into the system instead of a charge controller and inverter. The power made go's into my ring main hear at the house and is then used by that to power what ever is on that ring. So if as a total in a year
                        my orientation: Az, 90 deg, tilt 25 deg., annual output ~ 917 kWh/installed STC kW. for ease of numbers call it 1000 kWh a year all this power made is then knocked off what im pulling in from the grid so say I pay 18p per Kw hear at a 1000 Kwh i would save £180 or close there about in a year am i right or thinking this out if not can you put me right if so thanks
                        Martyn

                        Comment


                        • #13
                          Originally posted by pug View Post
                          JPM
                          As you know what you are on about solar wise I'm only just getting my head round this sun power thing if I put my hands on a grid tie inverter and wire that into the system instead of a charge controller and inverter. The power made go's into my ring main hear at the house and is then used by that to power what ever is on that ring. So if as a total in a year
                          my orientation: Az, 90 deg, tilt 25 deg., annual output ~ 917 kWh/installed STC kW. for ease of numbers call it 1000 kWh a year all this power made is then knocked off what im pulling in from the grid so say I pay 18p per Kw hear at a 1000 Kwh i would save £180 or close there about in a year am i right or thinking this out if not can you put me right if so thanks
                          Martyn
                          As I wrote previously, and reiterate, get yourself a copy of "Solar Power Your Home for Dummies" either as a free PDF download or a new and updated copy at bookstores/Amazon.

                          If you are doing this install/project yourself, at what looks to be your current level of needed solar/PV knowledge level, I'd say don't (yet). Or at least not without more information than you can get on a forum.

                          I believe all your questions and a lot of the basic information you'll find useful and probably necessary before you move forward will be answered in a much better and more thorough fashion than I can with some self education on your part.

                          If I were you, after the read, and a search through the references in that tome and other places, I'd then come back here and ask questions related to any knowledge gaps your information search creates.

                          Somewhat analogous to the GIGO principle, the better informed questions you then ask here (and elsewhere) will have more meat on them, and folks here and elsewhere who are at least or more informed and experienced about particular aspects of residential PV than I can add more and better info to their responses with a different outlook and perspective than mine alone. Help us help you.

                          None of us is as smart as all of us.

                          Take what you want of the above. Scrap the rest.
                          Last edited by J.P.M.; 12-06-2019, 06:16 PM.

                          Comment


                          • #14
                            Thanks will do its a hole new field to me will go back to basics and build my knowhow from there gives me something to do over the winter. And go from there
                            Martyn

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