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General: East West PV array efficiency

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    • CommentAuthorjon
    • CommentTimeSep 9th 2022
     
    There seems to be lots of websites giving recommendations for angles of solar panels (elevation and south/east/west facing). In particular, I've noticed that it's claimed that there's only a 20% or so reduction by going for an east-west split array. Does anyone know if these have been fully checked for UK latitudes?

    Reason is that I've run a spreadsheet simulation accounting for atmospheric extinction, panel angle (using spherical trig: not Haversine.. yet), panel efficiency at strike etc. I'm not getting the efficiencies claimed for east-west panels (& some other striking differences).

    Is it worth going all out and introducing Haversine or are manufacturers relying on southern European/USA data when giving recommendations? (can't see why going Haversine would make any difference but can see why using Southern European latitudes would make E-W more attractive)

    So here's what I'm getting (using data from panel tests so not specifically accounting for glass reflection: possible that the glass protection might have some effect if the panel tests didn't account for it)

    South facing: Sweet spot 35 to 44 degrees (used for comparison)
    East/west at 35 degrees: 33% reduction full year
    East/west at 25 degrees@ 30% reduction full year
    Flat: 25% reduction
  2.  
    Try PVGIS at
    https://re.jrc.ec.europa.eu/pvg_tools/en/

    This is an EU tool that allows you to put in your exact location (zoom the map) define roof angle and direction (or free standing) and system size then calculates expected PV output by month and annual total.

    Note when putting in direction (azimuth) south is '0' and its 3 and - from there.
    • CommentAuthorjon
    • CommentTimeSep 9th 2022
     
    Thanks Peter

    Seriously useful: Sweet spot south facing gives comparable, but when I go east or west I seem to get lower values (not sure why). Would just use that rather than carry on with mine, but because I'm modelling shadow at various times of year, probably worth introducing a 'bodge' factor to make mine the same as the PVGIS output (too many choices as to where to place stuff)

    Many thanks again: seriously useful
    • CommentAuthorJamster
    • CommentTimeSep 9th 2022
     
    And don't forget, the longer but lower generation period from E then W panels compared to S might give you more 'usable' (i.e., non-exported) energy? And that's without looking at the economics of invertor sizing, etc...
    • CommentAuthorjon
    • CommentTimeSep 9th 2022
     
    Thanks Jamster: yes have been thinking of that as well (I have 9 potential configurations)

    Turned out I'd forgotten to account for back reflection from clouds. Couldn't work out why I was getting different figures to PVGIS. Bodge factor introduced for that and it now matches up with PVGIS.

    Thinking of going near vertical for some sections as winter electricity important to keep the freezers going (about 20% of my annual electricity consumption: by timing the time of day they are working, I may be able to seriously cut the amount of grid power they use)
    • CommentAuthorjon
    • CommentTimeSep 9th 2022
     
    PS If anyone's interested in the option of timing freezers, am doing tests over next week. Can share results if interest.

    Looking at possibly using high saline buffers in part of the freezer but calculated heat loss and then what really happens are sometimes different. (all before I do any PV arrays as no point if it won't work)
    • CommentAuthorbhommels
    • CommentTimeSep 9th 2022 edited
     
    For a friend I played around with PVGIS when his installers offered to put some of his panels away from S to optimise output.
    My advice: put all your panels facing dead S if you can and buy a battery if you really have to. And I am not even in favour of batteries!

    Your situation might be more specific, however I found that as soon as you move the panels more than ~10 deg away from the ideal S facing orientation, the yields will be depressed by much more than you will ever gain in the early mornings/late afternoons/winter months etc. Especially winter yields are very low for E-W facing.
    Same goes for steeper angles. Unless you expect a lot of snow accumulation, the latitude angle minus another 15-20 degrees seems to be best (to make better use of the 50% diffuse light contribution we have here in the UK)

    As a rule of thumb, for a roughly S facing array, 1/3 of the power is generated in April-June, 1/3rd in July-September and the remaining 1/3 in the rest of the year.

    My panels are on a 43 deg roof. Unbeatable in February apparently but overall a lot less good than panels on a 25-35 deg roof.

    edit - angle definitions :-(
    • CommentAuthorphiledge
    • CommentTimeSep 9th 2022
     
    Posted By: jon (too many choices as to where to place stuff)


    Use optimisers and put the panels wherever you can. Put in what you can now and add more whenever you can do. With optimisers its a breeze to add panels, theyll help with shading and let you mix and match panel sizes.
  9.  
    Posted By: jonPS If anyone's interested in the option of timing freezers, am doing tests over next week. Can share results if interest.

    Looking at possibly using high saline buffers in part of the freezer but calculated heat loss and then what really happens are sometimes different. (all before I do any PV arrays as no point if it won't work)

    Yes please
    Post the results up here - possibly on a new thread of its own
    • CommentAuthortony
    • CommentTimeSep 10th 2022 edited
     
    I often recommend freezers to go super cold during peak generation -24 and then set stat to -16 for overnight using the freezer as a cold battery. Two stats work well with solar optimiser.

    For flat roofs E-W works well for PV panels
  11.  
    I did try this once, it worked but the savings were miniscule for a domestic freezer, they use really very little energy these days. I guess Jon has some more substantial freezers if they are using so much energy.

    http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16384&Focus=277867#Comment_277867
  12.  
    It would be interesting to know if the calculators factor in the fact that having an East/West orientation allows you to add up to double the number solar panels than you would get on the same size roof that is south facing?

    We have panels on the East and West side of our garage with 8 panels on each side, giving us 16x250W = 4kW. Had the garage faced North/South then we would only have fitted 8 panels on the south face and zero panels on the north side, giving us 8x250W = 2kW
    • CommentAuthorbhommels
    • CommentTimeSep 12th 2022
     
    Posted By: Pile-o-StoneIt would be interesting to know if the calculators factor in the fact that having an East/West orientation allows you to add up to double the number solar panels than you would get on the same size roof that is south facing?

    PVGIS just needs the array location, orientation, inclination and surface area and it returns yields. You could generate 2 plots, one for each side of the E-W array, and add them up afterwards.
  14.  
    Posted By: Pile-o-StoneIt would be interesting to know if the calculators factor in the fact that having an East/West orientation allows you to add up to double the number solar panels than you would get on the same size roof that is south facing?

    We have panels on the East and West side of our garage with 8 panels on each side, giving us 16x250w = 4kw. Had the garage faced North/South then we would only have fitted 8 panels on the south face and zero panels on the north side, giving us 8x250w = 2kw.



    Posted By: bhommelsPVGIS just needs the array location, orientation, inclination and surface area and it returns yields. You could generate 2 plots, one for each side of the E-W array, and add them up afterwards.

    I just did that and PVGIS gave an east + west array of 1 kWp each as 1.57 times annual production of a 1 kWp south facing array.
    That is for my location.
  15.  
    Posted By: Peter_in_HungaryI just did that and PVGIS gave an east + west array of 1 kWp each as 1.57 times annual production of a 1 kWp south facing array. That is for my location.

    Thanks for doing that. I often hear people dismiss having solar fitted because they don't have the 'ideal' south facing roof, so it's good to see that the additional roof real-estate allows you to generate more on E/W than on a N/S orientation.
    • CommentAuthorbhommels
    • CommentTimeSep 13th 2022 edited
     
    Posted By: Pile-o-Stone
    Thanks for doing that. I often hear people dismiss having solar fitted because they don't have the 'ideal' south facing roof, so it's good to see that the additional roof real-estate allows you to generate more on E/W than on a N/S orientation.

    If you want to make it a fair comparison you should look at kWh/kWp over the year (and include a N facing array for the N/S case ;-) ). That tells you how well your panels will be performing.
    Another consideration is that E-W array winter yields are disappointingly low, excarbating the issue many people have with Solar PV: i.e. that there is too much energy generated in summer and not enough in winter.
  17.  
    Posted By: bhommelsAnother consideration is that E-W array winter yields are disappointingly low, excarbating the issue many people have with Solar PV: i.e. that there is too much energy generated in summer and not enough in winter.

    correct, summer yield for E or W array is about 92% of S whilst winter yield is only about 48%

    Oh and a N array is 76% of S in summer and 26% in winter
    • CommentAuthorjon
    • CommentTimeSep 15th 2022
     
    Yes please
    Post the results up here - possibly on a new thread of its own

    Thanks Peter: Will do. Taking a while longer than expected but worth a new thread (if it shows signs of working)

    Use optimisers and put the panels wherever you can.

    Thanks Phil. Will look into optimisers: I can get up to 105sqm of panels if I eeked out every single location. Going to start with the easiest one (24sqm of East-West at 30°) because the all-in upfront costs/sqm are about 60% of doing it anywhere else. Looks as if I'll only get 80% relative to south facing.

    I guess Jon has some more substantial freezers if they are using so much energy.

    Turned out that the freezer I was going to use for the tests has a faulty thermostat (so permanently on at max). Makes it ideal for the tests, but took a while to work out why it was consuming so much power.
    • CommentAuthorphiledge
    • CommentTimeSep 15th 2022
     
    Posted By: jon Looks as if I'll only get 80% relative to south facing.


    But a a longer spread of generation that maybe more useable than a big peak over a shorter period.... depends on your usage and if youve got batteries.

    When I mentioned optimisers, I was referring to a Solaredge system rather than other manufacturers, who I know nothing about.

    If you decide on a large array spread over differing orientations dont get carried away sizing your inverter to match the theorectical max of the array. Unless we have multiple suns in the sky the whole array will never generate at max. PVGIS will give you historic hourly figures so you can see the likely max generation your array will produce through the best day of any year(s) you choose. Crunch the figures in Excel and youll likely get away with a smaller inverter.
    • CommentAuthorjon
    • CommentTimeSep 15th 2022
     
    Thanks Phil

    Leaning towards an array of microinverters at the moment: East face will never get blocked except in mid-winter for a month when half of it blocked out (at least according to my CAD projections): So I'll probably split that into two. The West side is slightly more problematic so will probably split that into three.

    Sizing at the moment is based on the spreadsheet (which tells me I'll be getting a best case insolation of 803w/sqm): worth reducing that?

    Difficult one because the build is exactly EW so I could split into perhaps three inverters linked to opposing panels (in which case my worst case combined insolation is 677w/sqm). But not sure it's worth the hassle.
  21.  
    Have decided to install my bifacial solar east west but vertically but with the ability to turn through 90 degree to make horizontal. Tried to calculate in theory the output on these 550w panels but gave up. Will just have to see what it does in reality.
    •  
      CommentAuthorfostertom
    • CommentTimeSep 16th 2022
     
    PVGIS will tell you.
    • CommentAuthorphiledge
    • CommentTimeSep 17th 2022
     
    Posted By: jon

    Leaning towards an array of microinverters at the moment

    I could split into perhaps three inverters linked to opposing panels


    Youll not need any central inverters if you are using micro inverters fitted to each panel. Or are you meaning optimsers which are different to microinverters??
  24.  
    Posted By: fostertomPVGIS will tell you.


    Not convinced PVGIS works for bifacial panels. I have Suntech 550w bifacial panels can mount upto 40 of them. I believe the 550w is only the front panel any addition from the rear has to be added so for conservative 20% for rear then panel becomes 660w. Mounted vertically I could see winter ouput being much higher then PVGIS suggests but will not know until I get actual figures.
  25.  
    @ renewablejohn
    Do bifacial panels have equal output back and front with the lower back output due to reflected light i.e. is the back output the same as the front if mounted upside-down?

    AFAICS mounting E/W vertically with +20% from the back seems to have little if any annual advantage over S at 35 deg. single sided panels including a higher winter output for S at 35 deg (180%) over E/W vertical

    What is the rational for mounting E/W on a movable framework?
  26.  
    Posted By: Peter_in_Hungary@ renewablejohn
    Do bifacial panels have equal output back and front with the lower back output due to reflected light i.e. is the back output the same as the front if mounted upside-down?

    AFAICS mounting E/W vertically with +20% from the back seems to have little if any annual advantage over S at 35 deg. single sided panels including a higher winter output for S at 35 deg (180%) over E/W vertical

    What is the rational for mounting E/W on a movable framework?


    Dont know the mechanics of front to back but assume front needs to go towards the sun as uplift from reflected is only upto 30% of front maximum. The advantage I believe is in generation in cloudy conditions ie the depths of winter as the front would now be restricted to reflected light but you still have the reflected light from the rear meaning overal winter generation will be far more. Link that with East West giving a far longer day than South facing and you have a very large advantage on winter generation. The disadvantage of East West mounting vertically is the peak midday is totally shaded. By being able to rotate 90 degrre the array becomes equivalent to south facing for the peak of the day.
    •  
      CommentAuthordjh
    • CommentTimeSep 18th 2022
     
    Posted By: renewablejohnBy being able to rotate 90 degrre the array becomes equivalent to south facing for the peak of the day.
    I'm not sure I understand what you're saying. What axis are the panels rotating around? I'd thought that the panels were going to be mounted vertically, facing E with the back facing W (or vice-versa) and then thought you were rotating about a horizontal axis so the panels could be made flat, facing upwards. But now it sounds like you're think about a single-axis tracking mechanism or somesuch?
  28.  
    Posted By: djh
    Posted By: renewablejohnBy being able to rotate 90 degrre the array becomes equivalent to south facing for the peak of the day.
    I'm not sure I understand what you're saying. What axis are the panels rotating around? I'd thought that the panels were going to be mounted vertically, facing E with the back facing W (or vice-versa) and then thought you were rotating about a horizontal axis so the panels could be made flat, facing upwards. But now it sounds like you're think about a single-axis tracking mechanism or somesuch?


    The bifacial panels face east west with pivot point north south, rotate through 90 degree and that makes the panel horizontal the panel is then equivalent to south facing at 0 degrees.
  29.  
    AIUI, vertical bifacial panels are like fence panels, for use in ground-mounted situations where the land inbetween is also useful for something else (farming, carparks, gardens, etc).

    This new study says that, when facing east+west, in summer they will generate as much power as a conventional sloped panel, and at more valuable times of the morning and evening. However in winter, a vertical bifacial facing north&south would perform better. They propose a mix of E-W and N-S oriented panels (round the sides of a field?). But it sounds like RJ has invented the solution, by swinging the panels to face South or east&west at different seasons of the year.
    https://doi.org/10.1016/j.segy.2022.100083
  30.  
    Posted By: WillInAberdeenAIUI, vertical bifacial panels are like fence panels, for use in ground-mounted situations where the land inbetween is also useful for something else (farming, carparks, gardens, etc).

    This new study says that, when facing east+west, in summer they will generate as much power as a conventional sloped panel, and at more valuable times of the morning and evening. However in winter, a vertical bifacial facing north&south would perform better. They propose a mix of E-W and N-S oriented panels (round the sides of a field?). But it sounds like RJ has invented the solution, by swinging the panels to face South or east&west at different seasons of the year.
    https://doi.org/10.1016/j.segy.2022.100083" rel="nofollow" >https://doi.org/10.1016/j.segy.2022.100083


    Thanks for finding this. I knew of the peaks for east west bifacial but had not realized the peak is so early in the morning. On this basis it looks like the rotation to horizontal generation will be far longer than originally expected.I actually intend rotating the panels between vertical and horizontal on a daily basis to achieve peak power output.

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