Solar Array Tilt

HenryHenry Posts: 6Registered Users
I'm getting ready to pick a company to install a solar ground mount DC rating 8.6 kw. The company I'm leaning to, a very large company in NJ, told me today they tilt all their ground mount arrays at 25 degrees. My Lat is 40.70N Long 74.17 W. Is there going to be an issue with 25 degrees, and if so how much?

Comments

  • CariboocootCariboocoot Posts: 17,615Banned ✭✭
    Re: Solar Array Tilt

    They tilt all their arrays to 25 degrees, eh? Guess they don't get around much.

    You can check for yourself what will work with the info found here:
    http://www.macslab.com/optsolar.html
  • mike95490mike95490 Posts: 7,967Solar Expert ✭✭✭✭
    Re: Solar Array Tilt

    I'd also use the PVWATTS caculator to plot the different angles over the year, I opted for more of a winter optimized tilt, because summers have longer days.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • jcgee88jcgee88 Posts: 154Solar Expert ✭✭
    Re: Solar Array Tilt
    mike90045 wrote: »
    I opted for more of a winter optimized tilt, because summers have longer days.

    Mike (or others): for a traditional fixed mount that you
    "set and forget" after initial installation:

    I don't understand the rationale for doing the winter tilt.
    Won't that dilute your summer harvest, when you have
    the most potential production? Yes, it would increase
    winter harvest, but increasing the larger summer amount
    to start with (including at the higher summer electricity rate)
    would capture more dollar value it would seem to me.

    I note that the referenced Tilt Paper also advises
    doing a winter mount.

    --

    I am debating making a change to my own recently
    installed array. My roof is aligned 30 degrees west
    of true south at Lat 37.5 degrees. We placed one
    facet of five panels at this azimuth tilted at 20 degrees
    (same as roof line). We placed the other facet of eight
    panels on my north roof, and tilted them up 30 degrees
    from the roof, for an effective 10 degree tilt. [See
    photos below.]

    [EDIT...roof angle is 20 degrees, corrected from earlier
    post which had 30 degrees; 5-panel set is 20 degree
    tilt angle, 8-panel set is 10 degrees tilt angle.]

    Because the two facets are physically close to each
    other, have the same azimuth, and are fairly close in tilt
    angle, I figured that they would perform about equally.
    Actually, going in we thought the 5-panel set should be
    slightly better than the 8-panel set. Neither expectation
    came out exactly correct.

    Starting about 2:30 pm in the afternoon, the power
    generation on the 5-panel starts to drift downward
    from the 8-panel set. The divergence reaches 20 watts
    per panel around 5 pm, then both sets converge around
    6 pm and uniformly diminish to zero as the sun sets.
    This is a 10% reduction over a 3-4 hour period, or
    an effective 3% loss on a daily basis.

    The change I am considering would be to the 5-panel facet,
    and could be one, or both, of the following:

    1. Lift the bottom edge of the facet by, say, 6", to
    have the facet be more perpendicular to midday
    sun. This reduces the tilt angle by 5 degrees.
    2. Lift the left (west) edge by, say, 6" to have the facet
    be more southernly facing.

    I wouldn't want to go more than 6" for either of the
    mods, to keep the facet's appearance somewhat normal.

    My contractor advises against the changes. First he thinks
    that the 5-panel facet, being installed closer to the
    roof than the 8-panel set, is suffering from heat effects.
    Second, when he ran PV-Watts, it shows that flattening
    actually reduces the annual production.

    Lastly, if I have the contractor do the work, it will likely
    cost at least $200. If you assumed the potential gain
    from one or both tilt angle mods is a best case 10%, the
    gain over 25 years is $200 at current electricity rates,
    i.e., no net dollar gain. That being said, perhaps I could
    do the work myself, in which case, the only cost would be
    new rail mounting parts.

    Net net, the economics are marginal, but if I am going
    to do it, I might as well do it now. Any suggestions?
  • nielniel Posts: 10,311Solar Expert ✭✭✭✭
    Re: Solar Array Tilt

    john, i believe you said your name was, i don't think i'd have mounted the pvs quite the way you did. the ones in the back, or north facing roof, are apt to be shadowed at some point by the peak of the roof. now for that set of pvs i would increase the tilt on them as they are nearly flat. flat would be good near solar noon in the summer, but most of the time the sun is far below from being directly above you and always is at the horizon during dawn and dusk. so why would one want to gain a watt or 2 during the solar noon while sacrificing nearly all of the potential outputs at other off times and angles?
    now it is similar when we talk of summer to winter productions as you may sacrifice much of your winter production just to reap a few more watts during the summer. adjusting for winter allows full winter production and that time of year pv power production is at a premium due to the low angles and shorter times. very little is actually sacrificed from the summer production when more geared for winter as the sun is out longer and more intensely during the summer with more morning/evening potential for power production. as an average angle it would be your latitude and you will be just shy of 40 degrees. to gear better for winter many add up to 15 more degrees and this is if you are aimed south. for pvs not facing south, like your 30 degrees to the west pvs, the sun will actually sit lower in the sky for that direction than solar noon and solar noon pv tilt angles would be off for those pvs facing other angles.
    as to those 30 degree off south westerly facing pvs if you raise the front pvs for a better angle then the whole back row will need raised up at least that much to stay out of the shadow of the front pvs, but if you can do it even some then you will benefit some from it, especially in the winter.
    hope i'm not confusing you with this as we are looking not for peak power, but overall power production. pv angles of latitude +10 to +15 degrees offers the best overall imho.
  • mike95490mike95490 Posts: 7,967Solar Expert ✭✭✭✭
    Re: Solar Array Tilt

    Summer, batteries are full by noon. Winter, still needs daily genset time, so winter angle is much more important, as in summer, the clear skies and long days do pretty well. I'm thinking of possibly adding a small tracker array for winter, but that will be a few more years in the future.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • CariboocootCariboocoot Posts: 17,615Banned ✭✭
    Re: Solar Array Tilt

    Latitude makes a big difference: the closer you are to the Equator, the less change between Winter/Summer. Way up North here there's a ten hour difference in the length of day between July and December, and the weather goes from sunny to gray. So sacrificing some potential Summer harvest to gain maximum Winter power is a good trade-off.

    Solar is very site specific.

    The three worst problems are:
    1). shadows on panels
    2). shadows on panels
    3). shadows on panels

    Beyond that there's insolation, ambient temperature, and of course shadows on panels. :p

    It doesn't hurt to go out and look at your roof twelve times a day every day for 365 days. Or at least do the equivalent. :D
  • jcgee88jcgee88 Posts: 154Solar Expert ✭✭
    Re: Solar Array Tilt

    Niel, thanks for your comments! I sense that your overall
    strategy can be interpreted as follows: summer light is
    so long and strong, that no extra help is needed; with
    short duration, weak winter light, you should do everything
    you can to maximize energy capture.
    niel wrote: »
    i don't think i'd have mounted the pvs quite the way you did. the ones in the back, or north facing roof, are apt to be shadowed at some point by the peak of the roof. now for that set of pvs i would increase the tilt on them as they are nearly flat...

    The potential roof peak shadowing has not been a problem, as
    the majority of the panels have been clearing the roof peak
    by 8:30 am. Even if we moved them a couple feet closer to
    the roof peak, there is a line of trees across the street that
    blocks the direct sunlight until 7:45 am.

    At only 10 degrees, these are pretty close to being flat,
    but the contractor advised against a steeper tilt to
    avoid them becoming "sails" during high wind conditions.
    The rail manufacturer ran a wind load analysis on the config
    to confirm that the 10 degree tilt was safe.

    The combination of tilt and distance from the roof peak
    was influenced as well by my requirement that the north-
    roof-mounted PV panels not be visible from the front of
    the house. We also had to contend with the existing
    roof vents, though we could have moved them if push
    came to shove.
    niel wrote: »
    as to those 30 degree off south westerly facing pvs if you raise the front pvs for a better angle then the whole back row will need raised up at least that much to stay out of the shadow of the front pvs, but if you can do it even some then you will benefit some from it, especially in the winter.
    hope i'm not confusing you with this as we are looking not for peak power, but overall power production. pv angles of latitude +10 to +15 degrees offers the best overall imho.

    Just by way of clarification, when I described changing
    the tilt of the 5-panel facet, I meant changing the entire
    facet's tilt. In other words, think of it as one solid plane
    that you are lifting from the bottom (or left side). Thus,
    there would be no shadowing of one panel by another. To
    implement this type of "facet tilt," I'd need to have
    increasingly taller legs for the rails as they go down the
    roof line.

    I am a bit confused as to whether you would recommend
    either or both of the tilt mods. Lifting from the bottom
    is an attempt to make this facet's performance closer to
    the other facet's. Lifting from the left side is meant to
    get the panel oriented more true south and increase
    harvest efficiency. I think either change would be
    beneficial and would not detract from the esthetics.
    I am tempted to experiment with one panel to see if
    changing either the up/down or left/right tilt would be
    worth the work to change the whole facet.
  • stephendvstephendv Posts: 1,571Solar Expert ✭✭
    Re: Solar Array Tilt
    jcgee88 wrote: »
    Niel, thanks for your comments! I sense that your overall
    strategy can be interpreted as follows: summer light is
    so long and strong, that no extra help is needed; with
    short duration, weak winter light, you should do everything
    you can to maximize energy capture.

    Remember the KEY difference for cariboocoot and mike's setups to yours is that theirs is off-grid. Off grid systems have very different priorities for solar harvest than grid tie. For grid-tie you want the most kWh/year, which usually means optimising the array for summer harvest.
    But if you're off-grid, then you have to optimize the array for winter harvest, when those precious photons are a scarce commodity. I'd guess that most off-gridders are throwing away a lot of summer production, because they simply can't use the excess.
  • nielniel Posts: 10,311Solar Expert ✭✭✭✭
    Re: Solar Array Tilt

    stephen,
    it doesn't matter if you are off grid or grid tied as max overall production will be the same. he may have a problem anyway with his indicating shading that may occur.

    john,
    ok i understand the front pvs as a whole you wish to reorient. go for it and try at least your latitude (37.5 degrees) and try to get it more pointed south. if you can place the other pvs on the north facing roof so that they are tilted similarly towards the southerly direction with at least the same latitude angle it should help your production.
    can you try to verify outputs now and after adjustment? you want to get an idea of the improvement you'll get.
  • stephendvstephendv Posts: 1,571Solar Expert ✭✭
    Re: Solar Array Tilt
    niel wrote: »
    stephen,
    it doesn't matter if you are off grid or grid tied as max overall production will be the same.

    It will likely be different, because off grid users would orient and size their PV for the worst solar months, not the best months. So assuming a static array, off grid users will likely have theirs at a much steeper angle than grid tie users to maximise winter production.
  • Dave AngeliniDave Angelini Posts: 4,097Solar Expert ✭✭✭✭
    Re: Solar Array Tilt
    stephendv wrote: »
    It will likely be different, because off grid users would orient and size their PV for the worst solar months, not the best months. So assuming a static array, off grid users will likely have theirs at a much steeper angle than grid tie users to maximise winter production.

    Most definitely! The winter solstice drives most all design! If you ever watch a dual axis track (anytime of year) you will learn quite a bit about the sun!
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

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