Solar Panel tilt angle...

alyazalyaz Solar Expert Posts: 114 ✭✭✭
I've been reading both here on the BB and a couple of PV books I have purchased. I've also checked out some sites such as NASA and PVWatts etc. In addition, I have discussed the proper tilt angle for our application/location, with an installer. I'm guessing from the reading/discussions I've done/had that this subject is a bit like discussing what the best make of solar panel is or who is prettier, J. Lo or Jennifer Anniston...

We're at about 49 degrees latitude. The one installer I've discussed this with swears that the best (year around production) 'fixed' tilt is 39 degrees. When I plug our parameters into PVWatts, it turns out that 39 degrees does in fact produce the highest readings. However, when I read most of the other materials, it seems that this angle is a bit low?

I don't mean to start up a further discussion on different philosophies, but would like to get advice on people's results from fixed tilt angles (relative to your latitude) or other resource materials.

Thanks...
3.3 kW solar.  3 Midnite Solar controllers; 5 lightening suppressors.  Magnum’s inverter; auto gen start, BMK.  Davidson 2 v FLA’s - 24v bank.  Perkins diesel gen.

Comments

  • BB.BB. Super Moderators, Administrators Posts: 32,007 admin
    Re: Solar Panel tilt angle...

    Partly depends on when you need the power... If you have A/C and need most of the power in the summers, tilting the panel a bit flat will give you more power.

    Also if you have Grid Tied solar and have time of use metering--You may get higher usage credits by maximizing your summer harvest.

    If you are off grid, you may want to maximize your winter usage to avoid generator fuel costs as you can only store a couple of days of usable power (no bill credits in summer for winter usage).

    Assuming Hawaii, the closer you are to the equator, the less panel tilt will affect your seasonal power collection.

    -Bill

    If you are in British Columbia / Vancouver Is, then tilt will be more important... Plus if you have snow, a high winter tilt will help the panels be self clearing.
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • solarixsolarix Solar Expert Posts: 713 ✭✭
    Re: Solar Panel tilt angle...

    The definitive website for correct, optimum panel tilt calculations is: http://www.macslab.com/optsolar.html
    According to MacsLab, for a fixed tilt, if your latitude is between 25° and 50°, use the latitude, times 0.76, plus 3.1 degrees.
    I find that PVWatts is a little in error when it comes to optimum panel tilt as they just use simple latitude.
  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Solar Panel tilt angle...

    Well at your 49* you're further North than I am in Nova Scotia at roughly 45* and I can tell you my experience, not just something in a book or some theory, but actual living experience. During Summer, when the sun is high overhead, my best overall production is with the panels at more or less 25*. That leaves enough tilt for rain to clean off the panels. In Winter, my best overall production by far is with the panels in a vertical position for three reasons.
    1) the sun is very low on the horizon, so vertical isn't that far off the "ideal", and withing 10 minutes of the sun poking it's face up over the morning South-East horizon, I'm getting a good 50% power.
    2) With snow on the ground, the production is even greater as the panels get both direct sunlight, and the reflected light off the snow.
    3) And finally, with the panels vertical, snow does not collect on them, thus no more wading through the snow with long handled scrapers, trying to get the snow off the panels and down on my head. No matter what some people may think, it takes very little snow cover to shut the system down to just a very few watts. Even a small bit of snow on one part of a panel shades and greatly reduces it's output.
    So if at all possible, design your system for at least two panel tilt angles. If you can't, then your yearly production will be a fraction of it's potential.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Solar Panel tilt angle...

    At 52 Lat, my experiences mirror Wayne's. Whacking great difference in power production from changing the angle seasonally up here!
  • alyazalyaz Solar Expert Posts: 114 ✭✭✭
    Re: Solar Panel tilt angle...

    Thanks gang. I think your experiences support that I spend the few extra dollars and take the time to ensure my new panels are as easily adjustable as possible.
    3.3 kW solar.  3 Midnite Solar controllers; 5 lightening suppressors.  Magnum’s inverter; auto gen start, BMK.  Davidson 2 v FLA’s - 24v bank.  Perkins diesel gen.
  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Solar Panel tilt angle...

    You won't be sorry. Oh, and don't do like my cousin and mount them with the bottom 6 inches off the ground. Until he gets them up higher, he has to keep the grass and weeds mowed in Summer, and the snow shoveled in Winter! Hahahaha
  • alyazalyaz Solar Expert Posts: 114 ✭✭✭
    Re: Solar Panel tilt angle...

    Alright, have my mounts welded up and they are adjustable.... another question though... some books talk about setting your tilt from vertical and others from horizontal... why is there not one standard for setting tilt, or is there, and the source I've read is just wrong?
    3.3 kW solar.  3 Midnite Solar controllers; 5 lightening suppressors.  Magnum’s inverter; auto gen start, BMK.  Davidson 2 v FLA’s - 24v bank.  Perkins diesel gen.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Solar Panel tilt angle...

    Normally the angle is degrees off horizontal zero. As in 90 being perpendicular to level horizon.

    I don't see how it could be referenced from vertical plumb.
  • jtdiesel65jtdiesel65 Solar Expert Posts: 239 ✭✭✭
    Re: Solar Panel tilt angle...

    I'm at 44.49.

    I would never do the fixed 39 degrees. Being off grid if I were to fix them, it would be at winter optimal due to scarcity of sun during winter.

    I used to manually angle the panels based on pv watts which was something like 5 different positions. Then I went to the ~15, ~45, ~65, ~45 rotation. Now, I only do 15 and 65. The reason being was that I wasn't seeing gain. Float hrs are still high in spring and fall. I angle for summer because I run AC units and dehumidifiers and the angle change makes a difference with these extra loads.

    One concern I had with completely vertical was wind.
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