Aiming at the sun (best fixed angle)

Gloves
Gloves Solar Expert Posts: 65 ✭✭✭✭
It's confirmed. I have a 120W solar panel on the way! :D

I'll be placing it on the back roof of my house. I would like to give this panel the best
chance to collect sun. Is there a specific way i can maximize the angle both vertically and horizontally?
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Comments

  • jcgee88
    jcgee88 Solar Expert Posts: 154 ✭✭
    Re: Aiming at the sun (best fixed angle)
    Gloves wrote: »
    Is there a specific way i can maximize the angle both vertically and horizontally?

    By far the best advice is: face it due south in a shade-free area.

    As for tilt angle, you can use PV-Watts to simulate various angles,
    and then you pick the best one. Otherwise, if you have a normally
    sloped roof, and you mount it due south/shade-free parallel to
    the roof, you're likely 95% as good as you can get.

    John
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Aiming at the sun (best fixed angle)

    Generally, face the panel south (not magnetic south) and tilt to your latitude. That will give you the namaximum output over the year.

    Or you can play with the pv watts website:

    http://www.nrel.gov/rredc/pvwatts/version1.html

    Use a derating factor of 0.52 for an of grid solar system using an ac inverter.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Aiming at the sun (best fixed angle)

    My favourite panel angle calculator:

    http://www.macslab.com/optsolar.html
  • Gloves
    Gloves Solar Expert Posts: 65 ✭✭✭✭
    Re: Aiming at the sun (best fixed angle)

    Good-Gad! those links are going to take some of my brain power to go through...
    (Tonight i got to prep for voting so maybe after that i'll read through those.)

    ok, I hear what you're saying...

    This is from Google earth, so North is up.
    wind-solar-on-house.jpg

    I should tilt it slightly south?

    Trying to gather what type of equipment i'll need to get the angle just right...
    Level/plumb bob/compass/protractor/star charts/horoscope charts/sun dial/prism ruler and possibly a measuring cup. Am i leaving anything out?
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Aiming at the sun (best fixed angle)
    Gloves wrote: »
    Trying to gather what type of equipment i'll need to get the angle just right...
    Level/plumb bob/compass/protractor/star charts/horoscope charts/sun dial/prism ruler and possibly a measuring cup. Am i leaving anything out?

    All you need is:
    A piece of coat hanger about 6" long, bent into an 'L', and some duct tape.
    Tape the coat hanger on to the bottom of the panel frame so it sticks up over and is parallel with the face, about 1/2" away.
    Wait for noon.
    Look at the shadow cast on the panel by the coat hanger. Tilt panel until hanger and hanger shadow are as close to equal length.
    That's it.
    :D
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: Aiming at the sun (best fixed angle)

    If you only have the one 120 watt panel, why not keep it on a mount that you can change both with the season if not with the time of day? A single 120 is small enough to facilitate moving easily.

    I have a couple of panels that I have wired with Anderson connectors that I can (and do) move with the season. When the fall days get really short and dark, I manually move them to follow the sun over the course of the day, moving them a few times a day when I notice that they are not perfectly lined up. In my case, I can extend the solar day with these panels because they begin harvest about 1 hour sooner than my fixed array, and they produce nearly 2 hours later in the late fall. It is not too much, but it does two things. The extra 8 amps for those two hours is is ~200 watt hours additional, or ~25% of my daily use ( a big deal when the days are short!) and they allow the batteries to maintain a surplus for an extra couple of hours in the later afternoon when they would be drawn down with lighter loads. In the afternoon the sat modem/radio etc might draw ~ 3 amps so instead of drawing down with that load, I am still charging (albeit slowly). Sane thing in the early morning, they capture harvest as soon as the sun breaks the horizon, giving me enough power for the radio/modem/etc. It just helps with the load shifting a bit.

    Tony
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Aiming at the sun (best fixed angle)

    Getting complicated...:roll:

    If you have morning clouds a South West installation may be better. If you have an afternoon marine layer--then perhaps a South East installation is better.

    If the solar station where the data has been collected is close to your home (similar in climate)--PV Watts (or others) which use real data will allow you to play with the numbers to see which gives you the most energy...

    And who knows--Perhaps you will focus on gathering the most energy in winter (less sun) for backup power with storms.

    Or during summer (fire alerts) maximize power...

    Your choice.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
    Re: Aiming at the sun (best fixed angle)
    Gloves wrote: »
    Trying to gather what type of equipment i'll need to get the angle just right...
    Level/plumb bob/compass/protractor/star charts/horoscope charts/sun dial/prism ruler and possibly a measuring cup. Am i leaving anything out?

    Steel-toed boots, hardhat, safety glasses, long sleeve shirt, gloves, sunblock, cup...
  • Gloves
    Gloves Solar Expert Posts: 65 ✭✭✭✭
    Re: Aiming at the sun (best fixed angle)

    Latitude and longitude of Fremont, California is:
    37° 32' 53" N / 121° 59' 15" W

    So I want to make sure the solar panel is facing -121° from perfectly flat or 37°?
    toward the south (true south)?

    I'm thinking it's the 37 that i'm going for.
    solar-tilt.gif

    Am i over thinking this? I'll probably just end up throwing that puppy on my roof,
    and duct tape it in place flat. Some time next year i'll probably add a 2nd solar
    panel, but i don't see myself with more than 2 unless i upgrade the whole darn
    system and go grid-tied.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Aiming at the sun (best fixed angle)

    Using PV Watts, 1,200 watts of panels (1.2 kWH because the smallest supported array is 1kW--just moved decimal point to left 1 spot for 1/10 real panel size), for SF Airport, facing SE (135 degrees) tilted at Latitude of 37.6 and 70 degrees (not sure what 121 degrees is--that is facing 1/2 to the ground). 0.52 derating:
    "Station Identification"
    "City:","San_Francisco"
    "State:","California"
    "Lat (deg N):", 37.62
    "Long (deg W):", 122.38
    "Elev (m): ", 5
    "PV System Specifications"
    "DC Rating:"," 1.2 kW" move decimal point one to the left for 0.12 kW
    "DC to AC Derate Factor:"," 0.520"
    "AC Rating:"," 0.6 kW"
    "Array Type: Fixed Tilt"
    "Array Tilt:"," 37.6"
    "Array Azimuth:","135.0"

    "Energy Specifications"
    "Cost of Electricity:","12.5 cents/kWh"

    "Results"
    "Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value ($)"
    1, 3.09, 54, 6.75 now 5.4 and $0.675 worth of electricity
    2, 3.99, 64, 8.00
    3, 4.68, 84, 10.50
    4, 5.81, 101, 12.62
    5, 6.20, 111, 13.88
    6, 6.24, 107, 13.38
    7, 6.76, 119, 14.88
    8, 6.21, 110, 13.75
    9, 5.97, 101, 12.62
    10, 4.72, 82, 10.25
    11, 3.35, 57, 7.12
    12, 2.82, 49, 6.12
    "Year", 4.99, 1040, 130.00 and 104.0 kWH per year $13.00 worth of power
    "Station Identification"
    "City:","San_Francisco"
    "State:","California"
    "Lat (deg N):", 37.62
    "Long (deg W):", 122.38
    "Elev (m): ", 5
    "PV System Specifications"
    "DC Rating:"," 1.2 kW"
    "DC to AC Derate Factor:"," 0.520"
    "AC Rating:"," 0.6 kW"
    "Array Type: Fixed Tilt"
    "Array Tilt:"," 70.0"
    "Array Azimuth:","135.0"

    "Energy Specifications"
    "Cost of Electricity:","12.5 cents/kWh"

    "Results"
    "Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value ($)"
    1, 3.03, 52, 6.50
    2, 3.68, 58, 7.25
    3, 4.03, 70, 8.75
    4, 4.65, 78, 9.75
    5, 4.61, 79, 9.88
    6, 4.39, 71, 8.88
    7, 4.84, 82, 10.25
    8, 4.72, 80, 10.00
    9, 4.95, 82, 10.25
    10, 4.27, 74, 9.25
    11, 3.25, 55, 6.88
    12, 2.81, 49, 6.12
    "Year", 4.10, 831, 103.88

    So, tilting the array to 70 degrees (just a random number) shows a little bit increase in winter, but 20% or more losses in summer.

    100 kWH is really 10.0 kWH per month (remember to divide everything by 10):
    • 10,000 WH per month / 30 days = 333 Watt*Hours per day
    So, if you use a reasonably efficient inverters, you will get around 333+ Watt*Hours per day for about 1/2 the year.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Aiming at the sun (best fixed angle)

    the latitude figure of 37 degrees is what you're looking for and pointed south. you can add up to 15 more degrees to realize a bit more winter gains.
    i don't think it to be wise to duct tape pvs flatly to a roof. a more elevated and secure mounting should be employed.
  • Gloves
    Gloves Solar Expert Posts: 65 ✭✭✭✭
    Re: Aiming at the sun (best fixed angle)

    BB... O M * G ! )!(@*$
    You realize that i just made a duct-tape reference in the "Solar Beginners Corner" forum. How am I supposed to make head or tales of this?

    LOL,
    J/K.

    I'll be pointing my Solar panel 37° and true south.... for starters that will get me some KWHs! I don't have fog every day like SF does, maybe 20 days out of the year.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Aiming at the sun (best fixed angle)

    Duck Tape / Duck Tape -- doesn't matter... ;)

    For example:
    • 4, 5.81, 101, 12.62
    4th month (April)
    5.81 is Hours of noontime sun per day
    101 kWHours (101,000 Watt*Hours) per month of April
    12.61 $ worth of kWH (at $0.125 per kWH hour) worth of power

    Now, the above was based on 1,200 watts worth of panels--because the program does not allow us to enter less than 1,000 watts (1 kW) of solar panels... So, since you have 1/10th the amount of solar power:
    • 4, 5.81, 10.1 kWH/Month, $1.262 per month
    Now, the 5.81 Hours of Sun per day... That is based on actual measurements of solar energy, averaged for the month of April. And it is also adjusted for solar angle (i.e., if the panel is facing the sun more, it would be more than 5.81 hours per day. If panel is "flat", then less than 5.81 hours per day).

    The way we can use hours of sun per day in this example:
    • 120 watts of solar panels
    • 5.81 hours of sun per day
    • 0.77 derating for solar panel (marketing numbers) and 5% solar charge controller losses
    • 0.80 battery charging/discharging losses
    • 0.85 AC inverter losses
    • 0.77*0.80*0.85=0.52 end to end efficiency (yes, you lose ~1/2 the panel ratings.
    So, now lets estimate the amount of energy a 120 watt panel will collect for an average April day:
    • 120 watts * 5.81 hours of sun * 0.52 sys eff = 363 Watt*Hours of energy
    Say you had a 30 watt laptop and a 13 watt CFL you wish to run:
    • 363 WH per day / (30 watts + 13 watts) = ~8.4 hours of use per night
    You can pick Sacramento or Fresno as possibly more representative of your weather. I try to be conservative--Folks tend to be happier when the system performs a bit better than expected--vs a bit worse.

    And, yes, I do have a sense of humor--I try to keep it a bit in check to avoid having the signal to noise ratio in the forum go in toilet. Nothing like a bunch of guys and engineering/electrician jokes flying around (i.e., deathly boring to everyone else). :roll:

    Go ahead and ask your detailed questions. It will make my typing a bit more directed to being helpful for you. :blush:

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Gloves
    Gloves Solar Expert Posts: 65 ✭✭✭✭
    Re: Aiming at the sun (best fixed angle)

    BB, Your calculations can't be beat. Every time i think i should ask, you already explain it. I'm looking forward to the nearly 8.5 hours of green energy a night.

    BTW, my laptop reads: 19V @ 3.42A . . I think that's a max of ~65W ?
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Aiming at the sun (best fixed angle)

    Roughly... There are losses in the power supply and the fact that average power is usually less than peak.

    Your best bet is to measure the power of each appliance with a Kill-a-Watt meter (AC) or a DC Amp*Hour / Watt*Hour meter.

    Solar electric power is expensive--~10x the cost of utility power. So you need to have an accurate estimate of your power needs before you build out your system.

    A good goal--Roughly 100 kWH per month (3,300 Watt*Hours per day). Many people find they can run an off-grid home on that amount of power with many modern appliances (and lots of conservation). It also is a reasonably sized/cost solar PV system.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
    Re: Aiming at the sun (best fixed angle)
    Gloves wrote: »
    BTW, my laptop reads: 19V @ 3.42A . . I think that's a max of ~65W ?

    You mean the power supply says that? The power supply for my netbook says 19v 1.56a, which would be 30w, but in Linux it shows that it's only actually using 9-13w normally, and 14w when charging the battery.

    I also have a car adapter that is rated for 19v 4.7A - 90W, but my little netbook will never draw that much.
  • Gloves
    Gloves Solar Expert Posts: 65 ✭✭✭✭
    Re: Aiming at the sun (best fixed angle)

    CHRISTMAS CAME EARLY TODAY!

    SO I now have a HUGE freakin' solar panel in my living room.
    *Correction*
    Now i have a huge freakin' solar panel in my office room. (wife didn't think it went well there)

    I didn't realize that they are so large. well you do know how large it is but then it arrives and it's quite large

    solar-pannel-box.jpg

    That's a 46" TV and it's way bigger than that!
    solar-pannel-tv.jpg

    Q U E S T I O N !!!

    How do I mount this bad boy? Do i need a mounting kit or what?
    I am going to do the 37° thing, by it's not a friendly angle to the slant of my roof. I'll I got was z brackets. I need all sorts of advice please!!!
  • solarix
    solarix Solar Expert Posts: 713 ✭✭
    Re: Aiming at the sun (best fixed angle)

    To add complexity to this not so simple equation, don't forget to take into account your utility rate plan (if you are grid tied). If you are (or should be) on a time-of-use rate where the peak afternoon hours are more expensive than the morning hours, aiming your PV westward is an advantage. Here, those hours are 3 times the cost of the morning hours, and even with afternoons being much more cloudy than the mornings, it is a definite advantage to point SW. Less overall energy harvested, but better cost savings.

    On the other hand - just stick the module up there and see what works best. Get going - you're burning daylight!
  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
    Re: Aiming at the sun (best fixed angle)

    I'd just whip up something from slotted angle iron. You can get it cheap pretty much anywhere:

    http://www.nextag.com/slotted-angle/shop-html

    Make sure you screw into the rafters and not just into the sheathing. Make sure you use THE CORRECT ROOF-SEALING GOOP! Plain old silicone just won't do.
  • Gloves
    Gloves Solar Expert Posts: 65 ✭✭✭✭
    Re: Aiming at the sun (best fixed angle)

    DWH, that's brilliant! A giant erector set!
    I didn't know they made erector sets that big.

    bc058.jpg

    Since i don't know what 'goop' to get. I'll just buy 6 or 7 of them, mix them all together. How can it go wrong?

    Now how many degrees of declination is true south again? 6 or 7° clockwise or was it 14° counterclockwise? I have no idea.

    According to this """map""" it seems it's 14.5°
    But should I trust this? I'm going to get a second opinion.
    ca_declination_map.png
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Aiming at the sun (best fixed angle)

    For SF Bay Area, Magnetic North is ~14.5 degrees to the North East (Red Needle on 14.5 degrees and the N on the compass will be facing true north).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: Aiming at the sun (best fixed angle)

    Go to Home Depot and ask for Uni-strut.

    http://www.unistrut.us/index.php?WP=about_display&P=po_mf

    Tony
  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
    Re: Aiming at the sun (best fixed angle)

    In my opinion, uni-strut is overly beefy for what he's doing. Also, since he has to build it with a tilt, it would a lot easier to work with slotted angle. Ether way would be strong enough for a single PV.
  • Gloves
    Gloves Solar Expert Posts: 65 ✭✭✭✭
    Re: Aiming at the sun (best fixed angle)
    dwh wrote: »
    I'd just whip up something from slotted angle iron. You can get it cheap pretty much anywhere:

    http://www.nextag.com/slotted-angle/shop-html

    Make sure you screw into the rafters and not just into the sheathing. Make sure you use THE CORRECT ROOF-SEALING GOOP! Plain old silicone just won't do.

    OK, I got the slotted-angle iron at Home Depot. i did see Uni-strut there... that stuff
    is REALLY heavy duty and I would probably have a hard time cutting it.

    Today I was able to figure the best way to mount it at the proper angles. Tomorrow
    I have to go back to the hardware store for some provisions and then cross my
    fingers there will be a decent break in the rain for the final setup. I can already see
    more of these SV panels on the roof in the near future.
  • Gloves
    Gloves Solar Expert Posts: 65 ✭✭✭✭
    Re: Aiming at the sun (best fixed angle)

    New question...

    I was just told something that contradicts what I was about to do.

    I have plans to tilt my solar panel 37° up from level with the earth.
    I was just told by a boating expert that the tilt should be 37° down from vertical.

    How do I angle the solar panel?
    where-is-the-sun.gif

    the black panels in my drawing, should I face them more toward sky or toward horizon?
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Aiming at the sun (best fixed angle)

    More towards the sky (flatter).

    You can see from my post #11 how much power it will cost you if you mount the panel at ~70 degrees instead.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: Aiming at the sun (best fixed angle)

    Think of it this way, to be simple. You want the panels as close to perpendicular to the sun for as much of the time as possible. Local conditions will vary as will time of day/time of year. You can decide for example to give up some summer harvest, (because you presumably have more any way in favour of winter harvest. Or vise versa. The same could be said for AM versus PM. There is no one setting that will be ideal, winter, summer spring and fall, morning and afternoon.

    As I said before, my orientation specifically targets morning because of site conditions. (secondarily, our summer afternoons are more often not punctuated by puffy cumulous clouds that cut down on harvest, giving further advantage to the morning).

    With one panel, I suggest paying around with certain orientations and see what works best for you,

    T
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Aiming at the sun (best fixed angle)

    you can do it either way or make it adjustable for optimizing for summer and winter. the 37 degrees would be the average highest angle that the sun is during the day for the whole year. from there the sun is either east or west of south and lower in the sky meaning a slightly higher angle off of the ground best suites. this could be any number up to 15 degrees added to the 37 degrees you have now for your latitude. if winter production isn't as important to you then just go with about that 37 degrees.
    your buddy wasn't that far off, but it isn't off of the vertical. he had 90-37=53 degrees. in actuality it is 37+up to 15=less than or equal to 52 degrees.
  • Gloves
    Gloves Solar Expert Posts: 65 ✭✭✭✭
    Re: Aiming at the sun (best fixed angle)

    After doing some more drawings on the computer. Turns out 37° from my level earth
    is where the sun is most. I might try playing around with the angle some once it's
    up. I live in sunny CA where there's a LOT of sun all of the time (excluding night ;) )

    where-is-the-sun2.jpg

    Awesome! now i got to wait for this storm to pass. Maybe next weekend will be
    clear enough for me to get to work.
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Aiming at the sun (best fixed angle)

    "After doing some more drawings on the computer. Turns out 37° from my level earth is where the sun is most."

    that statement is actually wrong as i tried to say to you in my previous post. that 37 degrees is at solar noon and the sun on average will not go higher in the sky, but it will go lower in the sky. remember the sun not only goes from east to west, but it rises from the easterly horizon and then up to solar noon (on average 37 degrees) and back down to set in the western horizon. the sun will spend more time at a lower angle meaning more than the 37 degrees on the pv will be able to harvest more power overall and that is especially true in winter where the solar intensities are lower and shorter in time duration.