Panel Angles

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  • yrtrncyrtrnc Solar Expert Posts: 47 ✭✭
    Re: Panel Angles

    What do you think of this site guys? http://energyworksus.com/solar_installation_position.html
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Panel Angles

    this is my general speak without rereading the thread.

    that site is ok as it can reveal an angle at a particular time of day/year and at best would be a starting point. the best angle is determined on what you are after. if you are selling to the grid then you may want to maximize the summer production. if you want a year round average then the latitude plus 15 degrees is good to use. finally some need to optimize winter production.

    the middle one is at latitude +15 because the latitude is only representing the highest point in the sky the sun reaches in the day and most times the sun sits lower to the horizon before and after solar noon. the +15 degrees semi-compensates for the lower to the sky angles without overly compensating due to side to side excursions. remember that solar noon +/-1 hour represents about 15 degrees to the side of solar noon so that 1 hr before and 1hr after solar noon the pv will only be off by 15 degrees and a tad more than 15 degrees at solar noon itself giving a bit more power from the off solar noon times.

    sometimes the best overall pv angle will not be good to use if there is snow involved as a tad more angle can cause the snow to leave the pv surface allowing for power production whereas the ideal theoretical angle may be non-productive due to that snow cover. this angle often corresponds well with the better winter angle for those in northerly latitudes, but if in a more southerly area with high altitudes the angle may need to be off the better collection angles to better rid snow by.
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Panel Angles
    niel wrote: »
    ...the middle one is at latitude +15 because the latitude is only representing the highest point in the sky the sun reaches in the day and most times the sun sits lower to the horizon before and after solar noon. the +15 degrees semi-compensates for the lower to the sky angles without overly compensating due to side to side excursions. remember that solar noon +/-1 hour represents about 15 degrees to the side of solar noon so that 1 hr before and 1hr after solar noon the pv will only be off by 15 degrees and a tad more than 15 degrees at solar noon itself giving a bit more power from the off solar noon times.
    This also means that if you have a seriously East or West of South facing angle for the panels, the sun will be lower in the sky during their peak production too, especially in winter, so adding even more degrees can be better.
    SMA SB 3000, old BP panels.
  • NorthGuyNorthGuy Solar Expert Posts: 1,925 ✭✭
    Re: Panel Angles
    inetdog wrote: »
    This also means that if you have a seriously East or West of South facing angle for the panels, the sun will be lower in the sky during their peak production too, especially in winter, so adding even more degrees can be better.

    Not necessarily. If you're facing East then most of the time the Sun will be to the side of the panel (mid-day) or behind them (in the evening).

    By making them more vertical, you get weak morning sun, but cut off most of the strong mid-day sun and all of the evening sun.

    If, however, you make them more horizontal, you will lose some of the morning sun, but you'll get much more of the mid-day sun, and also some of the evening sun.
  • SkiDoo55SkiDoo55 Solar Expert Posts: 414 ✭✭✭
    Re: Panel Angles

    That's correct for my Grid tied which wants summer peak, my arrays face 156° True(being added this summer) and the current operating array faces 246° True and the optium tilt is 22° at those azimuth angles. Mine are set at 18.5° just because that is the roof pitch and I loose very little for the slight difference. Would probably need some more tilt for an off grid installation for winter production
    GT3.8 w/4600W Trina 230W, TX5000 w/5000W ET-250W, XW4024 w/1500W ET-250W, 4 L16, 5500W Gen. (never had to use) Yet!!
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Panel Angles

    know that the sun sits lower to the horizon in the east or west directions and that 22 degree pitch is probably not optimal for gt collection geared with summer peaks in mind in those directions. it won't ever be a total loss as that flatter area will respond better to the sun as it swings higher in the sky towards the south. you will always reap some solar, but it can be argued to death what the best angle is.
  • SkiDoo55SkiDoo55 Solar Expert Posts: 414 ✭✭✭
    Re: Panel Angles

    Optimum angle per California Initiative per there calculator for those azimuth is @ 21 deg. And optimal for due south also. I loose about 200 kWh per year being at 18 deg. According to CSI Incentive calculator the second (new) system is forecast to produce at least 7,179 kWh for the year. Currently producing system was predicted to produce 6,329 kWh and actually produced 6,685 kWh last year. Averaging about 28 kWh per day right now until the 100's F come in. First system has produced 2,523 kWh so far this year. In Jan did 309 kWh and in Apr 744 kWh. Will put in some numbers in PV Watts and see what the difference is.

    Figured the CSI Calculator would be pretty close or on the conservative side as the state used that for paying out money on there rebates. It uses PV Watts numbers in it's calculations. They give the design factor for new system a 95.480% of optimum for geographic location.

    Ran some number on PV WattsV2

    5.0 kW DC, 18.5° tilt, 156° Az, .77% derate = 6727 kWh annual
    5.0 kW DC, 39.6° tilt, 156° Az, .77% derate = 6757 kWh annual
    5.0 kW DC, 39.6° tilt, 180° Az, .77% derate = 6886 kWh annual

    Looks like only about a 2.4% loss form PV Watts Defaults and installed angles of system for the year. on my 4.6 kW DC system I am actually producing better than what is forcast for the new system. it is producing 22% better than what PV Watts comes up with for it at it's currentl numbers.

    In both winter and summer I have some neighbor tree's shading. Morning shade on the south/east and late evening shade on the west, also, some afternoon power-lines. Rought calculation I am loosing 1.5 - 2.0 kW per day.
    GT3.8 w/4600W Trina 230W, TX5000 w/5000W ET-250W, XW4024 w/1500W ET-250W, 4 L16, 5500W Gen. (never had to use) Yet!!
  • coominyacoominya Registered Users Posts: 8 ✭✭
    Re: Panel Angles
    Thomas, I'll try to explain MPPT controllers for you. (For simplicity in this explanation, we'll ignore all system losses etc.)
    Lets assume you have a solar panel capable of putting out 5 amps @ 36 volts at it's most efficient point electrically. Now you take that panel and connect it directly to your 12 volt battery (or through a PWM controller). The battery instantly loads down the panels to say 12.7 volts, but the amperage stays at 5 amps. What the panel is CAPABLE of putting out is 5X36=180 watts. But you have reduced that to 12.7X5=63.5 watts. You've just installed a system that's throwing away over 115 watts!
    Now, replace your PWM controller with a MPPT controller and everything changes.
    Your MPPT controller, electronically finds that the Max Power Point of your panels is 36 volts, so it only loads the panels to that voltage. Thus what's going into your MPPT controller, is 36VX5A=180 watts. The MPPT controller, using it's electronics takes that 180 watts, and like an AC transformer, drops the voltage down to the battery voltage of 12.7, and since it has 180 watts to work with, it increases the current going to the battery to over 14 amps, even though the panels are only putting out 5 amps! This is the beauty of the MPPT controller and what it does.
    Hope this helps you grasp the understanding. (Keep in mind that this is a very simplified description, ignoring all system losses etc for simplicity)

    Thanks Wayne, a simple concept that you have managed to explain in a simple understandable manner. You should be drafting instruction manuals for a living.
  • faussfauss Registered Users Posts: 26 ✭✭
    My house faces almost east and west so are there any threads or pictures about trying to tip your panels south on an eastern facing roof. I get a bunch of morning sun and not alot of late sun. Also I live in the Pacific Northwest and I know I won't have perfect sun conditions.
  • alcatel99alcatel99 Registered Users Posts: 9 ✭✭
    still confused on tilt angle   i live at Latitude 34.889 " in North East Arizona  i am building my own ground mount for the solar panels i will not be able to change the rotation of mount east to west but will be able to change the vertical angle i looked up the settings in Solar Electric Hand book and his average seems to be around 50 " for year round  in Arizona is any one else in this part of AZ who can help out or recommend i have read through this thread but still unsure of angle to use.
    Thanks for any help
  • littleharbor2littleharbor2 Solar Expert Posts: 1,547 ✭✭✭✭
    Add the "Solar Tilt" app to your phone. Very versatile app  An extra bonus to this app is the tilt gauge that turns your phone into an angle finder

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric, 700 ah @24 volt AGM battery bank. Plenty of Baja Sea of Cortez sunshine.

  • BB.BB. Super Moderators, Administrators Posts: 30,952 admin
    If you are using this website:

    http://www.solarelectricityhandbook.com/solar-irradiance.html

    Note that it uses the angle measurement from vertical. So 50 degrees from vertical is equivalent to 40 degrees from horizontal (90-50=40 degrees).

    If you are at 35 degrees latitude, that is pretty close to the typical latitude=best overall yearly harvest (i.e., 90-35l at=45 degrees from vertical). I would not expect a lot of change in harvest with a 5 degree "change" (see below for PV Watts test).

    If you use something like PV Watts (and most other programs) seem to pretty much use tilt from horizontal measurements.

    PV Watts does not give a suggested best summer (typically +15 degrees flatter), yearly best harvest (typically = Latitude), or winter (typically +15 more tilt).

    Using PV Watts for Slow Low AZ, playing with the numbers for a fixed south facing array):
    https://pvwatts.nrel.gov/pvwatts.php

    20 degrees from horizontal (35-15=20): 6.26 hours of sun yearly average (daily average over one year)
    35 degrees from horizontal (35 = Latitude): 6.39 hours of sun yearly average
    45 degrees from horizontal (35+10 degrees): 6.28 hours of sun yearly average
    50 degrees from horizontal (35+15=50 summer): 6.17 hours of sun yearly average

    Of course, the above does not include the best/worst of summer/winter month harvest--Just total yearly average (may be best for GT solar systems; but for an off grid system, you may want more summer or winter harvest based on A/C and Refrigeration/irrigation/etc. loads/needs).

    So, from a "rule of thumb" design, the +/- and zero 15 to latitude seems to be pretty consistent with PV Watts.

    Of course, PV Watts is based on actual data (include weather, dust storms and panel temperature--As I recall)... So if you have, for example, afternoon thunderstorms during the wet season, changing tilt and/or direct facing (say more South East) may give you better harvest during stormy weather.

    One of our retired members here lived in Florida, and found facing more south east gave him better overall harvest (both because of weather and because panels were colder in the morning vs afternoons). However, the utility folks "pushing" GT solar wanted afternoon harvests (when folks turned on AC systems in the offices and after they headed home)--And they were surprised to see the variance in harvest results.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • alcatel99alcatel99 Registered Users Posts: 9 ✭✭
    Thanks Bill
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