two or more solar panels

Options
This is my first post, a question. I have no experience with these panels so what I,m asking may seem foolish. To gain better exposure from sun up to sundown, do two or more panels have to be at the same angle? Could one panel be set up for the first part of the day and a second panel be set up for the later part of the day? Would this create an imbalance between the panels, the stronger one feeding into the weaker one? My desire is to set up a cabin to be off-grid using solar panels.

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,471 admin
    Options
    Re: two or more solar panels

    Solar panels output their most energy when pointed within about 10 degrees of the sun (cosine function).

    The problem is, of course, the apparent motion of the sun across the sky. The solution to the problem is different for different people, their location, and their specific needs.

    Solution:

    1. Fixed mounting (roof, ground, etc.). Overall, the best collection of kWhr for a 1 year period is to mount the panel at your Latitude pointing due south (not magnetic south). If you are near St. Petersburg Florida, that would be at ~29 degrees from horizontal. Here are several links where you can estimate your power collection. This first one are PDF files where you look up the nearby city--you can see how tilting at Latitude and +/- 15 degrees will affect your power collection (tilt up more, better winter number, tilt back and you get more power in the summer, etc.). This other link allows you to plug in the numbers (including compass direction) and get your 1 year estimate. Use the numbers (like 5.4 kWhr/m2*day) as 5.4 hours of full sun equivalent.

    2. Fixed mounting with adjustable tilt. Same as above, but you manually set the tilt 2-4 times per year. Cheap, but you get closer to maximum power during each season.

    3. 1 Axis tracking. Tilted to Latitude, but tracks sun's motion across the sky. Collect even more power, but more parts, more expense, more things to go wrong. Sometimes it is cheaper to buy more solar panels on a fixed mount (1 or 2) than to go with tracking.

    4. 2 Axis tracking. Follows the sun across the sky exactly. Most power, more parts, more likely to fail, more expense. A good 1 axis tracker (with possible 2-4 position manual seasonal adjustment might be a good compromise).

    Generally, the only time that people would point 1 set of panels south and another set of panels west (for example), is because they don't have the room for mounting them all facing due south on their roof. Or in some cases, they will point a fixed array south west or so because they have morning fog (common in some coastal communities).

    Also, make sure you have NO SHADOWS on the array between roughly 9am and 3pm. Solar electric panels are very sensitive to shadowing and depending on the exact configuration, can dramatically affect power output (for example, partial shading on one panel in my 20 panel 3.5 kW array will cut its output in 1/2).

    There are no 100% correct answers as to what you must do for your installation... But with some more information (like where your cabin will be, snow/wind, what seasons you will be needing power, temperatures, how much power you need per day, type of loads, batteries or no batteries, 120 VAC or 12/24/48 VDC, generator backup, etc.) will help us give you some additional tips that many here have learned over the years so you don't end up spending more than you have to...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Options
    Re: two or more solar panels

    One consideration is the way the panels are set up. I would think that a series array would suffer by facing them in different directions because the shaded panel would serve to draw down the unshaded one.

    On the other hand, panel array in parallel MIGHT have an advantage. As Bill points out every situation is different. I, for example have two sets of identical panels in series/parallel. One set gets much better morning sun, the other better sun in the afternoon. I have never done a serious calc to determine if it would NET me more power if I pointed all four in the same direction. The reason I have done this is A: because my installation was easier and B: I like the extra early start in the morning because that is when I tend to draw larger loads, IE Thats when I tend to do my computer work, have the telephone on, satellite modem etc. That allows me to us more watt hours with out drawing my battery down further.

    Spend some time doing some calcs, (estimates) and see what works for you.

    Good luck,

    Icarus
  • System2
    System2 Posts: 6,290 admin
    Options
    Re: two or more solar panels

    I would suspect the output would be higher with the panel facing due south with the sun at high noon, rather than for example having the panel facing east to get the sunrise. Reason being, early morning, or late in the day, the suns rays have to travel through much more atmosphere than at high noon.
    Suns greatest intensity tends to be 10 AM to 2 PM. (standard time)
    If the panels are to be wired in series, they MUST face the same direction, otherwise one or the other will often be in the shade, cutting off the power from the producing panel.
    That's my story and I'm sticking to it. LOL
    However, if like Icarus, you have a higher demand first thing in the morning, it might be something to look at. Your overall output per day would be lower, but it would be supplied when you need it.
    Cheers
    Wayne
  • Solar Guppy
    Solar Guppy Solar Expert Posts: 1,989 ✭✭✭
    Options
    Re: two or more solar panels

    Depends on the local weather and how the panels are mounted

    My south east roof mounted arrays outperform the south west arrays by a large amount,

    1) The solar panels are not as hot in the AM hours, by the afternoon it's easily a 20c difference in the panel tempatures, so this compenstates if not outweighs the sun angle reduction

    2) In our rainy season ( 5 months of the year ), the afternoon thunderstorms/ cloud cover really reduce the south west generation

    My vote is with east or south/east over due south, this after building 7 arrays in the last few years.
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Options
    Re: two or more solar panels

    Solar Guppy make a good point.

    My afternoon sun is seldom as good as my morning in the summer due to cumulus (sp) clouds that pop up most every afternoon.

    Remember, you results may vary!

    Icarus
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Options
    Re: two or more solar panels

    It all depends on your climate . Where I am in Los Angeles's Coastal Area, we often have what the weathermen call "Marine Layer". It's some low level clouds / haze that generally burns off 10 or 11AM. My roof ridge line runs N-S. I could either mount panels on east side, or west side. I went with west, which has given me yearly averaged results comparable to some installs that were due south.
    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 ,