Optimum tilt for new fixed system

dale
dale Solar Expert Posts: 29 ✭
in Advanced Solar Electric Technical Forum #1
The data from the Solar Radiation Data Manual measured Lattitude (equinox), Lattitude + 15 (winter) and Lattitude -15 (summer). With the increased hours of daylight, optimizing for summer seems reasonable.

http://rredc.nrel.gov/solar/pubs/redbook/

The person who will be installing my panels said NJ says that 30 degrees is the optimal angle for panels. Since I'm about 41N13.

Since I need to do work on my roof, changing the angle of the roof to optimize the panels isn't that expensive, but I'd like to make sure it will be for the better. Any insights on this would be appreciated.

Thanks,
· Share on Twitter

Comments

  • GreenerPower
    GreenerPower Solar Expert Posts: 264 ✭✭✭✭✭✭
    #2
    Re: Optimum tilt for new fixed system

    An alternative is to put the panels on a support frame that's tiltable.
    You can adjust the angle a few times a year for better yield without doing anything to your roof.
    GP
    · Share on Twitter
  • dale
    dale Solar Expert Posts: 29 ✭
    #3
    Re: Optimum tilt for new fixed system

    Thanks. Do you know if the tiltable frames be controlled by a motor or do they require you to go on the roof. Would wind be a concern since it could get under them and put stress in ways they weren't designed to handle? They could be reinforced, but that is extra weight and expense.
    Thanks again
    · Share on Twitter
  • GreenerPower
    GreenerPower Solar Expert Posts: 264 ✭✭✭✭✭✭
    #4
    Re: Optimum tilt for new fixed system

    Frame mount are usually fixed or manually adjusted. You can easily build yourself with home improvement materials. Frames are usually aluminum to be light and to avoid rust. You can screw them with lag bolts to the roof beams to winstand hurricane wind-force. See this thread http://www.solar-guppy.com/forum/viewtopic.php?t=390&sid=682640d4f31e979c3e5485623d201f82 and that forum for more ideas.
    Motorized frames are usually tracking systems. Some are available here at WS store.

    You can also look at this http://www.sunposition.net/sunposition/spc/locations.php for your best sun angle for the higher insolation months
    GP
    · Share on Twitter
  • crewzer
    crewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    #5
    Re: Optimum tilt for new fixed system

    Interestingly enough, the PVWatts calculator indicates that an ~30 degree tilt is the optimal setting for a south-facing fixed-tilt utility-interactive array located in Newark, NJ (latitude = 40.7 degrees N). Annual output from a 2 kW array is estimated at 2,369 kWh.

    Output from the same array tilted at latitude is estimated at 2,366 kWh (virtually no difference), and tilted at latitude +15 degrees (~56 degrees) is estimated at 2,257 kWh (-4.7%).

    But, the 30 degree tilt configuration probably won't self-clean as well as the other two, especially when it comes to shedding snow in the winter.

    I'd probably go with something in the ~45 degree range (2,347 kWh/yr; -1%), and make up the difference from cleaner modules and less winter maintenance. :cool:

    HTH,
    Jim / crewzer
    · Share on Twitter
  • dale
    dale Solar Expert Posts: 29 ✭
    #6
    Re: Optimum tilt for new fixed system

    Crewzer, Greenpower,
    Thanks very much for your responses. The greater angle would certainly help shed snow. This is a big concern for people like me who live on the border of NJ/NY.

    My installer will be hesitant to change the angle since the rebate uses 30 degrees as the optimum. If 45 degrees is close to the optimum output, then this is really good news since it will help more people consider the switch.

    Crewzer,
    I'm not sure how you arrrived at the numbers for the annual output. Is this from a formula? It looked like the lattitude - 15 numbers were highest and with more daylight ...

    Thanks again for all your help!
    · Share on Twitter
  • crewzer
    crewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    #7
    Re: Optimum tilt for new fixed system

    Dale,

    Use the following link to take you to the NREL calculator "PVWatts". The click on "Newark". I used a 2.0 kW system for sizing, and then played with the tilt angles. You can plug in your planned system size for modeling purposes.

    See: http://rredc.nrel.gov/solar/codes_algs/PVWATTS/version1/US/New_Jersey/

    HTH,
    Jim / crewzer
    · Share on Twitter
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #8
    Re: Optimum tilt for new fixed system

    It depends on the application, if you are in a Grid-Tie situation, I'd stick with the max annual power. That gives the best payback.

    If you are off grid, I'd be tempted to align for better winter performance, as the shorter hours will shift my power budget to the generator. less generator is better for me. As the angle becomes less optimum toward summer, the longer days may make up for the reduced peak.

    Anyone developed a formula for this, or is it going to be a "seat-of-the-pants" guess ?
    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 ,

    · Share on Twitter
  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #9
    Re: Optimum tilt for new fixed system

    Dale,

    Also, another question is what is the $/kWh price on your electric bill, and what are the tiered rates (if you have them) and where are you on the tiers...

    Basically, for me, I have very high rates during summer noon-6pm, reasonable winter rates noon-6pm, and pretty low (for California) rates all other times (weekends and 6pm-noon).

    Gathering a few more watts during the winter may not offset your summer power usages (if you have A/C, water pump for irrigation, etc.)...

    In California with Time Of Use (TOU) metering and tiered rates, having my array optimized for "summer" rates, I can get 2-4x more $$ credits than optimizing a year round average by 10%-20%...

    You can probably look at your rates and construct a spread sheet (by monthly power generation/usage) and plug in a few numbers and see how it works out. For 1 year net metering (what we have here), you can generate the $$$$ credits in the summer and use the credits anytime during the year. Or, if you have a large summer power bill, if your system can move you down a tier or two in usage (in CA, lower tiers are cheaper $/kWh), even a smaller system can really save cash.

    Also, if you have the option of Time of Use or flat rate metering--check when you use your power--you can be in for some mighty nasty surprises if you cannot keep your loads to off-peak times.

    Your mileage may vary.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
    · Share on Twitter
  • System2
    System2 Posts: 6,290 admin
    #10
    Re: Optimum tilt for new fixed system

    Just thinking you should think a bit more about the shedding of snow. When snow builds up on them, unless you're prepared to go up there and clean them off, there will be many sunny days when they will be nothing more than useless bling on your roof.
    This may not be what you want to hear, but it's better to go into this project with your eyes open, than to later decide that solar is "useless" because it's not doing what you expected.
    Good luck and I hope things work out for you.
    Wayne
    · Share on Twitter

Categories