Mounting panels flat?

backroadbackroad Solar Expert Posts: 185 ✭✭
I'm putting together a second PV system dedicated to my swamp coolers and my 12/24 volt Sundanzer freezer. I'm curious as to how bad it would be to mount my 6 125 watt panels "flat" on the roof instead of a much more expensive route? :roll:

Comments

  • BB.BB. Super Moderators, Administrators Posts: 29,637 admin
    Re: Mounting panels flat?

    Using PV Watts for Prescott Az. Fixed array:

    Tilted 35 degrees:
    Month    Solar Radiation (kWh/m 2/day)
    1      5.28     
    2      5.71     
    3      6.15     
    4      6.78     
    5      7.06     
    6      7.07     
    7      6.33     
    8      6.51     
    9      6.59     
    10      6.52     
    11      5.58     
    12      4.99     
    Year      6.22      
    

    And zero degree tilt:
    Month    Solar Radiation (kWh/m 2/day)
    1      3.12     
    2      3.98     
    3      5.00     
    4      6.47     
    5      7.63     
    6      8.12     
    7      7.01     
    8      6.49     
    9      5.64     
    10      4.70     
    11      3.42     
    12      2.83     
    Year      5.37      
    

    You will "break even" or do better for ~May through August at zero degree tilt. The rest of the year, you will have significantly worse production (may not matter if summer only use).

    The only other issues that I can think of is panels with less than (roughly) 5 degree tilt will not self clean--So somebody will need to wipe/wash the dust/leaves off the panels once in a while.

    And panels mounted flat may run hotter than panels mounted 5 inches or more off the roof (hot panels, lower Vmp, lower output with MPPT charge controller). 5 to 10% worse???

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • solar_davesolar_dave Solar Expert Posts: 2,344 ✭✭✭✭
    Re: Mounting panels flat?

    Well cleaning panels in AZ is almost a requirement anyway, the rains are so in frequent. I end up hosing mine off about twice a month except in the monsoon season where they do get some natural cleaning rains.

    I think I would do at least a 5 or 10 degree tilt just to keep the major trash off them.
  • backroadbackroad Solar Expert Posts: 185 ✭✭
    Re: Mounting panels flat?

    I recon the pitch of the roof, (not to a solar benefit) would be more than enough to help keep them reasonably clean. I've never cleaned any of my panels in 8 years. OOPS.....The prickly pears and sahauro leaves have obviously not caused any issues. Should have plenty of panels to allow for the small loss, I hope. Math is my nemesis. I am trying to take some of the load off the main system, which has been inadequate. I've logged over 10,000 hours on the generator in the last 5 years and too much fuel used. Also have another 2000 watts of panels sitting here waiting for mounting. Thanx for the great input......
  • BB.BB. Super Moderators, Administrators Posts: 29,637 admin
    Re: Mounting panels flat?

    I would suggest you go back and look at your loads too... It is possible that they have wandered higher over the years and higher than you expected.

    Are you having to run the generator outside the ~3 months of the year with poor weather? How deeply are you cycling the battery on an average clear day, etc..

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • backroadbackroad Solar Expert Posts: 185 ✭✭
    Re: Mounting panels flat?

    The summer months are disasters. I do manage to keep the batteries @ 80% or better most of the time and I do use the genset almost everyday. Winter months are borderline not making enough power, but I am able to lighten up on the gen a bunch... full ..time fridge and chest freezer, at least one tv on 24/7, 2 ceiling fans. bedroom lamp 24/7, 2 laptops, cell phone chargers, satellite computer modem, occasional toaster, microwave for heating up things...... I know I don't have enough PV for the GIANT battery and this all concerns me greatly and it's going to be several months before I can get the additional panels up (750 watts for secondary system & 2000 watts for the main system are waiting in limbo. As a matter of fact, I'm almost ashamed to admit this stuff.
  • BB.BB. Super Moderators, Administrators Posts: 29,637 admin
    Re: Mounting panels flat?

    Starting with the battery:
    • 1,340 AH * 59 volts charging * 1/0.77 panel+controller deratings * 0.05 rate of charge = 5,132 Watt array Minimum
    • 1,340 AH * 59 volts charging * 1/0.77 panel+controller deratings * 0.10 rate of charge = 10,268 Watt array nominal
    • 1,340 AH * 59 volts charging * 1/0.77 panel+controller deratings * 0.13 rate of charge = 13,348 Watt array "cost effective" maximum

    If you are using 80% of the battery over night--Say 25% for day and night loads:
    • 1,340 AH * 0.25 used * 48 volts = 16,080 Watt*Hours = 16.1 kWH per day (not a small amount of energy)
    • 1,340 AH * 0.25 used * 48 volts * 1/0.52 system efficiency * 5.7 hours of sun (very sunny climate) = 5,425 Watt minimum array for 9 months of the year (no generator)

    So, at a first guess, yea, you should be looking at near a 5.5 kWatt array minimum would be a good investment.

    If you have "monsoons" that kill you for days/week or more at a time--You might want to revisit the generator and see if you can get it more fuel efficient (plus the larger array to limit generator run time during better, on average, weather/seasons).

    And, look at the big power users (A/C?) and possible electric cooking/hot water? Alternatives like GE Geosprings Heat Pump water heater, induction cook tops/ranges, wide mouth/cooking thermos for stews/soups, etc... And the old conversation themes of more insulation, double panel vinyl windows+low E glass, shading of building with plantings/screening, etc.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • backroadbackroad Solar Expert Posts: 185 ✭✭
    Re: Mounting panels flat?

    The 5,000 watt array was what I had figured on when I first bought the GB Battery, and now I wish I had gone larger when It was just a little more., I know, stinking thinking huh? We only use the window ac on rare occasions when the genset is on. genset is a 15K Hardy Perkins diesel that barely starts my air compressor when all other loads are diverted. Gas water heater. I have a brand new sundanzer chest freezer yet to be install to replace the other chest freezer. I have a thermostat controller for the old chest freezer to use it as a refrigerator but you know how wives are. Momma doesn't care fore the idea of a chest fridge.

    My plan is to keep plugging along on the upgrades ready to be installed. I had a knee replacement in March and having a spinal fusion the end of this week. Life is still great with better stuff to come.

    I do have a question about the Sundanzer freezer. It can be powered with either 12v or 24v. Would one be significantly better than the other. Both of my swamp coolers are current using 12 volt fans, but I understand they will still function well on 24 volt, but would need to be slowed down considerably. They do get noisy spinning on 24v. As I previously said, the plan for the second solar system is for the Sundanzer and the 2 coolers.
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Re: Mounting panels flat?
    backroad wrote: »
    I do have a question about the Sundanzer freezer. It can be powered with either 12v or 24v. Would one be significantly better than the other?

    Either is OK. Mostly it depends on the system voltage... if you have a 12 or 24 volt system, use what you have. They draw 4-5 amps at 12 volts and half of that at 24 volts, so voltage drop will not be too great at either voltage unless you have long thin wires between the battery and freezer.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • westbranchwestbranch Solar Expert Posts: 5,153 ✭✭✭✭
    Re: Mounting panels flat?
    backroad wrote: »
    We only use the window ac on rare occasions when the genset is on. genset is a 15K Hardy Perkins diesel that barely starts my air compressor when all other loads are diverted.

    I would look into the reason why it 'barely' starts on a 15Kw genset... It seems there is something amiss here... with that much power it should go like the wind...

    hth
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • backroadbackroad Solar Expert Posts: 185 ✭✭
    Re: Mounting panels flat?

    The air compressor is really on the large size even though the motor is only a 5 horse motor, even it's size is huge rated at 240 volt and 29 amps running and it's a capacitor start motor. My son is an electrician at our local copper mine with a vast knowlege with starting and motors. He did raise the parameters on the generator which did help. Originally when the compressor started it would flat shut the genset off. It's not running through the inverter whatsoever. When running the compressor, I flip the breaker off to the inverter/charger. This whole thing hasn't been anything major as I don't need the compressor all that often. Even considered downsizing the compressor.
  • westbranchwestbranch Solar Expert Posts: 5,153 ✭✭✭✭
    Re: Mounting panels flat?

    That is a brute! my old 230v 15 a 3 hp Crafstman got replaced with an older 6 cfm SpeedAire 20 gal. on 110v 15 amps that (seems to) sips power.. My 3000w Eu3000 doesn't even burp with it on ECO setting. Must be that motor??? or starting with a too high a tank pressure. Any way that could save you a bit of power and concern if changed out.

    hth
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • backroadbackroad Solar Expert Posts: 185 ✭✭
    Re: Mounting panels flat?

    Yes sir, a brute she is. I seem to always start it with zero pressure in the tank. Once it's started, it maintains greatly. tools used include a Coats 4040 tire machine, impact wrenches and die grinders. The compressor came out of a concrete batch plant and puts out about 25 cfm reliably..... Again, thankfully not needing to run often,
  • BB.BB. Super Moderators, Administrators Posts: 29,637 admin
    Re: Mounting panels flat?

    I have converted compressors to continuous run by adding a dump valved/controller (motor stays on, unloads to atmosphere when tank is full). Works well for running on limited AC input power--But 5 HP--Is going to still waste some fuel/energy on your power systems.

    Possibly a VFD (variable frequency drive) to add "soft start and/or a better pressure dump system (let compressor get to speed before closing dump valve) may help too.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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