Watts on Cloudy days

ZakarumeZakarume Solar Expert Posts: 143 ✭✭
Sorry for this Newb Question. If you have lets say 500 watts 24v panels on your roof. How many watts would you get? Panels are facing South and tilted at roughly 45 degrees.

Summer time?
Winter Time?
1460 Watts Solar @24v. 675 AH Battery Bank using 12 6v Trojan T-105. 1 Midnite Classic 150. 1500 Watt 24v Samlex Pure Sine Inverter

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Watts on Cloudy days
    Zakarume wrote: »
    Sorry for this Newb Question. If you have lets say 500 watts 24v panels on your roof. How many watts would you get? Panels are facing South and tilted at roughly 45 degrees.

    Summer time?
    Winter Time?

    Where? On what system?

    I can tell you that on average 500 Watts will put out 385 Watts most places in good sun.

    Panels do not perform the same everywhere. Latitude makes a big difference, especially when discussing angles. For example a 45 degree tilt at the Equator would be bad for output. Up here it would be good half the year, bad Summer & Winter.

    Output under cloudy skies? Define "cloudy". That can be anywhere from a few puffy white blobs of cotton to solid gray paste.

    One thing is certain; panel output drops off severely from changes in insolation whether due to sun angle or intensity. If you are in a location where "cloudy" figures in the forecast often it would be wise to maximize your array size.
  • BB.BB. Super Moderators, Administrators Posts: 29,637 admin
    Re: Watts on Cloudy days

    Using PV Watts for Springfield Mo, fixed array, south, 45 degrees, 500 Watts, 52% efficiency for Off Grid 120 VAC system (note, I had to do a 5kWatt system and put in the decimal point divide by 10 -- PV Watts only goes as small as 1kWatt):




    Month
    Solar Radiation
    (kWh/m 2/day)
    AC Energy
    (kWh)


    1
    4.10
    33.2



    2
    4.27
    30.9



    3
    5.15
    39.7



    4
    5.37
    38.6



    5
    5.40
    38.5



    6
    5.42
    35.9



    7
    5.56
    38.1



    8
    5.75
    39.7



    9
    5.36
    37.1



    10
    5.03
    37.2



    11
    3.97
    29.6



    12
    3.44
    26.9



    Year
    4.90
    425.3



    That is 26 to 40 kWH (or 26,00 to 40,000 WH per month, divide by days in a month for daily production). Or basically around 1 to 1.3 kWH per day or so.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • H2SO4_guyH2SO4_guy Solar Expert Posts: 213 ✭✭✭
    Re: Watts on Cloudy days

    I am in Missouri and have been getting 15 to 23% of panel rating. There have been 2 mostly sunny days in the last 16. I had to quit heating with electricity and pare down the electrical usage, but have not had to run a generator. It has been cheaper to heat with propane than to run a gas generator. Today at 3 PM it has been cloudy and 33% of panel rating has been harvested. So in your case if you had 500 watts of panels then about 1.65 kwh. I tried to way over panel, but wish I had put up the other 3k of panels now! I would have gotten about 1 more kwh of power today so far.

    When we had 1 good day of sun a 4.7k array put out 4.9 times panel rating. I thought that was great for December in Missouri. They are even mismatched panels too.

    Good luck and let us know how it turns out,

    Skip
    12K asst panels charging through Midnite Classic 150's, powering Exeltechs and Outback VFX-3648 inverter at 12 and 48 volts.  2080 AH @ 48 VDC of Panasonic Stationary batteries (2 strings of 1040 AH each) purchased for slightly over scrap, installed August 2013.  Outback PSX-240X for 220 volt duties.  No genny usage since 2014. 
  • mike95490mike95490 Solar Expert Posts: 8,429 ✭✭✭✭✭
    Re: Watts on Cloudy days

    Ha. watts on cloudy days. I get less then 10% of nameplate. With the weather the last 3 weeks, some really bad days, I got a whopping 1,100 wh from 5Kw of PV. Same time last year, but clear skys, I got about 12,000wh . This year, I'm burning red diesel (no road tax) in the generator for about 3 or 4 hours a day.
    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 ,

  • PhotowhitPhotowhit Solar Expert Posts: 5,011 ✭✭✭✭
    Re: Watts on Cloudy days

    I don't use much during the winter, but this winter has been particularly bad for solar. Harvest varies, I might get 1-2kwh, on somewhat cloudy days. We''ve had negative days even when just running the fridge in a very cool room. Home Sunday after a couple weeks in Florida... had a couple10 inch rain day yesterday... sometimes you just have to wait out the sun...lol.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Watts on Cloudy days

    Heavy overcast gives me next to nothing, or nothing. Thinner cloud cover can give me maybe 70%. Depends on thickness of cloud cover. No easy answer. If the sky is covered with thin bright clouds I can get good output, and if there happens to be an opening through which the sun shines, that light is added to what's already coming from the clouds and the output goes way up.
  • ZakarumeZakarume Solar Expert Posts: 143 ✭✭
    Re: Watts on Cloudy days

    I quess what i meant to say is Heavy Overcast clouds with rain here and there. I am still working to finish on solar but will eventually have 960 watts of solar. As far as what Cariboocoot, mine is going to be a fixed array. I read that in my area roughly 30 degree in summer and around 55 degree winter is best. since it is a fixed array was going with 45 degree year round
    1460 Watts Solar @24v. 675 AH Battery Bank using 12 6v Trojan T-105. 1 Midnite Classic 150. 1500 Watt 24v Samlex Pure Sine Inverter
  • xsnrgxsnrg Registered Users Posts: 10
    Re: Watts on Cloudy days

    Instantaneous numbers, for same equipment, angle, two days apart recently (solstice), same MPPT program, bulk function: I have 3x100w panels in series that I have seen 12-15w from. A good day sees 210-220. Instantaneous numbers don't tell the whole story of course, but is easy enough to see that thick cloud cover all day is not much fun. (12 or so of the last 14 days here at Latitude ~41)
  • mike95490mike95490 Solar Expert Posts: 8,429 ✭✭✭✭✭
    Re: Watts on Cloudy days

    Heres my daily harvest in watts for the last couple weeks.
    2181 2615 2226 2243 1494 340 1119 2245 2323 1746 292 2442 1906 598 336

    Some days are just not worth getting up for !
    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 ,

  • 2twisty2twisty Solar Expert Posts: 199 ✭✭✭
    Re: Watts on Cloudy days

    Yeah, the last two days out here in the West Texas desert have really sucked for solar. We've had thick overcast. My 2.1kW array was yielding about 300W today. Yay.

    Thank God for generators!
  • verdigoverdigo Solar Expert Posts: 428 ✭✭
    Re: Watts on Cloudy days

    This is my first winter worrying about batteries. I have never kept track of cloudy vs sunny days, but I sure didn't think Kentucky was this cloudy in the winter. I'll be doubling my array in the coming year given time and resources work in my favor.
  • PhotowhitPhotowhit Solar Expert Posts: 5,011 ✭✭✭✭
    Re: Watts on Cloudy days

    My 14-15th winter watching and this fall has been the worse I can recall in Missouri. That said, I'm enjoying getting back home and a sunny day today and pretty good week ahead! Bread maker going, chili in the crock pot and laundry in the washer, even ran my wheat grinder...
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
  • verdigoverdigo Solar Expert Posts: 428 ✭✭
    Re: Watts on Cloudy days

    Yep. The coming week doesn't look so bad but my faith in the weather channel has been challenged of late. Been relying on accu window more than usual.
  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Watts on Cloudy days

    Checked a while ago, heavy overcast and raining. One of my 1000 watt arrays was putting out the huge amount of 300 mw That's nearly 1/3 of a single watt. not bad for a 1000 watt array. On the other hand it's getting darker out there, so I'm sure it's down to zero by now. Oh well, tomorrow is another day. :p
  • solar_davesolar_dave Solar Expert Posts: 2,344 ✭✭✭✭
    Re: Watts on Cloudy days
    Checked a while ago, heavy overcast and raining. One of my 1000 watt arrays was putting out the huge amount of 300 mw That's nearly 1/3 of a single watt. not bad for a 1000 watt array. On the other hand it's getting darker out there, so I'm sure it's down to zero by now. Oh well, tomorrow is another day. :p

    Man that has to be tough to live with.

    This looks like a pretty good day here with 30kWh since dawn and the array is producing 8250 watts now at 1PM.
  • ZakarumeZakarume Solar Expert Posts: 143 ✭✭
    Re: Watts on Cloudy days

    This Missouri weather is so unpredictable. Had a couple of days this month and was producing ok wattage. Not completely done with the Array. Need to get 4 panels in place (960 watts). And now thinking when i remove the 4 - 100 watt renogy panels (400 watts). 2 going to camper. I am thinking about putting the other 2 in series on other side of home and running to a PWM charge controller to capture morning sun for more charging. It wont be much, but every bit helps. Suppose to be sunny here tomorrow. Now i have another question? What is your opinion on the Davis Vantage Vue weather station?. Been thinking about getting one
    1460 Watts Solar @24v. 675 AH Battery Bank using 12 6v Trojan T-105. 1 Midnite Classic 150. 1500 Watt 24v Samlex Pure Sine Inverter
  • xsnrgxsnrg Registered Users Posts: 10
    Re: Watts on Cloudy days

    Davis makes great equipment. I have a Vantage Pro 2 station that has been online many years now. Their solar radiation sensor is on my short list. My station on WU is KIAPOLKC2
  • mike95490mike95490 Solar Expert Posts: 8,429 ✭✭✭✭✭
    Re: Watts on Cloudy days

    I've discovered that the US weather service that PV watts bases it's data on, has incomplete coverage. While it reads automated data from the local airport, that is not used in the forecasts. This last week, has been listed as "sunny", has been foggy AM's till 1pm. But that forecast is not for MY zip code, it's for a town 20 miles away, 1,000' lower, and on the other side of a mountain. If you are planning a system in a small town, or a remote area, the NWS does not always have data for your specific area.
    :cry:
    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 ,

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