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  • Winter solstice efficiency

    Greetings from Longmont Colorado.
    The winter solstice is upon us today. More sunshine starting tomorrow!

    I installed a 13kW system last June and got about 80kWh/day in the summertime, or about 6.1Wh/kW efficiency. Just today I'm getting a lowly 2.8kWh/kW.

    What kind of efficiency are you guys getting?

  • #2
    Efficiency may be the wrong word, however, did you have a good sunny day today, we had clouds here in NJ.
    Yesterday was much more sunny.
    My 5.1KW system generated 19.5 kwH yesterday.
    Using your math put's me at 3.8, weekly average will be lower.

    I also doubt my orientation, latitude or tilt matches yours, so comparisons are not very helpful, right?

    Dennis
    SE5000 18 each SW185

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    • #3
      Since I'm off grid my 5000 watt system this sunny day went into absorb at 10:30 and I ended up with 11.8 kwh today.

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      • #4
        What does PVWatts estimate you might get for a sunny day given your location and orientation ? Use 10 % system losses and the hourly output option. Look for a sunny day around the winter solstice and stick a fork in it.

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        • #5
          Produced 54.865 kWh today on winter solstice. 17.28 kW system producing at 3.175 efficiency. Partly cloudy.

          All time record 129.966 kWh on 4/4/2015 with efficiency of 7.521 on that date. Panels are now over 4 years old.....probably never see that level of production again.

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          • #6
            I stuck a fork in it for you.

            Depending on your orientation - if mostly south and ~ 20 deg. tilt w/ no shade, a clear day might get you ~ 3.5 - 4.0 kWh/ S.T.C kW per day around the winter solstice. See PVWatts hourly output est. for Longmont CA data for 12/22.

            BTW, same orientation est. output for a clear 06/20 ~~ = 6.5 kWh/S.T.C. kW per day.

            What's your orientation ?

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            • #7
              Today is a bad day to use as a reference point because it's one of the few cloudy days. I produced 9.97 kWh; yesterday was a bright cold day; I produced 32.39 kWh.

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              • #8
                Originally posted by twelveparsex View Post
                Today is a bad day to use as a reference point because it's one of the few cloudy days. I produced 9.97 kWh; yesterday was a bright cold day; I produced 32.39 kWh.
                Then don't use it. It's pretty useless anyway. Where are you located, what is your array orientation, and what does PVWatts estimate output to be for a sunny day around this time of year ?

                Still a guess, but with reasonably accurate input, that's probably not a bad 1st approx. of clear day output for a day close to the chosen PVWatts day.

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                • #9
                  PVWatts indicates I should be getting about 3.7kWh/kW this time of year. Yesterday was not without some clouds here so I guess my 2.8kWh/kW is probably reasonable. I'll have to check it again when we get a cloudless day. Thanks JP for the PVWatts tip. I've used it before but never with the "hourly" granularity.

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                  • #10
                    Originally posted by DaveDE2 View Post
                    PVWatts indicates I should be getting about 3.7kWh/kW this time of year. Yesterday was not without some clouds here so I guess my 2.8kWh/kW is probably reasonable. I'll have to check it again when we get a cloudless day. Thanks JP for the PVWatts tip. I've used it before but never with the "hourly" granularity.
                    FWIW, you are most welcome. It's still little better than a dart throw.

                    Like our service ? Tell your friends.

                    Sometimes it's fun to find new uses for things not intended (or at least not talked about) by the originators.

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                    • #11
                      I have two arrays roughly the same wattage about 2 KW each. One is on a roof and other is pole mount. The roof mount is on a 8/12 pitch roof while the pole mount is current adjusted for 30 degrees off vertical. There is snow on the ground so the pole mount is getting a boost in irradiance as the snow reflects sun up on the panels. The roof array does not see that boost from snow. Coincidently the roof array had solid sheet of snow on it. I got my roof rake out and broke the bottom lip of the snow off and the snow slid off in sheets so the array was clear. I went down to my inverters around noon and the roof array was putting out around 500 watts on the inverter and the pole mount was putting out around 1450 watts. Any power I get off the roof fro the next three months is usually a bonus as they usually have snow on them

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                      • #12
                        Originally posted by peakbagger View Post
                        I have two arrays roughly the same wattage about 2 KW each. One is on a roof and other is pole mount. The roof mount is on a 8/12 pitch roof while the pole mount is current adjusted for 30 degrees off vertical. There is snow on the ground so the pole mount is getting a boost in irradiance as the snow reflects sun up on the panels. The roof array does not see that boost from snow. Coincidently the roof array had solid sheet of snow on it. I got my roof rake out and broke the bottom lip of the snow off and the snow slid off in sheets so the array was clear. I went down to my inverters around noon and the roof array was putting out around 500 watts on the inverter and the pole mount was putting out around 1450 watts. Any power I get off the roof fro the next three months is usually a bonus as they usually have snow on them
                        What are the azimuth's ? Something seems odd. The 8/12 pitch is ~ 33.7 deg. tilt and thus not that far off a 30 deg. tilt. To my experience it's not likely that any boost from snow would increase output by 1450/500 = 290 %. I've seen and estimated ~ 10-15 %. Additionally, the roof will still see some enhancement from the surroundings.

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                        • #13
                          Just had a completely cloudless day today and did 3.65kWh/kW efficiency. This agrees pretty well with PVWatts. So I guess my system is on par with what can be expected from a properly operating system. I'll check it again later in 4-6 months when things get more exciting.

                          DanS26 , that 7.521 number has got to be some sort of record. where are you and what is your set up?

                          Dave
                          Last edited by DaveDE2; 12-23-2016, 06:22 PM.

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                          • #14
                            Rain last couple days, some winter mix tonight. The diesel genset starts right up though.
                            Powerfab top of pole PV mount (2) | 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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                            • #15
                              Originally posted by Mike90250 View Post
                              Rain last couple days, some winter mix tonight. The diesel genset starts right up though.
                              Try to stay warm and dry Mike.

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