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My array's production has been poor this last week. I've been at work during the day, indoors, many miles away and can't speak to the weather conditions that might explain it. So, I'd like to lookup somewhere either by day or even by hour the historical weather conditions (sunny, partly cloudy, cloudy, etc) to correlate to my production numbers. I'd really like to download a range of dates for my zipcode, because I'm not interested in interpreting a bunch of fluffy websites.... I've tried to find this data and failed. Anyone else found this?
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I don't know of anything like that. However, what is your definition of poor performance? There was a recent thread on the same topic. This time of year you should expect to see your output dropping, perhaps by more than you thought.CS6P-260P/SE3000 - http://tiny.cc/ed5ozx -
National Weather Service has that. Unfortunately they don't indicate percent of insolation, but do describe sky conditions.
Here is my local report- just put in your zip code to get yours:
KLGB weather past 3 daysComment
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I use PV Output to see how my system is performing compared to others of a similar size in my area.
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What do you think your output should be this time of year ? Without that info you are wasting your time.
You will need to know what your max. clear day outout is estimated to be before you can know if your system is underperforming. One very approx. and therefore not very accurate method to get that is to run PVWatts using the hourly output option and compare PVWatts output for a clear day date that matchers a clear day date for you. Takes a bit of hit and miss to get the same PVWatts clear day and an actual clear day on the same/close dates.
A better, more practical and probably more accurate way to get more and better information is as Slopoke suggests - get several sites from PVoutput.org that are near you, find one/several with the same/close az./tilt and compare daily output/nameplate Watt. If reasonably close, they should track one another to a pretty fair degree and if performing nominally yours ought to probably do the same. I the local weather conditions do not change too rapidly as f(topography,local weather) I'd guess something within 10-20 miles of you location would be useful to check out.Comment
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I remembered that there is data available for at least a few places in the country. Maybe one is close to the OP.
CS6P-260P/SE3000 - http://tiny.cc/ed5ozxComment
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Very interesting... Is it possible it's this easy? There is a column titled solar percent possible... If it's that simple you can see this has been a bad week...
Code:Time . . . . . . Temp. Dew Relative Wind Wind Solar Solar Precip Quality . . . . . . . . . . . . Point Humidity DirectionSpeed Radiation Pct 1 hour Control (PST) . . . . . . . . . (f) (f) (%) (mph) (W/m*m) of psbl (inches) 13 Nov 8:00 pm PST 60 57 92 SE 2G03 0 -- 0.00 13 Nov 7:00 pm PST 60 56 88 SSW 2G04 0 -- 0.00 13 Nov 6:00 pm PST 61 55 81 W 2G04 0 -- 0.00 13 Nov 5:00 pm PST 61 55 80 W 5G08 13 8% 0.00 13 Nov 4:00 pm PST 63 55 75 WSW 6G09 161 35% 0.00 13 Nov 3:00 pm PST 63 53 69 WSW 6G10 257 37% 0.00 13 Nov 2:00 pm PST 64 52 66 WSW 8G13 395 45% 0.00 13 Nov 1:00 pm PST 65 52 63 WNW 7G10 274 28% 0.00 13 Nov 12:00 pm PST 66 50 57 NW 3G06 298 31% 0.00 13 Nov 11:00 am PST 64 50 60 WNW 3G05 317 36% 0.00 13 Nov 10:00 am PST 63 50 62 NNW 2G05 418 57% 0.00 13 Nov 9:00 am PST 59 50 72 S 3G04 297 59% 0.00 13 Nov 8:00 am PST 53 48 83 SE 3G04 107 49% 0.00 13 Nov 7:00 am PST 49 46 89 SE 2G04 9 -- 0.00 13 Nov 6:00 am PST 49 46 89 ESE 3G05 0 -- 0.00 13 Nov 5:00 am PST 50 47 88 ESE 3G05 0 -- 0.00 13 Nov 4:00 am PST 51 47 87 SE 3G05 0 -- 0.00 13 Nov 3:00 am PST 52 48 86 SE 3G05 0 -- 0.00 13 Nov 2:00 am PST 51 47 85 ESE 2G04 0 -- 0.00 13 Nov 1:00 am PST 51 47 86 ESE 3G05 0 -- 0.00 13 Nov 12:00 am PST 52 47 84 SE 2G11 0 -- 0.00 12 Nov 11:00 pm PST 53 48 83 SE 4G05 0 -- 0.00 12 Nov 10:00 pm PST 53 48 81 ESE 2G04 0 -- 0.00 12 Nov 9:00 pm PST 55 48 79 SE 3G04 0 -- 0.00 12 Nov 8:00 pm PST 56 49 77 ESE 3G04 0 -- 0.00 12 Nov 7:00 pm PST 57 49 75 SE 2G02 0 -- 0.00 12 Nov 6:00 pm PST 58 49 73 WNW 4G06 0 -- 0.00 12 Nov 5:00 pm PST 60 50 68 W 6G09 43 25% 0.00 12 Nov 4:00 pm PST 62 49 63 W 9G13 213 46% 0.00 12 Nov 3:00 pm PST 64 49 58 W 9G12 384 54% 0.00 12 Nov 2:00 pm PST 66 49 55 WSW 8G12 518 59% 0.00 12 Nov 1:00 pm PST 65 49 56 WSW 6G11 602 62% 0.00 12 Nov 12:00 pm PST 64 49 57 WSW 7G10 658 67% 0.00 12 Nov 11:00 am PST 64 47 55 W 4G07 468 52% 0.00 12 Nov 10:00 am PST 62 48 60 W 4G06 251 34% 0.00 12 Nov 9:00 am PST 61 50 68 WNW 4G06 200 39% 0.00 12 Nov 8:00 am PST 60 52 76 SSW 2G04 105 47% 0.00 12 Nov 7:00 am PST 58 53 83 SE 1G03 10 -- 0.00 12 Nov 6:00 am PST 58 53 83 SW 2G03 0 -- 0.00 12 Nov 5:00 am PST 59 53 83 S 2G04 0 -- 0.00 12 Nov 4:00 am PST 59 54 84 SW 2G04 0 -- 0.00 12 Nov 3:00 am PST 59 54 84 WNW 3G05 0 -- 0.00 12 Nov 2:00 am PST 59 54 84 W 3G05 0 -- 0.00 12 Nov 1:00 am PST 59 53 81 WSW 3G04 0 -- 0.00 12 Nov 12:00 am PST 59 52 77 W 1G04 0 -- 0.00 11 Nov 11:00 pm PST 59 51 75 NW 2G02 0 -- 0.00 11 Nov 10:00 pm PST 59 51 75 SSW 2G04 0 -- 0.00 11 Nov 9:00 pm PST 60 52 75 WNW 3G05 0 -- 0.00 11 Nov 8:00 pm PST 60 51 73 WNW 3G06 0 -- 0.00 11 Nov 7:00 pm PST 60 51 73 WNW 4G06 0 -- 0.00 11 Nov 6:00 pm PST 60 52 75 WNW 6G08 0 -- 0.00 11 Nov 5:00 pm PST 61 53 74 WNW 7G08 7 4% 0.00 11 Nov 4:00 pm PST 63 52 68 W 5G07 77 16% 0.00 11 Nov 3:00 pm PST 63 53 69 WSW 6G09 213 30% 0.00 11 Nov 2:00 pm PST 63 53 70 WSW 7G10 200 23% 0.00 11 Nov 1:00 pm PST 62 53 71 W 7G10 261 27% 0.00 11 Nov 12:00 pm PST 62 53 71 W 6G10 161 16% 0.00 11 Nov 11:00 am PST 63 52 69 W 4G06 112 12% 0.00 11 Nov 10:00 am PST 62 53 70 S 3G06 178 24% 0.00 11 Nov 9:00 am PST 61 51 70 ESE 5G08 117 23% 0.00 11 Nov 8:00 am PST 60 51 72 SE 3G04 29 13% 0.00 11 Nov 7:00 am PST 60 51 72 ENE 2G20 0 -- 0.00 11 Nov 6:00 am PST 60 51 72 SSE 2G03 0 -- 0.00 11 Nov 5:00 am PST 60 50 70 SW 2G03 0 -- 0.00 11 Nov 4:00 am PST 60 50 69 SE 2G04 0 -- 0.00 11 Nov 3:00 am PST 60 51 72 ESE 3G04 0 -- 0.00 11 Nov 2:00 am PST 60 52 74 SE 2G04 0 -- 0.00 11 Nov 1:00 am PST 60 52 76 SSE 3G04 0 -- 0.00 11 Nov 12:00 am PST 60 53 78 SE 3G04 0 -- 0.00 10 Nov 11:00 pm PST 59 53 80 NE 3G05 0 -- 0.00 10 Nov 10:00 pm PST 59 53 81 N 1G03 0 -- 0.00 10 Nov 9:00 pm PST 59 53 82 N 2G04 0 -- 0.00 10 Nov 8:00 pm PST 58 53 83 NW 3G04 0 -- 0.00 10 Nov 7:00 pm PST 59 53 82 NNW 3G05 0 -- 0.00 10 Nov 6:00 pm PST 59 53 80 WNW 4G06 0 -- 0.00 10 Nov 5:00 pm PST 62 54 75 W 6G08 42 23% 0.00 10 Nov 4:00 pm PST 64 54 70 W 6G10 207 44% 0.00 10 Nov 3:00 pm PST 65 54 69 WNW 8G11 382 53% 0.00 10 Nov 2:00 pm PST 66 53 64 WNW 9G11 518 58% 0.00 10 Nov 1:00 pm PST 66 53 61 WNW 7G10 456 46% 0.00 10 Nov 12:00 pm PST 67 52 58 S 5G09 579 59% 0.00 10 Nov 11:00 am PST 65 51 62 S 6G10 568 63% 0.00 10 Nov 10:00 am PST 62 52 68 SSE 5G10 441 59% 0.00 10 Nov 9:00 am PST 60 52 75 ESE 5G08 128 25% 0.00 10 Nov 8:00 am PST 58 51 78 ESE 5G09 50 22% 0.00 10 Nov 7:00 am PST 57 52 83 ENE 4G06 3 -- 0.00 10 Nov 6:00 am PST 56 53 87 NE 4G06 0 -- 0.00 10 Nov 5:00 am PST 55 53 91 ENE 3G04 0 -- 0.00 10 Nov 4:00 am PST 56 54 92 E 3G05 0 -- 0.00 10 Nov 3:00 am PST 56 54 94 E 2G04 0 -- 0.00 10 Nov 2:00 am PST 55 54 95 NE 2G04 0 -- 0.00 10 Nov 1:00 am PST 55 54 95 ENE 2G05 0 -- 0.00 10 Nov 12:00 am PST 56 55 95 SE 2G03 0 -- 0.00 09 Nov 11:00 pm PST 57 55 95 SE 3G06 0 -- 0.00 09 Nov 10:00 pm PST 57 56 94 WNW 2G04 0 -- 0.00 09 Nov 9:00 pm PST 58 56 94 NW 3G04 0 -- 0.00 09 Nov 8:00 pm PST 58 56 91 NNW 2G05 0 -- 0.00 09 Nov 7:00 pm PST 60 56 87 WNW 2G04 0 -- 0.00 09 Nov 6:00 pm PST 62 56 80 NNW 3G05 0 -- 0.00 09 Nov 5:00 pm PST 66 56 69 NNW 5G08 54 29% 0.00 09 Nov 4:00 pm PST 70 56 63 NNW 5G08 232 48% 0.00 09 Nov 3:00 pm PST 73 58 60 NW 7G09 403 56% 0.00 09 Nov 2:00 pm PST 74 58 56 WNW 7G09 537 60% 0.00 09 Nov 1:00 pm PST 76 53 44 NW 7G10 626 63% 0.00 09 Nov 12:00 pm PST 76 49 39 NNW 5G06 653 66% 0.00 09 Nov 11:00 am PST 73 47 40 NNW 4G06 607 66% 0.00 09 Nov 10:00 am PST 71 43 36 NW 3G04 507 67% 0.00 09 Nov 9:00 am PST 68 40 36 S 2G04 335 64% 0.00 09 Nov 8:00 am PST 59 38 45 SE 3G05 137 58% 0.00 09 Nov 7:00 am PST 53 37 54 ESE 3G05 15 -- 0.00 09 Nov 6:00 am PST 53 37 54 ESE 3G05 0 -- 0.00 09 Nov 5:00 am PST 54 38 54 ESE 2G04 0 -- 0.00 09 Nov 4:00 am PST 55 37 51 ESE 2G04 0 -- 0.00 09 Nov 3:00 am PST 58 37 45 E 2G03 0 -- 0.00 09 Nov 2:00 am PST 58 38 47 ESE 3G04 0 -- 0.00 09 Nov 1:00 am PST 60 38 43 ESE 2G04 0 -- 0.00 09 Nov 12:00 am PST 62 38 41 SE 3G04 0 -- 0.00 08 Nov 11:00 pm PST 61 36 39 ESE 2G04 0 -- 0.00 08 Nov 10:00 pm PST 62 35 36 ESE 3G04 0 -- 0.00 08 Nov 9:00 pm PST 62 38 41 SE 2G03 0 -- 0.00 08 Nov 8:00 pm PST 64 42 45 ESE 2G04 0 -- 0.00 08 Nov 7:00 pm PST 67 49 54 SE 1G02 0 -- 0.00 08 Nov 6:00 pm PST 71 51 50 NNE 2G04 0 -- 0.00 08 Nov 5:00 pm PST 77 45 32 NW 3G05 54 28% 0.00 08 Nov 4:00 pm PST 78 46 32 NNW 6G08 239 49% 0.00 08 Nov 3:00 pm PST 80 49 34 NNW 7G08 413 57% 0.00 08 Nov 2:00 pm PST 81 51 35 NNW 7G10 550 61% 0.00 08 Nov 1:00 pm PST 85 50 29 WNW 7G09 636 64% 0.00 08 Nov 12:00 pm PST 89 30 12 NW 5G07 665 67% 0.00 08 Nov 11:00 am PST 88 25 10 ENE 4G07 617 67% 0.00 08 Nov 10:00 am PST 84 28 13 E 4G08 520 69% 0.00 08 Nov 9:00 am PST 77 33 20 S 3G04 345 66% 0.00 08 Nov 8:00 am PST 67 32 27 SSE 4G04 137 57% 0.00 08 Nov 7:00 am PST 63 30 29 SSE 5G06 17 -- 0.00 08 Nov 6:00 am PST 62 30 29 SSE 5G07 0 -- 0.00 08 Nov 5:00 am PST 62 31 31 SE 5G06 0 -- 0.00 08 Nov 4:00 am PST 64 30 28 SE 4G06 0 -- 0.00 08 Nov 3:00 am PST 62 31 31 SE 5G07 0 -- 0.00 08 Nov 2:00 am PST 61 34 36 SE 4G06 0 -- 0.00 08 Nov 1:00 am PST 64 33 32 SE 4G05 0 -- 0.00 08 Nov 12:00 am PST 65 33 31 ESE 3G05 0 -- 0.00 07 Nov 11:00 pm PST 66 34 30 SE 3G06 0 -- 0.00 07 Nov 10:00 pm PST 65 36 34 SE 4G07 0 -- 0.00 07 Nov 9:00 pm PST 65 34 31 SE 4G07 0 -- 0.00 07 Nov 8:00 pm PST 67 37 33 SE 3G06 0 -- 0.00 07 Nov 7:00 pm PST 69 43 40 ESE 2G04 0 -- 0.00 07 Nov 6:00 pm PST 71 47 41 ENE 2G04 0 -- 0.00 07 Nov 5:00 pm PST 76 43 31 NW 5G08 60 31% 0.00 07 Nov 4:00 pm PST 80 35 20 WNW 8G11 245 50% 0.00 07 Nov 3:00 pm PST 83 36 19 W 10G13 420 57% 0.00 07 Nov 2:00 pm PST 85 38 19 W 9G12 556 61% 0.00 07 Nov 1:00 pm PST 86 36 17 WNW 7G10 640 64% 0.00 07 Nov 12:00 pm PST 86 34 16 NW 6G09 662 66% 0.00 07 Nov 11:00 am PST 85 32 15 WSW 3G05 620 67% 0.00 07 Nov 10:00 am PST 81 32 17 SSE 5G07 518 68% 0.00 07 Nov 9:00 am PST 74 36 25 SE 4G06 344 65% 0.00 07 Nov 8:00 am PST 65 34 31 SE 4G06 137 56% 0.00 07 Nov 7:00 am PST 61 33 35 ESE 5G06 18 -- 0.00 07 Nov 6:00 am PST 60 33 35 SE 5G06 0 -- 0.00 07 Nov 5:00 am PST 63 31 30 SSE 4G06 0 -- 0.00 07 Nov 4:00 am PST 62 31 31 SE 5G08 0 -- 0.00 07 Nov 3:00 am PST 65 30 27 ESE 6G07 0 -- 0.00 07 Nov 2:00 am PST 63 31 30 ESE 4G06 0 -- 0.00 07 Nov 1:00 am PST 65 31 28 ESE 4G06 0 -- 0.00 07 Nov 12:00 am PST 65 31 28 SE 3G05 0 -- 0.00 06 Nov 11:00 pm PST 61 32 33 ESE 3G05 0 -- 0.00 06 Nov 10:00 pm PST 62 31 31 ESE 3G05 0 -- 0.00 06 Nov 9:00 pm PST 64 30 28 ESE 3G06 0 -- 0.00
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Upon further review, I pulled those numbers from now backward to Oct 31 when my array went live. Importing into Excel, I see the highest "Solar Radiation (W/m*m) was 680 and the highest "Solar Pct of psbl" was 69%. Over the course of 2 weeks, the percent of possible is lower than I'd have expected (highest was 69% of possible?)....anyone care to comment on those columns and what they REALLY mean?Comment
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Very good suggestions on this board, thank you! So now I used pvoutput.org and loaded my data and compared to someone in a nearby city...I feel better- my efficiency (kWh / kW size) is slightly better and it looks like cloudy/weather is what's driving me to some bad days. Cool info out there, thanks to all!
2014-11-14_121827.jpg
2014-11-14_122003.jpgComment
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It looks like for example, at noon there is 298W of sun hitting each square meter of
panel, which is about 31% of the potential 1000W. Of course your 20% efficient panels
will turn the 298 W of sun into 60 W of electricity and a lot of heat.
At 8am you're running 49%, but the sun angle then is only capable of 218W sun = 44W
of electricity. I presume the % is low because of clouds at that time. I don't see much
about that until you are an owner and discover it. So a system working fine won't put
out much under overcast. The % won't change, but more power can be had at minimum
cost by increasing the total panels while keeping the rest of the system the same. This
approach is easier on a ground mount with plenty of space. Bruce RoeComment
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Not sure if you are confused on the data I pasted, or if I'm confused by your answer....but the big list of data that shows "Solar Pct of psbl" is from the weather site and has nothing to do with my array, but rather the weather conditions in my zipcode. So I'm curious if 69% is the highest for the last 2 weeks, what that really means from a weather perspective? And, then what would it take to get the weather to 100%? Because over the course of the last 2 weeks I have definitely seen hours of sunshine and no clouds!Comment
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It is only the weather stations associated with Mesowest that report the pct psbl value. I've sent them an email requesting clarification, we'll see if they respond. I couldn't find anything on their website that adequately explained it.CS6P-260P/SE3000 - http://tiny.cc/ed5ozxComment
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While not doubting Insaneoctane's veracity for one second, I share his question(s). I'm not at all sure what those numbers mean or where they come from. I spent a # of years studying the solar resource and believe I know a bit about it. The terms used on that table are sort of like ones I've seen before but usually not those used by either the NWS, or NREL or solar researchers. For example, this time of year in S.CA, a clear day solar noon sun will produce a horizontal solar flux of something like ~ 630-650+ W/m^2. A south facing surface tilted at ~ 20 deg. to the horiz. will see a solar flux about 30% greater due to the smaller angle of incidence.
Over the last, say, month there have been many totally sunny days in So. CA that would normally be defined as close to "100% of possible sunshine" days or at least in the very high 90's. hence my confusion about what the col. on insaneoctane's data paste with the heading "solar pct of psbl" means. ~60+% makes no sense to me in that context.
That column could be referencing something similar to what is generally referred to as a "clearness index". The clearness index is commonly defined as the horizontal solar flux received at the earth's surface at any spot on the earth divided by the solar flux received by a surface parallel to the horizontal surface but located "just above" the top of the earth's atmosphere. That index can either use instantaneous values, or summed over a period of time, commonly over hours, days, months or years. It's pretty universally accepted as an understood reference to how "clear" or "sunny" or "dirty" or "cloudy", etc a particular atmosphere is.
A typical sea level, mid lat., solar noon "clear day" instantaneous value for a clearness index might be something like .65 to .75, depending on atmospheric conditions of moisture, pollution, dust, etc. A completely overcast day might have values for the same time as low as ~ .12-.15 or so. Locations with higher ground elevations will commonly have higher clearness indices because the sun doesn't pass through as much atmosphere and so doesn't get attenuated as much.
Depending mostly on clouds, crap in the air and time of day, and to a lesser extent on season, most clearness index values are between .15 and .80 max. Hourly, daily or longer values are time integrated or sampling averages of instantaneous values.
The clearness index concept has been around for a long time, probably more than 60 years and is part of what is used when NREL came up with the TMYs. The TMYs are what PVWatts, SAM and most other solar estimating tools use to estimate the solar resource which is needed prior to system performance estimates. It's a long story.
In any case, looks like Slopoke's suggested solution path using PVoutput.org bore fruit.Comment
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It took a little bit of digging, but the folks at NOAA were helpful in explaining the "solar pct of psbl" value that we questioned.
The short version is that the value is the measured solar radiation as a percentage of the max possible radiation for that location, on a horizontal plane. The technique used to determine the max possible radiation is partially based on PALTRIDGE AND PLATT 1976, using 1370 W/m2 as the extra-terrestial irradiance constant that is adjusted by determining the sun's position first in ecliptic coordinates (based on the julian date with an eccentricity correction factor), then equatorial coordinates (using a fixed 23.5 deg obliquity of the ecliptic), and finally horizontal coordinates (based on the latitude / longitude of the weather station). No corrections for refraction are made.
The julian date and other solar position calculations are somewhat simpler than those used by PVWatts (based on Michalsky 1988), although I do not know enough about the strengths and weaknesses of each model to comment on the significance of the difference. The sky model used by PVWatts (Perez 1990) extends its estimate to the solar potential at a spot on earth's surface, while NWS calculation is strictly extra-terrestial in its estimation of solar potential, leading to a typical pct possible solidly less than 100%.
Each value in the table represents the 1 hr moving average, with the maximum possible radiation calculated backwards every 10 minutes from the time of measurement. Presumably, the measured radiation column also represents a similar rolling 1 hr average, although I did not ask about it.
TL;DR
J.P.M.'s guess looks right, +/- a few calculation details.Last edited by sensij; 11-19-2014, 01:09 PM. Reason: Removed incorrect understanding of measurement plane.CS6P-260P/SE3000 - http://tiny.cc/ed5ozxComment
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