Solar irradiance statistics (sunshine hitting the ground!)

lasitter

So there's lots of information about the amount of sunlight reaching the upper atmosphere, but I'm drawing a blank on statistics relative to the amount of sunlight reaching the ground (through cloud cover) at a given weather reporting station for a given day. I'd like to find this information for anywhere near me so that I can compare year over year available sunlight for a given month so I can know if my output has declined because of aging or growth of additional vegetation. Any help in finding a resource for this info would be great.

BB.

Weather Underground has lots of information and they even support personal weather stations (which can have solar energy sensors):

https://www.wunderground.com/pws/overview

Although, I could not find any historical solar irradiance data even though some weather stations do support.

And there is the old US Government data sets:

https://www.ncdc.noaa.gov/cdo-web/datasets 

And this site may give you exactly what you are looking for:

https://photovoltaic-software.com/principle-ressources/how-get-solar-radiation-data-world-free

In general, if you are debugging your system, you could look at the Imp-actual of the array--From what I have seen, Imp-array should range from 50% to 100% of rated value (assuming this is a GT inverter installation where 100% of "available" solar energy is transferred to the AC mains. If you see less than 50% of rated Imp-array on a good day around solar noon--I would suspect that you have an array/wiring/GT inverter issue.

If you have two or more parallel strings--Measure the current for each string. In general, the strings should match within 10% or better Iarray...

If you have an off grid / battery based system--That complicates the measurements/estimates a lot... The battery bank your daily loads are a huge influence in actual current/voltage of the array.

Here is a nice little table that shows High/Low/Average solar insolation for various cities--Shows what the "range" of yearly harvest variability can be over the long term:

https://www.altestore.com/howto/solar-insolation-data-usa-cities-a35/

-Bill

lasitter

BB: Thanks. What I'm really looking for is something like, July 2018 vs July 2019, amount of sunlight reaching the ground, so I could adjust for months that were more or less sunny / cloudy.