I was trying to calculate POA value at a solar plant for my Data Science project. I need to get the foretasted POA value up to next two days. I just have seen that their is a python tool called pvlib; which gives the POA value if I give inputs timezone, latitude, longitude, date, tilt and surface azimuth angle. Here is the code to get GHI and POA values in a time-series format of a day. But if I set the date from a very long future like from 2053, then still it gives me output. I think POA value depends on the weather data like Solar Radiation etc. Obviously we can not forecast weather after such long time. Then still why it gives any output. My background is computer science and Mathematics, have almost no knowledge in this domain, so may be my question may not be sound well researched.

Also it would be extremely helpful to me if I get exact formulation to calculate POA from timezone, latitude, longitude, date, solar radiation, tilt and surface azimuth angle or API link to get historical POA and forecasted POA value.

1 Answer 1


pvlib gives POA for clear-sky condition only; does not include any weather data for this estimation, uses only plant location, time and plant configuration. Clear sky POA is not same as actual POA.

  • A very good observation! Something also to note: weather service business isn't an exactly free business, the data you use must be paid for. If you haven't paid for weather data, chances are you don't have the weather data in the first place. There are today some exceptions such as GFS but it is not the best of weather models. ECMWF, one of the best models, is moving towards an Open Data model but as far as I know the data isn't open yet.
    – juhist
    Jun 30, 2023 at 17:45

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