'Clearness index of the best clear daysis very high' problem

[Solarian]

Hi,

I have a Ktcc value problem. As you see the attachment value is starting from 1.6 . I guess it should be around 1.1 . Attach file is for first half of 2017 and from meteocontrol datalogger. I can not understand why ktcc is very high in my ASCII datas. Could you please give me an advice regarding problem?

Thanks

BR

Onur Gunes

problem screen

[André Mermoud]

This means that your data are not correct.

It could be a problem of units, or more probably the calibration of the solarimeter.

[jorgelbachiller]

Hi,

I have the same problem with the clearness index and I have check the calibration and the units.

This data come from a wheather station which is weekly maintenance because we are alse checking the soiling on syte project. I have import this data asPVsyst standard format. (GHI and temperature)

The weather station has two horizontal pyranometers and other one on the inclined plane. Moreover, I have 2 panel which are checking the soiling, one photo cell. All of the have a normal range of irradiance.

[André Mermoud]

The clear day model is well established, and represents thre real data with an accuracy of 2 to 3% (depending on the Linke coefficient).

If you have measured data far over these values (daily sums), either you are not using the correct solar geometry (the latitude or altitude is incorrect), or your data are not correct.

I can't see any other possibility. This is physically impossible.

NB: It is possible to measure temporarily high irradiances, up to 1300 or even 1500 W/m2 perpendicularly to the sun. This is due to a bright sun cumulated with a reflexion on a neighbour cloud. But these are transitory phenomenons, during some few seconds or minutes. Never a full day.

[Pauline Deforche]

Hi,

 

I'm having the same issue with the Ktcc value when I'm inserting my own weather data file. (The value Ktcc starts at 1.8.) When I compare the weather profile with one from PVGIS (a TMY profile from the same location), my profile seems to align with reality in terms of magnitude and shape. Does anyone have an advice on how to resolve this issue?