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Re: Type 16a


I wanted to see the type 16a output compared to weather data input. So with iisibat I made a simple model with a type 9d data reader, the rad sol processor type 16a and the common output types (see the iisibat file attached).
The weather data I used contains mean monthly hour values, so in a month each day has the same value of radiation at the same hour.
Tilted surface mode is =2
shift in solar time = 7.5
latitude = 44.5
orientation = 90° (poiting west)
Site: Milan
from my graf, along every month I see the Tot and the Beam Rad on Surface 1 to vary while the radiation input is constant...It actually makes sense since weather data are mean values but I don't understand their trends:
referring to the 2nd part of thy year, Tot and Beam Rad grows along every month when acutally daylight is decreesing, so I would expect higher values at the beginning of every month, not at the end! I found a similar trend (but opposite, of course) in the first part of the year (I didn't include it in the file attached) even though in a less evident way...
Another thing concerning my simulation: as you can see in the months of september and october Tot and Beam Radiations are higher than their input at the end of the month!! how is it possible??? (At least this doesn't occur in the first part of the year)

Sorry for my belated answer.
You seem to have a timing problem between your data file and the way you configure Type16. The most obvious sign of that is the computed beam radiation, which is always 0 in the morning.
One possible reason is the shift angle. If your data file is in local standard time (which I couldn't check), it seems to me that:
LST = -15 (standard meridian for UTC+1, 15° East i.e. -15°)
LLoc = -9 (longitude... Approximatively) 9° East, i.e. -9° West
SHIFT = LST - LLoc = -15 -(-9) = -6
You have +7.5 (again if your data file uses another time convention it may be OK)

Another reason might be the fact that you don't start the simulation at hour 1. Sometimes the data reader gets confused and does not skip the appropriate number of lines, especially if you have header lines that you did not specify.

In both cases, I always recommend to plot the extraterrestrial radiation computed by Type16 and the global horizontal directly from the data file. When you take a look at those two plots, you will immediately see if there is a time shift problem (e.g. calculated sunrise later/earlier than the one in the data file, etc.)

I hope this helps,

Michaël Kummert


Michaël Kummert

Solar Energy Laboratory - University of Wisconsin-Madison
1303 Engr Res Bldg, 1500 Engineering Drive
Madison, WI 53706

Tel: +1 (608) 263-1589
Fax: +1 (608) 262-8464
E-mail: kummert@xxxxxxxxxxxxx

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