Dear Muhammad Ibrahim Munir,

Actually I am not clear about your question. Do you have GHI data and want to model it for prediction or what? What is the input and the output of the model that do you want?

May be you can search on the internet about decomposition model of solar radiation, there are so many version about it, it relate GHI with each components of it such as direct and diffuse radiation.

Here one example of it:

http://www.sciencedirect.com/science/article/pii/S1364032113005637

and here one of my paper about method to predict GHI from other meteorological data:

http://www.ijesd.org/papers/122-S017.pdf

Thanks.

Good morning.

The most common method is the one that you refer. But applying a model is not a trivial task since you have to have certain amount of inputs like albedo, water vapor, aod etc in a time resolution that fits to your data.

You may also try not to compare the exact values of the model with the measured ones. If you get the generic diurnal pattern of a clear sky day derived from the model, then you may just compare the pattern, the curvature of the data with the one from your model. That should give you a rough estimation of cloudless moments.

But all depend on your demands. If you need something more sophisticated you have to work a little bit more with the model estimations...

You can always check on the internet for novel research.

Hope that I helped you.

: )

Have a happy new year!

Melina.

Dear Muhammad,

have a look at

http://prod.sandia.gov/techlib/access-control.cgi/2012/122389.pdf

Cheers, Kees

@Stigter thank you so much for your insightful reference, I am reviewing it.

Dear Muhammad,

Could you please clarify your question? Are you looking for a clear sky model or a method to know the specific clear days during the year? The later cannot be absolutely predictable (for future purposes) since the clear days differ from year to year but the average number of these days for a specific location are averagely almost the same. The clearness index gives you an indication of how clear is a specific period of time, hourly, daily, or monthly depending on which clearness index. It  is defined as the ratio of the horizontal global irradiance to the corresponding irradiance available out of the atmosphere. However, you can find out the clear days from previously measured data if this is what you meant.

If you give more details about your question, it will be better to get more detailed answers.

Regards

Dear Khaled, thank you for your response. I am looking for a method to identify the specific clear days during the year. I do have the data for the daily extra terrestrial radiation as well as the data for the daily solar radiation so I believe I can find the daily clearness index. Also I am curious how to use the Daily Sunshine duration data which is available to me? Thank you so much for the help

One more thing, can you specify a method/procedure which is normally utilized to find out the ideal length of a day? So that I can use this ideal day length & compare it with the Sun shine duration data which I have to identify the clear days?

Obliged,

Ibrahim

 Dear Muhammad,

To identify the clear days during the year, the clearness index is the appropriate measure for that. To obtain the clearness index from measured data, the extra-terrestrial horizontal insolation is needed. So, using the calculated values of extraterrestrial horizontal insolation for any location and the measured global insolation on a horizontal surface for the same location, the clearness index for this location are determined. One of the clear-sky models is that described in Duffie and Beckman text book 'Solar Engineering of Thermal Processes'. Also, you will find useful information in Muhammad Iqbal's book 'An Introduction to Solar Radiation'. These references provide you with all relations of the solar radiation parameters and of course the clear sky solar radiation. 

Regards

Dear Muhannad,

Have a look to this article which may help you.

'Estimation of global radiation using clearness index

model for sizing photovoltaic system' by R. Kumar and L. Umanand, 2005.

Regards

Dear Khaled thank you so much for your response and help, can you please share the mentioned books with me?

Good morning.

here are some comments on your questions below:

1)Will I be using the avg or max Daily Sun shine duration data given that I employ the above employed methodology?

It depends on what is your temporal analysis. I would prefer the mean value. But you have to make sure that you have at least 80% of the daily data so that your mean value is representative for the particular day.

Either way I don't think that you can use these values as an offset to get the clear instances. You will have to visually inspect your outcome. Maybe you can get in this way the clear days (no clouds during the whole day).

2) How to identify the exact/ ideal day length of geographical locality?

the ideal day length duration is defined by the solar zenith angle (sza