I think you can use the Angström-Prescott’s formula, but you have to figure out what values should be used for the empirical constants. 

A. Angström, Solar and terrestrial radiation, Quarterly Journal of Royal Meteorological Society (1924) 50 121-125.

Martinez-Lozano, J., Tena, F., Onrubia, J., de la Rubia, J., 1984. The historical evolution

of the Ångström formula and its modifications: review and bibliography. Agric. For.

Meteorol. 33, 109–128.

Njau, E., 1996. Generalized derivation of the Ångström and Ångström-Prescott equations. Renewable Energy 7, 105–108.

Best wishes.

Hello,

If you just have the number of sunny hours, then there is no exact way to convert the data. The best thing you can do in my opinion is to use a simulated or observed data set of clearsky radiation variation with day and time and match it to your sunshine hours data. To avoid offsets I would distribute the sunny hours more randomly over the possible day-hours.

I think you can use the Angström-Prescott’s formula, but you have to figure out what values should be used for the empirical constants. 

A. Angström, Solar and terrestrial radiation, Quarterly Journal of Royal Meteorological Society (1924) 50 121-125.

Martinez-Lozano, J., Tena, F., Onrubia, J., de la Rubia, J., 1984. The historical evolution

of the Ångström formula and its modifications: review and bibliography. Agric. For.

Meteorol. 33, 109–128.

Njau, E., 1996. Generalized derivation of the Ångström and Ångström-Prescott equations. Renewable Energy 7, 105–108.

Best wishes.

Hi Eyasu,

Why you dont try to download the real solar data for your location or nearby city from one of the available sources (i.e. Meteonorm, SAM, TRNSYS). some of those data are freely available online.

Regards 

Dear Eyasu, what units do you want the 'solar radiation' to be expressed in? Joules per sq meter per day, for example, or what? And what about the spectrum of the solar radiation? And the spectral absorption coefficients for the algae? I am not sure you are trying to do something very meaningful here. May I ask exactly what you want to do with your answer please?

Dear Eyasu,

I am not sure about what do you need exactly. If you have just the sunshine hours, it is not enough to estimate the solar radiation. If you need the solar radiation for a specific area you can get it from one of the followings which are free sources: 

NREL provides good tools to get the solar irradiance data parts (Direct and diffused) at different locations. The following link contains different options and model:

http://www.nrel.gov/rredc/models_tools.html

Also, NASA provides through its website very useful data related to all solar irradiance (Direct and diffused) and clearness index as well. It covers solar and meteorological data from 10 years to more than 22 years (e.g. July 1983 to June 2005):

https://eosweb.larc.nasa.gov/cgi-bin/sse/[email protected]

I hope this may help you

Regards

If you could refer this book you can find all the answers you need

PRINCIPLES OF SOLAR ENGINEERING (3rd edition, 2015), D. Yogi Goswami, 

CRC Press (a Taylor and Francis Group)

ISBN: 978-1-4665-6378-0

Solar radiation data for a particular region is available in Meteorological station with the duration of sunshine.

If you want to measure solar radiation from sun then you should have Pyranometer by means it's possible to measure radiation.

There is a problem by using Angström-Prescott’s formula because you have to find the two regression constants which vary from a site to another and from a season to another.  The best way is to find a website to download the needed data for your work.

Why not use existing data, like the energyplus weather files database?

https://energyplus.net/weather

Not sure for which location you want this data, but maybe you can find a relatively close location at similar latitude and look at the weather file for that location. Data comes from different sources depending on the location but you can find additional information by looking at the Weather Data Sources page.

There is a good correlation between sunshine and global irradiation, but only on a _mean monthly_ basis. Coefficients of the regression vary with climatic area and have to be determined empirically using coupled sunshine and radiation data from the same area. For the Tropics in particular you can consult:

http://www.sciencedirect.com/science/article/pii/0038092X87900077

http://www.cder.dz/download/sipe_2.pdf

http://www.hindawi.com/journals/jse/2014/897970/

http://www.sciencedirect.com/science/article/pii/S0960148103003902

http://www.academia.edu/22684424/Relationship_between_global_solar_radiation_and_sunshine_duration_for_Onne_Nigeria

That being said, the sunshine solution is approximate and definitely not the best one to evaluate solar radiation. For Africa, there is a wealth of better data sources for the latter, e.g.

http://irena.masdar.ac.ae/

https://wui.cmsaf.eu/safira/action/viewProduktList?id=2

https://wui.cmsaf.eu/safira/action/viewProduktList?dId=2

Check also Table 1 in

https://www.researchgate.net/publication/298211145_Preliminary_survey_on_site-adaptation_techniques_for_satellite-derived_and_reanalysis_solar_radiation_datasets

and Chapter 19 in

http://www.wiley.com/WileyCDA/WileyTitle/productCd-0470446331.html

Finally, if you need spectral information, you can use my SMARTS model

http://www.solarconsultingservices.com/smarts.php

Article Preliminary survey on site-adaptation techniques for satelli...

There is many correlation between sunshine and direct or global irradiation presented in (for example):

http://www.cder.dz/download/sipe_2.pdf

http://www.sciencedirect.com/science/article/pii/S0011916407004778

ANGOSTROM EQUATION

National Cooperative Highway Research Program (NCHRP Report 2004) has a equation for calculating the percent sunshine.

Qs = asR*[A + B(Sc/100)]

where, Qs is the net short wave radiation, as is the surface short wave absorptivity, A and B are the constants that account for diffuse scattering and adsorption, respectively, Sc is the percent sunshine, and R* is the extraterrestrial radiation.

Thanks Amir Hossein for answering my question

You can use Angstrom equation to develop regression equation for a location using sunshine duration and component solar radiation and extra-terrestrial radiation . find the constant of regression,,, so that you can estimate solar radiation from sunshine duration and extra-terrestrial radiation.