Ouch! Usually the government has mapped the entire country. You find that document and then find the location in it.
Alternatively you find, perhaps, a big city near by and extrapolate to the location of interest.
If you're doing a large scale job an insolation monitoring system is usually installed and watched for one year at the precise location of interest.
Lastly and worstly you find a same-latitude city that someone can confirm has the "same weather" regarding over-cast type and frequency and use that city's data with +/- fudge-factors added.
@itsmoked thank you for your response, but I couldn't find prerecorded data for specific location in Ethiopia, that I am going to design for. Do you know any useful software that may help me in approximating the panel generating factor based on a given coordinate?
do a google search. there are many websites which give you at least a reasonable answer. It should be pretty good as you're close to the equator and the sun time doesn't change that much.
I think it's close to about 4 for East Africa like Kenya.
Abdi, the National renewable Energy Laboratory in the US provide a web based package called PVWATTS that allows you to calculate the output from a solar PV array. There are a range of input parameters including size, tilt, azimuth and importantly, location. The nearest average weather data is used in conjunction with your inputs to generate monthly and hourly PV outputs which you can use to size your system. A CSV can be downloaded. The URL is
