Average Solar Radiation & Hours per year     Assumptions

Solar Radiation available to PV collectors is measured as peak solar radiation at 1000 W / m2 per hr.,
and reported as xx hrs peak solar radiation per day per year
which varies at different parts of the world, for example:
 

Paris = avg. 3.34 hrs / day or 1219 hrs/yr,
      or  51 - 24 hr days/yr, or 14% of a year  
This is the northern latitude average, and includes Toronto,  Korea, etc.
 

Las Vegas = avg. 5.68 hrs / day or 2075 hrs/yr,
      or  86 - 24 hr days/yr, or 24% of a year 

This is the US "sun belt" average.