**5.1 Solar radiation**

In Israel, only 500 km from north to south, the cumulative solar irradiation reaching the atmosphere during a given day do not vary among locations, but it significantly fluctuates during the annual cycle. However, due to differences in overcast, the ground-reaching solar radiation substantially increases from north to south, as well as with the distance from the Mediterranean Sea. These differences are demonstrated in **Figure 5** by means of monthly cumulative solar radiation records of 19 years (1999–2017) from three research centers, located at: 1. the northwestern coastal Negev (Besor); 2. Negev Highlands (Ramat Negev); and, 3. Rift Valley, Arava (Paran). During the critical winter months (November–February), the amounts of ground-reaching solar radiation are 7–19% greater at Ramat Negev, and 15–40% greater at Paran, compared to the northern coastal region of Besor center (**Figure 5**). Apparently, these differences provide some advantage to southern regions. Yet, the temperature regime might restrict this advantage.
