Sunshine and Solar Radiation

Ireland normally gets between 1100 and 1600 hours of sunshine each year. The sunniest months are May and June. During these months, sunshine duration averages between 5 and 6.5 hours per day over most of the country. The extreme southeast gets most sunshine, averaging over 7 hours a day in early summer. December is the dullest month, with an average daily sunshine ranging from about 1 hour in the north to almost 2 hours in the extreme southeast. Over the year as a whole, most areas get an average of between 3 1/4 and 3 3/4 hours of sunshine each day. 1887 was the sunniest summer in the 100 years from 1881 to 1980, according to measurements made at the Phoenix Park in Dublin. A more recent summer, 1980, was the dullest.

Mean 1981 - 2010 Annual Sunshine hours

Mean 1981 – 2010 Annual Sunshine hours

The tendency for coastal regions to record more bright sunshine than inland areas is the result of the convective development of clouds over land. This daily development of cloud is due to the vertical air currents as a result of thermal heating of the ground. Upland areas are also prone to low values of bright sunshine because of greater cloudiness especially on slopes facing the prevailing winds.

The most important variations of daily bright sunshine are due to seasonal changes corresponding to changes in the sun’s elevation. The mean daily bright sunshine at Rosslare is almost 1.9 hours in winter, 5.3 hours in spring and 6.1 hours in summer.

Variation of seasonal sunshine hours

Variation of seasonal sunshine hours