*1.2. Solar Energy Potential in Ireland*

At the Earth's surface radiation can exist in three forms: direct radiation which comes directly from the sun; di ffuse radiation which has undergone scattering during its passage through the atmosphere; or reflected radiation from the ground [15]. Solar radiation distribution and intensity are the key factors in determining the e fficiency of solar PV systems and results are highly variable [16]. Ireland typically receives an annual solar radiation of 900 kWh m<sup>−</sup><sup>2</sup> [12] compared to Greece with 1890 kWh m<sup>−</sup><sup>2</sup> and Italy with 1680 kWh m<sup>−</sup><sup>2</sup> [17], where unsurprisingly, solar PV accounted for largest total electricity generation in 2017 (8.7% in Italy and 7.6% in Greece) [18]. As well as solar radiation, module e fficiency depends on the type of module and the module temperature [19]. The annual energy output (kWh) of the solar PV systems also depends on the peak rating of the solar PV installation (kWp) [12]. The measured performance of a 1.72 kWp rooftop grid connected PV system in Ireland is 885.1 kWh kWp−<sup>1</sup> year<sup>−</sup><sup>1</sup> [20]. The location of site and the tilt and orientation of solar PV panels are important for the energy output (kWh) of the solar PV systems [12]. For example, the site should be south facing of have a slight south-east or south-west orientation and should not be overshadowed by obstacles which could prevent sunlight getting to the system [21].
