Irradiance and Irradiation
•Irradiance:power density of sunlight (W/m2). Often referred to as intensity of sunlight.
•Irradiationis a measure of energy density of sunlight (kWh/m2). It is the integral of irradiance over a period of time (usually 1 day)
•Irradiation is usually expressed in peak sun hours (psh),i.e., the length of time at an irradiance of 1kW/m2needed to produce the daily irradiation obtained from integration of irradiance over a day. (see Fig. 2.3).