SOLAR RADIATION AND YIELD Alessandro Massi Pavan Sesto Val Pusteria June 22 nd 26 th, 2015
DEFINITIONS Solar radiation: general meaning Irradiation [Wh/m 2 ]: energy received per unit area Irradiance [W/m 2 ]: power received per unit area Yield [kwh/kw p ]: yearly output energy referred to the nominal power Solar constant: mean solar irradiance per unit area that would be incident on a plane perpendicular to the rays roughly 1,367W/m 2
AIR MASS l i l z AMl i = l i / l z AM0: outside the atmosphere AM1: at sea level with the sun directly overhead, useful in equatorial and tropical regions AM1.5: useful to represent the overall yearly average for mid-latitudes
SOLAR SPECTRA
THE DIFFERENT COMPONENTS OF SOLAR RADIATION Global Radiation (G) Direct Radiation (I) Reflected Radiation Direct Radiation Diffuse Radiation PV module Diffuse Radiation (D) Reflected Radiation (R) Ground G = I + D + R = f (geometric parameters, time, meteorology, shading)
GEOMETRIC PARAMETERS PV GENERATOR Tilt Angle ß [0 90 ]: slope of PV modules Azimuth Angle α [-180 180 ]: orientation of PV modules LOCATION Latitude L [0 90 ]: specify the north-south position of a point on the Earth s surface Solar Elevation [0 90 ]: is the altitude of the sun (i.e. the angle between the horizon and the center of the sun s disc)
SOLAR PATHS (TRIESTE) Azimuth [ ]
OPTIMIZED TILT ANGLES Daily Irradiation [MJ/m 2 /day Horizontal Vertical Month
TIME Hour Angle: converts the local solar time into the number of degrees which the sun moves across the sky t s solar time Declination of the Sun: is the angle between the equator and a line drawn from the center of the Earth to the center of the sun n day of the year
SOLAR RADIATION COMPONENTS Angle of incidence The direct, diffuse and reflected components are Surface Albedo ρ g Water 0.70 Dry leaves 0.30 Green Grass 0.26 Concrete 0.22 Dark wall 0.27 Bright wall 0.60
SOLAR IRRADIATION - ROME
SHADING CLINOMETRIC PROFILE Azimuth [ ]
SHADING PARALLEL ROWS Azimuth [ ]
http://re.jrc.ec.europa.eu/pvgis/
http://re.jrc.ec.europa.eu/pvgis/ EXAMPLE - TRIESTE
YIELD OF A PV PLANT E out = 365 P n PR G md P n : nominal power PR: Performance Ratio G md : global mean irradiation PR = 1 ε pu 1 ε gen 1 ε j 1 ε inv Ɛ pu : pick up losses (geometry, shading, soiling, albedo) Ɛ gen : generator losses (temperature, mismatch) Ɛ j : Joule losses Ɛ inv : inverter losses
Pick Up Losses LOSSES ε pu = ε geo + ε alb + ε soi Generator Losses ε gen = ε T + ε mis ε T = p (T CG 25) p power-temperature coefficient T CG cell temperature T a ambient temperature T NOCT Nominal Operating Cell Temperature G Solar Irradiance ε T = p T a + T NOCT 20 800 G 25
PR AND YIELD Shading 2% Albedo and Soiling 3% Temperature 5.5% Mismatch 2% Joule 2% Inverter 3% PR 84% The yield of a PV plant (with optimal tilt and azimuth angles, albedo 0.22) with a nominal power of 1kWp built in Trieste E out = 365 0.84 1 4.12 = 1,263kWh/year
THANK YOU! apavan@units.it Sesto Val Pusteria June 22 nd 26 th, 2015