Photovoltaic Systems Engineering The Solar Resource, cont. SEC598 Photovoltaic Systems Engineering (SEC501 Solar Engineering and Commercialization, I) Session 04 The Solar Resource, cont. August 29, 2017

Session 04 Components The Solar Resource Definitions Solar radiation Orientation Effects Shading Effects

The Solar Resource – the sun’s output Messenger & Ventre, Fig 2.2

The Solar Resource – atmospheric effects The Solar Constant = 1367 W/m2

The Solar Resource – air mass Markvart, Solar Electricity, Fig 2.2

The Solar Resource – Irradiance Häberlin, Photovoltaics, Fig 2.6

The Solar Resource – Definitions Sex Solar Irradiance, the power density at the outer edge of the atmosphere at a plane perpendicular to the direction of the sun Gex Extraterrestrial Irradiance, the power density at the outer edge of the atmosphere at a horizontal plane parallel to earth’s surface Hex Extraterrestrial Irradiation, the energy density at the outer edge of the atmosphere at a horizontal plane parallel to earth’s surface G Irradiance, the power density at the earth’s surface at a horizontal plane parallel to earth’s surface H Irradiation, the energy density at the earth’s surface at a horizontal plane parallel to earth’s surface

The Solar Resource – radiation paths to a horizontal surface Häberlin, Photovoltaics, Fig 2.29

The Solar Resource – radiation paths Markvart, Solar Electricity, Fig 2.7b

The Solar Resource – radiation paths to a tilted surface Häberlin, Photovoltaics, Fig 2.31

GG Global Irradiance HG Global Irradiation The Solar Resource – radiation paths to a tilted surface (the solar generator plane) GG Global Irradiance HG Global Irradiation Note: These variables are defined for a tilted surface

The Solar Resource – the sun’s output GAM1.5 = 1000 W/m2 Peak Solar Hours (PSH) Messenger & Ventre, Fig 2.3

The Solar Resource Orientation Effects

The Solar Resource - Calculations A calculation of the total energy produced by a photovoltaic system, with PV modules in fixed orientation, must take into account the local solar energy input, the orientation angles of the PV array, and the local latitude. This calculation can be carried out with PVWatts: http://pvwatts.nrel.gov

Comparison of two orientations in SW USA The Solar Resource PVWatts calculation: Comparison of two orientations in SW USA Messenger & Ventre, Fig 2.15

The Solar Resource – arbitrary module orientation

The Solar Resource – Orientation Effects Both tracking and fixed mounting options have been used in real world photovoltaic systems The choice between the two is often based on economic considerations When a fixed mounting system is used, the following guidelines are usually chosen (in the northern hemisphere): The modules point to the south (azimuth angle of 0o) The modules have a tilt angle (from the horizon) equal to the local latitude

The Solar Resource – Formulas Relation between incidence angle and other solar angles

The Solar Resource - Special Case South facing module, Solar noon yW = module azimuth = 0 w = hour angle = 0 qinc = incident angle = 0 b = tilt angle = f – d = qz = latitude = declination qz = zenith angle S Messenger & Ventre, Fig 2.15

Motion of Sun Diagram – Example #2 zenith Tropic of Cancer Latitude = 23.5o Summer Solstice Equinox Winter Solstice 23.5o 23.5o North Pole N S

The Solar Resource – The annual motion from the perspective of the celestial sphere Häberlin, Photovoltaics, Fig 2.3

The Solar Resource Shading Effects

The Solar Resource – Spacing Calculation Häberlin, Photovoltaics, Fig 2.37

The Solar Resource – Spacing Calculation Häberlin, Photovoltaics, Fig 2.34

The Solar Resource – Spacing Calculation Noon, for south-facing modules Messenger & Ventre, Fig 2.14

The Solar Resource – Spacing Calculation for tilted modules Arbitrary time, for south-facing modules Messenger & Ventre, Fig 4.14

References H.Häberlin, Photovoltaics, System Design and Practice, 2012, John Wiley and Sons, 978-1-119-99285-1 R.Messenger and A.Abtahi, Photovoltaics Systems Engineering, 4th Ed., 2017, CRC Press, 978-1-4987-7277-8 T.Markvart, Solar Electricity, 2nd Ed., 2000, John Wiley and Sons, 0-471-98852-9