1. 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

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

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

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

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

6. The Solar Resource – Irradiance
Häberlin, Photovoltaics, Fig 2.6

7. 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

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

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

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

11. 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

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

13. The Solar Resource
Orientation Effects

14. 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:

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

16. The Solar Resource – arbitrary module orientation

17. 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

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

19. 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

20. 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

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

22. The Solar Resource
Shading Effects

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

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

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

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

27. References
H.Häberlin, Photovoltaics, System Design and Practice, 2012, John Wiley and Sons,
R.Messenger and A.Abtahi, Photovoltaics Systems Engineering, 4th Ed., 2017, CRC Press,
T.Markvart, Solar Electricity, 2nd Ed., 2000, John Wiley and Sons,