1. Power Generation from Renewable Energy Sources
Fall 2013
Instructor: Xiaodong Chu
Office Tel.:

2. Flashbacks of Last Lecture
Plank’s law – wavelengths emitted by a blackbody depend on temperature
λ = wavelength (μm)
Eλ = emissive power per unit area of black body (W/m2-μm)
T = absolute temperature (K) 2

3. Flashbacks of Last Lecture
As sunlight passes through the atmosphere, less energy arrives at the earth’s surface
Air mass ratio of 1 (“AM1”) means sun is directly overhead
AM0 means no atmosphere
AM1.5 is assumed average at the earth’s surface 3

4. Flashbacks of Last Lecture
Solar declination, latitude and altitude angle
Masters, Figure 7.9 4

5. The Solar Resource – Solar Position at any Time of Day
The location of the sun at any time of day can be described in terms of its altitude angle and its azimuth angle

6. The Solar Resource – Solar Position at any Time of Day
What is solar time and hour angle ?

7. The Solar Resource – Solar Time and Civil (Clock) Time
Earth rotates once each day
360°with respect to earth-sun line
It seems that sun in the sky rises in the east and sets in the west each day

8. The Solar Resource – Solar Time and Civil (Clock) Time
Sunrise and Sunset measured in circles
Each hour, the sun moves 15 degrees in the sky 0°
0hr
1hr
15°
30°
2hr
3hr
45°
60°
4hr
5hr
75°
18hr
270°
6hr
90°
180°
12hr

9. The Solar Resource – Solar Time and Civil (Clock) Time
Sun rises in east, moves 15°/hour from East to West, transits at noon, sets in west

10. The Solar Resource – Solar Position at any Time of Day
How to compute the altitude angle and azimuth angle?

11. The Solar Resource – Solar Position at any Time of Day
The azimuth angle is greater than or less than 90o If
otherwsie

12. The Solar Resource – Solar Position at any Time of Day

13. The Solar Resource – Sun Path Diagrams for Shading Analysis
Shading patterns at a site are a very important consideration for PV
A sketch of the altitude and azimuth angles is needed for trees, buildings and other obstructions along the sun path, which indicates periods of time when the sun will be behind the obstruction and the site be shaded

14. The Solar Resource – Sun Path Diagrams for Shading Analysis
Could you make the superposition of obstructions onto a sun path diagram using some simple tools, e.g., a compass, protractor and plumb bob?

15. The Solar Resource – Sun Path Diagrams for Shading Analysis

16. The Solar Resource – Sun Path Diagrams for Shading Analysis
Estimate the energy lost due to shading

17. Standard Clock Time Every Longitude at slightly different time
It’s 6 pm (sunset).
Every Longitude at slightly different time
It’s 9 pm.
It’s 3 pm.
It’s midnight.
It’s noon.
It’s 3 am.
It’s 9 am.
It’s 6 am (sunrise).

18. Clock Time = Position of Sun
It’s 6 pm (sunset).
Observers move through times
It’s 9 pm.
It’s 3 pm.
It’s midnight.
It’s noon.
It’s 3 am.
It’s 9 am.
It’s 6 am (sunrise).

19. Clock Time Time Zones: 24, roughly 15°apart 6 pm 5 pm 4 pm 9 pm 3 pm
12 am
12 pm
9 am
3 am
6 am

20. Solar Time vs. Clock Time
Solar time varies across time zones
Time Zone’s Solar Noon
Clock Noon FOR ALL
Sun’s path seen from time zone center
Eastern Observer’s Solar Noon
Western Observer’s Solar Noon
Time Zone
East side
West side
Rising
Setting

21. Solar Time vs. Clock Time
Solar time varies across time zones
Time Zone’s Solar Noon
Clock Noon FOR ALL
Solar noon is (Degrees)(4 minutes/degree) earlier than clock noon
Degrees East of TZ center
Eastern Observer’s Solar Noon
Time Zone
East side
West side
Rising

22. Solar Time vs. Clock Time
Solar time varies across time zones
Time Zone’s Solar Noon
Clock Noon FOR ALL
Clock Noon FOR ALL
Solar noon is (Degrees)(4 minutes/degree) earlier than clock noon
Solar noon is (Degrees)(4 minutes/degree) Later than clock noon
Degrees East of TZ center
Degrees West of TZ center
Eastern Observer’s Solar Noon
Western Observer’s Solar Noon
Time Zone
East side
West side
West side
Rising
Setting

23. The Solar Resource – Solar Time and Civil (Clock) Time
Connect local clock time and solar time
The longitude correction between local clock time and solar time
Local Time Meridian
The difference between a 24-hour day and a solar day
Equation of Time

24. The Solar Resource – Solar Time and Civil (Clock) Time
The relationship between local standard clock time and solar time

25. Question
Jinan , 117°E is in the China Standard Time (center: 120°E), solar noon occurs at on March 22nd
(Degrees)(4 minutes/degree) = (3) x (4) = 12 minutes later
E = 7.53 minutes early
Solar noon in Jinan at 12:4:28
Degrees East of TZ center
Degrees West of TZ center
Western Observer’s Solar Noon
Time Zone
East side
West side

26. The Solar Resource – Sunrise and Sunset
Estimate times of sunrise and sunset
The altitude angle is zero
Solve it
Convert it to time

27. The Solar Resource – Sunrise and Sunset
Sunrise/sunset adjustment factor to account for refraction and the upper-limb definition of sunrise

28. The Solar Resource – Sunrise and Sunset

29. The Solar Resource – Clear Sky Direct-Beam Radiation
Solar flux striking a collector will be a combination of direct-beam radiation that passes in a straight line through the atmosphere to the receiver, diffuse radiation that has been scattered by molecules and aerosols in the atmosphere, and reflected radiation that has bounced off the ground or other surface in front of the collector

30. The Solar Resource – Clear Sky Direct-Beam Radiation
Estimate the extraterrestrial solar insolation that passes perpendicularly through a surface just outside of the earth’s atmosphere, which depends on
The distance between the earth and the sun, varying with the time of year
The intensity of the sun, rising and falling with a fairly predictable cycle (about 11 years), i.e., sunspot activity
Ignoring sunspots
where SC is called the solar constant, which is an estimate of the average annual extraterrestrial insolation

31. The Solar Resource – Clear Sky Direct-Beam Radiation
Attenuation of incoming radiation is a function of the distance that the beam has to travel through the atmosphere as well as factors such as dust, air pollution, atmospheric water vapor, clouds, and turbidity
where IB is the beam portion of the radiation reaching the earth’s surface (normal to the rays), A is an apparent extraterrestrial flux, k is a dimensionless factor called the optical depth, and m is the air mass ratio

32. The Solar Resource – Clear Sky Direct-Beam Radiation
Example 7.8 on page 412 of the textbook