Chapter 2

2. Chapter 2 Solar Radiation The Sun • Solar Radiation • Sun-Earth Relationships • Array Orientation • Solar Radiation Data Sets

3. A false color image of the sun enhances the turbulent nature of the sun’s photosphere, including a roiling surface, sunspots, and giant flares.

4. Even over the vast distance, an enormous amount of energy reaches Earth from the sun.

5. Solar irradiance is solar power per unit area.

6. The inverse square law states that irradiance is reduced in proportion to the inverse square of the distance from the source.

7. Solar irradiation equals the total solar irradiance received over time.

8. The electromagnetic spectrum is the range of all types of electromagnetic radiation, which vary with wavelength.

9. The wavelength distribution of extraterrestrial solar radiation forms a spectral signature unique to the sun.

10. Solar radiation in Earth’s atmosphere includes direct, diffuse, and albedo radiation.

11. Air mass is a representation of the amount of atmosphere radiation that must pass through to reach Earth’s surface.

12. Peak sun hours is an equivalent measure of total solar irradiation in a day.

13. Insolation maps rate locations by their average daily peak sun hours.

14. The atmosphere absorbs extraterrestrial radiation at certain wavelengths, resulting in an attenuated spectral distribution for terrestrial radiation.

15. A pyranometer measures total global solar irradiance from the whole sky.

16. Diffuse solar irradiance can be measured by adding a shadowing device to a pyranometer, which blocks the direct component of total global irradiance.

17. Handheld pyranometers use less accurate and lower cost sensors than precision pyranometers but are more suitable for field measurements.

18. A pyrheliometer measures the direct component of solar irradiance, which is important when installing concentrating collectors.

19. Reference cells output a certain electrical current in proportion to solar irradiance received.

20. The ecliptic plane is formed by Earth’s elliptical orbit around the sun.

21. The equatorial plane is tilted 23.5° from the ecliptic plane. As Earth revolves around the sun, this orientation produces a varying solar declination.

22. The summer solstice occurs when the Northern Hemisphere is tilted towards the sun. The winter solstice occurs when the Northern Hemisphere is tilted away from the sun.

23. The fall and spring equinoxes occur when the sun is directly in line with the equator.

24. Standard time organizes regions into time zones, where every location in a time zone shares the same clock time.

25. The Equation of Time adjusts for variations in Earth’s orbit and rotation that affect solar time.

26. An analemma shows how sun position, at the same time of day, changes throughout the year.

27. Solar azimuth and altitude angles are used to describe the sun’s location in the sky.

28. The sun’s path across the sky at various times of the year can be illustrated on a diagram. The diagrams change for different latitudes.

29. The solar window is the area of sky containing all possible locations of the sun throughout the year for a particular location.

30. The orientation of an array surface is described using azimuth and tilt angles.

31. Energy production at certain times of the year can be maximized by adjusting the array tilt angle.

32. The average seasonal declinations define the optimal tilt angles for those periods.

33. The National Renewable Energy Laboratory (NREL) provides solar radiation data for various locations, times of the year, and south-facing array orientations.