Publisher: Earthscan, UK Homepage: earthscan.co.uk/?tabid=101808

1. Energy and the New Reality, Volume 2:C-Free Energy SupplyChapter 2: Solar Energy L. D. Danny Harveyharvey@geog.utoronto.ca Publisher: Earthscan, UKHomepage: www.earthscan.co.uk/?tabid=101808 This material is intended for use in lectures, presentations and as handouts to students, and is provided in Powerpoint format so as to allow customization for the individual needs of course instructors. Permission of the author and publisher is required for any other usage. Please see www.earthscan.co.uk for contact details.

2. Framework • Solar flux density on a plane perpendicular to the sun’s rays at the mean Earth-Sun distance, Qs, is 1370 W/m2 • The intercepted solar radiation flux (Qs x πRe2) is about 11000 times the 2005 world primary power demand of 15.3 TW • About 0.8% of the world’s desert area (or 80,700 km2) covered with 10% efficient modules would be all that is required to generate the total world electricity consumption in 2005 of about 18000 TWh • However, cumulative installation of PV panels to date is only 25 km2 • The solution is to directly use solar energy where-ever possible (for passive heating and ventilation, for thermal-driven cooling, and for daylighting), and to use solar electricity only where electricity really is needed.

3. This chapter discusses: • Photovoltaic generation of electricity • Solar-thermal generation of electricity • Solar thermal energy for space heating and for hot water • Solar thermal energy for air conditioning • Industrial uses of solar thermal energy • Direct uses of solar energy for desalination, in agriculture and for cooking

4. Chapter 4 (Buildings) of Volume 1 discusses passive (as opposed to active) uses of solar energy, with the building itself serving as a collector of solar energy. These passive uses are • Passive heating • Passive ventilation • Daylighting

5. Chapter 11 (Community-Integrated Energy systems with Renewable Energy) of this volume discusses seasonal underground storage of solar thermal energy for space heating and for domestic hot water

6. Figure 2.1a Stereographic sun path diagram Source: Computed using The Solar Tool developed by Square One Research, available through Ecotech (ecotech.com)

7. Figure 2.1b Stereographic sun path diagram Source: Computed using The Solar Tool developed by Square One Research, available through Ecotech (ecotech.com)

8. Figure 2.1c Stereographic sun path diagram Source: Computed using The Solar Tool developed by Square One Research, available through Ecotech (ecotech.com)

9. Figure 2.1d Stereographic sun path diagram Source: Computed using The Solar Tool developed by Square One Research, available through Ecotech (ecotech.com)

10. Figure 2.2a Solar irradiance, daily variation, clear sky

11. Figure 2.2b Solar irradiance, daily variation , clear sky

12. Figure 2.2c Solar irradiance, daily variation, clear sky

13. Figure 2.2d Solar irradiance, daily variation, clear sky

14. Figure 2.2e Solar irradiance, daily variation, clear sky

15. Figure 2.2f Solar irradiance, daily variation, clear sky

16. Figure 2.2g Solar irradiance, daily variation, clear sky

17. Figure 2.2h Solar irradiance, daily variation, clear sky

18. Figure 2.2i Solar irradiance, daily variation, clear sky

19. Figure 2.3a Solar irradiance, annual variation, clear sky

20. Figure 2.3b Solar irradiance, annual variation, clear sky

21. Figure 2.3c Solar irradiance, annual variation, clear sky

22. Figure 2.4a Solar irradiance on windows in June, clear sky

23. Figure 2.4b Solar irradiance on windows in December, clear sky

24. Figure 2.5 Annual average solar irradiance (W/m2) at ground level on a horizontal surface Source: Henderson-Sellers and Robinson (1986, Contemporary Climatology, Longman, Harlow, U.K)

25. Supplemental Figure: Solar irradiance on a horizontal surface, kWh/m2/yr Source: Prepared from data file obtained from the NASA Surface Meteorology and Solar Energy website, power.larc.nasa.gov

26. Supplemental Figure: Solar irradiance on a surface tilted toward the equator at an angle equal to the latitude angle, kWh/m2/yr Source: Prepared from data file obtained from the NASA Surface Meteorology and Solar Energy website, power.larc.nasa.gov

27. Supplemental Figure: Ratio of annual irradiance on a surface tilted at the latitude angle to the annual irradiance on a horizontal surface Source: Prepared from data files obtained from the NASA Surface Meteorology and Solar Energy website, power.larc.nasa.gov

28. Supplemental Figure: Ratio of local annual irradiance on a surface tilted at the latitude angle to the maximum annual irradiance on a horizontal surface anywhere Source: Prepared from data files obtained from the NASA Surface Meteorology and Solar Energy website, power.larc.nasa.gov

29. Two broad ways of making electricity from solar energy: • Photovoltaic (PV) • Solar thermal

30. PV Electricity • Electromagnetic radiation (including light) comes in packets called photons, each with energy hv, where h=Plank’s constant and v is the frequency of the radiation • Electrons in an atom exist in different energy levels • A photon can bump an electron to a higher energy level if the energy of the photon exceeds the difference in energy from one level to the next

31. PV electricity (continued) • When a solid forms, two outer energy bands are formed, often separated by a gap • The lower energy band is called the valence band, the upper the conduction band • In a conductor, electrons occur in both bands and they overlap • In an insulator, the valence band is filled and the conduction band is empty, and the two bands do not overlap • In a semi-conductor, electrons occur in both bands and there is a small gap between the bands

32. PV electricity (continued) • Silicon is a semi-conductor with a valence of 4 (4 electrons in the outer shell) • Two semiconductor layers are used – one layer (called the n-type layer) is doped with atoms have an valence of 5 (the extra electron is not taken up in the crystal lattice and so it free to move), and the other layer (called the p-type layer) is doped with atoms having a valence of 3, so there are empty electron sites (called holes) • The juxtaposition of the n- and p layers is called a p-n junction.

33. Figure 2.6 Steps in the generation of electricity in a photovoltaic cell Source: US EIA (2007, Solar Explained, Photovoltaics and Electricity)

34. Figure 2.7 Layout of a silicon solar cell Source: Boyle (2004, Renewable Energy, Power for a Sustainable Future, 65-104, Oxford University Press, Oxford)

35. Components of a PV system • Module – consists of many cells wired together • Support structure • Inverter – converts DC module output to AC power at the right voltage and frequency for transfer to the grid • Concentrating mirrors or lens for concentrating PV systems

36. Types of PV cells • Single-crystalline • Multi-crystalline • Thin-film amorphous silicon • Thin-film compound semiconductors • Thin-film multi-crystalline • Nano-crystalline dye-sensitized cells • Plastic cells

37. Thin-film compound semiconductors • Cadmium telluride (CdTe) • Copper-indium-diselenide (CuInSe2, CIS) • Copper-indium-gallium-diselenide (CIGS) • Gallium arsenide (GaAs)

38. Table 2.3 Best efficiencies achieved as of 2009

39. Figure 2.8 Trend in efficiency of PV cells and modules Source: Extended from IEA (2003, Renewables for Power Generation, Status and Prospects, International Energy Agency, Paris)

40. Figure 2.9. Structure of the GaInP/GaInAs/Gemulti-junction Cell Source: Kinsey et al (2009, Progress in Photovoltaics: Research and Applications 16, 503-508)

41. Figure 2.10 Organic Semiconductors Source: Rand et al (2007, Progress in Photovoltaics: Research and Applications 15, 659–676)

42. Figure 2.11 Dye-sensitized Solar Cell Source: McConnell (2002, Renewable and Sustainable Energy Reviews 6, 271–295, http://www.sciencedirect.com/science/journal/13640321)

43. Factors affecting module efficiency • Solar irradiance – efficiency peaks at around 500 W/m2 for non-concentrating cells • Temperature – efficiency decreases with increasing temperature, more so for c-Si and CIGS, less for a-Si and CdTe • Dust – can reduce output by 3-6% in desert areas

44. Figure 2.12a Module efficiency vs solar irradiance, theoretical calculations Source: Topic et al (2007,Progress in Photovoltaics: Research and Applications 15, 19–26)

45. Figure 2.12b Module efficiency vs solar irradiance, measurements Source: Mondol et al (2007, Progress in Photovoltaics: Research and Applications 15, 353–368)

46. System efficiency is the product of • Module efficiency • Inverter efficiency • MPP-tracking efficiency

47. Figure 2.13a Inverter & MPP Efficiency, calculated

48. Figure 2.13b Inverter & MPP Efficiency, measured Source: Mondol et al (2007, Progress in Photovoltaics: Research and Applications 15, 353–368)

49. Figure 2.14 Current-voltage combinations (MPP) giving the maximum power production for different solar irradiances on the module Source: Hastings and Mørck (2000,Solar Air Systems: A Design Handbook. James & James, London)

50. Figure 2.15 MPP-tracking efficiency Source: Abella and Chenlo (2004, Renewable Energy World, vol 7, no 2, pp132–146)