C2: NĂNG LƯỢNG ĐIỆN MẶT TRỜI

Transcription

1 C2: NĂNG LƯỢNG ĐIỆN MẶT TRỜI 1. Nguồn năng lượng mặt trời 2. Tế bào quang điện 3. Đặc tuyến I-V của pin quang điện 4. Công nghệ chế tạo pin quang điện 5. Đặc tính làm việc của pin quang điện 6. Hệ điện mặt trời độc lập 7. Hệ điện mặt trời hòa lưới Năng lượng tái tạo 1 The Solar Resource Before we can talk about solar power, we need to talk about the sun Need to know how much sunlight is available Can predict where the sun is at any time Insolation : incident solar radiation Want to determine the average daily insolation at a site Want to be able to chose effective locations and panel tilts of solar panels Năng lượng tái tạo 2 1

2 The Sun and Blackbody Radiation The sun 1.4 million km in diameter 3.8 x MW of radiated electromagnetic energy Blackbodies Both a perfect emitter and a perfect absorber Perfect emitter radiates more energy per unit of surface area than a real object of the same temperature Perfect absorber absorbs all radiation, none is reflected Năng lượng tái tạo 3 Plank s Law Plank s law wavelengths emitted by a blackbody depend on temperature E λ = λ exp 1 λt (7.1) λ = wavelength (µm) E λ = emissive power per unit area of blackbody (W/m 2 -µm) T = absolute temperature (K) Năng lượng tái tạo 4 2

3 Electromagnetic Spectrum Visible light has a wavelength of between 0.4 and 0.7 µm, with ultraviolet values immediately shorter, and infrared immediately longer Source: en.wikipedia.org/wiki/electromagnetic_radiation Năng lượng tái tạo K Blackbody Spectrum The earth as a blackbody Figure 7.1 Area under curve is the total radiant power emitted Năng lượng tái tạo 6 3

4 Stefan-Boltzmann Law Total radiant power emitted is given by the Stefan Boltzman law of radiation E = Aσ T 4 (7.2) E = total blackbody emission rate (W) σ = Stefan-Boltzmann constant = 5.67x10-8 W/m 2 -K 4 T = absolute temperature (K) A = surface area of blackbody (m 2 ) Năng lượng tái tạo 7 Wien s Displacement Rule The wavelength at which the emissive power per unit area reaches its maximum point λ = max 2898 T (7.3) T = absolute temperature (K) λ = wavelength (µm) λ max =0.5 µm for the sun, T = 5800 K λ max = 10.1 µm for the earth (as a blackbody), T = 288 K Năng lượng tái tạo 8 4

5 Extraterrestrial Solar Spectrum Figure 7.2 Năng lượng tái tạo 9 Air Mass Ratio As sunlight passes through the atmosphere, less energy arrives at the earth s surface h 1 = path length through atmosphere with sun directly overhead h 2 = path length through atmosphere to spot on surface β = altitude angle of the sun Figure 7.3 Năng lượng tái tạo 10 5

6 Air Mass Ratio h 1 m h sin β 2 air mass ratio = = (7.4) 1 Figure 7.3 Air mass ratio of 1 ( AM1 ) means sun is directly overhead (m=1) AM0 means no atmosphere AM1.5 is assumed average at the earth s surface (m=1.5) Năng lượng tái tạo 11 Solar Spectrum on Surface m increases as the sun appears lower in the sky. Notice there is a large loss towards the blue end for higher m, which is why the sun appears reddish at sun rise and sun set Năng lượng tái tạo 12 6

7 The Earth s Orbit One revolution every days Distance of the earth from the sun d 8 360( n 93) = sin km (7.5) 365 n = day number (Jan. 1 is day 1) d (km) varies from 147x10 6 km on Jan. 2 to 152x10 6 km on July 3 (closer in winter, further in summer) Note that the angles in this chapter are in degrees Năng lượng tái tạo 13 The Earth s Orbit In one day, the earth rotates The earth sweeps out what is called the ecliptic plane Earth s spin axis is currently Equinox equal day and night, on March 21 and September 21 Winter solstice North Pole is tilted furthest from the sun Summer solstice North Pole is tilted closest to the sun Năng lượng tái tạo 14 7

8 The Earth s Orbit Figure 7.5 For solar energy applications, we ll consider the characteristics of the earth s orbit to be unchanging Năng lượng tái tạo 15 Solar Declination Solar declination δ the angle formed between the plane of the equator and the line from the center of the sun to the center of the earth δ varies between +/ Assuming a sinusoidal relationship, a 365 day year, and n=81 is the spring equinox, the approximation of δ for any day n can be found from δ 360 = 23.45sin ( 81 ) (7.6) 365 n Năng lượng tái tạo 16 8

9 The Sun s Position in the Sky Another perspective- Solar declination Figure 7.6 Predict where the sun will be in the sky at any time Pick the best tilt angles for photovoltaic (PV) panels Năng lượng tái tạo 17 Solar Noon and Collector Tilt Solar noon sun is directly over the local line of longitude Rule of thumb for the Northern Hemisphere - a south facing collector tilted at an angle equal to the local latitude During solar noon, the sun s rays are perpendicular to the collector face Figure 7.8 Năng lượng tái tạo 18 9

10 Altitude Angle β N at Solar Noon Altitude angle at solar noon β N angle between the sun and the local horizon βn = 90 L + δ (7.7) Zenith perpendicular axis at a site Figure 7.9 Năng lượng tái tạo 19 Example 7.2 Tilt of a PV Module Find the optimum tilt angle for a south-facing PV module located at in Tucson (latitude 32.1 ) at solar noon on March 1 From Table 7.1, March 1 is day n = 60 Năng lượng tái tạo 20 10

11 Example 7.2 Tilt of a PV Module The solar declination δ is 360 ( ) 360 δ = 23.45sin n 81 = 23.45sin ( ) = The altitude angle is βn = 90 L + δ = = 49.6 To make the sun s rays perpendicular to the panel, we need to tilt the panel by tilt = 90 β N = 40.4 Năng lượng tái tạo 21 Solar Position at Any Time of Day Described in terms of altitude angle β and azimuth angle of the sun ϕ S β and ϕ S depend on latitude, day number, and time of day Azimuth angle (ϕ S ) convention positive in the morning when sun is in the east negative in the evening when sun is in the west reference in the Northern Hemisphere (for us) is true south Hours are referenced to solar noon Năng lượng tái tạo 22 11

12 Altitude Angle and Azimuth Angle Altitude Angle Azimuth Angle Figure 7.10 Năng lượng tái tạo 23 Altitude Angle and Azimuth Angle Hour angle H- the number of degrees the earth must rotate before sun will be over your line of longitude If we consider the earth to rotate at 15 /hr, then 15 hour angle H = ( hours before solar noon ) (7.10) hour At 11 AM solar time, H = +15 (the earth needs to rotate 1 more hour) At 2 PM solar time, H = -30 Năng lượng tái tạo 24 12

13 Altitude Angle and Azimuth Angle sin β = cos L cosδ cos H + sin Lsin δ (7.8) cosδ sin H sin φs = cos β (7.9) H = hour angle L = latitude (degrees) Test to determine if the angle magnitude is less than or greater than 90 with respect to true southtanδ if cos H, then φs 90, else φs > 90 (7.11) tan L Năng lượng tái tạo 25 Example 7.3 Where is the Sun? Find altitude angle β and azimuth angle ϕ S at 3 PM solar time in Boulder, CO (L = 40 ) on the summer solstice At the solstice, we know the solar declination δ = Hour angle H is found from (7.10) 15 H = (-3 h) = 45 h The altitude angle is found from (7.8) sin β = cos 40cos 23.45cos ( 45) + sin 40sin = β = sin ( ) = 48.8 Năng lượng tái tạo 26 13

14 Example 7.3 Where is the Sun? The sin of the azimuth angle is found from (7.9) ( ) cos sin 45 sin φ S = = cos 48.8 Two possible azimuth angles exist 1 = sin = 80 φ S ( ) ( ) 1 φ S = 180 -sin = 260 or 100 Apply the test (7.11) tan tan cos H = cos( 45 ) = δ = = tan L tan 40 φ = 80 (80 west of south) S Năng lượng tái tạo 27 Sun Path Diagrams for Shading Analysis Now we know how to locate the sun in the sky at any time This can also help determine what sites will be in the shade at any time Sketch the azimuth and altitude angles of trees, buildings, and other obstructions Sections of the sun path diagram that are covered indicate times when the site will be in the shade Năng lượng tái tạo 28 14

15 Sun Path Diagram for Shading Analysis Trees to the southeast, small building to the southwest Can estimate the amount of energy lost to shading Figure 7.15 Năng lượng tái tạo 29 California Solar Shade Control Act The shading of solar collectors has been an area of legal and legislative concern (e.g., a neighbor s tree is blocking a solar panel) California has the Solar Shade Control Act (1979) to address this issue No new trees and shrubs can be placed on neighboring property that would cast a shadow greater than 10 percent of a collector absorption area between the hours of 10 am and 2 pm. Exceptions are made if the tree is on designated timberland, or the tree provides passive cooling with net energy savings exceeding that of the shaded collector First people were convicted in 2008 because of their redwoods Năng lượng tái tạo 30 15

16 The Guilty Trees were Subject to Court Ordered Pruning Source: NYTimes, 4/7/08 Năng lượng tái tạo 31 Solar Time vs. Clock Time Most solar work deals only in solar time (ST) Solar time is measured relative to solar noon Two adjustments For a longitudinal adjustment related to time zones For the uneven movement of the earth around the sun Problem with solar time two places can only have the same solar time is if they are directly north-south of each other Solar time differs 4 minutes for 1 of longitude Clock time has 24 1-hour time zones, each spanning 15 of longitude Năng lượng tái tạo 32 16

17 World Time Zone Map Source: Năng lượng tái tạo 33 US Local Time Meridians (Table 7.4) Time Zone Eastern Central Mountain Pacific Eastern Alaska Alaska and Hawaii Local Time Meridian Năng lượng tái tạo 34 17

18 Solar Time vs. Clock Time The earth s elliptical orbit causes the length of a solar day to vary throughout the year Difference between a 24-h day and a solar day is given by the Equation of Time E n is the day number ( ) E = 9.87 sin 2B 7.53B 1.5sin B minutes (7.12) 360 B = 364 ( n ) -81 (degrees) (7.13) Năng lượng tái tạo 35 Solar Time vs. Clock Time Combining longitude correction and the Equation of Time we get the following: Solar Time (ST) = Clock Time (CT) + 4 min ( LT Meridian Local Longitude ) + E (min) degree (7.14) CT clock time ST solar time LT Meridian Local Time Meridian During Daylight Savings, add one hour to the local time Năng lượng tái tạo 36 18

19 Example 7.5 Solar Time vs. Local Time Find Eastern Daylight Time for solar noon in Boston (longitude 71.1 W) on July 1 July 1 corresponds to n = 182 From the Equation of Time (7.12) and (7.13) we obtain B = ( n 81) = (182 81) = E = 9.87sin 2B 7.53cos B 1.5sin B = 3.5 min ( ) ( ) ( ) Năng lượng tái tạo 37 Example 7.5 Solar Time vs. Local Time The local time meridian for Boston is 75, so the difference is , and we know that each degree corresponds to 4 minutes Using (7.14) ( )( ) CT = ST 4 min/ ( 3.5min) CT = 12 : min = 11: 49.9 AM EST But we need to adjust it for Daylight Savings, so add 1 hour CT = 12 : 49.9 AM EDT Năng lượng tái tạo 38 19

20 Sunrise and Sunset Can approximate the sunrise and sunset times Solve (7.8) for where the altitude angle is zero sin β = cos L cosδ cos H + sin Lsin δ (7.8) sin β = cos L cosδ cos H + sin Lsinδ = 0 (7.15) sin Lsinδ cos H = = tan Ltan δ cos L cosδ (7.16) 1 Hour angle of sunrise H SR = cos ( tan Ltan δ ) (7.17) + sign on H SR indicates sunrise, - indicates sunset H SR Sunrise (geometric) = 12 : 00 (7.18) 15 / h Năng lượng tái tạo 39 Sunrise and Sunset Weather service definition is the time at which the upper limb (top) of the sun crosses the horizon, but the geometric sunrise is based on the center There is also atmospheric refraction Adjustment factor Q Q = cos L cosδ sin H SR (min) (7.19) Subtract this from the geometric sunrise Năng lượng tái tạo 40 20

21 Clear Sky Direct-Beam Radiation Direct beam radiation I BC passes in a straight line through the atmosphere to the receiver Diffuse radiation I DC scattered by molecules in the atmosphere Reflected radiation I RC bounced off a surface near the reflector Figure 7.18 Năng lượng tái tạo 41 Extraterrestrial Solar Insolation I 0 Starting point for clear sky radiation calculations I 0 passes perpendicularly through an imaginary surface outside of the earth s atmosphere I 0 depends on distance between earth and sun and on intensity of the sun which is fairly predictable Ignoring sunspots, I 0 can be written as I 0 360n = SC cos (W/m ) (7.20) SC = solar constant = kw/m 2 n = day number These changes are due to the variation in earth s distance from the sun Năng lượng tái tạo 42 21

22 Extraterrestrial Solar Insolation I 0 In one year, less than half of I 0 reaches earth s surface as a direct beam On a sunny, clear day, beam radiation may exceed 70% of I 0 Figure 7.19 Năng lượng tái tạo 43 Attenuation of Incoming Radiation Can treat attenuation as an exponential decay function IB = Ae km (7.21) I B = beam portion of the radiation that reaches the earth s surface A = apparent extraterrestrial flux k = optical depth m = air mass ratio from (7.4) Năng lượng tái tạo 44 22

23 Attenuation of Incoming Radiation km IB = Ae (7.21) From curve fits of the table data, A and k are approximately A = sin ( n 275 ) (W/m ) (7.22) k = sin ( n 100 ) (7.23) 365 Năng lượng tái tạo 45 Solar Insolation on a Collecting Surface Direct-beam radiation is just a function of the angle between the sun and the collecting surface (i.e., the incident angle θ): I = I cosθ BC B Diffuse radiation is assumed to be coming from essentially all directions to the angle doesn t matter; it is typically between 6% and 14% of the direct value. Reflected radiation comes from a nearby surface, and depends on the surface reflectance, ρ, ranging down from 0.8 for clean snow to 0.1 for a shingle roof. Năng lượng tái tạo 46 23

24 Solar Insolation on a Collecting Surface, cont. ( ) 1 cos Σ IRC = ρ IBH + IDH 2 Năng lượng tái tạo 47 Tracking Systems Most residential solar systems have a fixed mount, but sometimes tracking systems are cost effective Tracking systems are either single axis (usually with a rotating polar mount [parallel to earth s axis of rotation), or two axis (horizontal [altitude, up-down] and vertical [azimuth, east-west] Ballpark figures for tracking system benefits are about 20% more for a single axis, and 25 to 30% more for a two axis Năng lượng tái tạo 48 24

25 Monthly and Annual Insolation For a fixed system the total annual output is somewhat insensitive to the tilt angle, but there is a substantial variation in when the most energy is generated Năng lượng tái tạo 49 US Annual Insolation Năng lượng tái tạo 50 25

26 Worldwide Annual Insolation In 2007 worldwide PV peak was about 7800 MW, with almost half (3860 MW) in Germany, 1919 MW in Japan, 830 in USA and 655 in Spain Năng lượng tái tạo 51 Tế bào quang điện Năng lượng tái tạo 52 26

27 Năng lượng tái tạo 53 Năng lượng tái tạo 54 27

28 Mức năng lượng Năng lượng tái tạo 55 Năng lượng tái tạo 56 28

29 Năng lượng tái tạo 57 Năng lượng tái tạo 58 29

30 Năng lượng tái tạo 59 Năng lượng tái tạo 60 30

31 Năng lượng tái tạo 61 Phổ năng lượng mặt trời Năng lượng tái tạo 62 31

32 Năng lượng tái tạo 63 Hiệu suất quang điện theo mức năng lượng Năng lượng tái tạo 64 32

33 Mối nối p-n Năng lượng tái tạo 65 Năng lượng tái tạo 66 33

34 Năng lượng tái tạo 67 Năng lượng tái tạo 68 34

35 Diode dùng mối nối p-n Năng lượng tái tạo 69 Năng lượng tái tạo 70 35

36 Tế bào quang điện Năng lượng tái tạo 71 Năng lượng tái tạo 72 36

37 Năng lượng tái tạo 73 Năng lượng tái tạo 74 37

38 Năng lượng tái tạo 75 Năng lượng tái tạo 76 38

39 Năng lượng tái tạo 77 Năng lượng tái tạo 78 39

40 Năng lượng tái tạo 79 Năng lượng tái tạo 80 40

41 Năng lượng tái tạo 81 Năng lượng tái tạo 82 41

42 Năng lượng tái tạo 83 Năng lượng tái tạo 84 42

43 Năng lượng tái tạo 85 Ghép các tế bào quang điện Năng lượng tái tạo 86 43

44 Năng lượng tái tạo 87 Năng lượng tái tạo 88 44

45 Năng lượng tái tạo 89 Năng lượng tái tạo 90 45

46 Năng lượng tái tạo 91 Năng lượng tái tạo 92 46

47 Năng lượng tái tạo 93 Đặc tuyến I-V của pin quang điện Năng lượng tái tạo 94 47

48 Năng lượng tái tạo 95 Năng lượng tái tạo 96 48

49 Năng lượng tái tạo 97 Tác động của nhiệt độ và cường độ bức xạ Năng lượng tái tạo 98 49

50 Năng lượng tái tạo 99 Tác động do bóng che Năng lượng tái tạo

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