Solar Resources. 14 Auguest P.Ravindran, Elective course on Solar Energy and it Applications Auguest 2012 : Solar Resources

Transcription

1 Solar Resources 14 Auguest 2012

2 Solar Radiation 1. Spectral irradiance (1) What is that and why we care? (2) How to express? (3) How to use the two expressions? 2. Solar radiation (1) Treat the sun as a blackbody: power, spectrum... (2) Solar radiation in space: How to calculate the power density on a plate given the distance away from the sun? (not considering the atmospheric effect) 3. Atmospheric effect (1) What is that? (2) The influence on the light striking on the earth? Spectrum, power, and direction. (3) How to quantify the reduction of the light when passing through the atmosphere?

3 Spectral irradiance: concepts

4 Spectral irradiance: how to express

5 Spectral irradiance: how to express

6 Solar radiation model: blackbody radiation

7 Solar radiation in space

8 Atmospheric effect: Influence by the earth s atmosphere

9 Atmospheric effect: spectrum, power, and direction

10 Atmospheric effect: Air Mass (AM)

11 Atmospheric effect: Air Mass (AM)

12 About solar Radiation 1. Sun s position (1) Declination angle (2) Elevation angle (3) Azimuth angle 2. Solar radiation data (1) How to measure? (2) How to present? 3. Energy capturing by a PV module (1) Fixed plate (2) Plate module with tracking (1-axis, 2-axis) (3) Concentrator PV module (static, 1-axis, 2-axis)

13 Sun s position: declination angle

14 Sun s position: elevation angle

15 Sun s position: elevation angle

16 Sun s position: elevation angle

17 Sun s position: azimuth angle The location of the sun (relative to us) is described in terms of its altitude, and azimuth

18 Relationship of the earth to the sun at different times of the year

19

20 The Earth and the Sun

21 The Earth and the Sun The Tropic of Cancer (23 1/2 N) and the Tropic of Capricorn (23 1/2 S), mark the farthest points north and south of the equator where the sun's rays fall vertically. The Arctic Circle (66 1/2 N) and the Antarctic Circle (66 1/2 S), mark the farthest points north and south of the equator where the sun appears above the horizon each day of the year. Inside the Arctic circle, the sun never rises for the winter months.

22 Nature of the solar resource The sun The source of all power on the earth radiates at about 5,777º K P.Ravindran, Elective course on Solar Energy and it Applications Auguest 2012 : Solar (Blackbody Resources equivalent)

23 Spectral power distribution of the sun 2.4 Energy distribution (kw/m 2 /µm) Spectral power distribution of 6000K blackbody Actual Spectral power distribution of the sun Wavelength (µm -1 )

24 Solar Irradiance The amount of the suns energy that reaches the earth (before entering the atmosphere) The average value of irradiance per year is called the solar constant (G sc )and is equivalent to 1353, 1367 or 1373 W/m 2 depending on who you believe 1353 (±1.5%) from Thekaekara (1976) derived from measurements at very high atmosphere and used by NASA 1367 (±1%) Adopted by the World Radiation Centre 1373 (±1-2%) from Frohlich (1978) - derived from satellite data

25 Earth s orbit isn t circular

26 Insolation on a vertical surface in winter is greater than on a horizontal surface Characteristics of Incident Solar Radiation Figure 6.8: Daily clear-day insolation as a function of month and collector orientation.

27 Earth s orbit: Variation in radiation 360n Gon = G sc cos 365 G on = Irradiance G sc = Solar constant n = day number (number of days since 1st January) Note: cosine is for degrees

28 Ionosphere In the upper part of the earth atmosphere (but also on any other planet with a substantial atmopshere) radiation from the sun is causing the ionization of gas molecules. A shell of electrons and ions is formed as the lower part of the magnetosphere D layer (60-90km) Lyman-alpha ionizes NO, hard X-rays may ionize N 2 and O 2. E layer (90-120km) soft X-ray and fuv ionizes O 2. The shape is determined by the equilibrium of ionization and recombination. F layer (200 - >500km), solar radiation ionizes O

29 Solar Atmosphere Photosphere: Lowest and coldest part, source of solar light, T 5750K, Location of sunspots (colder elements T 4000K, paired footprints of magnetic loops) Chromosphere: Transparent to most of the visual light, emission of H-alpha, T heats up to K, location of prominences (looping structures connected to sunspots) Transition zone: rapid increase of temperature up to ~ K Corona: Outermost part of the solar atmophere Structured with streamers and filaments Coronal holes: open filed lines source of solar wind SOHO ESA

30 Solar Corona

31 Solar Wind Stream of charged particles from the sun Electrons & Protons mostly, few heavier ions Originating from the corona Ions escape through open field lines coronal holes Coronal mass ejection CME: Massive eruption and particle discharge Particles in corona (Plasma) have a Maxwellian energy distribution v av 145 km/s At solar minima (11 year cycle) terminal escape velocity v 400 km/s at ecliptic plane In high latitudes v km/s Density ~ 6 protons cm -3, T ~ 10 5 K, Magnetic field ~ AU

32 Parker Spiral Eugene Parker calculated 1958 the speed of the solar wind assuming radial outflow carrying the frozen in solar magnetic field with it. Due to this the solar magnetic field is twisted in a spiral form. Interaction between the solar magnetic field and the plasma in the interplanetary medium (solar wind) is responsible for changes in the field polarity

33 How much solar energy? The surface receives about 47% of the total solar energy that reaches the Earth. Only this amount is usable.

34 Measuring the Sun s Energy Irradiance: the amount of power received from the sun over a given area of earth» Typically measured in Watts per Square-Meter Cumulative Irradiance: the amount of energy that hits an area over a certain period of time» Typically measured in Watt-Hours per Square-Meter

35 Incident angle

36 Effects of Atmosphere The lower the angle of the Sun in the sky, the more atmosphere the Sun s rays must pass through to reach earth and therefore the less energy those rays have when they reach earth.

37 The Sun s Path

38 Solar Irradiance

39 Tilt and Orientation Factor (TOF)

40 Part 1: Short-Term Prediction Broken Clouds Cause Significant Variability of Available Sunlight at a Solar Power Array Solar Irradiance Measurements Golden, CO July 3, 2004 Figure courtesy of Tom Stoffel (NREL) Direct (Beam) Global (Total, with direct beam weighted by solar zenith angle) Diffuse (Sky) The presence of clouds results in abrupt and significant changes in available sunlight with respect to clear sky conditions.

41 Solar derived renewable energy sources Renewable energy provides around 8 % of the world s energy Wind energy is the fastest growing energy resource, followed by photovoltaics Studies suggest renewables could rise to % share by 2050 RES radiant wind waves hydro biomass geothermal tidal Solar derived

42 Characteristics of Incident Solar Radiation The energy from the sun reaching the earth per day: Insolation = incident solar radiation N. Europe 600 Btu/ft 2 /d 6800 kj/m 2 /d 79 W/m 2 Equator 2000 Btu/ft 2 /d kj/m 2 /d 266 W/m 2

43 Characteristics of Incident Solar Radiation Energy released from the fusion of hydrogen nuclei to produce helium nuclei Surface ~ 6000 C Core 40 x 10 6 C

44 Characteristics of Incident Solar Radiation Intensity of EM radiation from the sun received at the top of the earth s atmosphere 9 % UV, 40% visible, 50 % IR Only ½ of this reaches surface Absorbed by atmospheric gases Figure :Spectrum of solar radiation reaching the earth at the top of the atmosphere and at ground level.

45 Characteristics of Incident Solar Radiation Albedo

46 Fig What Happens to Sunlight? 30% Albedo 51%?? 19% Absorbed

47 Characteristics of Incident Solar Radiation Relatively constant temperature of the earth is a result of the energy balance between incoming solar radiation and the energy radiated from the earth. Most of the IR radiation emitted from the earth is absorbed by CO 2 and H 2 O (and other gases) in the atmosphere and then reradiated back to earth or into outer space The reradiation back to earth is called the atmospheric greenhouse effect Earth temperature is maintained ~ 40 C higher than it would be with no atmosphere (-15 C)

48 Characteristics of Incident Solar Radiation Insolation at the top of the earth s atmosphere solar constant = 1354 W/m 2 = 429 Btu/ft 2 /h 1kWh/m 2 / day = Btu/ft 2 /day

49 Characteristics of Incident Solar Radiation - Incoming solar radiation spread out - More atmospheric scattering - More direct incoming solar radiation - Less atmospheric scattering

50 Characteristics of Incident Solar Radiation Insolation is lowest in winter when the need for heat is highest in Europe. Figure 6.5: Insolation values for a clear day on a horizontal surface located at 40 N latitude, as a function of the month and the hour of the day. Fig. 6-5, p. 167

51 Characteristics of Incident Solar Radiation Sun s elevation, or angle above the horizon is called its altitude Altitude is a function of latitude Further north you are the lower in the sky the sun will be As fall moves into winter the sunrise and sunset points of the sun s motion across the sky move gradually southward Figure : Yearly and hourly changes in the sun s position in the sky for 40 N. Also shown are the solar altitude θ (angle above the horizon) and the solar azimuth φ (angle from true south).

52 Characteristics of Incident Solar Radiation Insolation reaching the surface is composed of direct, diffuse and reflected components Insolation is usually measured on a horizontal surface Figure : Components of solar radiation.

53 Solar irradiance, daily variation, clear sky

54 Solar irradiance, daily variation, clear sky

55 Solar irradiance, daily variation, clear sky

56 Solar irradiance, daily variation, clear sky

57 Solar irradiance, daily variation, clear sky

58 Solar irradiance, daily variation, clear sky

59 Solar irradiance, daily variation, clear sky

60 Solar irradiance, daily variation, clear sky 1200 Irradiance (W/m2) o N 30 o N 0 o N Module Tilted at Latitude Angle, 21 Dec Solar Hour

61 Solar irradiance, daily variation, clear sky 1200 Irradiance (W/m2) o N 30 o N 60 o N Sun-Tracking Modules, 21 Dec Solar Hour

62 Solar irradiance, annual variation, clear sky Equator Irradiance (W/m 2 ) Sun-tracking Slope=Latitude-Declination Slope=Latitude Horizontal 0 J F M A M J J A S O N Month D

63 Solar irradiance on windows in June, clear sky Radiation (W m -2 ) East North South West North Time (Hours)

64 Solar irradiance on windows in December, clear sky Irradiance (W/m 2 ) South East West North Time (Hours)

65 Earth is tilted 23.45

66 Earth is tilted On the winter solstice (December 21) The north pole has its maximum angle of inclination away from the sun Everywhere above N ( ) is in darkness for 24 hours, Everywhere above S is in sunlight for 24 hours the sun passes directly overhead over the tropic of Capricorn (23.45 S) On the equinox (March 22 & September 22) Both poles are equidistant the day is exactly 12 hours long the sun passes directly overhead over the equator The sun tracks a straight line across the sky On the summer solstice (June 22) The reverse of the winter solstice

67 Solar geometry Beam radiation δ φ φ = Latitude δ = Declination the between the earth s axis of rotation and the surface of a cylinder through the earth s orbit

68 Solar geometry: Declination n δ = 23.45sin δ n = Declination = day number (number of days since 1st January) Note: sine is for degrees

69 Solar geometry: Hour angle ω Beam radiation Rotation

70 Solar geometry: Hour angle The angular displacement of the sun east or west of the local meridian due to the rotation of the earth Denoted by (ω) 15 per hour noon is zero, so morning negative, afternoon positive Depends on Apparent Solar Time

71 Solar geometry: Hour angle L EQT AST = LCT + TZ AST = Apparent solar time LCT = Local clock time TZ = Time zone L = Longitude (west = + ve ) EQT = Equation of time

72 Solar geometry: Equation of time Sunrise and sunset are asymmetrical the plane of the Earth's equator is inclined to the plane of the Earth's orbit around the Sun the orbit of the Earth around the Sun is an ellipse and not a circle

73 Solar geometry: Equation of time Equation of time (min) Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

74 Solar geometry: Equation of time EQT cos B sin B = cos 2B sin 2B Where EQT = Equation of time n = day number ( n ) 360 B= 1 365

75 System design Irradiance: global radiation on a tilted surface Ground Beam 1+ cos β 1 cos β Gt = ( G Gd) Rbt, + Gd + Gρ 2 2 Sky G t = Total irradiance on a tilted surface (W m -2 ) G d = Diffuse irradiance (W m- 2 ) G = Total irradiance on a horizontal surface (W m -2 ) R b,t = ratio of beam radiation on the tilted surface to that on a horizontal surface β = Surface angle ρ = Ground albedo (reflectivity) 0.2 for bare earth ρ = Ground albedo (reflectivity) 0.7 for snow

76 Coronal mass ejections Massive bursts of solar plasma and electromagnetic radiation out of the solar corona Occurrence mostly at high solar activities like flares Originating out of active regions on the sun surface (sunspots) Cause of geomagnetic storms when earth is hit by the ejected plasma Can inject power in terawatt scale into the magnetosphere

77 Solar Resources 16Auguest 2012

78 "I'd put my money on the sun and solar energy. What a source of power! I hope we don't have to wait till oil and coal run out before we tackle that." Thomas Edison ( )

79 How much energy comes from the Sun? The sun provides about 1000 watts per square meter at the Earth's surface in direct sunlight (this reference intensity is often called "one sun" by solar energy scientists). This is enough power to power ten 100 watt light bulbs, or 50 twenty watt compact fluorescent light bulbs!

80 Introduction,cont. The World s Power Consumption Currently, the entire world uses, on a continuous basis:» 14 TW = 14 Terawatts = 14 x W By the year 2050, the world will be consuming:» TW Professor Roedel s electrical power consumption 2010 Electrical Energy Usage: 5168 kwh for the year 5168 kwh = 5,168,000 Wh = 1.86 x J One year = 365 days * 24 hours/day * 3600 sec/hr = 3.15 x 10 7 sec Average Power = Energy Usage/Time = (1.86 x J)/(3.15 x 10 7 sec) 2010 Average Power Requirement: 590 W = 4.2 x Earth s usage But if everyone on the planet needed 590 W, the earth would now require, 590 * 7.09 x 10 9 = 4.2 TW (for electricity, only)

81 The Solar Resource The Sun delivers to the Earth» 100,000 TW Rewriting this as power density, reaching the earth s atmosphere p solar = P solar A earth = 1366 W m 2 The Solar Constant And the amount that reaches the earth s surface p solar 1000 W m 2

82 Reflected 3 % Energy in = Energy out Incoming solar energy 100% Radiated from clouds + atmosphere 60% Absorbed by clouds + atmosphere 19 % Radiated from 6% earth 6% Reflected 3 % Direct 21% Scattered 29% Conduction/ convection 33% Net 105% terrestrial 113% radiation 8% Figure : Energy balance for the earth. The earth receives about 50% of the incident solar radiation: 21% is from direct radiation and 29% is scattered through the clouds. The energy leaving the earth s surface comes from evaporation and conduction to the atmosphere (33%), and infrared radiation (noted here as terrestrial radiation). Most of the infrared radiation (113%) is absorbed by the atmosphere and reradiated back to the surface (the greenhouse effect ). In order to have temperature equilibrium at the earth s surface, the energy input must equal the energy output. For this figure, 50% (incident radiation) = 3% (reflected) + 33% (evaporation) + 14% (net terrestrial radiation: 113% + 6% 105%).

83 Solar Energy Solar Energy is the Basis for Essentially all Renewable Energy Sources Solar Energy Incident On Earth Annually: 160 Times the World s Proven Resources of Fossil Fuels 15,000 Times the World s Annual Use of Energy Solar Energy can be used Directly: (solar thermal, photovoltaics, daylighting) or Indirectly: (wind, hydroelectric, biomass)

84 Solar Energy Cycle

85 Solar Energy Sun is a High Temperature Radiator (6000 C) Earth is a Low Temperature Receiver Solar Energy is Received as Short Wavelength Radiation 30% Reflected by Atmosphere 70% Re-radiated As Long Wavelength Radiation Atmosphere Acts like Glass on a Solar Collector

86 Solar Energy Basics Incident Solar Energy Varies Based on: Length of Travel Through Atmosphere Latitude, Seasons Atmospheric Clarity Cloud Cover, Pollution Time of Day Angle and Orientation of Collector Surface Sun Angle Highest in Summer (73.5 ) and Lowest in Winter (26.6 ) (at 12:00 pm, 40 lat.)

87 Seasonal Solar Angles Connecticut: Highest Summer 73º Lowest Winder 27º

88 Solar Energy-Basics Direct & Diffuse Radiation Beam Radiation from Sun Scattered when Penetrating Atmosphere Flat Plate Collectors, Passive Solar & Daylighting Makes Use of Both Direct & Diffuse Radiation Concentrating Collectors use Primarily Beam Radiation Ratio of Beam to Diffuse Varies by Local Climate Cloudier Climates ~ 50% beam / 50% diffuse Clear Climates ~ 80% beam / 20% diffuse

89 The Sun s Orbit

90 The Sun s Orbit (Northern Hemisphere) First Day of Summer Sun appears vertically above the Tropic of Cancer (latitude of N) First Day of Winter Sun appears vertically above the Tropic of Capricorn (latitude of S) First Day of Spring, Fall Sun appears vertically above the Equator (latitude of 0 0 N) All other days The declination angle deviation of sun from above equator 360( n 80) δ = sin 365

91 The Sun s apparent motion, perspective view

92 The Sun s apparent motion, edge view

93 Solar angles α = altitude ψ = azimuth ω = hour angle Apparent motion arc Zenith Horizon Your position

94 Essential Information in Solar Design The sun s light is an energy source. The sun s light that strikes the earth varies across the surface of the earth. The seasons are a natural response to the varying intensity of sunlight striking the earth s surface due to the tilting of the earth and the thickness of the earth s atmosphere. The sun s light that strikes a building varies during the year, and during a day, due to the movement of the sun from east to west. The sun s light that strikes a building can be controlled by the placement (orientation) of the building on its site, and by the design of the building s overall shape, and the placement of openings.

95 The solar resource

96 References J.Nelson, The Physics of Solar Cells, Imperial College Press, 2003 R.A.Messenger and J.Ventre, Photovoltaic Systems Engineering, 3 rd Edition, CRC Press, 2010 Various wikipedia webpages

97 Solar geometry: Sun angles Zenith W θ z N α s γ s South E

98 Solar geometry: Sun angles θ z = Zenith angle the angle between the vertical (zenith) and the line of the sun α s = Solar attitude angle the angle between the horizontal and the line to the sun γ s = Solar azimuth angle the angle of the projection of beam radiation on the horizontal plane (with zero due south, east negative and west positive)

99 Solar geometry: Sun angles Horizontal θ z α s δ φ Beam radiation

100 Solar geometry: Collector angles Zenith θ z W α s θ β N γ s γ South E

101 Solar geometry: Collector related β = Collector Slope(collector angle) the angle between the plane of the collector and the horizontal γ = Surface azimuth angle the deviation of the projection on a horizontal plane of the normal to the collector from the local meridian (with zero due south, east negative and west positive) θ = Angle of incidence the angle between the beam radiation on the collector and the normal

102 Solar geometry: Collector angles Horizontal β φ (φ - β) Beam radiation θ Normal

103 System design Irradiance: Variables Latitude at the point of observation Orientation of the surface in relation to the sun Day of the year Hour of the day Atmospheric conditions

104 System design Irradiance on a horizontal surface G bn, G b Gb = Gbn, cosθ z G b = Beam Irradiance normal to the earth s surface (W/m 2 ) G b,n = Beam Irradiance (W/m 2 ) θ z = Zenith angle

105 System design Tilt: Beam radiation G bn, G bt, Gbt, = Gbn, cosθ G b,t = Beam Irradiance normal to a tilted surface (W/m 2 ) G b,n = Beam Irradiance (W/m 2 ) θ = Angle of incidence

106 System design Irradiance on a tilted surface Beam radiation

107 System design Irradiance on a tilted surface: Optimum tilt 1 ( tan ) β φ + tan δ opt β opt = Optimum surface angle (degrees) φ δ = Latitude (degrees) = Declination (degrees)

108 System design Irradiance: the atmosphere Air mass 1.5 Air mass 1.0 Beam radiation

109 System design Irradiance: Beam, reflected and diffuse Direct Beam Beam Reflected Diffuse Building Reflected Ground Reflected

110 System design Irradiance: Beam and diffuse

111 System design Irradiance: Beam and diffuse: Clearness index k K = = I I o H H o k K I I o H H o = Hourly clearness index = Daily clearness index = Hourly global radiation on a horizontal surface (kj m -2 h -1 ) = Hourly extraterrestrial radiation on a horizontal surface (kj m -2 h -1 ) = Daily global radiation on a horizontal surface (kj m -2 day -1 ) = Daily extraterrestrial radiation on a horizontal surface (kj m -2 day -1 )

112 System design Calculating monthly average daily global radiation: Clearness index K = H H o K H H o = Monthly average clearness index = Monthly average daily global radiation on a horizontal surface (kj m 2 /day) = Monthly average daily extraterrestrial radiation on a horizontal surface (kj m 2 /day)

113 System design Calculating monthly average daily global radiation H H o = a + b n n max H = Monthly average daily global radiation on a horizontal surface (kj m -2 day -1 ) H o = Monthly average daily extraterrestrial radiation on a horizontal surface (kj m -2 day -1 ) a = Constant b = Constant n = Average day length (hours) n max = Maximum day length (hours)

114 System design Calculating monthly average, daily irradiance Sunshine hours as a % of maximum possible a b Location Range Ave Alburquerque (USA) Buenos Aires (Argentina) Darien (China) Hamburg (Germany) Honolulu (Hawaii) Malange (Angola) Nice (France) Poona (India) dry Poona (India) monsoon Kisangani (Zaire) Tamanrasset (Algeria)

115 Solar Radiation Long-term solar irradiation measurements are the basis for developing databases, which help us to calculate output. Being able to predict the output of our PV system, and this will allow us to know whether it is working adequately or not Predicting output will help us to calculate the cost of the energy generated over a given time period Pyranometers measure irradiance. Typically, you will use a handheld pyranometer that uses a silicon cell or photodiodes and you will set it adjacent to the array, in the same plane as the array not as precise but appropriate for construction Pyrheliometers measure direct solar radiation (and ignore diffuse).

116 Solar Radiation

117 Solar radiation data: measurement

118 System design Irradiance: measurement of global irradiance: pyranometer

119 Measuring Solar Radiation Pyranometer this is a thermoelectrical pile which produces an electromotive force (emf) when solar radiation falls onto it. The measurement of the emf permits determination the irradiation (instant value in W/sq.m.). The horizontal assembly measures the overall horizontal solar irradiation. The German Solar Energy Society Planning and Installing Solar Thermal Systems: A Guide for Installers, Architects and Engineers. Earthscan: Frieberg, Germany.

120 Pyranometers measure light intensity Sensitivity approximately 70 µv/wm - ² The upper dome contains the incident surface sensor, while the lower sensor measures only indirect light intensity from ground

121 Solar radiation data: how to present

122 Solar radiation data: how to present

123 Temperature: Photovoltaics produce heat as a by-product of the process by which sunlight is changed to electricity. They must be installed so that they are vented, as overheating will decrease their efficiency. Photovoltaics actually work better in cold weather situations. Contrary to most peoples' intuition, photovoltaics actually generate more power at lower temperatures with other factors being equal. This is because photovoltaics are electronic devices and generate electricity from light, not heat. Like most electronic devices, photovoltaics operate more efficiently at cooler temperature. In temperate climates, photovoltaics will generate less energy in the winter than in the summer, but this is due to the shorter days, lower sun angles and greater cloud cover, not the cooler temperatures.

124 Rain and snow: Rain will not adversely affect a pv array system since during periods of rainfall the solar irradiance is already low. Roof mounted pv arrays can be covered with snow in the winter. If the array is covered, it will not work. In snowy climates, sloped arrays are preferred to flat installations as theoretically the sun will penetrate the snow, heat the dark pv layer, melt the base of the snow and it will slide off of the panel. It is important to prevent such snow from piling up at the base of the array, or sliding uncontrolled onto passers by below the installation. Sometimes it is necessary to shovel the array. Care must be taken not to damage it.

125 Dirt and pollution: Any factor that reduces light transmittance to the pv surface will reduce the output of the system. If dirt is allowed to accumulate (more likely in urban areas), the output can be reduced by 2% to 6%. The higher value occurs if the slope of the array is less than 30 degrees. The occasional heavy rainstorm is usually sufficient to clean the array. If pv is installed on a wall surface, rain can keep it clean if the array is exposed to such. Otherwise, the surface can be cleaned in the same way as window systems would be.

126 Shading: AVOID SHADING THE PANEL. The shaded area will not reduce the output proportionally to the area shaded -- loss is much higher. Within a chain of modules the output will be that of the weakest (shaded) module. If shade cannot be avoided at certain times, be sure to gang the affected modules together on the same circuit, leaving the sunny modules to fully function. This goes for seasonal shading due to trees or vines, and even the shade from deciduous trees in the winter when they are bare. Watch for plant growth over time that can shade the panels.

127 Orientation: It is essential to provide unobstructed access to sunlight to optimize efficiency. Due south is ideal but deviations up to 45 degrees only result in a 10% loss of power. As a rule, BIPV installations are best when oriented south and tilted at an angle of 15 degrees higher than the site latitude; ie. The further north you go, the more vertical the panel as the sun angles are low in the sky and the system performs better when the rays strike at a right angle (less reflectance). If using the system for AC rather than heating electrical supply, vary the installation for the time of year.

128 World comparison of annual sunshine hours: This chart compares the annual number of hours of sunshine received for various cities around the world. Canadian cities (red box) are generally better than cities like Berlin and London where greener high tech buildings are more often found.

129 Factors affecting module efficiency Solar irradiance efficiency peaks at around 500 W/m 2 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

130 Variability 6 Xcel Wind Farm, Minnesota 1.5 GW Wind in 10 GW Peak System Load 3 Solar PV GW 4 2 Load - Wind Wind MW Day Wind variability: up to 100% of capacity on calm days Load variability: 30% - 50% of peak predictable to a few percent 20% Wind Energy by 2030, Energy Efficiency and Renewable Energy, DOE/GO (2008) Minutes since start of day Solar variability: up to 70% of capacity due to clouds and 100% at night Generation variability < load variability: compensate ~ with existing reserves Generation variability > load variability requires new reserves ~ renewable capacity High penetration requires high reserves

131 Solar Angles Hour Angle ω = 12 T Sunrise Angle ω sunrise = cos 1 ( tanφ tanδ)

132 Solar Angles Altitude sinα = sinδ sinφ + cosδ cosφ cosω Azimuth cosψ = sinα sinφ sinδ cosα cosφ

133 Altitude - Azimuth

134 Module Tilt

135 Effect of module orientation

136 Optimal fixed angle (south facing module)

137 Alternative fixed angle

138 Characteristics of Incident Solar Radiation Insolation at earth s surface varies between 0 and 1050 W/m 2 Depends on latitude, season, time of day, cloudiness Figure 6.4: Motion of the earth around the sun, illustrating the seasons and the tilt of the earth s axis. (controls latitude and season)

139 PV Energy Concepts Performance Factor Considerations Perpendicular Solar Incidence will Yield Highest Output Solar Array Tilt Selection can Optimize Seasonal Performance Tilt 20º - 50º may Optimize Year Round Performance Colder Ambient Temperatures will Increase Efficiency Shading Effects of Collector Arrangements and Adjacent Buildings will Reduce Output Tree Shading Effects may not be Excessive if Deciduous Trees are Involved, Analysis Required.

140 Where/when does the sun shine?

141 Summer Solstice (June 21)

142 December 21

143 Longitude and Latitude

144 Another view. During Equinox s

145 Azimuth / Altitude (height) Source: NOAA

146 Solar Resource in India 5 trillion kwh/year theoretical potential Sunny areas Most of the country receives more than 4kWh/m 2 /day More than 300 sunny days in the most part of the country Potential being mapped by IMD, and few other institutes. IMD, MNRE has published solar energy resource handbook

147 Solar radiation map of India If one percent of the land is used to harness solar energy for electricity generation at an overall efficiency of 10%; 492 x 10 6 MU/year electricity can be generated

148 Radiation paths are critical Over a year, radiation peaks near the summer solstice. Direct radiation is straight from the sun, while global adds reflected light from the clouds and other objects

149 Solar Module Annual Tilt Summer Solstice NP Spring Winter Solstice NP SP NP SP tilt NP SP Fall Modules are tilted at latitude angle to be aimed at sun on equinoxes; at solstices, they are off by the obliquity angle SP

150 You are here! Zenith (up) Zenith Angle To Sun North Pole Solar Declination Angle Horizontal Plane Latitude Angle Equatorial Plane Zeni Equator Sun s zenith angle is measured from local vertical Zenith Angle of Sun South Pole

151 Optimum Solar Module Tilt Website calculations Month Sun Altitude Array Tilt Array Points to: JAN South FEB South PV ARRAY: SOLAR NOON TILT DATA Latitude = 28 Degrees North MAR South APR South MAY 82 8 South JUN 85 5 South JUL 82 8 South AUG South SEP South OCT South NOV South DEC South Array Tilt = 90 degrees - Sun Altitude

152 Solar Energy Systems Decomposition What are the functions of a solar energy system? Collect & Distribute Energy Start Collect Energy Regulate Energy Store Energy Control Energy Distribute Energy Use Energy Each function drives a part of the design, while the interfaces between them will be defined and agreed upon to ensure follow-on upgrades

153 Summary: Received solar energy varies widely as evidenced by climate records and vegetation Dry desert areas indicate lots of sun and low moisture! This variability affects the economic viability of a system Solar energy systems are simple, robust, and easy to install and maintain

154 Solar Resource in India 5 trillion kwh/year theoretical potential Sunny areas - Most of the country receives more than 4kWh/m 2 /day - More than 300 sunny days in the most part of the country Potential being mapped by IMD, and few other institutes. IMD, MNRE has published solar energy resource handbook

155 Solar is the Cheapest Energy Source for the Consumer

156 Sales are Growing Prices are Dropping

157 Global Renewable Energy Historic Growth 30% 20% 40%

158 International Deployment of PV 78 % On grid Source: IEA (

159 Solar Radiation

160 Solar Radiation Solar Spectrum most the energy received from the sun is electromagnetic radiation in the form of waves. Electromagnetic Spectrum is the range of all types of electromagnetic radiation, based on wavelength.

161 Solar Radiation Atmospheric Effects: Solar radiation is absorbed, scattered and reflected by components of the atmosphere The amount of radiation reaching the earth is less than what entered the top of the atmosphere. We classify it in two categories: 1. Direct Radiation: radiation from the sun that reaches the earth without scattering 2. Diffuse Radiation: radiation that is scattered by the atmosphere and clouds

162 Solar Radiation

163 Solar Radiation Air Mass represents how much atmosphere the solar radiation has to pass through before reaching the Earth s surface Air Mass (AM) equals 1.0 when the sun is directly overhead at sea level. AM = 1/ Cos Өz We are specifically concerned with terrestrial solar radiation that is, the solar radiation reaching the surface of the earth. At high altitudes or in a very clear days, Peak Sun may be more than 1000 W/m^2 but it is a practical value for most locations Peak Sun Hours is the number of hours required for a day s total radiation to accumulate at peak sun condition.

164 Solar Radiation Zenith is the point in the sky directly overhead a particular location as the Zenith angle Өz increases, the sun approaches the horizon. AM = 1/ Cos Өz

165 Solar Radiation-peak sun Hrs Example problem of Peak sun hours per day: If during the day we have 4 hours at 500 Wh/m^2 and 6 hours at 250 Wh/m^2 we should compute the peak sun hours per day as follow: First, multiply 4hs x 500 W/m^2 and add to it 6hs x 250 W/m^2 This will equal 3500 Wh/m^2 Second, we know that by definition Peak Sun is 1000 W/m^2, so if we divide the total irradiation for the day by Peak Sun we will obtain Peak Sun hours. That is, Peak Sun Hours = Total Irradiation [Wh/m^2] / Peak Sun [W/m^2] = Peak Sun hours In our specific problem: Peak Sun Hours = 3500 Wh/m^2 / 1000 W/m^2 = 3.5 Peak Sun hours Note: most solar irradiation data is presented in Peak Sun Hours units

166 Solar Radiation-insolation Insolation; this is an equivalent term for solar irradiation and can be expressed in KWh/m^2/day or peak sun hours

167 Solar Radiation Two major motions of Earth affect the apparent path of the sun across the sky: 1. Its yearly revolution around the sun 2. Its daily rotation about its axis These motions are the basis for solar timescale and the reason why we have seasons, days and nights Ecliptic Plane is the plane of Earth s orbit around the sun Equatorial Plane is the plane containing Earth s equator and extending outward into space

168 Solar Radiation

169 Solar Radiation Solar Declination is the angle between the equatorial plane and the ecliptic plane The solar declination angle varies with the season of the year, and ranges between 23.5º and +23.5º

170 Solar Radiation Summer Solstice is at maximum solar declination (+23.5º) and occurs around June 21st Sun is at Zenith at solar noon at locations 23.5º N latitude Winter Solstice is at minimum solar declination (-23.5º) and occurs around December 21st At any location in the Northern Hemisphere, the sun is 47º lower in the sky at noon on winter solstice than on the summer solstice Days are significantly shorter than nights

171 Solar Radiation Equinoxes occur when the solar declination is zero. Spring equinox is around March 21st and the fall equinox occurs around September 21st Sun is at Zenith at solar noon on the equator. Around the equinoxes the daily [rate of] change in radiation is at maximum as oppose to change of declination during the solstices when it is at its minimum

172 Solar Radiation Solar Altitude Angle is the vertical angle between the sun and the horizon added to the Zenith angle is equal to 90º Azimuth Angle is the horizontal angle between a reference direction. In the solar industry we call south 180º and this angle will range between 90º (east) and 270º (west)

173 Solar Radiation Solar Window is the area of sky between sun paths at summer solstice and winter solstice for a particular location

174 Solar Radiation Incidence Angle is the angle between the direction of direct radiation and a line exactly perpendicular to the array angle

175 Solar Radiation Array orientation is defined by two angles: 1. Tilt angle is the vertical angle between the horizontal and the array surface

176 Solar Radiation 2. Array Azimuth Angle is the horizontal angle between a reference direction typically south- and the direction an array surface faces

177 Solar Radiation Maximum energy gain will be achieved by orienting the array surface at a tilt angle close to the value of the local latitude In high latitudes arrays should be very steep and vice versa For optimal performance the tilt angle should be adjusted from the latitude angle by an amount equal to the average declination during that time During the summer the average declination is +15º, so we should have a tilt of latitude minus 15º to make the array perpendicular to the average solar path during the summer. Array Azimuth angle will be optimal when that array is due south. Sun trackers allow the PV array to change the tilt angle, the azimuth angle, or both generally is not considered cannot be made cost effective

178 Solar Radiation

179 Solar Radiation Computer models and the average climate conditions are used to calculate an optimal tilt angle factor aka correction factor we have to subtract from the latitude. In our area we use an optimal tilt angle factor of 15º By making our tilt angle equal to the latitude angle minus this angle factor, we will improve the performance of our PV array Example for our area: If we look at dataset provided by NREL, we can see that for a 0º tilt we would have 4.7 peak sun hours and for a latitude - 15º tilt we would have 5.3 peak sun hours In other words, we would have an output roughly 13% higher by using this correction factor You can calculate this percentage as follows: ( ) / 4.7 =.127 or 12.7%

180 Solar Radiation With NREL dataset we can find the most convenient tilt for our system and use the average peak sun hours of this tilt to calculate the annual production of our system. Annual energy production = Avg peak sun hours per year [hr/day] x 365 Days x system size [Kw] = [KWh/year] Example: For a 4 KW system, located in San Francisco where we can expect 5.3 peak sun hours per day the annual production of the system will be equal to 7738 KWh/yr =(4KW x 5.3 peak sun hours per day x 365 days) If we multiply this result by the number of years that we expect the system to be producing energy and we divide the cost of the PV system by this number, we will know how much it cost each KWh produced. In our example: 7738 KWh/yr x 25 years = KWh. Let s say that this system cost $26500 after rebate, then $26500/ KWh =13.5 /KWh

181 Typical Inclinations Solar Radiation

182 Pyranometer (Total Radiation) Pyrheliometer (Beam/direct Radiation)

183 Radiometer (Short & long wave Radiation) Tracking System

184 Atmosphere: 30% +weather +day/night 1,380 W/m2 1,000 W/m2 Angle: 0 ~ 40% Shading / dirt : 0 ~ 80% Temperature: 5 ~ 20% Inverter: ~ 2% BOS: ~2% PV: 85%

185 Shading vs. Space Fixed Trackers +30% energy

186 Kimberley (Canada) vs. Abu Dhabi - 35 C +14% efficiency Hot & Dirty!

187 Tracking vs Fixed % Track Fixed :00:00 9:00:00 12:00:00 15:00:00 18:00:00 21:00:00 tracked = fixed + 40%

188 Laboratory vs. Practical Commercial Module Range Laboratory Cells Histories of Silicon Photovoltaic Module and Cell Efficiencies Ref.: Martin A. Green; "Silicon Photovoltaic Modules: A Brief History of the First 50 Years"; Prog. Photovolt: Res. Appl. 2005; 13: (Published online 18 April 2005 in Wiley InterScience ( DOI: /pip.612)

189 Energy Costs P.Ravindran, Elective course on Solar Energy and it Applications Auguest 2012 : Solar Resources

190 Photovoltaic Cells During the past 25 years, efficiency of energy capture by photovoltaic cells has increased from less than 1% of incident light to more than 10% in field conditions. Invention of amorphous silicon collectors has allowed production of lightweight, cheaper cells. Currently $100 million annual market.

191 Solar Radiation Peuser, Felix A., Remmers, Karl-Heinz, and Schnauss, Martin Solar Thermal P.Ravindran, Systems: Successful Elective course Planning on Solar and Energy Construction. and it Applications Earthscan: Auguest Frieberg, 2012 : Germany. Solar Resources

192 Irradiance, Irradiation and Insolation Solar irradiance is the power of solar radiation per unit surface area. It is expressed in W/m 2 Solar irradiation is the energy of solar radiation over a given period of time. It is expressed in kwh/m 2 Insolation is a measure of solar radiation energy received on a given surface area in a given time. It is commonly expressed as average irradiance in kilowatthours per square meter per day kwh/m²/day

193 Solar Radiation as a Function of the Weather This graph shows the approximate global solar irradiation values on a horizontal plane as a function of the weather. On clear days there are very high levels of irradiance which can be in the order of 800 to 1000 W/sq.m. while on completely overcast days only 200 W/sq.m. or less are obtained. Seasons can also have an effect on irradiance levels. Peuser, Felix A., Remmers, Karl-Heinz, and Schnauss, Martin Solar Thermal Systems: Successful Planning and Construction. Earthscan: Frieberg, Germany.

194 Average Annual Solar Insolation

195 Average Annual Solar Insolation

196 Solar Window The German Solar Energy Society Planning and Installing Solar Thermal Systems: A Guide for Installers, Architects and Engineers. Earthscan: Frieberg, Germany.

197 Solar Window The German Solar Energy Society Planning and Installing Solar Thermal Systems: A Guide for Installers, Architects and Engineers. Earthscan: Frieberg, Germany.

198 Sun-Earth Geometry Revolution and Rotation Peuser, Felix A., Remmers, Karl-Heinz, and Schnauss, Martin Solar Thermal Systems: Successful Planning and Construction. Earthscan: Frieberg, Germany.

199

200 Angular Denomination The German Solar Energy Society Planning and Installing Solar Thermal Systems: A Guide for Installers, Architects and Engineers. Earthscan: Frieberg, Germany.

201 Collector Azimuth Azimuth is the number of degrees of variation from true North (South)

202 Collector Tilt The most amount of radiation will strike a flat surface when it is perpendicular to sun. So, tilt angle is the angle between horizontal surface of the earth and the solar collector plate when it is perpendicular to the sun.

203 Collector Tilt Boyle, Godfrey Renewable Energy. Second Edition. Oxford University Press: USA.

204 Collector Tilt Boyle, Godfrey Renewable Energy. Second Edition. Oxford University Press: USA.

205 0 Latitude 30 Latitude 60 Latitude

206 Solar geometry: Sun angles cosθ = cosφcosδ cosω+ sinφsinδ cosγ z s sinφcosδ cosω sinφsinδ = cosα s θ Z φ δ ω γ s α s = Zenith Angle = Latitude = Declination = Hour angle = Solar azimuth angle = Solar attitude angle Note: γ & ω should be the same sign

207 Solar geometry: Sun angles: Sunset angle and day length cosω = tanδ tanφ s ω s δ φ = Sunset angle = Declination = Latitude 2 Day length = cos tan tan 15 1 ( δ φ) Note: Day length is in hours

208 Solar geometry: Collector angles cosθ = cosα sinγ sin βsinγ s + cosα cosγ sin βcosγ + sinα cos β s s Sun angles Earth angles s s ( ) ( ) cosθ = sinδ sinφcos β cosφsin βcosγ + cosδ cosω cosφcos β sinφsin βcosγ + cosδsin βsinγ sinω θ α s γ γ s β δ φ ω = Angle of incidence = Solar attitude angle = Surface azimuth angle = Solar azimuth angle = Collector slope = Declination = Latitude = Hour angle

209 System design Irradiance on a tilted surface (facing the equator) Northern hemisphere R bt, R bt, ( ) + ( ) cos φ β cosδ cosω sin φ β sinδ = cosφcosδ cosω+ sinφsinδ Southern hemisphere ( + ) + ( + ) cos φ β cosδ cosω sin φ β sinδ = cosφcosδ cosω+ sinφsinδ R b,t = ratio of beam radiation on the tilted surface to that on a horizontal surface φ = Latitude (degrees) β = Surface angle δ = Declination (degrees) ω = Hour angle (degrees)

210 Solar geometry: Collector angles Northern Hemisphere cosω = tanδ tan ( φ β) ss Southern Hemisphere ω ss δ φ β = Sunset angle = Declination = Latitude = Collector slope cosω = tanδ tan ( φ + β) ss

211 System design Irradiance on a tilted surface G bn, G bn, G bt, G b R bt, Gbt, Gbn, cosθ = = = G G cosθ cosθ cosθ b bn, z z R b,t = Ratio of Beam Irradiance normal to the earth s surface to Beam Irradiance normal to normal to a tilted surface

212 System design Irradiance: the atmosphere Effects of Rayleigh scattering and atmospheric absorption 2400 Direct Normal Spectral Irradiance Wm -2 µm O 3 H 2 O O 2 H 2 O, CO 2 Extraterrestrial Air mass 1.0 Rayleigh Attenuation O 3 H 2 O H 2 O, CO 2 H 2 O Wavelength µm -1

213 System design Irradiance: global irradiance

214 Variation of solar irradiance (%): Variation of solar irradiance with orientation and tilt for 52 o N tilt west sout h east 10 o o o o o o o o o 72 **this must be measured for the precise latitude in question.

215 Site suitability: US Site suitability is a function of the total number of sunlight hours available over the year. At present this is more a function of economics due to the high cost of pv versus its current efficiency.

216 Solar cell efficiency

217 Advantages and Disadvantages Advantages All chemical and radioactive polluting by products of the thermonuclear reactions remain behind on the sun, while only pure radiant energy reaches the Earth. Energy reaching the earth is incredible. By one calculation, 30 days of sunshine striking the Earth have the energy equivalent of the total of all the planet s fossil fuels, both used and unused! Disadvantages Sun does not shine consistently. Solar energy is a diffuse source. To harness it, we must concentrate it into an amount and form that we can use, such as heat and electricity. Addressed by approaching the problem through: 1) collection, 2) conversion, 3) storage.

218 Solar irradiance, annual variation, clear sky o N Irradiance (W/m 2 ) Sun-tracking Slope=Latitude-Declination Slope=Latitude 0 Horizontal J F M A M J J A S O N Month D

219 Solar irradiance, annual variation, clear sky o N Irradiance (W/m 2 ) Sun-tracking Slope=Latitude-Declination Slope=Latitude Horizontal J F M A M J J A S O N Month D