Renewable Energy Technologies I PDF

PHYS7320 Renewable Energy Technologies I 1 Section 2. Solar Energy and PV Technologies Solar Energy : Source and Characterisitcs Using Solar Energy PV Technologies in Inorganic Solar Cells PV Technologies in...

PHYS7320 Renewable Energy Technologies I 1 Section 2. Solar Energy and PV Technologies Solar Energy : Source and Characterisitcs Using Solar Energy PV Technologies in Inorganic Solar Cells PV Technologies in Organic Solar Cells 2 Solar Resource Base There is an abundance of solar resource on Earth, which makes solar energy a promising and increasingly competitive source of renewable energies R Perez et al., The IEA SHC Solar Update 50 (2) 2009. 3 Energy from the Sun 44 Energy from the sun The Sun has produced energy by nuclear fusion for 4 billion years and it will continue to do so for another 5 billion years The composition of sunlight at the top of the Earth’s atmosphere is roughly 50% infrared radiation (heat), 40% visible light and 10% ultraviolet radiation (solar spectrum UV-vis-IR) Solar energy is effectively inexhaustible! 55 Energy from the sun The amount of energy that the Earth receives from the Sun every hour is approximately 626 exajoules (EJ), which is equivalent to more than the total amount of primary energy consumed by humans worldwide in one year However, some of this energy is reflected back into space and some is absorbed in the atmosphere Typical range of average solar intensity at different Earth’s surface is 100 to 300 Watt per meter square (W/m2) and the solar power technology will only produce an average electrical output of 5 to 10 W/m2 Nevertheless, we expect solar power to be one of the most important renewable technologies in the future 66 Solar radiation Solar radiation is the solar energy in the form of light spectrum (UV-Vis-IR) that can be captured and turned into useful forms of energy, such as heat and electricity, using a variety of technologies The technical feasibility and economical operation of these technologies at a specific location depends on the available solar resource Definition of some technical terms Solar irradiance (Power): It is the power of solar radiation per unit area, measured in unit of W/m2 It can be expressed as the amount of solar energy per unit time per unit area (i.e. P/A = E/tA) Solar irradiation (Energy): It is the energy of solar radiation per unit area, measured in unit of Wh/m2 It can be expressed as the power per unit area over a given period of time (i.e. E/A = Pt/A) 77 Solar Irradiance on the Earth Surface Average light intensity (power) of sunshine falling on a surface 8 Solar Irradiance on the Earth Surface Average light intensity (power) of sunshine falling on a surface in selected locations in Europe, North America, and Africa 99 Solar irradiance During the day, solar irradiance typically increases gradually in the morning as the sun rises, reaches a peak around noon when the sun is directly overhead, and then gradually decreases as the sun sets in the evening Solar irradiance is not constant throughout the day, as it varies depending on the position of the sun in the sky 1010 Solar irradiance and solar irradiation 1111 Peak sun hours (Solar insolation) Peak sun hours (PSH), also called solar insolation, indicates the daily amount of solar irradiation (energy) received on a surface It is equivalent to the number of hours in a day during which the the sunlight intensity at the peak of 1,000 W/m² For example: The daily solar irradiation (energy) incident on a surface is 4.8 kWh/m2 (area under the blue curve), which is equal to 4.8 PSH (area under the box) 12 Peak sun hours (Solar insolation) Peak sun hours (PSH), also called solar insolation, indicates the daily amount of solar irradiation (energy) received on a surface It is equivalent to the number of hours in a day during which the the sunlight intensity at the peak of 1,000 W/m² For example: The average solar power incident on a surface is 400 W/m2 for 12 hours PSH can be calculated as: 400 W/m2 × 12 hours = 4.8 kWh/m2 = 4.8 PSH 13 Peak sun hours (Solar insolation) Peak sun hours (PSH), also called solar insolation, indicates the daily amount of solar irradiation (energy) received on a surface It is also defined as the number of hours in a day during which the intensity of the sunlight is equivalent to an average of 1,000 watts per square meter (W/m²) Why is 1,000 W/m2 commonly used as reference? 1,000 W/m2 is the standard reference value that represents the amount of solar irradiance present on a clear day at noon at the sea level near equator 14 Variation of solar radiation The solar irradiance at the top of atmosphere is always constant, with the measured average value approximately 1,366 W/m² (called solar constant) It can vary slightly with changes in solar activity and the distance between the sun and the Earth over the course of a year However, the actual amount of solar radiation that reaches the Earth's surface will be less than the solar constant due to atmospheric absorption reflection and scattering The solar irradiance is approximately 1,000 W/m² on the earth surface at sea level on a clear day at solar noon near equator The amount of solar radiation that reaches the Earth's surface also depends on a number of factors such as the location, altitude, latitude, time of day and year, and weather conditions Typical average solar intensity at the Earth’s surface is 100 to 300 W/m² 15 15  Variability of solar radiation in short period …effect of latitude and time of day, time of year 16 16 Variability of solar radiation The amount of solar radiation that reaches any one spot on the Earth's surface varies according to: Geographic location (latitude) Combination of these Related to solar angle Time of day three factors (position of the sun) Season (time of year) Local landscape Local weather *In the next section, we will discuss how the solar radiation is affected by the Earth's atmosphere, including its absorption, scattering, and reflection by various atmospheric components 17 17 Variability of solar radiation due to the sun’s position The project effect can be used to explain changes in the light intensity (irradiance) on the Earth's surface that are caused by the position of the sun Projection effect The amount of sunlight Case b onto a portion of the earth relative to its tilt Case a Case a Case b Case a: The sunlight is projected directly overhead Case b: The sunlight is projected at an angle to the normal of the surface 18 18 Geographic location (latitude) The angle of the sun's rays varies with latitude, and the projection effect causes equal amounts of sunlight to be spread over different surface areas Low latitudes receive more solar energy and experience warming Higher latitudes receive less solar energy and experience cooling 19 19 Time of day Noon Morning Evening (Sunrise) (Sunset) Light irradiance varies throughout the day due to changes in the angle of incoming sunlight, which can be explained by the projection effect 20 20 Season (time of year) In different seasons, the position of the sun in relation to the Earth varies throughout the year This variation in sun position results from the tilt of the Earth's axis as it orbits the sun Consequently, the length of daytime also varies as a result of these changes in the Earth's axial tilt during different seasons The Earth's axis is tilted at an angle of approximately 23.5 degrees relative to its orbital plane Different parts of the planet receive varying amounts of sunlight depending on their orientation relative to the sun 21 21  Season (time of year) In different seasons, the position of the sun in relation to the Earth varies throughout the year This variation in sun position results from the tilt of the Earth's axis as it orbits the sun Consequently, the length of daytime also varies as a result of these changes in the Earth's axial tilt during different seasons In the Northern Hemisphere, during the summer months, such as June, the hemisphere is tilted towards the sun This tilt leads to an increased amount of sunlight on the region The daytime become longer, with Winter months in Summer months in extended periods of daylight, while North hemisphere North hemisphere the nights become shorter 22 22  Season (time of year) In different seasons, the position of the sun in relation to the Earth varies throughout the year This variation in sun position results from the tilt of the Earth's axis as it orbits the sun Consequently, the length of daytime also varies as a result of these changes in the Earth's axial tilt during different seasons In the Northern Hemisphere, during the winter months, such as Dec, the hemisphere is tilted away the sun This tilt leads to an decreased amount of sunlight on the region The nights become longer, with Winter months in Summer months in extended periods of night time, North hemisphere North hemisphere while the daytime become shorter 23 23  Season (time of year) In different seasons, the position of the sun in relation to the Earth varies throughout the year This variation in sun position results from the tilt of the Earth's axis as it orbits the sun Consequently, the length of daytime also varies as a result of these changes in the Earth's axial tilt during different seasons At the equator, the length of daytime remains relatively constant throughout the year, as the angle of the sun's rays changes only slightly with the seasons Winter months in Summer months in North hemisphere North hemisphere 24 24  Season (time of year) In different seasons, the position of the sun in relation to the Earth varies throughout the year This variation in sun position results from the tilt of the Earth's axis as it orbits the sun Consequently, the length of daytime also varies as a result of these changes in the Earth's axial tilt during different seasons At higher latitudes, such as in the polar regions, the changes in the angle of the sun's rays are more dramatic, resulting in extreme variations in the length of daytime and night time between the summer and winter months The North Pole experiences periods Winter months in Summer months in of continuous daytime in summer North hemisphere North hemisphere and continuous night time in winter 25 25 Season (time of year) The length of daytime varies with the seasons due to changes in the tilt of the Earth's axis as it orbits the sun Period of Daylight Length of day (sunrise to sunset) in northern latitudes as a function of day of the year (Loomis and Connor, 1996) 26 26 Solar angle: combination of latitude, time of day and year Determine the sun’s position in the sky, resulting in variation of solar radiation 27 27  Local weather As sunlight passes through the atmosphere, some of it is absorbed, scattered, and reflected by: Air molecules Water vapor Clouds Dust Pollutants Forest fires Volcanoes Atmospheric conditions can reduce direct beam radiation by 10% on clear, dry days and by 100% during thick, cloudy days Source: 2012 Jim Dunlop Solar 28  Local weather Example of global (total) irradiance on a horizontal surface for a mostly clear day and a mostly cloudy day in Greenbelt, MD (Thekaekara, 1976): (a) global solar radiation for the day was 27.1 MJ/m2; (b) global solar radiation for the day was 7.3 MJ/m2 Source: www.powerfromthesun.net 29  Variability of solar radiation throughout the year …the effect due to the Earth’s atmosphere 30 30 Direct and diffuse solar radiation diffuse Direct 31 Direct and diffuse solar radiation Solar radiation can be classified in two categories: Direct radiation (beam radiation): The radiation comes straight from the sun without scattering Diffuse radiation: The radiation is scattered by the atmosphere and clouds. On the ground this appears to come from all over the sky For a horizontal surface, global (total) solar radiation (G) is the sum of direct radiation (B) and diffuse radiation (D) G=B+D Additionally, there is reflected radiation that describes sunlight reflected from non- atmospheric objects such as the ground 32  Direct and diffuse solar radiation When the sun is very high (e.g. noon) and sky is clear, direct radiation is around 85% and diffuse radiation is around 15% of total radiation When the sun goes lower, the percent of diffuse radiation keeps increasing When the sun is 10o above the horizon (e.g. sunset or sunrise), diffuse radiation is around 40% Ratio of direct to diffuse radiation varies with latitude and climate Photovoltaic and solar hot water systems can make use of both direct radiation and diffuse radiation Concentrated solar power, on the other hand, requires a lot of direct radiation Concentrated solar power plant Reference: Ft exploring; Encyclopaedia of Geomorphology, Mahammad Naqi 33 Air mass number At lower angle of sunlight, the Atmospheric effects amount of radiation reaching the earth is less than the overhead. atmospheric scattering atmospheric absorption The air mass number (AM#) is a parameter used to quantify the path length of sunlight through the Earth's atmosphere before reaching the Earth's surface AM# is commonly used to characterize the spectral distribution and intensity of solar radiation at different locations and times Air mass number is defined as the length of hypotenuse divided by object height: AM = c/h 34 34 Air mass number The AM# is the ratio of the actual passage through the atmosphere and the thickness of the atmosphere Elevation angle 𝜷 of the sun Angle of incidence (elevation angle) of the sun: 𝜷 The air mass number is: AM# = 1 / sinβ 35 Air mass number The attenuation of sunlight power through the atmosphere relates to the AM#, is roughly: Attenuation (%) = 100% [1-exp(–AM#/3.826)] For AM1, the attenuation is 23% (77% of sunlight left) When AM is increased: direct radiation is reduced and diffuse radiation is increased, resulting in reduced total amount of solar radiation Left figure shows: Absorption and scattering of sunlight in clear sky days and directly through the atmosphere (AM1 case) Sunlight power (irradiance) on earth surface at sea level on a clear day at solar noon is: 0.77*1366W/m² = 1052 W/ m² Solar irradiance at the top of atmosphere (AM0) while the sun is directly above that surface (i.e. at AM#1 case) We can calculate the solar irradiance at different locations and times 36  The spectrum of radiation from the sun AM1.5 spectrum is a standard for solar cells or concentrators testing It because AM1.5 is a good representation of the yearly average irradiance in numerous populated cities located within mid- latitudes AM1.5 Global includes both direct and diffuse sunlight. AM1.5 Global: Used for testing of Flat Panels (Integrated power intensity: 1000 W/m²) AM1.5 Direct: Used for testing of concentrators (900 W/m²) AM0: Solar spectrum at the top of the atmosphere, outer space (1366 W/m²) Source of data: http://www.nrel.gov/rredc/smarts/ 37  The spectrum of radiation from the sun In the AM1.5 spectrum, certain peaks, particularly in the infrared (IR) region, may appear diminished or missing. This phenomenon is a result of the absorption of specific wavelengths by atmospheric gases and water vapor, including H2O, CO2, O3, and others. AM1.5 Global includes both direct and diffuse sunlight. AM1.5 Global: Used for testing of Flat Panels (Integrated power intensity: 1000 W/m²) AM1.5 Direct: Used for testing of concentrators (900 W/m²) AM0: Solar spectrum at the top of the atmosphere, outer space (1366 W/m²) Source of data: http://www.nrel.gov/rredc/smarts/ 38 The spectrum of radiation from the sun 2.5 Ultra Visible Infrared Violet Light Heat Spectral irradiance (Watts/m2/nm) (~9%) (~40%) (~50%) 2.0 1.5 1.0 0.5 AM0 0.0 280 460 560 660 760 860 960 1,460 1,060 1,160 1,260 1,360 1,560 1,660 1,995 2,495 2,995 3,495 3,995 360 Note Wavelength (nm) 1 nanometer (nm) = 10-9 m 39 Solar spectrum at Earth’s surface O3 O2 H2O H2O H2O H2O CO2 H2O 40 40 The spectrum of radiation from the sun Solar spectrum Electromagnetic spectrum The full solar spectrum represents only a portion of the electromagnetic (EM) wave spectrum 41 Summary In physics, the Sun can be approximated as a blackbody that emits radiation based on its temperature, which is approximately 5500 degrees Celsius 42 42  Energy balance for the earth-atmosphere system (Incoming and outgoing energy) 43 43 Energy balance for the earth-atmosphere system Solar radiation contains infrared, visible and incoming solar ultraviolet radiation radiation 100% The majority of energy from the Sun reaches Earth in the form of visible light reflected radiation 29% atmospheric absorption Approximately half of the incoming solar 23% energy actually reaches the ground (48%) The remaining portion is either reflected reflected back by low-level, thick, white clouds or ice, by clouds 22% and the Earth's surface (22% + 7%), or it gets surface absorbed by the atmosphere (23%) absorption 48% reflected by surface 7% 44 Energy balance for the earth-atmosphere system After the solar energy is absorbed by the incoming solar Earth or the atmosphere, it is primarily outgoing heat radiation 100% re-emitted as heat in form of radiation or 71% through processes such as evaporation of water vapors and convection of warm air reflected atmospheric radiation emission 29% 59% atmospheric window atmospheric 12% absorption 23% greenhouse gases and The energy leaving clouds the earth surface reflected by clouds 22% evaporation surface convection absorption 30% surface 48% radiation radiation back reflected 117% to surface by surface 100% 7% 45 Energy balance for the earth-atmosphere system outgoing incoming solar heat radiation 71% 100% The earth itself also emits heat in the form of thermal radiation due to Earth internal heat source reflected atmospheric radiation emission 29% 59% atmospheric window atmospheric 12% absorption 23% greenhouse gases and The energy leaving clouds the earth surface reflected by clouds 22% evaporation surface convection absorption 30% surface 48% radiation radiation back reflected 117% to surface by surface 100% 7% 46 Energy balance for the earth-atmosphere system Without the effect of greenhouse gases, the energy radiated out into space outgoing incoming solar heat radiation (71%) should be equal to the energy 71% 100% retained within the Earth (76%) reflected atmospheric radiation emission 29% 59% atmospheric window atmospheric 12% absorption 23% greenhouse gases and The energy leaving clouds the earth surface reflected by clouds 22% evaporation surface convection absorption 30% surface 48% radiation radiation back reflected 117% to surface by surface 100% 7% 47 Energy balance for the earth-atmosphere system A higher concentration of greenhouse outgoing incoming solar radiation gases will radiate more heat back to heat 71% 100% the surface The surface temperature will increase to restore thermal equilibrium reflected atmospheric radiation emission 29% 59% atmospheric window atmospheric 12% absorption 23% greenhouse gases and The energy leaving clouds the earth surface reflected by clouds 22% evaporation surface convection absorption 30% surface 48% radiation radiation back reflected 117% to surface by surface 100% 7% 48 Energy balance for the earth-atmosphere system The Earth receives 340W/m2 of energy from the Sun (29% is reflected back into space 71% is absorbed by the Earth’s surface and the atmosphere) The Earth’s surface warms and emits heat (infrared radiation) Greenhouse gases absorb heat emitted from the Earth’s surface and their temperature increases Ø The warmed greenhouse gases radiate heat back to the Earth’s surface (and also out into space) Ø Surface temperatures rise due to the heat from the greenhouse gases Usually, the amount of energy entering a system should equal the amount of energy leaving a system Ø If a system took more energy, the system would increase in temperature Ø If it released more energy, temperature would decrease 49 Sources of Energy The Earth has three primary sources of energy: solar energy, geothermal (earth) energy and tidal (moon) energy Solar energy: 99.895 % Sun Earth Moon Solar Hydro Wind Wave Biomass Geothermal Tidal As the energy moves through the system, Geothermal Tidal energy: it is changed in different forms energy: 0.013 % 0.002 % (mechanical energy, chemical energy, etc.) 50 Energy flow of the planet earth The energy inputs to the earth that convert into different forms of renewable energies 51 Section 2. Solar Energy and PV Technologies Solar Energy : Source and Characterisitcs Using Solar Energy PV Technologies in Inorganic Solar Cells PV Technologies in Organic Solar Cells 52 Using solar energy Using solar energy does not change the biosphere energy balance Ø Energy absorbed by water or land, in photosynthesis, or used by humans is ultimately lost as heat Solar energy is abundant but diffuse Ø Varies with season, latitude, and atmospheric conditions Using solar energy requires turning a diffuse, intermittent source into a form (fuel, electricity) that can be used Collection, conversion, and storage of solar energy are difficult and must be cost effective Sunlight can be used passively or actively 53 Using solar energy passively or actively? Active solar systems: The solar systems use mechanical or electrical components to collect and distribute solar energy These systems actively capture solar radiation and convert it into usable forms of energy Passive solar systems: The solar systems rely on natural principles of heat transfer and building design to maximize the utilization of solar energy without the need for mechanical or electrical components These systems work by optimizing the building's orientation, layout, insulation, and use of materials to passively collect, store, and distribute solar heat and light All solar design starts from a simple base - Passive Solar First Passive solar applies both to buildings and equipment 54 Using solar energy in three ways Solar Photovoltaic (PV) Active Solar System Concentrating solar thermal electric power Solar thermal systems Active/ Passive Ø Active solar thermal systems Solar System Ø Passive solar heating, passive solar space heating Photovoltaic systems (light directly into DC electricity) *We will discuss the topic on Solar PV in more detail during the next lecture 55 Concentrating solar thermal electric power 56 56 Concentrating solar power (CSP) Concentrating solar thermal electric power, or in short, just concentrating solar power (CSP) plants produce electric power by converting the sun's energy into high-temperature heat using various mirror configurations The heat is then channeled through a conventional generator The plants consist of two parts: one that collects solar energy and converts it to heat, and another that converts heat energy to electricity Concentrating solar energy (CSP) Technologies Ø Parabolic Trough Systems Ø Power Tower Systems Ø Dish/Engine Systems 57 https://www.youtube.com/watch?v=rO5rUqeCFY4&t=47s 58  Parabolic Trough Systems Solar energy -> Heat energy -> Mechanical energy -> Electricity Solar energy heats up the receiver tube located at the focal point, containing the thermal or molten salt The heated fluid transfer heat to another closed-loop water circulation connected to the electrical generator 59  Power Tower Systems Solar energy is used to heat up a central receiver that contains the working fluid, typically a ceramic material known for its excellent heat absorption properties The heat from the receiver is then transferred to generate high-pressure steam, connected to the electrical generator Solar energy -> Heat energy -> Mechanical energy -> Electricity https://www.youtube.com/watch?v=QTNU1JMhzxA 60 Dish/Engine Systems Solar energy heats up the working fluid within the receiver, causing the gas expand and drive the pistons of the Stirling engine Solar energy -> Heat energy -> Mechanical energy -> Electricity 61 61 Solar thermal system 62 62 Active solar thermal system Solar collectors are installed on the rooftop to harness heat energy from the sun 63 Principles of flat-panel solar collector Solar collector Some systems have backup components that can use fossil fuels as a supplementary heating source, particularly during periods of low sunlight or high demand of hot water 64 Rooftop hot water 65 65 Passive solar heating The position of the sun varies throughout different seasons. The design and layout of a house can be optimized to capture more heat during winter and minimize heat gain during summer 66  Solar building siting Additionally, the house is constructed using insulating materials that facilitate the trapping of solar heat inside the house during winter while preventing heat from entering during summer 67  Passive hot-air solar heating This passive heating method allows sunlight to enter the building and heats up the air inside. It relies on the principles of solar radiation, natural convection, and proper building design to passively collect, store, and distribute heat 68