ESET 222 Solar Fundamentals Winter 2024 PDF

ESET 222 Wind & Solar Energy Winter 2024 Professor: Arun Hor. Solar Fundamentals Solar Radiation THE SUN: The sun is a gaseous body composed mostly of hydrogen, with some helium and traces of heavier elements. The sun fuses hydrogen into helium at its core under intense pressure and heat which then...

ESET 222 Wind & Solar Energy Winter 2024 Professor: Arun Hor. Solar Fundamentals Solar Radiation THE SUN: The sun is a gaseous body composed mostly of hydrogen, with some helium and traces of heavier elements. The sun fuses hydrogen into helium at its core under intense pressure and heat which then releases enormous amount of energy that radiates outward. This is called fusion process. The radiation from the inner core is not visible since it is strongly absorbed by a layer of hydrogen atoms closer to the sun's surface. Heat is transferred through this layer by convection. The surface of the sun, called the photosphere, is at a temperature of about 6000K and closely approximates a blackbody. It takes four hydrogen atoms to fuse into each helium atom. During the process some of the mass is converted into energy. Solar Radiation THE EARTH: Earth is the third planet from the Sun and the only astronomical object known to harbor life. According to radiometric dating and other sources of evidence, Earth formed over 4.5 billion years ago. Moon is earth's only natural satellite. Earth revolves around the Sun in 365.26 days, a period known as an Earth year. Earth takes 24 hours to rotate about its own axis. Solar Radiation A blackbody absorbs all radiation incident on its surface and emits radiation based on its temperature. Blackbodies derive their name from the fact that, if they do not emit radiation in the visible range, they appear black due to the complete absorption of all wavelengths. Atmospheric effects have several impacts on the solar radiation at the Earth's surface. The major effects for photovoltaic applications are summarized in the figure. Solar Radiation Radiation: It is a form of energy that emanates from a source in the form of waves or particles. Travelling at the speed of light (186,000 mi/sec), in a single hour, the amount of power from the sun that strikes the Earth is more than the entire world consumes in an year. Each hour 430 quintillion(1018)Joules of energy from the sun hits the Earth. That's 430 with 18 zeroes after it! In comparison, the total amount of energy that all humans use in a year is 410 quintillion Joules. An astronomical unit (AU) is the average distance between earth and the sun (93 million miles) and is used as a measuring unit for other distances in the solar system. Solar Insolation Photon: A photon is a fundamental unit of electromagnetic radiation. The high energy photons released in fusion reactions at the sun’s core take a very long time to reach the surface, losing energy along the way. Photon travel time is estimated to be tens of thousands of years. Upon reaching the sun’s surface, photons escape as visible light. Solar Insolation Solar Energy Basics Solar radiation – energy coming from the sun in the form of waves and small particles Solar noon – time of day when the sun is at it’s highest point in the sky Solar constant – energy of 1000 W/m2 at the equator at sea level at solar noon Solar Insolation Solar Energy Basics Solar irradiance – measure of solar power striking a specific location Solar irradiation – total amount of solar energy accumulated on an area over a period of time Insolation – another term for solar irradiation Solar Insolation Solar Irradiance: It is the power of solar radiation per unit area, commonly expressed in W/m2 or kW/m2. Solar Irradiation: It is the total amount of solar energy accumulated on an area over time, commonly expressed in Wh/m2 or kWh/m2. Solar irradiation also called Solar Insolation quantifies the amount of energy received on a surface over time, and is the principal data needed for sizing and estimating the performance of PV systems. The best place to find solar insolation data for a specific location is through the National Renewable Energy Laboratory (NREL) website. Solar Insolation Solar insolation can be calculated by applying the formula: H = E x t where, H is solar insolation (Wh/m2) ; E = average solar irradiance (W/m2) ; t = time (hour) Example: If the average solar irradiance is 600 W/m2 over 8 hrs, what is the total solar insolation over this period? H = Et = 600 x 8 = 4800 Wh/m2 = 4.8 kWh/m2 Solar Spectrum: Almost all the energy received from the sun is electro-magnetic radiation. Electro-magnetic radiation is radiation in the form of waves with electric and magnetic properties. The waves vary in lengths depending on source and energy level. The wavelength determines the properties of the radiation. Solar Insolation Extremely short wavelength (trillionth of a meter) radiation is called gamma rays which is high-energy radiation produced by sub-atomic reactions. Extremely long wavelength (millions of meters) radiation takes the form of radio waves, which are useful for transmitting data over long distances. In between are X-rays, ultra-violet radiation, visible light, and infra red radiation. The electro-magnetic spectrum is the range of all types of electro magnetic radiation, based on wave lengths. Solar Insolation Solar Radiation The Solar energy from the sun is redistributed as follows: When solar radiation passes through the earth atmosphere, it is Reflected Scattered Absorbed Transmitted 174 PW= 174 Petawatts (PW i.e.1015 w)=1.74 X 1017 watts Source: http://www.askmeaboutgreen.com/ Solar Radiation Peak sun hours calculations for a typical location: One peak sun hours = 3.6 MJ/m² = 1 kWh/m² Peak sun hours map ▪ Sunlight is nuclear electromagnetic radiation ▪ Sunlight comprised of a broad frequency spectrum ▪ Mostly visible (400 nm to 780 nm), Infrared, & ultraviolet ▪ X-rays, Gamma-rays Micro- & Radio-waves in small quantities ▪ Atmosphere & oceans act as filters Infrared ▪ The sun is a massive nuclear fusion reaction Visible Solar Radiation Spectrum Ultraviolet Solar Radiation Solar Radiation Direct, Diffuse and Reflected Radiation Direct radiation reaches on the earth surface directly from the sun Diffuse radiation reaches on the earth from the clouds or earth atmosphere Reflected radiation is radiation from the clouds, ground, buildings, trees, etc Solar Radiation Components of solar radiation Direct radiation (Ed) Diffuse radiation (Ef) Global solar radiation (Eg) Eg = Ed + Ef Reflected radiation (Er) Total radiation (Et) Et = Ed + Ef + Er Solar Radiation Air Mass AM (m=h2/h1) If h1=1 and h2=1 then AM=1 If h1=1 and h2=1.5 then AM=1.5 If h1=1 and h2=2 then AM=2 The amount of solar radiation on the earth surface depends on how much atmosphere it passes through before reaching the earth’s surface Solar Radiation The sun’s height above the horizon is called altitude. The sun’s apparent location in the sky east or west of true south is called azimuth. Solar Radiation Zenith angle, altitude angle and azimuth angle Solar Insolation Solar altitude and azimuth angle of sun Altitude angle define the height of sun Azimuth angle define the off-south position in the horizon Solar Radiation The sun’s zenith angle and solar radiation Zenith is the point in the sky directly overhead to a location When the sun is at zenith, the influence of atmosphere is minimum Higher zenith angle have more influence on sun’s rays INSOLATION reaching on the earth surface Solar Radiation Air mass and solar spectrum Air mass effects only direct radiation Higher the air mass lower the direct radiation on the earth surface Latitude & Longitude Solar Radiation The rotation of the earth about its axis also causes the day and night phenomenon. The length of the day and night depends on the time of the year and the latitude of the location. For places in the northern hemisphere, the shortest solar day occurs around December 21 (winter solstice) and the longest solar day occurs around June 21 (summer solstice). In theory, during the time of the equinox, the length of the day should be equal to the length of the night. video Solar Window Solar window – The area in the sky that is between the sun path of the winter solstice (December 21) and the sun path for the summer solstice (June 21) for the hours of 9:00 am to 3 pm Highest average insolation on a PV module – Tilt equal to latitude Solstice & Equinoxes March 21 June 21 Dec. 21 Sep. 21 video Photovoltaic Power The earth revolves around the sun in an elliptical orbit, making one revolution every 365.25 days. The eccentricity of the ellipse is small and the orbit is, in fact, quite nearly circular. The point at which the earth is nearest the sun, the perihelion, occurs on January 3, at which point it is a little over 147 million kilometers away. At the other extreme, the aphelion, which occurs on July 4, the earth is about 152 million kilometers from the sun. This variation in distance is described by the following relationship: where n is the day number, with January 1 as day 1 and December 31 being day number 365. Following table-1.1 provides a convenient list of day numbers for the first day of each month. It should be noted that trigonometric angles are in degrees, not radians. Photovoltaic Power Photovoltaic Power video Solar Declination The declination angle, denoted by δ, varies seasonally due to the tilt of the Earth on its axis of rotation and the rotation of the Earth around the sun. If the Earth were not tilted on its axis of rotation, the declination would always be 00. However, the Earth is tilted by 23.450 and the declination angle varies plus or minus this amount. Only at the spring and fall equinoxes is the declination angle equal to 00.The rotation of the Earth around the sun and the change in the declination angle is shown below. video Photovoltaic Power Solar Declination: The angle formed between the plane of the equator and a line drawn from the center of the sun to the center of the earth is called the solar declination, δ. It varies between the extremes of. Exact values of declination, which vary slightly from year to year, can be found from video Computed values of solar declination on the twenty-first day of each month are given below: Solar Declination The declination of the sun is the angle between the equator and a line drawn from the center of the Earth to the center of the sun. The seasonal variation of the declination angle is shown below. Photovoltaic Power Photovoltaic Power Solar position at any time of day: The location of the sun at any time of day can be described in terms of its altitude angle β and its azimuth angle φs. By convention, the azimuth angle is positive in the morning with the sun in the east and negative in the afternoon with the sun in the west. Notice that the azimuth angle shown in fig. below uses true south as its reference, and this will be our assumption unless otherwise stated. Photovoltaic Power The altitude angle is the angle between the sun and the local horizon directly beneath the sun. From figure below we can write down the following relationship by inspection: where L is the latitude of the site. Notice in the figure the term zenith is introduced, which refers to an axis drawn directly overhead at a site. Photovoltaic Power Solar Insolation Solar Radiation Measuring Equipment of solar irradiance Handheld pyranometer Pyranometer in the plane of PV system Pyranometer with shaded ring Solar Fundamentals Cell Voltage and Current Voltage: inversely proportional to temperature for crystalline silicon. When temperature increases, voltage decreases. Cell Voltage almost remains constant at 0.5V-0.6V. Current: directly proportional to cell surface area. When surface area increases, current increases. A typical commercially-available silicon cell produces a current between 28 and 35 milliamps per square centimeter. Conversion Efficiency Percentage of solar energy falling on the cell/module converted to electrical energy. Affected by factors such as: Interface connections between modules Shading Cleaning Reflection off the panels Solar Radiation Sun-Path for typical location (Latitude = 40) It is a curve between solar altitude and solar azimuth angle of sun Solar Radiation Fixed installation of PV system Optimum tilt angle = Latitude +150 (winter) = Latitude – 150 (summer) Solar Radiation One-axis PV Tracking systems Single axis tracking increases solar radiation 15 to 25% Solar Radiation Sun 2-axis tracking PV systems Two axis tracker increases solar radiation up to 30% Solar Radiation