April 14, 2010 1 ESCI-61 Introduction to Photovoltaic Technology Lecture #2 Solar Radiation Ridha Hamidi, Ph.D.
April 14, 2010 2 The Sun The Sun is a perpetual source of energy It has produced energy for about 4.6 billions of years, and it is expected to exist for another 5 billion years Because the Earth is only a tiny sphere in the vastness of space, it receives only about one billionth of the Sun s energy output. More energy from sunlight strikes the earth in one hour than all of the energy currently consumed on the planet in one year The amount of solar energy reaching the surface of the planet is so vast that in one year it is about twice as much as will ever be obtained from all of the Earth's nonrenewable resources of coal, oil, natural gas, and mined uranium combined
April 14, 2010 3 Yearly Solar Fluxes & Human Energy Consumption Solar Wind Biomass Primary Energy Use (2005) Electricity (2005) 3,850,000 EJ 2,250 EJ 3,000 EJ 487 EJ 57 EJ
April 14, 2010 4 Prefixes of the SI kilo, mega, giga, tera, peta, exa, zetta, yotta milli, micro, nano, pico, femto, atto, zepto, yocto Example, for temperatures 9 F = C + 32 C = ( F 32) 5 9 5
April 14, 2010 5 The Sun The sun is a giant nuclear fusion, or thermonuclear, reactor that runs on hydrogen fuel. It radiates energy in all directions as electromagnetic radiation Because the Earth is only a tiny sphere in the vastness of space, it receives only about one billionth of the Sun s energy output. Most ultraviolet radiation is absorbed by the ozone layer in the lower atmosphere. Visible light, heat, and a small amount of ultraviolet radiation reach the troposphere. About 34% of this solar energy is reflected back into space. The un-reflected radiation interacts with the Earth and degrades into heat, which the atmosphere radiates. Greenhouse gases slow the radiation of heat from the atmosphere into space. These gases help keep the Earth warm by acting somewhat like the glass in a greenhouse. Without the natural greenhouse effect, the Earth would be as cold as Mars and life as we know it would not exist.
April 14, 2010 6 Definitions Radiation Energy that expands outward from a source in the form of waves or particles Solar Irradiance (Solar Power) Intensity of the solar power (W/m 2 ) Solar Irradiation (Solar Energy) Total amount of solar energy accumulated on an area over time (Wh/m 2 ) Insolation Solar energy that reaches Earth s surface over the course of a day (KWh/m 2 /day) Solar Constant Average extraterrestrial solar power (irradiance) at a distance of 1 AU (93 million miles) from the Sun (1366 W/m 2 )
April 14, 2010 7 Energy & Power Energy is the ability to do work or to cause change Common units of energy: Joule, Calorie, BTU, Watt- Hour, Therm 1 BTU = 1055 J, 1 Cal = 4.18 J, 1 Wh = 3600 J, 1 Therm = 100,000 BTUs Power is the amount of work done or energy transferred per unit of time Power = Energy / Time or Energy = Power x Time Common units of power: Watt, Horse-Power 1 KW = 1.36 HP
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April 14, 2010 10 Electromagnetic Spectrum Many different forms of electromagnetic radiation exist, each having a different wavelength and energy content.
April 14, 2010 11 Electromagnetic Spectrum The Sun emits light primarily in the visible spectrum, but it also emits at other wavelengths Organisms vary in their ability to sense different parts of the spectrum.
April 14, 2010 12 Atmospheric Effects Solar radiation is absorbed, scattered, and reflected by components of the atmosphere Ozone, carbon dioxide, water vapor, other gases and particles Cloud cover, dust, storms, air pollution, volcanic eruptions
April 14, 2010 13 5% 46% 49%
April 14, 2010 14 Image Source: http://www.suntricity4life.com/sites/mnedd/_files/image/energy.jpg
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April 14, 2010 16 Solar Radiation Light from the sky dome Direct from the sun Everywhere but the sun Entire sky We call it Direct (beam) Diffuse (sky) Global (total) Global is the sum of direct and diffuse
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April 14, 2010 20 Air Mass The amount of solar radiation that is absorbed or scattered in the atmosphere depends on how much atmosphere it passes through before reaching Earth s surface. Air Mass (AM) is a representation of the relative distance of atmosphere that solar radiation must travel through to reach Earth s surface. AM0 : outside Earth s atmosphere AM1.0 : when the sun is directly overhead at sea level AM = 1 / cos θ, where θ is the zenith angle AM depends upon the time of day, the time of year, and the altitude and latitude of the specified location AM1.5 is considered representative of average terrestrial conditions in the US and is commonly used as a reference condition in rating modules and arrays
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April 14, 2010 23 Peak Sun One third of total solar energy at Earth s outer atmosphere is either reflected from clouds back into space, or scattered and absorbed by the atmosphere Peak sun is an estimate of peak solar irradiance reaching Earth s surface Generally accepted value is 1,000 W/m 2 or 1 KW/m 2 Peak sun hours is the number of hours required for a day s total solar irradiation to accumulate at peak sun condition
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April 14, 2010 25 Peak Sun For example Average irradiance is 600 W/m 2 over 8 hours Total irradiation = 600 x 8 = 4,800 Wh/m 2 = 4.8 peak sun hours References Solar Radiation Data Manual on NREL site http://rredc.nrel.gov/solar/pubs/redbook/ Solmetric Insolation Lookup Tool http://www1.solmetric.com/cgi/insolation_lookup/go.cgi
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April 14, 2010 27 Solar Radiation Data Manual http://rredc.nrel.gov/solar/pubs/redbook/ http://rredc.nrel.gov/solar/old_data/nsrdb/1991-2005/tmy3/by_state_and_city.html
April 14, 2010 28 Solar Radiation Data Manual http://rredc.nrel.gov/solar/pubs/redbook/ http://rredc.nrel.gov/solar/old_data/nsrdb/1991-2005/tmy3/by_state_and_city.html
April 14, 2010 29 Peak Sun - Sacramento Source : http://firstlook.3tiergroup.com/
April 14, 2010 30 Solar Irradiance 18 TWe correspond to an energy output of 13,567 Mtoe per year. World total primary energy supply (TPES) in 2006: 11,741 Mtoe (Mega Tons of Oil Equivalent) Image Source: http://www.ez2c.de/ml/solar_land_area/
April 14, 2010 31 Land Areas Location / Desert Africa, Sahara Australia, Great Sandy China, Takla Makan Middle-East, Arabian South America, Atacama U.S.A., Great Basin Desert Size / km 2 9,064,960 388,500 271,950 2,589,910 139,860 492,100 Area required / km 2 (*) 144,231 141,509 178,571 138,889 136,364 170,455 (*) assuming a conversion efficiency from incident sunlight to electricity of 8 %