Renewable energy – solar energy

Renewable energy – solar energy

Prepared by

Wan, Man Pun Assistant Professor School of Mechanical & Aerospace Engineering MA0100 – Environmental Sustainability

Solar energy Solar energy is the energy sorce that sustains life on Earth for all plants, animals, and people. Solar energy can be tapped directly (e.g., PV or solar-thermal); indirectly as with wind, biomass, and hydropower; or as fossil fuels. Sunlight is by far the largest carbon-free energy source on the planet. Some interesting facts: -

More solar energy strikes the Earth in an hour (4.3 × 1020 J) than all the energy consumed on the planet in a year (4.1 × 1020 J).

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Each year the Earth receives about 10 times as much energy from sunlight as that contained in all the known reserves of coal, oil, natural gas, and uranium combined.

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Earth’s energy balance (re-visited) Extra-terrestrial radiation

Terrestrial radiation

3 [http://earthobservatory.nasa.gov/Features/EnergyBalance/page6.php]

Insolation reaching Earth’s surface

[https://www.e-education.psu.edu/earth103/files/earth103/module03/sw%20in%20erbe_total%202.png]

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Apparent path of the sun 21 Jun 21 Mar

21 Dec 21 Sept

21 Dec

21 Jun

Northern Hemisphere

Equinoxes

Southern Hemisphere

Jun solstice

Dec solstices5

Position of the sun w.r.t. a horizontal surface

z – zenith angle  - hour angle

s – solar altitude  - declination

s – solar azimuth  - latitude

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Sun charts Latitude = 0o (e.g., Singapore)

Jun 21

Latitude = 30o (e.g., Shanghai) Dec 21

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Solar radiation spectrum

[http://en.wikipedia.org/wiki/File:Solar_Spectrum.png] 8

Radiation intensity of a black body Plank’s law Spectral radiation intensity emitted by a black body at absolute T

I b 

C1

1

5 exp C2   1  T  



Plank’s constants: C1 = 3.746 x 10-16 Wm2, C2 = 0.014384 mK  - wavelength

Stefan-Boltzmann law 

I b   I b d  T 4 0

Stefan-Boltzmann constants:  = 5.67 x 10-8 W/(m2K4)

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Terrestrial solar radiation Total solar radiation and its components The total solar radiation incident on a surface consist of 3 components: beam, diffuse and reflected radiation I = Ib + Id Ib – direct beam solar radiation, the solar radiation that reaches the Earth’s surface without being modified in the atmosphere. Id – diffuse solar radiation, the portion of radiation scattered by the atmosphere that reaches the Earth’s surface and the reflected energy from the surroundings.

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Insolation Solar constant The insolation on a surface that faces the sun and is just outside Earth’s atmosphere, the solar constant,

ISC  1366 W/m2

Irradiance Instantaneous radiant power incident on a surface, per unit area (W/m2)

Insolation Integration of irradiance for a specific period of time (J/m2)

Peak Sun Hours (PSH) the power received by a unit area of horizontal surface during total daylight hours with the corresponding hypothetical number of hours for which irradiance would have been constant at one kW/m2.

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Insolation

PSH representation

[Foster et al., Solar Energy, CRC Press, 2010] 12

Monthly average daily extra-terrestrial insolation on a horizontal surface (Ho, in MJ/m2)

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[Foster et al., Solar Energy, CRC Press, 2010]

Measurement of terrestrial solar radiation Radiation from the entire sky vs direct solar radiation

Pyranometer for global solar radiation measurement

Pyrheliometer with sun trakker for direct solar radiation measurement 14

[Foster et al., Solar Energy, CRC Press, 2010]

Solar collector

Flat plate solar collector (Concentration ratio, C = 1)

A Geometric concentration ratio, C  a Ar I Flux concentration ratio, C  r Ia

Aperture area Energy collecting area

Energy flux at collecting area Energy flux at aperture

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Solar collector

Concentrating collector (Concentration ratio, C > 1)

[http://www.entrepreneur.com/businessid eas/graphics/solartube.jpg]

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Solar collector Concentrating collector

[http://www.edmundoptics.com/images/c atalog/3093_la_Good.jpg]

Compound parabolic concentrator

[http://www.ucsusa.org/assets/images/ce/trough.jpg]

Parabolic trough collector

[http://infohost.nmt.edu/~helio/images/figure1array.JPG]

Heliostats

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Solar thermal systems Since solar irradiance is transient, solar thermal collectors are usually accompanied by energy storage and control devices to provide a more stable supply of energy.

Solar still

Domestic hot water system

Industrial solar thermal system

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Photovoltaic cells The photovoltaic (PV) effect

Create a potential barrier by doping n-p junction n-side

p-side

Voltage difference

[NREL, 1982] 19

Photovoltaic cells Typical I-V curve of a crystalline PV module, 1000 W/m2 solar irradiance

[Foster et al., Solar Energy, CRC Press, 2010] 20

Photovoltaic cells Environmental parameters that affects PV performance

PV module current diminishes as solar irradiance decreases

PV module voltage drops as temperature increases

[Foster et al., Solar Energy, CRC Press, 2010] 21

PV arrays A group of PV modules connected together

Connect in parallel for increasing current Connect in series for increasing voltage

[Foster et al., Solar Energy, CRC Press, 2010] 22

End

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