Unit1_156_12
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1 MSE 156/256 - Solar Cells, Fuel Cells and Batteries: Materials for the Energy Solution Bruce Clemens Department of Materials Science and Engineering Stanford University Unit I: Solar Resource • Solar spectrum - how the sun delivers energy • Solar spectrum compared to black body radiation • How much energy does the sun deliver • Atmospheric effects • Distribution of Solar Resource • Photon Flux: How many photons at each energy come from the sun Electromagnetic Radiation E H Electromagnetic radiation characterized by: Speed of light 3 x 10 8 m/s • Wavelength • Frequency • Photon energy Planck Constant
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Transcript of Unit1_156_12
1
MSE 156/256 - Solar Cells, Fuel Cells and Batteries: Materials for the Energy Solution
Bruce Clemens
Department of Materials Science and Engineering Stanford University
Unit I: Solar Resource • Solar spectrum - how the sun delivers energy • Solar spectrum compared to black body radiation • How much energy does the sun deliver • Atmospheric effects • Distribution of Solar Resource • Photon Flux: How many photons at each
energy come from the sun
Electromagnetic Radiation
E HElectromagnetic radiation characterized by:
Speed of light 3 x 108 m/s • Wavelength
• Frequency
• Photon energy
Planck Constant
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Solar Spectra Solar irradiance
Amount of power delivered per area per unit wavelength range
Integrate solar irradiance over wavelength
wavelength
2000
1500
1000
500
043210
1200
1000
800
600
400
200
0
AM0 5960 K Spectra
AM0 = Air Mass 0 (no atmosphere)
Solar Constant The total energy flux (energy per time per area) incident on a unit area perpendicular to a beam outside the Earth’s atmosphere
Earth
Sunlight beam
Unit area
Solar Spectra: Wavelength
2000
1500
1000
500
043210
1200
1000
800
600
400
200
0
AM0 5960 K Spectra
AM0 = Air Mass 0 (no atmosphere)
Compare Solar Radiation to Blackbody Radiation
Planck’s Constant
Boltzmann’s Constant
Solid angle subtended by sun from earth
Density of photon modes Geometry, conversion
Occupation probability earth sun
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Solar Energy Hitting the Earth
The total energy flux incident on a unit area perpendicular to a beam outside the Earth’s atmosphere
Solar Constant
The earth intercepts an area
Radius of earth
Total power intercepted by earth
This is distributed over the total surface area of earth
Average energy flux incident on a unit surface area:
This corresponds to an annual average of:
Recall that each person in US uses ~ 11.3 kW = 100,000 kW hr/year
Scattering
Diffuse component Absorption
Albedo
Atmosphere Effects
Atmosphere
Air Mass = 1 Air Mass =
• In this area, about 30% of light is diffuse (averaged over the year)
• Flat photovoltaic panels can use this diffuse light
• Concentrating systems, which rely on focusing directional light, cannot
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Air Absorption Air Mass Factor
= angle of sun from horizon
AM0 no air
AM1.5
About Seattle WA at 12:00 noon at the equinox
2000
1500
1000
500
03.02.52.01.51.00.50.0
AM0 5960 Kelvin Blackbody AM1.5 (Including diffuse)
AM1.5 Spectra Includes: • Direct radiation • Diffuse radiation scattered from air • Diffuse radiation scattered from ground • http://rredc.nrel.gov/solar/spectra/am1.5/
H2O
CO2
Earth
Atmosphere
Solar Resource with Air
Again integrate over wavelength to find total power density
Recall for AM0 we get 1367 W/m2
For AM1.5 we get 1000 W/m2
Reduction due to atmosphere for AM1.5
2000
1500
1000
500
03.02.52.01.51.00.50.0
1400
1200
1000
800
600
400
200
0
AM0 5960 Kelvin Blackbody AM1.5 (Including diffuse)
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Solar Power Potential Hitting 3% of the Earth’s
Land Harvested with 15%
Efficiency
Coal
Oil
Natural Gas
Nuclear Hydro
World Power Sources, Solar Power Potential
Worldwide Solar Resource
Estimate of Available Solar Power • Use 10% of unused land • 1/2 of which is covered by 10% efficiency cells
128,000 TW Striking earth surface
80 TW available
15 TW Solar array 780 km on a side
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USA Solar Power Resource
To make our 11,300 Watts, each person needs a PV array about 60 feet on a side
The stuff had better be cheap! - and abundant
Solar Spectra: Photon Energy Solar spectra as a function of photon energy
Also sometimes useful to consider photon flux density
Can relate to our old buddy irradiance
Power per area in wavelength increment
Power per area in corresponding photon energy increment
4
3
2
1
0
x1021
43210
AM1.5 5960 K Spectra
Divide power density by energy per photon
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Solar Spectra: Photon Flux
Number of photons per area per time per energy increment
We can integrate this to find the photon flux in a given energy range (for example the photons that have a energy greater than the bandgap in a photovoltaic device)
This will be important when we discuss PV efficiency.
4
3
2
1
0
x1021
43210
2.0
1.5
1.0
0.5
0.0
x1021
AM1.5 5960 K Spectra
MSE 156/256 - Solar Cells, Fuel Cells and Batteries: Materials for the Energy Solution
Stanford University Autumn 2012
Unit I: Solar Resource • Solar spectrum - how the sun delivers energy • Solar spectrum compared to black body
radiation • How much energy does the sun deliver • Atmospheric effects • Distribution of Solar Resource • Photon Flux: How many photons at each
energy come from the sun
Unit 2: Semiconductors – a critical component of a solar cell
Coming Up:
