Post on 12-Aug-2020
Lecture 1Overview: Sun, Earth, and the Solar Cell
M. A. Alam
alam@purdue.edu
Electrical and Computer Engineering
Purdue University
West Lafayette, IN USA
Theory and Practice of Solar Cells: A Cell to System Perspective
1
M. A. Alam, PV Lecture Notes
33
Outline
1) Introduction: A short history of solar energy
2) The story of the sun and sunlight
3) Earth’s atmosphere determine sunlight on ground
4) Solar cells are extremely inefficient
5) Levelized cost of electricity as a savior
6) ConclusionsM. A. Alam, PV Lecture Notes
44
Solar resources and potential
Solar energy can meet world energy demand
1000-fold extra!
Source: OECD Observer No. 258/59 December 2006
𝐴 = 510 × 1012 𝑚2
𝑃 = 103 𝑊/𝑚2
𝐷 = 0.1 − 0.3𝑃𝑇~ 50 − 150 𝑃𝑊
𝑊 = 7.7 × 109
𝑃 = 2.5 × 103 𝑊𝑃𝑇~ 2 𝑇𝑊
M. A. Alam, PV Lecture Notes
55
Even a small-state like Indiana..
Source: Nate
Lewis
(Caltech)
M. A. Alam, PV Lecture Notes
A brief history
Great benefits for telephone users and for all mankind will come
From this forward step in harnessing the limitless power of the sun.
-- Bell Telephone Laboratories, 1954.
Use in Telstar in 1962 and other satellites thereafter Increasing terrestrial deployment all over the world
6
77
Off-grid application …
On/off grid
Scalability
Siting
Speed of installation
Peak profile vs. demand
M. A. Alam, PV Lecture Notes
88
Types of Solar Energy Converter
Photo: Brightsource Energy,
http://ecotechdaily.com/wp-content/uploads/2008/04/brightsource2_620px.jpgPhoto: Stirling Energy Systems,
www.wapa.gov/ES/pubs/esb/1998/98Aug/Graphics/Pg5b.jpg
Source: TGW, http://openlearn.open.ac.uk/file.php/1697/220880-1f1.29.jpgPhoto: Ausra, Inc.,
www.instablogsimages.com/images/2007/09/21/ausra-solar-farm_5810.jpg
9
Top ten corporate users
M. A. Alam, PV Lecture Notes
1010
Outline
1) Introduction: A short history of solar energy
2) The story of the sun and sunlight
3) Earth’s atmosphere dictates sunlight on ground
4) Solar cells are extremely inefficient
5) Levelized cost of electricity as a savior
6) Conclusions
M. A. Alam, PV Lecture Notes
1111
Actors: Sun, Earth, Solar cell, and bank
Sun Temp. 5777 K
Distance: 1.496𝑥1011 𝑚Earth Radius: 4000 miles
Temperature: 300K
Irradiance ... 1000 W/𝑚2
PV Max. Efficiency = 1/3
Bank interest – 4-5%
M. A. Alam, PV Lecture Notes
1212
Sun is a nuclear reactor
M. A. Alam, PV Lecture Notes
1313
The extraterrestrial solar intensity is easily calculated
𝑟𝑠 𝑑
0 0.5 1 1.5 2
x 1012
100
101
102
103
104
105
Ear
th
Satu
rn
Mar
s
Jupiter
d (m)
𝐼 0𝑑
(W/m
2)
𝐼𝑠 = 𝜎 𝑇𝑠4
𝜎 = 5.67 × 10−8W
m2K4𝐼0(𝑑) = 𝐼𝑠
𝑟𝑠𝑑
2
1414
Measuring sun’s temperature without a thermometer
𝐼0 𝑑 = 𝜎𝑇𝑠4 = 𝐼𝑠
𝑟𝑠𝑑
2
𝜃 = 2 𝑟𝑠/𝑑
𝜎 is known from SB relation
𝐼𝑠 is known from balloon experiment𝑟𝑠 d
Measure 𝜃 by angle-ratio
𝑑 is known by Newton’s law
𝑟𝑠 is determined.
M. A. Alam, PV Lecture Notes
Temperature of the Sun
𝜎 = 5.67 ∗ 10−8𝑊
𝑚2𝐾4(SB constant)
𝐼0(𝑟𝑝) = 1367𝑊/𝑚2 (solar constant)
𝑟𝑝 = 1.496 × 1011 𝑚 (earth to sun radius)
𝑟𝑠 = 6.963 × 108 (radius of sun)
𝑇𝑠 =𝐼0 𝑟𝑝 × 4𝜋𝑟𝑝
2
𝜎 4𝜋 𝑟𝑠2
14
= 5775.8 𝐾
M. A. Alam, PV Lecture Notes
15
1616
Outline
1) Introduction: A short history of solar energy
2) The story of the sun and sunlight
3) Earth’s atmosphere and sunlight on ground
4) Solar cells are extremely inefficient
5) Levelized cost of electricity as a savior
6) ConclusionsM. A. Alam, PV Lecture Notes
Only a fraction of sunlight arrives at the
ground (and that is a very good thing!)
𝑇𝑝 = 𝑇𝑠𝑟𝑠2𝑑
1 − 𝛼
𝜖
𝛼 = albedo of the planet𝜖 = emissivity of the planetd = planet − earth distance
𝑃𝑎𝑏𝑠 = 1 − 𝛼 𝑃𝑝𝑙𝑎𝑛𝑒𝑡𝑃𝑒𝑚𝑖𝑡 = 𝜖 𝜎 𝑇𝑝
4 × 4 𝜋 𝑟𝑝2
𝑃𝑒𝑚𝑖𝑡 = 𝑃𝑎𝑏𝑠
1382.62 × 1 − 𝛼= 987W/m2
17
0
100
200
300
400
1300
1350
1400
1450
J F M A M J J A S ON DMonth
ly
(kW
-hr/m2)
𝐼 0(W
/m2)
Extra-
terrestrial
Monthly GHI
21 June21 Dec.
3 Jan.21 March
23 Sep.3 July
Solstice
23.45°
𝐼0(𝑑𝑛) = 𝐼0 (𝑑)(1 + Δ cos 2𝜋 𝑑𝑛 /𝐷)
Δ = 2(𝑅max– 𝑅min)/𝑑
Sunlight varies with seasons
18
1919
Sunlight depends on latitude
http://www.ez2c.de/ml/solar_land_area/
M. A. Alam, PV Lecture Notes
N
S
JulySep.
Nov.𝜃𝑍
𝛾𝑆
W
ES
N
Solar intensity changes with day, season, and latitudes
𝐼𝐷𝑁𝐼 = 𝐼0 𝑑𝑛 𝑇(𝜃𝑍 𝑡 )
𝐴𝑀(𝑡) = 1/ cos 𝜃𝑍(𝑡)
𝑇 𝜃𝑍 𝑡 = 𝑐1𝜏𝐴𝑀 𝑡 𝑐2
𝑐1 ∼ 1, 𝑐2 ∼ 0.67
𝜏 ≡ 1 − 𝛼
20
Direct normal irradiance (DNI)
Direct and diffused light
21
𝐼𝐺𝑁𝐼 = 𝐼𝐷𝑁𝐼 cos(𝜃𝑍) + 𝐼𝐷𝐻𝐼 𝑘𝑡 = 𝐼𝐺𝐻𝐼/𝐼0cos(𝜃𝑧)
Diffused horizontal irradiance
Global horizontal irradiance
4 8 12 16 200
0.2
0.4
0.6
0.8
1
4 8 12 16 200
0.2
0.4
0.6
0.8
1
(a)
Time (h) Time (h)
Inso
lation (
kW
/m2)
GH
I (k
W/m
2)
Cloudy day
Clear
day
DHI
DNI
GHI
(b)
PV intensity is easily determined
Washington DC (June 15, 2014, clear; June 19, 2014 cloudy)
22
Atmosphere and solar spectrum
𝐹𝐵𝐵 =𝐸2
4𝜋2ℏ2𝑐21
𝑒 Τ𝐸 𝑘𝐵𝑇𝑠 − 1𝐸𝑝𝑒𝑎𝑘 ∼ 2.8 𝑘𝐵 𝑇𝑠𝐸𝑎𝑣𝑔 ∼ 2.7 𝑘𝐵 𝑇𝑠
23
0 500 1000 1500 20000
0.5
1
1.5
2
2.5
0 500 1000 1500 20000
0.2
0.4
0.6
0.8
1
0 500 1000 1500 20000
0.5
1
1.5
2
2.5Mars Earth
𝜆 (nm) 𝜆 (nm) 𝜆 (nm)
𝐼(W
/m2/n
m)
𝐼(W
/m2/n
m)
𝐼(W
/m2/n
m)Extraterrestrial
Surface
(30° zenith)
AM0
AM1.5D
AM1.5G
AM0
BB (5777K)
(a) (b) (c)
Standard olar spectrum and air-mass (AM)
𝐹𝐵𝐵 =𝐸2
4𝜋2ℏ2𝑐21
𝑒 Τ𝐸 𝑘𝐵𝑇𝑠 − 1
𝐸𝑝𝑒𝑎𝑘 ∼ 2.8 𝑘𝐵 𝑇𝑠𝐸𝑎𝑣𝑔 ∼ 2.7 𝑘𝐵 𝑇𝑠
Global (G) includes diffused light, but direct (D) does not.
24
2525
Outline
1) Introduction: A short history of solar energy
2) The story of the sun and sunlight
3) Earth’s atmosphere and sunlight on ground
4) Solar cells are extremely inefficient
5) Levelized cost of electricity
6) Conclusions
M. A. Alam, PV Lecture Notes
M. A. Alam, PV Lecture Notes
26
Photoelectric effect and solar cells
UVelectron
metal
Sunlightelectron
p-n junction
load
Why PV spectrum matters
27
𝐸𝑐
𝐸𝑣
Only 33% efficient
Lost in cell-to-module transition
M. A. Alam, PV Lecture Notes 28
An Inefficient Machine!
29
𝜂𝐴 ∼ 1/2
𝜂𝑁 = 2/𝜋
𝜂𝑆𝑄 = 1/3
𝜂 = 𝜂𝑁 × 𝜂𝑆𝑄 × 𝜂𝑀 × 𝜂𝐴=2
𝜋×1
3×5
6×1
2∼
1
10
𝜂𝑀 = 4/5
M. A. Alam, PV Lecture Notes
Collection of
independent
2-level PV
nm
p-n junction solar cellCell
ModulePanel
Rooftop
PVSolar farm
nm-𝜇m cm-m km
Fabrication,
Device physics,
Manufacturing
Reliability, LCOE
Course outline: A multiscale problem
M. A. Alam, PV Lecture Notes
30
A magnificent multiscale problem:Atom-to-farm perspective
31
Length
Time
s
ns
year
decade
nm cm m km
Material
Storage
50 100 150 200
5
10
15
20
25
30
35
40
45
50 -1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
DeviceProcess
Reliability
Solar Farm
Module
Mm
17 orders
15 orders
An atom-to-system approach for PV research. M. A. Alam, PV Lecture Notes
3232
Outline
1) Introduction: A short history of solar energy
2) The story of the sun and sunlight
3) Atmosphere dictates sunlight on ground
4) Solar cells are extremely inefficient
5) Levelized cost of electricity as a savior
6) Conclusions
M. A. Alam, PV Lecture Notes
3333
Solar energy is not free
LCOE =Cost
Energy produced
Energy produced = Insolation x efficiency x lifetime
Cost = cost of converter + maintenance + interest
M. A. Alam, PV Lecture Notes
… with drop cost of energy produced
Acwa Power
5.84 cents!
Taqnia
5 cents!
M. A. Alam, PV Lecture Notes
34
Resources (http://nanohub.org/groups/pv)
M. A. Alam, PV Lecture Notes
35
ADEPT 1D
PV Analyzer
PV Panel SimOPV Lab
Conclusions
Photovoltaics is an important source of
renewable energy
The combination of sun, earth, PV
technology, and financing determine the
trajectory of the industry.
The spectacular drop in cost has fueled the
growth of the PV industry.
Our goal is the end-to-end understanding
of PV technology.
M. A. Alam, PV Lecture Notes
36
Self-test questions
What is the peak and average energy of the solar
spectrum? What is the energy flux density on the
surface of the sun?
What fraction of the sky (in solid angles) does the sun
cover?
What wavelengths of light are absorbed by
atomospheric oxygen?
What is the difference between AM0 vs. extraterrestrial
spectrum?
Calculate the DNI intensity on June 15 for at time when
the Azimuth angle is 50 degrees?
M. A. Alam, PV Lecture Notes
37