4. Energy from the Sun
Yearly Solar fluxes & Human Energy Consumption
• The total solar energy absorbed by Earth's atmosphere, oceans and land masses
is approximately 3,850,000 exajoules (EJ) (1018 joules) per year. (70% of
incoming sunlight) (1 Joule = energy required to heat one gram of dry, cool air
by 1˚ C)
• 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
non-renewable resources of coal, oil, natural gas, and mined uranium combined.
• As intermittent resources, solar and wind raise issues.
5. Solar Cells Background
• 1839 - French physicist A. E. Becquerel first recognized the photovoltaic
effect.
• Photo+voltaic = convert light to electricity
• 1883 - first solar cell built, by Charles Fritts, coated semiconductor selenium
with an extremely thin layer of gold to form the junctions.
• 1954 - Bell Laboratories, experimenting with semiconductors, accidentally
found that silicon doped with certain impurities was very sensitive to light.
Daryl Chapin, Calvin Fuller and Gerald Pearson, invented the first practical
device for converting sunlight into useful electrical power. Resulted in the
production of the first practical solar cells with a sunlight energy conversion
efficiency of around 6%.
• 1958 - First spacecraft to use solar panels was US satellite Vanguard 1
6. PV Solar for Electricity
Photovoltaics
• For the 2 billion people without access to electricity, it would be cheaper to
install solar panels than to extend the electrical grid.
• Providing power for villages in developing countries is a fast-growing market
for photovoltaics. The United Nations estimates that more than 2 million
villages worldwide are without electric power for water supply, refrigeration,
lighting, and other basic needs, and the cost of extending the utility grids is
prohibitive, $23,000 to $46,000 per kilometer in 1988.
• A one kilowatt PV system* each month:
– prevents 150 lbs. of coal from being mined
– prevents 300 lbs. of CO2 from entering the atmosphere
– keeps 105 gallons of water from being consumed
– keeps NO and SO2 from being released into the environment
* in Colorado, or an equivalent system that produces 150 kWh per month
7. How Solar Cells Work
1. Photons in sunlight hit the
solar panel and are absorbed
by semiconducting materials,
such as silicon.
2. Electrons (negatively charged)
are knocked loose from their
atoms, allowing them to flow
through the material to
produce electricity.
3. An array of solar cells
converts solar energy into a
usable amount of
direct current (DC) electricity.
http://teams.eas.muohio.edu/solarpower/video/solarcell2.mpeg
9. PV Cells History
First Generation – Single Junction Silicon Cells
89.6% of 2007 Production
45.2% Single Crystal Si
42.2% Multi-crystal SI
• Large-area, high quality and single junction devices.
• High energy and labor inputs which limit significant progress in reducing
production costs.
• Single junction silicon devices are approaching theoretical limit efficiency
of 33%. Achieve cost parity with fossil fuel energy generation after a
payback period of 5–7 years. (3.5 yr in Europe)
• Single crystal silicon - 16-19% efficiency
• Multi-crystal silicon - 14-15% efficiency
10. PV Cells History
Second Generation – Thin Film Cells
CdTe 4.7% & CIGS 0.5% of 2007 Production
New materials and processes to improve efficiency and reduce cost.
As manufacturing techniques evolve, production costs will be dominated by constituent material
requirements, whether this be a silicon substrate, or glass cover. Thin film cells use about 1% of the
expensive semiconductors compared to First Generation cells.
The most successful second generation materials have been cadmium telluride (CdTe), copper indium
gallium selenide (CIGS), amorphous silicon and micromorphous silicon.
Trend toward second gen., but commercialization has proven difficult.
2007 - First Solar produced 200 MW of CdTe solar cells, 5th largest producer in 2007 and the first to
reach top 10 from of second generation technologies alone.
2007 - Wurth Solar commercialized its CIGS technology producing 15 MW.
2007 - Nanosolar commercialized its CIGS technology in 2007 with a production . capacity of
430 MW for 2008 in the USA and Germany.
2008 - Honda began to commercialize their CIGS base solar panel.
CdTe – 8 – 11% efficiency (18% demonstrated)
CIGS – 7-11% efficiency (20% demonstrated)
Payback time < 1 year in Europe
11. Solar Cells Background
Third Generation – Multi-junction Cells
• Third generation technologies aim to enhance poor electrical performance of
second generation (thin-film technologies) while maintaining very low
production costs.
• Current research is targeting conversion efficiencies of 30-60% while retaining
low cost materials and manufacturing techniques. They can exceed the theoretical
solar conversion efficiency limit for a single energy threshold material, 31%
under 1 sun illumination and 40.8% under the maximal artificial concentration of
sunlight (46,200 suns).
• Approaches to achieving these high efficiencies including the use of
multijunction photovoltaic cells, concentration of the incident spectrum, the use
of thermal generation by UV light to enhance voltage or carrier collection, or the
use of the infrared spectrum for night-time operation.
• Typically use fresnel lens (3M) or other concentrators, but cannot use diffuse
sunlight and require sun tracking hardware
• Multi-junction cells – 30% efficiency (40-43% demonstrated)
17. Advantages & Disadvantages
Larger, Si-based photovoltaic cells
Typically made of a crystalline Si wafers sawed from Si ingots
Dominant technology in the market
More than 86% of the commercial production of solar cells
high-efficiency
Maximum theoretical efficiency of 33.7%
Advantages
Broad spectral absorption range (Eg=1.12eV)
Disadvantages
High costs: Expensive manufacturing technologies
Extracting Si from sand and purifying it before growing the crystals
Growing and sawing of ingots is a highly energy intensive process
Much of the energy of higher energy photons, at the blue and violet end of the spectrum,
is wasted as heat
Not more energy-cost effective than fossil fuel sources
18. Thin Film Photovoltaics
• Amorphous Silicon
• Gallium Arenide and Indium Phosphide
• Cadmium Telluride
• Copper Indium Diselenide (CIS) or
19. Thin Film Photovoltaics
• CIGS- copper-indium-gallium-
selenide
• Thin film growth and deposition
on glass/polymer/flexible foil
substrate
• High efficiency-19.6% (I. Repins
et al. 2008)
• CdTe- Cadmium Telluride
• Efficiency-16.7% (Wu X et al.
Oct. 2001)
• High cost due to Tellurium
availability
• a-Si- Amorphous Silicon
• 10.1% Efficiency (S. Benagli, et
al. Sept. 2009)
20. Thin Film Technology
Silicon deposited in a continuous on a base material
such as glass, metal or polymers
Thin-film crystalline solar cell consists of layers
about 10μm thick compared with 200-300μm layers
for crystalline silicon cells
PROS
Low cost substrate
and fabrication
process
CONS
Not very stable
21. How Organic Solar Cells Work
1. Photon absorption, exactions are
created
2. Exactions diffusion to an interface
3. Charge separation due to electric
fields at the interface.
High Work Function Electrode
4. Separated charges travel to the
electrodes. Donor Material
E
Acceptor Material
Low Work Function
Electrode
22. Developed to reduce the costs of the first generation cells
Deposition of thin layers of materials on inexpensive
substrates: Mounted on glass or ceramic substrates
Reduce high temperature processing
Production costs will then be dominated by material
requirements
Compared to crystalline Si based cells they are made
from layers of semiconductor materials only a few
micrometers thick
Reduces mass of material required for cell design
23. Advantages and Disadvantages
Advantages
Lower manufacturing costs
Much less material require
Lower cost/watt can be achieved
Lighter weight (reduced mass)
Flexibility: allows fitting panels on curved surface, light or flexible
materials like textiles
Even can be rolled up
Disadvantages
Inherent defects due to lower quality processing methods reduces
efficiencies compared to the first generation cells
26. Cost Trends - Photovoltaics
100
COE cents/kWh
80
60
40
201980 1990 2000 2010 2020
Current cost is 16-25 cents Levelized cents/kWh in constant $20001
per kWh Source: NREL Energy Analysis Office
Updated: June 2002
27. Residential Cost
2 Kilowatt system: $16-20,000 (installed)
- Could meet all needs of a very energy efficient
home.
- $8-10 per Watt
5 Kilowatt system: $30-40,000 (installed)
-Completely meets energy needs of most
conventional homes.
-$6-8 per Watt
(Estimates from U.S. Department of Energy)
28. Energy Payback Time
• EPBT is the time necessary for a photovoltaic panel
to generate the energy equivalent to that used to
produce it.
A ratio of total energy used to manufacture a PV
module to average daily energy of a PV system.
• At present the Energy payback time for PV systems
is in the range 8 to 11 years
36. References
1. K. BOWER. et al., Polymers, Phosphors, and Voltaics for Radioisotope
Microbatteries, CRC press, New York, (2002).
2. QYNERGY Corporation, Press Announcement –Qynergy Announces
Breakthrough in Power Cell Performance, September 5, 2005
3 H.FLICKER, J. LOFERSKI, T. ELLERMAN, IEEE Transactions on
Electronic Devices, 11, 1-2-8 (1964)
4 P. RAPPAPORT, J. LOFERSKI, E. LINDER, RCA Rev., 17, pp. 100-134
(1956)
5. H. GUO, A. LAL, IEEE Transducers, 1B3.1, pp. 36-39, (2003)
6 CREE RESEARCH INC., Product Specifications, (1998-2000)
8 T. KOSTESKI, Tritiated Amorphous Silicon Films and Devices, PhD diss.,
University of Toronto, (2001)
