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School of Electrical and Computer Engineering
Solar 101for the Duke Energy Academy
June 23, 2014
Peter Bermel
Purdue School of Electrical and Computer Engineering
Outline
› The solar resource
› Approaches to harvesting solar power
› Solar photovoltaics technologies
› Recent and future growth in solar
Purdue School of Electrical and Computer Engineering
In principle, solar energy can scale to supply a large portion of global energy demand.
The solar resource & potential
Over 1000 times extra!
Source: OECD Observer No. 258/59 December 2006
Purdue School of Electrical and Computer Engineering
The solar spectrum
Source: Robert Rohde, Global Warming Art – http://en.wikipedia.org/wiki/Sunlight”
Purdue School of Electrical and Computer Engineering
Insolation
� Incoming solar radiation
� Take into account movement of the sun throughout the day and throughout different seasons
� Also weather patterns
� Energy per unit area per unit time (kWh/m2/day)
Purdue School of Electrical and Computer Engineering
Solar land area to supply all US power
Source: Nate Lewis (Caltech)
Purdue School of Electrical and Computer Engineering
Electrical power generation
Photo: Brightsource Energy, http://ecotechdaily.com/wp-content/uploads/2008/04/brightsource2_620px.jpg
Source: TGW, http://openlearn.open.ac.uk/file.php/1697/220880-1f1.29.jpg
Photo: Stirling Energy Systems,http://www.wapa.gov/ES/pubs/esb/1998/98Aug/Graphics/Pg5b.jpg
Photo: Ausra, Inc.,http://www.instablogsimages.com/images/2007/09/21/ausra-solar-farm_5810.jpg
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Photovoltaic cell operation
� Light absorption / charge
generation (photovoltaic
effect) � Carrier thermalization
� Charge separation� Photon reemission
� Charge collection� Nonradiative recombination
http://en.wikipedia.org/wiki/Image:Solar_cell.png
Eg
= max. VOC
Conduction band
Valence band
Excess energy above Eg heat
I
VVOC
ISC
dark
light
Purdue School of Electrical and Computer Engineering
I
VVOC
ISC
Maximum power rectangle
VOC, open circuit voltage
ISC, short circuit current
FF, fill factor = max. power rectangle
VOC . ISC
dark
light
IL RP
RS
Circuit model
Solar photovoltaics: electrical engineering
η = VOC x ISC x FF
Pinc
Power conversion efficiency
Purdue School of Electrical and Computer Engineering
Photovoltaic technologies
› Major categories:
– Silicon
• Single crystal
• Polycrystalline
• Amorphous silicon
• Microcrystalline
– CIGS
– Cadmium telluride
– Multijunction Source: Impact Lab,
http://www.impactlab.com/wp-content/uploads/2008/06/solar-energy.jpg
Monocrystalline silicon PV
› One of the first, and still
dominant, cell
technologies
› Advantages:
– Process is mature
– Relatively high efficiencies
› Disadvantages
– High materials usage
– High costs
– Batch processing
Czochralski process for creating monocrystalline silicon ingots
Ingots are then sawed into individual wafers
Source: DOE Solar Energy Technologies Program, http://www1.eere.energy.gov/solar/silicon.html
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Polycrystalline silicon PV
› Manufacturing
improvement; decreases:
– Costs
– Kerf loss
› Disadvantages:
– Lower electronic quality
– Increased fragility
– More difficult to textureEvergreen’s string ribbon process
Source: http://www.evergreensolar.com/images/technology/stringribbon/diagram_string_ribbon_en.jpg
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CIGS (Copper Indium Gallium Diselenide)
› Engineered for direct
bandgap at target
wavelength
› Promising efficiencies:
up to 20.4%
› Sticking point –
manufacturing
processes:
– Vacuum deposition
– Inkjet-style printing
CIGS manufacturingSource: Ibid.
CIGS cell diagramSource: AIST (Japan),
http://www.yet2.com/publish/techofweeks/tow0043972/20080323_cigs01.jpg
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CdTe (Cadmium Telluride)
› Advantages:
– Direct bandgap with
efficiencies up to 19.6%
– Inexpensive fabrication process, proven at GW
scale
› Disadvantages:
– Susceptible to degradation
– Cd toxicity concerns
– Te feedstock issues
CdTe cell diagramSource: http://www.mtl.kyoto-u.ac.jp/groups/awakura-g/index-e.html
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Multijunction PV
› Combines two or more
materials into a stack
› Allows for more efficient
use of each photon in solar
spectrum � record efficiencies
› Challenges with lattice and
current matching can
greatly increase costsSchematic of triple-junction cell
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Solar research is growing
› Solar research has seen
increased investment from
many players:
– US government
– Venture capital
– Manufacturers
› Drivers:
– Rising energy costs
– Environmental concerns
– Energy security Solar R&D Investments (in millions)
Source: Solar Energy Industries Association (2013)
$0
$500
$1,000
$1,500
$2,000
$2,500
2006 2007 2008 2009 2010 2011
PV OEMs
VC&PE
Government R&D
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Purdue Has Unique Expertise in PV + TPV Energy Systems
TPV portable power generator*
Solar PV electricity for homes†
*R. Pilawa-Podgurski et al., APEC 25, 961 (2010); P.
Bermel et al., Opt. Express 18, A314 (2010)
‡ G. Lush & M. Lundstrom, Solar Cells 30, 337 (1991); Q..
Guo et al., J. Am. Chem. Soc. 132, 17384 (2010); M. A.
Alam et al., J. Mat. Res. 28, 541, (2013); L. Varghese
et al., Adv. Opt. Mater. (2013).
† Lafayette Magazine, “Sun Power,” August 17 (2011).
Thin-film PV from new materials ‡
pbermel@purdue
.edu
ECE Grad Open House,
Prof. Bermel
19
Purdue School of Electrical and Computer Engineering
Solar installations growing rapidly
› Solar is transitioning from
niche to mainstream
› Improved efficiencies, lower
costs enable rapid growth
› 32,000 MW installed in 2012
› Over half of new energy
capacity solar in Q1 2014!
› New Duke solar installation at
Indy airportInstalled solar capacity (MW)
Source: Solar Energy Industries Association (2013)
0
20000
40000
60000
80000
100000
120000
2003 2006 2009 2012
Europe
APAC
Americas
China
MEA
ROW
Purdue School of Electrical and Computer Engineering
Solar costs approaching “grid parity”
› Potential for huge drop in installed costs of solar system through variety of sources
› Solar power on track to match grid prices in a variety of locations:
“grid parity”
Source: Emanuel Sachs (MIT)
Purdue School of Electrical and Computer Engineering
Conclusions
› Solar resource is large enough to meet future energy
needs
› Two mechanisms to convert photons into power – solar
thermal and solar PV
› Technological landscape is diverse in terms of
applications, maturity, and costs
› Thin-films expected to be major players in the near-term
› Solar market has been and will continue growing rapidly
› Grid parity already happening in certain places