Solar 101 for the Duke Energy Academy - Purdue University 101... · Solar 101 for the Duke Energy Academy June 23, 2014 ... ... ›Disadvantages

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

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

Purdue School of Electrical and Computer Engineering

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

Purdue School of Electrical and Computer Engineering

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

Purdue School of Electrical and Computer Engineering

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

Purdue School of Electrical and Computer Engineering

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

Purdue School of Electrical and Computer Engineering

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

Purdue School of Electrical and Computer Engineering

Best Solar PV Efficiencies

Purdue School of Electrical and Computer Engineering

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

Purdue School of Electrical and Computer Engineering

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