Title: The Role of Photovoltaics in Our Energy Future
1The Role of Photovoltaics in Our Energy Future
- Tracie J. Berniard
- National Renewable Energy Laboratory
- tracie_berniard_at_nrel.gov
2Overview
- The National Renewable Energy Laboratory
- Opportunities for Renewables
- The issue of cost
- Next generation PV Thin Films
- CdTe thin film PV Laboratory vs. Manufacturing
- Looking Ahead
3National Renewable Energy Laboratory
(NREL)Golden, CO
- Biomass
- Wind
- Geothermal
- Hydrogen and Fuel Cells
- Advanced Vehicles and Fuels
- Others
- Photovoltaics NCPV (materials device
development, measurements characterization,
etc) - www.nrel.gov
4Opportunities for Renewables
11/2000
- CO2 emission levels
- Rising energy costs
- Population growth and developing nations
- Fossil fuel age WILL end
5Opportunities for Renewables
- In 1999 U.S. CO2 gas emissions were 5.6 billion
tons, up 28 from 1983. - Nearly 99 of this total was energy-related
emissions. - AEO2001 projects 7.5 billion tons of gas in 2020
- source www.eia.doe.gov
6Opportunities for Renewables
- Despite gains in energy efficiency, demand for
energy is expected to rise due to world
population growth
World Population by 2050 9 billion
source www.pbs.org/wgbh/nova/worldbalance
7Opportunities for Renewables
- Energy consumption in U.S. outweighs our
production - Largest consumed sources are petroleum, natural
gas and coal
source www.eia.doe.gov
8Opportunities for PV
- Renewables make up smallest percentage (6)
- Of global PV demand, U.S. only 15, and we export
70 of PV we produce. - The earth receives more energy from the sun in 1
hr than the world uses in a yr
Based on 2002 data www.eia.doe.gov
9Opportunities for PV
- Quotes from the U.S. Energy Outlook as of 2001
Report - Many experts believe that the age of fossil
fuels is only an interlude between pre- and
post-industrial eras dominated by the use of
renewable energy. - The far future seems likely to belong to
renewable sources of energy. - www.eia.doe.gov
10The Issue of Cost
- Lowest priced (module only) solar modules to
date - Crystalline Si 3.20/Wp (Kyocera, U.S.)
- 18/kWh in S. California
- Thin Film a-Si 3.59/Wp (Kaneka, Germany)
- 20/kWh in S. California
Module only
source www.solarbuzz.com
11The Issue of Cost
Cost Trends for Entire PV System
- First Solar is selling their modules in Europe
now for 2.10/Wp (large quantities). - BOS 1/Wp
- System 3/Wp
source www.solarbuzz.com
12PV Physics Review
Dark
Vmp
FF
Jmp
Voc
Jsc
Light
Fill Factor, FF (VmpImp)/VocIsc Efficiency, ?
(VocIscFF)/Pin
13PV Physics Review
- p-n junction
- built-in potential
- any e-h pairs created within or near the
depletion region will contribute to the
generated current
14PV Physics Review
- Decrease Eg, absorb more of the spectrum
- But not without sacrificing output voltage
- CdTe and GaAs ideally suited
15Next Generation PV Thin Films
- Strong light absorbers (a 105/cm), so need less
materials (1-2?m for CdTe) - Large area fabrication high volume
manufacturing - However, complex materials systems
- Key technologies a-Si, CIGS and CdTe
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17CdTe Thin Film PV
Standard NREL Laboratory CdTe Devices
p-n junction formation
SnO2 coated 7059 5000Ã…
CBD CdS 800Ã…
CSS CdTe 8-10?m
post-processing treatments
V-CdCl2
DAGCu Ag Backcontact
Chemical Etch
Gets routine devices of 12-14
18CdTe Thin Film PV
Superstrate Structure
19CdTe Thin Film PV
J. Sites, CSU, based on optical data
20CdTe Thin Film PV
- Highest achieved laboratory efficiency to date is
16.5 (Wu et al., NCPV Program Review, 2001) - Some key advances in processing
- Vapor-CdCl2 treatment / ZTO buffer layer
- Backcontact (Cu)
- CTO transparent front contact
21CdTe Thin Film PV
- CdCl2 post-deposition treatment gives better cell
efficiency -
- Elimination of fast-recombination centers in
the CdTe film - Reduction of recombination centers at the
junction - Elimination of small grains at the the grain
boundaries
Ref Doug H. Rose et al., Prog. Photovolt Res.
Appl. 7, 331 (1999)
22CdTe Thin Film PV
- Solution CdCl2 meant that an etch was necessary
to remove surface contamination left behind
AFM images of CdCl2 Treated CdTe surfaces
Vapor CdCl2
Solution CdCl2
Y. Mahathongdy, M.S. Thesis, Colorado School of
Mines, 1999
23CdTe Thin Film PV
24CdTe Thin Film PV
- Nitric Phosphoric (NP) Etched Device
- Te-rich layer believed to improved backcontact
Cu2Te? - Penetration down grain boundaries reason for
thick CdTe
25CdTe Thin Film PV
Thinner CdTe Possible
- Zn2SnO4 (ZTO), buffer layer can improve Rsh
- - Reduces probability of forming TCO/CdTe
junction when CdS thinned - - Can act as an etch-stop during backcontact
formation - Less aggressive etches being studied
Ref X. Wu et al., 26th IEEE PVSC, 347, 1997
26CdTe Thin Film PV
- Cadmium stannate (CTO), Cd2SnO4, can replace SnO2
as transparent front contact (TCO) - (CTO), resistivity ? 1.5x10-4 ?-cm two-six
times smaller than SnO2 ? 8.6x10-4 ?-cm? lower
Rs, i.e. improved FF
Ref X. Wu et al., 26th IEEE PVSC, 347, 1997
27CdTe Thin Film PV
- Laboratory vs. Manufactured Devices
- First Solar, Inc. www.firstsolar.com
-
- Module efficiency 9 (device 14) - scale up
issue - Differences in processing
- High-rate vapor transport deposition (HRVTD)
for CdTe RD 100 Award with NREL
28CdTe Thin Film PV
- Laboratory vs. Manufactured Devices
Patent 5,945,163
- Implemented 2002, and has been able to produce
2.10/Wp modules - Second generation now under construction, aim of
1/Wp modules
29Future Direction of Thin Film PV
- Engineered Devices Process Control
- Substrate Structure and Flexible Substrates
(metal foil, polymers)
30Future Direction of Thin Film PV
- Building Integrated Products
- Niche Consumer and Military Markets
- Infrastructure Distributed vs. Centralized PV
power
31PV Future Bright
- U.S. huge untapped market
- On-going research (thin film and others)
- Import Renewables?
32PV Future Bright
RPS Becomes Official in Maryland
Uni-Solar Receives Order for 2.4 MW of Thin-Film
France-Based Solar Plant Triples PV Capacity
Solar Photovoltaics for U.S. Missile Defense
Solar power will bring light to rural bus stops
- Sharp Readies to Boost Solar PV Production
Solar Energy Powers Equestrian Trails
33Summary
- Renewables, including PV, are the future of
energy - PV currently selling for 4.92/Wp avg total
system cost, goal 1.50-2.00/Wp - Thin film PV is likely next generation solar
technology to get us there - Thin film PV industry is in its infancy, with new
materials and manufacturing advances to come
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35Cadmium Issues
- How Much Cadmium is There in a 50 W Module?
- 3 µm thick CdTe, 2-foot x 4-foot module
- 0.0003 cm x 24 (2.54 cm/) x 48 (2.54 cm/)
2 cm2 (14 gms CdTe) - But, only half of this is Cd, so 7 gm/50 Watt
panel 1 Cd unit - Typical household installation 3000 Wpeak 60
(50 Watt panels) 60 Cd units - How does this compare to other consumer items?
(Example My house) - Legend suggests Cd in Size AA NiCd battery
about same as 50 Watt panel - 8 Size D Batteries (32 Cd units)
- 4 Power tool batteries (16 Cd units)
- 2 Laptop batteries (8 Cd units)
- 6 Cordless phone battery packs (12 Cd units)
- 2 Cell phone batteries (4 Cd units)
- Total 72 units of Cd.
- Plus, lots of Cd-plated hardware (nuts, bolts,
fixtures)!