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The Role of Solar Electricity in Sustainable Building (Smart Windows)
Quantum Photovoltaic Group Keith Barnham, Ian Ballard, Andreas Ioannides, David Johnson,
Marianne Lynch, Massimo Mazzer, Tom Tibbits,(Cell design, cell characterisation and modelling)
Experimental Solid State Physics, Imperial College London, London SW7 2BW, UK http://www.sc.ic.ac.uk/~q_pv
John Roberts, Geoff Hill, Cath Calder
(Sample growth and fabrication)EPSRC National Centre for III-V Technology, University of Sheffield, Sheffield S1 3JD, UK
Tim Green (Systems, local power networks, storage)
Electrical Engineering, Imperial College London, SW7 2AZ
Optical Products Ltd, SolarStructure, Permasteelisa Centre for Integrated Photonics
Growth in World PV Capacity
PV installations World-wide increased by 57% in 2004
UK PV one of lowest in EU but a 40%/yr increase would generate 23% by 2023
P.Maycock, Renewable Energy World, Aug. 2005.
The Three Generations of PV First Generation
Crystalline and poly-crystalline Si ~15% efficiency, ~ $3/Wp
Second Generation Thin film cells CdTe, CuInSe2 (10-15)% effic., ~ $(1-2)/Wp
Third Generation expensive - III-V cells (400-1000)x concentration for
large scale power < $1/Wp. Our Target (1000x) Our Present State
(200x) Silicon - no concentration
M.A.Green, “Photovoltaics for the 21st Century II”,
Electrochemical Soc. Proc. Vol. 2001-10, 1, (2001).
http://www.pvsystem.net/ Shibuya, Japan
The First BIPV Building in Japan
First Generation cells in BIPV
Cell Efficiency ~ 15%
Power Glass™ Power Glass™ represents a new breed of solar cell design that balances solar cell efficiencies and manufacturing costs with broad applications and uses. Power Glass™ solar cells operate at as much as 50%, or half, the efficiency of conventional opaque amorphous solar cells yet costing as little as 25%, or one fourth, to produce.
http://www.xsunx.com/tech-power.htm
XsunX, Inc.Aliso Viejo, CA (USA)
Second Generation Thin Film Cells in BIPV
Cell Efficiency ~ 7%
Efficiency versus band- gap
GaAs cells highest single junction efficiencies
Lower Eg => higher efficiency
No lower Eg III-V alloys lattice matched to GaAs or Ge substrates
Multi-junction approaches also would like bulk-cell with band-gap ~ 1.1 mm ~ 1.1 eV
Can grow InyGa1-yAs bulk cells on virtual substrates but never dislocation free
SB-QWSC lowers GaAs absorption edge without dislocations
GaAsP/InGaAs Strain-Balanced QWSC
Advantages:
Can vary absorption band-edge and absorb wider spectral range without strain-relaxation
No dislocations
Higher barriers than GaAs
=> reduced recombination
single junction so can cope
with varying spectra
Balance stress between layers to match lattice parameter of the
substrate
17
19
21
23
25
27
29
0.1 1 10 100 1000Concentration (suns)
Eff
icie
nc
y (%
)
Control pn cell
pn prediction
GaAs record
SB-QWSC
SB-QWSC predicted
SB-QWSC Efficiency vs. Concentration
50 well SB-QWSC ~ 2% higher efficiency than p-n control
65 well cell should achieve World record at 500x
Single Junction Cell World Record
What is the Electricity DEMAND in Buildings?
63% of electricity in UK used in buildings
Sunlight on buildings ~ 7x electricity consumption in the buildings
DEMAND similar through year, peaks daily ~2x BASELOAD –
Nuclear only provides baseload
3rd Generation cells on 25% of S-facing walls replace all nuclear contribution
At 500x a UK semiconductor facility could produce cells
= 5 nuclear reactors in 10 years
00:00 03:00 06:00 09:00 12:00 15:00 18:00 21:00 24:00
5
6
7
8
9
10
Po
we
r D
em
and
[MW
]
Time of Day
Mar 20th Aug 13th Feb 11th
Imperial College London
Novel Application of 3rd Generation CellsSolarstucture Ltd– new company for Building Integrated Concentrator PV
Curtain walls (glass facades) => Use tracking blinds to cut direct
sunlight to remove glare and
reduce air conditioning demand
Our cells are very small (~ 1mm)high efficiency (~ 30%) need 500 x concentrators to reduce costsThe concentrators must track the sun
Third Generation Cells in Concentrators (Smart Windows)
Unique advantages: No transmission of direct sunlight Reduce a/c requirementsMax diffuse sunlight - for illumination(2 – 3) x power from Silicon BIPV Provide electricity at peak times Cell cooling provides hot water
(500 – 1000)x concentration Transparent modules 1 mm solar cells Cell efficiency ~ 30% innovative 2-axis tracking adds ~ 20% to façade cost
Heat
Diffuse Daylight
Diffuse Daylight
Solar Cells
Direct Sunlight
Lenses
Front Glass
ElectricityHeat
Diffuse Daylight
Diffuse Daylight
Solar Cells
Direct Sunlight
Lenses
Front Glass
Electricity
65%
21%
22% (cell cooling)
6%
DirectSunlight
Diffuse Sunlight Available for
Illumination
Electricity
31% (IR rad.)
Smart WindowsEnergy Budget
Thin 2nd Generation Cells
Beneficial Detrimental
11%
6%
Electricity
80%
80%
Usable Heat
Heat Dispersion
Heat Dispersion
Light Reflection
DirectSunlight
Diffuse Sunlight
10%
10%
Annual electricity generation as a function of the curtain wall slope
90° = vertical wall
The maxima correspond to the latitude angle, i.e.:
37.8° for S.Francisco51.5° for London
San Francisco
0
50
100
150
200
250
300
350
30 45 60 75 90Window Tilt/deg
Ele
ctri
c E
ner
gy
(kW
h/m
2 /y)
SolarSkin - South SolarSkin - SE/SWSharpST - South SharpST - SE/SW
London
0
20
40
60
80
100
120
140
30 45 60 75 90Window Tilt/deg
Ele
ctri
c E
ner
gy
(kW
h/m
2/y
)
SolarSkin -South SolarSkin - SE/SWSharpST - SE/SW SharpST - South
Comparison with 2nd Generation BIPV
SB-QWSC + Ge 32%
vertical S - W facing wall in London
World record 3-junction cell
35% harvests same
electrical energy over year
Compare SB-QWSC + Ge with multi-junction Cell
MJ cell optimised for one spectrum, one temperature.
Tunnel Junctions problematic at high conc. high current
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
0.50
0 28 56 84 112 140 168 196 224 252 280 308 336 364
Day
En
erg
y/(
kW
h/m
2/d
ay
)
QWSC+Ge Triple Junction
Conclusions
• 3rd generation cells, higher efficiency-lower cost in concentrators can help maintain > 40% per year PV market expansion
• Smart-windows alone could replace the nuclear component quicker than new-build
• Smart windows – new active architectural component