Transcript The Role of Solar Electricity in Sustainable Building (Smart Windows)

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
M.A.Green, “Photovoltaics for the 21st Century II”,
Electrochemical Soc. Proc. Vol. 2001-10, 1, (2001).
 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
First Generation cells in BIPV
Cell Efficiency
~ 15%
http://www.pvsystem.net/
Shibuya, Japan
The First BIPV Building in Japan
Second Generation Thin Film Cells in BIPV
Cell Efficiency ~ 7%
Power Glass™
XsunX, Inc.
Aliso Viejo, CA (USA)
http://www.xsunx.com/tech-power.htm
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.
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
Balance stress between layers to
match lattice parameter of the
substrate
Advantages:
Can vary absorption bandedge and absorb wider
spectral range without strainrelaxation
No dislocations
Higher barriers than GaAs
=> reduced recombination
 single junction so can cope
with varying spectra
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
29
Efficiency (%)
27
Single Junction
Cell World Record
25
23
Control pn cell
21
pn prediction
GaAs record
19
SB-QWSC
SB-QWSC predicted
17
0.1
1
10
100
Concentration (suns)
1000
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 –
Power Demand [MW]
10
9
Imperial
College
London
8
7
Mar 20th
Aug 13th
Feb 11th
6
Nuclear only provides baseload
5
 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
Time of Day
18:00
21:00
24:00
Novel Application of 3rd Generation Cells
Solarstucture Ltd– new company for Building Integrated Concentrator PV
Our cells are very small (~ 1mm)
high efficiency (~ 30%)
need 500 x concentrators to reduce costs
The concentrators must track the sun
 Curtain walls (glass facades) =>
 Use tracking blinds to cut direct
sunlight to remove glare and
reduce air conditioning demand
Third Generation Cells in
Concentrators (Smart Windows)
(500 – 1000)x concentration
 Transparent modules
1 mm solar cells
 Cell efficiency ~ 30%
 innovative 2-axis tracking
 adds ~ 20% to façade cost
Unique advantages:
No transmission of direct sunlight
Reduce a/c requirements
Max diffuse sunlight - for illumination
(2 – 3) x power from Silicon BIPV
Provide electricity at peak times
Cell cooling provides hot water
Lenses
Direct
Sunlight
Diffuse
Daylight
Solar
Cells
Diffuse
Daylight
Front
Glass
Heat
Electricity
Smart Windows
Energy Budget
Electricity
Beneficial
21%
Direct
Sunlight
Usable
Heat
Diffuse
Sunlight
65%
Thin 2nd Generation Cells
Detrimental
22% (cell cooling)
31% (IR rad.)
11%
Heat Dispersion
Available for
Illumination
10%
Direct
Sunlight
6%
10%
Diffuse
Sunlight
80%
Heat
Dispersion
80%
Light
Reflection
6%
Electricity
Comparison with 2nd Generation BIPV
SolarSkin - South
SharpST - South
SolarSkin - SE/SW
SharpST - SE/SW
Electric Energy (kWh/m 2/y)
350
San Francisco
300
250
200
150
100
50
90° = vertical wall
0
30
45
60
75
Window Tilt/deg
SolarSkin -South
SharpST - SE/SW
90
SolarSkin - SE/SW
SharpST - South
140
Electric Energy (kWh/m2/y)
Annual electricity
generation as a
function of the
curtain wall slope
London
120
The maxima
correspond to the
latitude angle, i.e.:
100
80
37.8° for S.Francisco
51.5° for London
60
40
20
0
30
45
60
75
Window Tilt/deg
90
Compare SB-QWSC + Ge with multi-junction Cell
World record 3junction cell
35%
harvests same
electrical energy
over year
QWSC+Ge
Triple Junction
0.50
0.45
Energy/(kWh/m 2/day)
SB-QWSC + Ge
32%
vertical S - W facing
wall in London
0.40
0.35
0.30
0.25
0.20
0.15
0.10
0.05
0.00
0
28 56
84 112 140 168 196 224 252 280 308 336 364
Day
MJ cell optimised for one spectrum, one temperature.
Tunnel Junctions problematic at high conc. high current
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