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SOLAR RESOURCE
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Solar resource
Radiation from the Sun
Atmospheric effects
Insolation maps
Tracking the Sun
PV in urban environment
2
Solar resource
Solar resource is immense
◦ Human energy use: 4.0x1014 kWh/year
◦ Solar resource on Earth’s surface: 5.5x1017 kWh/year
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Solar resource
Solar resource is immense
◦ Human energy use: 4.0x1014 kWh/year
◦ Solar resource on Earth’s surface: 5.5x1017 kWh/year
Solar power systems covering the areas defined by the dark disks could provide more than the
world's total primary energy demand (assuming a conversion efficiency of 8%).
Local solar irradiance averaged over three
years from 1991 to 1993 (24 hours a day)
taking into account the cloud coverage
available from weather satellites
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Solar resource
Solar resource is immense
◦ Human energy use: 4.0x1014 kWh/year
◦ Solar resource on Earth’s surface: 5.5x1017 kWh/year
Solar resource is global and democratic
Solar resource is relatively constant but depends on
◦ atmospheric effects, including absorption and scattering
◦ local variations in the atmosphere, such as water vapour, clouds, and
pollution
◦ latitude of the location
◦ the season of the year and the time of day
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Solar resource
2
4
04 sunR
TP
Total radiative power (Stefan Boltzman) T=5762K
Surface area of sun
Power radiated per unit area
5.96x107 W/m2
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Solar resource
2
4
04 sunR
TP
02
2
4
4P
D
RS sun
Ratio of surface areas of the 2
spheres
Distance Sun-Earth
Solar constant average energy
flux incident at the Earth’s orbit:
1366 W/m2
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Solar resource
2
4
04 sunR
TP
Rsun 6.96x105 km
Davg 1.5x108 km
REarth 6.35x103 km
44 2
2S
R
RS
Earth
Earth
Energy incident on EarthAverage energy incident per
unit area of surface of Earth:
342 W/m2Total area of Earth
02
2
4
4P
D
RS sun
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Solar resource
Earth-Sun motion
23.7 º
365 days and 6 hours
Polar axis
365
2360cos033.01
n
S
H
H(W/m2) is radiant power density outside the atmosphere; S is solar constant; n is day of the year9
Earth-Sun motion◦ Solar declination: angle between line joining centres of Earth and Sun and the
equatorial plane
Solar resource
Polar axis
+23º 27’0º
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Solar resource
Polar axis
+23º 27’0º
Autumnal equinox
Earth-Sun motion◦ Solar declination: angle between line joining centres of Earth and Sun and the
equatorial plane
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Solar resource
Polar axis
+23º 27’0º
Autumnal equinox
Earth-Sun motion◦ Solar declination: angle between line joining centres of Earth and Sun and the
equatorial plane
-23º 27’
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Earth-Sun motion◦ Solar declination: angle between line joining centres of Earth and Sun and the
equatorial plane
Solar resource
Polar axis
+23º 27’0º Vernal and
automnal equinox
-23º 27’
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Solar resource
Earth-Sun motion◦ Solar declination: angle between line joining centres of Earth and Sun and the
equatorial plane
365
2842sin
180
45.23 n
Declination in radians; n is the number of the day (Jan 1st = 1)14
Solar resource
Earth-Sun motion
E
O
S
N
a – solar elevation
0ºy – solar azimuth
0º
-90º
90º
a
ay
a
coscos
sinsinsincos
coscossinsinsin
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Solar resource
Optimum orientation: facing south (north in the southern hemisphere)
Optimum inclination: local latitude – but not quite
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Solar resource
Atmospheric effects
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Solar resource
Atmospheric effects on solar radiation at the Earth's surface:
a reduction in the power of the solar radiation due to absorption,
scattering and reflection in the atmosphere;
a change in the spectral content of the solar radiation due to greater
absorption or scattering of some wavelengths;
the introduction of a diffuse or indirect component into the solar
radiation; and
local variations in the atmosphere (such as water vapour, clouds and
pollution) which have additional effects on the incident power, spectrum
and directionality.
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Solar resource
Air Mass is a measure of the reduction in the power of
light as it passes through the atmosphere and is
absorbed by air and dust
cos
1AM
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Solar resource
0,0
0,5
1,0
1,5
2,0
2,5
0 200 400 600 800 1000 1200 1400 1600 1800 2000
Wm
-2n
m-1
Wavelength (nm)
AM0 - Extraterrestrial
AM1.5 - Global
AM1.5D - Direct
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Solar resource
0,0
0,5
1,0
1,5
2,0
2,5
0 200 400 600 800 1000 1200 1400 1600 1800 2000
Wm
-2n
m-1
Wavelength (nm)
Photon flux F [photons/s/m2]
Power density H [W/m2]
Spectal irradiance F [W/m2/mm] is
the power density at a given
l(mm)
sm
photons2
F
00 i
FdFH llll
22 lm
hc
mm
WF F
l
hc
m
WH F
2
m
hcE
mll
24.1
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Solar resource
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Solar resource
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Solar resource
Insolation: Incoming Solar Radiation
Typical units: kWh/m2/day
Affected by latitude, local weather patterns,…
Šúri M., Huld T.A., Dunlop E.D. Ossenbrink H.A., 2007.
Potential of solar electricity generation in the European
Union member states and candidate countries. Solar
Energy, 81, 1295–1305, http://re.jrc.ec.europa.eu/pvgis/.
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25
Yearly sum of global irradiation on vertical surface (kWh/m2)
period 1981-1990
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Yearly sum of global irradiation on horizontal surface (kWh/m2)
period 1981-1990
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Yearly sum of global irradiation on optimally-inclined surface (kWh/m2)
period 1981-1990
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Yearly sum of global irradiation on 2-axis tracking surface (kWh/m2)
period 1981-1990
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Solar resource
Šúri M., Huld T., Dunlop E.D., Albuisson M., Lefèvre M., Wald L., 2007.
Uncertainties in photovoltaic electricity yield prediction from fluctuation of
solar radiation. Proceedings of the 22nd European Photovoltaic Solar
Energy Conference, Milano, Italy 3-7.9.2007
Coastal areas and higher
mountains face wider
variations (up to 10%)
Winter is much more
variable (up to x6) than
summer months
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Solar tracking
Compared to PV with modules fixed at optimum angle:
Changing inclination twice a year contributes only marginally
Comparison of electricity yield from fixed and suntracking PV systems in Europe [JRC, 2008] 33
Solar tracking
Comparison of electricity yield from fixed and suntracking PV systems in Europe [JRC, 2008] 34
Solar tracking
Comparison of electricity yield from fixed and suntracking PV systems in Europe [JRC, 2008] 35
Solar tracking
Compared to PV with modules fixed at optimum angle:
Changing inclination twice a year contributes only marginally (2-4%)
1-axis tracking PV with vertical or South-inclined axis generates only 1-4%
less than 2-axis tracking system
1-axis tracking PV with horizontal axis oriented E-W typically performs
only slightly better than fixed mounting systems
Comparison of electricity yield from fixed and suntracking PV systems in Europe [JRC, 2008] 36
16351577 1537
1436
12691177
0
500
1000
1500
2000
2-axes NS inclined Vertical NS hor EW hor Fixed
kW
h/W
p/y
ea
rSolar tracking
Gaspar et al, Exploring One-Axis Tracking Configurations For CPV Application, CPV7, Las Vegas 2011
•An inclined axis tracking system orientated in the north-
south direction is able to closely follow the Sun throughout
the year, and have a relatively high acceptance for CPV
applications.
•The vertical tracking, with optimum inclination, features a
similar performance that an inclined axis tracking system
orientated in the north-south direction.
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Solar tracking
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Solar tracking
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0
50
100
150
200
250
300
350
1 2 3 4 5 6 7 8 9 10 11 12
Avera
ge s
um
of
blo
bal
irra
dia
tio
n k
Wh
/m2
Month
Fixed angle 0º
Fixed angle 33º
Vertical axis 33º
Inclined axis 33º
2-axis tracking
0%
50%
100%
150%
200%
Fixed
angle 0º
Fixed
angle 33º
Vertical
axis 33º
Inclined
axis 33º
2-axis
tracking
Avera
ge s
um
of
blo
bal
irra
dia
tio
n
kW
h/m
2
Solar tracking
PVGIS exercise: Lisbon
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Solar tracking
Shadowing effect
Ground cover ratio = PV area / total area
E. Narvarte et al, Tracking and Ground Cover Ratio, Prog. Photovolt: Res. Appl. 2008; 16:703–714
Horizontal
tracking
Inclined
tracking
2-axis
tracking
GCR = PV density
1 /GCR
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PV in urban environment
N. Gomes et al, PV potential in urban environment using LIDAR data, 2010, Solar Energy
Carnaxide (38.43° N, 9.8 W)
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PV in urban environment
N. Gomes et al, PV potential in urban environment using LIDAR data, 2010, Solar Energy 43
PV in urban environment
N. Gomes et al, PV potential in urban environment using LIDAR data, 2010, Solar Energy 44
PV in urban environment
N. Gomes et al, PV potential in urban environment using LIDAR data, 2010, Solar Energy 45
PV in urban envir
http://www.fcsh.unl.pt/e-geo/energiasolar/ 46
PV in urban envir
http://www.fcsh.unl.pt/e-geo/energiasolar/ 47
PV in urban envir
http://www.lisboaenova.org/pt/cartasolarlisboa 48
PV in urban envir
http://www.lisboaenova.org/pt/cartasolarlisboa 49
PV in urban environment
N. Gomes et al, PV potential in urban environment using LIDAR data, 2010, Solar Energy
• Procedure for estimating the PV potential of an urban region using
LiDAR data based on the Solar Analyst extension for ArcGIS.
•PV potential of the 538 buildings to be around 11.5 GWh/year for an
installed capacity of 7MW, which corresponds to 48 % of the local
electricity demand.
•For low PV penetration (about 10% of total roof area) the PV potential
is well estimated by considering no shade and the local optimum
inclination and orientation.
•For high PV penetration (i.e. covering close to all roof area) the PV
potential is well estimated by considering a horizontal surface with the
footprint area of the buildings.
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PV in urban environment
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THE ROLE OF BUILDING FACADES
1490
932
717 708
180
778
575
391 392
150
0
400
800
1200
1600
Optimum tilt South facing
facade
East facing
facade
West facing
facade
North facing
facade
kW
h/k
Wp
/yr
LISBON
OSLO
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THE ROLE OF BUILDING FACADES
14%
-29%
-45% -46%
-86%
20%
-11%
-40% -40%
-77%
-100%
-80%
-60%
-40%
-20%
0%
20%
40%
Optimum tilt South facing
facade
East facing
facade
West facing
facade
North facing
facade
LISBON
OSLO
Comparison with
horizontal surface
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THE ROLE OF BUILDING FACADES
Solar facades?
Typical 4 storey building
Roof area:
10x10m2 = 100m2
Annual solar PV production on roof:
18.6 MWh/day
(with optimum orientation/inclination)
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Solar facades?
Typical 4 storey building
Roof area:
10x10m2 = 100m2
Facades area:
4 facades
x 4 storeys
x 3m
x 10m = 480m2
Total area:
580m2
THE ROLE OF BUILDING FACADES
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Solar facades?
Typical 4 storey building
Roof area:
10x10m2 = 100m2
Facades area:
4 facades
x 4 storeys
x 3m
x 10m = 480m2
Total area:
580m2
Annual solar PV production on roof and facades:
18.6 + 38.1 = 56.7 MWh/day
THE ROLE OF BUILDING FACADES
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Solar facades?
Typical 4 storey building
Roof area:
10x10m2 = 100m2
Facades area:
4 facades
x 4 storeys
x 3m
x 10m = 480m2
Total area:
580m2
Annual solar PV production on roof and facades:
38.1+ 18.6 = 56.7 MWh/day
Facades can increase the PV area dramatically (x5.8) and,
although with less than optimum inclination/orientation may
contribute significantly to the overall production (x3).
THE ROLE OF BUILDING FACADES
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17% decrease in mismatch between supply and demand during sunlight
hours (+32% covered area)
Solar facades
THE ROLE OF BUILDING FACADES
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19% decrease in mismatch between supply and demand during sunlight
hours (+46% covered area)
Solar facades
THE ROLE OF BUILDING FACADES
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THE ROLE OF BUILDING FACADES
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THE ROLE OF BUILDING FACADES
Redw
eik
et
al, S
ola
r Energ
y97 (
2013)
332–341
61
Solar facades
THE ROLE OF BUILDING FACADES
Redw
eik
et
al, S
ola
r Energ
y97 (
2013)
332–341
Redw
eik
et
al, S
ola
r Energ
y97 (
2013)
332–341
62
PV in urban environment
Solar facades
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THE ROLE OF BUILDING FACADES
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65
66
PV in urban environment
Conclusions
• Facades can play a relevant role for PV production in
the urban environment
• Lower production for less than optimum
orientation/inclination
• Relatively higher production in winter
• Relatively higher production during earlier and later
hours of the day
• Mutual shading of buildings needs to be taken into
account
• GIS tools for assessment of solar potential of facades
needs further development
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Next class
Further readingM. Šúri,et al, Potential of solar electricity generation in the European Union
member states and candidate countries. Solar Energy, 81 (2007) 1295–1305
M. Šúri et al, Uncertainties in photovoltaic electricity yield prediction from
fluctuation of solar radiation. Proc. 22nd European Photovoltaic Solar Energy
Conference, Milano, Italy 2007
T. Huld et al, Comparison of Potential Solar Electricity Output from Fixed-
Inclined and Two-Axis Tracking Photovoltaic Modules in Europe, Prog.
Photovolt: Res. Appl. 2008; 16:47–59
E. Narvarte et al, Tracking and Ground Cover Ratio, Prog. Photovolt: Res. Appl.
2008; 16:703–714
68