energia solar fotovoltaica, mc brito solarsolar.fc.ul.pt/pv_course/pv classes - resource -...

Solar resource, 6/10/2009Energia Solar Fotovoltaica, MC Brito

Mestrado Integrado Engenharia da Energia e do Ambiente, Faculdade Ciências da Universidade de Lisboa, 1/12

OnOn thethe webweb

Course webpage!http:// solar.fc.ul.pt/PV_course

PV bloghttp://solar-fcul blogspot comhttp://solar-fcul.blogspot.com

Group page: http:// solar.fc.ul.pt

OnOn thethe webweb

Solar Solar resourceresource

Radiation from the Sun Atmospheric effects Insolation maps Tracking the Sun Tracking the Sun



Solar Solar resourceresource Solar resource is immense

◦ Human energy use: 4.0x1014 kWh/year

◦ Solar resource on Earth’s surface: 5.5x1017 kWh/year

Solar Solar resourceresource 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


2

4

0 4 sunR

TP

Total radiative power (Stefan Boltzman) T=5762K

Surface area of sun

Power radiated per unit area5.96x107 W/m2




2

4

0 4 sunR

TP

02

2

4

4P

D

RS sun

Ratio of surface areas of the2 spheres

Distance Sun-Earth

Solar constant averageenergy flux incident at theEarth’s orbit: 1366 W/m2


2

4

0 4 sunR

TP

Rsun 6.96x105 km

Davg 1.5x108 km

REarth 6.35x103 km

44 2

2 S

R

RS

Earth

Earth Energy incident on Earth Average energy incident

per unit area of surface ofEarth: 342 W/m2Total area of Earth

02

2

4

4P

D

RS sun

Solar Solar resourceresource Earth-Sun motion

23.7 º

Polar axis

365 days and 6 hours

365

2360cos033.01

n

S

H



Solar Solar resourceresource Earth-Sun motion◦ Solar declination: angle between line joining centres of Earth and Sun and

the equatorial plane

Polar axis

+23º 27’

-23º 27’

0º Vernal andautomnal equinox

Solar Solar resourceresource Earth-Sun motion◦ Solar declination: angle between line joining centres of Earth and Sun and

the equatorial plane

365

2842sin

180

45.23 n

Solar Solar resourceresource Earth-Sun motion

– solar elevation

coscos

sinsinsincos

coscossinsinsin

E

O

S

N

0º– solar azimuth

0º

-90º

90º



Solar Solar resourceresourceAtmospheric effects

Solar Solar resourceresourceAtmospheric 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.

Solar Solar resourceresource Air Mass is a measure of the reduction in the power

of light as it passes through the atmosphere and isabsorbed by air and dust

cos

1AM




1.5

2.0

2.5

AM0 - Extraterrestrial

AM1.5 - Global

0.0

0.5

1.0

0 200 400 600 800 1000 1200 1400 1600 1800 2000

Wm

-2n

m-1

Wavelength (nm)

AM1.5D - Direct


1.5

2.0

2.5 Photon flux [photons/s/m2]

Power density H [W/m2]

Spectal irradiance F [W/m2/m] is the power density at a given(m)

sm

photons2

hW

hc

m

WH

2

m

hcE

24.1

0.0

0.5

1.0

0 200 400 600 800 1000 1200 1400 1600 1800 2000

Wm

-2n

m-1

Wavelength (nm)

00 i

FdFH

22 hc

mm

WF





Solar Solar resourceresource 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 the2007. 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/



Yearly sum of global irradiation on vertical surface (kWh/m2)period 1981-1990

Yearly sum of global irradiation on horizontal surface (kWh/m2)period 1981-1990

Yearly sum of global irradiation on optimally-inclined surface (kWh/m2)period 1981-1990



Yearly sum of global irradiation on 2-axis tracking surface (kWh/m2)period 1981-1990



Solar Solar resourceresource Coastal areas and higher

mountains face widervariations (up to 10%)

Winter is much more variable (up to x6) than

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

summer months

Solar Solar trackingtrackingCompared 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]

Solar Solar trackingtracking




Solar Solar trackingtracking


Solar Solar trackingtrackingCompared 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


250

300

350

n k

Wh

/m2

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

Ave

rag

e su

m o

f b

lob

al i

rrad

iati

on

kW

h/m

2

Solar trackingSolar tracking

PVGIS exercise: Lisbon

0

50

100

150

200

1 2 3 4 5 6 7 8 9 10 11 12

Ave

rag

e su

m o

f b

lob

al i

rrad

iati

on

Month



Solar Solar trackingtrackingShadowing effect

Ground cover ratio = PV area / total area

Inclinedtracking

2-axis tracking

E. Narvarte et al, Tracking and Ground Cover Ratio, Prog. Photovolt: Res. Appl. 2008; 16:703–714

Horizontal tracking

g

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