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Contents
} The sun as energy source } Sun‐Earth relationships } Solar radiation measurements } Quality control of solar radiation data } Solar radiation estimation
} From meteorological data } Models for the estimation of the beam component } From Satellite images
} Databases and tools } Typical Meteorological Years
1 GEEN 4830 – ECEN 5007
El espectro electromagné0co
The electromagne.c spectrum is a con.nuum of all electromagne.c waves arranged according to frequency and wavelength. Energy = h·∙f Planck’s constant h = 6.62·∙10-‐34 J·∙s
ENERGY
3·∙106 GHz
2 GEEN 4830 – ECEN 5007
Bands adopted by the Interna.onal Commission on Illumina.on (Commission Interna.onal de l'Eclairage, CIE) UV, visible e IR
λ (nm)
UV C UV B UV A Visible IR A IR B IR C
400 3000 1400 760 315 280 100 106
3·∙106 7.5·∙105 105 300
f (GHz)
0.3 m (300 nm)
3 m (3000 nm)
Shortwave solar radia.on Longwave solar radia.on
The electromagne0c spectrum
3 GEEN 4830 – ECEN 5007
Black body A black body is an ideal object that absorbs 100% of the radia.on that hits it. It also emits the maximum radia.on at all wavelengths and all direc.ons at a given temperature. The spectral ( or monochroma.c) p ) emissive power of a black body. ebλ is the energy emited per .me and area units at each wavelength, and it is a func.on of temperature
[ ]1/51
2 −⋅= TCb e
Ce λλ λ(W·∙m-‐2 ·∙μm-‐1) Planck’s equa.on
KT m →→ µλ
4-281 mmW107427.3 µ⋅⋅=C Km104388.1 4
2 ⋅⋅= µC
4 GEEN 4830 – ECEN 5007
For a black body, as the temperature increases:
0 5 10 15 20100
101
102
103
104
105
106
107
108
300 K
1000 K2500 K5777 K
Pot
enci
a em
isiv
a es
pect
ral (
Wm
-2µm
-1)
λ (µm)
λbe
-‐ The emissive power increases for every wavelength
-‐ The rela.ve amount of energy emifed at short wavelengths increases
-‐ The posi.on of the maximum emissive power is displaced to shorter wavelengths
Black body radia0on
5 GEEN 4830 – ECEN 5007
Stefan-‐Boltzmann’s Law
The total emissive power is the radia.on emifed by the black body at all wavelengths, and is given by:
[ ]∫−⋅
=∫=∞=
=
∞==
λ
λλ
λλ λ λ
λλ
0/51
0 12d
eCdee TCbb
4Teb σ=
Stefan-‐Boltzman’s constant σ = 5.6866·∙10-‐8 W·∙m-‐2K-‐4
Wien’s Law
The wavelengths corresponding to the maximum emifed power is inversely propor.onal to temperature Tmax
8.2897=λ (μm)
(W·∙m-‐2)
Black body radia0on
6 GEEN 4830 – ECEN 5007
The irradiance (at a point of a surface) is the radiant power of all wavelengths incident from all upward direc.ons on a small element of surface containing the point under considera.on divided by the area of the element. SI unit is W·∙m-‐2. The spectral irradiance is the irradiance at a given wavelength per unit wavelength interval. The SI unit is W m–3, but a commonly used unit is W m–2 μm–1.
remit
2
0 ⎟⎠⎞⎜
⎝⎛=
⋅rreI emit
bn λλ
Irradiance; spectral irradiance
7 GEEN 4830 – ECEN 5007
8 GEEN 4830 – ECEN 5007
Solar Spectrum. Solar constant
Solar Constant
NASA 1353WRC 1367
SCG (W·∙m-‐2)
SCG = 4921 kJ·∙m-‐2·∙h-‐1
SCG = 0.082 MJ·∙m-‐2·∙min-‐1
0,0 0,5 1,0 1,5 2,0 2,5 3,0
0
500
1000
1500
2000
2500λnI 0
⋅
(W·∙m-‐2 ·∙m-‐1)
λ (μm)
Total Radiative flux (at all wavelengths) inciding on a surface perpendicular to the sun rays at a distance of 1 AU
hfp://rredc.nrel.gov/solar/spectra/am0/ 9 GEEN 4830 – ECEN 5007
0,0 0,5 1,0 1,5 2,0 2,5 3,0
0
500
1000
1500
2000
2500
0,0 0,5 1,0 1,5 2,0 2,5 3,0
0
500
1000
1500
2000
2500
λnI 0⋅
(W·∙m-‐2 ·∙μm-‐1)
λ (μm)
Black body @ 5777 K Size of the Sun @ 1 AU
Extraterrestrial solar spectrum
Visible http://mesola.obspm.fr/solar_spect.php
hfp://rredc.nrel.gov/solar/standards/am0/wehrli1985.new.html
UV IR
The Sun as a blackbody
10 GEEN 4830 – ECEN 5007
¡The Sun is a high quality energy source!
} Aprox. 95% of the extraterrrestrial solar radiation can be converted to work
⎟⎠⎞⎜
⎝⎛ −=⎟⎟⎠
⎞⎜⎜⎝
⎛−=
KKQ
TTQW SunSun
ambSun 5777
30011
GEEN 4830 – ECEN 5007 11
Extraterrestrial solar radiation
I!0n =GSC
r0r
"#$
%&'2
=GSCE0
I!0 = I!0n cos!z
I!0 =GSC
r0r
"#$
%&'2
cos!z =GSCE0 cos!z
On a normal surface
On a horizontal surface
12 GEEN 4830 – ECEN 5007
Average solar irradiance on the Earth
GSC = 1367 W·m-2
Earth radius = 6740 km. The intercepted solar radia.on is
propor.onal to πR2
The energy received on 1 day is distributed on an area 4πR2
The average solar irradiance on the top of the atmosphere is 342 W·∙m-‐2
13 GEEN 4830 – ECEN 5007
14 GEEN 4830 – ECEN 5007
Rayleigh���diffusion Mie diffusion
Beam ���irradiance
Diffuse ���irradiance
Albedo irradiance
Beam ���irradiance
Interac.on between solar radia.on and atmospheric components
15 GEEN 4830 – ECEN 5007
(Clear Day)
Absorp0on %
8
100%
Air molecules 1
1 to 5
0.1 a 10
5 Dust, aerosols
Moisture 0.5 to 10
2 to 10
Diffuse %
Reflec0on to space %
Beam
83% to 56% 11% to 23% 5% a 15%
Interac.on between solar radia.on and the Earth’s atmosphere
16 GEEN 4830 – ECEN 5007
Scafering (change in direc.on per air molecules)
00.10.20.30.40.50.60.70.80.91
0.3 1.3 2.3 3.3
Longitud onda (micras)
Coef
. tra
nsm
isió
n es
cate
rin
θz=20º z = 0 m.
Atmosphere
Earth
θz
17 GEEN 4830 – ECEN 5007
Atmosphere
Earth
θz
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Longitud de onda (micras)
Coe
f. tra
nsm
isió
n oz
ono
Absorp.on by ozone
θz=20º Lo=0.2
18 GEEN 4830 – ECEN 5007
Lo = Ozone layer thickness (cm)
0.2
0.25
0.3
0.35
0.4
0.45
0.5
-90 -70 -50 -30 -10 10 30 50 70 90
Latitud (º)
Espe
sor c
apa
ozon
o (c
m) Enero
FebreroMarzoAbrilMayoJunioJulioAgostoSeptiembreOctubreNoviembreDiciembreNorte Sur
19 GEEN 4830 – ECEN 5007
Absorp.on by gases (CO2, O2)
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0.3 0.8 1.3 1.8 2.3 2.8 3.3 3.8
Longitud de onda (micras)
Coe
f. tr
ansm
isió
n po
r mez
cla
de g
ases
θz=20º z = 0 m.
Atmosphere
Earth
θz
20 GEEN 4830 – ECEN 5007
Absorp.on by water molecules
0
0.10.2
0.30.4
0.5
0.60.7
0.80.9
1
0.3 0.8 1.3 1.8 2.3 2.8 3.3 3.8
Longitud de onda (micras)
Coe
f. tr
ansm
isió
n po
r abs
orci
ón d
el
vapo
r de
agua
θz=20º T=25ºC RH=50%
Atmosphere
Earth
θz
21 GEEN 4830 – ECEN 5007
Absorp.on and diffusion by aerosols
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0.3 0.8 1.3 1.8 2.3 2.8 3.3 3.8
Longitud de onda (micras)
Coe
ficie
nte
tran
smis
ión
aero
sole
s
θz=20º α=1.3 β=0.15 τaa(absorp.on)
τas(difussion)
Atmosphere
Earth
θz
22 GEEN 4830 – ECEN 5007
τa(total afenua.on)
0
500
1000
1500
2000
0,3 1,3 2,3 3,3
Longitud de onda (micras)
W/m
2 · µm
Extraterrestre5777 KInIdhIT
Solar radia.on on the Earth’s surface
nd = 94 θz=20º z = 0 m. α=1.3 β=0.15 Ts=25ºC RH=50% Lo = 0.3
O3
O2
H2O CO2 H2O
23 GEEN 4830 – ECEN 5007
CHARACTERISTICS OF SOLAR RADIATION Cycles
Solar energy reaches the earth in a discon.nuous form, resul.ng in different cycles:
} Daily cycle: } accounts for 50% of the total availability of daily hours.
} Another effect of the daily cycle is the modula.on of the received energy throughout the day.
} Seasonal cycle: } modula.on of the received energy throughout the year.
24 GEEN 4830 – ECEN 5007
SOLAR RADIATION CHARACTERISTICS Low density
} The maximum possible amount of solar radia.on received by the surface of the atmosphere at 1 AU is 1367 W/m2
} Large surfaces are needed to achieve high power outputs.
} To increase the density concentra.on should be used.
} Only the direct component of solar radia.on can be concentrated.
25 GEEN 4830 – ECEN 5007
SOLAR RADIATION CHARACTERISTICS Dependence on geography (la0tude)
} Under clear sky condi.ons: the solar radia.on depends mainly on the la.tude.
} La.tude effect is equivalent to the modifica.on of the angle of incidence of solar radia.on.
} For the modula.on of the received energy the following can be used: } Solar tracker } Tilted Plane
} The inclina.on of the recep.on plane means: } Modifica.on of the la.tude effect } Modifica.on of the annual distribu.on.
26 GEEN 4830 – ECEN 5007
SOLAR RADIATION CHARACTERISTICS Random character
} Solar radia.on on the Earth's surface is modulated by clima.c condi.ons.
} Clear sky condi.ons are not common. } The la.tude indicates a maximum range, but the energy received is determined by local clima.c condi.ons.
27 GEEN 4830 – ECEN 5007
SUN-‐EARTH RELATIONSHIPS Sun-‐Earth distance
} The earth revolves around the Sun in an elliptical orbit, with the Sun in one of its foci.
} The amount of solar radiation incoming to the Earth is inversely proportional to the square of the Sun – Earth distance.
} The distance is measured in astronomical units (AU) equivalent to the mean Sun ‐ Earth distance.
28 GEEN 4830 – ECEN 5007
SUN-‐EARTH RELATIONSHIPS Declina0on
} Eclip.c plane (ECLP): the plane of Earth's revolu.on around the Sun } Equatorial plane (EQUP): the plane containing the equator } The Polar axis is .lted 23.5o with respect to the normal to the ECLP.
w ECLP and EQUP cross in the equinoxes and the distance is maximum in the sols.ces.
w The angle in a specific moment between both planes is called DECLINATION
29 GEEN 4830 – ECEN 5007
SUN-‐EARTH RELATIONSHIPS Rela0ve posi0on sun-‐horizontal surface
w Zenith angle (θ ) and solar elevation (α)
w Azimuth (ψ) = angle between the observer meridian and the solar meridian
w Hourly angle (ω) = angle between the sun position and the south meridian 15o=1hour; +E /‐W.␣
w Sunrise angle (ωs) = sunset angle (horizon)
30 GEEN 4830 – ECEN 5007
SUN-‐EARTH RELATIONSHIPS Rela.ve posi.on Sun -‐ inclined surface
} Considering a south orienta.on, the diagram shows how a surface inclined β in a la.tude φ is similar to a horizontal surface in a la.tude φ-‐β.
31 GEEN 4830 – ECEN 5007
EXTRATERRESTRIAL SOLAR RADIATION Hourly radia.on over horizontal surface
} The extraterrestrial radia.on on a normal surface (perpendicular to the Sun´s rays) is expressed as:
( ) 02
0 EIrrII scoscn ==
w For an horizontal surface
zscEII θcos00 =
32 GEEN 4830 – ECEN 5007
SOLAR RADIATION ON THE EARTH SURFACE Direct solar radia.on (beam)
} Is the radia.on coming directly from the Sun disk.
} It has a direc.onal character and can be concentrated.
} Accounts for approx. 90% of the solar radia.on on clear sky days, and can be null in cloud covered days.
} As a direc.onal component, the contribu.on on a surface is the perpendicular projec.on over this surface: beam radia.on is the radia.on on a plane perpendicular to the sun´s rays.
I = B cos θ It can be maximized with solar trackers.
33 GEEN 4830 – ECEN 5007
SOLAR RADIATION ON THE EARTH SURFACE Diffuse solar radia.on
} Part of the solar radia.on is absorbed by the atmospheric components. Another part is reflected by these components producing direc.on changes and energy reduc.on.
} Diffuse radia.on = the part of this radia.on that reaches the earth´s surface.
} Diffuse radia.on has three components: } Circumsolar } Horizon band } Blue sky
34 GEEN 4830 – ECEN 5007
SOLAR RADIATION ON THE EARTH SURFACE Reflected solar radia.on
} Radia.on coming from the reflec.on of the solar radia.on on the ground or on other nearby surfaces.
} Usually is small, but in occasionally can account for up to 40% of the solar radia.on on a given surface.
35 GEEN 4830 – ECEN 5007
Meteorological Sta0on at the Seville Engineering School (since 1984)
Solar radia0on measurement
36 GEEN 4830 – ECEN 5007
Measurement of Solar Radia0on
§ Since 1830, Herschel, Beloni and Pouillet developed instruments, capable of measuring the intensity of solar radia.on
§ Precise determina.on of the solar constant in the early 1900’s, during the energy crisis and solar energy development in 1970s.
§ Need to befer understand global climate change in the 1980s and 1990s.
37 GEEN 4830 – ECEN 5007
Solar radia0on sensors
GEEN 4830 – ECEN 5007 38
Solar radiation sensors
GEEN 4830 – ECEN 5007 39
} Rotating shadowband radiometer } Measures global + diffuse } Calculates direct from global +
difusse measurements
Measurement of Solar Radia.on
§ Broad-‐band global solar irradiance: Pyranometer
§ Diffuse radia.on is measured with a pyranometer and a shading device (disc, shadow ring, or band) that excludes direct solar radia.on
§ Response decreases approximately as the cosine of the angle of incidence.
§ Measures energy incident on a flat surface, usually horizontal
40 GEEN 4830 – ECEN 5007
Global irradiance } Most readily available data, required for many different applica.ons
} Difficult to model } Sensi.ve to the albedo of the surroundings
Measurement } No absolute reference for calibra.on } Cosine effect (correc.on required) } Many instruments available
41 GEEN 4830 – ECEN 5007
Global irradiance measurement – error sources
} Calibra.on errors } Stability } Non-‐Linearity } Shadows and reflec.ons from the surroundings } Cosine effect } Spectral transmissivity of the dome } Thermal offset of the dome } Temperature dependence } Cleanliness of the dome } Leveling
42 GEEN 4830 – ECEN 5007
Diffuse irradiance measurement – error sources
Same as global, plus } Geometry of shading device } Incorrect alignment of shading device
43 GEEN 4830 – ECEN 5007
} Easy to model } Sensi.ve to afenua.on } It is the main component under clear
sky
Measurement } Precise calibra.on (absolute –cavity-‐
radiometer) } Requires con.nuous tracking
5.7 º
Eppley Labs pyrheliometer (NIP) & tracker
Direct normal (beam) irradiance measurement
44 GEEN 4830 – ECEN 5007
} Calibra.on errors } Calibra.on stability } Linearity } Spectral transmissivity of the window } Incorrect alignment, obstacles } Temperature dependence } Window cleanliness
Direct normal (beam) irradiance measurement – error sources
45 GEEN 4830 – ECEN 5007
Measurement of Solar Radia.on The Baseline Surface Radia.on Network (BSRN) hfp://www.bsrn.awi.de/en/home/bsrn/
§ The BSRN was recently (early 2004) designated as the global baseline network for surface radia.on for the Global Climate Observing System (GCOS). The BSRN sta.ons also contribute to the Global Atmospheric Watch (GAW). § Proposed by the World Climate Research Program (late 1980s) § Objec.ve: high accuracy surface irradiance measurement all over the world
§ Valida.on of satellite es.ma.on models § Valida.on of radia.on codes for climate models
46 GEEN 4830 – ECEN 5007
Measurement of Solar Radia.on – BSRN Sta.ons The SURFRAD network Sta.on at Boulder, CO. La0tude: 40.13 degrees North Longitude: 105.24 degrees West Eleva0on: 1689 meters Time Zone: Local Time + 7 hours = UTC Installed: July 1995
The Boulder SURFRAD instruments are located on the deck at SRRB's Table Mountain Test Facility, located 8 miles north of Boulder. These instruments are part of a larger set maintained at this loca.on and used for annual intercomparisons and other research.
47 GEEN 4830 – ECEN 5007
Contents
} Quality control of solar radiation data } Solar radiation estimation
} From meteorological data } Models for the estimation of the beam component } From Satellite images
} Databases and tools } Typical Meteorological Years
48 GEEN 4830 – ECEN 5007
Quality control of solar radiation data
} Different procedures, all based on data filtering by: } Comparison with physical constraints, other measurements,
models. } Visual inspection by experienced staff
} An example follows (see also http://rredc.nrel.gov/solar/pubs/qc_tnd/ for a different, more exhaustive procedure)
49 GEEN 4830 – ECEN 5007
Quality control of solar radia.on data
1. Physically Possible Limits 2. Extremely Rare Limits 3. Comparisons vs other measurements 4. Comparisons vs model 5. Visual inspec.on
50 GEEN 4830 – ECEN 5007
FILTER 1: Physically Possible Limits
Subscripts: go = Global horizontal, do = diffuse horzontal, D = beam
Io = extraterrestrial irradiance; Itop = irradiance at minimum zenith angle
Units: W m-‐2
Lower limit Irradiance Upper limit 0 Igo Io
0 Ido Itop+10
0 ID Io
51 GEEN 4830 – ECEN 5007
FILTER 2: Extremely Rare Limits
Subscripts: go = Global horizontal, do = diffuse horizontal, D = beam
Z: zenith angle; m = air mass; Eo = Sun – Earth distance correc.on factor
Io = extraterrestrial irradiance; Itop = irradiance at minimum zenith angle
Units: W m-‐2
52 GEEN 4830 – ECEN 5007
FILTER 3: Comparison vs other measurements
Lower limit Irradiance Upper limit
(Igo-‐Ido)-‐50 Wm-‐2 ID·∙cosZ (Igo-‐Ido)+50 Wm-‐2
ID·∙cosZ-‐50 Wm-‐2 Igo-‐Ido ID·∙cosZ+50 Wm-‐2
|Igo-‐Ido – ID cos z|± 50 Wm-‐2
Subscripts: go = Global horizontal, do = diffuse horizontal, D = beam
Z: zenith angle; m = air mass; Eo = Sun – Earth distance correc.on factor
Io = extraterrestrial irradiance; Itop = irradiance at minimum zenith angle
Units: W m-‐2
53 GEEN 4830 – ECEN 5007
FILTER 4: Comparison vs model
Comparison vs a model. The model has to be adapted to the clima.c characterisi.cs of the Sta.on.
Example: Hourly beam-‐to-‐extraterrestrial irradiance plofed against clearness index (NREL’s quality control procedure)
54 GEEN 4830 – ECEN 5007
FILTER 5: Visual Inspec.on
0
200
400
600
800
1000
1200
1400
-‐8 -‐6 -‐4 -‐2 0 2 4 6 8
hora solar
irrad
ianc
ias
W/m
2
IDmedidaigid
55 GEEN 4830 – ECEN 5007
Visual inspec.on
0 2 4 6 8 10 12 14 16 18 20 22 240
200
400
600
800
1000
1200
1400
GMT(h)
I(W/m
2)
Estación: Cáceres (SAMCA) 18/11/2007
56 GEEN 4830 – ECEN 5007
Time offset Incorrect .me stamp
0
100
200
300
400
500
600
700
800
900
-8 -6 -4 -2 0 2 4 6 8
Ighoras sol
t1torto
tocaso
t2
dm dt
0
100
200
300
400
500
600
700
800
900
-8 -6 -4 -2 0 2 4 6 8
Ighoras solIgcorregida
torto tocaso
t2t2't1'
t1
57 GEEN 4830 – ECEN 5007
CLASSICAL ESTIMATION OF SOLAR RADIATION Models depend on the variable to es.mate and on the available data and their characteris.cs:
} Es.ma.on of daily or monthly global horizontal or direct normal irradia.on from sunshine dura.on
} Es.ma.on of hourly values from daily values of global horizontal irradia.on
} Es.ma.on of global irradia.on on .lted surfaces } Es.ma.on of the beam component from global horizontal irradia.on
} Etc.
58 GEEN 4830 – ECEN 5007
Es.ma.on of daily or monthly global horizontal irradia.on from sunshine dura.on } Angstrom – type formulas
H/H0 = a + b (s/s0) } Where
} H is the monthly average of the daily global irradia.on on a horizontal surface
} H0 is the monthly average of the daily extraterrestrial irradia.on on a horizontal surface
} s is the monthly average of the daily number of hours of bright sunshine,
} s0 is the monthly average of the daily maximum number of hours of possible sunshine
} a and b are regression constants
59 GEEN 4830 – ECEN 5007
Es.ma.on of direct normal irradia.on from sunshine dura.on
0
100
200
300
400
500
600
700
800
900
1000
-8 -6 -4 -2 0 2 4 6 8
hora solar / h
E bn /
W·m
-2
60 GEEN 4830 – ECEN 5007
Decomposi0on models (es0ma0on of beam and diffuse components from global horizontal)
GEEN 4830 – ECEN 5007 61
Kd – KT models
Modelos Kt-Kd diarios
0
0.2
0.4
0.6
0.8
1
1.2
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
Kt
Kd
Collares Muneer Liu-Jordan GTER00-05 Ruth and Chant GTERD00-05
62 GEEN 4830 – ECEN 5007
SOLAR RADIATION ESTIMATION FROM SATELLITE IMAGES
63 GEEN 4830 – ECEN 5007
SOLAR RADIATION ESTIMATION FROM SATELLITE IMAGES
} Energy balance
tase0 EEII ++=
( )aseg EIIA
I −−−
= 011
64 GEEN 4830 – ECEN 5007
Measured
Modeled
Measured - Estimated
Modeled
THE SATELLITE Meteorological satellites
} In meteorology studies frequent and high density observa.ons on the Earth's surface are required.
Conven.onal systems do not provide a global cover.
w An important tool to analyse the distribu.on of the clima.c system are the METEOROLOGICAL SATELLITES. These can be:
ð Polar satellites
ð Geosta.onary: In Europe, the system of geosta.onary meteorological satellites is called METEOSAT
65 GEEN 4830 – ECEN 5007
THE SATELLITE Satellite classifica.on
Related to the type of orbit :
Polar satellites: placed in polar orbits, modifying its perspec.ve and distance to the Earth.
Resolu.on 1m to 1km.
Geosta.onary satellites: placed in the geosta.onary orbit that is, the place in the space where the Earth's afrac.on force is null. It is an unique circumference where all the geosta.onary satellites are situated in order to cover the whole Earth's surface. The resolu.on of these satellites are maximum at the equator, and decrease in all direc.ons.
66 GEEN 4830 – ECEN 5007
METHODOLOGY Advantages
} The geosta.onary satellites show simultaneously wide areas.
} The informa.on of these satellites is always referred to the same .me window.
} It is possible to analyse past climate using satellite images of previous years.
} The u.lisa.on of the same detector to evaluate the radia.on in different places.
67 GEEN 4830 – ECEN 5007
METHODOLOGY Disadvantages
} The range of the brilliance values of cloud cover (90-‐255) and of the soils (30-‐100) overlap.
} The digital conversion results in imprecision for low values of brilliance.
} The image informa.on is related to an instant, while the radia.on data is es.mated in a hourly or daily period.
} The spectral response of the detector is not in the same range of that of conven.onal pyranometers.
68 GEEN 4830 – ECEN 5007
METHODOLOGY Physical and sta.s.cal models
} The purpose of all models is the es.ma.on of the solar global irradia.on on every pixel of the image.
} The exis.ng models are classified in: physical and sta/s/cal depending of the nature of the approach to evaluate the interac.on between the solar radia.on and the atmosphere.
} Both types of models show similar error ranges.
69 GEEN 4830 – ECEN 5007
METHODOLOGY Physical and sta.s.cal models
STATISTICAL MODELS
} Based on rela.onships (usually sta.s.cal regressions) between pyranometric data and the digital count of the satellite.
} This rela.on is used to calculate the global radia.on from the digital count of the satellite.
} Simple and easy to apply.
} They do not need meteorological measurements.
} The main limita.ons are:
} The needed of surface data.
} The lack of universality.
70 GEEN 4830 – ECEN 5007
METHODOLOGY Physical and sta.s.cal models
PHYSICAL MODELS
} Based on the physics of the atmosphere. They consider:
} The absorp.on and scafer coefficients of the atmospheric components.
} The albedo of the clouds and their absorp.on coefficients.
} The ground albedo.
} Physical models do not need ground data and are universal models.
} Need atmospheric measurements.
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4. DATA BASES AND TOOLS
EUROPE } HELIOCLIM1 and HELIOCLIM.
} h+p://www.helioclim.net/index.html } h+p://www.soda-‐is.com/eng/index.html
} ESRA (European Solar Radia0on Atlas). } h+p://www.helioclim.net/esra/
} PVGIS (Photovoltaic Gis) } h+p://re.jrc.cec.eu.int/pvgis/pv/
} SOLEMI (Solar Energy Mining) } h+p://www.solemi.de/home.html
USA Na0onal Solar Radia0on Database
} h+p://rredc.nrel.gov/solar/old_data/nsrdb/1991-‐2005/tmy3 NASA
} h+p://eosweb.larc.nasa.gov/sse/ WORLD } METEONORM.
} h+p://www.meteotest.ch/en/mn_home?w=ber } WRDC (World Radia0on Data Centre)
} h+p://wrdc-‐mgo.nrel.gov/
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The Na.onal Solar Radia.on Database } Project Par.cipants -‐ Primary project funding came from NREL with support from the following collaborators: } The Atmospheric Sciences Research Center, State University of New York at Albany
} Climate Systems Branch, Na.onal Aeronau.cs and Space Administra.on
} Na.onal Clima.c Data Center, U.S. Department of Commerce } Northeast Regional Climate Center, Cornell University } Solar Consul.ng Services, Colebrook, New Hampshire } Solar Radia.on Monitoring Laboratory, University of Oregon.
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The Na.onal Solar Radia.on Database } Measured Data -‐ About 40 sta.ons in the updated NSRDB include measured solar data, supplied by these agencies: } Atmospheric Radia.on Measurement (ARM) Program, DOE } Florida Solar Energy Center, State of Florida } Integrated Surface Irradiance Study (ISIS) and Surface Radia.on Budget Measurement (SURFRAD) Networks, NOAA/ARL, NOAA/ESRL/Global Monitoring Division
} Measurement and Instrumenta.on Data Center, NREL } University of Oregon Solar Radia.on Monitoring Laboratory Network } University of Texas Solar Energy Laboratory.
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The Na.onal Solar Radia.on Database. TMY3 } The TMY3s are data sets of hourly values of solar radia.on and meteorological elements for a 1-‐year period. Their intended use is for computer simula.ons of solar energy conversion systems and building systems to facilitate performance comparisons of different system types, configura.ons, and loca.ons in the United States and its territories. Because they represent typical rather than extreme condi.ons, they are not suited for designing systems to meet the worst-‐case condi.ons occurring at a loca.on.
} hfp://rredc.nrel.gov/solar/old_data/nsrdb/1991-‐2005/tmy3.
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Statistical characterization of the solar resource
} The statistical characterization of solar radiation requires long series of MEASURED data } Sunshine hours – good availability } Global horizontal (GH) – good availability } Direct Normal (DNI) – poor availability
} The statistical distribution of solar radiation depends on the aggregation periods } Monthly and yearly values of global irradiation have normal
distribution } The distribution of yearly values of DNI is not normal (Weibul?)
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Solar resource assessment for CSP plants 1. Estimate the solar resource from readily available information
1 Surface measurements 1 On site 2 Nearby
2 Satellite estimates 3 Sunshine hours 4 Qualitative information
2. Set up a measurement station 1. Datalogger 2. Pyrheliometer 3. Pyranometer (global and diffuse) 4. Meteo (wind, temperature, RH)
3. Maintain the station (frequent cleaning!)
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Solar resource assessment for CSP plants
5. Perfom quality control of measured data 6. Compare estimates with measurements and assess solar
resource (DNI, Global) } After 1 year of on-site measurements } 1 year is not significant:
} long term estimates should prevail } Analysis must be made by experts
7. Elaborate design year(s) from measured data } Time series -1 year- of hourly or n-minute values
} Typical } Percentiles (P50, P90, P10)
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