Appraisal of solar resources

Appraisal of Solar
Resources
LUIS MARTIN POMARES
IrSOLaV

Solar Technology Advisors S.L.
Plaza de Manolete, 2, 11-C
28020 Madrid
Tel. +34 91 383 58 20
February, 2013

SOLAR TECHNOLOGY ADVISORS

Index
• INTRODUCTION
• SOLAR RADIATION CHARACTERISTICS
• CLASSICAL EVALUATION OF SOLAR RADIATION
• INTERACTION OF SOLAR RADIATION WITH THE
ATMOSPHERE
• STUDY OF DIRECT SOLAR RADIATION
• SOLAR RADIATION DATA
• SOLAR RADIATION DATA FROM SATELLITE AND
NWPM
• GENERATION OF TIME SERIES FOR SIMULATION
• SOLAR RADIATION DATABASES ON THE INTERNET


Introduction

 Solar resources evaluation is a necessary first step for
the study of any energy system.
 The objective is the determination of the solar radiation
collected in a specific site, for its use in a specific solar
technology.
 As inputs, it is necessary to have information related to
the source and to the technology.
 The methodologies can be classified as: classical
evaluation (from measurements), and evaluation from
satellite images.


Introduction

To obtain solar radiation data it is possible:
 To measure it: global?, diffuse? Direct normal?
 And / or derive the needed variable (classical evaluation)
 To estimate using satellite images or NWPM (mainly
global).
 And / or derive the needed variable (classical evaluation)

 Once solar radiation data are available, the
generation of a series for simulation it is
possible.
 As a first step of all this subjects, it is necessary
to study the nature of the solar resource.


SOLAR RADIATION
CHARACTERISTICS
Solar energy reaches the earth in a
discontinuous form, showing cycles or
periods:
Daily cycle: accounts for 50% of the total
availability of daily hours.
Another effect of the daily cycle is the modulation
of the received energy throughout the day.
Seasonal cycle: modulation of the received energy
throughout the year.


SOLAR RADIATION
CHARACTERISTICS: Low Density
 The maximum possible amount of solar radiation
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 concentration should be used.
 A limitation to concentration is that this only has any
effect on the direct component of solar radiation.


SOLAR RADIATION CHARACTERISTICS:
Geographic variation

 In clear sky conditions: the solar radiation
depends mainly on the latitude.
 Latitude effect is equivalent to the modification of
the angle of incidence of solar radiation.
 For the modulation of the received energy the
following can be used:
 Solar tracker
 Plane inclination
 The inclination of the reception plane means:
 Modification of the latitude effect
 Modification of the annual distribution.


SOLAR RADIATION CHARACTERISTICS:
Random situations
 Solar radiation on the earth´s surface is modulated by climatic
conditions.
 Clear sky conditions are not common.
 The latitude indicates a maximum range, but the energy
received is determined by local climatic conditions.


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 incoming solar radiation to the earth
is inversely proportional to the sun´s square distance.
 The distance is measured in astronomical units (AU)
equivalent to the mean earth-sun distance.


Solar constant and solar geometry
 Is the amount of solar energy incident in 1m2 of
surface perpendicularly exposed to the solar rays and
placed at 1 AU of distance.
 Changes slightly with time, but can be considered as
constant.
 Ion = 1367 W/m2.(WRC).
 The solar radiation has participation in
several electromagnetic spectral ranges.
Solar geometry is well known

We can estimate with high accuracy the solar irradiation at the
top of the atmosphere at every moment and every place


SUN-EARTH RELATIONSHIPS:
Sun declination
 Considering the ecliptic plane (ECLP) as the plane of
earth´s revolution around the Sun and the equatorial
plane (EQUP) as the plane containing the equator:
 Polar axis is tilted 23.5º with respect to the
perpendicular of the ECLP.
 ECLP and EQUP cross in the
equinoxes and the distance is
maximum in the solstices.
 The angle in a specific moment
between both planes is called
DECLINATION


SUN-EARTH RELATIONSHIPS: Relative
position sun-horizontal surface
These are trigonometric relationships between the sun´s position in
the sky and specific coordinates on the earth surface

In a specific moment the following must
SOL
ZENITH
be considered:

• zenith (θ ) angle and solar
TRAYECTORIA SOLAR

(+) MAÑANA W
(-) ESTE
θz
z elevation (α)
• azimuth (ψ) = angle between the
-ψ ψ α observer meridian and the solar meridian
S
0
N
• hourly angle (ω) = angle between the
+ψ sun position and the south meridian
PROYECCION DE LA
TRAYECTORIA SOLAR
15º=1hour; +E /-W.
E • Sunrise angle (ωs) = sunset angle
(horizon)


Hourly radiation over horizontal
surface

 One specific day: the extraterrestrial
radiation over a perpendicular surface
to the Sun´s rays is expressed as:

 Placing this surface over the earth, it
is necessary to take into account the
cosine of the incident angle:


surface

 The main phenomena that take place when the solar
radiation through the atmosphere are:
Absorption by the atmospheric components.
Diffusion or scattering.


Interaction of solar radiation with
the atmosphere
Radiation at the top of atmosphere

Absorption (ca. 1%)
Ozone.……….…....

Rayleigh scattering and absorption (ca. 15%)
Air molecules..……

Scatter and Absorption (ca. 15%, max. 100%)
Aerosol…….………..…...……

Clouds………….……….. Reflection, Scatter, Absorption (max. 100%)

Water Vapor…….……...……… Absorption (ca. 15%)

Direct normal irradiance at ground


surface

 The main phenomena that take place when the solar
radiation through the atmosphere are:
Absorption by the atmospheric components.
Diffusion or scattering.

 As a consequence, the solar radiation has modified its
nature, and mainly its directional component:

G = I cos θ + D + R


Solar radiation components

RADIATION REFLECTED BY CLOUDS

GROUND ALBEDO

ABSORPTION

SCATTERING

DIRECT NORMAL RADIATION

DIFUSE RADIATION


Phenomena through the atmosphere


SOLAR RADIATION ON THE EARTH SURF
Direct solar radiation
 Is the radiation coming directly from the Sun disk.
 Have a vector character and can be concentrated.
 Can be 90% of the solar radiation on clear sky
days, and can be null in cloud covered days.
 As a directional component, the contribution on a
surface is the perpendicular projection over this
surface: beam radiation is the radiation perpendicular
to the sun's rays, then:
Ih = I cos θ
 With solar trackers it can be maximised.
I ≅ DNI


Diffuse solar radiation
 A part of the solar radiation that is lost when it is
absorbed by the atmospheric components. Another
part is reflected by these components producing
direction changes and energy reduction.
 Diffuse radiation = the part of this radiation that
reaches the earth's surface.
 Diffuse radiation has three components:
Circumsolar
Horizon band
Blue sky


Reflected solar radiation
 Is the radiation coming from the reflection of the
solar radiation on the ground or on other nearby
surfaces.
 Usually is small, but can be around 40% of the solar
radiation.


Ley of Beer
In  I0  e(  k L )  I0  e(   m )  I0  T

In   In d    I0  e(  k L ) d   ISC e  m

Clear sky models or transmitance models
Bn  I CS  (TRToTgTwTa  0.013) Yang

Bn  ICS  exp[0.8662 TLAM 2 mp  R ]
C
ESRA


The concept of optical mass

Aproximation to plane-
parallel
1
m
cos

Karsten equation

m  (sin  0.15(  3.885)1.253 )1


Air mass: variability

35

30

25
Masa relativa de aire

20

15

10

5

0
4 6 8 10 12 14 16 18 20


Sensibility of ESRA model to TL

Influence of TLINKE and altitude above sea level on DNI for clear sky

Dia juliano=200, z=500, Lat=37º N Long=-2º E TL=4, dia juliano=200, Lat=37º N Long=-2º E
1200 1000
TL=2 z=0 m
TL=4 900 z=500 m
1000 TL=6 z=1000 m
800

700
800
DNI (Wh m-2)

600

DNI (Wh m-2)
600 500

400
400
300

200
200
100

0 0
0 2 4 6 8 10 12 14 16 18 20 22 24 0 5 10 15 20 25
Hora Hora


Components and non-dimensioanl
indexes
Components of solar radiation in horizontal surface

IG  IB cos  ID
Clear sky or transparency index
IG
kt 
I0
Difuse radiation fraction
ID
kd 
IG
Beam radiation transmitance
IB
kb 
I0


Estimation of beam solar radaition

Correlations to estimate difuse radiation fraction

G (1  kd )
Ib  1.0  0.09kt kt  0.22 

sen( )
 
kd  0.9511  1.1604kt  4.388kt 2  16.638kt 3  12.336kt 4 0.22  kt  0.8 
0.165 k  0.8 
 t 

Correlations to estimate beam transmitance

I b  kb I o kb  0.002  0.059kt  0.994kt 2  5.205kt 3  15.307kt 4  10.627kt 5


Phenomena through the atmosphere
 Spectral distribution of solar
radiation for a s standard atmosphere
-- an "average" atmosphere with
specified characteristics -- compared
to the extraterrestrial radiation at the
average Earth/sun distance.
 Direct normal radiation
 Diffuse radiation
The relationship between direct and
diffuse radiation depends on the
position of the sun in the sky. The sun
in Figure is at an elevation angle of
about 42º, giving a relative air mass
of about 1.5. (If the sun is directly
overhead, the relative air mass is 1,
by definition.)


SOLAR RADIATION DATA
 Due to the climatic factors that modify the solar radiation received on
the earth´s surface, it is impossible to know beforehand the energy
that will be received by the system.
 Then it is necessary to use data of solar radiation of the past years.
 In the evaluation of solar radiation on a specific site, can assume two
cases:
 In the evaluation of solar radiation on a specific site, can assume two
cases:
 Estimation of the solar radiation (global or its components), in sites
with any information related to solar radiation:
 FROM MEASUREMENTS
(AND/ OR USING CLASSICAL EVALUATION MODELS)
 The estimation of the solar radiation and its components, in sites
without any previous information.
 EVALUATION FROM SATELLITE IMAGES
 EVALUATION FROM NWPM
(AND/ OR USING CLASSICAL EVALUATION MODELS)


MEASUREMENTS OF SOLAR RADIATION
 UNCERTAINTY OF ONE INSTRUMENT Distribution of the observations.
If there are n comparisons of an operational instrument holding
constant the measured variable and all other relevant parameters, and
establishing a true value using a reference standard, the results can be
represented as in Fig.

 The accuracy with which a meteorological variable should be measured
changes with the specific purpose which it is intended that
measure. For most operational and research purposes, the
determination of required accuracy aims to ensure compatibility of
data, both in space and time. In cases where it is difficult to ascertain
the absolute accuracy, it is usually enough to take measures to ensure
that the data are sufficiently compatible for users.


MEASUREMENTS OF SOLAR RADIATION
 SOLAR RADIATION


Measuring Solar Radiation:
Pyrheliometers Direct Normal Radiation
EKO MS-54

 Measures direct beam irradiance
 Typically used for calibration transfers
 Normally defined with an opening angle of 5 Middleton DN5
 If used in conjunction with pyranometers, the
optical flat protecting entrance should match the
optical material of the pyranometer domes
 Relatively easy to characterize
 4 major manufacturers:
• EKO Instruments (Japan)
• Eppley Instruments (USA)
• Kipp & Zonen (Netherlands)
• Middleton Solar [Carter Scott Design] (Australia)
 Normally mounted on passive or active solar
tracking systems


Measuring Solar Radiation: Pyranometers
Global Horizontal Radiation

Tilted Irradiance

 Most pyranometers use a thermopile as means of converting solar
irradiance into an electrical signal.
 Silicon cell pyranometers are also available, but are not recommended b
WMO.
 Advantage of the thermopile is that it is spectrally neutral across the
entire solar spectrum (domes may have spectral dependencies).
 Disadvantage is that the output is temperature dependent and the
instruments must ‘create’ a cold junction.


Measuring Solar Radiation: Silicon
Pyranometers
 Instrument’s spectral response is non-linear and does not match solar
spectrum.
 General calibrations are through comparison with pyranometers, therefore
there are spectral mismatch problems.
 LiCor is the primary instrument manufacturer and recognizes these
problems:
 “The spectral response of the LI-200 does not include the entire solar
spectrum, so it must be used in the same lighting conditions as those under
which it was calibrated.”
–Pyranometer sensors are calibrated
against an Eppley Precision Spectral
Pyranometer (PSP) under natural daylight
conditions. Typical error under these
conditions is ±5%. (LiCor)

–Similar problems arise when using
sensors calibrated in one climate regime
and used in a different regime.


Rotating Shadowband Radiometer RSR2
 LI-COR Terrestrial Radiation Sensors
 Irradiance Inc. (www.irradiance.com)
 LI-200 Pyranometer is a silicon photodiode
calibrated from LI-COR ±5%
 RSR2 Head unit includes a moving
shadowband that momentarily casts a
shadow over a LI-200 pyranometer
 Motor controller contains circuit to control
the exact movement of shadowband LI-200 Pyranometer
 Correction provided by Algorithm
 Measurement:
 Global Horizontal Irradiance
 Diffuse Horizontal Irradiance
 Calculation:
 Direct Normal Irradiance
RSR2 Headunit RSR2 Motor Controller


Espectral measurements


Solar trackers


Data logger

 For continuous recording automatic data logger are required.
 The main requirement in terms of exposure must be the lack of
obstructions to the solar beam at all times and seasons.
Furthermore, the exact location of the instrument must be chosen so
that the incidence of fog, smoke and air pollution is as representative
as possible of the surrounding geographic area.


Measuring Solar Radiation:
Typical BSRN-like stations


Measurement recomendations

 Know exactly what temporal reference of the
masurements you are using (TSV, GMT, Local etc)

 Register with enough temporal resolution, almost 10
minutes to register the dinamic of cloud transients.

 Follow BSRN recomendation for maintenance of
instruments. Cleaning every day radiometers, calibrate
once per year each instrument,…

 Secure the relation G=B cos θ + D. Some solar trackers
have embeded this filter in its program to activetes
realtime alarms when measurement is worng.


SOLAR RADIATION DATA FROM SATELLITE AND
NWP MODELS

 FROM SATELLITE
 The satellite
 Methodology
 Example of models application

 FROM NWP MODELS
 General overview
 Main models
 Main characteristics


Meteorological Satellite population


Satellite classification
According to the type of orbit :
Polar satellites: placed in polar
orbits, modifying its
perspective and distance to the
earth. The resolutions of these
satellites are around 1m to
1km.
Geostationary satellites: placed in the geostationary orbit that is, the place
in the space where the earth's attraction force is null. It is an unique
circumference where all the geostationary satellites are situated in order
to cover the whole earth's surface. The resolutions of these satellites are
higher in the sub satellite point on the equator, and go decreasing in all
directions.


Meteorological satellites

 In meteorology studies frequents observations and with
high density on the earth’s surface are required.
Conventional systems do not provide a global cover.
 An important tool to analyse the distribution of the
climatic system are the METEOROLOGICAL SATELITES.
These can be:
 Polar satellites.
 Geoestationary: In EUROPE and part of ASIA, the
system of geosttationary meteorolgical satellites
is called METEOSAT.


Meteosat Satellite coverage

Meteosat Prime Meteosat East
 Spatial resolution 2.5 km at sub satellite, eg. About 3x4 km in Europe
 Temporal resolution 1h.
 Current Coverage: Meteosat Prime up to 1991-2005,
Meteosat East 1999 - 2006


SOLAR RADIATION DATA FROM SATELLITE:
ADVANTAGES

 The geostationary satellites shows
simultaneously big land areas.
 The information of these satellites is always
referred to the same window and can be put on
top.
 There are the possibility to know previous
situations using satellite images of previous
years.
 The utilization of the same detector to evaluate
the radiation in different places.

Solar radiation derived from
satellite images
Satellite to irradiance: general procedure
• Meteosat – Goes - Mtsat
• 60’, 30’ or 15’ images in the visible
position assessment geometric
corrections – pixels averaging
model to obtain global irradiance


Summary of the methodology
METHODOLOGY OF THE STATISTICAL MODELS:
• Cloud cover index determination.
• Hourly clearness index determination (hourly global radiation).
• Daily clearness index determination (daily global radiation).
BASED ON RELATIONSHIPS BETWEEN:
• The measurement of the solar radiation.
• The value of the digital count form the satellite image (corresponding
to the measures locations)


Clearness index=Global radiation
 The geostationary satellites shows simultaneously big
land areas.
 A relationship is evaluated using the ground data
simultaneous to the satellite images. This relationship is
applied to the whole image.
 As meaningful variables:
 Cloud cover index.
 Declination


AOD (Aerosol Optical Depth
estimations)
Estimations from MODIS (Moderate Resolution
Imaging spectroradiometer) on NASA’s Terra satellite
http://earthobservatory.nasa.gov/
AOD and water vapor vertical content estimations from satellite


SOLAR RADIATION DATA FROM NWP MODELS

 Executed based on the initial conditions from which
differential equations describing the evolution of the
atmosphere are solved.


SOLAR RADIATION DATA FROM NWP MODELS


Index
• INTRODUCTION
ATMOSPHERE
NWPM
• GENERATION OF TIME SERIES FOR
SIMULATION
• SOLAR RADIATION DATABASES ON THE INTERNET


Generation of series for simulation

 Typical Meteorological Year (TMY) is a methodology for such a
purpose that has evolved along the time.
 The starting point was the method developed in Sandia National
lab that partially used the database SOLMET/ERSATZ (1951-1976)
[5] formed by 248 stations, from which 26 had available
measurements of solar radiation components for the EEUU.
 The method consisted in the concatenation of typical months to
generate a year with 8760 values of the considered variables:
average, maximum and minimum temperature and dew
temperature, wind velocity and global solar irradiance.
 Filkenstein-Schafer statistic was used to select typical months.
Several improvements and variations to the initial TMY
methodology have been suggested along the time yielding to
newer versions like TMY2 y TMY3.



 Nevertheless, the essence of the method remains practically
unchanged. However, TMY methodology was developed to create
typical meteorological years and not typical solar years, which
have, despite the similarity, a different meaning in the framework
of the CPS industry.
 Since 2010 a selected group of Spanish institutions and companies
closely related to the CSP industry have been working within the
AENOR framework (Spanish Association for Standardization and
Certification) on standards for the industry.
 Part of this work consists of the development of a methodology for
generating a year of solar irradiance data and other influencing
variables to be used by the CSP industry.



 Due to the wide range of different data that can be used for
generating the ASR six types of data have been established:
 direct measured data
 indirect measured data
 derived data
 synthetic data
 satellite data and
 data from numerical model (NWP model).
 This distinction implies different request to the quality, usage and
treatment of the data according to its different nature.
 Therefore, the procedure allows the generation of the ASR by
combining these kinds of data whenever the boundary conditions
of quality and representativeness are fulfilled


Index
• INTRODUCTION
ATMOSPHERE
NWPM
• GENERATION OF TIME SERIES FOR SIMULATION
• SOLAR RADIATION DATABASES ON THE
INTERNET


Radiometric Databases
 Baseline Surface Radiation Network (BSRN)


Radiometric Databases
 Baseline Surface Radiation Network (BSRN)
 World radiation data centre (WRDC)
 Meteonorm

SSE
Radiometric Databases: SSE from NASA
http://eosweb.larc.nasa.gov/sse/
 Surface
Meteorology and
 Solar Energy
(SSE) Datasets
 And Web
interface

 Monthly data
 Free upon
Growing over the last 7 years to nearly 14,000
registration
users, nearly 6.4 million hits and 1.25 million  1ºx1º (120x120
data downloads
km) resolution


Solar radiation derived from satellite images
SWERA Project

The SWERA project provides easy access to high quality renewable energy resource
information and data to users all around the world. Its goal is to help facilitate renewable
energy policy and investment by making high quality information freely available to key user
groups. SWERA products include Geographic Information Systems (GIS) and time series data


Comercial data from satellite

• Irsolav
• Solemi (DLR)
• 3Tier
• Solargis
• ….


Some measurements in India


IrSOLaV activities
 Ciemat promoted a spin-off company for solar resource
characterization services (www.irsolav.com). Thus IrSOLaV
interacts with the industry needs and supply data and
consulting services on solar resource and also collaborates
with Ciemat in R&D.
 IrSOLaV and Ciemat develops R&D programs in the solar
resource field and collaborates with international scientific
groups (DLR, NREL, NASA, JRC, CENER, Universities…)
through European projects (COST project) or other
initiatives (Task 46 SHC/IEA)
 Within Spain IrSOLaV and CIEMAT collaborates with
universities (UAL, UJA, UPN) and support the industry
through agreements for doing specific research on solar
resource knowledge (forecasting, model
improvements, atmospheric physics, etc)

Appraisal of solar resources

Empfohlen

Empfohlen

Weitere ähnliche Inhalte

Was ist angesagt?

Was ist angesagt? (20)

Ähnlich wie Appraisal of solar resources

Ähnlich wie Appraisal of solar resources (20)

Mehr von IrSOLaV Pomares

Mehr von IrSOLaV Pomares (20)

Appraisal of solar resources