appraisal of solar resources

Appraisal of Solar Resources

LUIS MARTIN POMARESIrSOLaV

Solar Technology Advisors S.L.Plaza de Manolete, 2, 11-C28020 MadridTel. +34 91 383 58 20

February, 2013

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

SOLAR TECHNOLOGY ADVISORS

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.


Index




INTERNET


SOLAR RADIATION CHARACTERISTICSSolar 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.


Index

• INTRODUCTION• SOLAR RADIATION CHARACTERISTICS• CLASSICAL EVALUATION OF SOLAR

RADIATION• INTERACTION OF SOLAR RADIATION WITH THE



INTERNET


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

SOL

ZENITH

TRAYECTORIA SOLAR

(+) MAÑANA

(-) ESTE

TRAYECTORIA SOLARPROYECCION DE LA

W

E

0NS

zθz

αψ-ψ

+ψ

In a specific moment the following mustbe considered:

• zenith (θ ) angle and solar elevation (α) • azimuth (ψ) = angle between the observer meridian and the solar meridian• hourly angle (ω) = angle between thesun position and the south meridian

15º=1hour; +E /-W.• 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:

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


INTERNET




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


Rayleigh scattering and absorption (ca. 15%)

Absorption (ca. 1%)

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

Reflection, Scatter, Absorption (max. 100%)

Absorption (ca. 15%)

Ozone.……….…....

Aerosol…….………..…...……

Water Vapor…….……...………

Clouds………….………..

Air molecules..……

Direct normal irradiance at ground

Radiation at the top of atmosphere



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

DIFUSE RADIATION

DIRECT NORMAL RADIATION

SCATTERING

ABSORPTION

GROUND ALBEDO


http://badc.nerc.ac.uk/data/meteosat/meteosat.jpg

Phenomena through the atmosphere


Index




INTERNET


SOLAR RADIATION ON THE EARTH SURFDirect 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


SOLAR RADIATION ON THE EARTH SURFDiffuse 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


SOLAR RADIATION ON THE EARTH SURFReflected 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

( ) ( )0 0 0

( )0

e e

e

k L mn

k L mn n SC

I I I I T

I I d I d I e

( 0.013)n CS R o g w aB I T T T T T

Clear sky models or transmitance models

Yang

2exp[ 0.8662 ]C AMn CS L p RB I T m ESRA


The concept of optical mass

1

cosm

Aproximation to plane-

parallel

1.253 1(sin 0.15( 3.885) )m

Karsten equation


Air mass: variability

4 6 8 10 12 14 16 18 200

5

10

15

20

25

30

35

Hora decimal

Mas

a re

lativ

a de

aire


Sensibility of ESRA model to TL

0 2 4 6 8 10 12 14 16 18 20 22 240

200

400

600

800

1000

1200

Hora

DN

I (W

h m

-2)

Dia juliano=200, z=500, Lat=37º N Long=-2º E

TL=2

TL=4TL=6

0 5 10 15 20 250

100

200

300

400

500

600

700

800

900

1000

Hora

DN

I (W

h m

-2)

TL=4, dia juliano=200, Lat=37º N Long=-2º E

z=0 m

z=500 mz=1000 m

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


Components and non-dimensioanl indexes

Components of solar radiation in horizontal surface

cosG B DI I I

Clear sky or transparency index

Difuse radiation fraction

Beam radiation transmitance

0

Gt

Ik

I

Dd

G

Ik

I

0

Bb

Ik

I


Estimation of beam solar radaition

2 3 4

1.0 0.09 0.22

0.9511 1.1604 4.388 16.638 12.336 0.22 0.8

0.165 0.8

t t

d t t t t t

t

k k

k k k k k k

k

Correlations to estimate beam transmitance

(1 )

( )d

b

G kI

sen

b b oI k I

Correlations to estimate difuse radiation fraction

2 3 4 50.002 0.059 0.994 5.205 15.307 10.627b t t t t tk k k k k k


SOLAR RADIATION ON THE EARTH SURFPhenomena 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.)


Index




INTERNET


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

Measures direct beam irradiance Typically used for calibration transfers Normally defined with an opening angle of 5 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

EKO MS-54

Middleton DN5


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 by 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

Correction provided by Algorithm Measurement:

Global Horizontal Irradiance Diffuse Horizontal Irradiance

Calculation: Direct Normal Irradiance

LI-200 Pyranometer

RSR2 Headunit RSR2 Motor Controller


http://www.irradiance.com/

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.


Index


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


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

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

Meteosat Prime Meteosat East


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 satellitehttp://earthobservatory.nasa.gov/AOD and water vapor vertical content estimations from satellite


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


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



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




INTERNET


Radiometric Databases


Baseline Surface Radiation Network (BSRN)

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


Radiometric Databases: SSE from NASA

Surface Meteorology and

Solar Energy (SSE) Datasets

And Web interface

Growing over the last 7 years to nearly 14,000 users, nearly 6.4 million hits and 1.25 million data downloads

SSE

Monthly data Free upon

registration 1ºx1º (120x120

km) resolution

http://eosweb.larc.nasa.gov/sse/

Solar radiation derived from satellite imagesSWERA 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)


http://www.irsolav.com/

THANKS FOR YOUR ATTENTION !

appraisal of solar resources

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