The document discusses solar resource assessment for solar PV power plants. It describes the importance of solar resource assessment for investment decisions in renewable energy projects. Key factors in solar resource assessment are discussed such as the types of solar irradiation data needed including direct normal irradiation, global horizontal irradiation, and diffuse horizontal irradiation. Methods for obtaining this data are also outlined including ground measurements and satellite-derived data. The characteristics, advantages, and disadvantages of each method are provided. Validation of satellite data with ground measurements is described as important for obtaining accurate solar resource estimates.

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‘Solar Resource Assessment for Solar PV Power Plants’
Presented at: “Capacity Building Programme for SBI Officials”
Er. Abhinav Jain
E&F Division, TERI

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The Importance of Solar Resource Assessment
a) Renewable energy technologies have distinctively different characteristics from more
conventional energy supplies, such as fossil-fuel or nuclear facilities;
b) Furthermore, the energy output is variable according to the variances of the resource,
requiring, in some cases, some form of storage system to stabilize the output to meet load
demand;
c) Investment decisions are based on various considerations, such as the Life Cycle Cost (LCC)
of a system.
LCC Graph

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Characteristics of Solar Irradiation Data
What kind of Irradiation Data is needed ?
a) Type:
I. Direct Normal Irradiation (DNI)
II. Global Horizontal Irradiation (GHI)
III. Diffuse Horizontal Irradiation (DHI)
b) Sources:
I. Ground Measurements;
II. Satellite derived Data.
c) Properties of Irradiation Data:
I. Spatial variability;
II. Inter-annual variability;
III. Long-term drifts.

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Direct Normal Irradiation (S)
It is the irradiance of the sun emitted from the solid angle of the sun’s disc, received by a unit surface held perpendicular to the
solar beam. It includes a small quantity of irradiance that is scattered by the intervening medium along this axis of the cone. The
solar constant is a special case, as it pertains to the value outside the earth’s atmosphere and it is denoted by So. The term “Beam
Solar Radiation” is used to denote the direct solar beam, incident on a horizontal surface.
Diffuse Horizontal Irradiation (Ed)
It is the downward irradiance scattered by the atmospheric constituents and reflected and transmitted by the cloud and incident
on a unit horizontal surface. This irradiance comes from the whole hemisphere of solid angle of 2π with the exception of the solid
angle subtended by the sun’s disc.
Global Horizontal Irradiation (Eg)
This is the irradiance that reaches a horizontal unit surface. It is made up of the direct solar beam irradiance and the scattered
diffuse solar irradiance. Since the direction of the incident solar beam changes continually from sunrise to sunset, the cosine
effect or cosine law comes into play.
Thus the Global Irradiation at a place can be written as:
Eg = S cos θ + Ed (Where ‘θ’ is the angle of incidence)
Characteristics of Solar Irradiation Data (Contd.)

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Ground measurements vs. Satellite derived data
Ground Measurements
Advantages:
a) High accuracy (depending upon the
sensors)
b) High time resolution.
Disadvantages:
a) High costs for installation and O&M;
b) Soiling of the sensors;
c) Sometimes sensor failure;
d) No possibility to gain data of the past.
Satellite Data
Advantages:
a) Spatial resolution;
b) Long term data (more than 20 years)
c) Effectively no failures;
d) No soiling;
e) No ground site necessary;
f) Low costs.
Disadvantages:
a) Lower time resolution;
b) Lower accuracy in particular at high time
resolution.

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How to get bankable Meteo Data ?
Quality checked Ground
Measurements to gain highly
accurate data.
Derivation of Irradiation from
Satellite Data to get:
a) Spatial distribution;
b) Long-term time series.
Validation of Satellite Data with
Ground Measurements.
Result: Accurate hourly time series, Irradiation maps and Long-term annual mean.

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Ground Measurements
REQUIRED INSTRUMENTS (HARDWARE & SOFTWARE)
 Details of the Hardware (s):
 Pyranometer ;
 Pyranometer with Shaded Ring/Balls ;
 Pyrheliometer ;
 Automated Solar Tracker System;
 Data Logger (with Inbuilt memory)
 Dedicated Personal Computer (PC)/Laptop System (with sufficient memory storage)
 Various communication technologies/Networking Interfaces like GPRS/GSM, Serial Port etc. (as per
the requirement)
 Cables & other accessories;
 Continuous Power Supply System (with back-up UPS/Battery bank)
 Details of the Software (s):
 Data Acquisition Software (including QA/QC) for the Data Logger System (including Real-time
Interface)
 Software for generating Reports, Charts, Customized Reports etc.
 Spatial Data Mapping Software like ArcGIS Desktop v10, GE Small-World CST etc.
 Software/Database to store Solar Radiation Data (MS SQL v2010, ORACLE v11G etc.)

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Jan 2010
Global horizontal radiation
Global tilted radiation
Feb 2010
Mar 2010
Global
radiation
(kWh/m2)
Apr 2010
May 2010
Date of the month
Jun 2010
Date of the month
Example of Time Series Solar Radiation Data (NISE Campus)

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Satellite Platforms & Instruments
Primary Instruments:
 The VISSR Atmospheric Sounder (VAS)
 The Advanced Very High Resolution Radiometer (AVHRR)
 The High Resolution Infrared Radiation Sounder (HIRS)
Observational Platforms:
 Equatorial: These satellites generally orbit the
earth in a west-to-east direction, following a
sinusoidal path that crosses the equator at least
twice per orbit. As a result, these satellites do not
pass over every location on earth, and generally do
not pass over the Polar Regions at all;
 Polar: These satellites, also known as Polar Orbiting
Environmental Satellites (POES) orbit the earth
from the north to the South Pole, while the earth
rotates underneath;
 Geostationary: In this configuration, the orbit of
the satellite is such that it is always over the same
point on the earth’s surface, so that it constantly
looks at the same region.

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Validation
(Comparing Ground Measurements & Satellite Data: Time Scales)
 Ground measurements are typically pin point
measurements which are temporally integrated;
 Satellite measurements are instantaneous spatial
averages;
 Hourly values are calculated from temporal and spatial
averaging (cloud movement)

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Validation (Contd.)
Comparing Ground Measurements & Satellite Data: Sensor Size

12. Creating Innovative
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Validation (Contd.)
Comparing Ground Measurements & Satellite Data: Sensor Size
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Ahmedabad
Global tilted ground measured
Global tilted satellite derived
Bhopal
Jodhpur
Global
tilted
radiation
(kWh/m20
Jaipur
Months
New Delhi
Months
General difficulties: Point versus Area
and Time integrated versus Area
integrated.
Global Tilted Time Series Data for NW-India.

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Month
s
Ahmedaba
d
Bhopal Jodhpur Jaipur New Delhi
Jan 4.54 4.3889 4.31 4.25 3.7
Feb 5.44 5.2 5.06 5.01 4.56
Mar 6.35 6.2389 6.04 6.11 5.73
Apr 6.95 7.0389 6.73 7.08 6.69
May 6.99 6.7528 6.97 7.25 6.79
Jun 6.02 5.5333 6.55 6.65 6.26
Jul 4.31 4.0056 5.46 5.13 5.3
Aug 4.31 3.8028 5.42 4.89 4.94
Sep 5.18 5.2028 5.85 5.45 5.25
Oct 5.26 5.325 5.31 5.05 4.67
Nov 4.65 4.7278 4.49 4.28 3.93
Dec 4.23 4.5778 4.12 3.74 3.31
Months
Ahmedaba
d
Bhopal Jodhpur Jaipur New Delhi
Jan 4.801 4.688 4.378 4.229 3.685
Feb 5.585 5.563 5.204 5.053 4.689
Mar 6.374 6.261 6.157 6.056 4.689
Apr 7.018 6.853 7.062 6.889 6.786
May 7.368 7.049 7.517 7.257 7.063
Jun 6.144 5.946 7.063 6.835 6.618
Jul 4.854 4.659 6.234 5.910 5.841
Aug 4.425 4.059 5.621 5.379 5.455
Sep 5.463 5.254 6.011 5.807 5.305
Oct 5.777 5.802 5.696 5.595 5.329
Nov 4.931 4.876 4.732 4.636 4.348
Dec 4.538 4.433 4.183 3.997 3.585
Stations MPE MBE RMSE
Ahmedabad -5.120 0.255 0.301
Bhopal -4.693 0.220 0.326
Jodhpur -5.125 0.294 0.362
Jaipur -4.783 0.229 0.358
New Delhi -4.192 0.189 0.463
Ahmedabad
Bhopal
Jodhpur
Jaipur
New Delhi
-5 -4 -3 -2 -1 0
(a)
MPE
MPE
Stations
* Statistical parameters (MPE, MBE and RMSE) for Global Horizontal Irradiation.
Ground Measurements & Satellite Data of Global Horizontal Irradiation (kWh/m2)
Validation (Results)

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Adjusting Ground & Satellite Data
Simple Method: Scaling with the MPE (Mean Percentage Error)
 E.g. with a MPE of (– 5 %), every value is multiplied with (1.05)
+ Suitable for Average values;
+ Very easy to apply.
- Modification of frequency distribution at the extreme end:
• A factor > 1 may produce unrealistic high values;
• A factor < 1 may omit high values.
Advance Method: Error analysis and correction functions.
 Analysis of the Deviations:
 At clear sky ? (e.g. due to incorrect atmospheric data)
 During cloud situations ? (e.g. incorrect cloud modelling)
Ref. Paper: http://www.geospatialworld.net/Paper/Application/ArticleView.aspx?aid=30355

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NREL India Solar Resource Data-sets
Source: http://www.nrel.gov/international/ra_india.html

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Annual Global Horizontal Irradiation (GHI)

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Annual Direct Normal Irradiation (DNI)

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SRRA Stations

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http://niwe.res.in/department_srra.php
List of SRRA Stations

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India Solar Atlas

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India Solar Atlas (Data Finder)

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Sample Solar Radiation Data-sets

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Solar Radiation Maps of India

24. Contact Us
CORPORATE OFFICE
Darbari Seth Block, IHC Complex, Lodhi Road,
New Delhi - 110 003, INDIA
Tel. (+91 11) 2468 2100 and 41504900
Fax (+91 11) 2468 2144 and 2468 2145
For general inquires contact
mailbox@teri.res.in
Thanks You
Abhinav Jain
Mo- 8882828606
Email- Abhinav.jain@teri.res.in