TECHNICAL REPORT. Solar Energy - Field Pyranometers - Recommended practice for use

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1 TECHNICAL REPORT Is0 TR 9901 First edition O a Dit document mag slechts op een stand-alone PC worden geinstalleerd. Gebruik op een netwerk is alleen. toestaan als een aanvullende licentieovereenkomst voor netwerkgebruik met NEN is afgesloten. This document may only be used on a stand-alone PC. Use in a network is only permitted when a supplementary license agreement for us in a network with NEN has been concluded. Solar Energy - Field Pyranometers - Recommended practice for use inergie solaire - Pyranometres de champ - Pratique recommandee pour I emploi Reference number lso/tr 990 1: 1990(E)

2 ISO/TR 9901:1990(E) Contents Page 1 Scope......* Normative references * Definitions ~ Pyranometer selection m Selection related to pyranometer type r Selection related to the measuring specifications Recommended practice for use General Pyranometer for measurement of global radiation on a horizontal or tilted plane Pyranometer for diffuse solar radiation Pyranometer for reflected global radiation... 9 Annexes A Commentary on ventilation systems A.1 Need for ventilation ~ A.2 Types of ventilation systems A.3 Specifications for ventilation systems B Estimation of the losses of reflected direct solar radiation due to the shade of the pyranometer itself C Bibliography IS All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from the publisher. International Organization for Standardization Case Postale 56 l CH-1211 Geneve 20 l Switzerland Printed in Switzerland ii

3 ISO/TR 9901:1990(E) Foreword IS0 (the International Organization for Standardization) is a worldwide federation of national standards bodies (IS0 member bodies). The work of preparing International Standards is normally carried out through IS0 technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work, IS0 collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. The main task of technical committees is to prepare International Standards, but in exceptional circumstances a technical committee may propose the publication of a Technical Report of one of the following types: - type 1, when the required support cannot be obtained for the publication of an International Standard, despite repeated efforts; - type 2, when the subject is still under technical development or where for any other reason there is the future but not immediate possibility of an agreement on an International Standard; - type 3, when a technical committee has collected data of a different kind from that which is normally published as an International Sfandard ( state of the art, for example). Technical Reports of types 1 and 2 are subject to review within three years of publication, to decide whether they can be transformed into International Standards. Technical Reports of type 3 do not necessarily have to be reviewed until the data they provide are considered to be no longer valid or useful. ISO/TR 9901, which is a Technical Report of type 2, was prepared by Technical Committee ISO/TC 180, Solar energy. The scope of ISO/TC 18O/SC 1 is the measurement and recording of climatic data in relation to solar energy utilization. This Technical Report on recommended practice for the use of field pyranometers has been prepared as an adjunct to the work of ISO/TC 18O/SC 1 on the calibration and specification of pyranometers. Annexes A, B and C of this Technical Report are for information only.... III

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5 TECHNICAL REPORT ISOlTR 9901 :I 990(E) practice for use 1 Scope This Technical Report gives recommended practice for the use of field pyranometers in solar energy applications (e.g. testing of solar collectors or other devices, and monitoring of solar systems). It is applicable for both indoor and outdoor use of pyranometers, when measuring global and reflected solar radiation, or radiation from a solar simulator. The measurements may be carried out on either a horizontal or an inclined surface, and the pyranometer may be combined with a sun-shading device to measure diffuse radiation. 4 Pyranometer selection 4.1 Selection related to pyranometer type There are several criteria for selection of the pyranometer type as follows: a) task-specific criteria, such as the accuracy requirements for the selected incident angle and temperature ranges and maximal response time; b) operational criteria, such as dimensions, weight, stability and maintenance; 2 Normative references The following standards contain provisions which, through reference in this text, constitute provisions of this Technical Report. At the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this Technical Report are encouraged to investigate the possibility of applying the most recent editions of the standards indicated below. Members of IEC and ISO maintain registers of currently valid International Standards. IS0 9060:19901), Solar energy - Specification and classifka tion of instruments for measuring hemispherical solar and direct solar radiation. IS0 9847:-l, Solar energy - Calibration of field pyranometers by comparison to a reference pyranometer. 3 Definitions For the purposes of this Technical Report, the definitions given in IS apply. c) economic criteria, such as when networks have to be equipped. For solar energy applications, only thermoelectric and photoelectric instruments should be used. Thermoelectric pyranometers are generally more accurate over a wide range of conditions. Solar photovoltaic cells (otherwise known as Siliconpyranometers) also offer a few advantages; they are inexpensive, small in size, have a fast response time and, if properly designed and mounted, a good cosine response. When overall accuracy requirements are not too high, or where constant spectrum conditions exist (as with artificial sources), they may be used to measure the incoming radiation when calibrated under the working conditions. NOTE 1 First class instruments are not necessary for all applications. 4.2 Selection related to the measuring specifications As a first step, all possible ranges of measuring parameters (temperature, irradiance, angle of incidence, tilt angle) should be compiled. It should be remembered that the ranges of measuring parame- 1) To be published.

6 ISO/TR 99Ol:d 990(E) ters met in indoor tests are usually smaller than those met in outdoor tests. Reference should be made to information about measuring and physical specifications of pyranometers given by If the accuracy of secondary standard pyranometers is not sufficient (especially for high incidence angles) it is recommended that the hemispherical solar radiation be measured using both a pyrheliometer and a shaded pyranometer for incident radiation and direct radiation respectively. - the IS0 classification of pyranometers given in IS (which defines the specifications to be met by different categories of instrument), and - the data specification sheet from the manufacturer, or preferably from an independent test institute. (Specification items are listed in IS0 9060:1990, table 1. Annex A gives information on ventilation systems. A future International Standard will cover the characterization of pyranometers.) 5 Recommended practice for use 5.1 General Unless otherwise stated the use of pyranometers is the same both for the sun as the radiation source and for an artificial light source (solar simulator). A basic check list for the use of field pyranometers is given in table 1. Equipment Table 1 - Check list for field pyranometers Object Control Maintenance GI ass dome Local pollution, sand Wipe clear and dry (outside) Frozen snow, rime, frost De-ice and wipe Glass dome (in- Condensation water Remove the outer dome and dry it side) Pyranometer Rubber washer Perishing Sensing surface Black and even Lubricate or replace Report, check the sensitivity and when necessary replace the instrument Desiccator Colour of desiccant Replace Spirit level Horizontal Adjust Operational state Unusual noise, or air current Report, and when necessary replace Ventilator Heating Formation of rime or frost Electrical check or replace Shading Contact device box Air ducts Dirt Clean Shadow Position relative to the dome (morning Adjust and afternoon) Shading ring Paint, dirt Clean and paint when necessary Angle to horizontal Adjust Shading disk Motor Replace Stability of the mount Adjust or replace Contacts Corrosion, humidity and dirt Clean and tighten the box Loose junctions Tighten the junctions or replace As a wide variety of data acquisition and recording systems are used with pyranometers it is diffi- Data acquisition cult to give a check list for this equipment. Reference should be made to the manufacturer s instructions.

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