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NOTICE

This report was prepared as an account of work sponsored by the United States Government. Neither the United States nor the United States Department of Energy, nor any of their employees, nor any of their contractors, subcontractors, or their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness or usefulness of any information, apparatus, product or process disclosed, or represents that its use would not infringe privately owned rights.

SERI/TR-642-761 UC CATEGORIES: UC-59,61,62,63

A SIMPLIFIED CLEAR SKY MODEL FOR DIRECT AND DIFFUSE INSOLATION ON HORIZONTAL SURFACES

RICHARD E, BIRD ROLAND L. HULSTROM

FEBRUARY 1981

PREPARED UNDER TASK No. 1093.00

Solar Energy Research Institute

A Division of Midwest Research Institute

1617 Cole Boulevard Golden, Colorado 80401 Prepared for the U.S. Department of Energy Contract No. EG-77-C-01-4042

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TR-761

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PREFACE

The work documented here was performed by the SERI Renewable Resource Assessment Branch for the U.S. Department of Energy under Task No. 1093.00. The report compares several simple global horizontal insolation models with several rigorous radiative transfer models and describes an improved, simple, global insolation model. We would like to thank J. V. Dave of IBM for providing data sets from his Spherical Harmonics code.

Richard E. Bird Senior Scientist

Approved for SOLAR ENERGY RESEARCH INSTITUTE Roland L. Hulstrom, Chief Renewable Resource Assessment Branch

iii

TABLE OF CONTENTS

1.0 Introduction????????????????????????????????????????????????????????? 1

2.0 Description of Models ??????????????????????????????

3

2.1 Atwater and Ball Model?????????????????????????????????????????? 3

2.2 Davies and lia.y Model. ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? 4

2.3 Watt Model ???????????????????????????????????????. ~?????????????? 5

2. 4 Hoyt Model. ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? 6

2.5 2. 6

LBaircdisMandoHdaensle.n..M ...o.d.e..1.3.?..?.?.?.?.?.?.?.?.?.?.?.?.?.?.?.?.?.?.?.?.?.?.?.?.?.?.?.?.?.?.?.?.?.?.?.?.?.?..?.?

7 7

2.7 Rigorous Codes. ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? 10

3.0 Model Comparisons ???????????????????????????

13

3.1 Transmittance Comparisons ??????????????????????????????????????? 13 3.2 Irradiance Co11Iparisons ??--. ?????????????????????????????????????? ~ 15

4.0 Summary and Conclusions ?????????????????????????????????????????????? 27

s.o References ??????????????????????????????????????????????????????????? 29

Appendix A: Tabulated Model Data????????????????????????????????????????? 31

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