THE NEGEV SOLAR RADIATION SURVEY - TMY V.3
Total Page:16
File Type:pdf, Size:1020Kb
STATE OF ISRAEL Ministry of National Infrastructures Research and Development Division DATA PROCESSING FOR THE NEGEV RADIATION SURVEY: SEVENTH YEAR Annual report on the eighth year of research Part 3 - Typical Meteorological Year v. 3.0 Prof. D. Faiman, Dr. D. Feuermann, Dr. P. Ibbetson, and Prof. A. Zemel DEPARTMENT OF SOLAR ENERGY AND ENVIRONMENTAL PHYSICS THE JACOB BLAUSTEIN INSTITUTE FOR DESERT RESEARCH BEN-GURION UNIVERSITY OF THE NEGEV SEDE BOQER CAMPUS, 84990 ISRAEL Dr. A. Ianetz, Dr. V. Liubansky and Dr. I. Seter RESEARCH, DEVELOPMENT AND ENGINEERING BRANCH THE METEOROLOGICAL SERVICE BET DAGAN, 50250 ISRAEL Research funded under contract No. 2000-1-101/2000-11-007 DECEMBER 2001 RD-13-01 1 TABLE OF CONTENTS CHAPTER (English Language Text) Pages 1 Introduction 2 2 TMY Construction 3 3 The Data Format 3 4 Some comparative observations 4 5 Conclusions 5 6 Bibliography 6 TABLES 1 Arad Monthly direct beam averages 8 2 Beersheba Monthly direct beam averages 8 3 Besor Farm Monthly direct beam averages 8 4 Eilat Monthly direct beam averages 9 5 Hazeva Monthly direct beam averages 9 6 Sede Boqer Monthly direct beam averages 9 7 Sedom Monthly direct beam averages 10 8 Yotvata Monthly direct beam averages 10 9 Format for TMY v.3 and annual data files 10 10 Relative ranking of Negev Radiation Survey stations (beam) 11 11 Sede Boqer monthly global horizontal averages 11 12 Relative ranking of Negev Radiation Survey stations (global) 11 FIGURES 1 Stations of the Negev radiation survey 12 2a Monthly mean daily direct beam radiation averages 13 2b Monthly TMY daily direct beam radiation averages 13 3 Monthly TMY daily global horizontal radiation averages 14 Publication Documentation Page 15 TABLES (see File 3, of this TMY v.3 series) Arad TMY tables 16-17 Beersheba TMY tables 18-19 Besor Farm TMY tables 20-21 Eilat TMY tables 22-23 Hatzeva TMY tables 24-25 Sede Boqer TMY tables 26-27 Sedom TMY tables 28-29 Yotvata TMY tables 30-31 2 THE NEGEV SOLAR RADIATION SURVEY - TMY v.3 David Faiman, Daniel Feuermann, Peter Ibbetson and Amos Zemel The Center for Energy and Environmental Physics The Jacob Blaustein Institute for Desert Research Ben-Gurion University of the Negev Sede Boqer Campus, 84990 Israel and Amiran Ianetz, Vera Liubansky and Ilan Seter Research Development and Engineering Branch The Meteorological Service P.O. Box 25, Bet Dagan, 50250 Israel 1. INTRODUCTION A Typical Meteorological Year (TMY) consists of twelve monthly files of actual hourly meteorological data selected in a particular manner [1]. The months will not, in general, have come from the same year. Instead, each will have been chosen as being a “typical” representative of the month in question and, ideally, the choice for each will have been made from very many years of accumulated data. The reason for taking actual months of data rather than averaged files is that the former preserve correlations (both known and unknown) that exist among the different measured parameters (e.g. solar radiation and ambient temperature) and also correlations that exist over a period of several days among values of any given parameter. These correlations are often of great importance when one tries to simulate the performance of an energy conversion system that has characteristic time-scales of several days (e.g. passive solar buildings [2], swimming pools [3], etc.). The term “typical” is somewhat subjective in that its choice depends, to a large extent, on how the data are to be used. For agricultural purposes it might, for example, be sensible to select typical months on the basis of rainfall and ambient temperature. The present study, however, is part of the Negev Radiation Survey, the aims of which are to provide data of relevance to the performance of solar power stations. Clearly, therefore, the relevant criterion for this purpose is solar energy. There are in fact two solar radiation components that are measured: the global horizontal radiation and the normal direct beam component. For any given Negev site the former is found to vary by approximately ± 5 % from year to year. On the other hand, year to year variations of more than 30 % have been observed in the direct beam component, over the comparatively few years that this study has been in progress. Since, moreover, solar power plants will have to be designed in a manner that will enable them to meet contractual obligations - irrespective of weather fluctuations - it is the direct beam component of the solar radiation that is the critical parameter on which the term “typical” must be based. We expect, therefore, that simulation of a solar power station using one of these TMY files will provide quantitative information about how the system should behave in a typical year. It 3 will not, however, provide any indication as to how the system would behave in an “unusually poor” (from the standpoint of weather) or an “unusually good” year. This information can only come from using data from such years. Again, in an ideal situation where a great many years of data exist, one could construct “unusually poor” and “unusually good” meteorological years in order to meet the needs of such system simulations but this is not yet the situation in which the Negev Radiation Survey finds itself. Fig.1 shows the locations of the meteorological stations involved in the Negev Radiation Survey. At the present stage, the Survey contains up to eleven years of data from the eight stations, Arad, Beersheba, Besor Farm, Eilat, Hatzeva, Sede Boqer, Sedom and Yotvata. One of the original stations (Sapir Center) had to be abandoned owing to a lack of available personnel to maintain the instrumentation and this station was subsequently replaced by the one at Hatzeva. An additional station, Mitzpe Ramon,started up in 1998, but there are not yet enough data for a TMY. 2. TMY CONSTRUCTION As already indicated, our TMY files have been chosen for typicality of the direct beam component of the solar radiation. For sites at which we have an odd number of years of data we “tried to choose” the year whose monthly direct beam average rendered it the median year of the available set. On the other hand, where an even number of years of data were available we “tried to choose” the year whose monthly mean was closest to the average taken over all of the years in the set. The words “tried to choose” have been used because sometimes this was not possible owing to large amounts of missing data in the desired file. In such cases a “second best” choice was made. Regarding missing data, even relatively complete files occasionally have a few hours, or days, when one or more instruments were not working properly. In such cases our practice was to replace the entire day of partially corrupt or missing data by a similar, but complete, day of data taken from a different year. In this way, although the day-to-day correlation information is lost, real data are always used. Tables 1-8 display the monthly average values of direct beam radiation recorded by each of the stations during the eleven-year period 1989-1999. Values in bold characters indicate the specific months that were ultimately chosen for each site as the basis for TMY v.3. 3. THE DATA FORMAT The raw data provided by the Israel Meteorological Service include hourly average values of: direct beam radiation; global horizontal radiation; shadow-band pyranometer data; dry-bulb temperature; relative humidity (or alternatively, from some stations, the wet-bulb temperature); wind speed and wind direction. Of the solar radiation data only direct beam and global horizontal are archived, the shadow-band data having been used for consistency checks only. Humidity data have been processed using algorithms given in the ASHRAE chapter on psychrometrics [4] in order to compute the humidity ratio. The present report is accompanied by a CD-ROM which contains, in addition to the TMY v.3 files for each of the 8 stations in the Negev Radiation Survey, a complete set of all of the historic data files from which the TMYs have been constructed. The latter, although using an identical format to the TMYs, differ in that they frequently contain gaps in the measured data. 4 These are indicated by the entries “-999” (or “-9” in the case of wind data). Thus, any algorithm which has been designed to access the TMY files will also be able to access the files corresponding to individual years provided the appropriate caution lines have been inserted to prevent the program from misinterpreting missing data as negative input numbers. The present study employs a format which the University of Wisconsin originally established for the US SOLMET TMY diskettes so that the latter could interface with their TRNSYS simulation program. One diskette was used for each site. For each of the 12 monthly data files, the format allocates successive columns to: month, hour, direct beam, global horizontal, ambient temperature, humidity ratio, wind speed, wind direction, with units as shown in Table 9. Time is specified in Israel Standard Time (i.e. without daylight saving) for Time Zone UT+2 hr. Time bins are hourly integrals specified at the end of the hour (e.g. Hour #1 indicates integrals from midnight till 1 am). As a historical note we point out that our own TMY v.1 was not widely distributed owing to the relatively small number of data years upon which it was based [5]. The subsequent TMY v.2 contained some v.2.0 files (Beersheba, Eilat, Hatzeva, Sedom) and some v.2.1 files (Arad, Besor Farm, Sede Boqer, Yotvata).