MEASUREMENTS OF GLOBAL SOLARRADIATION IN NIGERIA

Foreword

Nigeria lies in the tropics and therefore receives a great amount of solar energy which could bejudiciously harnessed for various applications. However, there appears to be no record of direct andextensive measurement of solar radiation in Nigeria to facilitate and encourage the rational use of thisenergy.

To correct this situation, the Nigerian Building and Road Research Institute established thirtysolar energy measurement stations spread over the country. The global solar radiation data thusobtained by direct measurement on horizontal surfaces are presented in readily useable tabular formin this report. The data presented in this report are the first known comprehensive direct measurement records of solar radiation in Nigeria.

This report will be an invaluable aid to architects, building scientists, engineers and solar energytechnologists in the design of energy efficient buildings, development of efficient solar devices andapplications of solar energy in the field of agriculture.

A. O. MADEDORDirector

December 1990

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to· ~(\.1:; and the inteqrated values of global solarr .Il.a'iu- simultaneously on the same chart.rhus d nistorv IS rnamtained for current andfuture use. A photovoltaic array provided withthe equipment supplies power to the recordingsystem. The pyranometer is a silicon based instru-ment which has been temperature compensatedfrom - 20°C to +400C and has been designedfor the measurement of total sun and sky radia-tion (global radiation)' It is calibrated in com-parison to a thermal response pyranometer havinga useful band passof 0.28 to 2.8. micron.

SUMMARY

This report summarises, in tabular form, the records of global solar radiation on a horizontalsurface recorded at 30 stations in Nigeria. Integrated values o+ "ourly and daily SUMS of global radia-tion recorded with LM-3000/10 solar recorder are giver fN each month In the units of

watt-hours/m2 tNherever the data ar= avai.abre The records ra l",~ +rom a few months at some stationsto about 12 months at some others. Monthly means are also calculated and tabulated.

1. INTRODUCTION

Extensive solar data for Nigeria are notavailable as no detailed measurements of solarradiation have been earned out either bythe Meteorological Department or anv other organi-sation in the country. Theoretically calculatedreliable solar data are also not available. Therefore,measurement and subsequent production oflong term solar radiation data in the form oftables and maps are of utmost practical siqnifi-cance to building scientists, architects, engineersand solar technologists for the design of energyefficient buildings and development of efficientand economic solar devices. Meteorology andagriculture are other fields where solar energy'data find frequent applications.

2. THE SOLAR STATIONS

With the aim of determining the distributionof solar radiation in Nigeria, a network of 30 solarradiation stations was established throughout thecountry. These stations are Abuja, Akure, Azare,Bauchi, Benin, Calabar, Enugu. Ibadan, Ilaro,Ilorin, Jos, Kaduna, Kano, Katsina, Koko (nearYelwa), Lagos, Lokoja, Maiduguri, Makurdi,Minna, New Bussa, Nguru, Obudu, Onitsha,Owerri, Port-Harcourt, Serti (Gongola State),Sokoto, Warri and Yola. These solar experimentalsites include all the State capitals and some otherpoints characterised by low or high altitude, e.g.Obudu in Cross River State. Most of the sites arelocated in higher institutions of learning like·Universities and Polytechnics, so that the recor-ders remain under the supervision of qualifiedpersonnel having research orientation. The spreadof solar stations throughout Nigeria is shown in

.Fig.1.

3. THE SOLAR RECORDING SYSTEM

The solar equipment installed at these stationsis the LM-300/10 solar record ing system (solarintegrator) obtained from Hollis Observatory,U.S.A. and is shown in Fig.2. This recordingsystem is unique in that it records both the instan-

4. THE RECORDING OF GLOBAL SOLARRADIATiON ON A HORIZONTAL SUR-FACE

The recording of global solar radiation (direct+ diffuse) was carried out at all the 30 stationsmentioned above for about a year. A typicalrecord of solar data is shown in Fig. 3 for AzareStation (Lat. 11055'N, Long. 100 iO'E) for twodays, one cloudy and the other clear. The Instan-taneous values of solar intensity can be read fromthis tyge of curve along the vertical axis inwatts/m2 for any time from sunrise to sunset.The integrated values of solar rad iation over agiven time interval can be derived from a series ofevent marks on the top of the chart denoted bylong ( II ) and short ( I )marks. For examplethe global radiation on the horizontal surfacefor the clear day shown in Fig.3 is about5.2 kWh/m2/day. Due to error in the chartspeed and event marking system of the recorders,the integrated values of global radiation cannot beread directly as should have been the case for anormal instrument. However, a method was de-vised to determine integrated values of globalradiation from the time scale and the event markson the charts. In this way, hourly and daily varia-tion of solar radiation in the units of watt-hours/m2 have been prepared for those days andmonths for which the charts seemed to be good.The time is given in local apparent solar time(L.A.T.) for the place and day. In this system,the sun is at zenith at solar noon. The daily andmonthly means of solar radiation are also tabu-

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lated. In certain months, the data is not availablefor all the days and mean monthly values in suchcases represent only the mean of those days onwhich data are available. Due to unexpected failureof the majority of instruments, regular and longterm recording of the data could not be carried out.Therefore, data are presented here for whateverdays SId months they are available. For some ofthe stations, either there is no record ing at all orit is very meagre. In view of all this, the initiallim of determining the distribution of solar radia-tion over Nigeria in the form of a map could not

be immediately carried out. But the results pre-sented here are quite useful as practically no suchinformation was available to users in the past inthis country.

ACKNOWLEDGEMENT:The cooperation and contributions of all theResearch Associates in all the 30 solar stationsthroughout the country and that of Messrs. L. K.Komolafe and J. O. Ojosu are acknowledged.Mr. G. N. Omange assisted in the preparation of thisreport for publication.

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