## Raja and Twidell model

Three neighbouring observatories for which the insolation-sunshine records are available are also included in the study. Monthly and yearly maps are constructed, for daily global insolation, based on data for 40 locations. The isolines are compared with results obtained in India and with world solar insolation maps.

Solar energy

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Quoted from: Raja I A ,  Twidell J W . Distribution of global insolation over Pakistan[J]. Solar Energy, 1990, 44( 2):63-71.https://www.sci-hub.ren/10.1016/0038-092x(89)90106-0

Raja I A ,  Twidell J W . Diurnal variation of global insolation over five locations in Pakistan[J]. Solar Energy, 1990, 44(2):73-76.https://www.sci-hub.ren/10.1016/0038-092x(90)90068-n

ABSTRACT

There are only five observatories measuring global insolation in Pakistan, which cannot represent the solar climate of the country. However 37 observatories, distributed fairly well over the entire country, record sunshine. Therefore insolation-sunshine empirical equations are developed to estimate global insolation over Pakistan. Three neighbouring observatories for which the insolation-sunshine records are available are also included in the study. Monthly and yearly maps are constructed, for daily global insolation, based on data for 40 locations. The isolines are compared with results obtained in India and with world solar insolation maps.

INTRODUCTION

From the point of view of solar energy utilization over a region, one of the most attractive and practical ways of presenting spatial variation of insolation is to map the iso-radiation contours. A number of regional studies have been made to construct such insolation maps. These maps provide basic information on solar energy potential in pictorial form and are most important for planning applications.

In attempting to prepare solar insolation maps, themain problem is the inadequacy of the measured data. However, research in this field over the last few decades has minimised this problem. A number of empirical correlations have been developed with a few measured input parameters for making the estimate of global insolation.

A detailed study of the solar climate of Pakistan is being undertaken by the authors to prepare a "solaratlas" for the country. In earlier studies, the distribution of monthly mean values of global, direct and diffuse insolation (measured/estimated) over the country, and the frequency analysis of measured global insolation over five locations have been assessed. The frequency distribution of the number of consecutive days could not be done due to missing daily data of global insolation for the period under investigation.

The work is in progress and will be presented after filling the gaps with estimated values. In this paper hourly data are presented on the availability of solar energy, and its diurnal and annual variation at five locations in Pakistan. The data are essential for many design purposes, such as long term average hourly global insolation for approximating many transient processes in solar energy applications. The present study is based on the work of Barry. Similar studies have been carried out by many researchers with the data from different locations worldwide.

Raja and Twidellprovided the following equations using the data from five main observatories in Pakistan and by taking into account the effffect of latitude Φ:
$$𝐻/𝐻_0 = 0.335 + 0.367 𝑆/𝑆_0 ,$$
$$𝐻/𝐻_0 = 0.388 cos Φ + 0.367 𝑆/𝑆_0$$

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IA Raja, JW Twidell (2021). Raja and Twidell model, Model Item, OpenGMS, https://geomodeling.njnu.edu.cn/modelItem/50b4c33b-bfe7-4da7-a706-5c4b240c8207

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