Jamil Ahmad

Optimum tilt angle for solar collectors used in India

International journal of ambient energy, Apr 1, 2009

ABSTRACT Flat-plate solar collectors are widely used at New Delhi in India for water heating purp... more ABSTRACT Flat-plate solar collectors are widely used at New Delhi in India for water heating purposes. The roofs of many residential premises in the capital city are fitted with such collectors. This article examines the theoretical aspects of choosing a tilt angle for the solar flat-plate collectors used at New Delhi and makes recommendations on how the collected energy can be increased by varying the tilt angle. In this paper, the collector surface is assumed to be facing South and the calculations are based upon the measured values of hourly global and diffuse solar radiation on a horizontal surface in the capital city. The beam component of the horizontal global radiation is estimated as the difference between the global and diffuse solar radiation. The solar radiation on a tilted surface is calculated as the angle of tilt is varied from 0° to 90°. It is shown that very nearly optimal energy can be collected if the angle of tilt is varied seasonally, four times a year.

Optimization of Tilt Angle for Solar Collector to Receive Maximum Radiation

The Open Renewable Energy Journal, Feb 19, 2009

This article examines the theoretical aspects of choosing a tilt angle for the solar flat-plate c... more This article examines the theoretical aspects of choosing a tilt angle for the solar flat-plate collectors used at ten different stations in the world and makes recommendations on how the collected energy can be increased by varying the tilt angle. In this paper, the collector surface is assumed to be facing toward equator. For Indian stations, the calculations are based upon the measured values of monthly mean daily global and diffuse solar radiation on a horizontal surface. For other stations, the calculations are based upon the data of monthly mean daily global solar radiation and monthly average clearness index on a horizontal surface. It is shown that nearly optimal energy can be collected if the angle of tilt is varied seasonally, four times a year. Annual optimum tilt angle is found to be approximately equal to latitude of the location. It is found that the loss in the amount of collected energy is around 1 % if the angle of tilt is adjusted seasonally instead of using opt for each month of the year. The loss of energy when using the yearly average fixed angle is around 15 % compared with the monthly optimum tilt.

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Optimization of Tilt Angle for Solar Collector to Receive Maximum Radiation

The Open Renewable Energy Journal, 2009

This article examines the theoretical aspects of choosing a tilt angle for the solar flat-plate c... more This article examines the theoretical aspects of choosing a tilt angle for the solar flat-plate collectors used at ten different stations in the world and makes recommendations on how the collected energy can be increased by varying the tilt angle. In this paper, the collector surface is assumed to be facing toward equator. For Indian stations, the calculations are based upon the measured values of monthly mean daily global and diffuse solar radiation on a horizontal surface. For other stations, the calculations are based upon the data of monthly mean daily global solar radiation and monthly average clearness index on a horizontal surface. It is shown that nearly optimal energy can be collected if the angle of tilt is varied seasonally, four times a year. Annual optimum tilt angle is found to be approximately equal to latitude of the location. It is found that the loss in the amount of collected energy is around 1 % if the angle of tilt is adjusted seasonally instead of using opt for each month of the year. The loss of energy when using the yearly average fixed angle is around 15 % compared with the monthly optimum tilt.

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Estimation of global solar radiation using clear sky radiation in Yemen

Journal of Engineering Science and Technology Review, Jun 1, 2012

In this communication, the usability of clear sky radiation for predicting the average global sol... more In this communication, the usability of clear sky radiation for predicting the average global solar radiation has been investigated. For this aim, the various regression analyses were applied by using S/S o and S/S nh parameters. Also, equations which represent the two periods of the year, winter and summer, were developed by using these parameters. The equations developed by using S/S o and S/S nh have approximately the same results. Having the better values of the equations developed by using the change of summer and winter is another result. In addition, the use of the RMSE and MBE in isolation is not an adequate indicator of model performance. Using the t-statistic method and the harmony of results obtained with each method prove that the results are reliable.

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Evaluation of Atmospheric Transmittance for Composite Climate

Agricultural Engineering International: The CIGR Journal, 2008

In this paper, an attempt has been made to estimate the cloudiness/haziness factors and atmospher... more In this paper, an attempt has been made to estimate the cloudiness/haziness factors and atmospheric transmittances for the composite climate of New Delhi (latitude:28.58o N; longitude: 77.02o E; elevation: 216 m above msl). To predict the hourly variation of beam and diffuse radiation on a horizontal surface for any day, atmospheric transmittances for beam and diffuse radiation have been introduced to take into account the uncertain behaviour of atmospheric conditions. For the present study, the hourly data of global and diffuse solar radiation on a horizontal surface for a period of 11 years (1991–2001) have been used and analyzed using polynomial regression analysis. The data have been obtained from the Indian Meteorological Department, Pune, India. It has been observed that there is about 11% maximum and 01% minimum root mean square error between predicted and observed values of hourly varying beam radiation for clear (blue sky) weather condition.

format_quoteHourly global and diffuse solar radiation data for 11 years were collected, providing a robust dataset for analysis of New Delhi's climate.format_quote

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Study of Models for Predicting the Mean Hourly Global Radiation from Daily Summations

Open Environmental Sciences, 2008

It is mandatory to predict the hourly solar radiation received during the average day of each mon... more It is mandatory to predict the hourly solar radiation received during the average day of each month for different solar energy applications, particularly in design methods, Scientists have developed methods to achieve this using different input parameters. The objective of this study is to compare statistically existing models for estimating the mean hourly global radiation incident on a horizontal surface from mean daily global radiation and to recommend one that best fits measured data from five Indian locations chosen namely, Bangalore, Jodhpur, Mumbai, New Delhi and Srinagar. From our results it is observed that Collares-Pereira and Rabl model as modified by Gueymard (CPRG) yields the best performance for estimating mean hourly global radiation incident on a horizontal surface for Indian regions. In addition to CPRG model, Collares-Pereira and Rabl (CPR) and Whillier /Liu and Jordan (WLJ) models yield better performance than Newell, Baig and Garg models. Moreover each model gives an average amount of under-estimation in the calculated value.

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Estimation of Hourly Global Solar Radiation for Composite Climate

Open Environmental Sciences, 2008

In this communication, an attempt has been made to estimate hourly global solar radiation for the... more In this communication, an attempt has been made to estimate hourly global solar radiation for the composite climate of New Delhi (latitude: 28.58 0 N, longitude: 77.20 0 E, elevation: 216 m above mean sea level) using regression analysis based on the model proposed by Al-Sadah et al. (1990). More than 39000 data of hourly solar radiation on a horizontal surface measured at New Delhi were compared with hourly data calculated by various calculation models. Comparison between estimated and measured values shows that the constants derived for New Delhi provide good estimates of the hourly global radiation except for the morning and evening hours. The present results are comparable with the Liu and Jordan (1960) and Collares-Pereira and Rabl (1979) models which also correlate hourly values and daily totals of the global radiation.

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Evaluation and comparison of hourly solar radiation models

International Journal of Energy Research, 2009

... 17 420.00 116.11 416.00 207.08 333.33 246.53 281.12 260.39 EVALUATION AND COMPARISON OF HOURL... more

Solar radiation models-A review

International Journal of Energy Research, 2011

In the design and study of solar energy, information on solar radiation and its components at a g... more In the design and study of solar energy, information on solar radiation and its components at a given location is very essential. Solar radiation data are required by solar engineers, architects, agriculturists and hydrologists for many applications such as solar heating, cooking, drying and interior illumination of buildings. For this purpose, in the past, several empirical correlations have been developed in order to estimate the solar radiation around the world. The main objective of this study is to review the global solar radiation models available in the literature. There are several formulae which relate global radiation to other climatic parameters such as sunshine hours, relative humidity and maximum temperature. The most commonly used parameter for estimating global solar radiation is sunshine duration. Sunshine duration can be easily and reliably measured and data are widely available.

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