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Edinburgh Napier University (2006)

Modelling hourly and daily diffuse solar radiation using world-wide database

Munawwar, Saima

Titre : Modelling hourly and daily diffuse solar radiation using world-wide database

Auteur : Munawwar, Saima

Université de soutenance : Edinburgh Napier University

Grade : Doctor of Philosophy (PhD) 2006

Solar energy is an alternative to fossil fuels for more sustainable and reliable energy options ; with a huge potential to meet many times the present world energy demand. Readily available solar radiation data is a key to design and simulation of all solar energy applications. Whereas, global radiation is a frequently measured parameter, diffuse irradiance is often not measured, and therefore needs to be estimated from robust, reliable models. This research project aims to develop regional diffuse solar radiation models on both hourly and daily levels (using nine world-wide sites) for each of the following countries : India, Japan, Spain and UK. Qualitative analysis is performed to investigate the bearing of sunshine fraction, cloud cover and air mass on the clearness index (kt) -diffuse ratio (k) relationship, fundamental to presently proposed modelling. This is followed by a quantitative assessment by developing a series of hourly models based on these parameters along with global radiation, and comparing the performance results with the conventional k-kt model. Eventually, after thorough statistical evaluation, optimal region-wise hourly models are recommended. Daily radiation models are inherently different from their hourly counterparts and, nevertheless, are required for various other applications. Therefore, models for daily diffuse radiation are developed using daily sunshine fraction and daily-averaged cloud cover along with daily clearness index to estimate daily diffuse ratio. As in hourly modelling, all possible combinations of the parameters under focus are used to develop a set of models for each location. Statistical analysis similar to that in case of hourly radiation models is performed. This is followed by validating the daily models against other sites within a region to be able to safely propose region-based models for each of the four countries. It is revealed that uncertainty in measurements plays an important role in establishing the accuracy with which models can be used. Through this work, important parameters for hourly and daily diffuse radiation models are established. The proposed models are believed to provide reasonable accuracy if used within a given region where diffuse solar radiation is not measured. A case study for the futuristic sustainable production of solar electricity for India is also included to demonstrate the application of solar radiation.

Mots clés : Solar energy ; radiation ; diffuse irradiation ; measurement models ; global ; reliable ;

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