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A correlation model for the diffuse fraction was recently developed on the basis of a data set obtained in the western part of the Taiwanese mainland. However, it is widely agreed that no existing diffuse fraction correlation model is applicable to all geographical regions and climatic conditions, which is a viewpoint stated from a macro perspective. This study re-justifies this viewpoint through the consideration of a rather small geographical region: Taiwan. The topographic profile of the Taiwanese mainland primarily comprises the high-rise Central Mountain Ranges running from north–northeast to south–southwest, which separate the mainland into eastern and western parts. Furthermore, there are a number of small, remote islands around the Taiwanese mainland. The humidity over the sky dome of these small islands, carried from the moist sea (or ocean) air, is usually greater than that of the Taiwanese mainland. This results in different diffuse fraction patterns between these two geographical regions due to the climatic factor of atmospheric constituents. Two diffuse fraction correlation models for Taiwan were developed using in situ data sets for the eastern part of the Taiwanese mainland and an island in the Penghu archipelago, respectively. In particular, one case considered the topographic effect on modeling the diffuse fraction in Taiwan, while the other considered the geographical effect. Statistical assessments indicate that each correlation model developed in the present study performed better than the previous one developed using the in situ data set for the western part of the Taiwanese mainland, with both applied to the specific site where the data set was used for the model's development. This work demonstrates the need to consider the effects of topography and geography when modeling the diffuse fraction in Taiwan. [ABSTRACT FROM AUTHOR]

Most remote islands are characterized by small populations, many of whom live under the poverty line, poor geographical accessibility and lack of electricity. As such, the solar still, which has a low capital cost, easy operation and less need of maintenance, is recommended to be used in remote islands possessing rich solar irradiance. Against this backdrop, the present study aimed to design and fabricate an effective solar still suitable for application in the remote islands with low freshwater sources but easy access to sea water and rich solar irradiance. Integrating a conventional passive double-slope solar still with an evacuated solar water heater, fins and wick material improves the heat transfer rate through the brine in the basin and increases effective evaporative surface area. Experiments were conducted using batch mode operation during the periods September to October 2021 for the passive solar stills and November 2021 for the active solar still. Experimental results reveal that the augmentation of fins, wicks and a solar water heater influences the overall distillate output of the solar still. The combined use of fins, wicks and a solar water heater increases the average daily productivity by 147% and the average daytime hourly productivity by 245% compared to the conventional passive solar still under similar average solar radiation levels. Using the present design, the active solar still under the solar environment of the testing location can provide 4.4 L of potable water per day. However, to achieve the minimum requirement of 7.5 L/day per person set by WHO, the present design should be modified by increasing the absorber area of the active solar still by 63% and adding eight more evacuated tubes to the solar water heater. The estimated cost per liter of potable water generated by the active (modified) solar still showed that bottled water sold in a typical remote county (Penghu) in Taiwan was 117–283% more expensive than the water generated by the still. [ABSTRACT FROM AUTHOR]