Modelling of annual sunlight availability on vertical shelves: A case study in Thailand

Abstract

Limited cultivation areas in major cities have led to the possibility of vertical farming (the practice of growing crops in vertically stacked layers). However, one of the drawbacks of vertical farming is the limited availability of solar energy at the lower shelves. This study presents a model for predicting the annual sunlight availability on vertical shelves. The model uses the shelf’s structure, orientation, hourly solar radiation, and sunshine duration as inputs to Rhinoceros 3D or RHINO (a 3D computer graphics and computer-aided design application software with the Grasshopper plug-in). The calculated solar energy available at each level of the shelves from RHINO was converted to photosynthetic photon flux density (PPFD) and daily light integral (DLI) using spreadsheet software. This study investigated a vertical farm, in Chiang Mai, Thailand, with six parallel shelves at 1-meter spacing. Each shelf contained three levels with a spacing of 0.5 meters. Both north–south and east–west orientations were investigated. The model could predict PPFD and DLI at every level on the considered shelves. The north–south orientation provided uniform PPFD and DLI throughout the year. The top level of the shelves experiences the highest PPFD (1,949.86μmol*m-2*s-1) and DLI (36.80 mol*m-2*day-1). The PPFD and DLI values at the middle and bottom level were approximately 60% and 50% of the values at the top level, respectively. This information can be used for cultivation planning when considering vertical farming in urban areas. This study provides a sustainable means for future food production.