Solar irradiation comparison of long-span ETFE-covered solar greenhouse

Abstract

The solar greenhouse has been utilised to prolong the growing season of agricultural products in the UK. Transparent foil has been utilised as a substitute for glass in solar greenhouses to minimise the shadow produced by the supporting supports. Although simple polytunnels are regularly utilised, long-span and highly curved membrane structures, which are well-known in architectural design, are infrequently employed in solar greenhouses. The long-span membrane structure should cast less shadow by incorporating more structurally efficient curved geometry.

This study intends to present a solar greenhouse framework featuring three alternatives for long-span membrane designs: (1) pneumatic air-supported structure, (2) tensile membrane structure, and (3) pneumatic cushion structure. Structural analysis and ray-tracing simulations were conducted to examine the impacts of varying sizes of primary structural components and the influence of membrane geometry. The chosen option was also examined to assess its performance across different orientations and lengths.

The findings indicate that the tensile membrane structure is the most optimum option, with 3.61 % and 4.57 % higher solar irradiance among the three long-span membrane structures. Its horizontal radiation transmission could reach 81 % in both summer and winter. The orientation calculations indicate that an East-West orientated tunnel is optimal for maximising winter sun irradiation in UK. Although the tunnel length enhances average solar irradiation, the long-span design already offers a considerable unshaded region, rendering the impact of additional tunnel length negligible. Further research is required for other plan configurations and for assessing other solar greenhouse factors.