Straight-through all-glass evacuated tube solar collector for low and medium temperature applications

Abstract

A straight-through all-glass evacuated tube collector (ETC) made of high-quality borosilicate glass was developed for large-scale low and medium temperature solar hot water systems. It consists of an inner and outer tube without a free end and was shown to be mechanically stable with a thermal expansion coefficient of (3.3 ± 0.1) × 10−6 K−1. Due to turbulent conditions in the straight-through all-glass tube, a higher heat transfer rate could be achieved than in a Dewar-tube ETC, leading to increased heat extraction and decreased heat losses. The photo-thermal efficiency was improved, indicating that a straight-through tube could be more cost-effective. At the same time, active flow in the tube can result in a better water quality as the accumulation time in the tube was short.