Renewable energy represents an attractive solution to fulfil two requirements: indoor air quality and energy efficiency. Passive solar systems are easy to implement and effective in areas with high solar potential. The Unglazed Transpired Solar Collector (UTSC) is made of metal cladding with perforations, installed at several centimetres from a building wall, creating thus a cavity, allowing to preheat the fresh air. Several measurements were performed on an innovative perforated solar wall model. This study is a preliminary approach of an analysis on the importance of the orifice shape of the perforated panel as a heat transfer influencing parameter. Both the fluid dynamics and thermal behaviours were investigated. The more complex dynamics of the lobed flows results in a better heat transfer rate. Changing the geometry of the perforations will increase on one hand the orifice's perimeter and it would generate complex fluid dynamics, resulting in higher mixing between the primary flow and the ambient and thus a higher efficiency of heat recovery of these devices. The comparison of a conventional UTSC with a new geometry with innovative perforation leads to interesting results, with almost 40% increase in thermal efficiency. (C) 2016 Elsevier Ltd. All rights reserved.