Experimental validation of an improved concept of building integrated photovoltaic panels Olympia Zogou, Herricos Stapountzis * University of Thessaly, Mechanical Engineering Department, Volos, Greece article info Article history: Received 9 February 2011 Accepted 21 May 2011 Available online 17 June 2011 Keywords: Photovoltaics cooling Photovoltaic/Thermal collectors HVAC abstract Recent progress in the implementation of the Energy Performance of Buildings Directive resulted in a significant increase of rooftop PV installations in European buildings. In certain cases the PV installation is extended to cover also south- or west-facing walls byair cooled Building Integrated PV panels (BIPV). The cooling effect maintains a highconversion efficiency of the panels and the heated air may be exploited by the HVAC or service water heating system. Sizing and design of the double façade system is critical to its energetic performance. In this paper, the transient thermal behavior of the basic structural module of a double-skin photo- voltaic façade is experimentally investigated in real insolation conditions.Theresults are employed in the validation and further improvement of integration of a BIPV concept to the HVAC system of a building. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Greece is a country with plenty of sunshine. The total horizontal solar radiation lies around 1400 kWh/m 2 year in the north and may reach 1700 kWh/m 2 year in certain parts of the south. This potential is increasingly exploited for the production of domestic hot water and electricity. During the last decade, the idea of additionally exploiting the rejected heat of the photovoltaic modules is gaining attention. One example is the PV/T collectors [1], the development of which was promoted in Europe by the adoption of the Directive 2002/91/EC [2]. This Directive and the associated series of European Standards established a common calculation methodology for the integrated energy performance of buildings and laid down the requirements of minimum building energy performance standards. Although rooftop installation is the most common mode of PV application in buildings, vertical installation in the form of south or west-facing double façadesis gaining attention. The heat transfer in doublefaçades is the subject of several papers [3e11]. Each paper focuses on a specific configuration that may be related to an existing building façade concept, including PV façades. Mei et al. [3] studied the thermal performance of a specific type of ventilated PV façade, consisting of a PV panel, an air gap and an inner double glazing. Fux [6] investigated the convective heat transfer rate in both internal sides of a double façade system. Manz [9,10] investigated heat transfer by natural convection of air layers within tall, vertical, rectangular cavities with a prescribed aspect ratio. Fossa et al. [11] investigated the effect of the geometrical configuration of heat sources on the heat transfer with natural convection in an open channel. Solanki et al. [12] report on the design, fabrication and performance assessment of a PV/T solar air heater. Typical electrical efficiency figures of the order of 10% and thermal efficiency of the order of 35% are reported for the specific design of PV/T collector for various climatic conditions. Agrawal and Tiwari [13] report on the installation of a building integrated photovoltaic thermal (BIPVT) system as the rooftop of a building to produce thermal energy for space heating. The BIPVT system, fitted with optimal slope on the rooftop with an effective area of 65 m 2 , annually produces a net electrical exergy of 16 MWh and a net thermal energy of 1.5 MWh. Gan [14] employed CFD to assess the effect of the size of air gap between PV modules and the building envelope on the PV performance in terms of cell temperature for a range of roof pitches and panel lengths. To reduce possible overheating of PV modules and hot spots near the top of modules he suggested a minimum air gap of 0.12e0.15 m for multiple module installation and 0.14e0.16 m for single module installation depending on roof pitches. Skoplaki and Palyvos [15] reviewed the correlations found in the literature which link cell temperature with standard weather variables and material/system-dependent properties. Although numerous investigations appeared in the literature regarding PV/T collectors during the recent years, there is room for additional experimental research work, to improve understanding of different design concepts and layouts, in different climatic conditions. In the present paper, the building block of * Corresponding author. Tel.: þ30 24210 74003; fax: þ30 24210 74052. E-mail address: erikos@uth.gr (H. Stapountzis). Contents lists available at ScienceDirect Renewable Energy journal homepage: www.elsevier.com/locate/renene 0960-1481/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.renene.2011.05.034 Renewable Energy 36 (2011) 3488e3498