Development of an Innovative Smart Multi-Functional PV Flexible Element Based on Thin Film Silicon Solar Cells on ETFE for Building Integration
The building envelops are now becoming real “active skins” with a very important energetic potential. The paradigm of architecture undergoes a soft equilibrium among aesthetic and utility, varies along history and tends naturally, but unconsciously, towards an increase of the energy consumption per inhabitant and home. The struggle for an improvement of the energy requirements of the buildings, and specifically, the activation of the skin of the buildings as electric energy generators, aims to a neutral energy balance. Modern technologies can help the building to achieve the equality in production and consumption of energy by devices with a high degree of integration and aesthetics. Thin film solar cells (TFSC) have attracted a great interest in last years in the building sector because of their interesting properties as integrated elements [1,2]. This is mainly motivated by (i) their thermal behavior and performance at low light conditions (shadow, not orientated, etc.), (ii) the possibility to use different materials as substrates (glass, steel, polymers, etc.) and (iii) their ability to be manufactured in an aesthetic way (semitransparent, coloured, etc.). This makes a thin film module to be well integrated in a non intrusive way. The use of new building materials is directed to ensure that all new buildings have the minimum environmental impact possible. An alternative to traditional solutions is ETFE polymer (a co-polymer of ethylene and tetrafluoroethylene), which has been used for the past 20 years for atria and other overhead glazing. Nowadays, ETFE polymer, a transparent plastic related to Teflon, is considered the building material of the future and is replacing glass and plastic in some of the most innovative buildings [3]. In this context, the purpose of this work is to develop an innovative multi-functional flexible photovoltaic element composed by colored semitransparent solar cells, which shows several of the following features: enhanced modularity; simplicity of installation and utilization; suitability for use in a distributed generation configuration; flexibility in the utilization; easiness to integrate in buildings. In addition, different colors and transparencies can make many different esthetically pleasing results possible. To achieve this objective, the multi-functional PV element will be developed by following the next steps: a) Development of TFSC based on a-Si:H technology (superstrate configuration) using ETFE foils as substrate following the basic structure of ordinary a-Si:H solar cells. b) Microscopic holes, formed by laser patterning, will make the solar cell semi-transparent, adjusting the transmittance by changing the area of the holes [4]. c) Incorporation of lighting devices (LED) on the edge of the device, providing added value to the building element. d) Encapsulation process of the PV element by the stack colored EVA+ETFE as backsheet. Therefore, the final multi-functional PV flexible element will have the following structure: ETFE substrate / TFSC based on a-Si:H (superstrate configuration) / LED devices /colored EVA / ETFE backsheet.