Smart windows for zero carbon energy buildings

There is an urgent need for sustainable and efficient usage of energy in buildings, which currently accounts for 40% of the world’s energy consumption. In Europe, directives have been established to improve energy efficiency and to ensure that all new buildings are nearly zero energy buildings (NZEB). In Latin American and Caribbean (LAC) countries, this is also a top priority and policies are being enforced to implement incentives for renewable energies and promote energy efficiency. WINNER aims to contribute to these ambitious and important goals by developing an innovative smart window system capable of generating energy for self-consumption at the same time as filtering out part of the IR radiation incident on the building, therefore reducing the energy demands for air conditioning, especially in hot climates. In this context, the main objective of the project is to develop an innovative building-integrated photovoltaic system based on smart windows. By introducing suitable nanoparticles on façade surfaces receiving direct sunlight it is possible to build luminescent solar concentrators (LSC), which, on one hand, down-shift the solar spectrum towards the range where the solar cells have an optimal response, and, on the other hand, are able to redirect part of the incident light to the windowpane perimeter, therefore reducing the amount of radiation on the surface and contributing to the smart climatization of the building.

During the first half of the project, an extensive state-of-the-art review of materials to produce a luminescent solar concentrator (LSC) was performed. An initial selection of materials was done considering the requirements of: (i) matching the emission wavelength to the spectral peak of the external quantum efficiency (EQE) of the side-mounted PV cells; (ii) provide adequate colour and degree of transparency, which are determined by the type and density of luminophores and the properties of the supporting polymeric medium; (iii) have high efficiency and stability; (iv) enable adequate processability with up-scalable techniques. In parallel, materials deposition technologies were also analysed and several technologies were selected as the most appropriate and able to ensure both low-cost/high productivity and high performance of the LCS prototypes: (i) ultrasonic spray, doctorblade (knife-coating) and (ii) polymer multilayer (PML). An initial optimisation of process parameters was conducted. In parallel with the development of the LSC, the design of the smart window was completed. Taking into account market trends and smart functionality of the window, a conceptual design was developed and agreed among all project partners. The design considered thermal, acoustic, ergonomic and luminosity aspects. The smart window was decided to integrate not only the PV cells on the window frame, but also all the basic electronic components for an autonomous mode of operation, including batteries and miniaturised balance-of-system elements. A maximum power point tracker (MPPT) was included for each branch of the PV system, which has a very different output due to the different positioning on the window frame. The design was conducted and initial electronic components were acquired and tested. Also, a new laboratory for the final validation of the smart-window in hot climates (Dominican Republic) was defined and its construction was started. First prototypes will be built during the next period and extensively validated, demonstrating the potential of the smart window to generate electricity in buildings in a sustainable way. In addition, through the diffusion of the results, the project will contribute to the promotion of renewable energies globally and more specifically in the LAC region. The exploitation of alternative energies in these countries can increase technology transfer opportunities and have an important impact in improving the national economies.