Within the building energy saving strategies, BIPV (building integrated photovoltaic systems) present a promising potential based on the close relationship existing between these multifunctional systems and the overall building energy balance. Building integration of STPV (semi-transparent photovoltaic) elements affects deeply the building energy demand since it influences the heating, cooling and lighting loads as well as the local electricity generation. This work analyses over different window-to-wall ratios the overall energy performance of five STPV elements, each element having a specific degree of transparency, in order to assess the energy saving potential compared to a conventional solar control glass compliant with the local technical standard. The prior optical characterization, focused to measure the spectral properties of the elements, was experimentally undertaken. The obtained data were used to perform simulations based on a reference office building using a package of specific software tools (DesignBuilder, EnergyPlus, PVsyst, and COMFEN) to take proper account of the STPV peculiarities. To evaluate the global energy performance of the STPV elements a new Energy Balance Index was formulated. The results show that for intermediate and large façade openings the energy saving potential provided by the STPV solutions ranges between 18% and 59% compared to the reference glass

The objective of this work is to obtain a universal model for calculating the annual angular reflection losses (AAL) of PV modules working in real conditions, useful in the prediction or assessment of the annual performance of PV systems. Instantaneous angular losses (AL) can be calculated by using an analytical model, formerly developed by the authors, that has proved to be in good agreement with the experimental data. In this paper we have used this model to calculate AAL in an hourly basis at 79 different sites all over the world and considering ten different tilt angles, from horizontal to vertical, for south (north) oriented PV modules at north (south) hemisphere sites. From the analysis of the results, we propose an easy‐to‐use mathematical expression for the calculation of AAL. The model has three different versions that are to be used depending on the availability of the local radiation data. The most detailed expression of the model fits with high degree of accuracy the local AAL data, the second version consists of a global term plus a local weather‐descriptive one, and the third version is a universal global model dependent only on the latitude and the PV module tilt angle. Copyright © 2004 John Wiley & Sons, Ltd.

Building retrofit offers the opportunity to reduce energy consumption, improve energy efficiency and increase the use of renewable energy sources. The photovoltaic (PV) technology can be integrated into the building envelope, where conventional construction materials can be easily substituted by PV modules. Prices are competitive with some other solutions and good architectural building integrated photovoltaics (BIPV) solutions enhance the appearance of the buildings. All this makes BIPV an attractive solution for effectively and sustainably retrofitting building envelopes, providing savings in materials and in conventional electricity consumption and, at the same time, improving the energy efficiency of the buildings. This paper shows a building retrofit case study in which standard PV modules are integrated into a new ventilated façade, aiming at serving as an easy-to-implement example for large-scale actions.