Search

Solar radiation incident at building facades and elements in an urban context is essential in determining the energy production on building rooftops and vertical facades. The proper determination of solar irradiance incident on a vertical facade needs quality input of the components of solar radiation and a high resolution digital surface model with the heights of buildings and other elements in the urban area of study. In this work a thorough methodology for modeling PV generation, in hourly basis, at building facades with open available data and methods is presented. Hourly data of satellite-derived solar irradiance is used with high resolution digital model from LIDAR information to estimate with the Sandia model the PV generation of five small arrays at west, south and east facades of a building in Madrid. PV output modeled for west and south arrays are in rather good agreement with the monitored experimental data of the production. RMSE of 8% and 12% was observed for the monthly power predicted for west and south facades, respectively. The east facade case was much more challenging due to variability of shadows it receives from the nearby large deciduous trees throughout the year, which results in high uncertainty in the shading influence estimation. Anyway, the methodology proves the benefits and possibilities of detailed estimation of PV production in building facades from open available information regarding both solar resource, open modeling tools and urban topography, even in a very challenging conditions associated to the variability of trees canopy.

This paper assesses two steady-state photovoltaic (PV) module temperature models when applied to building integrated photovoltaic (BIPV) rainscreens and curtain walls. The models are the Ross and the Faiman models, both extensively used for PV modules mounted on open-rack support structures in PV plants. The experimental setups arrange the BIPV modules vertically and with different backside boundary conditions to cover the mounting configurations under study. Data monitoring over more than a year was the experimental basis to assess each model by comparing simulated and measured temperatures with the help of four different metrics: mean absolute error, root mean square error, mean bias error, and coefficient of determination. The performance ratio of each system without the temperature effect was calculated by comparing the experimental energy output with the energy output determined with the measured temperatures. This parameter allowed the estimation of the PV energy with the predicted temperatures to assess the suitability of each temperature model for energy-prediction purposes. The assessment showed that the Ross model is the most suitable for predicting the annual PV energy in rainscreen and curtain-wall applications. Highlighted is the importance of fitting the model coefficients with a representative set of in situ monitored data. The data set should preferably include the inner (backside) temperature, i.e., the air chamber temperature in ventilated façades or the indoor temperature in curtain walls and windows.

Accurate and robust modeling of the characteristic I-V curve of a photovoltaic module is essential in many applications focused on forecasting and predicting photovoltaic (PV) performance. The single diode equivalent model has been used extensively for representing the working principles of solar cells. This work presents a simple methodology for solving the single diode equation from the manufacture’s datasheet parameters, by combining the Lambert-W function and an iterative procedure on the ideality factor of the diode, which has a fast convergence and robustness. The model has been assessed by comparing with experimental I-V curves measured for different modules at indoor and outdoor conditions with good results. Sensitivity analysis has been also done to indicate the possible impact of the uncertainty of the initial parameters that input the model.

This study aims at contributing to the progress of the modeling of the thermal behavior of Building Integrated Photovoltaic (BIPV) modules, a progress that runs way behind the pace of development in other areas of characterization of PV modules, such as the electrical one. To this end, a model based on the physics of heat transfer and optics is proposed, allowing the calculation of the temperature of BIPV modules and their thermal transmittance (U-value) in real operating conditions. The main contribution of this model is to include the impact of some parameters not considered so far, like the solar irradiance and the electrical efficiency. After being validated with experimental data, the model has been used to simulate single and double PV glazing, that compared later with common glazing with the same composition and configuration demonstrate the non-equivalent performance between them, showing differences of about 35% in the U-value under high irradiance conditions. This way, a clear disagreement with the current standard testing procedures occurs, something that should be reviewed. The tool proposed allows the complete study of the thermal behavior of BIPV modules and can help in the development of new specific standard procedures for a more realistic characterization of BIPV modules.

This paper reviews the main energy-related features of building-integrated photovoltaic (BIPV) modules and systems, to serve as a reference for researchers, architects, BIPV manufacturers, and BIPV designers. The energy-related behavior of BIPV modules includes thermal, solar, optical and electrical aspects. Suitable standardization to evaluate heat transfer and solar heat gain by BIPV modules still need to be developed further since BIPV elements behave differently to the building elements they substitute. The optical properties of BIPV modules, such as light transmittance or color rendering, also play a role in the search for a good balance between energy saving, electricity generation, aesthetics and visual comfort. However, architecturally adapted BIPV design may affect the electrical performance also, by reducing the efficiency of BIPV modules and systems compared to standard photovoltaic (PV) ones. This is not the sole challenge for the electrical designers, as the special operating conditions of BIPV systems such as non-homogeneous irradiance complicate the electrical design and the forecasting of BIPV performance. The aim of this review is to present the current state of knowledge of the aspects mentioned above, to promote continued progress in BIPV and to inform suitable standardization efforts.

Atmospheric factors, such as clouds, wind, dust, or aerosols, play an important role in the power generation of photovoltaic (PV) plants. Among these factors, soiling has been revealed as one of the most relevant causes diminishing the PV yield, mainly in arid zones or deserts. The effect of soiling on the PV performance can be analyzed by means of I–V curves measured simultaneously on two PV panels: one soiled and the other clean. To this end, two I–V tracers, or one I–V tracer along with a multiplexer, are needed. Unfortunately, these options are usually expensive, and only one I–V tracer is typically available at the site of interest. In this work, the design of a low-cost multiplexer is described. The multiplexer is controlled by a low-cost single-board microcontroller manufactured by ArduinoTM, and is capable of managing several pairs of PV panels almost simultaneously. The multiplexer can be installed outdoors, in contrast to many commercial I–V tracers or multiplexers. This advantage allows the soiling effect to be monitored on two PV panels, by means of I–V indoor tracers. I–V curves measured by the low-cost multiplexer are also presented, and preliminary results are analyzed, This research was funded by the Spanish Ministry of Economy, Industry, and Competitiveness “PVCastSOIL” project No ENE2017-83790-C3-1-2-3-R, in collaboration with the European Regional Development Fund

This work attempts to shed some light on the impact of organic soiling due to pollen on solar photovoltaic (PV) power generation. Apart from introducing several soiling-related pollen features, the previous works reporting soiling by pollen have been reviewed. Local observations from late winter to early spring showed that a rooftop PV system experienced both uniform and non-uniform soiling issues, which were mainly caused by pollen from nearby cypress specimens. In addition, this work publishes preliminary results regarding an artificial soiling test performed with pollen. In this test, soda lime float glass coupons were artificially soiled with fresh cypress pollen. A linear relationship was found between the pollen mass density (ρA) and the glass averaged transmittance (TAVE) for values up to 9.1 g/m2. In comparison with other artificial soiling tests performed with different soiling agents, the transmittance loss caused by pollen cypress deposition was relatively high and spectrally selective.

Building Integrated Photovoltaics (BIPV) in commercial and office buildings can be designed with the aim of reducing the electricity consumption from the conventional local grid. This paper stresses the importance of matching the photovoltaic (PV) generation local profile with the building’s load shape to reach around 100% self-consumption indexes and to improve the self-sufficiency degree of the building, without storage nor load management. For that purpose, this paper proposes a methodology that helps BIPV designers to achieve these targets. Its application to a real case shows that the different facades of the building envelope may play a role in the local PV production if their orientations receive sufficient insolation during the hours of electrical consumption. In particular, in the North Hemisphere the possibilities that offer all the external surfaces of the building that are not oriented to the North should be taken into consideration in a first approach, and then those which achieve the best production-consumption match should be analyzed and compared to select the optimum solution.

This paper aims at improving the clarity and coherence of PV (photovoltaics) technical potential assessment, that is, calculation of the electricity that can be supplied by large-scale deployment of PV systems. A step-by step method, compiling the main variables and processes involved, and including the packing factor in the technical potential equations, is proposed for this purpose. The influence of latitude and some design parameters, such as the shading criterion and tilt angle is analyzed. The paper supplies easy-to-use tools for estimating technical PV potential, as well as PV system land-use requirements. Analytical expressions and graphic examples, and a comparison of some case studies with existing PV plant data are included.

The optical characterization of different PV modules for integration in buildings (BIPV) is presented in this paper. The investigated PV modules are laminated glasses (PV laminates) suitable for integration in façades and windows. They are made of different PV cell technologies and some of them present a certain transparency degree, making possible to combine daylighting properties with solar control and electrical generation. The approach is based on spectral UV/vis/NIR reflectance and transmittance measurements of the different considered samples, both at normal incidence and as a function of the angle of incidence when it is possible. The European standard protocols are used to determine the luminous and the solar characteristics of each sample, enabling the optical assessment of these PV modules as building elements. The results indicate the good properties of PV laminates in terms of daylighting and solar control capabilities allowing a feasible efficient integration in building façades and windows. The obtained characteristic parameters can be used to simulate the influence in the energy balance of a building of different types of PV modules integrated in façade or window elements. © 2015 Elsevier B.V. All rights reserved.

A Typical Meteorological Year (TMY) is frequently used in solar power for long-term energy yield analysis. Different approaches have been reported focusing on concentrating solar power or photovoltaic power plants that have established different relative contributions of the involved variables (mainly solar irradiance components and temperature) according to the application. For PV applications the estimation of the spectral gains and losses requires of on-site spectral measurements. Long-term analysis of the spectral influence on PV technologies has been performed for over seven years of measured spectral global tilted irradiance in Madrid. The experimental spectra were measured with an EKO spectroradiometer in the wavelength range of 300–1100 nm. The TMY methodology has been used to create a typical spectral year of global tilted irradiance that can be used for computing the spectral factor. This paper shows the different steps in applying the TMY methodology to spectral irradiance and the resulting spectral factors computed for seven different PV technologies. Thus, this approach can effectively be used to characterize the long-term spectral influence of PV technologies in a selected site.

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.

This paper presents the results of measuring global solar irradiation in horizontal and vertical surfaces North, South, East and West with the aim to determine the energy loads in which buildings are subjected to in Mexico city, in order to provide the necessary information firstly, for planning and design of new buildings and secondly, for cost benefit analysis in the adaptation of already built structures. Solar irradiation on vertical surfaces plays a major role to determine thermal and energy performance of a building especially important for analysis of active and passive solar systems. A full year data of measurements (2014) have been compiled and analyzed. In addition, the hourly data of this horizontal and vertical measurements were compared with hourly radiation data calculated by means of two different models: the isotropic sky model (Hottel and Woertz model) and one anisotropic sky model (Perez model). The performance of the models were assessed by two common statistical parameters: the relative root mean square error (RMSE) and the mean bias error (MBE). Perez model presented better performance through the year in north, east and west façades, and the isotropic model in south façade.