Aerosol-induced losses in the solar potential

The atmospheric aerosol loading may significantly influence the performance in solar power production. The impact can be very different both in space (even in short distance) and time (shortterm fluctuations as well as long-term trend). Aiming to ensure a high degree of generality, this study is focused on the aerosol impact on the collectable solar energy. Thus, the results are independent of solar plants characteristics. A new methodology for estimating the average daily,monthly, and yearly losses in the solar potential due to aerosols is proposed. For highlighting the loss in the overall solar potential, a new ideal scenario is defined as a reference for the atmospheric aerosol background. A new equation for computing the solar potential loss is proposed to adjust for possible biases. In a departure from similar studies, the analysis relies on ground measurements (BSRN and AERONET), always more accurate than remotely sensed satellite data. The seldom discussed impact of aerosol type is considered. As a general conclusion, the monthly and yearly reductions of the solar potential due to aerosols are estimated at 12 locations spread around the globe, amounting to losses of the solar potential ranging from 0.6% to as high as 7.2%

A Semi-Analytical Model for Separating Diffuse and Direct Solar Radiation Components

The knowledge of the solar irradiation components is required by most solar applications. When only the global horizontal irradiance is measured, this one is typically broken down into its fundamental components, beam and diffuse, by applying an empirical separation model. This study proposes a semi-analytical model for diffuse fraction, defined as the ratio of diffuse to global solar irradiance. Starting from basic knowledge, a general equation for diffuse fraction is derived. Clearness index, relative sunshine, and the clear-sky atmospheric transmittance are highlighted as robust predictors. Thus, the model equation implicitly provides hints for developing accurate empirical separation models. The proposed equation is quasi-universal, allowing for temporal (from 1-min to 1-day) and spatial (site specificity) customization. As a proof of theory, the separation quality is discussed in detail on the basis of radiometric data retrieved from Baseline Surface Radiation Network (BSRN), station Magurele, Romania. For temperate continental climate, overall results show for the diffuse fraction estimation a maximum possible accuracy around 7%, measured in terms of normalized root mean square error. One of the many options of implementing the semi-analytical model is illustrated in a case study

Nowcasting the Output Power of PV Systems

This paper presents an innovative procedure for nowcasting the energy production of PV systems. The procedure is relayed on a new version of two-state model for forecasting solar irradiance at ground level and a simplified description of the PV system. The results of testing the proposed procedure against on field measured data are discussed. Generally, the proposed procedure demonstrates a better performance than the main competitor based on ARIMA forecasting of the clearness index

Simple vs complex models for solar cells

In this paper three different procedures for extracting the current-voltage characteristics of a crystalline photovoltaic module are studied. Each procedure is associated to a solar cell model characterized by a well-defined degree of complexity. The results emphasize that the simple models approximate the current-voltage characteristics of a solar cell as good as the more complex models. Even if all the procedures analysed in this paper approximate well the measured characteristics, the specific model parameters experience a large dispersion. From a broader perspective, the results raise a question mark on the ability of the current procedures to accurately extract the solar cell parameters

Nowcasting the Output Power of PV Systems

This paper presents an innovative procedure for nowcasting the energy production of PV systems. The procedure is relayed on a new version of two-state model for forecasting solar irradiance at ground level and a simplified description of the PV system. The results of testing the proposed procedure against on field measured data are discussed. Generally, the proposed procedure demonstrates a better performance than the main competitor based on ARIMA forecasting of the clearness index

On the Nature of the One-Diode Solar Cell Model Parameters

The one-diode model is probably the most common equivalent electrical circuit of a real crystalline solar cell. Extensive research has focused on extracting model parameters from measurements performed in standard test conditions (STC), aiming to replicate the current-voltage characteristics (I-V). This study started from finding that, for the same solar cell, different scientific reports yield significantly different sets of parameters, all allowing for highly accurate replication of the measured I-V characteristics. This observation raises a big question: What is the true physical set of parameters? The present study attempts to address this question. For this purpose, a numerical experiment was conducted. The results show that there is an infinity of distinct sets of parameters that can replicate the I-V characteristics at STC via the one-diode model equation. The diode saturation current IS and the diode ideality factor compensate each other to preserve the open-circuit voltage VOC, always an input data point. Some possible approaches (e.g., the link between VOC and IS) that can lead to the physical set of parameters are discussed, highlighting their strengths and weaknesses. There is enough room for future research on finding a universal approach able to guarantee the accurate extraction of the one-diode model physical parameters

Spectral Factor of Colored Solar Cells: A Case Study on the Main Urban Areas in Romania

PV modules for Building-Integrated Photovoltaic (BIPV) applications are made of different colors aimed at raising the visual aesthetic of the building. But a colored coating applied to the surface of a basic PV module is inherently associated to a decrease in conversion efficiency. From a different perspective, the efficiency of a PV module is evaluated under the industry standard test conditions (STC). Due to spectral mismatch, the efficiency of a PV module operating in outdoor conditions may substantially differ from the standard value evaluated at STC. In this study, the influence of spectral solar irradiance distribution on the colored PV module efficiency is evaluated in terms of spectral factor (SF). SF quantifies the relative power gain or loss caused by the spectral difference from STC. The theory is illustrated with a case study on the main four urban areas in Romania. The actual solar radiation spectrum is estimated with the simple Leckner spectral solar irradiance model, based on atmospheric parameters retrieved from the Aerosol Robotic Network (AERONET). The results emphasize that the aesthetic of BIPV comes at a high energy cost: depending on the color, a coating applied on the surface of a crystalline silicon PV module may reduce its conversion efficiency even by half

Impact of Aerosol on the Estimation Accuracy of Solar Radiation

The paper is focused on the solar irradiance estimation in clear-sky conditions and an aerosol-loaded atmosphere. Two parametric models developed by our group and three empirical models are tested. The estimates of the parametric models are based on three atmospheric parameters (ozone, nitrogen dioxide and water vapor column content) and the aerosol properties quantified by means of several specific parameters (Ångström turbidity coefficient, single scattering albedo, asymmetry factor). The empirical models contain no inputs for aerosol properties. Data collected from 10 stations were used to test the models. The inputs for the parametric models were retrieved from Aerosol Robotic Network - AERONET. Global and diffuse solar irradiance data at high-quality standards were retrieved from the Baseline Surface Radiation Network BSRN. A comparative analysis of the models’ accuracy in estimating clear-sky solar irradiance is discussed from the perspective of aerosol proprieties