高精度自动跟踪太阳光系统研制

为了提高太阳能光伏发电的效率,设计了一种高精度自动跟踪太阳光的系统。该系统主要采用粗、细调互补型信号采集相结合的方式,实现了对太阳光的大范围、高精度的自动跟踪,实际跟踪精度高达0.1°立体角。实验结果表明:该系统操作简单,跟踪精度高,平均输出功率比固定式光伏发电系统提高了30.7%。     

Modelling photovoltaic modules with neural networks using angle of incidence and clearness index

A neural network for modelling photovoltaic modules using angle of incidence and clearness index is proposed. Engineers require methods to estimate the output of a photovoltaic plant depending on meteorological conditions. Therefore, models for the grid inverter and the generator must be provided, and their outputs must be combined. The connection between both models is related to the maximum power point of the generator and how it is tracked by the inverter. That maximum power point under specific conditions of irradiance and module temperature is determined by the I–V curve of the module, which must be simulated under those conditions. Algebraic procedures were used to simulate the I–V curve. Recently, neural networks have been used for the same purpose. Previous methods only take into account the irradiance and the module temperature. The model proposed is based on neural networks, and it uses not only the irradiance and the module temperature but also the angle of incidence and the instantaneous clearness index as additional inputs. The normalised clearness replaces the standard clearness index because it allows the removal of the hourly trend found in this last index. This new model improves the results obtained with previous ones as it can distinguish amongst samples with the same solar irradiance and temperature values but with different angle of incidence and instantaneous clearness index. Results show that this model could be used to improve the accuracy of the tools used to forecast the output of photovoltaic plants. Copyright © 2014 John Wiley & Sons, Ltd.     

Influence of the underneath cavity on buoyant‐forced cooling of the integrated photovoltaic panels in building roof: a thermography study

Airflow around building‐integrated photovoltaics (BIPV) has a significant impact on their hygrothermal behavior and degradation. The potential of reducing the temperature of BIPV using an underneath cavity is experimentally and numerically investigated in literature. Most of the models are oversimplified in terms of modeling the impact of 3D flow over/underneath of PV modules, which can result in a non‐uniform surface temperature and consequently a non‐homogenous thermal degradation. Moreover, the simultaneous presence of radiation and convection related to upstream wind, in addition to the combined impact of back‐ventilation and surface convection, is barely addressed in literature. However, these simplifications can result in the unrealistic loading climate conditions. This paper aims to present a unique experimental setup to provide more realistic climate conditions for investigating the ventilation potential of the underneath. The setup consists of a solar simulator and a building prototype with installed PV, placed inside an atmospheric wind tunnel to control upstream wind velocity. Thermography is performed using an infrared camera to monitor the surface temperature of the BIPV. The potential of an underneath cavity with various cavity heights and PV arrangement is further investigated in this paper. The outcome would be eventually useful in the development of practical guidelines for BIPV installation. Copyright © 2013 John Wiley & Sons, Ltd.     

Regional forecasts of photovoltaic power generation according to different data availability scenarios: a study of four methods

The development of methods to forecast photovoltaic (PV) power generation regionally is of utmost importance to support the spread of such power systems in current power grids. The objective of this study is to propose and to evaluate methods to forecast regional PV power 1 day ahead of time and to compare their performances. Four forecast methods were regarded, of which two are new ones proposed in this study. Together, they characterize a set of forecast methods that can be applied in different scenarios regarding availability of data and infrastructure to make the forecasts. The forecast methods were based on the use of support vector regression and weather prediction data. Evaluations were performed for 1 year of hourly forecasts using data of 273 PV systems installed in two adjacent regions in Japan, Kanto, and Chubu. The results show the importance of selecting the proper forecast method regarding the region characteristics. For Chubu, the region with a variety of weather conditions, the forecast methods based on single systems' forecasts and the one based on stratified sampling provided the best results. In this case, the best annual normalized root mean square error (RMSE) and mean absolute error (MAE) were 0.25 and 0.15 kWh/kWh_avg, respectively. For Kanto, with homogeneous weather conditions, the four methods performed similarly. In this case, the lowest annual forecast errors were 0.33 kWh/kWh_avg for the normalized RMSE and 0.202 kWh/kWh_avg for the normalized MAE. Copyright © 2014 John Wiley & Sons, Ltd.     

Toward multiple maximum power point estimation of photovoltaic systems based on semiconductor theory

Environmental conditions, such as temperature, non‐uniform irradiation, and solar shading, deeply affect the characteristics of photovoltaic (PV) modules in PV‐assisted generation systems. Several local maximum power points (MPPs) are found in the power–voltage curve of PV systems constructed by series/parallel‐connected PV modules under partially shaded conditions. The characteristics of PV systems change unpredictably when multiple MPPs occur, so the actual MPP tracking (MPPT) becomes a difficult task. Conventional MPPT methods for the PV systems under partially shaded conditions cannot quickly find the actual MPP such that the optimal utilization of PV systems cannot be achieved. Based on the p–n junction semiconductor theory, we develop a multipoint direct‐estimation (MPDE) method to directly estimate the multiple MPPs of the PV systems under partially shaded conditions and to cope with the mentioned difficulties. Using the proposed MPDE method, the multiple MPPs of the PV systems under partially shaded conditions can be directly determined from their irradiated current–voltage and power–voltage characteristic curves. The performances of the proposed MPDE method are evaluated by examining the characteristics of multiple MPPs of PV systems with respect to different shading strengths and numbers of the shaded PV modules and also tested using the field data. The experimental results demonstrate that the proposed MPDE method can simply and accurately estimate the multiple MPPs of the PV systems under partially shaded conditions. The optimization of MPP control models and the MPPT for PV systems could be achieved promisingly by applying the proposed method. Copyright © 2014 John Wiley & Sons, Ltd.     

Analyses of structurally modified quasi‐solid‐state electrolytes using electrochemical impedance spectroscopy for dye‐sensitized solar cells

Electrochemical properties of structurally modified quasi‐solid‐state electrolytes were examined using porous substrates (PSs). The PS was prepared into two categories by a phase inversion method with a brominated poly(phenylene oxide) (BPPO): the sponge and finger types. Effects of the humidification and cosolvent compositions on the morphology of the PS were analyzed by scanning electron microscopy. In all cases of the PSs, a higher V_OC was observed of about 0.1 V than that of a liquid electrolyte owing to a suppressed back electron charge transfer. In addition, the PS prepared by the polymer solution of 1 : 4 : 1 (BPPO : N‐methyl‐2‐pyrrolidone : butyl alcohol) with the humidification process showed better photovoltaic properties in terms of the current density and conversion efficiency owing to the appropriate combinations of pore size, tortuosity, and interconnectivity. Effects of the pore structures were intensively examined using electrochemical impedance spectroscopy. The impedance results revealed that large pores at the surface layers are advantageous for a lower R_S and R_TiO2. Meanwhile, the straight inner structure is beneficial for the facile I^?/I₃^? diffusion, thus lowering R_Pt. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39739.     

Thermotropic systems with fixed domains exhibiting enhanced overheating protection performance

Within this study, a time saving photo‐initiated miniemulsion polymerization process (duration of polymerization was 15 min) was established in order to encapsulate a paraffin wax with an acrylate polymer shell. The obtained freeze‐dried latex was an off‐white powder exhibiting spherical particles with mean diameters around 400 nm and a concentration of paraffin wax around 56%. Mixing the reaction product with a UV‐curable resin matrix resulted in thermotropic overheating protection glazings with high light‐shielding efficiency. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40417.     

Matched‐dual‐polymer electrochromic lenses,using new cathodically coloring conducting polymers,with exceptional performance and incorporated into automated sunglasses

Reported are syntheses of several new monomer precursors of cathodically coloring conducting polymers (CPs), based on a propylene dioxythiophene skeleton. These are shown to yield CPs—both as homopolymers and as copolymers—that are nearly “perfectly” matched electrochemically and electrochromically with a set of anodically coloring poly(aromatic amines), for use in dual‐polymer electrochromic lenses. Resulting dual‐polymer electrochromic lenses display very high light/dark contrast (typically up to 70/7% or 50/0.5% Transmission (integrated over visible spectrum, vs. air reference), Haze < 2%, very high cyclability (> 10 K cycles), multiyear shelf life, appealing transparent to dark‐blue‐black transition, and excellent optical memory. Dramatic lowering of switching time, from 8 to < 1 s, is demonstrated using unique applied‐potential algorithm resident on inexpensive Microcontroller chip. Working, practical dual‐polymer electrochromic spectacles are demonstrated with electrochromic lenses retrofitted to spectacles meeting ANSI Z87.1, GL‐PD 10–12 (U.S. military) specifications. These incorporate photosensor, rechargeable Li battery, Microcontroller, allow for automated operation. Ab‐initio‐design spectacles, also conforming to above specifications, are also demonstrated, with components seamlessly hidden within frame. To the best of our knowledge, the electrochromic lenses and sunglasses reported herein represent the best visible‐region electrochromic performance for dual‐polymer CP electrochromic systems to date and the first practical implementation in working sunglasses. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41043.     

Modeling photon transport in fluorescent solar concentrators

Fluorescent solar concentrators (FSC) can concentrate light onto solar cells by trapping fluorescence through total internal reflection. In an ideal FSC, the major obstacle to efficient photon transport is the re‐absorption of the fluorescence emitted. In order to decompose the contribution of different photon flux streams within a FSC, the angular dependent re‐absorption probability is introduced and modeled in this paper. This is used to analyze the performance of different FSC configurations and is also compared with experimental results. To illustrate the application of the modeling, the collection efficiency of ideal devices has also been calculated from the re‐absorption probability and is shown to be useful for estimating non‐ideal losses such as those due to scattering or reflection from mirrors. The results also indicate that among the FSCs studied, the performance of those surrounded by four edge solar cells is close to ideal. The rapid optimization of FSCs has also been presented as another practical application of the models presented in this paper. © 2014 The Authors. Progress in Photovoltaics: Research and Applications published by John Wiley & Sons, Ltd.