Current–voltage curve translation by bilinear interpolation

By means of bilinear interpolation and four reference current–voltage (I–V) curves, an I–V curve of a photovoltaic (PV) module is translated to desired conditions of irradiance and PV module temperature. The four reference I–V curves are measured at two irradiance and two PV module temperature levels and contain all the essential PV module characteristic information for performing the bilinear interpolation. The interpolation is performed first with respect to open‐circuit voltage to account for PV module temperature, and second with respect to short‐circuit current to account for irradiance. The translation results over a wide range of irradiances and PV module temperatures agree closely with measured values for a group of PV modules representing seven different technologies. Root‐mean‐square errors were 1·5% or less for the I–V curve parameters of maximum power, voltage at maximum power, current at maximum power, short‐circuit current, and open‐circuit voltage. The translation is applicable for determining the performance of a PV module for a specified test condition, or for PV system performance modeling. Copyright © 2004 John Wiley & Sons, Ltd.     

Exploiting existing dams for solar PV system installations

Recognizing the issues of land shortage and growing concerns for protecting natural lands, installers and project developers, with the help of scientists and engineers, continuously try to locate alternative spots for photovoltaic (PV) system installations. In the present paper a novel approach is suggested and analysed: installing solar PV systems on the downstream face of existing dams. This approach provides advantages that could favour even large‐scale systems with a capacity of several MWp. First, produced energy could cover water reservoirs' needs supporting energy‐intensive processes as water pumping and treatment in a sustainable manner. Moreover, energy provision to inhabited areas near the dams and the subsequent creation of independent mini grids could mitigate energy poverty. In the case of hydroelectric dams, the so‐created hybrid system (PV‐hydro) could become notably efficient, because the intermittent solar energy would be counterbalanced by the flexibility of hydropower. Finally, we found a notable number of existing water reservoirs in Africa that are either under‐utilized or non‐powered. That unexploited energy potential can also be amplified by PV‐system installation. The analysis included data collection from various sources. Datasets have been cross‐checked and extended in the newly created GIS‐based model, enabling the selection of the most suitable sites in South Africa, taken as case studies. Following their identification, the selected dams have been analysed using the PVGIS tool in order to estimate the annual energy production. The results have been very encouraging, indicating that PV systems on the face of dams are an advantageous option for renewable energy production. © 2015 The Authors. Progress in Photovoltaics: Research and Applications published by John Wiley & Sons Ltd.     

Investigation to estimate the short circuit current by applying the solar spectrum

The influence of the solar spectrum is investigated to estimate the outdoor short circuit current (I_sc) of various photovoltaic (PV) modules. It is well known that the solar spectrum always changes. Hence, it is rare to fit the standard solar spectrum AM1·5G defined in standard IEC 60904‐3. In addition, the spectral response (SR) of PV module is different depending on the material. For example, crystal silicon (c‐Si) has broad sensitivity that the wavelength range is between 350 and 1150 nm; meanwhile, amorphous silicon (a‐Si) has relatively narrow sensitivity comparing to c‐Si. Since I_sc of the PV module decides by multiplying the solar spectrum and SR together, it is necessary to investigate the solar spectrum to estimate the outdoor I_sc in addition to the solar irradiance and module temperature. In this study, the spectral mismatch is calculated and the outdoor I_sc is estimated in the whole year. Copyright © 2007 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.     

Environmental life cycle assessment of roof‐integrated flexible amorphous silicon/nanocrystalline silicon solar cell laminate

This paper presents an environmental life cycle assessment of a roof‐integrated flexible solar cell laminate with tandem solar cells composed of amorphous silicon/nanocrystalline silicon (a‐Si/nc‐Si). The a‐Si/nc‐Si cells are considered to have 10% conversion efficiency. Their expected service life is 20 years. The production scale considered is 100 MW_p per year. A comparison of the a‐Si/nc‐Si photovoltaic (PV) system with the roof‐mounted multicrystalline silicon (multi‐Si) PV system is also presented. For both PV systems, application in the Netherlands with an annual insolation of 1000 kWh/m² is considered. We found that the overall damage scores of the a‐Si/nc‐Si PV system and the multi‐Si PV system are 0.012 and 0.010 Ecopoints/kWh, respectively. For both PV systems, the impacts due to climate change, human toxicity, particulate matter formation, and fossil resources depletion together contribute to 96% of the overall damage scores. Each of both PV systems has a cumulative primary energy demand of 1.4 MJ/kWh. The cumulative primary energy demand of the a‐Si/nc‐Si PV system has an uncertainty of up to 41%. For the a‐Si/nc‐Si PV system, an energy payback time of 2.3 years is derived. The construction for roof integration, the silicon deposition, and etching are found to be the largest contributors to the primary energy demand of the a‐Si/nc‐Si PV system, whereas encapsulation and the construction for roof integration are the largest contributors to its impact on climate change. Copyright © 2012 John Wiley & Sons, Ltd.     

Greenhouse gas emissions associated with photovoltaic electricity from crystalline silicon modules under various energy supply options

The direct and indirect emissions associated with photovoltaic (PV) electricity generation are evaluated, focussing on greenhouse gas (GHG) emissions related to crystalline silicon (c‐Si) solar module production. Electricity supply technologies used in the entire PV production chain are found to be most influential. Emissions associated with only the electricity‐input in the production of PV vary as much as 0–200 g CO₂‐eq per kWh electricity generated by PV. This wide range results because of specific supply technologies one may assume to provide the electricity‐input in PV production, i.e., whether coal‐, gas‐, wind‐, or PV‐power facilities in the “background” provide the electricity supply for powering the entire PV production chain. The heat input in the entire PV production chain, for which mainly the combustion of natural gas is assumed, adds another ∼16 CO₂‐eq/kWh. The GHG emissions directly attributed to c‐Si PV technology alone constitute only ∼1–2 g CO₂‐eq/kWh. The difference in scale indicates the relevance of reporting “indirect” emissions due to energy input in PV production separately from “direct” emissions particular to PV technology. In this article, we also demonstrate the utilization of “direct” and “indirect” shares of emissions for the calculation of GHG emissions in simplified world electricity‐ and PV‐market development scenarios. Results underscore very large GHG mitigation realized by solar PV toward increasingly significant PV market shares. Copyright © 2011 John Wiley & Sons, Ltd.     

Energy,cost and LCA results of PV and hybrid PV/T solar systems

Hybrid photovoltaic/thermal (PV/T) solar systems provide a simultaneous conversion of solar radiation into electricity and heat. In these devices, the PV modules are mounted together with heat recovery units, by which a circulating fluid allows one to cool them down during their operation. An extensive study on water‐cooled PV/T solar systems has been conducted at the University of Patras, where hybrid prototypes have been experimentally studied. In this paper the electrical and thermal efficiencies are given and the annual energy output under the weather conditions of Patras is calculated for horizontal and tilted building roof installation. In addition, the costs of all system parts are included and the cost payback time is estimated. Finally, the methodology of life cycle assessment (LCA) has been applied to perform an energy and environmental assessment of the analysed system. The goal of this study, carried out at the University of Rome ‘La Sapienza’ by means of SimaPro 5·1 software, was to verify the benefits of heat recovery. The concepts and results of this work on energy performance, economic aspects and LCA results of modified PV and water‐cooled PV/T solar systems, give a clear idea of their application advantages. From the results, the most important conclusion is that PV/T systems are cost effective and of better environmental impact compared with standard PV modules. Copyright © 2005 John Wiley & Sons, Ltd.     

PV pumping systems: a useful tool to check operational performance

From the daily water demand, total head and the daily average irradiation, is possible to determine the size of the PV generator for pumping systems. However, once the equipment is acquired, some tests are recommended, specially to verify its performance. One of the most relevant parameters to qualify a pumping system is the daily water delivered (m³/day) as a function of daily irradiation (Wh/m²). Facilities that fit different boundaries conditions, as for example constant total head (m) are not easily available, and just few laboratories have this capability. In this way, a simple instrumentation with the capability to determine the daily performance of PV pumping systems is presented. The proposed test tools use a hydraulic circuit with two motopumps, one connected to the PV system and the other to the electric grid. The total head is maintained constant by the variable‐speed drive connected to the grid. Copyright © 2006 John Wiley & Sons, Ltd.     

A simplified model based on clearness index for estimating yearly performance of hybrid PV energy systems

A simplified model for estimating the energy contribution of PV converter in a hybrid PV–wind system is presented. The simplified model determines the yearly solar fraction, that is the fraction of energy demand provided by PV, and the remaining loss of load (LOL) is assumed to be provided by wind turbines. The novel model is based on simulation results derived from 8 years of measured hour‐by‐hour solar irradiation data from five different locations in the world. The system performance is simulated by the PV–wind energy simulation program of the Cardiff School of Engineering (ARES). An hourly constant load profile is assumed. The performance of a PV system is primarily dependent on the solar irradiation distribution in a given location for the period of time in question. The new model correlates the location dependence observed in the yearly solar fraction curves of different data sets with one of the most characteristic solar irradiation distribution parameters, the yearly clearness index of the respective solar irradiation data. The new model requires the yearly clearness index value, which is commonly available for most locations throughout the world, as input. As the novel model is validated with solar irradiation data from different locations in the world, it could be used for predicting the solar fraction in a hybrid PV system with a very high level of accuracy, for a wide range of climates. Copyright © 2002 John Wiley & Sons, Ltd.     

The effect of electron damage on silicon solar cells coated with diamond‐like carbon films

The unique properties of the diamond‐like carbon (a:DLC), such as high mechanical hardness and abrasive resistance, optical transparency in the visible and IR spectral regions and high thermal conductivity, provide this material with advantages over other types of protecting materials for solar cells. Furthermore, the a:DLC films are inert to corrosive gases and other corrosive agents. Resistance to radiation damage of the a:DLC films deposited on solar cells is very important for space application. In the study we investigate the effect of electron damage on silicon solar cells coated with a:DLC films. We measure the I – V characteristic and the spectral response and calculate the values of the seven parameters of the double exponential solar cell model (usually not investigated) as a function of electron fluence irradiation. In addition we obtain also the usual external parameters I_sc, V_oc, I_m, V_m, FF, and efficiency) of the solar cells. We investigate solar cells with and without anti‐reflecting coating coated with a:DLC films which were exposed to electron radiation. The main findings show that the solar cells with a:DLC films of thickness up to 500 nm degrade similarly to regular silicon cells exposed to electron irradiation. The degradation of the spectral response of the solar cell is mainly in the range of longer wavelengths and the irradiation affects the solar cell parameters (mainly the reverse saturation currents). Copyright © 2000 John Wiley & Sons, Ltd.     

Distributed power generation versus grid extension: an assessment of solar photovoltaics for rural electrification in Northern Ghana

The competitiveness of distributed solar photovoltaic (PV) power generation for rural electrification in northern Ghana is assessed and compared with the conventional option of extending the national grid and increasing the capacity for centralised power generation. A model is constructed to calculate the life‐cycle cost (LCC) of the two options and to test the sensitivity of different parameters. All calculations are based on information from the GEF/UNDP pilot region in the East Mamprusi District. In addition to the economic aspect, issues of quality and environmental effects are discussed. The LCC of distributed PV is lower than that of a grid extension for an electricity demand corresponding to solar home systems of 140 W_p or smaller. Thus, distributed PV is cost competitive for purposes of lighting, entertainment, information and basic public facilities, such as schools and hospitals. The LCC for the option of grid extension with central power generation is dominated by the cost of low‐voltage micro‐grids within the communities. Important factors are the density of households and the penetration (fraction of households electrified), as they affect the line length per connected household. The relatively low cost of regional medium‐voltage grids makes the geographical location of each community less important than expected. Battery replacement every fifth year makes up the major part of the LCC of solar home systems and is also responsible for the large energy input in the production of the systems. This could limit both future cost reductions of distributed PV and its potential to mitigate greenhouse gas emissions. Copyright © 2002 John Wiley & Sons, Ltd.     

Performance,cost and life‐cycle assessment study of hybrid PVT/AIR solar systems

An alternative and cost‐effective solution to building integrated PV systems is to use hybrid photovoltaic/thermal (PV/T) solar systems. These systems consist of PV modules with an air channel at their rear surface, where ambient air is circulating in the channel for PV cooling and the extracted heat can be used for building thermal needs. To increase the system thermal efficiency, additional glazing is necessary, but this results in the decrease of the PV module electrical output from the additional optical losses of the solar radiation. PV/T solar systems with air heat extraction have been extensively studied at the University of Patras. Prototypes in their standard form and also with low‐cost modifications have been tested, aiming to achieve improved PV/T systems. An energetic and environmental assessment for the PV and PV/T systems tested has been performed by the University of Rome ‘La Sapienza’, implementing the specific software SimaPro 5·1 regarding the life‐cycle assessment (LCA) methodology applied. In this paper electrical and thermal energy output results for PV and PV/T systems are given, focusing on their performance improvements and environmental impact, considering their construction and operation requirements. The new outcome of the study was that the glazed type PV/T systems present optimum performance regarding energy, cost and LCA results. Copyright © 2005 John Wiley & Sons, Ltd.     

Experimental solar spectral irradiance until 2500 nm: results and influence on the PV conversion of different materials

In this work, results are presented concerning solar spectral irradiance measurements performed in Madrid in the wavelength range 250–2500 nm, that is, extending the spectral range far away from the wavelengths where PV semiconductors are active. These data were obtained considering a horizontal receiver surface during selected clear days covering the four seasons of the year. PV materials having different spectral responses (m‐Si, a‐Si, CIGS, CdTe) have been considered to calculate spectral factors (SF) taking as reference the standard solar spectrum AM1.5 defined in standard IEC 60904‐3. From these SFs, the influence of natural solar spectral variations in PV conversion has been established. It is shown, for example, that PV technologies based on a‐Si are highly favored, from the spectral point of view, in spring–summer compared to other technologies having broader spectral responses, which are more favored in autumn–winter. From the experimental measured solar spectra, we have calculated Weighed Solar Spectra (WSS) corresponding to the four seasons of the year and also to the whole year. The WSS represents, for a certain period of time, the solar spectrum weighed over the irradiance level. SFs have been calculated for different WSSs showing spectral gains for the four PV materials during almost the full year. Otherwise, it is also shown in this work how the near‐IR part of the solar spectrum affects the evaluation of the solar resource as a whole when reference solar cells made of different PV materials are used. For typical m‐Si, a‐Si, CIGS, and CdTe solar cells, the ratio of I_sc over global irradiance is not constant along a given day showing variations that depend on the season and on the PV material considered. © 2006 John Wiley & Sons, Ltd.     

Life‐cycle greenhouse gas emissions and energy payback time of current and prospective silicon heterojunction solar cell designs

Silicon heterojunction (SHJ) cells offer high efficiencies and several advantages in the production process compared to conventional crystalline silicon solar cells. We performed a life‐cycle assessment to identify the greenhouse gas (GHG) footprint, energy payback time (EPBT) and cumulative energy demand of four different SHJ solar cell designs. We analyse these environmental impacts for cell processing and complete systems for both current and prospective designs. On the basis of in‐plane irradiation of 1700 kWh/m², results for current designs show that life‐cycle GHG emissions could be 32 gCO₂‐eq/kWh for complete SHJ photovoltaic (PV) systems (module efficiencies of 18.4%), compared with 38 gCO₂‐eq/kWh for conventional monocrystalline silicon systems (module efficiency of 16.1%). The EPBT of all SHJ designs was found to be 1.5 years, compared with 1.8 years for the monocrystalline PV system. Cell processing contributes little (≤6%) to the overall environmental footprint of SHJ PV systems. Among cell processing steps, vacuum based deposition contributes substantially to the overall results, with 55–80%. Atomic layer deposition of thin films was found to have a significantly lower environmental footprint compared to plasma enhanced chemical vapour deposition and sputtering. Copper‐based compared with silver‐based metallization was shown to reduce the impact of this processing step by 74–84%. Increases in cell efficiency, use of thin silicon wafers and replacement of silver‐based with copper‐based metallization could result in life‐cycle GHG emissions for systems to be reduced to 20 gCO₂‐eq/kWh for SHJ systems and 25 gCO₂‐eq/kWh for monocrystalline system, while EPBT could drop to 0.9 and 1.2 years, respectively. Copyright © 2014 John Wiley & Sons, Ltd.     

Enhancing the power output of PV modules by considering the view factor to sky effect and rearranging the interconnections of solar cells

The solar diffuse radiation incident on a photovoltaic (PV) module is unevenly distributed along the module's width because its solar‐cells “see” different view‐factor values with respect to their position. This fact causes PV modules to experience undesired power losses brought about by current mismatch. The paper addresses this issue and presents new interconnection strategies for the module's cells. The proposed interconnections are shown to introduce power gain vis‐à‐vis the all‐series connected module. Having established the theoretical framework, a case study is examined, comparing two sites with considerable different amounts of diffuse radiation with the aim of quantifying the power production enhancement with regard to the site's prevailing annual extent of diffuse radiation. It is found, for example, that by converting the all‐series cell interconnection into parallel strips in Desert Rock (NV, USA), each module can be supplemented with a 6.5 [kW_ph] annually on average. The study may have financial implications for the PV industry which strives to increase power generation while maintaining reduced costs. Copyright © 2017 John Wiley & Sons, Ltd.     

The present status and future direction of technology development for photovoltaic power generation in Japan

In 2004 NEDO established the PV Roadmap Toward 2030 PV2030 as a long‐term strategy for PV R&D. In this Roadmap, PV is expected by 2030 to supply approximately 50% of residential electricity consumption (cumulative installed capacity in the range of 100 GW). In terms of economic efficiency, electricity costs are targeted to equal commercial use, approximately 14 Yen/kW h, by 2020 and industrial use, approximately 7 Yen/kW h, by 2030. For future PV systems, it is essential to improve the stand‐alone capabilities of PV system with electricity storage and to develop community‐based PV systems using multi‐function inverters. Advanced technological innovations beyond the existing levels are also essential. Therefore, NEDO is undertaking 2‐year projects for preliminary research to make clear the next R&D of solar cells and PV system technology. Copyright © 2005 John Wiley & Sons, Ltd.     

Framework for the analysis of the potential of the rooftop photovoltaic system to achieve the net‐zero energy solar buildings

New renewable energy is attracting considerable attention as a future energy source. The photovoltaic (PV) market, in particular, has grown significantly during the past decade. The use of the rooftop PV system in buildings in urban environments is being actively promoted. This research was conducted to develop a framework for the analysis of the potential of the rooftop PV system to achieve the net‐zero energy solar buildings in terms of energy supply. To verify the feasibility of the proposed framework, a total of 5418 elementary school facilities located in 16 administrative divisions in South Korea were selected as case studies. This research (i) collected information on the elementary school facilities, the rooftop PV system, and the meteorological and geographical characteristics by region; (ii) conducted an energy supply analysis by applying the rooftop PV system; (iii) conducted an energy demand analysis; (iv) analyzed the energy substitution effect; (v) presented the current status of the energy supply and demand in each region using the geographical information system; (vi) analyzed the causal relationship between the energy supply and demand by region; and (vii) proposed an energy supply and demand strategy by region. This research can help elementary school facility managers or policymakers conduct an energy supply and demand analysis as well as propose an energy supply and demand strategy. It can be used as part of an educational facility improvement program. The framework proposed in this research can also be applied to any other country or sector in the global environment. © 2013 The Authors. Progress in Photovoltaics: Research and Applications published by John Wiley Ltd.     

PV water pumping systems based on standard frequency converters

Standard frequency converters (FCs) are evaluated in this work as a universal solution for photovoltaic (PV) water pumping systems. FCs can be connected directly to a PV generator to power centrifugal submersible pumps driven by three‐phase asynchronous induction motors. In comparison with dedicated products, the use of standard FCs and centrifugal motopumps encompasses several advantages: power range, broad range of products and technological independence. This paper describes the main rules to implement standard FCs in PV pumping systems, and presents a model to estimate its performance from standard pumps manufacturers' data. The experimental validation of the model is also presented. Copyright © 2003 John Wiley & Sons, Ltd.     

Optimal sizing of photovoltaic‐hydro power plant

The work presents a technological concept of energetically independent and ecologically sustainable system of electric energy production by joint operation of photovoltaic (PV) and hydro electric (HE) power plant as a unique technological system of solar hydroelectric (SHE) power plant. The sustainability of such system is based exclusively on the solar energy input, as the renewable and pure energy resource, and the use of hydro energy, due to the possibility of its continuous production of energy and its well‐known flexibility in covering the consumers' needs. For the purpose of connecting all relevant values into one integral SHE system, a mathematical model was developed for selecting the optimal size of the PV power plant as the key element for estimating the technological feasibility of the overall solution. The model was tested on electric energy supply from the island of Vis in Croatia. The obtained power of the PV power plant was 41 MW_p which corresponds to collector field of approximately 25 ha, while the estimated related storage was 20 hm³. The results show that the subject model describes the SHE very well and that the proposed concept of joint operation of PV and HE power plants is real and possible. The application of such sustainable SHE systems could significantly increase PV industry worldwide, i.e. the share of solar energy in energy balances of numerous countries. Proposed hybrid simulation‐dynamic programming model is suitable to optimize PV plant in accordance with system characteristics. Copyright © 2009 John Wiley & Sons, Ltd.     

On the role of solar photovoltaics in global energy transition scenarios

The global energy system has to be transformed towards high levels of sustainability in order to comply with the COP21 agreement. Solar photovoltaic (PV) offers excellent characteristics to play a major role in this energy transition. The key objective of this work is to investigate the role of PV in the global energy transition based on respective scenarios and a newly introduced energy transition model developed by the authors. A progressive group of energy transition scenarios present results of a fast growth of installed PV capacities and a high energy supply share of solar energy to the total primary energy demand in the world in the decades to come. These progressive energy transition scenarios can be confirmed. For the very first time, a full hourly modelling for an entire year is performed for the world, subdivided in 145 sub‐regions, which is required to reflect the intermittent character of the future energy system. The model derives total installed solar PV capacity requirements of 7.1–9.1 TWp for the electricity sector (as of the year 2015) and 27.4 TWp for the entire energy system in the mid‐term. The long‐term capacity is expected to be 42 TWp and, because of the ongoing cost reduction of PV and battery technologies, this value is found to be the lower limit for the installed capacities. Solar PV electricity is expected to be the largest, least cost and most relevant source of energy in the mid‐term to long‐term for the global energy supply. Copyright © 2017 John Wiley & Sons, Ltd.