Lessons from a PV pumping programme in south Morocco

This paper presents the experience of a PV pumping project being carried‐out in the South of Morocco since 1997. At present, the project has reached 18 villages, affecting 15 000 people. Total involved photovoltaic power is 46 kW_p, and the total volume of pumped water since the installation of the systems approaches 0.7 × 10⁶ m³. About half the PV systems are based on dedicated inverters, while the rest are based on standard frequency drivers. Both perform very similarly in terms of both efficiency and reliability. Wells have been selected to provide good water taste, and pumped water is distributed to all the individual houses. Average daily water consumption in summer varies from 13 to 50 litres per person depending on ease of water access and ‚urban proximity’︁. The maintenance infrastructure is based on an agreement between the European supplier company and a local NGO, which is in charge of all the local organizations. Copyright © 2005 John Wiley & Sons, Ltd.     

Six‐element circuit for maximum power point tracking in photovoltaic‐motor systems with variable‐frequency drives

A low‐cost circuit was developed for stable and efficient maximum power point (MPP) tracking in autonomous photovoltaic‐motor systems with variable‐frequency drives (VFDs). The circuit is made of two resistors, two capacitors, and two Zener diodes. Its input is the photovoltaic (PV) array voltage and its output feeds the proportional‐integral‐derivative (PID) controller usually integrated into the drive. The steady‐state frequency–voltage oscillations induced by the circuit were treated in a simplified mathematical model, which was validated by widely characterizing a PV‐powered centrifugal pump. General procedures for circuit and controller tuning were recommended based on model equations. The tracking circuit presented here is widely applicable to PV‐motor system with VFDs, offering an efficient open‐access technology of unique simplicity. Copyright © 2010 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.     

Towards understanding consumption in multi‐user solar energy systems: the cases of villages in Argentina and Cuba

Research on the electrification of remote villages by means of decentralized renewable energy systems increasingly requires consideration of the characteristics of the user communities. Particularly for communities with multi‐user systems (MUS), in order to achieve optimal design and sizing of the system and efficient energy distribution among users, it is important to consider the social characteristics of the community in addition to technical and economic aspects. The solar energy supply is always limited, and distribution of the energy among the users is mainly a matter of coordinating who can use how much at what time, which is influenced by various factors. What we need first of all is knowledge of the actual power needs of each household over a period of time. With the aim of determining typical patterns of energy consumption in households with similar characteristics, the present preliminary research study uncovers the factors that determine energy consumption in five solar power villages in Cuba and Argentina. Correlation and regression analysis of data from surveys and energy consumption measurements showed that type and number of electrical appliances are the most important, but not sufficient, factors for explaining differences in household energy consumption. Demographic factors, occupations, daily routine and other social factors also have an impact on the development of a household's energy consumption. Copyright © 2004 John Wiley & Sons, Ltd.     

The character of power output from utility‐scale photovoltaic systems

Power produced by utility‐scale solar photovoltaic (PV) systems has fluctuations on both short and long time scales. Power spectral density (PSD) analysis provides information on the character of these power fluctuations. Examination of the correlation and step size of the power output between several PV sites within a multi‐site system allows assessment of geographic diversification for addressing intermittency. Both techniques provide insight into the characteristics of firm power and/or demand response required to accommodate large‐scale PV deployment. Copyright © 2007 John Wiley & Sons, Ltd.     

Sustainability of PV water pumping programmes: 12‐years of successful experience

This paper presents the key points to assure the sustainability of a PV water pumping program that has supplied 5 million m³ of water in the last 12 years to approximately 40 000 people. Key aspects for success have been the proper consideration of user's priorities, rigorous technical quality assurance, and maintenance structure set up. The present work mainly focuses on the maintenance structure aspects: some results to characterize the maintenance carried out, such as the mean time to failure parameter (MTTF) or the failure typology, are shown. Copyright © 2010 John Wiley & Sons, Ltd.     

Progress in markets for grid‐connected PV systems in the built environment

In the last decade of the 20th century a wide variety of promotion strategies increased the market penetration of small grid‐connected PV systems world‐wide. The objective of this paper is to assess the impact of these promotion strategies on the market for and on the economic performance of small grid‐connected PV systems. The most important conclusions of this analysis are: Pure cost‐effectiveness is not crucial for private customers. Affordability is rather what counts. Non‐monetary issues play an important role for a substantial increase in market deployment. Comprehensive accompanied information and education activities are also important along with financial incentives. There are still considerable barriers in the market: on the one hand transparent and competitive markets exist in only a few countries; on the other hand non‐monetary transaction costs still represent a major barrier. Progress with respect to cost reduction has been achieved, but mainly for non‐module components. Copyright © 2004 John Wiley & Sons, Ltd.     

Revitalization and analysis of operation of the autonomous photovoltaic system of the Uacari Floating Lodging House,Amazon‐Brazil

This paper presents the main problems found in photovoltaic systems in the Amazon Region and the actions to be performed for restructuring and correcting the operation of such systems. These problems and solutions are exemplified on the basis of the diagnosis and revitalization of the 2.5‐kWp photovoltaic installation that belongs to the central module of the Uacari Floating Lodging House. The paper was accomplished as part of the agreement between the Group of Studies and Development of Energy Alternatives (GEDAE) and the Mamirauá Institute of Sustainable Development to assess several photovoltaic facilities in the area covered by the institute. Concluding the paper, some operational results of the revitalized system are presented. Copyright © 2011 John Wiley & Sons, Ltd.     

The performance of PV‐t systems for residential application in Bangkok

This paper focused on the performance of photovoltaic‐thermal (PVT) systems working in Bangkok for residential applications. The PVT system is one which produces both electricity and low temperature heat at the same time. This paper investigated the performance of PVT systems that use different types of commercial solar PV panels. The characteristics of the PV panels were used as input parameters in the simulation. Each system comprises 2 m² of PVT collector area. Water draw patterns are those with a typical consumption of medium size houses in Bangkok, and the measured monthly average city water temperature of Bangkok has been used to estimate the energy output. The results show that the optimum water flow rate is 20 kg/h for all types of PVT collectors and the effect of water flow can improve the cell efficiency of PV cells. Moreover, the total energy output from the PVT collectors, which had glass covers is very significantly higher than those without one. The c‐Si PVT panel gave the best performance with the highest rate of primary energy reduction. The payback time of each system is 6.4, 11.8, and 13.4 years for a‐Si, mc‐Si, and c‐Si types of PVT system, respectively. This investigation concludes that from the viewpoint of system performance, c‐Si PVT is the most promising type than whereas from the viewpoint of economy, a‐Si PVT has the fastest payback time. Copyright © 2012 John Wiley & Sons, Ltd.     

Household energy use patterns and social organisation for optimal energy management in a multi‐user solar energy system

Multi‐user systems (MUS) for electrification of rural villages have specific advantages compared with individual systems (SHS). However, as MUS serve multiple consumers, shared energy use presents a challenging problem to the communities. Despite the increased performance of MUS over SHS, they still produce a limited amount of available energy, and users cannot consume as much electricity as they wish without considering the needs of the other users. This means that energy distribution among village residents has to be organised and energy consumption has to be controlled. There are different ways to achieve energy distribution. One possibility is to leave it to the users themselves to organise rational energy use according to their needs and daily routines. For the development of a self‐managed scheme, knowledge is required not only of the users' total energy consumption, but also of their individual energy use patterns. With knowledge of the community's energy consumption habits, rules for adequate energy use can be developed more accurately. The present study describes community energy management in a Cuban village using a central photovoltaic installation. Applying different methods, data were collected in order to identify individual energy use patterns and to investigate how villagers distribute energy and what rules of use are in effect. We wanted to find out whether their energy management leads to well‐adapted energy use patterns and reasonable system performance. The results show that the village residents have developed rules and agreements for coordination of their energy use that have led to good adaptation to the dynamics of energy production. Copyright © 2006 John Wiley & Sons, Ltd.     

Operational performance of grid‐connected PV systems on buildings in Germany

This paper presents operational performance results of grid‐connected PV systems in Germany, as collected and elaborated for the Photovoltaic Power Systems Programme (PVPS) of the International Energy Agency (IEA). Performance ratios obtained from 235 PV installations in Germany and from 133 PV plants in other countries are compared and discussed. For Germany, a significant rise in PV system performance and reliability was observed for new PV installations due to higher component efficiencies (e.g., inverter) and increased availabilities. There is a lack of long‐term experience in performance and reliability of PV systems, owing to the absence of monitoring programmes. As an outcome of IEA PVPS collaborative work, Task 2 provides reliable and worldwide monitoring performance data and results (www.task2.org). Technical and operational data is available for system planning and comparison, for teaching and training purposes as well as for future developments of financing schemes (e.g., feed‐in‐tariffs) in order to stimulate the PV market. Copyright © 2004 John Wiley & Sons, Ltd.     

Measurement and simulation of vibrations of PV‐modules induced by dynamic mechanical loads

The dynamic behavior of PV‐modules is analyzed by different methods. Outdoor measurements of the deflection show their dynamic behavior under wind loads and the correlation between wind velocity and mechanical deflection. Indoor tests were performed with acoustic excitation of the modules with monitoring of the deflection. The frequency range of the resonance frequencies of different modules was between 10 and 100 Hz. Numerical calculations, based on FEM‐modeling, yielded a very good agreement with the experimental results. Copyright © 2011 John Wiley & Sons, Ltd.     

Photovoltaic power plant experience at Arizona Public Service: a 5‐year assessment

Arizona Public Service (APS) currently has over 4·9 MW_dc of grid‐connected photovoltaic systems that have been installed in its service territory over the past five years. Most of this installed PV capacity is in support of the Arizona Corporation Commission Environmental Portfolio Standard goal that encourages APS to generate 1·1% of its energy generation through renewable resources by 2007, with 60% of that amount from solar. During this time, much has been learned regarding performance, cost, maintenance, installation and design. This paper presents an assessment of these topics and a perspective associated with this PV experience. Published in 2005 by 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.     

Assessment of the adequacy of EN ISO 15927‐4 reference years for photovoltaic systems

The long‐term performance prediction of photovoltaic systems requires representative meteorological data from a particular location. Among the numerous proposals in the field of solar energy, most of them include procedures oriented towards the generation of test reference years (TRYs). These synthetic years are composed of the concatenation of 12 actual months of the time series of meteorological measurements. Using TRYs to simulate the performance of different types of solar energy systems reduces the computational effort of the simulation and simplifies the analysis of the results. In this sense, the technical standard EN ISO 15927‐4 describes a procedure for constructing a reference year suitable for evaluation of the annual heating and cooling long‐term needs in buildings. In this work, the adequacy of the EN ISO 15927‐4 reference year for photovoltaic systems was studied. The electricity production obtained by simulation with this TRY was compared with that obtained by the Weather Year for Solar Systems. This latter reference year only uses the monthly thermal energy collected by the system as a selection parameter of typical months. This comparison was performed for seven locations in the USA considering two 5.6 kWp grid‐connected photovoltaic systems that only differ in the solar tracking system. The suitability of the EN ISO 15927‐4 reference year for the estimation of the electrical energy generated by a photovoltaic system has been proved, showing good results in the annual and daily predictions in most of the cases studied. Copyright © 2015 John Wiley & Sons, Ltd.     

Channel capacity per user in a power and rate adaptive hybrid DS/FFH‐CDMA cellular system over Rayleigh fading channels

The theoretically achievable average channel capacity (in the Shannon sense) per user of a hybrid cellular direct sequence/fast frequency hopping code‐division multiple‐access (DS/FFH‐CDMA) system, operating in a Rayleigh fading environment, was examined. The analysis covers the downlink transmission and leads to the derivation of a novel expression between the average channel capacity available to each system's user under simultaneous optimal power and rate adaptation and the system's parameters, providing an optimistic upper bound, useful for practical modulation and coding schemes. The final derived closed‐form expression can be useful for the design of the DS/FFH‐CDMA system because it provides a theoretical tool for the initial quantitative analysis. Finally, avoiding the application of complex theoretical algorithm or lengthy simulation, we theoretically derived numerical results to illustrate the presented analysis. Copyright © 2011 John Wiley & Sons, Ltd.     

Frequency resource allocation strategy with QoS support in hybrid cellular and Device‐to‐Device networks

Hybrid networks, comprising a conventional cellular network overlaid with Device‐to‐Device (D2D), offer efficient way to improve system throughput. In this paper, a novel orthogonal frequency‐division multiple access channel‐assignment method is proposed for hybrid network. The proposed approach is optimal in terms of throughput and is subjected to a sensible QoS requirement, which guarantees that macrocell and D2D achieve a prescribed data rate and outage probability, respectively. Our solution consists of two phases. In the first phase, the minimum sub‐channels are allocated to the macrocell to satisfy their data rate requirements. This problem is mapped to the 0‐1 Knapsack Problem and solved by integer programming based Lagrange dual approach. In the second phase, the redundant sub‐channels are allocated to D2D pairs to maximize the throughput of D2D networks. An interference management scheme is proposed to guarantee the outage probability of D2D communications. A cluster is taken as the unit for frequency reuse among D2D pairs. The problem of clustering is mapped to the MAX k‐CUT problem in graph theory and is solved by graph‐based heuristic algorithm. Extensive simulations demonstrate the superior performance of the proposed solution compared with the existing scheme. Copyright © 2014 John Wiley & Sons, Ltd.     

System memory effects in the sizing of stand‐alone PV systems

Models based on daily energy balance (or long‐term models) have been widely used as a tool in the stand‐alone photovoltaic (PV) system sizing, mainly with the purpose of obtaining analytical expressions of the relation between the generator size and the storage capacity of the battery. The system can then be designed to meet the reliability requirements of the specific case. However, such models represent the complex operation of a stand‐alone system in an oversimplified way. There is little research so far on the reliability and improvement of such models. Validation and possible modification of a long‐term system model requires comparison of the simulated state of charge (SOC) of the battery with that obtained from an experimental system. In this work, experimental data from a 6‐month operation of a basic stand‐alone PV system have been analysed and compared with modelling results. One obvious improvement that could be applied to the long‐term system model is to account for a charging efficiency of the battery, and this possibility is examined in the present work. However, comparison with the modelling results shows that the data cannot be fitted by simply taking into account battery inefficiency. A method to account for system memory effects in the increase of the battery SOC, imposed by the operation of the regulator, is necessary to accurately model the macroscopic diurnal charging/discharging process. Copyright © 2012 John Wiley & Sons, Ltd.     

CDNPatch: a cost‐effective failover mechanism for hybrid CDN‐P2P live streaming systems

Among the most well‐established live media distribution technologies is content delivery network (CDN), which improves user‐perceived quality of service by delivering content from proxy servers deployed at the Internet's edge. In recent years, CDN providers started to tap into their subscribers' peer‐to‐peer (P2P) capacity to alleviate their server costs. Under the inherent peer dynamics, a major challenge of these hybrid CDN‐P2P systems is to provide efficient failure recovery with good quality of service guarantees at a reduced server cost. In this work we propose a cost‐effective failover solution named CDNPatch to address the aforementioned problem. CDNPatch enables peers to periodically precompute a few backup content suppliers by efficient information exchange and maintenance algorithms, and leverages auxiliary CDN servers and an economic server provisioning algorithm to reduce the chance of playback interruption occurring to peers. Our simulation results show that CDNPatch can mask the impact of peer dynamics of 3 real P2P systems, namely, SOPCast, PPStream, and PPTV, with 100 % failure recovery success rate and a failure recovery time less than 1 second at a cost of small P2P communication overhead of less than 1 kilobits per second, while using only 10%, 21%, and 51%, respectively, of the pure CDN scheme's server consumption.     

Life cycle assessment and cost analysis of very large‐scale PV systems and suitable locations in the world

Although the Sahara region has a high potential for solar power plants, the amount of installed photovoltaic (PV) system remains relatively low. This paper aims to evaluate these potentials of PV system installation in terms of environmental and economic viewpoints with indices of cost, energy, and greenhouse gas (GHG) emission. Two 1‐GW very large‐scale PV systems are simulated at Ouarzazate in Morocco and at Carpentras in France. The evaluation was performed using life cycle assessment. The lowest energy consumption and GHG emission are obtained while assuming cadmium telluride module. The result of our simulation shows that energy payback time is 0.9 years and CO₂ emission rate is 27.4 g‐CO_2‐eq/kWh in the Ouarzazate case. In cost estimation, generation costs are 0.06 USD/kWh in Ouarzazate and 0.09 USD/kWh in Carpentras in the case of 3% interest rate and 0.5 USD/W for multicrystalline silicon PV module price. In addition, by adapting 15% internal rate of return for 20% of budget, the generation costs become 0.09 USD/kWh in Ouarzazate and 0.13 USD/kWh in Carpentras under the same condition. Furthermore, the selection for suitable locations to install solar power plants in term of GHG emission is identified using geographical information system. Very high‐potential locations (lower than 38 g‐CO_2‐eq/kWh) could be obtained in North Chili, east and west Sahara, and Mexico. Copyright © 2015 John Wiley & Sons, Ltd.