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Ageing of a wind turbine and its components is inevitable. It will affect the reliability and power generation of the turbine over time. Therefore, performing the ageing assessment of wind turbines is of significance not only to optimize the operation and maintenance strategy of the wind turbine but also to improve the management of a wind farm. However, in contrast to the significant number of research on wind turbine condition monitoring and reliability analysis, little effort was made before to investigate the ageing led performance degradation issue of wind turbines over time. To fill such a technology gap, four SCADA-based wind turbine ageing assessment criteria are proposed in this paper for measuring the ageing resultant performance degradation of the turbine. With the aid of these four criteria, a reliable information fusion based wind turbine ageing assessment method is developed and verified in the end using the real wind farm SCADA data. It has been shown that the proposed method is effective and reliable in performing the ageing assessment of a wind turbine. [ABSTRACT FROM AUTHOR]

As wind energy production increases, reliability and fault-tolerant operation capability of wind energy systems are becoming more important. Modern wind energy production systems use power electronic converters which are unfortunately proved to be one of their most fragile parts and responsible for most of the system downtime. Real-time fault monitoring, fault diagnosis and proper system reconfiguration in these converters are therefore mandatory for fault-tolerant operation of the converter and the whole system. In this paper, a comprehensive fault-tolerant power electronics interface for wind energy systems with doubly-fed induction generators is presented and validated. The same power production capability will be guaranteed. The proposed solution also includes a robust and very fast open-circuit switch fault diagnosis algorithm, which is not sensitive to the operation conditions and is therefore suitable for this application. Simulation, Hardware in the Loop validation and experimental tests are carried out to demonstrate the effectiveness of the proposed approach. [ABSTRACT FROM AUTHOR]

The use of wind-power generation (WPG) increases supply-side variability, and hence reduces the reliability of power generation. Even if WPG is forecasted to deal with such a problem, the uncertainty of WPG cannot be fully resolved because of its randomness and intermittent nature. This paper proposes a two-step energy-storage system (ESS) sizing and operation strategy for enhancing the WPG reliability. From the analysis of WPG data, it is determined that the uncertainty that leads to deterioration in reliability affects the instantaneous changes in WPG significantly. In this regard, ESS sizing and operation strategies are designed based on the frequency-domain analysis using the discrete Fourier transform (DFT). The ESS sizing is firstly determined to filter out high-frequency components, and the ESS operation is determined considering the ESS sizing constraints for reducing the difference between the actual WPG and its forecasting. A case study is presented using the data from a large-scale wind farm with 4782 MW total capacity of 42 plants located in Columbia River Gorge, United States. The numerical results obtained demonstrate that the proposed ESS method can reduce the root-mean-squared error by up to 26% and further reduce by about 3% compared to the conventional method with the ESS. [ABSTRACT FROM AUTHOR]

Wind power producers are getting ready to participate in electricity markets as well as conventional units. This poses challenges to power system operators. Wind speed forecasting error increases power imbalance at real time operation, and hence, profits of wind power producers decrease due to balancing costs. A recently proposed scheme for reducing wind power plants power imbalance and increasing their profits is to team up each wind power producer with a non-wind generating firm. The joint firm participates in the market by bidding the joint supply function as a single unit. The objectives of this paper are 1) improving the efficiency of this scheme by considering both benefits and losses of positive and negative balancing prices, 2) determining the optimal generation capacity for the joined firm for maximum profitability of the scheme, and 3) performing sensitivity analysis on different parameters to determine the range of profitability of the scheme in different conditions. In order to evaluate the efficiency of the model, behavior of other generating firms should be known. To this end, supply function equilibrium model is used to determine the optimal behavior of generating firms considering their interactions. Performance of the improved scheme is discussed using a test system. [ABSTRACT FROM AUTHOR]

In developing countries, mini-grids are seen as an important option to improve electrification rates in rural areas. In order to be successful, mini-grids face issues of operation and sizing of generation capacities. Current studies on the optimal sizing of mini-grids do not include capacity expansion feedbacks regarding the operator's or investor's long-term economic performance on growth in electricity usage, e.g. gap between demand and supply impacting the operator's income. Using a System Dynamics model, this paper compares the impact from two capacity expansion strategies on rural mini-grid operator's long-term economic performance. The two capacity expansion strategies are: a strategy with minimized costs and a strategy where only diesel power is allowed. Research shows that a cost-minimized capacity expansion strategy might not be the most beneficial solution for the operator's long term financial performance. Specifically, the high investment costs prohibit the implementation of the cost-minimized expansion strategy. In addition, the diesel-only expansion strategy suffers from high operational costs, which creates long-term challenges as the share of diesel increase. Therefore, the timeline of the investments and when to implement different strategies is important, creating a benefit for a System Dynamics approach. [ABSTRACT FROM AUTHOR]

This paper deals with the sizing and rough optimization of a renewables-based farm devoted to energy production in a stand-alone marine context. The studied hybrid farm consists in combining wind turbines, tidal turbines, diesel generators, and pumped hydroelectric storage. The main sizing and optimization constraint is to achieve a compromise between the hybrid system overall cost, for a period of 15 years, and the CO 2 emission minimization. The proposed sizing and optimization study is first based on the different available renewable sources, wind and tidal currents, characterization. This preliminary study is essential. Indeed, it will provide the renewables sources basic information in terms of wind and tidal speed potential for the hybrid farm components choice. After presenting the hybrid farm different components, the simulation constraint is defined (energy conservation at the grid) in order to form a power exchange network at the grid level but in a stand-alone context. The optimization results are analyzed to explore wind turbines, tidal turbines, and the proposed pumped hydroelectric storage sizes on the targeted objectives. [ABSTRACT FROM AUTHOR]

Operations and maintenance costs of the wind power generation systems can be reduced through the implementation of opportunistic maintenance policies at suitable indenture and maintenance levels. These maintenance policies take advantage of the economic dependence among the wind turbines and their systems, performing preventive maintenance tasks in running systems when some other maintenance tasks have to be undertaken in the wind farm. The existing opportunistic maintenance models for the wind energy sector follow a static decision making process, regardless of the operational and environmental context. At the same time, on some occasions policies do not refer to practical indenture and maintenance levels. In this paper, a maintenance policy based on variable reliability thresholds is presented. This dynamic nature of the reliability thresholds, which vary according to the weather conditions, provides flexibility to the decision making process. Within the presented model, multi-level maintenance, capacity constraints and multiple failure modes per system have been considered. A comparative study, based on real operation, maintenance and weather data, demonstrates that the dynamic opportunistic maintenance policy significantly outperforms traditional corrective and static opportunistic maintenance strategies, both in terms of the overall wind farm energy production and the Life Cycle Cost. [ABSTRACT FROM AUTHOR]

Accurate wind speed prediction is a significant factor in improving and optimizing wind power production. Particularly, reliable short-term wind speed forecasting contributes to the real-time optimization of wind farm operation. However, this short-term forecasting task remains challenging due to the strong stochastic nature and dynamic uncertainty of wind speed. This paper proposes a hybrid model that consists of the Empirical Wavelet Transform (EWT), Expectation Propagation (EP) algorithm and Gaussian process regression with the Student- t Observation Model (GPR -t ) for short-term wind speed forecasting. The proposed approach firstly extracts meaningful information from a short-term wind speed series and subsequently models the inherent uncertainty and the dynamic features of the wind speed time-series. Additionally, the wind speed series presents a time-varying characteristic. Thus, this study adopts a moving window approach in the prediction processes, thereby permitting the proposed model to respond quickly to the dynamic characteristic of wind speed. To examine the forecasting performance of the suggested hybrid model, the validation of the proposed model is performed against several other existing models with half-hour and hourly wind speed data obtained from a windmill farm located in northwestern China. The computational results demonstrate that the proposed hybrid approach generates satisfactory point predictive accuracy and interval forecasting performance. [ABSTRACT FROM AUTHOR]

Tidal energy is one of promising solutions for reducing greenhouse gas emissions and it is estimated that 100 TWh of electricity could be produced every year from suitable sites around the world. Although premature gearbox failures have plagued the wind turbine industry, and considerable research efforts continue to address this challenge, tidal turbine gearboxes are expected to experience higher mechanical failure rates given they will experience higher torque and thrust forces. In order to minimize the maintenance cost and prevent unexpected failures there exists a fundamental need for prognostic tools that can reliably estimate the current health and predict the future condition of the gearbox. This paper presents a life assessment methodology for tidal turbine gearboxes which was developed with synthetic data generated using a blade element momentum theory (BEMT) model. The latter has been used extensively for performance and load modelling of tidal turbines. The prognostic model developed was validated using experimental data. [ABSTRACT FROM AUTHOR]

Pumped storage power plants are key components to stabilize electric distribution networks with high amount of intermittent power sources as, e.g., solar and wind power plants. Tailored mathematical models are important for the transient and the stationary analysis of such plants. A comprehensive mathematical model of a variable speed operated pumped storage power plant, which incorporates reversible pump turbines in combination with doubly fed induction machines, is developed in this paper. Special emphasis is laid on an accurate description of important dynamic effects (e.g., water hammer) and of the energy losses of the system. Based on this model, optimal stationary operating points are determined, which minimize the overall system losses and systematically take into account the operating constraints. [ABSTRACT FROM AUTHOR]

Electricity generated using photovoltaic system can only be commercial if the photovoltaic modules operate reliably for 20–25 years under field conditions. Understanding the performance degradation of photovoltaic modules is critical for optimizing its financial viability. Performance degradation of photovoltaic modules is due to multiple factors such as installation site and module technologies. In order to gain insight on performance degradation of crystalline silicon PV technology in harsh environment, a degradation effects study of c-Si photovoltaic modules in desert environment was carried. The main contribution of this paper is focused on the evaluation of c-Si PV modules performance that operated in extreme environmental conditions. This evaluation usually consists of I-V curve field measurements and visual inspections. [ABSTRACT FROM AUTHOR]

This paper proposes an analytic dispatch for tidal power plants that centralizes the discharge period in the tides extremes. Since the tide cycles are well predicted by a sinusoidal function, this method provides an accurate power generation as shown in the comparative tests. Furthermore, an optimal generation estimation method is derived considering that all stored water is discharged during the tides extremes, i.e., discharging at maximal water head. This method calculates a more realistic maximal power generation, which is especially simple in double-effect operation mode (power production in ebb and flood tides), since the reservoir geometry is not explicitly considered. The proposed methods are compared with a classical analytic solution and an optimal dispatch formulation. [ABSTRACT FROM AUTHOR]

Abstract: Recent changes in the operation and planning of power systems have been motivated by the introduction of Distributed Generation (DG) and Demand Response (DR) in the competitive electricity markets' environment, with deep concerns at the efficiency level. In this context, grid operators, market operators, utilities and consumers must adopt strategies and methods to take full advantage of demand response and distributed generation. This requires that all the involved players consider all the market opportunities, as the case of energy and reserve components of electricity markets. The present paper proposes a methodology which considers the joint dispatch of demand response and distributed generation in the context of a distribution network operated by a virtual power player. The resources' participation can be performed in both energy and reserve contexts. This methodology contemplates the probability of actually using the reserve and the distribution network constraints. Its application is illustrated in this paper using a 32-bus distribution network with 66 DG units and 218 consumers classified into 6 types of consumers. [Copyright &y& Elsevier]

Abstract: Many candidate sites for tidal stream power extraction are tidal channels, and the power that can be generated from these sites will be directly related to the amplitude and phase of the principal tidal constituents driving flow through the channel. This paper investigates this interaction between energy extraction and tidal constituents, and also the effect that power extraction may have on harmonics of the principal constituents (i.e. compound tides and overtides). Firstly, the variation in power extraction and available power (defined as the fraction of extracted power removed by idealised tidal turbines) are investigated over a spring/neap tidal cycle using a simple theoretical model. Results from the model are used to derive analytical bounds to the variation in power at spring and neap tide. These bounds are shown to depend on the channels natural dynamic balance and are of practical importance to tidal stream device developers looking to supply power to the electricity grid. Secondly, changes in the higher harmonics in channel flow rate are investigated for deployments of tidal farm in channels of various length and geometry. Specifically, it is shown that in general if the turbines provide a uniform drag resistance to the flow through the channel, even harmonics in the flow rate will decay with power extraction (leading to a more symmetric tide), whilst odd harmonics in the flow rate may decay or increase depending on the natural tidal dynamics. These variations can have significant effect on residual flows and the local environment. Throughout the paper results from the theoretical model are compared with a complex numerical model of energy extraction from the Pentland Firth. Good agreement is shown in all cases. [Copyright &y& Elsevier]

Abstract: In order to stabilize water supply for remote regions and deserts, it is not only necessary to improve the power generation system, but also to improve its maintenance strategy. Photovoltaic pumping systems need to be maintained periodically. Both maintenance efficiency improvement and reduction of its cost are desired. Augmented Reality (AR) is one of the promising technologies that will be able to improve efficiency in maintenance and reduce human errors. AR expands the surrounding real world by superimposing computer-generated information on a user’s view. It presents the information more intuitively than the legacy interfaces such as paper-based instruction documents. In this paper, an augmented reality platform for photovoltaic pumping system maintenance tasks is proposed. In order to locate the repairer in the working environment and then to overlay the virtual objects, a tracking method is developed. A scenario which takes a user by the hand through maintenance tasks is described. Experiments are conducted in order to evaluate the accuracy and reliability of the proposed tracking method. [Copyright &y& Elsevier]

Abstract: This paper deals with the numerical modeling of a catenary moored spar-type wind turbine in the integrated coupled analyses. The current spar-type wind turbine is inspired by the Hywind concept. In this paper, different hydrodynamic models based on the Morison formula, Pressure integration method and Panel method considering the mean drift, first and second order forces are studied. A floating wind turbine in deep water depth supporting a 5-MW turbine system is considered. Simo-Riflex (DeepC), HAWC2 and FAST codes are used to carry out the coupled wave–wind-induced analyses. The results show that the damping and inertia forces of the mooring lines are important for the tension responses; especially, the damping of the mooring lines can help to damp-out the high-frequency elastic-deformations of the mooring system. However, the motion responses are not significantly affected by the mooring line damping-effects. The drift and second order forces do not significantly affect the motion and tension responses. However, the heave motion is more affected by the drift and second order forces. The results indicate that either the Morison formula considering the instantaneous position of the structure or first order hydrodynamic forces based on the Panel method and considering the quadratic viscous forces can provide accurate results for the slender spar-type wind turbines. Considering the second order forces is found to be 10–15 times more time consuming while the responses are not significantly affected for the present floating wind turbine. The coupled aero-hydro-servo-elastic code-to-code comparison of HAWC2 and FAST codes shows that the dynamic motion responses, structural responses at the tower–spar interface and at the blade root as well as the power production are in good agreement. [Copyright &y& Elsevier]

Abstract: This paper assesses the potential of harnessing solar radiation in different regions of Iran. In this regard, solar radiation maps are generated for five different cases: total radiation on a south facing fixed surface tilted at the latitude angle; total radiation on a surface tilted at the latitude angle with East–West tracking; total radiation on a surface tilted at the latitude angle with azimuth tracking; direct beam radiation on a horizontal surface with East–West tracking; and direct beam radiation on a surface with two axis tracking. The first three cases are generally applicable to photovoltaic (PV) power plants while the last two are generally used for concentrating solar power (CSP) plant design. In the second part of the paper, a 5 MW PV power plant is considered for 50 cities of Iran. Capacity factors, electricity generated and annual greenhouse gases emission reductions are compared. The results show a great potential for central and southern parts of the country. [Copyright &y& Elsevier]

Abstract: The variability of renewable energy is widely recognised as a challenge for integrating high levels of renewable generation into electricity systems. However, to explore its implications effectively, variability itself should first be clearly understood. This is particularly true for national electricity systems with high planned penetrations of renewables and limited interconnection such as the UK. Variability cannot be considered as a distinct resource property with a single measurable parameter, but is a multi-faceted concept best described by a range of distinct characteristics. This paper identifies relevant characteristics of variability, and considers their implications for energy research. This is done through analysis of wind, solar and tidal current resources, with a primary focus on the Bristol Channel region in the UK. The relationship with electricity demand is considered, alongside the potential benefits of resource diversity. Analysis is presented in terms of persistence, distribution, frequency and correlation between supply and demand. Marked differences are seen between the behaviours of the individual resources, and these give rise to a range of different implications for system integration. Wind shows strong persistence and a useful seasonal pattern, but also a high spread in energy levels at time scales beyond one or two days. The solar resource is most closely correlated with electricity demand, but is undermined by night-time zero values and an even greater spread of monthly energy delivered than wind. In contrast, the tidal resource exhibits very low persistence, but also much greater consistency in energy values assessed across monthly time scales. Whilst this paper focuses primarily on the behaviour of resources, it is noted that discrete variability characteristics can be related to different system impacts. Persistence and predictability are relevant for system balancing, whereas statistical distribution is more relevant when exploring issues of asset utilisation and energy curtailment. Areas of further research are also identified, including the need to assess the value of predictability in relation to other characteristics. [Copyright &y& Elsevier]

Abstract: This paper presents a new methodology to accurately characterize and predict the annual variation of wind conditions. The estimate of the distribution of wind conditions is necessary to quantify the available energy (power density) at a site, and to design optimal wind farm configurations. A smooth multivariate wind distribution model is developed to capture the coupled variation of wind speed, wind direction, and air density. The wind distribution model developed in this paper avoids the limiting assumption of unimodality of the distribution. This method, which we call the Multivariate and Multimodal Wind Distribution (MMWD) model, is an evolution from existing wind distribution modeling techniques. Multivariate kernel density estimation, a standard non-parametric approach to estimate the probability density function of random variables, is adopted for this purpose. The MMWD technique is successfully applied to model (i) the distribution of wind speed (univariate); (ii) the joint distribution of wind speed and wind direction (bivariate); and (iii) the joint distribution of wind speed, wind direction, and air density (multivariate). The latter is a novel contribution of this paper, while the former offers opportunities for validation. Both onshore and offshore wind distributions are estimated using the MMWD model. Recorded wind data, obtained from the North Dakota Agricultural Weather Network (NDAWN) and the National Data Buoy Center (NDBC), is used in this paper. The coupled distribution was found to be multimodal. A strong correlation among the wind condition parameters was also observed. [Copyright &y& Elsevier]

Abstract: In this paper, an artificial neural network (ANN) is used for the generation of ambient temperature hourly time series for some Spanish locations. The model was trained and tested with ten locations and different years of data. Results show that the proposed artificial neural network provides a better approach than other methods. The aim of this paper is to provide a complete description of this ANN so that, it can be used by anyone avoiding all the design, training and testing process again. [Copyright &y& Elsevier]

Abstract: The increasing interest among architects and planners in designing environmentally friendly buildings has led to a desire to explore and integrate renewable sources of energy. Roof mounted wind turbines is a technology that presents a high potential for integration within the built environment. However, there is a state of uncertainty regarding the feasibility of these wind turbines. This paper argues that part of this uncertainty is attributed to uninformed decisions about positioning and locating urban wind turbines. This is underpinned by lack of consideration to the accelerating effect of different roof shapes, buildings'' heights and surrounding urban configurations. This paper aims to present the results of Computational Fluid Dynamics (CFD) simulations for the purpose of identifying the effect of different roof shapes on the energy yield and positioning of roof mounted wind turbines covering different buildings'' heights within different urban configurations under different wind directions. Results from this investigation suggest that an increase in energy yield could be achieved which can reach 56.1% more electricity in the case of a vaulted roof if an informed wind assessment above buildings'' roofs is carried out. [Copyright &y& Elsevier]

Abstract: The effect of blade flutter and electrical loading on the sound level of two different size wind turbines was investigated at the Conservation and Production Research Laboratory near Bushland, TX. Data were collected on two blade designs tested on a wind turbine rated at 1 kW, and there also was a third blade tested on an improved version of the same wind turbine. The 1 kW wind turbines were used for off-grid water pumping. If the 1 kW wind turbines were electrically loaded, the start of blade flutter was delayed from 700 to 900 rpm when the blade length was reduced 9.2%, and no blade flutter occurred when the shorter fiberglass blades were stiffened. However, if there was no electrical load (e.g. offline), the shorter stiffer blades would start to flutter at 1050 rpm. For the 10 kW wind turbine, two blade designs were tested for off-grid water pumping, and a third blade design was tested on a utility grid-tie system. The original blades fluttered when the 10 kW off-grid wind turbine was offline at a rotor speed of 260 rpm, but the second blade design (different airfoil) appeared to never flutter at any rotor speed when offline. For the 10 kW wind turbine, the sound emission of the second blade design was approximately the same as that of the third blade design – both had lower sound emissions than the original blade design. Blade flutter increased the average sound power level on the 1 kW wind turbine 15–20 dB and on the 10 kW wind turbine 5–7 dB. A procedure was developed which allowed the best blade design for sound emission to be identified even though the microphone measurement position varied (due to different tower heights) and electrical loading was different (on-grid, off-grid, or offline). This paper should be of help to design engineers interested in designing wind turbines with a lower sound emission, and test engineers collecting and analyzing sound level data of existing wind turbines. This paper may also help in the validation of computer codes that are used to predict whether blade flutter will occur on large MW size wind turbines. [Copyright &y& Elsevier]

Abstract: An original proposal for the deployment of photovoltaic (PV) systems in offshore environments is presented in this paper. Crystalline PV panels are considered where they are deployed on pontoon type structures and there are six case study examples precedent practise of such deployments in lakes and reservoirs (but not seas). The authors put forward an alternative based on flexible thin film PV that floats directly on the waterline. The paper then concentrates on the techno-economic appraisal of offshore PV systems in comparison to conventional marine renewable energy technologies. The difficulties of comparing offshore technology projects developed in various countries, using different currencies and in different years are overcome so that such comparisons are made on an equitable basis. The discounted cost of electricity generated by each scheme is determined, including capital expenditure (CAPEX) and yearly operation and maintenance (O&M) costs. Actual wind, tidal (current turbines and barrages) and wave projects were considered in the analysis alongside crystalline and thin film PV. Thin film PV was found to be economically competitive with offshore wind energy projects for latitudes ranging from 45°N to 45°S. The specific yield, assessed in terms of GWh/km2 was higher for thin film PV than for wind, wave and tidal barrage systems. In addition the specific installed capacity, expressed in MW/km2 was also higher than the other conventional technologies considered (excluding tidal current turbines). [Copyright &y& Elsevier]

Abstract: With the increasing penetration of renewable energy into energy market, it is urgent to solve the problem of fluctuations of renewable energy sources (RES). Energy storage technology is regarded as one method to cope with the unstable nature of RES. One of these technologies is compressed air energy storage (CAES), which is a modification of the basic gas turbine technology. Electric power supplied by CAES can meet peak-load requirement of electric utility systems. Because there is heat waste in the existing CAES systems during compression process, fossil fuels are used to improve the expansion work to generate peak power. In order to avoid the use of fuels and keep high efficiency of system, CAES system with thermal energy storage (TES) is designed to capture and reuse the compressed air heat. This paper uses a thermodynamic model of a CAES system with TES to analyze the effect of TES on system efficiency. Besides, this paper evaluates the influence of temperature and pressure on the utilization of heat in TES. Results show that even when power efficiency reaches maximum, there is still a proportion of thermal energy left in TES for other use. Meanwhile, the utilization of heat in TES can be affected by pressure in the air storage chamber. With appropriate selection of pressure limits, the utilization of compressed air heat can be optimized. [Copyright &y& Elsevier]

Abstract: Cyprus is planning to develop in the next few years one solar thermal power plant with a capacity of about 50 MW. Therefore, in this paper solar power systems are analyzed with respect to their technical characteristics, the cost of electricity produced and the land area required. The latter is very important for Cyprus as seaside areas are very expensive. Such a solar power station however should be located near the sea close to an existing power station. An additional reason is that such a solar plant can be combined with solar desalination to produce fresh water from seawater which is also a precious commodity for Cyprus. Based mainly on their industrial maturity and the advantages mentioned in this paper, the parabolic trough system seems to be to best one to apply. From a preliminary investigation of the various possible areas the author believes that the Vasilikos area near to the existing Vasilikos power station is the most suitable for such a system to be installed. [Copyright &y& Elsevier]

This paper proposes a mathematical model for a solar Dish/Stirling system. Firstly, it is presented a methodology to calculate the appropriate angles and characterize the solar tracking control system for the city of Itajubá-MG/Brazil, in order to maximize the heat flow on the cavity of the receiver. Secondly, it was developed an algorithm for sizing and to determine the effects of opto-geometric parameters on the overall efficiency of the Dish/Stirling system. The model allows defining different configurations and geometric distances between the concentrator and the receiver, in order to obtain the desired heat in the receiver cavity. Finally, it is carried out a thermal balance for the evaluation of the maximum efficiency and overall efficiency of the system. The results obtained for a concentrator with a diameter of 10.5 [m] and solar irradiation of 1000 W/m 2 are: theoretical maximum working temperature in the receiver surface of 1596 K and a maximum thermal efficiency of 68%. It is observed that for collectors between 10 and 20 m of diameter, the overall efficiency variation is not significant (23–25%), since the variation of the temperature of the receiver and the thermal losses in the cavity are minimal for the evaluated conditions. [ABSTRACT FROM AUTHOR]

The optimal design of a wind farm with the aim of increasing the exploitation rate and power production is one of the challenging problems in the field of renewable energies. In this paper, the effect of using different hub height wind turbines in a farm on total power is studied. An exact mathematical formulation is presented in terms of the interaction matrix for multi-turbine wake effects considering different hub height wind turbines, and a new mixed-integer quadratic optimization model is developed. Then, the model is generalized to include the changes in wind characteristics and uncertain parameters. The model is solved using the linearization technique and an iterative method. The performance of the model and solution algorithm is evaluated by solving different problems borrowed from the literature. The computation results show the possibility of having a high-quality solution in a reasonable time in almost all cases. [ABSTRACT FROM AUTHOR]

The repowering of already installed wind farms is considered one of the most promising and cost-effective short-term strategies to scale-up wind capacity. In this study, we apply Markowitz's mean-variance (MV) portfolio optimization theory to explore alternative repowering actions in Spain. The efficient portfolios – a direct outcome of the MV optimization – offer optimal repowering alternatives to current wind farm generation mixes. They deliver the highest possible average power output (yield) for a given level of supply risk. Different repowering scenarios are considered in this paper that range from a full restructuring of the existing wind generation mix to restricting by certain amounts the percentage of down-/uprating of each reference region. Results show that, depending on the configuration of the MV portfolio optimization problem, hourly fluctuations in the aggregate power supply can be reduced as much as 12–31%, while retaining the current level of energy productivity. In addition, for the level of energy supply risk experienced with the existing portfolio of Spanish wind farms; we can derive more efficient mixes that boost-up productivity by 16–55%. This work aims at providing valuable insight for energy policy-making in the direction of optimally repowering future renewable generation. [ABSTRACT FROM AUTHOR]

Currently, two maximum power point tracking (MPPT) units are used in hybrid photovoltaic (PV)/fuel cell (FC) systems, one for the PV subsystem and the other one for the FC stack, which significantly complicates the system implementation, and increases cost. This paper addresses this problem by presenting a novel fast and highly accurate unified MPPT technique for extracting maximum output power from hybrid PV/FC energy conversion systems. It is the only unified MPPT technique reported in the literature that uses a single algorithm to concurrently track the maximum power points (MPPs) of both PV module and FC stack used in a hybrid PV/FC system. A hybrid PV/FC energy conversion system has been built to evaluate the performance of the method. It is experimentally verified that the proposed MPPT method performs a very fast and highly accurate MPPT process, so that, the MPPT efficiency in the PV and FC subsystems is more than 99.60% and 99.41%, respectively, along with a very short convergence time of at most 12 ms and 33 s, respectively. Comparison between the MPPT method presented in this work and the state-of-the-art MPPT methods has been also performed that explicitly demonstrates the method has the highest MPPT efficiencies (99.60%, and 99.41%) along with the shortest convergence time (12 ms) compared to the state-of-the-art MPPT methods, while it concurrently performs two tasks (tracking two MPPs) but others perform only one task (tracking one MPP). [ABSTRACT FROM AUTHOR]

Corrective maintenance and time-based maintenance have been widely employed in wind farms. However, the actual maintenance strategy is much more complex and diverse, and also maintenance actions do not always return the system to “as good as new” condition. Moreover, dependencies exist in multi-component systems, and it is more economical to perform preventive maintenance whenever a repair opportunity presents itself. For an opportunistic maintenance strategy, when the system is shut down for maintenance, the maintenance time of other still functioning parts can be moved up to take advantage of the huge downtime losses. In this paper, an opportunistic maintenance approach is proposed for wind turbines considering an imperfect maintenance schedule that is based on reliability. A hybrid hazard rate model is used to describe imperfect maintenance and explain the effects of corrective maintenance action. Comparative examples are used to illustrate the economic advantages of opportunistic maintenance. Simulation results demonstrate the impact that various maintenance costs (fixed downtime cost and preventive replacement cost) have on the economic benefit of opportunistic maintenance strategy. The simulation analysis also provides the optimal opportunistic maintenance reliability threshold using the fruit fly optimization algorithm to provide guidance for the actual operation and maintenance of wind farms. [ABSTRACT FROM AUTHOR]

Abstract: Wave energy is increasingly being seen as an alternative source of low-emissions power particularly for Australia, as Australia has abundant wave resources. This paper, using the performance characteristics of wave energy converters (WEC), resource measurements along Australia''s southern coastline and global resource estimates, models projections of the future uptake of wave energy globally and in Australia. Globally, wave farms are projected to be installed up to a presumed maximum limit of 500 GW. In Australia there is more variability in the amount of wave farms installed, with differences across the different WEC. The outcome globally and in Australia depends on variations in the average power generated by the WEC and the carbon price path. In Australia, the majority of projected WEC installations are in the state of Victoria, which has relatively high demand and currently highly-emissions intensive sources of generation compared to states with better wave resources. When a dispatchable, or continuous power ability is added to wave energy''s output the uptake of wave energy increases in Australia, in those states with the best resources. When the amount of wave energy extractable in any region is increased or decreased it has a large effect on output in Victoria in particular, which generates power from wave energy up to 30% of the total extractable resource under the dispatchable power scenario. Wave energy has the potential to make a significant contribution to electricity generation globally and in Australia. This paper is part two of a series of papers, the first being . [Copyright &y& Elsevier]

Abstract: In recent years, growing attention has been paid to the use of renewable resources to produce electricity. One of the main drawbacks of generating electricity through wind power is the randomness of input, which obviously results in a random output of energy. This means that peak output does not always coincide with peak demand. Nevertheless, demand drives prices, making output regulation essential. Thus, improvements in energy management aimed at satisfying demand and increasing profits need to include output regulation mechanisms. This calls for the introduction of new equipment for energy storage and new management strategies. This paper presents a simulation model, which incorporates the important equipment that compose the wind-H2 energy system (wind turbines, inverters, electrolysers, H2-storage tank, fuel cells,…) and the random elements of the stochastic environment in which the energy system evolves (wind speed, wind speed forecast error and electricity prices). The main contribution of the paper is to present and analyze a set of new proposed management policies named “peaking strategies”, which are based on the conversion of electricity into hydrogen during price troughs and the use of the stored hydrogen to produce electricity during the day''s demand (thus price) peaks. We present a very flexible set of management policies with different levels of participation of the decision maker: some decisions can be made by the decision maker while leaving others to optimization processes. To achieve such a decision framework we break down the management policy into a set of decisions with different time horizon (strategic, tactical and operational decisions). [Copyright &y& Elsevier]

Abstract: Frequent tropical cyclones pose great risks and obstacles to the development of offshore wind farms in the coastal regions of China and other areas in the Pacific, where development of wind energy is gaining momentum. This paper aims to identify and evaluate the economic risks of tropical cyclones on offshore wind farms within the Economic Exclusive Zone (EEZ) of China and help improve decision-making for planners and investors. The risks of tropical cyclone impact in this paper are defined by the statistical extreme wind climate and the annual expected economic losses of offshore wind farms. A probabilistic tropical cyclone event model is applied to evaluate 20-year, 30-year, 50-year and 100-year recurrence of extreme wind speeds by geographical location. Combining a damage model derived from empirical loss data and an investment cost model within a Geographical Information System (GIS), the annual expected economic losses of offshore wind farms from tropical cyclones are evaluated and shown on a spatially continuous risk map. Results are given in terms of annual economic risks and damage losses based on occurrence of an average recurrence interval. Implications on identifying offshore wind potential and cost and setting design parameters for offshore wind turbines are then discussed. The impact of tropical cyclones on offshore wind farms likes a double-edged sword, which might be advantageous for some regions in terms of increasing full-loaded hours of turbines, but also disadvantageous for others due to its destructive effects. However, specific design standards and insurance of turbines would help reduce risks and economic losses of offshore wind farms in tropical cyclone prone areas and expand exploitable locations for future offshore wind farms. [Copyright &y& Elsevier]

This paper elaborates on the costs and benefits of expanding the Austrian transmission system and the implementation of innovative grid-impacting technologies (e.g. flexible AC transmission systems (FACTS), dynamic line rating (DLR)) to support further integration of renewable energy sources for electricity generation (RES-E). Therefore, a fundamental market model has been developed - respecting DC load flows - and applied for analysing different future scenarios, notably for the time horizon 2020, 2030 and 2050. Up to 2020 and 2030, special focus is put on the finalisation of the so-called “380 kV-level transmission ring” in Austria to enable enhanced RES-E integration. The results confirm that transmission power line expansion in the states of Salzburg and Carinthia is important to connect imports from Germany with pumped hydro storage capacities, on the one hand, and the wind farms in the east with the pumped hydro storages in the western part of Austria, on the other hand. For 2050, the results indicate that the implementation of FACTS and DLR can reduce RES-E curtailment significantly. [ABSTRACT FROM AUTHOR]

This paper addresses a multistage electricity generation expansion planning (GEP) incorporating large-scale energy storage systems (ESSs). The proposed coordinated GEP-ESS planning aims at minimizing the planning cost and environmental pollution at the same time, while it considers large-scale ESSs. Problem is expressed as a mixed-integer nonlinear programming and solved using PSO algorithm. Problem is solved subject to practical constraints of the network. ESS capacities are installed to support peak load level and reducing planning cost and environmental pollution. A typical test system including several existing and candidate generating units is considered to evaluate the proposed methodology. ESSs with various capacities are considered as candidate ESSs. Considering a large number of generating units and ESSs capacities increases the flexibility of the planning. Simulation results demonstrate that utilizing ESSs significantly reduces GEP cost as well as decreases the environmental pollution. [ABSTRACT FROM AUTHOR]

In this paper we develop and verify a static model for a photovoltaic array power production prediction by integrating manufacturers’ and on-line data. The static model is a fundamental part of dynamic models that are used to predict the photovoltaic array power production along a prediction horizon, and it is important to assess its limit performance to (i) reach maximum accuracy in the power production prediction, and to (ii) enable monitoring of the photovoltaic plant for alerting the owner in the case of unexpectedly low performance. The static model is developed in two subsequent steps: (i) power production model parameters are identified on manufacturers’ data, and (ii) a model corrector is identified on on-line solar irradiance and the photovoltaic array temperature data, which significantly improves accuracy of the static power production model compared to the model identified on manufacturers’ data only. Verification is performed on measurements of solar irradiance components, the PV array temperature and the output power during a 17-month time period. The proposed combination of the model initialization with manufacturers’ data and on-line data-based correction shows very high model accuracy, and enables adaptation to different system setups. It also incorporates robustness to systematic solar irradiance prediction errors. [ABSTRACT FROM AUTHOR]

This paper examines combinations of photovoltaic (PV) generation plus battery energy storage for islanded electricity systems from energetic and economic perspectives, using hourly solar resource data, and 17 household-scale demand profiles, for Christchurch, New Zealand. Optima for normalised storage, expressed as a proportion of annual demand, and for energy returned on energy invested (EROEI), occurred at energy penetrations ranging from 2.50 to 4.00. The ratio of maximum to minimum daily demand predicted optimal storage capacity and EREOI. Improved optimal EROEI values occurred following reductions in embodied energy and at lowered penetrations with longer battery lifetimes. Energy spillage at the optimal penetrations was spread relatively evenly over the year, with the exception of several weeks during winter, and final discharge depths averaged 3.1%. Economic optima, expressed as net present cost, occurred at energy penetrations ranging from 3.00 to 5.00. Reductions in PV panel and battery capital costs, and a longer battery lifetime, reduced the penetrations at which economic optima occurred, and in some cases these coincided with energetic optima. It is suggested that both energetic and economic optima need to be evaluated in the planning process, and that the role of secondary loads be investigated in future research programmes. [ABSTRACT FROM AUTHOR]

Wind turbine layout optimization in wind farm is one of the most important technologies to increase the wind power utilization. This paper studies the wind turbine layout optimization with multiple hub heights wind turbines using greedy algorithm. The linear wake model and the particle wake model are used for wake flow calculation over flat terrain and complex terrain, respectively. Three-dimensional greedy algorithm is developed to optimize wind turbine layout with multiple hub heights for minimizing cost per unit power output. The numerical cases over flat terrain and complex terrain are used to validate the effectiveness of the proposed greedy algorithm for the optimization problem. The results reveal that it incurs lower computational costs to obtain better optimized results using the proposed greedy algorithm than the one using genetic algorithm. Compared to the layout with identical hub height wind turbines, the one with multiple hub height wind turbines can increase the total power output and decrease the cost per unit power output remarkably, especially for the wind farm over complex terrain. It is suggested that three-dimensional greedy algorithm is an effective method for more benefits of using wind turbines with multiple hub heights in wind farm design. [ABSTRACT FROM AUTHOR]

This paper proposes a feasibility analysis of grid connected photovoltaic energy systems in Algerian dairy farms considering technical and economic requirements and respecting the local specific characteristics and legislations. The aim is to design an optimal solar system satisfying the farms' electric needs for each Algerian region and investigate the feasibility as well as the impact of replacing the existing conventional systems with solar energy systems. Real electricity consumption data from experimental dairy farms are recorded using typical herd size for each region and projected herd size according to the livestock intensification policy followed by the government. The pilot farms are determined to be the farms of the technical institute of breeding ITELV. The electricity consumptions of a set of Algerian family farms, ranging from 10 to 30 milking cows, were analyzed. It is found that the average energy requirements are between 330 kWh/cow/year and 560 kWh/cow/year, which is considerably lower than north European and North American dairy farms consuming up to 2900 kWh/cow/year. The results indicate that the on-farm self-produced electricity is able to achieve the energy balance between forecasted photovoltaic generation and farm energy demand with a cost of electricity ranging from −0.008 $/kWh to 0.033 $/kWh. [ABSTRACT FROM AUTHOR]

This paper uses monthly data from Aug. 2004 to Feb. 2014 and employs the Autoregressive Distributed Lag bounds test approach to study the short and long-run relationship of renewable and non-renewable electricity with economic growth in Greece. Dummies reveal most of the major energy policy adaptations taking place in Greece to overcome the economic crisis and reach stipulated renewable energy targets. Results show that in the short-run, fossil sources play the baseload role in electricity production and there is a clear substitution effect between sources, while in the long-run, fossil sources contribute to the development of renewable energy sources as backup energy. [ABSTRACT FROM AUTHOR]

This paper deals with a dynamic analysis on a low concentration solar power plants coupled with Organic Rankine Cycles (ORC), which can be an alternative to PV systems because of their capability of providing a smoother electricity production due to their thermal inertia. At least within certain restraints, moreover they are able to exploit diffused solar radiation. The dynamic model of a plant with static Compound Parabolic Collectors and an ORC system, using a rotary volumetric expander, was developed using the simulation tool AMESim. All the main components of the plant are modelled: solar collectors field, heat transfer fluid circuit, heat exchangers and the ORC system. The plant response to the radiation of different days was analyzed to quantify the daily production and the trend of various plant parameters. Real ambient conditions were employed for the simulations by using data obtained by historical series. The results showed that the employment of a volumetric expansion device with variable rotating speed allows the plant to operate at different radiations and ambient temperatures without the need of any storage system or external heat sources. Results can be extended to other applications, such as low temperature waste heat recovery or geothermal systems. [ABSTRACT FROM AUTHOR]

The work reported here addresses load matching improvement in Net Zero Energy Buildings (Net-ZEBs). The related relevant literature shows that currently research work is mainly focused on improving the load matching of individual buildings. In this paper the concept of a Cooperative Net Zero Energy Community (CNet-ZEC) is introduced, extending discussion to the enhancement of load matching at a wider community level. Both building and community levels are compared in order to assess the work proposed here, through the analysis of three distinct scenarios where five Net-ZEBs work individually or in community. The results presented here were obtained through a detailed simulation based on 1-min resolution stochastic load profiles and recorded weather data. The results indicate that over the period of a year the CNet-ZEC has the potential to increase the electrical demand covered by onsite electricity generation up to 21% and the on-site generation that is used by the building up to 15%. The following elements are considered by the CNet-ZEC in order to produce those results: (i) demand heterogeneity of the buildings integrating the community; (ii) the higher number of controllable devices; and (iii) the potential higher amount of energy available to satisfy the community demand. [ABSTRACT FROM AUTHOR]

Abstract: Based on the Kalina cycle, the solar-boosted system with an auxiliary superheater is investigated in the current paper. To predict the system performance, the corresponding calculation model is built. In accordance with engineering practice, the maximum pressure of the system is within 3 MW and the pinch point temperature difference of the regenerator is not less than 0.5 °C in this paper. Then based on the characteristics of the Kalina solar system, the verification items are given to verify the correctness of the calculation model. Afterward the model is proven to be correct by sampling check a set of calculation data. Further, parameter performance analyses are carried out on the system. Results show that the system pressure difference is an important performance benchmark that can be used to evaluate the thermal efficiency of the power generation cycle. Furthermore, the relationship between the optimal mass flow rate and total heat transfer rate is noticeable in the solar system since solar radiation is changed with time. And the corresponding approximate expression is thus derived for optimal operation. Finally, an application case is designed by using direct normal solar radiation data in Tosashimizu city of Japan based on average hourly statistics. [Copyright &y& Elsevier]

Abstract: Electricity generation from renewable sources of energy will be a key part in the development of future strategies for many countries globally. This renewable electricity generation will be hugely important for Ireland, due to its lack of fossil fuel resources. The extremely good wind resource available provides Ireland with the opportunity of generating vast amount of electricity from wind energy. Large-scale wind electricity generation reached 1264 MW installed capacity by January 2010 in Ireland. However, micro scale wind electricity generation has not been very popular in Ireland to-date. The unclear economics of micro wind turbines, under Irish conditions, is considered the biggest obstacle for expanding micro wind turbine installation in Ireland. This paper presents a methodology to accurately evaluate the economic viability of a micro wind turbine on a case-by-case basis. The methodology utilises the software programmes HOMER and Microsoft Excel 2007 for the energy and economic analyses. This paper also presents a realistic economic analysis of a number of micro wind turbines available in Ireland. [Copyright &y& Elsevier]

Abstract: Despite possessing a very large potential of renewable energy sources, Australia has lagged behind other developed countries in embracing renewable energy. Various programs and policies have been devised and implemented by Australian governments. Nevertheless, the proportion of renewable energy in electricity generation in Australia has not increased significantly. This paper seeks to explain why Australia has difficulties in adopting renewable energy by using the Political Aspect of Innovation (PAI) framework to examine the causes and barriers that have blocked the taking up of renewable energy. The PAI framework is concerned specifically with public innovation policy in Australia and the way it aims to encourage and support investment in new technology development. The paper finally outlines some future suggestions for charting the progression of the Australian energy system toward a transformative sustainable future. [Copyright &y& Elsevier]

Abstract: This paper presents a proposal of sustainable management model alternative for electrification of remote communities in the Amazon region, considering the Brazilian regulation policy. This paper presents also a case study of the electrification in a river-dwelling community in the State of Pará, Brazil, within the scope of the Program for Electric Power Service Universalization in Brazil. The community shall be provided with electrification facilities through a small biomass-based power plant, directly firing residues produced by the local economic activity. The objective of the paper is to make a proposal for a sustainable management model that is suitable for the community’s isolation conditions, considering the high costs with operation and maintenance related to the supply for isolated consumers in small locations. A simulation is conducted for the operation of the small biomass-based power plant; the generation costs are determined; the legal aspects are analyzed; and a suggestion for the management model is presented. [Copyright &y& Elsevier]

Abstract: Large integration of intermittent wind generation in power system has necessitated the inclusion of more innovative and sophisticated approaches in power system investment planning. The intermittent nature and uncertainties of wind power generation will cause the investors encounter risk in their investment decisions. Main factors such as uncertainties in demand, fuel price, wind power generation which affect long-term planning have been considered in the proposed model. To overcome this problem i.e. risk impacts on decisions, this paper presents improved incentive mechanisms for wind power investment. The mechanism has been investigated based on system dynamics modeling. In the proposed mechanism, wind power generations will recover a part of their investment cost through incentive mechanisms. In this paper, different incentive methods some of which are dependent to market conditions are being proposed. The functionality of these incentive mechanisms on wind generation investment are illustrated by simulation studies. [Copyright &y& Elsevier]

Abstract: Energy from waste (EfW) has been identified as a source of ‘green electricity’ and has been used as a way of reducing greenhouse gas (GHG) emissions. Nevertheless, selecting an EfW strategy for municipal solid waste management is a challenging task not least because of the uncertainty involved in quantifying the potential economic and environmental impacts. This paper analyses five alternatives for managing the municipal solid waste of Sydney for their ‘green electricity’ and GHG savings potential under conditions of uncertainty. The impact of paper recycling on the ranking of alternatives was investigated, too. Our analysis shows that maximizing EfW generation potential does not result in greater GHG saving. A combination of food and green waste composting, recycling of metals, paper, glass and plastics while only landfilling waste fractions that are not recyclable may result in the best GHG savings. Furthermore, recycling of paper does not always achieve the best outcome; anaerobic digestion or composting may yield better results from an environmental and energy generation perspective. [Copyright &y& Elsevier]

Abstract: In recent years the decentralized rural electrification is becoming cost effective and convenient for areas where grid extension is very difficult. The present paper deals with the electrification of dense forest areas of Uttarakhand state in India by Integrated Renewable Energy Optimization Model (IREOM). The IREOM consists of locally available renewable energy resources such as Micro-Hydropower (MHP), biomass, biogas, wind and solar photovoltaic (SPV) systems have been used to meet electrical energy and cooking energy needs of a cluster of villages. The paper includes the selection of different system components, sizing and development of a general model to find out optimal combination of energy subsystems for the selected study area in order to minimize the cost of energy (COE) generation for a required reliability values. The sizing of different renewable energy system components has been carried out so that they are suitable for four different seasonal load profiles. The two reliability values are considered for the selection of optimum solution of year round application. The model developed for this purpose, has been found to be quite useful in optimizing the renewable energy system sizes that are available in market. The proposed model totally depends on the renewable energy systems and eliminates the use of conventional energy systems. [Copyright &y& Elsevier]

Abstract: This paper presents the results of an experimental study of a PV/diesel hybrid system without storage. Experimental results show that the sizing of a PV/diesel hybrid system by taking into account the solar radiation and the load/demand profile of a typical area may lead the diesel generator to operate near its optimal point (70–80% of its nominal power). The present paper shows that for a reliability of a PV/diesel hybrid system, the rated power of the diesel generator should be equal to the peak load. By the way, it has been verified through this study that the functioning of a PV/diesel hybrid system is efficient for higher load and higher solar radiation. [ABSTRACT FROM AUTHOR]