Weather data and probability analysis of hybrid photovoltaic–wind power generation systems in Hong Kong

This paper describes a simulation model for analyzing the probability of power supply failure in hybrid photovoltaic–wind power generation systems incorporating a storage battery bank, and also analyzes the reliability of the systems. An analysis of the complementary characteristics of solar irradiance and wind power for Hong Kong is presented. The analysis of local weather data patterns shows that solar power and wind power can compensate well for one another, and can provide a good utilization factor for renewable energy applications. For the loss of power supply probability (LPSP) analysis, the calculation objective functions and restraints are set up for the design of hybrid systems and to assess their reliability. To demonstrate the use of the model and LPSP functions, a case study of hybrid solar–wind power supply for a telecommunication system is presented. For a hybrid system on the islands surrounding Hong Kong, a battery bank with an energy storage capacity of 3 days is suitable for ensuring the desired LPSP of 1%, and a LPSP of 0% can be achieved with a battery bank of 5 days storage capacity.     

A simplified model for estimating the monthly performance of autonomous wind energy systems with battery storage

This paper presents a simplified algorithm to estimate the monthly performance of autonomous small-scale wind energy systems with battery storage. The novel model is drawn based on the simulation results, using eight-year long hour-by-hour measured wind speed data from five different locations throughout the world. An hourly constant load profile is used. The renewable energy simulation program (ARES) of the Cardiff School of Engineering is used. The ARES simulates the battery state of voltage (SoV) and is able to predict the system performance.The monthly performance values obtained from the simulations are plotted against increasing energy to load ratios for varying battery storage capacities to obtain performance curves. The novel method correlates the monthly system performance with the parameters of the Weibull distribution function, thus offering a universal use. The monthly performance curves are mathematically represented using a 2-parameter function. The novel method is validated by comparing the simulated performance values with those estimated from the simplified algorithm. The standard errors calculated in estimation of the system performance using the simplified algorithm are further presented for each battery capacity.     

Optimisation and techno-economic analysis of autonomous photovoltaic–wind hybrid energy systems in comparison to single photovoltaic and wind systems

A techno-economic analysis for autonomous small scale photovoltaic–wind hybrid energy systems is undertaken for optimisation purposes in the present paper. The answer to the question whether a hybrid photovoltaic–wind or a single photovoltaic or wind system is techno-economically better is also sought. Monthly analysis of 8 year long measured hourly weather data shows that solar and wind resources vary greatly from one month to the next. The monthly combinations of these resources lead to basically three types of months: solar-biased month, wind-biased month and even month. This, in turn, leads to energy systems in which the energy contributions from photovoltaic and wind generators vary greatly. The monthly and yearly system performances simulations for different types of months show that the system performances vary greatly for varying battery storage capacities and different fractions of photovoltaic and wind energy. As well as the system performance, the optimisation process of such hybrid systems should further consist of the system cost. Therefore, the system performance results are combined with system cost data. The total system cost and the unit cost of the produced electricity (for a 20 year system lifetime) are analysed with strict reference to the yearly system performance. It is shown that an optimum combination of the hybrid photovoltaic–wind energy system provides higher system performance than either of the single systems for the same system cost for every battery storage capacity analysed in the present study. It is also shown that the magnitude of the battery storage capacity has important bearings on the system performance of single photovoltaic and wind systems. The single photovoltaic system performs better than a single wind system for 2 day storage capacity, while the single wind system performs better for 1.25 day storage capacity for the same system cost.     

PV–wind hybrid system performance: A new approach and a case study

Until now, there is no internationally accepted guideline for the measurement, data exchange and analysis of PV–Wind Hybrid Systems. As there is a need for such a tool, so as to overcome the barrier that the lack of confidence due to the absence of reliability means for the development of the market of Hybrid Systems, an effort has been made to suggest one tool for PV–Wind Hybrid Systems. The suggested guidelines presented in this work are based on the existing guidelines for PV Systems, as a PV–Wind Hybrid system can be roughly thought of as a PV System to which wind generation has been added. So, the guidelines for PV Systems are valid for the PV–Wind System, and only the part referred to wind generation should be included. This has been the process followed in this work. The proposed method is applied to a case study, the CICLOPS Project, a 5 kW PV, 7.5 kW Wind Hybrid system installed at the Isolated Wind Systems Test Site that CIEMAT owns in CEDER (Soria, Spain). This system has been fully monitored through a year and the results of the monitoring activity, characterizing the long-term performance of the system are shown in this work.     

Study of a solar PV–diesel–battery hybrid power system for a remotely located population near Rafha, Saudi Arabia

This study presents a PV–diesel hybrid power system with battery backup for a village being fed with diesel generated electricity to displace part of the diesel by solar. The hourly solar radiation data measured at the site along with PV modules mounted on fixed foundations, four generators of different rated powers, diesel prices of 0.2–1.2US$/l, different sizes of batteries and converters were used to find an optimal power system for the village. It was found that a PV array of 2000 kW and four generators of 1250, 750, 2250 and 250 kW; operating at a load factor of 70% required to run for 3317 h/yr, 4242 h/yr, 2820 h/yr and 3150 h/yr, respectively; to produce a mix of 17,640 MWh of electricity annually and 48.33 MWh per day. The cost of energy (COE) of diesel only and PV/diesel/battery power system with 21% solar penetration was found to be 0.190$/kWh and 0.219$/kWh respectively for a diesel price of 0.2$/l. The sensitivity analysis showed that at a diesel price of 0.6$/l the COE from hybrid system become almost the same as that of the diesel only system and above it, the hybrid system become more economical than the diesel only system.     

The effect of model generated solar radiation data usage in hybrid (wind–PV) sizing studies

Wind speed and solar radiation characteristics belonging to past years of a region are the main input parameters in wind–photovoltaic hybrid system (WPHS) sizing studies. Classically, these data are fed to several scenarios with different solar panel, wind turbine, and storage battery number combinations. The solutions with minimal cost which also satisfy the desired maximum loss of energy probability are selected. Since the utilized data have random fluctuations because of atmospheric phenomenon, past years’ data are unlikely to appear in a similar manner in future years. Hence, using a robust model that characterizes the general behavior of the data instead of directly using past data should yield more accurate sizing solutions. In order to compare the sizing accuracy obtained by directly using the data to the accuracy obtained by indirect modeling from data, an analytical solar radiation model is first explained. Using this model, 3-year solar radiation data of three geographical sites are analyzed. It was observed that the differences between sample-by-sample hourly recordings corresponding to different years are significantly larger than the difference between these recordings and the data model obtained from an arbitrary year. This provides a hint that a sizing approach carried out using the data of a previous year would not be accurate in producing the same Loss of Load Probability (LLP) for a future year. On the contrary, the accuracy would improve if a generic analytical model of the solar radiation is used in the sizing process. This foresight is tested by comparing the LLPs obtained in the two ways mentioned above. Results obtained using available data are in accordance with the aforementioned propositions.     

风光互补独立供电系统优化匹配设计实例

以系统的最小安装成本为优化目标,以系统的供电可靠性为约束条件,对内蒙古满洲里市某居民家庭用电风光互补独立供电系统进行基于计算机仿真计算的优化匹配设计。     

Optimal sizing method for stand-alone hybrid solar–wind system with LPSP technology by using genetic algorithm

System power reliability under varying weather conditions and the corresponding system cost are the two main concerns for designing hybrid solar–wind power generation systems. This paper recommends an optimal sizing method to optimize the configurations of a hybrid solar–wind system employing battery banks. Based on a genetic algorithm (GA), which has the ability to attain the global optimum with relative computational simplicity, one optimal sizing method was developed to calculate the optimum system configuration that can achieve the customers required loss of power supply probability (LPSP) with a minimum annualized cost of system (ACS). The decision variables included in the optimization process are the PV module number, wind turbine number, battery number, PV module slope angle and wind turbine installation height. The proposed method has been applied to the analysis of a hybrid system which supplies power for a telecommunication relay station, and good optimization performance has been found. Furthermore, the relationships between system power reliability and system configurations were also given.     

The importance of control strategies in PV–hydrogen systems

The control strategy for a photovoltaic (PV) system with a hydrogen (H₂) subsystem consisting of an electrolyzer, pressurized hydrogen gas storage, and fuel cell has been investigated. Detailed computer simulation models for TRNSYS have been developed, tested, and verified against a reference system, namely the PHOEBUS plant in Jülich, Germany. The basic control strategy and main logical control variables for a PV–H₂ system are described. System performance indicators, parameters, and constraints that can be used to analyze the performance of PV–H₂ systems have been identified. The results from a time series simulation for a typical year are presented. Finally, the importance of selecting smart control strategies is demonstrated.     

Battery behavior prediction and battery working states analysis of a hybrid solar–wind power generation system

Lead–acid batteries used in hybrid solar–wind power generation systems operate under very specific conditions, and it is often very difficult to predict when the energy will be extracted from or supplied to the battery. Owing to the highly variable working conditions, no battery model has achieved a good compromise between the complexity and precision. This paper presents a simple mathematical approach to simulate the lead–acid battery behaviors in stand alone hybrid solar–wind power generation systems. Several factors that affect the battery behaviors have been taken into account, such as the current rate, the charging efficiency, the self-discharge rate, as well as the battery capacity. Good agreements were found between the predicted results and the field measured data of a hybrid solar–wind project. At last, calculated from 1-year field data with the simulation model, the time-series battery state-of-charge (SOC) has been statistically analyzed considering the monthly and hourly variations as well as the probability distributions. The results have shown the battery working states in the real hybrid solar–wind power generation system.     

风光互补发电系统中光伏方阵最佳倾角的计算方法

介绍一种计算风光互补发电系统中光伏方阵的最佳倾角的方法。用最小二乘法确定光伏方阵的最佳倾角:先计算出倾角β下各月倾斜面上的太阳能方阵发电量与风机发电量之和,然后减去各月负载耗电量的差,再求出一年内上述差值的平方和,能使得此平方和取得最小值的倾角即为方阵最佳倾角β。根据此方法确定出的最佳倾角可以使太阳能和风机发电量相对不足的月份的发电量尽量接近负载需求量,同时又可以解决有的月份风光发电量远大于负载需求,造成极大浪费的问题。     

Optimization of diesel engine performances for a hybrid wind–diesel system with compressed air energy storage

Electricity supply in remote areas around the world is mostly guaranteed by diesel generators. This relatively inefficient and expensive method is responsible for 1.2 million tons of greenhouse gas (GHG) emission in Canada annually. Some low- and high-penetration wind-diesel hybrid systems (WDS) have been experimented in order to reduce the diesel consumption. We explore the re-engineering of current diesel power plants with the introduction of high-penetration wind systems together with compressed air energy storage (CAES). This is a viable alternative to major the overall percentage of renewable energy and reduce the cost of electricity. In this paper, we present the operative principle of this hybrid system, its economic benefits and advantages and we finally propose a numerical model of each of its components. Moreover, we are demonstrating the energy efficiency of the system, particularly in terms of the increase of the engine performance and the reduction of its fuel consumption illustrated and supported by a village in northern Quebec.     

An integrated model for performance simulation of hybrid wind–diesel systems

Stand-alone hybrid systems have turned into one of the most promising ways to handle the electrification requirements of numerous isolated consumers worldwide. The proposed wind–diesel–battery hybrid system consists of a micro-wind converter, a small diesel-electric generator—basically operating as a back up energy production system—and a lead-acid battery bank that stores the wind energy surplus during high wind speed periods. In this context the present work is focused on presenting a detailed mathematical model describing the operational behavior of the basic hybrid system components, along with the representative calculation results based on the developed mathematical model. Accordingly, an integrated numerical algorithm is built to estimate the energy autonomy configuration of the hybrid system under investigation. Using the proposed numerical algorithm, the optimum configuration selection procedure is verified by carrying out an appropriate sensitivity analysis. The proposed methodology may equally well be applied to any other remote consumer and wind potential type, in order to estimate the optimum wind–diesel hybrid system configuration that guarantees long-term energy autonomy.     

A new hybrid solar photovoltaic/ phosphoric acid fuel cell and energy storage system; Energy and Exergy performance

Present work investigates the performance of a combined solar photovoltaic (PV) and Pumped-Hydro and Compressed-Air energy storage system to overcome the challenges of using solar energy systems. This energy system, which is one of the newest hybrid systems, is able to generate electricity and store energy. To examine the solar PV performance the climatic conditions of Shiraz (in Iran) and Abu Dhabi (in UAE) are considered. The results revealed that, the required pump work, which must be supplied by PV system, is equal to 2.85 and 2.62 MJ/m³ for isothermal and isentropic processes, respectively. Furthermore, the total system efficiency is equal to 76.5%. In addition, the total exergy destruction of hybrid system for isentropic process is 8.91% less than that isothermal process. In addition, instead of the solar PV system, a phosphoric acid fuel cell is coupled to the storage system and the results are compared with the main system.     

Multi-objective optimization of the hybrid wind/solar/fuel cell distributed generation system using Hammersley Sequence Sampling

As the development of China's economy, environmental problems in China become more and more serious. Solar energy and wind energy are considered as ones of the best choices to solve the environmental problems in China and the hybrid wind/solar distributed generation (DG) system has received increasing attention recently. However, the instability and intermittency of the wind and solar energy throw a huge challenge on designing of the hybrid system. In order to ensure the continuous and stable power supply, optimal unit sizing of the hybrid wind/solar DG system should be taken into consideration in the design of the hybrid system. This paper establishes a multi-objective optimization framework based on cost, electricity efficiency and energy supply reliability models of the hybrid DG system, which is composed of wind, solar and fuel cell generation systems. Detailed models of each unit for the hybrid wind/solar/fuel cell system were established. Advanced ε-constraints method based on Hammersley Sequence Sampling was employed in the multi-objective optimization of the hybrid DG system. The approximate Pareto surface of the multi-objective optimization problems with a range of possible design solutions and a logical procedure for searching the global optimum solution for decision makers were presented. In this way, this work provided an efficient method for decision makers in the design of the hybrid wind/solar/fuel cell system.     

The performance of a remote wind–diesel power system

The collection and analysis of 6 months of continuously recorded field data from a small remote wind–diesel power system at a coastal farm site is reported. The power system and the data acquisition unit are described and the performance characteristics of the major components discussed. Analysis of the field data has led to a number of recommendations for possible improvement in component sizing and control strategy. The siting of the turbine is excellent by international standards and the annual wind energy produced is greater than the demand. However, almost a fifth of the wind energy generated has to be dumped due to the short-term oversupply of power and over one-quarter of the total energy supplied still comes from the diesel generator as a result of transient energy deficits. An operational strategy that can deal with this paradox of alternating supply and demand excesses could lead to further operational improvements.     

Dynamic performance assessment of an isolated wind–diesel power system with superconducting magnetic energy storage unit under turbulent wind and load disturbances

This paper presents modelling and control aspects of an isolated wind–diesel system equipped with a superconducting magnetic energy storage (SMES) unit. The SMES unit is located at the induction generators' terminal bus, for exchanging real and reactive powers in four quadrants, with the wind–diesel system. The system components are modelled by non‐linear equations for accurate dynamic performance assessment and the SMES unit is modelled as a controllable current source. The control of the SMES unit is exercised through a multi‐input–multi‐output (MIMO) self‐tuning regulator (STR). The STR uses the local voltage and frequency measurements and generates appropriate signals for the control of the SMES unit. The SMES coil current deviation forms a part of one of the regulated variables of the STR for achieving a continuous control. The complete model of the hybrid system is developed and the parameters of the STR are adjusted for quality improvement of the power supply under turbulent wind. The scheme is then tested for load disturbances. The simulation results show the positive impact of the proposed scheme on the quality of the power supply both under turbulent wind as well as load disturbances. Copyright © 2002 John Wiley & Sons, Ltd.     

Theoretical variations of the thermal performance of different solar collectors and solar combi systems as function of the varying yearly weather conditions in Denmark

The thermal performances of solar collectors and solar combi systems with different solar fractions are studied under the influence of the Danish design reference year, DRY data file, and measured weather data from a solar radiation measurement station situated at the Technical University of Denmark in Kgs. Lyngby. The data from DRY data file are used for any location in Denmark. The thermal performances of the solar heating systems are calculated by means of validated computer models. The measured yearly solar radiation varies by approximately 23% in the period from 1990 until 2002, and the investigations show that it is not possible to predict the yearly solar radiation on a tilted surface based on the yearly global radiation.The annual thermal performance of solar combi systems cannot with reasonable approximation be fitted to a linear function of the annual total radiation on the solar collector or the annual global radiation. Solar combi systems with high efficient solar collectors are more influenced by weather variations from one year to another than systems with low efficient solar collectors.The annual thermal performance of solar collectors cannot be predicted from the global radiation, but both the annual thermal performance and the annual utilized solar energy can with a reasonable approximation be fitted to a linear function of the yearly solar radiation on the collector for both flat plate and evacuated tubular solar collectors. Also evacuated tubular solar collectors utilize less sunny years with large parts of diffuse radiation relatively better than flat plate collectors.     

The wind/hydrogen demonstration system at Utsira in Norway: Evaluation of system performance using operational data and updated hydrogen energy system modeling tools

An autonomous wind/hydrogen energy demonstration system located at the island of Utsira in Norway was officially launched by Norsk Hydro (now StatoilHydro) and Enercon in July 2004. The main components in the system installed are a wind turbine (600 kW), water electrolyzer (10 Nm³/h), hydrogen gas storage (2400 Nm³, 200 bar), hydrogen engine (55 kW), and a PEM fuel cell (10 kW). The system gives 2–3 days of full energy autonomy for 10 households on the island, and is the first of its kind in the world. A significant amount of operational experience and data has been collected over the past 4 years. The main objective with this study was to evaluate the operation of the Utsira plant using a set of updated hydrogen energy system modeling tools (HYDROGEMS). Operational data (10-min data) was used to calibrate the model parameters and fine-tune the set-up of a system simulation. The hourly operation of the plant was simulated for a representative month (March 2007), using only measured wind speed (m/s) and average power demand (kW) as the input variables, and the results compared well to measured data. The operation for a specific year (2005) was also simulated, and the performance of several alternative system designs was evaluated. A thorough discussion on issues related to the design and operation of wind/hydrogen energy systems is also provided, including specific recommendations for improvements to the Utsira plant. This paper shows how important it is to improve the hydrogen system efficiency in order to achieve a fully (100%) autonomous wind/hydrogen power system.     

Estimation of monthly Angström–Prescott equation coefficients from measured daily data in Toledo, Spain

In this study, daily global radiation for Toledo (39°53′05″N, 4°02′58″W, Spain) were utilized to determine monthly-specific equations for estimating global solar radiation from sunshine hours and to obtain improved fits to monthly Angström–Prescott's coefficients.Models were compared using the root mean square error (RMSE), the mean bias error (MBE) and the t-statistic. According to our results, all the models fitted the data adequately and can be used to estimate the specific monthly global solar radiation.Average RMSE and MBE for comparison between observed and estimated global radiation were 1.260 and −0.002 MJ m⁻² day⁻¹, respectively. The t-statistic was used as the best indicator, this indicator depends on both, and is more effective for determining the model performance. The agreement between the estimated and the measured data were remarkable and the method was recommended for use in Toledo (Spain).