Pre-feasibility study of stand-alone hybrid energy systems for applications in Newfoundland

A potential solution for stand-alone power generation is to use a hybrid energy system in parallel with some hydrogen energy storage. In this paper, a pre-feasibility study of using hybrid energy systems with hydrogen as an energy carrier for applications in Newfoundland, Canada is explained. Various renewable and non-renewable energy sources, energy storage methods and their applicability in terms of cost and performance are discussed. HOMER is used as a sizing and optimization tool. Sensitivity analysis with wind speed data, solar radiation level, diesel price and fuel cell cost was done. A remote house having an energy consumption of 25 kW h/d with a 4.73 kW peak power demand was considered as the stand-alone load. It was found that, a wind–diesel–battery hybrid system is the most suitable solution at present. However, with a reduction of fuel cell cost to 15% of its current value, a wind–fuel cell system would become a superior choice. Validity of such projection and economics against conventional power sources were identified. Sizing, performance and various cost indices were also analyzed in this paper.     

Hybrid renewable energy systems for power generation in stand-alone applications: A review

It has become imperative for the power and energy engineers to look out for the renewable energy sources such as sun, wind, geothermal, ocean and biomass as sustainable, cost-effective and environment friendly alternatives for conventional energy sources. However, the non-availability of these renewable energy resources all the time throughout the year has led to research in the area of hybrid renewable energy systems. In the past few years, a lot of research has taken place in the design, optimization, operation and control of the renewable hybrid energy systems. It is indeed evident that this area is still emerging and vast in scope. The main aim of this paper is to review the research on the unit sizing, optimization, energy management and modeling of the hybrid renewable energy system components. Developments in research on modeling of hybrid energy resources (PV systems), backup energy systems (Fuel Cell, Battery, Ultra-capacitor, Diesel Generator), power conditioning units (MPPT converters, Buck/Boost converters, Battery chargers) and techniques for energy flow management have been discussed in detail. In this paper, an attempt has been made to present a comprehensive review of the research in this area in the past one decade.     

Wave energy resources: Wave climate and exploitation

In identifying the most convenient zones for harvesting wave energy, it is natural to be attracted by the areas where we find the highest mean energy values. The obvious examples are the storm belts. A more careful analysis reveals that for practical use other factors need to be taken into account. Some of the main ones are the energy spread in frequency and direction, and its seasonality, without discussing the cost of the structure basically related to the conditions to be withstood. This reveals that other areas, in particular the equatorial ones, can be conveniently used, and be possibly advantageous from various points of view. Based on the results of the ECMWF ERA-Interim reanalysis and of altimeter data, we have carried out a comparative analysis between two locations with opposite characteristics, in the North Atlantic and in the Equatorial Pacific respectively. The quantified results confirm that less energetic, but more regular and less extreme, areas have a potential comparable to that of the classically considered storm belts.     

Automatic management of energy flows of a stand-alone renewable energy supply with hydrogen support

This work deals with the design and construction of an automation system for controlling the electric energy flows that take place at the continuous current bus (DC Bus) of a wind–solar system with hydrogen support. The automation system is based on a Siemens PLC s7_313C_2DP. This PLC was equipped with a Micro Memory Card (MMC) of 2 MB in order to allow the massive storage of data related to the control and monitoring of the test-bed. This system has to perform the required switching between the components of the hybrid electric energy generator. These elements are: photovoltaic generator, wind-turbine generator, fuel-cell system, and electrolyzer.     

Power management strategies for a stand-alone power system using renewable energy sources and hydrogen storage

A stand-alone power system based on a photovoltaic array and wind generators that stores the excessive energy from renewable energy sources (RES) in the form of hydrogen via water electrolysis for future use in a polymer electrolyte membrane (PEM) fuel cell is currently in operation at Neo Olvio of Xanthi, Greece. Efficient power management strategies (PMSs) for the system have been developed. The PMSs have been assessed on their capacity to meet the power load requirements through effective utilization of the electrolyzer and fuel cell under variable energy generation from RES (solar and wind). The evaluation of the PMS has been performed through simulated experiments with anticipated conditions over a typical four-month time period for the region of installation. The key decision factors for the PMSs are the level of the power provided by the RES and the state of charge (SOC) of the accumulator. Therefore, the operating policies for the hydrogen production via water electrolysis and the hydrogen consumption at the fuel cell depend on the excess or shortage of power from the RES and the level of SOC. A parametric sensitivity analysis investigates the influence of major operating variables for the PMSs such as the minimum SOC level and the operating characteristics of the electrolyzer and the fuel cell in the performance of the integrated system.     

Approaches for developing a sizing method for stand-alone PV systems with variable demand

Accurate sizing is one of the most important aspects to take into consideration when designing a stand-alone photovoltaic system (SAPV). Various methods, which differ in terms of their simplicity or reliability, have been developed for this purpose. Analytical methods, which seek functional relationships between variables of interest to the sizing problem, are one of these approaches.A series of rational considerations are presented in this paper with the aim of shedding light upon the basic principles and results of various sizing methods proposed by different authors. These considerations set the basis for a new analytical method that has been designed for systems with variable monthly energy demands.Following previous approaches, the method proposed is based on the concept of loss of load probability (LLP)—a parameter that is used to characterize system design. The method includes information on the standard deviation of loss of load probability (σ_LLP) and on two new parameters: annual number of system failures (f) and standard deviation of annual number of failures (σ_f).The method proves useful for sizing a PV system in a reliable manner and serves to explain the discrepancies found in the research on systems with LLP<10⁻². We demonstrate that reliability depends not only on the sizing variables and on the distribution function of solar radiation, but on the minimum value as well, which in a given location and with a monthly average clearness index, achieves total solar radiation on the receiver surface.     

The role of nuclear energy in the more efficient exploitation of fossil fuel resources

The energy theory of value, being a valuable addition to the debate on the rational exploitation of man's energy reserves, is applied in order to clarify the presently confused energy input/output relations for nuclear and solar systems as they interact with fossil fuel. It is shown on the basis of purely energetics considerations that the nuclear route—at present and in future—is a very efficient way to stretch out and finally to substitute for the limited fossil fuel resources. This is particularly true if one considers the transistory phase where the substituting process has to exhibit a rapid exponential growth rate. The energetical effectiveness of the production of a synthetic fuel, as for example hydrogen by water splitting processes, is addressed at the end and serves to give an idea how effectively the energy available in fossil fuels can be amplified by virtue of the coupling of nuclear energy into the process.     

Theory and Applications of Ignition with Variable Activation Energy

The determination of critical conditions for thermal ignition of combustible materials has been traditionally studied by the use of one overall reaction with bounded parameter values for the activation energy and other chemical constants, Significant errors can occur in the values of the threshold parameters for ignition when there are two (or more) simultaneous reactions present with distinct values of the chemical constants. Recent work with simultaneous parallel reactions showed the thresholds for ignition could be lowered in this case. In this paper, motivated by experimental results for forest litter and coal, it is shown that for sequential reactions (different values of parameters in different temperature ranges) that the threshold conditions are changed (safer for lower ambient temperatures and less safe for higher ambient temperatures).The mathematical analysis is summarised and a detailed analysis is given for the forest litter and crushed coal applications. The experimental results show that variable activation energy does occur and that this extension of the classical Frank-Kamenetskii theory is needed. Here the analysis is confined to the slab geometry only but the ideas developed can easily be extended to more general systems, including those involving mass transport, consumption, and phase changes.     

Analysis of a small wind-hydrogen stand-alone hybrid energy system

In this article, detailed modeling, simulation, and analysis of an isolated wind-hydrogen hybrid energy system is presented. Dynamic nonlinear models of all the major subsystems are developed based on sets of empirical and physical relationships. The performance of the integrated hybrid energy system is then analyzed through digital simulation. Design of dynamic controllers and supervisory control schemes are also presented. Expected behaviors during sudden load variation, wind speed change and hydrogen pressure drop are observed under both stochastic and step-variation conditions. MATLAB-Simulink^TM is employed for dynamic system modeling. This exercise, in essence, outlines a process of wind-hydrogen off-grid system control synthesis and performance evaluation. Finally, results of the analysis are summarized, limitations of the simulation study are identified, and scope for future work is indicated.     

Feasibility analysis of stand-alone renewable energy supply options for a large hotel

This paper provides a feasibility analysis of renewable energy supply (RES) for a stand-alone supply large-scale tourist operation (with over 100 beds). The analysis utilises the power load data from a hotel located in a subtropical coastal area of Queensland, Australia. The assessment criteria of the analysis are net present cost, renewable factor and payback time. Due to the limited number of RES case studies in tourist operations and the absence of studies for large resorts, requiring facilities with a higher degree of comfort such as air-conditioning, it is not possible to establish with confidence the viability of RES in this industry. The specific operational characteristics of the tourism accommodation sector, such as 24-h operation, comfort provision and low tolerance for failure necessitates a separate assessment of RES viability for this sector, rather than relying on similar assessments from other commercial sectors. This study uses RES assessment software tools, HOMER (National Renewable Energy Laboratory, US) and HYBRIDS (Solaris Homes, Queensland, Australia), in order to compare diesel generator-only, RES-only and RES/diesel hybrid technologies. HOMER uses hourly load data, whilst HYBRIDS uses average daily energy demand for each month. The modelling results demonstrate that RES, in principle, has the potential to adequately and reliably meet power demand for a stand-alone large-scale tourist accommodation. Optimisation modelling demonstrates that 100% of power demand can be supplied by a RES-only configuration. A hybrid diesel/RES configuration provides the lowest NPC result with a resultant RF of 76%. In comparison to the diesel generator-only configuration, NPC is reduced by 50% and Greenhouse Gas (GHG) emissions by 65%. The payback time of the hybrid RES scenario is 4.3 years. Results indicate that wind energy conversion systems (WECS), rather than photovoltaics, are the most economically viable RES for large-scale operations. Large-scale WECS (over 1000 kW) are more efficient and economical than multiple small-scale WECS (0.1–100 kW). Both modelling tools produced similar results, with HYBRIDS producing on average slightly higher NPC results than HOMER. The modelling and resulting data from the analysis indicate that RES is technically feasible and economically viable as a replacement for conventional thermal energy supply for large-scale tourist operations dependent on stand-alone power supplies.     

World energy resources: a survey

The World Energy Conference published Survey of energy resources 1974 in September 1974 to coincide with the 9th WEC meeting, held in Detroit. This is the third in a series of surveys by WEC, the previous volumes having been published in 1962 and 1968. Dr Albert Parker, CBE, was responsible for these earlier surveys and here he reviews the most recent one which was compiled by a team from the US Atomic Energy Commission's Oak Ridge National Laboratory with the assistance of an international panel of advisors.     

Integration of a hydrogen economy into the German energy system: an optimising modelling approach

Possible limitations of the oil supply are increasingly triggering the search for alternative fuels, especially hydrogen. This paper describes a novel modelling approach developed to assess the geographic and temporal set-up of an infrastructure for a hydrogen-based transport system in Germany till 2030 and to analyse the effects on the national energy system. The results show that the fossil hydrogen production dominates while the infrastructure is being developed and that the mix between gas and coal is highly sensitive to the price ratios. Even in this case, a remarkable CO₂ reduction is achievable. In the first decade, decentralised plants play an important role, but also industrial by-product hydrogen. The introduction of hydrogen in areas with high population density minimises infrastructure costs. Liquefied hydrogen is economic with large plants and dispersed hydrogen demand. In the long run, co-production of electricity and hydrogen in IGCC plants (with CCS) is a promising option, particularly under restrictive CO₂ regimes     

An analytical approach for optimising a set of α and ε values for solar energy applications

An analytical method for optimising a set of α and ε values for specified set of operating conditions (plate temperature, ambient temperature, number of glass covers, wind velocity, solar flux etc.) has been proposed. The absorptivity (α)-emissivity (ε) curves obtained suggest the existence of an optimum (α, ε) set, which would maximise the useful energy from a collector.     

A six-phase synchronous generator for stand-alone renewable energy generation: Experimental analysis

This paper presents the steady-state behavior of a SPSG (six-phase synchronous generator) configured to operate as a stand-alone electric energy source in conjunction with a hydro power plant. A purely experimental treatment is provided with the emphasis placed on operating regimes that illustrate the advantages of using SPSG. In particular, it is shown that the generator can supply two separate three-phase loads which represent an additional advantage. Last but not least, outputs of the two three-phase windings can be used to supply a single three-phase load through an interconnecting six-phase to three-phase transformer, in which case failure of one three-phase winding does not lead to the system shutdown and the load can be still supplied from the remaining healthy winding. Experimental results include loading transients with independent three-phase resistive load at each of the two three-phase winding sets, and measured steady-state characteristics for various configurations and operating conditions.     

独立太阳能电站后期管理问题的思考

<正>一前言电站的后期管理是项目运行过程的重中之重,科学的管理办法将保障投资者或广大用户的实际利益。青海省光明工程、中德合作kfw项目的实施建设,虽然解决了青海省周边偏远无电地区农牧民群众的基本生活用电问题,但在项目实施过程     

Supervisor control for a stand-alone hybrid generation system using wind and photovoltaic energy

A comprehensive supervisor control for a hybrid system that comprises wind and photovoltaic generation subsystems, a battery bank, and an ac load is developed in this paper. The objectives of the supervisor control are, primarily, to satisfy the load power demand and, second, to maintain the state of charge of the battery bank to prevent blackout and to extend the life of the batteries. For these purposes, the supervisor controller determines online the operation mode of both generation subsystems, switching from power regulation to maximum power conversion. Decision criteria for the supervisor based on measurable system variables are presented. Finally, the performance of the supervisor controller is extensively assessed through computer simulation using a comprehensive nonlinear model of the plant.     

Dynamic response of a stand-alone wind energy conversion systemwith battery energy storage to a wind gust

A mathematical model of each element of a stand-alone wind energy conversion system is developed. The model variables are expressed in the d-q rotor reference frame. The wind turbine was considered as the only source of power in this study. Using this model, the system response to a recorded wind gust is investigated by calculating the generator current, the rectifier current, the load current, the battery charging current and the battery voltage. The calculated results are then verified by comparing them with actual values obtained from a data acquisition system. Good agreement was achieved between the experimental and analytical results     

Improving the assessment of wave energy resources by means of coupled wave-ocean numerical modeling

Sea waves energy represents a renewable and sustainable energy resource, that nevertheless needs to be further investigated to make it more cost-effective and economically appealing. A key step in the process of Wave Energy Converters (WEC) deployment is the energy resource assessment at a sea site either measured or obtained through numerical model analysis. In these kind of studies, some approximations are often introduced, especially in the early stages of the process, viz. waves are assumed propagating in deep waters without underneath ocean currents. These aspects are discussed and evaluated in the Adriatic Sea and its northern part (Gulf of Venice) using locally observed and modeled wave data. In particular, to account for a “state of the art” treatment of the Wave–Current Interaction (WCI) we have implemented the Simulating WAves Nearshore (SWAN) model and the Regional Ocean Modeling System (ROMS), fully coupled within the Coupled Ocean Atmosphere Wave Sediment Transport (COAWST) system. COAWST has been applied to a computational grid covering the whole Adriatic Sea and off-line nested to a high-resolution grid in the Gulf of Venice. A 15-year long wave data set collected at the oceanographic tower “Acqua Alta”, located approximately 15 km off the Venice coast, has also been analyzed with the dual purpose of providing a reference to the model estimates and to locally assess the wave energy resource. By using COAWST, we have quantified for the first time to our best knowledge the importance of the WCI effect on wave power estimation. This can vary up to 30% neglecting the current effect. Results also suggest the Gulf of Venice as a suitable testing site for WECs, since it is characterized by periods of calm (optimal for safe installation and maintenance) alternating with severe storms, whose wave energy potentials are comparable to those ordinarily encountered in the energy production sites.     

Improving voltage harmonic compensation of a single phase inverted-based PEM fuel cell for stand-alone applications

Fuel cell (FC) is an efficient energy conversion technology that is growing rapidly and will have a significant role to play in a number of energy end-use sectors, from small-scale applications to large-scale power plants. In this paper, two new methods for voltage harmonic compensation of a stand-alone single phase inverted-based FC are presented and evaluated. The stand-alone power system under study consists of: 1) Proton-Exchange-Membrane (PEM) FC with unidirectional DC/DC converter, which converts the DC voltage delivered by the FC to the DC bus voltage; 2) single-phase pulse width modulated (PWM) inverter; 3) transformer; 4) passive filter; and 5) linear and non-linear loads. The dynamic model of this system and the non-sinusoidal output-based controls applied to the PWM inverter for voltage regulation and harmonic compensation are detailed in this paper, and evaluated by simulation under different linear and non-linear loads. Simulation results show the effectiveness of the two purposed methods for voltage harmonic compensation to acceptable levels defined in grid codes.     

Sizing optimization,dynamic modeling and energy management strategies of a stand-alone PV/hydrogen/battery-based hybrid system

This paper presents a sizing method and different control strategies for the suitable energy management of a stand-alone hybrid system based on photovoltaic (PV) solar panels, hydrogen subsystem and battery. The battery and hydrogen subsystem, which is composed of fuel cell (FC), electrolyzer and hydrogen storage tank, act as energy storage and support system. In order to efficiently utilize the energy sources integrated in the hybrid system, an appropriate sizing is necessary. In this paper, a new sizing method based on Simulink Design Optimization (SDO) of MATLAB was used to perform a technical optimization of the hybrid system components. An analysis cost has been also performed, in that the configuration under study has been compared with those integrating only batteries and only hydrogen system. The dynamic model of the designed hybrid system is detailed in this paper. The models, implemented in MATLAB-Simulink environment, have been designed from commercially available components. Three control strategies based on operating modes and combining technical-economic aspects are considered for the energy management of the hybrid system. They have been designed, primarily, to satisfy the load power demand and, secondarily, to maintain a certain level at the hydrogen tank (hydrogen energy reserve), and at the state of charge (SOC) of the battery bank to extend its life, taking into account also technical-economic analysis. Dynamic simulations were performed to evaluate the configuration, sizing and control strategies for the energy management of the hybrid system under study in this work. Simulation results show that the proposed hybrid system with the presented controls is able to provide the energy demanded by the loads, while maintaining a certain energy reserve in the storage sources.