Paradigm shift in urban energy systems through distributed generation: Methods and models

The path towards energy sustainability is commonly referred to the incremental adoption of available technologies, practices and policies that may help to decrease the environmental impact of energy sector, while providing an adequate standard of energy services. The evaluation of trade-offs among technologies, practices and policies for the mitigation of environmental problems related to energy resources depletion requires a deep knowledge of the local and global effects of the proposed solutions. While attempting to calculate such effects for a large complex system like a city, an advanced multidisciplinary approach is needed to overcome difficulties in modeling correctly real phenomena while maintaining computational transparency, reliability, interoperability and efficiency across different levels of analysis. Further, a methodology that rationally integrates different computational models and techniques is necessary to enable collaborative research in the field of optimization of energy efficiency strategies and integration of renewable energy systems in urban areas. For these reasons, a selection of currently available models for distributed generation planning and design is presented and analyzed in the perspective of gathering their capabilities in an optimization framework to support a paradigm shift in urban energy systems. This framework embodies the main concepts of a local energy management system and adopts a multicriteria perspective to determine optimal solutions for providing energy services through distributed generation.     

Grid integrated renewable DG systems: A review of power quality challenges and state-of-the-art mitigation techniques

Increased energy demands due to rapid industrialization, environmental concerns with fossil fuel–based generation, diminishing fossil energy resources, transmission network congestion, and technical performance deterioration are the motivations behind the integration of small renewable distributed generation (DG) units and turning the existing power systems into a restructured one. Optimizing the technical benefits offered by DG placement is a well-known challenge for distribution network operators (DNOs) for both fossil and renewable energy resource–based DGs, but renewable DG systems have several power quality (PQ) challenges associated additionally. Power quality is a very significant characteristic of renewable DG systems because today's loads are more sensitive to PQ disturbances and penetration of renewable energy as well as nonlinear loads is proliferating in distribution power networks. So the need for innovative power quality improvement (PQI) techniques becomes inevitable due to ongoing reformation in traditional distribution networks by the integration of renewable energy. This article presents a comprehensive analysis of power quality challenges with grid integration of renewable DG systems and current research status of associated mitigation techniques. Firstly, this paper puts emphasis on theoretically illustrating all the crucial power quality challenges associated with grid integration of renewable energy, and secondly, a thorough survey, of all PQI techniques introduced till date, is elaborated along with highlighting the opportunities for future research. Furthermore, all the crucial power quality issues, the impact of high penetration of renewable energy and mitigation techniques on power quality, are demonstrated also by simulating a grid integrated PV-based DG system in MATLAB/Simulink. This article is believed to be very beneficial for academics as well as industry professionals to understand existing PQ challenges, PQI techniques, and future research directions for renewable energy technologies.     

A multi‐predictor model to estimate solar and wind energy generations

Recent technological developments in renewable energy systems and significant growth of solar and wind energy have made these 2 renewable sources potential viable alternatives for conventional energy sources. However, due to intermittent nature, their reliability and availability are not similar to traditional sources. Hence, it is crucial to estimate the solar and wind availability and contribution more accurately. There are various factors affecting the generation capacity of renewable sources. There has been a vast research on the impact of factors related to climate condition such as wind speed, air temperature, and humidity on renewable energy generation. However, there are several other factors with indirect impact on renewable capacity and generation mostly overshadowed by the climate factors. In this study, a multi‐predictor regression model is developed and presented for solar and wind energy generation capacity across the USA. Our study of 50 states shows how the generation capacity can be affected by several indexes including human development index. Variables with the more significant impacts have been chosen using a regression analysis. A recommendation on the best transformation of the response variables and sensitivity analysis of the results has also been presented. The results provide a model to estimate the generation capacity using significant predictors. For instance, the impact of population growth on the wind turbine generation can be explored using these models.     

Bi‐objective optimization of a grid‐connected decentralized energy system

Motivated by the increasing transition from fossil fuel–based centralized systems to renewable energy–based decentralized systems, we consider a bi‐objective investment planning problem of a grid‐connected decentralized hybrid renewable energy system. In this system, solar and wind are the main electricity generation resources. A national grid is assumed to be a carbon‐intense alternative to the renewables and is used as a backup source to ensure reliability. We consider both total cost and carbon emissions caused by electricity purchased from the grid. We first discuss a novel simulation‐optimization algorithm and then adapt multi‐objective metaheuristic algorithms. We integrate a simulation module to these algorithms to handle the stochastic nature of this bi‐objective problem. We perform extensive comparative analysis for the solution approaches and report their performances in terms of solution time and quality based on well‐known measures from the literature.     

Optimal operation of DC smart house system by controllable loads based on smart grid topology

From the perspective of global warming mitigation and depletion of energy resources, renewable energy such as wind generation (WG) and photovoltaic generation (PV) are getting attention in distribution systems. Additionally, all-electric apartment houses or residence such as DC smart houses are increasing. However, due to the fluctuating power from renewable energy sources and loads, supply-demand balancing of power system becomes problematic. Smart grid is a solution to this problem. This paper presents a methodology for optimal operation of a smart grid to minimize the interconnection point power flow fluctuation. To achieve the proposed optimal operation, we use distributed controllable loads such as battery and heat pump. By minimizing the interconnection point power flow fluctuation, it is possible to reduce the electric power consumption and the cost of electricity. This system consists of photovoltaic generator, heat pump, battery, solar collector, and load. To verify the effectiveness of the proposed system, results are used in simulation presented.     

An approach for the integration of renewable distributed generation in hybrid DC/AC microgrids

This paper presents an investigation of a hybrid DC/AC integration paradigm to establish microgrids (MGs) by using a conventional three-phase local power delivery system. This approach adds an additional DC power line to the local power distribution system in order to collect energy generated by distributed domestic renewable sources. The local renewable distributed generation (DG) works in conjunction with the conventional grid utility to reduce the power draw from the grid. Researchers designed an energy conversion station to mix energy from the local DGs with energy from the grid utility. This approach, therefore, uses a continuous energy mixing strategy for DC integration of local generation and grid energy to supply energy to MG consumers via the conventional three-phase power distribution system. Thus, local distributed renewable generators do not have to contend with AC integration problems, such as AC stability and line synchronization. This approach can facilitate the transformation of conventional local power distribution systems into reliable MGs in an affordable way for stakeholders and it is a step towards construction of future smart grids.     

Sizing of integrated renewable energy system based on load profiles and reliability index for the state of Uttarakhand in India

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.     

Reliability/cost implications of PV and wind energy utilization insmall isolated power systems

The application of renewable energy in electric power systems is growing rapidly due to enhanced public concerns for adverse environmental impacts and escalation in energy costs associated with the use of conventional energy sources. Photovoltaics and wind energy sources are being increasingly recognized as cost effective generation sources in small isolated power systems primarily supplied by costly diesel fuel. The utilization of these energy sources can significantly reduce the system fuel costs but can also have considerable impact on the system reliability. A realistic cost/reliability analysis requires evaluation models that can recognize the highly erratic nature of these energy sources while maintaining the chronology and interdependence of the random variables inherent in them. This paper presents a simulation method that provides objective indicators to help system planners decide on appropriate installation sites, operating policies, and selection of energy types, sizes and mixes in capacity expansion when utilizing PV and wind energy in small isolated systems     

Photovoltaic deployment strategy in Japan and the USA—an institutional appraisal

Photovoltaic (PV) is a renewable energy technology, along side with other modular energy generation technologies such as micro-turbines, fuel cells, etc., which will enable the alternative distributed generation paradigm compared to the incumbent fossil fuel based centralized generation paradigm. Distributed generation utilizing renewable energy resources offers opportunities for significant carbon dioxide and emissions reductions thus contributing solutions to broader climate change issues.     

基于虚拟储能的微网风光储容量优化配置方法研究

风光储互补发电系统能够提高微网系统的稳定性.为了提升微网储能资源的合理配置,文章基于虚拟储能和电力弹簧概念,提出了计及主配储能协同的微网风光储容量双层优化配置方法,并利用改进的粒子群算法对风光储容量双层优化配置方法求解.最后,通过算例分析表明,文章配置方法提高了微网系统调节能力,降低了电压偏移率.     

Application of geothermal energy for heating and fresh water production in a brackish water greenhouse desalination unit: A case study from Algeria

The aim of this paper was to outline a proposed a new brackish water greenhouse desalination unit powered by geothermal energy for the development of arid and relatively cold regions, using Algeria as a case study. Countries which have abundant sea/brackish water resources and good geothermal conditions are ideal candidates for producing fresh water from sea/brackish water. The establishment of human habitats in these arid areas strongly depends on availability of fresh water. The main advantage of using geothermal energy to power brackish water greenhouse desalination units is that this renewable energy source can provide power 24 h a day. This resource is generally invariant with less intermittence problems compared to other renewable resources such as solar or wind energy. Geothermal resources can both be used to heat the greenhouses and to provide fresh water needed for irrigation of the crops cultivated inside the greenhouses. A review of the geothermal potential in the case study country is also outlined.     

Distributed photovoltaic generation and energy storage systems: A review

Currently, in the field of operation and planning of electrical power systems, a new challenge is growing which includes with the increase in the level of distributed generation from new energy sources, especially renewable sources. The question of load redistribution for better energetic usage is of vital importance since these new renewable energy sources are often intermittent. Therefore, new systems must be proposed which ally energy storage with renewable energy generators for reestablishment of grid reliability. This work presents a review of energy storage and redistribution associated with photovoltaic energy, proposing a distributed micro-generation complex connected to the electrical power grid using energy storage systems, with an emphasis placed on the use of NaS batteries. These systems aim to improve the load factor, considering supply side management, and the offer of backup energy, in the case of demand side management.     

秸秆发电项目燃料资源的可靠性研究

阐述了对可再生能源进行评价的方法,重点分析和探讨了秸秆发电项目燃料资源评估应该考虑的因素。通过分析表明,秸秆资源总量、可获得量、可利用量及有效供应时间都直接影响燃料资源的可靠性。所得结论为今后秸秆发电项目的设计和审批提供依据和参考。     

Stochastic scheduling of power system in the presence of electric vehicle and renewable sources considering security and economic indexes using an improved mutation particle swarm optimization (M-PSO) algorithm

Increased air pollution and global temperature as well as motor vehicle fuel consumption have depleted fossil fuel resources and increased environmental problems caused by the consumption of such fuels. In addition to methods such as combined heat and power (CHP) technology and distributed generation (DG) of energy at the consumption site, renewable energy sources and EVs are considered suitable methods for achieving this goal, which is prepared by the grid or battery electric energy. Generation uncertainty due to the lack of solar radiation and constant wind blow at different hours of the day is the only challenge for using renewable energies. Moreover, system reliability is a concept that refers to the safe and reliable operation of the system. In general, the wider and more important the system, the more attention that is paid to calculating its reliability in planning and decision making. This study aims to examine the problem of probabilistic power system planning by calculating the power system reliability, evaluating the effect of the presence of these vehicles on security and economic indicators and renewable energy sources, and modeling uncertainties using a Least Squares Generative Adversarial Network (LSGANs) method with generating various scenarios for solar irradiance and wind speed. Furthermore, the Kantorovich distance matrix (KDM) is used to reduce the number of generated scenarios. In the proposed model, the conditional value-at-risk (CVaR) method is implemented to assess and control the risk caused by uncertainties of the proposed problem. Using the power stored in the EV battery is evaluated to cover wind and solar energy source uncertainties.     

Towards 100% renewable energy systems: Uncapping power system flexibility

Relying almost entirely on energy from variable renewable resources such as wind and solar energy will require a transformation in the way power systems are planned and operated. This paper outlines the necessary steps in creating power systems with the flexibility needed to maintain stability and reliability while relying primarily on variable energy resources. These steps are provided in the form of a comprehensive overview of policies, technical changes, and institutional systems, organized in three development phases: an initial phase (penetration up to about 10%) characterized by relatively mild changes to conventional power system operations and structures; a dynamic middle phase (up to about 50% penetration) characterized by phasing out conventional generation and a concerted effort to wring flexibility from existing infrastructure; and the high penetration phase that inevitably addresses how power systems operate over longer periods of weeks or months when variable generation will be in either short supply, or in over-abundance. Although this transition is likely a decades-long and incremental process and depends on the specifics of each system, the needed policies, research, demonstration projects and institutional changes need to start now precisely because of the complexity of the transformation. The list of policy actions presented in this paper can serve as a guideline to policy makers on effectuating the transition and on tracking the preparedness of systems.     

Water desalination systems powered by renewable energy sources: Review

Water and energy are two of the most important topics on the international environment and development agenda. The social and economic health of the modern world depends on sustainable supply of both energy and water. Many areas worldwide that suffer from fresh water shortage are increasingly dependent on desalination as a highly reliable and non-conventional source of fresh water. So, desalination market has greatly expanded in recent decades and expected to continue in the coming years. The integration of renewable energy resources in desalination and water purification is becoming increasingly attractive. This is justified by the fact that areas of fresh water shortages have plenty of solar energy and these technologies have low operating and maintenance costs.The present paper presents a review for the work that has been achieved during the recent years in the field of desalination by renewable energies, with emphasis on technologies and economics. The review also includes water sources, demand, availability of potable water and purification methods. A comparative study between different renewable energy technologies powered desalination systems as well as performance and economics have been done. Finally, some general guidelines are given for selection of desalination and renewable energy systems and the parameters that need to be considered.     

Renewable energy resources as an alternative to modify the load curve in Northern Cyprus

The average annual increase in electricity consumption and peak demand in Northern Cyprus (N. Cyprus) during the past 20 years have been 7.1 and 5.5%, respectively. In recent years, the demand for electricity has been stretched to its limits in winter. This raised the question of whether renewable energy resources could be utilized to reduce the level of peak demand. Indeed, Cyprus being a Mediterranean island, enjoys an abundance of solar energy, and preliminary studies showed that a considerable potential of wind energy is also available. Utilization of renewable energy for space heating, water heating, pumping and power generation would increase electrical reserve margins, raise system load factor, improve load following capabilities, and reduce the need for capacity expansion. Currently, solar water heating which leads to a saving of at least 72 GWh energy per annum and a significant reduction in CO₂ emission has been extensively used in N. Cyprus. In N. Cyprus, despite the availability of renewable energy resources constructing renewable base-load, electrical power stations has not been found feasible. However, constructing such systems is recommended for two reasons: firstly, as a supplement to saving fuel and secondly, expanding capacity. In this context, the economic analysis for both solar and wind energy systems, has shown a reasonable internal rate of return (IRR). Although, the IRR is higher for wind energy systems, the availability of wind is limited to a few locations and therefore energy distribution is required.     

Sustainable energy system design with distributed renewable resources considering economic,environmental and uncertainty aspects

Electricity generation using renewable energy generation technologies is one of the most practical alternatives for network planners in order to achieve national and international Greenhouse Gas (GHG) emission reduction targets. Renewable Distributed Generation (DG) based Hybrid Energy System (HES) is a sustainable solution for serving electricity demand with reduced GHG emissions. A multi-objective optimisation technique for minimising cost, GHG emissions and generation uncertainty has been proposed in this paper to design HES for sustainable power generation and distribution system planning while considering economic and environmental issues and uncertainty in power availability of renewable resources. Life cycle assessment has been carried out to estimate the global warming potential of the embodied GHG emissions from the electricity generation technologies. The uncertainty in the availability of renewable resources is modelled using the method of moments. A design procedure for building sustainable HES has been presented and the sensitivity analysis is conducted for determining the optimal solution set.     

Island breezes

What does 40% renewable energy look like on a small island grid? As with most things in life, the answer is, "It depends." It depends on the characteristics of the thermal generation mix, the diversity of the variable renewable resources, the capabilities and characteristics of the renewable generation technology, and the characteristics of the transmission grid. Island systems face challenges in these areas not experienced by large, integrated systems. In spite of this, Hawaiian grids are targeting--and on one island have recently reached--40% of electrical energy from the islands' abundant renewable resources. The steps to reach this goal are outlined in a recent agreement between the Hawaiian Electric utility; the governor of Hawaii; the Hawaii Department of Business, Economic Development, and Tourism; and the State of Hawaii Office of the Consumer Advocate. The U.S. Department of Energy (DOE) also participated. Information on this energy agreement, part of the Hawaii Clean Energy Initiative, can be found at hawaiicleanenergy.com or www.heco.com.     

Making microgrids work

Distributed energy resources including distributed generation and distributed storage are sources of energy located near local loads and can provide a variety of benefits including improved reliability if they are properly operated in the electrical distribution system. Microgrids are systems that have at least one distributed energy resource and associated loads and can form intentional islands in the electrical distribution systems. This paper gives an overview of the microgrid operation. Microgrid testing experiences from different counties was also provided.