Integration Of Renewable Sources Research Articles

Recent results on the integration of variable renewable electric power into the US grid

ABSTRACT

Renewable energy integration in smart grids-multicriteria assessment using the fuzzy analytical hierarchy process

Unlike the traditional way of efficiency assessment of renewable energy sources integration, the smart grid concept is introducing new goals and objectives regarding increased use of renewable electricity sources, grid security, energy conservation, energy efficiency, and deregulated energy market. Possible benefits brought by renewable sources integration are evaluated by the degree of the approach to the ideal smart grid. In this paper, fuzzy analytical hierarchy process methodology for the integration efficiency has been proposed, taking into account the presence of multiple criteria of both qualitative and quantitative nature, different performance indicators, and the uncertain environment of the smart grid. The methodology has been illustrated on the choice of the size and location of a distributed generator in the radial distribution feeder.

Performance Analysis of Unbalance Radial Feeder with Time Varying Composite Load

The focus of this paper is to present performance indices for unbalance radial feeder having different characteristic and composition of time varying static ZIP load models. These provide a framework for benchmarking of distribution automation projects. 15 minutes characteristics time interval for load flow and load modeling are considered to meet smart grid implementation criterion. A forward-backward sweep method is employed for load flow solution. Developed performance indices were illustrated on modified IEEE 37 node test feeder. Performance indices are useful for analysis, operational, planning and integration of stochastic renewable sources.

A new scenario generation-based method to solve the unit commitment problem with high penetration of renewable energies

Abstract Optimal operation of power systems with high integration of renewable power sources has become difficult as a consequence of the random nature of some sources like wind energy and photovoltaic energy. Nowadays this problem is solved using the Monte Carlo Simulation (MCS) approach, which allows the consideration of important statistical characteristics of wind and solar power production, such as the correlation between consecutive observations, the diurnal profile of the forecasted power production, and the forecasting error. In this paper, a new model of the unit scheduling of power systems with significant renewable power generation based on the scenario generation/reduction method combined with the priority list (PL) method is proposed that finds the probability distribution function (PDF) of a determined generator be committed or not. This approach allows the recognition of the role of each generation unit on the day-ahead unit commitment (UC) problem with a probabilistic point of view, which is important for acquiring a cost-effective and reliable solution. The capabilities and performance of the proposed approach are illustrated through the analysis of a study case, where the spinning reserve requirements are probabilistically verified with success.

Demand-side management in smart grid operation considering electric vehicles load shifting and vehicle-to-grid support

• Optimization-based demand-side strategy, including electric vehicles. • Profit maximization of the agents and renewable sources integration are pursued. • The proposed methodology is illustrated on the IEEE 37-bus distribution grid . • Demand side management along with V2G can effectively flatten daily load curve. Demand fluctuation in electric power systems is undesirable from many points of view; this has sparked an interest in demand-side strategies that try to establish mechanisms that allow for a flatter demand curve. Particularly interesting is load shifting, a strategy that considers the shifting of certain amounts of energy demand from some time periods to other time periods with lower expected demand, typically in response to price signals. In this paper, an optimization-based model is proposed to perform load shifting in the context of smart grids. In our model, we define agents that are responsible for load, generation and storage management; in particular, some of them are electric vehicle aggregators. An important feature of the proposed approach is the inclusion of electric vehicles with vehicle-to-grid capabilities; with this possibility, electric vehicles can provide certain services to the power grid, including load shifting and congestion management. Results are reported for a test system based on the IEEE 37-bus distribution grid; the effectiveness of the approach and the effect of the hourly energy prices on flattening the load curve are shown.

Impact of Demand Response on Unit Commitment in Microgrid Environment

Demand response program (DRP) aims to reshape an inconsistent load demand and motivates the customers to reduce their energy consumption to get financial benefit. In this paper demand response based unit commitment (DRUC) model is used to study the impact of DRP on generation scheduling and total cost of the system. DRUC model describes the customer behavior for different incentive values and variation in the price elasticity matrix. The simulation study is carried out with a low voltage microgrid system with and without integration of solar and wind renewable sources (RS). It is found from the results that with the increase in incentive value and price elasticity matrix elements, customers tend to participate more in DRP which increases customer benefits and reduces total utility cost. It is also observed that integration of RS significantly reduces the total cost of the system.

Control Energy Consumption and System Performance in Vector Control of Voltage Source Converters

Power electronics plays an important role in the control and conversion of modern electric power systems. In particular, to integrate various renewable energies using DC transmissions and to provide more flexible power control in AC systems, significant efforts have been made in the modulation and control of power electronics devices. Pulse width modulation (PWM) is a well developed technology in the conversion between AC and DC power sources, especially for the purpose of harmonics reduction and energy optimization. As a fundamental decoupled control method, vector control with PI controllers has been widely used in power systems. However, significant power loss occurs during the operation of these devices, and the loss is often dissipated in the form of heat, leading to significant maintenance effort. Though much work has been done to improve the power electronics design, little has focused so far on the investigation of the controller design to reduce the controller energy consumption (leading to power loss in power electronics) while maintaining acceptable system performance. This paper aims to bridge the gap and investigates their correlations. It is shown a more thoughtful controller design can achieve better balance between energy consumption in power electronics control and system performance, which potentially leads to significant energy saving for integration of renewable power sources.

Optimization of Experimental Model Parameter Identification for Energy Storage Systems

The smart grid approach is envisioned to take advantage of all available modern technologies in transforming the current power system to provide benefits to all stakeholders in the fields of efficient energy utilisation and of wide integration of renewable sources. Energy storage systems could help to solve some issues that stem from renewable energy usage in terms of stabilizing the intermittent energy production, power quality and power peak mitigation. With the integration of energy storage systems into the smart grids, their accurate modeling becomes a necessity, in order to gain robust real-time control on the network, in terms of stability and energy supply forecasting. In this framework, this paper proposes a procedure to identify the values of the battery model parameters in order to best fit experimental data and integrate it, along with models of energy sources and electrical loads, in a complete framework which represents a real time smart grid management system. The proposed method is based on a hybrid optimisation technique, which makes combined use of a stochastic and a deterministic algorithm, with low computational burden and can therefore be repeated over time in order to account for parameter variations due to the battery’s age and usage.

A Novel Distributed Direct-Voltage Control Strategy for Grid Integration of Offshore Wind Energy Systems Through MTDC Network

Although HVDC transmission systems have been available since mid-1950s, almost all installations worldwide are point-to-point systems. In the past, the lower reliability and higher costs of power electronic converters, together with complex controls and need for fast telecommunication links, may have prevented the construction of multiterminal DC (MTDC) networks. The introduction of voltage-source converters for transmission purposes has renewed the interest in the development of supergrids for integration of remote renewable sources, such as offshore wind. The main focus of the present work is on the control and operation of MTDC networks for integration of offshore wind energy systems. After a brief introduction, this paper proposes a classification of MTDC networks. The most utilized control structures for VSC-HVDC are presented, since it is currently recognized as the best candidate for the development of supergrids, followed by a discussion of the merits and shortcomings of available DC voltage control methods. Subsequently, a novel control strategy—with distributed slack nodes—is proposed by means of a DC optimal power flow. The distributed voltage control (DVC) strategy is numerically illustrated by loss minimization in an MTDC network. Finally, dynamic simulations are performed to demonstrate the benefits of the DVC strategy.

Renewable energy integration for smart sites

Use of distributed renewable energy sources for domestic energy consumption will increase in the near future, due to its advantages as being clean and infinite energy generation possibility. This trend allows more efficient energy consumption because of reducing transmission loses and dependence of domestic appliances to grid distribution. This study investigates potentials of a smart site concept based on domestic renewable energy generation. The study addresses site scale integration of hybrid renewable sources and grid energies as well as investigates possible advantages of the use of hybrid renewable energy systems based on solar and wind power. A continuous energy mixing strategy is used for DC integration of hybrid renewable energy (wind+solar) and the grid energy to meet site power demand. The proposed case study demonstrates that the smart site with hybrid renewable sources considerably reduces energy dependence of the house appliances to the grid which in turn presents a feasible solution for implementation of distributed generation provision for future smart grids.

Application of STATCOM to Increase Transient Stability of Wind Farm

In this paper we interested to the study the necessary of Facts to increase the transient stability on the presence of faults and the integration of new renewable source, like wind energy, these lasts make the electrical grid operate in a new conditions, the STATCOM is one of the important Facts element, It provides the desired reactive-power generation and absorption entirely by means of electronic processing of the voltage and current waveforms in a voltage source converter (VSC). This function is identical to the synchronous condenser with rotating mass. In present work we propose a transient stability improvement using STATCOM under faults, in the first time we study the transient stability with and without STATCOM for clearly his advantages. In the second time we know the relation between the reactive power injecting by a STATCOM and the critical clearing time, some simulation results are given, commented and discussed.

Evaluating and Planning Flexibility in Sustainable Power Systems

Power systems have traditionally been designed to provide flexibility in a context where demand is met by bulk generation. The integration of variable and uncertain renewable generation sources, such as wind, increases the flexibility needed to maintain the load-generation balance. This paper aims to provide a systematic approach to evaluate the flexibility level and investigate the role of flexibility in generation planning and market operation. An “offline” index is proposed to estimate the technical ability of both the individual generators and the generation mix to provide the required flexibility. A dedicated unit construction and commitment (UCC) algorithm, able to consider plant investment and operation costs, is developed to determine the optimal investments in flexible generating units. Market simulation models are then implemented to determine the profits obtained from providing flexibility in different market designs. An adapted RTS-96 system is used to test the proposed models and the flexibility metric. Results demonstrate the validity of the UCC algorithm and the coherence of the proposed flexibility index. The analysis of the profits of flexibility shows that the market design plays an important role in the efficient deployment and subsequent profitability of flexibility resources.

A bilevel model for electricity retailers' participation in a demand response market environment

Demand response programmes are seen as one of the contributing solutions to the challenges posed to power systems by the large-scale integration of renewable power sources, mostly due to their intermittent and stochastic nature. Among demand response programmes, real-time pricing schemes for small consumers are believed to have significant potential for peak-shaving and load-shifting, thus relieving the power system while reducing costs and risk for energy retailers. This paper proposes a game theoretical model accounting for the Stackelberg relationship between retailers (leaders) and consumers (followers) in a dynamic price environment. Both players in the game solve an economic optimisation problem subject to stochasticity in prices, weather-related variables and must-serve load. The model allows the determination of the dynamic price-signal delivering maximum retailer profit, and the optimal load pattern for consumers under this pricing. The bilevel programme is reformulated as a single-level MILP, which can be solved using commercial off-the-shelf optimisation software. In an illustrative example, we simulate and compare the dynamic pricing scheme with fixed and time-of-use pricing. We find that the dynamic pricing scheme is the most effective in achieving load-shifting, thus reducing retailer costs for energy procurement and regulation in the wholesale market. Additionally, the redistribution of the saved costs between retailers and consumers is investigated, showing that real-time pricing is less convenient than fixed and time-of-use price for consumers. This implies that careful design of the retail market is needed. Finally, we carry out a sensitivity analysis to analyse the effect of different levels of consumer flexibility.

Information Requirements for Motivated Alignment of Manufacturing Operations to Energy Availability

Resources facilitating energy driven manufacturing operations are limited and integration of renewable sources into supply increases volatility of availability. In addition to aligning energy supply to demand, aligning demand to energy availability can help to avoid losses for oversupply and costly reserve power stations causing high energy prices. Therefore in manufacturing industry staff members with responsibility for process planning and control should behave energy aware. Today there often is a lack of motivation for energy related organisational changes, especially in sensitive manufacturing systems. This work presents information requirements for increasing this motivation with the example of electricity.

Smart Grid, Smart Controllers and Home Energy Automation—Creating the Infrastructure for Future

Integration of unpredictable renewable power sources into the Grid is leading to the development of wide area control algorithms and smart grid. Smart meters are the first step in the building a smart consumer interface. Much more, however, would be required in building a smart grid than just smart meters. This paper explores the conceptual architecture of smart grid. It highlights the need for additional infrastructure to realize full potential of smart grid. The information presented in this paper is an attempt to uncover what the future in smart grid could be and what infrastructure would be required to tap its potential. As smart grid evolves, more functionality would be built in the constituents. The paper also proposes mathematical basis for some of the controller algorithms.

Comparative Evaluation of Three-Phase Current Source Inverters for Grid Interfacing of Distributed and Renewable Energy Systems

Despite the rapid growth of self-commutated inverter technology, the well-known current source inverter (CSI) has not achieved significant practical application so far. This raised the question regarding the fundamental criteria that could either prevent or promote the use of such inverters, especially considering emerging fields of application such as grid integration of renewable sources. This paper will, thus, focus on a systematic comparison between circuits based on the CSI and voltage source inverter (VSI). For such purpose, dimensionless benchmark factors were derived. The pulse width-modulated CSI with its inherent step-up capability alongside the indirect CSI (ICSI) with only two high-frequency switches features very interesting characteristics in terms of low switching losses and high inductor power density. However, both topologies show constraints with respect to the provision of reactive power. Two experimental setups have been implemented demonstrating the technical feasibility of different CSI solutions as a grid interface.

Increasing the penetration of renewable energy resources in S. Vicente, Cape Verde

In this article different scenarios are analysed with the objective of increasing the penetration of renewable energies in the energy system of S. Vicente Island in Cape Verde. An integrated approach is used to analyse the electricity and water supply systems. The H 2RES model, a tool designed to simulate the integration of renewable sources and hydrogen in the energy systems of islands or other isolated locations, is applied. There is no other source of fresh water available to supply the population of S. Vicente, apart from desalinated seawater. The electricity supply system of this Island is based on fossil fuel and wind. S. Vicente has important wind resources that are not fully used because of its intermittent nature. The topography of this Island is relatively uniform, with the exception of Mont Verde, a 774 m high mountain located in its centre, which could be suitable for pumped hydro storage. The present analysis incorporates the possibility of using pumped hydro as a storage technique to increase the penetration of renewable energy sources, using desalinated seawater. The results show that is possible to have more than 30% of yearly penetration of renewable energy sources in the electricity supply system, together with more than 50% of the water supplied to the population produced from wind electricity.

Long length HTS cable with integrated FCL property

The past years have shown the growth of bottlenecks in electric power grids, among other reasons caused by the increasing demand of energy in the form of electricity and by the large-scaled integration of renewable sources. As solving of these challenges by means of traditional solutions appears to be more and more problematic, the need for new technology solutions has become apparent. The HTS cable technology demonstrates a great potential in solving of grid congestion issues. In addition to their large power transport capacity and low losses, modern-generation HTS cables also have an integrated fault-current limiting (FCL) property. Applications of such cables in power grids will help to solve fault-current issues when connecting new generators, and dispersed and large-scale renewable sources. As HTS cables, used in current projects, are limited to hundreds of meters in length, they have still not been used for energy transport over long distances. The Dutch DSO Alliander, together with Ultera, is working on the development of a 6 km FCL HTS cable for installation in the Alliander's HV grid. In order to get the low-loss benefits of the HTS technology, a cooling system with a high efficiency is needed. The FCL HTS cable will be cooled by one cooling station at each end of the cable, using a liquid nitrogen coolant. Alliander and Ultera have established and work to achieve technical performance targets believed to be required to realise a 6 km long, 50 kV retrofit system with a power rating of 250 MVA with cooling stations only at the two ends of the cable system. These targets aim to reduce the superconductor's AC loss at a nominal current, reduce the heat leak of the thermally insulating envelope, increase the voltage rating and reduce the friction coefficient of the coolant flow.

Energy Balance of Microalgal-derived Biodiesel

Microalgae have been discussed to be a potential biomass source for the production of biodiesel. This article investigates the renewability of microalgal-sourced biodiesel by analyzing the fossil energy requirements for the microalgal biomass production and fuel conversion process. The results of the analysis carried out in this article indicates that with the present day scenario, the fossil fuel inputs into microalgae biodiesel production outweighs the energy outputs obtained. However, it is further shown that with the integration of renewable electricity generation systems and non-conventional nutrient sources, microalgal-derived biodiesel can be truly considered to be a renewable fuel.

Cleaner energy for sustainable future

This special issue of the Journal of Cleaner Production focuses on “Energy for Sustainable Future”. It is designed to mirror the increasing relevance of renewable energy sources and improved efficiency as crucial topics for practitioners in industry, for governmental policy makers, as well as for civic service providers, researchers, and educators. The purpose of this special issue is to serve as a catalyst for dialogue. The global warming related to CO 2 emissions, coupled with steeply rising energy prices and the recent global financial institutional melt-down are causing massive societal concerns and give rise to increasing demand for ways to improve societal and individual energy efficiency and for ways to shift increasingly to alternative, low or non-carbon based energy systems. Until recently, industrial energy efficiency improvements have focused on improvements on efficiency rather than on the integration of renewable sources. The aim of this special issue is the identification of policies to support the development and implementation of technologies and management approaches we can employ to make the transition to more sustainable societies. The collection of papers in this special issue provide a foundation for students, researchers, scholars, practitioners and policy makers interested in making sustainable development more than a metaphor. The papers include focus upon ways for: (a) Improving industrial process to achieve improvements in energy efficiency. (b) Minimising waste disposals and reducing their impact through better management. (c) Reducing CO 2 emissions by making progress toward lower carbon, renewable energy based systems, (d) Improving production of biofuels and hydrogen production systems, facilitated by employing cleaner production and novel LCA tools. (e) Improving integration of advanced materials and energy efficient equipment in different industrial sectors. Current and future developments in national and world economies are closely connected to sustainable, efficient and safe usage of raw materials and upon energy based on cleaner production concepts and approaches that are ecologically and economically appropriate for the short and for the long-term future of society. These challenges have received considerable attention in the media and scientific journals over the last several years. The idea of developing a specialised conference focussed upon them was put forward on various occasions. Focus upon them became reality on the 5th and 6th May 2008 in the historic Castle of Veszprém, Hungary, the current premises of the Hungarian Academy of Science which hosted the Workshop. The Workshop was a stimulating event and an overwhelming success, with nearly 100 contributors from Africa, North America, Asia and Europe, representing 28 countries. After a comprehensive selection and thorough reviewing procedure 11 papers were selected for this special issue.