Energy storage sizing for wind power: impact of the autocorrelation of day-ahead forecast errors

International audienceAvailability of day-ahead production forecast is an important step towards better dispatchability of wind power production. However, the stochastic nature of forecast errors prevents a wind farm operator from holding a firm production commitment. In order to mitigate the deviation from the commitment, an energy storage system connected to the wind farm is considered. One statistical characteristic of day-ahead forecast errors has a major impact on storage performance: errors are significantly correlated along several hours. We thus use a data-fitted autoregressive model that captures this correlation to quantify the impact of correlation on storage sizing. With a Monte Carlo approach, we study the behavior and the performance of an energy storage system (ESS) using the autoregressive model as an input. The ability of the storage system to meet a production commitment is statistically assessed for a range of capacities, using a mean absolute deviation criterion. By parametrically varying the correlation level, we show that disregarding correlation can lead to an underes- timation of a storage capacity by an order of magnitude. Finally, we compare the results obtained from the model and from field data to validate the model

Real-time testing of energy storage systems in renewable energy applications

Energy storage systems provide a promising solution for the renewable energy sector to facilitate large-scale grid integration. It is thus very important to explore means to validate their control scheme and their behaviour in the intended application before actual commissioning. This paper presents a reduced-scale hardware-in-the-loop simulation for initial testing of the performance of energy storage systems in renewable energy applications. This relieves the need of selecting and tuning a detailed model of the energy storage element. A low-power test rig emulating the storage element and the power converter is interfaced with a real time digital simulator to allow dynamic experimental tests under realistic conditions. Battery energy storage for smoothing the output power of a variable speed wind turbine is considered in this paper; however the proposed test methodology can be easily adapted for other storage elements in renewable energy, distributed generation and smart grid applications. The proposed HIL simulation is detailed and the experimental performance is shown

Reliability and quality of service of an off-grid wind powered roadside unit in a motorway vehicular environment

Wind-powered base stations and roadside units have been considered as a cost effective greening solution in windy countries which also have limited solar irradiation. The practicality of such a system increases significantly in sparse areas such as countryside and motorways. The deployment of standalone off-grid wind powered roadside units could alleviate the common issues related to grid connected renewable energy farms. Hence, there is need to study the feasibility of an off-grid wind powered roadside unit for seamless connectivity. Unlike the conventional usage of reliability analysis of fault-tolerant systems, in this paper, reliability is redefined in the context of availability of intermittent wind for powering a roadside unit (RSU) in a UK motorway vehicular environment. Transient analysis of energy consumption (energy demand) of the RSU and harnessed wind energy are carried out along with real measurements for developing respective generic energy models. Further, a generalised methodology is developed to determine the minimum battery size for achieving a certain reliability standard and quality of service. Several reliability indices such as loss of load probability (LOLP), loss of load expectation (LOLE), energy index of reliability (EIR), mean time between failures (MTBF), mean time to recovery (MTTR), forced outage rate (FOR), etc. are obtained for the RSU. The performance results reveal that with a standard micro-turbine and a reasonably small battery, an RSU achieves a good reliability of 99.9% with significant improvement in the quality of service

Impact of Wind Speed Correlation on the Operation of Energy Storage Systems

Renewable resources technologies such as wind power currently demonstrate a worldwide popularity thanks to their environmental friendly status and their economic potential. The variability of the wind power output implies the use of practical solutions such as energy storage systems in order to retain the power system stability and reliability. The wind geographical correlation between different wind farms also impacts the system reliability. This paper studies the effects of the wind speed correlation level on the performance of the associated energy storage system (ESS). Wind correlated model using Weibull probability distribution and Nataf transformation is presented. Energy storage system model and energy management algorithm are developed. Both are applied to a modified IEEE-RTS power generation and load model. The case simulation results indicate that the wind speed correlation level between two wind farms impacts the power distribution inside energy storages and that it needs to be considered in order not to overestimate ESS benefits on the system

Modeling and Comparison of Synchronous Condenser and SVC

In this thesis, a synchronous condenser is modeled in PSCAD/EMTDC and compared with the PSCAD built-in model. After the model verification, a comparison between a conventional synchronous condenser and a superconducting synchronous condenser is made by simulating different cases in a grid setup. Finally, comparison between a conventional synchronous condenser, a superconducting synchronous condenser and an SVC is made in a grid setup by simulating different factors that affect the performance of reactive power compensation units. The simulations have shown that the difference in the results between the implemented synchronous condenser model and the PSCAD built- in model was less than 5~\%. Moreover, by increasing the order of the solver, more accurate results were obtained. Also, during the faults, injection of more reactive power by the superconducting synchronous condenser than the conventional synchronous condenser due to its low synchronous reactance was observed. As the SVC injects reactive power proportional to the square of its terminal voltage, during faults that cause less voltage drop on its terminals, such as the case observed in single phase to ground faults, it showed a better performance, whereas, during severe faults, such as two phase to ground and three phase to ground faults, synchronous condensers brought the load voltage to the nominal value quicker