Wind Engineering

Increasing amounts of wind turbines are connected to electrical power systems in order to mitigate the negative environmental consequences of conventional electricity generation. There are, however, fundamental differences between conventional and wind power generation, particularly regarding the controllability of the prime mover and the generator types used to convert mechanical energy into electricity. These differences relate to the interaction of wind turbines with the power system, including their impact on its dynamic behaviour. In order to investigate the impact of wind power on power system dynamics, adequate models are essential. However, generally accepted models for representing wind turbines in power-system dynamics simulations are presently not generally available. In this paper, various approaches and challenges for the simulation of power system dynamics are discussed and the associated modelling is analysed.

This paper summarises two reports that were commissioned to analyse impacts of increasing the wind power penetration on the Island of Ireland. The first report was commissioned by Northern Ireland Electricity (NIE) and assesses the contribution renewable sources can make to the Northern Ireland electricity system. The second report was commissioned by the Commission for Energy Regulation (CER) and the Office for the Regulation of Electricity and Gas (Ofreg); it examines the possible effects increasing wind generation would have on the combined systems of Northern Ireland and the Republic of Ireland. The reports undertake a detailed analysis of the potential wind resource available, and the likely impact it may have on the respective transmission and distribution systems. The possible effects that increased amounts of wind generation may have on the system operation are examined and various economic implications are assessed.

Ireland is a facing a critical time in the formation of a robust renewable energy (RE) policy, due to its size, relative isolation, grid infrastructure, and fuel import dependency. The inherent intermittency and unpredictability of wind power make its increased penetration into the electricity network an area requiring significant further analysis. This paper details the state of the Irish electricity system at the end of 2003, describes the status of the electricity market and puts into perspective the technical issues which need to be resolved to increase wind penetration on the island of Ireland.

The penetration of wind energy into small, lightly interconnected power systems, as in Ireland, is increasing. It is therefore important to study how wind farms will interact dynamically with conventional generators and loads. For the future, we need to asses the impact this will have on the stability of the whole system. To investigate this interaction, dynamic simulation studies of the system, with the inclusion of wind turbine generators (WTGs), are important. This requires these generators to be represented in power-system simulation studies to at least the same detail as conventional machines. This paper analyses the dynamic models for WTGs available during 2003 to the Irish Transmission system operator, ESB National Grid. The paper focuses on the modelling of Doubly-Fed Induction Generators (DFIGs). A comparison of the models was carried out and the main conclusions drawn are discussed.

This paper reviews the present purpose and functioning of grid codes for the proper operation of ‘national’ power networks. Now that embedded generation, including especially windfarms, may have total capacities large enough to compare with previous central generating plant, the grid codes are being changed to accommodate such generation. Modern wind turbines need to operate under new and challenging constraints that require the introduction of both new technology and sympathetic grid regimes. The most important characteristics affecting both the grid and the turbines are examined. It is concluded that modern wind turbines can generally be designed to support the maintenance of grid supply, frequency and voltage more effectively than present central plant. However, the manner in which that is achieved needs to be different in many respects from current codes that were developed around the characteristics of central and conventional plant. Indications of the necessary changes in grid codes are given.

This paper explores technical and other issues arising from using shaped timber for a 1 metre long high efficiency blade for a small 600 W wind turbine. Two readily available Australian grown softwood timber species, radiata pine and hoop pine, were selected. Reasons for selecting these timbers are detailed in the paper. The fatigue life of the both timbers was determined using four point flexural testing. Results show that hoop pine is 25% stronger and 6% more fatigue resistant than radiata pine. A fatigue test procedure for the 1 m blade has been created based on the aeroelastic response of a 2.5 m long composite wind turbine blade and wind data from the Australian Bureau of Meteorology. Blade fatigue-life predictions, using Miners rule for fatigue damage accumulation, indicated effectively unlimited fatigue-life for a blade constructed from hoop pine, with the turbine operating at design performance in wind speeds up to 20 m/s. The blade's life was reduced to a few months when it was constructed from radiata pine for the same operating conditions to 20 m/s. However for an upper wind speed of 17 m/s, the predicted blade fatigue-life is effectively unlimited for both species. Test blades were machined in both radiata pine and hoop pine on a 3-axis milling machine with tool paths created using Pro/Manufacture software. Some of the important issues with respect to creating the blades out of timber are discussed.

The economics of offshore wind farms are presently less favorable than for onshore wind energy. Consequently there is a strong need for significant cost reductions in order to become competitive. About 70% of the electricity cost of offshore wind farms is determined by the initial investment costs, which mainly consist of the wind turbines, foundations, internal and external grid-connections and installation. Possible cost reductions until 2020 are explored for each of these components. Technological developments and cost reduction trends in both the offshore and onshore wind sector are analyzed. Information is also taken from offshore oil and gas sector and from the experience with high-voltage submarine transmission of electricity. Where possible, cost reduction trends are quantified using the experience curve concept, or otherwise based on expert judgments. Main drivers for cost reduction appear to be (a) design improvements and upscaling of wind turbines, (b) the continuing growth of onshore wind capacity, and (c) the development and high utilization rates of purpose-built installation vessels. Other factors are: reduction of steel prices, technological development of HVDC converter stations and cables, standardization of turbine and foundation design, and economies of scale for the wind turbine production. It is concluded that under different growth scenarios, investment costs of offshore wind farms may decline about 25–39% by 2020. Assuming an identical decline of annual O&M costs, the levelized electricity production costs are reduced from 6.8–7.2 to 4.2–5.4 €ct/kWh.

One of the characteristics of wind energy, from the grid point of view, is its non-dispatchability, i.e. generation cannot be ordered, hence integration in electrical networks may be difficult. Short-term wind power prediction-tools could make this integration easier, either by their use by the grid System Operator, or by promoting the participation of wind farms in the electricity markets and using prediction tools to make their bids in the market. In this paper, the importance of a short-term wind power-prediction tool for the participation of wind energy systems in electricity markets is studied. Simulations, according to the current Spanish market rules, have been performed to the production of different wind farms, with different degrees of accuracy in the prediction tool. It may be concluded that income from participation in electricity markets is increased using a short-term wind power prediction-tool of average accuracy. This both marginally increases income and also reduces the impact on system operation with the improved forecasts.

A new Wind Atlas of Poland has been developed and established as a digital data base. The atlas compiles wind data of Poland and off-shore areas of the Baltic Sea. It includes maps of wind speed, air temperature and solar radiation. In addition, maps show the Weibull parameters of the statistical distribution of the wind speed. Time series of wind speed and wind direction are available every 6 km. Data are provided at 50 m, 75 m, 100 m, 125 m or 150 m above the surface. The wind data are validated with in-situ measurements of wind speed and with operational results from existing wind power plants. To access the huge amount of data a new interface was developed, which allows extremely fast access to the data. This Digital Wind Atlas of Poland is adapted to the needs of the wind industry and is probably the most advanced wind atlas of Poland of today.