Current Issue : July-September Volume : 2025 Issue Number : 3 Articles : 5 Articles
In response to the limited power operation mode of wind farms, an active power optimization scheduling method for wind farms is proposed based on the state evaluation of wind turbines. This method achieves optimal operational control of wind farms. The computational complexity is relatively low. Firstly, the indicators in the comprehensive scoring system for wind turbines are defined. Additionally, the fuzzy entropy method is employed to calculate and rank the overall deterioration of power up-regulation/down-regulation. Then, wind turbines are classified according to their operational state, and the power regulation capacity of each class of wind turbines is determined. Subsequently, the active power optimization scheduling of wind farms is implemented based on the classification and ranking of wind turbines. Finally, a simulation test is conducted using historical data from a wind farm. The results demonstrate that the proposed method can achieve higher power command tracking accuracy under different power limitation levels of wind farms. Moreover, power scheduling based on the comprehensive deterioration ranking of the turbines can effectively reduce power fluctuation differences, load fatigue differences, and overall power fluctuations between the turbines. The standard deviation of the power fluctuation coefficient has been reduced to 0.0705, marking a 9.85% decrease compared to the previous scheme....
Wind power has become the most important source of electricity generation in Germany, providing more than a quarter of its electricity consumption in 2022. The growth in wind power generation has been mainly driven by an increase in installed capacity, but other factors have also contributed significantly and have been less investigated. Here, we decompose the increase in German wind power generation into its driving factors: rotor swept area, number of operating turbines, available input wind power density and the relation between input wind power and generated electricity—here called system efficiency. Additionally, input wind power density is decomposed into its components: hub height change, new wind profiles due to new locations and annual variations. We find that the increase in average rotor swept area had the biggest positive impact on the change in output, closely followed by the increase in the number of operating turbines. Input wind power density increased moderately due to increasing hub heights; however, output power density remained almost constant as system efficiency, that is, the amount of input wind power converted to electricity, declined by 5.9 percentage points between 2005 and 2022. Approximately 66% of this decrease occurred due to turbine ageing, 16% due to the combined decrease in specific power and 16% due to increase in input power density caused by taller turbines. Lastly, we show that there is a trade- off between output power density and average capacity factor. The recent decline in average specific power from 400 to 380 W/m2 has lowered the total output power by about 1.2% compared to a scenario without a change in specific power, but average capacity factors increased by 4.5%....
The Betz constant is the well-known aerodynamic limit of the maximum power which can be extracted from wind using wind turbine technologies, under the assumption that the wind speed is uniform across a blade disk. However, this condition may not hold for large wind turbines, since the wind speed may not be constant along their height; rather, it may vary with the location due to surface friction from tall buildings and trees, the topography of the Earth’s surface, and radiative heating and cooling in a 24 h cycle. This paper derives a new power coefficient for large wind turbines based on the power law exponent model of the wind gradient and height. The proposed power coefficient is a function of the size of the rotor disk and the Hellmann exponent, which describes the wind gradient based on wind stability at various locations, and it approaches the same value as the Betz limit for wind turbines with small rotor disks. It is shown that for large offshore wind turbines, the power coefficient was about 1.27% smaller than that predicted by the Betz limit, whereas for onshore turbines in human-inhabited areas with stable air, the power coefficient was about 8.7% larger. Our results are significant in two ways. First, we achieve generalization of the well-known Betz limit through elimination of the assumption of a constant wind speed across the blade disk, which does not hold for large wind turbines. Second, since the power coefficient depends on the location and air stability, this study offers guidelines for wind power companies regarding site selection for the installation of new wind turbines, potentially achieving greater energy efficiency than that predicted by the Betz limit....
Wind power forms the major contributor to Germany’s goal of transforming the energy sector and becoming climate-neutral until 2045. The increasing installation of wind turbines comes with an increasing demand for rare-earth elements, especially neodymium, praseodymium and dysprosium, to produce high-performing magnets. However, these elements are considered to be critical raw materials because of their supply risk and economic importance. The European Commission aims to ensure supply chain resilience by improving the circularity of these critical raw materials. After an average of 20 years, wind turbines transition into their End-of-Life phase. This work aims to map the present and future potential of NdFeB magnets used in wind turbines in Germany to be introduced into a circular economy resulting in material amounts of potentially recycled magnets and secondary rare-earth elements considering different potential End-of-Life pathways....
Semi-annual climate oscillations in theWestern Hemisphere (20 S–35 N, 150W– 20 E) were studied via empirical orthogonal function (EOF) eigenvector loading patterns and principal component time scores from 1980 to 2023. The spatial loading maximum for 850 hPa zonal wind extended from the north Atlantic to the east Pacific; channeling was evident over the southwestern Caribbean. The eigenvector loading maximum for precipitation reflected an equatorial trough, while the semi-annual SST formed a dipole with loading maxima in upwelling zones off Angola (10 E) and Peru (80 W).Weakened Caribbean trade winds and strengthened tropical convection correlated with a warm Atlantic/cool Pacific pattern (R = 0.46). Wavelet spectral analysis of principal component time scores found a persistent 6-month rhythm disrupted only by major El Nino Southern Oscillation events and anomalous mid-latitude conditions associated with negative-phase Arctic Oscillation. Historical climatologies revealed that 6-month cycles of wind, precipitation, and sea temperature were tightly coupled in theWestern Hemisphere by heat surplus in the equatorial ocean diffused by meridional overturning Hadley cells. External forcing emerged in early 2010 when warm anomalies over Canada diverted the subtropical jet, suppressing subtropical trade winds and evaporative cooling and intensifying the equatorial trough across the Western Hemisphere. Climatic trends of increased jet-stream instability suggest that the semi-annual amplitude may grow over time....
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