Sensitivity of nocturnal low-level jets to land-use parameters and meteorological quantities

Abstract. The increasing hub height of wind turbines aims at optimizing the wind energy yield at one location and offers the possibility to provide new areas for wind power, for example forests. Inhomogeneous environmental conditions of locations for wind turbines as well as the hub heights of more than 100 m cause challenges for flow models and their potential for wind power assessment. This includes special features of the wind field like low-level jets (LLJs), frequently observed local wind maxima in the nocturnal boundary layer. To characterize the dependencies of LLJs, the micro-scale model HIRVAC2D (HIgh Resolution Vegetation Atmosphere Coupler 2D) is applied in the study. The model HIRVAC2D is capable of modelling different vegetation types by explicitly considering the highly resolved structure of varying plant parameters. Beyond that, the model enables the resolution of temporally variable atmospheric circulation patterns during day- and night-time with typical thermal stratifications. In this way, HIRVAC2D is suitable to capture the nocturnal LLJ development and its characteristics. Results of several HIRVAC2D simulations are presented in order to deduce quantitatively the sensitivity of LLJs to vegetation and model parameters as well as meteorological quantities. It is shown that the geostrophic wind speed is an important criterion for the development of LLJs within a height range between 50 and 300 m. For a geostrophic wind speed of 4 m s−1, a nocturnal LLJ occurs remarkably more frequent as for a wind speed of 10 m s−1. To interpret and evaluate this result regarding possible wind power applications, a frequency distribution of the geostrophic wind speed was calculated over 30 years exemplarily at two locations using the meso-scale model COSMO in climate mode. Additionally, the type of land use has an impact on the height and intensity of LLJs. For a grassland site, the nocturnal LLJ is noticeably more frequent in the considered height range, but with a smaller wind speed and at a lower height above ground in comparison to deciduous or coniferous forests.

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A Climatology of Nocturnal Low-Level Jets at Cabauw

Journal of Applied Meteorology and Climatology ◽

10.1175/2009jamc1965.1 ◽

2009 ◽

Vol 48 (8) ◽

pp. 1627-1642 ◽

Cited By ~ 101

Author(s):

P. Baas ◽

F. C. Bosveld ◽

H. Klein Baltink ◽

A. A. M. Holtslag

Keyword(s):

Wind Speed ◽

Ground Level ◽

Geostrophic Wind ◽

Stable Stratification ◽

Radiative Cooling ◽

Inertial Oscillation ◽

Stable Boundary Layers ◽

Above Ground Level ◽

Low Level ◽

Low Level Jets

Abstract A climatology of nocturnal low-level jets (LLJs) is presented for the topographically flat measurement site at Cabauw, the Netherlands. LLJ characteristics are derived from a 7-yr half-hourly database of wind speed profiles, obtained from the 200-m mast and a wind profiler. Many LLJs at Cabauw originate from an inertial oscillation, which develops after sunset in a layer decoupled from the surface by stable stratification. The data are classified to different types of stable boundary layers by using the geostrophic wind speed and the isothermal net radiative cooling as classification parameters. For each of these classes, LLJ characteristics like frequency of occurrence, height above ground level, and the turning of the wind vector across the boundary layer are determined. It is found that LLJs occur in about 20% of the nights, are typically situated at 140–260 m above ground level, and have a speed of 6–10 m s−1. Development of a substantial LLJ is most likely to occur for moderate geostrophic forcing and a high radiative cooling. A comparison with the 40-yr ECMWF Re-Analysis (ERA-40) is added to illustrate how the results can be used to evaluate the performance of atmospheric models.

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Assessment of nocturnal low-level jets during the FESSTVaL campaign 2020 for wind energy applications

10.5194/ems2021-166 ◽

2021 ◽

Author(s):

Eduardo Weide Luiz ◽

Stephanie Fiedler

Keyword(s):

Wind Power ◽

Wind Turbines ◽

Vertical Wind Shear ◽

Ground Level ◽

High Temporal Resolution ◽

Missing Measurements ◽

Low Level ◽

Prevailing Wind Direction ◽

Meteorological Observatory ◽

Low Level Jets

Due to the increasing contribution of wind power to electricity in Europe, an exact wind characterization at the height of wind turbines is important. Nocturnal Low Level Jets (NLLJ) can influence the winds at typical blade heights and therefore influence the wind power production. However, due to the often missing measurements with a sufficient precision and resolution, the occurrence frequency and spatio-temporal characteristics of NLLJs are still poorly understood. The present work characterizes the properties of NLLJs, measured with a Doppler lidar at the Lindenberg Meteorological Observatory &#8211; Richard A&#223;mann Observatory (Germany), during the period of June&#8211;August 2020, and evaluates the representation of NLLJs in state-of-the-science re-analysis products. The vertical profiles of 10-minute mean winds from the lidar are statistically analysed using automated detection tools. These allow to determine the frequency of occurrence, height and wind speed in the core of NLLJs as well as the vertical wind shear and momentum transport with a high temporal resolution. We intercompare NLLJ results from different previously-used identification tools to estimate the uncertainty. Our automatic detections identified NLLJs in more than about 60% of the summer nights in 2020, with NLLJ cores between 70m and 500 m above ground level and a core speed of ~3&#8211;25 m/s. The prevailing wind direction in NLLJ cores is southwest. A considerable amount of NLLJ cores occurred at heights that are in the range of modern wind turbines and rotor sizes on land, with wind speeds of ~3-12 m/s. We use the measurements of NLLJs to evaluate their representation in the ERA5 re-analysis of the European Centre for Medium-Range Weather Forecasts and plan to compare the NLLJs to regional high-resolution re-analyses developed in the research area Climate Monitoring and Diagnostics in the Hans-Ertel Centre for Weather Research. &#160;The first comparisons suggest a frequent co-occurrence of NLLJs in the measurements and ERA5 re-analysis, but the strength and height of NLLJ cores often differ. Possible reasons are the model&#8217;s vertical resolution and the parameterization of vertical mixing in the stable boundary layer. Future work includes extending the NLLJ analysis to more lidar measurements and other regional re-analysis data.

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Performance Enhancement of Proposed Namaacha Wind Farm by Minimising Losses Due to the Wake Effect: A Mozambican Case Study

Energies ◽

10.3390/en14144291 ◽

2021 ◽

Vol 14 (14) ◽

pp. 4291

Author(s):

Paxis Marques João Roque ◽

Shyama Pada Chowdhury ◽

Zhongjie Huan

Keyword(s):

Wind Speed ◽

Wind Power ◽

Wind Turbines ◽

Power Output ◽

Wind Farm ◽

Wind Farms ◽

Operating Conditions ◽

Wake Effect ◽

Wind Generators ◽

Wind Potential

District of Namaacha in Maputo Province of Mozambique presents a high wind potential, with an average wind speed of around 7.5 m/s and huge open fields that are favourable to the installation of wind farms. However, in order to make better use of the wind potential, it is necessary to evaluate the operating conditions of the turbines and guide the independent power producers (IPPs) on how to efficiently use wind power. The investigation of the wind farm operating conditions is justified by the fact that the implementation of wind power systems is quite expensive, and therefore, it is imperative to find alternatives to reduce power losses and improve energy production. Taking into account the power needs in Mozambique, this project applied hybrid optimisation of multiple energy resources (HOMER) to size the capacity of the wind farm and the number of turbines that guarantee an adequate supply of power. Moreover, considering the topographic conditions of the site and the operational parameters of the turbines, the system advisor model (SAM) was applied to evaluate the performance of the Vestas V82-1.65 horizontal axis turbines and the system’s power output as a result of the wake effect. For any wind farm, it is evident that wind turbines’ wake effects significantly reduce the performance of wind farms. The paper seeks to design and examine the proper layout for practical placements of wind generators. Firstly, a survey on the Namaacha’s electricity demand was carried out in order to obtain the district’s daily load profile required to size the wind farm’s capacity. Secondly, with the previous knowledge that the operation of wind farms is affected by wake losses, different wake effect models applied by SAM were examined and the Eddy–Viscosity model was selected to perform the analysis. Three distinct layouts result from SAM optimisation, and the best one is recommended for wind turbines installation for maximising wind to energy generation. Although it is understood that the wake effect occurs on any wind farm, it is observed that wake losses can be minimised through the proper design of the wind generators’ placement layout. Therefore, any wind farm project should, from its layout, examine the optimal wind farm arrangement, which will depend on the wind speed, wind direction, turbine hub height, and other topographical characteristics of the area. In that context, considering the topographic and climate features of Mozambique, the study brings novelty in the way wind farms should be placed in the district and wake losses minimised. The study is based on a real assumption that the project can be implemented in the district, and thus, considering the wind farm’s capacity, the district’s energy needs could be met. The optimal transversal and longitudinal distances between turbines recommended are 8Do and 10Do, respectively, arranged according to layout 1, with wake losses of about 1.7%, land utilisation of about 6.46 Km2, and power output estimated at 71.844 GWh per year.

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Wind Power Generating Potential at the University of North Texas Campus

Volume 6: Energy, Parts A and B ◽

10.1115/imece2012-89082 ◽

2012 ◽

Author(s):

Rambod Rayegan ◽

Yong X. Tao ◽

Frank Y. Fang

Keyword(s):

Wind Speed ◽

Wind Power ◽

Power Density ◽

Wind Turbines ◽

North Texas ◽

University Of North Texas ◽

Average Wind Speed ◽

Wind Speed Data ◽

Weather Stations ◽

The University

This study utilizes two sets of wind speed data at 3 m above the ground surface level retrieved from two on-campus weather stations to study the wind power generating potential at the University of North Texas Campus. Weather stations have been installed approximately 5 miles away from each other. The mean wind speed data of 10 minute intervals in a one-year period from February 1st 2011 to January 31st 2012 has been adopted and analyzed. The numerical values of the dimensionless Weibull shape parameter (k) and Weibull scale parameter (c) have been determined. Monthly average wind speed and standard deviation, power generation, and power density at the sensor level for both locations has been discussed. Lower values of wind speed were found during summer months and higher during spring months. The results show that the wind power density in the area is fair enough to be considered as a renewable power source for the University. Thereafter annual energy production by using two wind turbines with nominal capacities of 100 and 3.5 kW for both weather stations has been studied. Initial costs of using each turbine to maintain power demands of selected buildings have been compared. In order to utilize wind energy, it is recommended to install highly efficient wind turbines for electricity supply of campus buildings with lower power demands. Using grant monies to maintain the initial costs of the installation of wind turbines make them economically more desirable. Since wind power potential is low during summer, PV panels as proper supplements to the power generating system are suggested.

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WRF-Simulated Low-Level Jets over Iowa: Characterization and Sensitivity Studies

10.5194/wes-2020-113 ◽

2020 ◽

Author(s):

Jeanie A. Aird ◽

Rebecca J. Barthelmie ◽

Tristan J. Shepherd ◽

Sara C. Pryor

Keyword(s):

Wind Speed ◽

Wrf Model ◽

Stable Stratification ◽

Detection Algorithm ◽

The State ◽

Sensitivity Analyses ◽

Vertical Resolution ◽

Low Level ◽

Sensitivity Studies ◽

Low Level Jets

Abstract. Output from high resolution simulations with the Weather Research and Forecasting (WRF) model are analyzed to characterize local low level jets (LLJ) over Iowa. Analyses using a detection algorithm wherein the wind speed above and below the jet maximum must be below 80 % of the jet wind speed within a vertical window of approximately 20 m–530 m a.g.l. indicate the presence of a LLJ in at least one of the 14700 4 km by 4 km grid cells over Iowa on 98 % of nights. Nocturnal LLJ are most frequently associated with stable stratification and low TKE and hence are more frequent during the winter months. The spatiotemporal mean LLJ maximum (jet core) wind speed is 9.55 ms−1 and the mean height is 182 m. Locations of high LLJ frequency and duration across the state are seasonally varying with a mean duration of 3.5 hours. LLJ are most frequent in the topographically complex northwest of the state in winter, and in the flatter northeast of the state in spring. Sensitivity of LLJ characteristics to the: i) LLJ definition and ii) vertical resolution at which the WRF output is sampled are examined. LLJ definitions commonly used in LLJ literature are considered in the first sensitivity analysis. These sensitivity analyses indicate that LLJ characteristics are highly variable with LLJ definition. Further, when the model output is down-sampled to lower vertical resolution, the maximum LLJ wind speed and mean height decrease, but spatial distributions of regions of high frequency and duration are conserved.

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Method for estimating the wind power micro and minigeneration applied to a city with a subtropical climate in south America

Research Society and Development ◽

10.33448/rsd-v10i12.20009 ◽

2021 ◽

Vol 10 (12) ◽

pp. e105101220009

Author(s):

Ricardo Guicho ◽

José Hilário Delconte Ferreira ◽

Gabriela Medeiros ◽

Jair Antônio Cruz Siqueira ◽

Samuel Nelson Melegari de Souza ◽

...

Keyword(s):

Land Use ◽

Wind Speed ◽

Wind Power ◽

Clean Energy ◽

Developed Countries ◽

Subtropical Climate ◽

Energy Potential ◽

Historical Series ◽

Clean Energy Source ◽

Sentinel 2

The search for renewable resources has become necessary for sustainable development. Wind energy is a clean energy source and of global importance, but most studies refer to high altitude and are carried out by researchers in developed countries. In this work, the objective was to evaluate the potential of micro and mini-generation (low heights) wind power in Cascavel-PR, a city located in southern Brazil, as an example of the application of the proposed methodology. For this purpose, wind speed and direction data were used, with a historical series of 21 years (1997-2017). The land use and occupation were performed in a semi-automatic way using Sentinel-2 satellite images. To generate the maps, an algorithm was created in Spring software, which correlated the land use and land cover information, the wind speed kriging and the formula coefficient values according to the identified obstacles. With this it was possible to conclude that regarding the period, spring is considered the season of the year with the greatest energy potential, where the highest averages for speed and power were estimated. It was also noted that the 40-meter-high range has the greatest potential and that the prevailing winds come from the northeast.

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Features of operation of wind power stations as an supplementary source of electricity for non-traction consumers of railway electric mains

Theory and practice of metallurgy ◽

10.34185/tpm.3.2019.06 ◽

2019 ◽

pp. 36-41

Author(s):

Kachan Yu ◽

Kuznetsov V

Keyword(s):

Renewable Energy ◽

Wind Speed ◽

Wind Power ◽

Wind Turbines ◽

Power Supply ◽

Renewable Energy Sources ◽

Wind Farms ◽

Energy Sources ◽

Railway Transport ◽

Supply Systems

Purpose. Identify the features of operation of wind farms as an auxiliary supplier of electricity for non-traction consumers of railway networks and analyze the main factors that directly affect the use of wind farms due to the random nature of wind flow and additional factors due to the above conditions in different climates. The research methodology is based on modern methods of computational mathematics, statistics and information analysis using modern computer technology. Findings. The need to use renewable energy sources in the power supply systems of non-traction consumers of railway transport is obvious. Given the constant growth of prices and tariffs for electricity in Ukraine, more and more attention is paid to its savings and the search for the cheapest and most affordable alternative sources. The authors consider issues related to the possibility of using additional generation of electricity in the power supply systems of railway transport through the use of wind turbines, including for non-traction consumers. The analysis of wind flow features in some regions of Ukraine was carried out, and the measurement of wind speed in Zaporizhia and Dnipropetrovsk regions was obtained with the help of a compact wind speed sensor manufactured by Micro-Step-MIS LLC (Russia). The obtained values of wind speed were recorded and stored digitally. The received information of the above device was processed. The authors conclude that in the case of using wind turbines as an additional power source in the networks of non-traction consumers of railway power supply systems it is economically advantageous to connect them directly to these networks and fully use all electricity produced by them, reducing its consumption from this power supply system. The originality is that the use of renewable energy sources in the power supply systems of non-traction consumers of railway transport, in particular wind turbines, is proposed. Practical implications. Introduction of wind power plants as an auxiliary supplier of electricity for non-traction consumers of railway power grids in order to minimize electricity costs. Keywords: renewable energy sources, quality of electric energy, wind power plant, power supply networks of railway transport, non-traction consumers of railway electric networks, electricity production, wind speed.

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Influence of the Heights of Low-Level Jets on Power and Aerodynamic Loads of a Horizontal Axis Wind Turbine Rotor

Atmosphere ◽

10.3390/atmos10030132 ◽

2019 ◽

Vol 10 (3) ◽

pp. 132 ◽

Cited By ~ 1

Author(s):

Xuyao Zhang ◽

Congxin Yang ◽

Shoutu Li

Keyword(s):

Wind Speed ◽

Power Spectrum ◽

Wind Turbine ◽

Horizontal Axis ◽

Horizontal Axis Wind Turbine ◽

Aerodynamic Loads ◽

Low Level ◽

Low Level Jets ◽

Inflow Conditions ◽

Swept Area

The influence of the heights of low-level jets (LLJs) on the rotor power and aerodynamic loads of a horizontal axis wind turbine were investigated using the fatigue, aerodynamics, structures, and turbulence code. The LLJ and shear inflow wind fields were generated using an existing wind speed spectral model. We found that the rotor power predicted by the average wind speed of the hub height is higher than the actual power in relatively weak and shallow LLJ inflow conditions, especially when the LLJ height is located inside the rotor-swept area. In terms of aerodynamic loads, when the LLJ height is located inside the rotor-swept area, the root mean square (RMS) rotor thrust coefficient and torque coefficient increase, while the RMS rotor unbalanced aerodynamic load coefficients, including lateral force, longitudinal force, tilt moment, and yaw moment, decreased. This means that the presence of both positive and negative wind shear in the rotor-swept area not only increases the rotor power but also reduces the unbalanced aerodynamic loads, which is beneficial to the operation of wind turbine. Power spectrum analysis shows no obvious difference in the power spectrum characteristics of the rotor torque and thrust in LLJ inflow conditions with different heights.

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Wind speed and shear associated with low-level jets over Northern Germany

Meteorologische Zeitschrift ◽

10.1127/0941-2948/2014/0551 ◽

2014 ◽

Vol 23 (3) ◽

pp. 295-304 ◽

Cited By ~ 16

Author(s):

Stefan Emeis

Keyword(s):

Wind Speed ◽

Northern Germany ◽

Low Level ◽

Low Level Jets

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Wind conditions over the Baltic Sea – comparing reanalysis data sets with observations

10.5194/egusphere-egu2020-21897 ◽

2020 ◽

Author(s):

Christoffer Hallgren ◽

Erik Sahlée ◽

Stefan Ivanell ◽

Heiner Körnich ◽

Ville Vakkari

Keyword(s):

Baltic Sea ◽

Wind Power ◽

Reanalysis Data ◽

Data Sets ◽

The Baltic Sea ◽

Data Set ◽

Low Level ◽

Seasonal And Diurnal Variations ◽

Low Level Jets ◽

The Baltic

The potential of increasing the amount of offshore wind energy production in the Baltic Sea has been of great interest for many countries and wind power companies for a long time. From a meteorological point of view, there are several special wind characteristics that are observed in this area that needs to be taken into consideration when planning for a wind farm. For example, as the Baltic Sea is a semi-enclosed basin surrounded by coastlines in all directions, phenomenon such as low-level jets occur frequently.In order to create a climatology of the wind conditions over the Baltic Sea, with wind power applications in mind, four different state-of-the-art reanalysis data sets (MERRA2, ERA5, UERRA and NEWA) have been compared with measurements from LIDAR systems and high meteorological towers (Anholt, Finnish Ut&#246;, FINO2 and &#214;stergarnsholm). The performance of the data sets has been analyzed in terms of stability and governing synoptic weather conditions as well as seasonal and diurnal variations. By selecting the most suitable reanalysis data set and using the observations to make corrections, a climatology for wind conditions over the Baltic Sea, focusing on the low-level jets, has then been constructed.

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