Land-based Wind Research Articles

Wind farm and solar park effects on plant-soil carbon cycling: uncertain impacts of changes in ground-level microclimate

Global energy demand is increasing as greenhouse gas driven climate change progresses, making renewable energy sources critical to future sustainable power provision. Land-based wind and solar electricity generation technologies are rapidly expanding, yet our understanding of their operational effects on biological carbon cycling in hosting ecosystems is limited. Wind turbines and photovoltaic panels can significantly change local ground-level climate by a magnitude that could affect the fundamental plant–soil processes that govern carbon dynamics. We believe that understanding the possible effects of changes in ground-level microclimates on these phenomena is crucial to reducing uncertainty of the true renewable energy carbon cost and to maximize beneficial effects. In this Opinions article, we examine the potential for the microclimatic effects of these land-based renewable energy sources to alter plant–soil carbon cycling, hypothesize likely effects and identify critical knowledge gaps for future carbon research.

Collision risk and micro-avoidance rates of birds with wind turbines in Flanders

Capsule Local factors can lead to strong variation in mortality rate and collision risk that obscures possible effects of turbine size in wind farms.Aims The impact of bird collisions was studied at eight land-based wind farm sites with a total of 66 small to large turbines in order to assess the mortality rate and collision risk.Methods Searches for collision fatalities were performed under all turbines with a minimum search interval of 14 days. Mortality rate was calculated with corrections for available search area, scavenging and search efficiency. Flight movements of birds crossing five of the wind farm sites were recorded during a minimum of four days per site. Actual collision risk was then calculated as the number of collision fatalities relative to the average surveyed flight intensity.Results Mortality rate was 21 birds per turbine per year on average. Most fatalities were local common species (e.g. gulls) but rarer species were also found (e.g. terns, raptors and waders). Collision risk of gulls was 0.05% and 0.08% on average for birds, respectively, flying at turbine and rotor height through the wind farms (0.09% and 0.14% maximum). Large gulls had a significant higher collision risk than small gulls at rotor height. Mortality rate and collision risk were not significantly related to turbine size. The results were integrated in a widely used collision risk model to obtain information of micro-avoidance, i.e. the proportion of birds that fly through the wind farm but avoid passing through the rotor swept area of the turbines. For gulls, this micro-avoidance was 96.1% and 96.3% on average for birds, respectively, flying at turbine and rotor height through the wind farms.Conclusion The results indicate that local factors can lead to strong variation in mortality rate and collision risk that obscures possible effects of turbine size in wind farms. However, large turbines have more installed capacity (MW), so repowering wind farms with larger but fewer wind turbines, could reduce total mortality at certain locations.

Opportunities and Challenges of Wind Power Generation in China

China's wind power market development is set to continue its growth trend of 2011. The newly added installed capacity will be in the range of 15-18GW and is expected to reach approximately 18GW. By 2015, the installed wind power capacity will reach 100GW. The percentage of decentralized wind power will further increase, but large-scale development and land-based wind power development will still be the focus, while the ratio of decentralized wind power has the potential to reach a maximum of 30%. As power grid corporations continue to improve their ultra-high voltage power transmission lines, intelligent power grids and other infrastructure, the power grids' ability to absorb wind power electricity on a largescale, and the scale of cross-region wind power transmission will increase, with the wind power grid-connection rate also significantly increase. The wind power manufacturing industry has entered a low-profit era; competition will intensify, the market will become more mature, and wind power manufacturers will face greater market challenges. However, the wind power industry's maturity and lowering costs have enhanced wind power's competitiveness compared to traditional energy sources. Wind power has become a highstrength emerging power supply technology and its contribution to China's electricity mix will gradually increase.

Large-eddy simulation of offshore wind farm

A hybrid numerical capability is developed for the simulation of offshore wind farms, in which large-eddy simulation is performed for the wind turbulence, and a potential flow based method is used for the simulation of the ocean wave field. The wind and wave simulations are dynamically coupled. The effect of wind turbines on the wind field is represented by an actuator disk model. This study focuses on the effect of wind-seas, and the turbine motion is treated as negligibly small. A variety of fully-developed and fetch-limited wind-sea conditions and turbine spacings are considered in the study. Statistical analyses are performed for the simulation results, with a focus on the mean wind profile, kinetic energy budget in the wind field, and the wind turbine power extraction rate. The results indicate that the waves have appreciable effect on the wind farm performance. The wind turbines obtain a higher wind power extraction rate under the fully developed wind-sea condition compared with that under the fetch-limited condition. This higher extraction rate is caused by the faster propagating waves and the lower sea-surface resistance on the wind when the wind-seas are fully developed. The wave-induced difference can be as high as 8% with the commonly used turbine spacing in commercial land-based wind farms, sx = 7 (with sx being the ratio of streamwise turbine spacing to the turbine diameter). Such level of difference is noteworthy considering the previous understanding that direct wave-induced disturbance to the wind field decays exponentially away from wave surface.

Off-shore wind farm development: Present status and challenges

Abstract Offshore wind farm (OWF) is an emerging technology in the wind energy conversion system. These wind resources are abundant, stronger, and are more consistent in terms of their availability than land-based wind resources. As a matter of fact significantly higher energy production is achieved due to larger wind turbine ratings and stronger wind profiles. This paper highlights the present scenario and challenges in development of offshore wind power. The challenges and opportunities that exist in the development stages of an offshore wind farm project, from exploration to erection and installation of wind turbines, construction of platforms and laying of sea cables, up to maintenance and de-commissioning, involving important technical aspects are addressed. An application of high voltage direct current (HVDC) transmission for integration of large scale offshore wind farm with onshore grid is attractive as compared to high voltage alternating current (HVAC) transmission system. To make the offshore wind farm feasible, reliable and secure, the different aspects in its planning, design and operation are also reviewed in this paper.

High-Power-Density Power Conversion Systems for HVDC-Connected Offshore Wind Farms

Offshore wind farms are rapidly growing owing to their comparatively more stable wind conditions than onshore and land-based wind farms. The power capacity of offshore wind turbines has been increased to 5MW in order to capture a larger amount of wind energy, which results in an increase of each component's size. Furthermore, the weight of the marine turbine components installed in the nacelle directly influences the total mechanical design, as well as the operation and maintenance (O&M) costs. A reduction in the weight of the nacelle allows for cost-effective tower and foundation structures. On the other hand, longer transmission distances from an offshore wind turbine to the load leads to higher energy losses. In this regard, DC transmission is more useful than AC transmission in terms of efficiency because no reactive power is generated/consumed by DC transmission cables. This paper describes some of the challenges and difficulties faced in designing high-power-density power conversion systems (HPDPCSs) for offshore wind turbines. A new approach for high gain/high voltage systems is introduced using transformerless power conversion technologies. Finally, the proposed converter is evaluated in terms of step-up conversion ratio, device number, modulation, and costs.

풍력발전기의 에너지 비용 산출에 대한 고찰

Large offshore wind farms have actively been developed in order to meet the needs for wind energy since the land-based wind farms have almost been fully developed especially in Europe. The key problem for the construction of offshore wind farms may be on the high cost of energy compared to land-based ones. NREL (National Renewable Energy Laboratory) has developed a spreadsheet-based tool to estimate the cost of wind-generated electricity from both land-based and offshore wind turbines. Component formulas for various kinds and scales of wind turbines were made using available field data. In this paper, this NREL estimation model is introduced and applied to the offshore wind turbines now under designing or in production in Korea, and the result is discussed.

Time domain-based gear contact fatigue analysis of a wind turbine drivetrain under dynamic conditions

This paper presents a general approach to predict the contact fatigue life of the gears in the drive-train system of a wind turbine under dynamic conditions. A simplified predictive pitting model that estimates service lives is presented and validated by comparisons with published experimental evidence. Finally, the predictive model is used to estimate the contact fatigue lives of the sun gear and planetary gears in the drive-train system of the National Renewable Energy Laboratory’s 750kW land-based wind turbine based on time domain simulations. The occurrence frequencies of different wind speeds are described by the generalized gamma distribution. The time series of the torques in the main shaft are obtained from a global dynamic response analysis of the wind turbine. The time series of the gear contact forces is obtained from a dynamic analysis of the gearbox using multi-body simulation. The two-parameter Weibull distribution, the three-parameter Weibull distribution, and the generalized-gamma distribution are used to fit the long-term probabilistic distribution of the gear tooth contact pressures. The case study shows the validity of the approach presented in this paper.

Time Domain Modeling and Analysis of Dynamic Gear Contact Force in a Wind Turbine Gearbox with Respect to Fatigue Assessment

The gearbox is one of the most expensive components of the wind turbine system. In order to refine the design and hence increase the long-term reliability, there has been increasing interest in utilizing time domain simulations in the prediction of gearbox design loads. In this study, three problems in time domain based gear contact fatigue analysis under dynamic conditions are discussed: (1) the torque reversal problem under low wind speed conditions, (2) statistical uncertainty effects due to time domain simulations and (3) simplified long term contact fatigue analysis of the gear tooth under dynamic conditions. Several recommendations to deal with these issues are proposed based on analyses of the National Renewable Energy Laboratory’s 750 kW land-based Gearbox Reliability Collaborative wind turbine.

A study on the prediction of lateral buckling load for wind turbine tower structures

A method to evaluate the structural safety of lateral buckling load is presented, using FEM analysis for a wind turbine tower with a thin circular wall. Europe, the U.S., and Japan already have long histories of research into wind power due to its high efficiency. The tower structure that supports a wind turbine is one important research area. There are three types of tower that vary by structural composition: a cylindrical tower with a circular cross-section, a jacket tower with a truss structure, and a hybrid tower. This paper investigates an accident involving a 600kW wind turbine that occurred in JeJu, Korea in October of 2010. The results from a numerical analysis are compared with the actual collapse mode observed at the accident. Some buckling modes and wind speeds at which non-linear buckling response occurs are predicted via the arclength method for a land-based cylindrical stationary tower. The evaluation method is used accident (experiment), analytical, linear and nonlinear finite element method (beam and shell) to analyze the result of predicted buckling load of tower. The result of nonlinear FEM shell model was found to exhibit similar behavior to the accident situation during buckling. It is concluded that this paper provides buckling analysis process and method used for the slender shell structures: the predicted buckling load and analysis methodology. In this paper, The results from the numerical estimation show good agreement with those of the analytical calculation, indicating that the arc-length method effectively improved the convergence. We found out buckling limit load of the accident wind turbine tower and wind speed at buckling point. The result of nonlinear FEM shell model was found to exhibit similar behavior to the actual accident (experiment) situation during buckling. The presented buckling evaluation method will be useful for both static design and dynamic performance evaluation of land-based wind turbines, as well as sea-based wind turbines.

Assessing the uncertainties of using land-based wind observations for determining extreme open-water winds

For the assessment of the safety of the Dutch flood defences extreme open-water winds need to be computed. There are, however, no sufficiently long and reliable in-situ data available. On the other hand, there is a rich dataset of decades of measurements at certain coastal and relatively close by inland stations. A commonly used two-layer model for neutral atmospheres was thought to provide reasonably accurate open-water winds from the available data, given that the model assumptions seemed plausible for the extreme winds of interest. However, the model results were deemed inaccurate and not usable. Given that this was unexpected, many of the model assumptions were analysed and, with the gained further insight, their validity and contribution to the invalidity of the deemed simple model approach assessed. Our conclusion is that the quality of the model results is significantly affected by at least two aspects: the assumption of neutral stability in the model, and – equally important – the assumption of independence between the surface roughness and the wind speed.

The top-down model of wind farm boundary layers and its applications

A simple model for the interactions of large wind farms with the turbulent atmospheric boundary layer, augmented for wake effects, is used to examine several important aspects of power degradation in large wind farms. It is shown that when combined with a model for internal boundary layer growth following the start of a wind farm, the model can explain measured power degradation trends. The model is then used to re-examine the advantages of off-shore wind farms. It is shown that the smaller roughness length over ocean that leads to faster hub-height winds compared with land-based wind farms is largely overshadowed by the wind turbines themselves.

Wave- and Wind-Induced Dynamic Response of a Spar-Type Offshore Wind Turbine

This paper addresses coupled wave and wind-induced motions of spar-type 5-MW wind turbines in harsh and operational environmental conditions. Global dynamic motion responses have been analyzed by aero-hydro-servo-elastic time-domain simulations. The aerodynamics is based on an advanced blade element momentum theory. Panel method and Morison formula accounting for the instantaneous position of the structure are applied for hydrodynamics. Hydrodynamic drag and considering geometrical updating introduce nonlinearities. Hydrodynamic nonlinearities were found to cause excitation of the natural frequencies in the low frequency range more than in the wave frequency range. Extrapolation methods are applied to estimate the maximum responses. A previous study showed that the uncertainty of such an extrapolation for the present concept is less than 2%. In this study it is found that the mean values of the dynamic responses are primarily wind induced and the standard deviations of the responses are primarily wave induced. However, the standard deviation of the nacelle surge motion under operational conditions is primarily wind induced. The maximum of the responses under operational and survival conditions are wind induced and wave induced, respectively. For the present turbine, a power of 5 MW can be achieved at a mean wind speed greater than 15 m/s, whereas the rated wind speed for the original land-based wind turbine is approximately 11 m/s. It is found that the wind turbulence does not affect the dynamic motion and structural responses significantly. However, turbulence affects power production. The ratio of the bending moment and the shear force in the tower-spar interface under a 100-year environmental condition to the corresponding responses associated with the rated wind speed can be as high as 1.5 and 2.3, respectively. It is therefore important to consider survival environmental conditions in the ultimate limit state checks of floating turbines, whereas operational conditions are normally most critical for land-based wind turbines. Moreover, it is shown that under survival conditions, the normalized maximum responses, i.e., (maximum mean)/(standard deviation), corresponding to an upcrossing rate of 0.0001 based on five 1-h analyses varies between 4 and 6, whereas for operational cases the normalized maximum varies between 2 and 4.

Estimating Wave Height Distributions in the Seto Inland Sea, Ise Bay and Tokyo Bay of Japan Generated by 3 Giant Typhoons in the Showa Era

Shallow water wave hindcastings are conducted in the Seto Inland Sea, Ise Bay and Tokyo Bay for each of the so-called 3 giant typhoons in the Showa Era (Muroto Typhoon in 1934, Makurazaki Typhoon in 1945 and Isewan Typhoon in 1959). The computations follow the spatial distribution of time-dependent wave height and maximum value. The sea wind distributions given as the driving forces are estimated using a method which transforms the land-based measurement wind data into the wind data at sea or coastal stations and applies a spatial interpolation technique to the data. The main conclusion is that any of the typhoons may have generated the largest wave height over the past 90 years in the sea area of the typhoon path.

Lightning protection of wind turbines – a comparison of measured data with required protection levels

Latest wind turbine lightning protection systems have been refined to the point where lightning damage is now relatively rare. This is increasingly important as wind turbines move offshore where access for maintenance is more difficult than for most land-based wind farms. Manufacturers have been trying to make sure that the lightning protection systems they install comply with the highest protection levels stipulated in the relevant IEC standards. In this study, data from the Nysted Offshore Wind farm in Denmark and that from a large number of other wind turbines worldwide is reviewed to show the range of lightning currents that have been measured on wind turbines currently in operation. These current values are compared with the required protection levels within the standards.

Coastal erosion dynamics on the permafrost-dominated Bykovsky Peninsula, north Siberia, 1951–2006

This study investigates the rate of erosion during the 1951-2006 period on the Bykovsky Peninsula, located north-east of the harbour town of Tiksi, north Siberia. Its coastline, which is characterized by the presence of ice-rich sediment (Ice Complex) and the vicinity of the Lena River Delta, retreated at a mean rate of 0.59 m/yr between 1951 and 2006. Rates ranged from 434 m of erosion to 92 m of accretion during these 56 years and exhibited large variability (?=45.4). Ninety-seven percent of the rates observed were less than 2 m/yr and 81.6% were less than 1 m/yr. No significant trend in erosion could be recorded despite the study of five temporal subperiods within 1951-2006. Erosion modes and rates actually appear to be strongly dependant on the nature of the backshore material, erosion being stronger along low-lying coastal stretches affected by past or current thermokarst activity. The juxtaposition of wind records monitored at the town of Tiksi and erosion records yielded no significant relationship despite strong record amplitude for both data sets. We explain this poor relationship by the only rough incorporation of sea-ice cover in our storm extraction algorithm, the use of land-based wind records vs. offshore winds, the proximity of the Peninsula to the Lena River Delta freshwater and sediment plume and the local topographical constraints on wave development.Keywords: coastal erosion, permafrost, Arctic, climate change, Russia(Published: 15 September 2011)Citation: Polar Research 2011, 30, 7341, DOI: 10.3402/polar.v30i0.7341

Investigation on installation of offshore wind turbines

Wind power has made rapid progress and should gain significance as an energy resource, given growing interest in renewable energy and clean energy. Offshore wind energy resources have attracted significant attention, as, compared with land-based wind energy resources, offshore wind energy resources are more promising candidates for development. Sea winds are generally stronger and more reliable and with improvements in technology, the sea has become a hot spot for new designs and installation methods for wind turbines. In the present paper, based on experience building offshore wind farms, recommended foundation styles have been examined. Furthermore, wave effects have been investigated. The split installation and overall installation have been illustrated. Methods appropriate when installing a small number of turbines as well as those useful when installing large numbers of turbines were analyzed. This investigation of installation methods for wind turbines should provide practical technical guidance for their installation.

Challenges and solutions of remote sensing at offshore wind energy developments

Radar is becoming an important tool used to gather data on bird and bat activity at proposed and existing land-based wind energy sites. Radar will likely play an even more important role at the increasing development of wind energy offshore, given both the lack of knowledge about bird and bat activity offshore and the increased difficultly in obtaining offshore information. Most radar studies to date have used off-the-shelf or modified marine radars. However, there are several issues that continue to hinder the potential usefulness of radar at wind energy sites, with offshore sites providing a particular suite of challenges. We identify these challenges along with current or developing solutions.

A 45-Year Wave Hindcast System in the Inner Bay Areas and Inland Sea of Japan Using SDP Measurements-Based Winds -Tokyo Bay Case-

A long-term wave hindcast system applicable for the wave computations over a 45-year period at an arbitrary location of Tokyo Bay area is reconstructed. Hourly sea wind distributions estimated by making use of an analogy between land-based SDP wind measurement data and coast- and sea-based wind measurement data are given on the coastal sea area and those made by recompiling the NCEP/NCAR reanalysis surface wind product on the open ocean. Wave computation is based on a backward ray tracing model on a nested grid with very high space resolution. Comparison between hindcasts and measurements for wave height over a long period of 10 to 23 years at 5 stations situated inside and outside of Tokyo Bay verified a reasonable performance of the system.

Avian Issues for Offshore Wind Development

Wind energy is the fastest growing source of electricity in the U. S., and the energy potential in the offshore environment is enormous. Environmental concerns have focused on effects on birds, and in this paper we briefly review these effects in the context of methods for assessing preconstruction risk and postconstruction impact. Federal statutes and legislation, including the National Environmental Policy Act, Federal Energy Act of 2005, the Endangered Species Act, and the Migratory Bird Treaty will require that prospective developers conduct some form of avian risk assessment prior to construction. Such preconstruction studies should utilize a Before-After-Control-Impact (BACI) design.Offshore wind farms pose three primary threats to birds: barrier effects due to flight avoidance, habitat loss (due to displacement), and fatalities resulting from collisions with turbine blades. All have been demonstrated at land-based and coastal wind farms, and flight avoidance and shifts in habitat use have been demonstrated in the offshore environment for a limited number of species in Europe. The additive effect of these impacts to bird populations may be trivial under current levels of development, but could become ecologically significant as offshore installations increase as projected.Interpreting the ecological significance of these effects requires additional research, especially on understanding the importance of winter foraging habitat and population delineation, particularly for waterfowl. Such research and preconstruction studies will be expensive, and we suggest public funding of these efforts and private-public partnerships as is currently underway in some states.