157 research outputs found
Fish schooling as a basis for vertical axis wind turbine farm design
Most wind farms consist of horizontal axis wind turbines (HAWTs) due to the
high power coefficient (mechanical power output divided by the power of the
free-stream air through the turbine cross-sectional area) of an isolated
turbine. However when in close proximity to neighbouring turbines, HAWTs suffer
from a reduced power coefficient. In contrast, previous research on vertical
axis wind turbines (VAWTs) suggests that closely-spaced VAWTs may experience
only small decreases (or even increases) in an individual turbine's power
coefficient when placed in close proximity to neighbours, thus yielding much
higher power outputs for a given area of land. A potential flow model of
inter-VAWT interactions is developed to investigate the effect of changes in
VAWT spatial arrangement on the array performance coefficient, which compares
the expected average power coefficient of turbines in an array to a
spatially-isolated turbine. A geometric arrangement based on the configuration
of shed vortices in the wake of schooling fish is shown to significantly
increase the array performance coefficient based upon an array of 16x16 wind
turbines. Results suggest increases in power output of over one order of
magnitude for a given area of land as compared to HAWTs.Comment: Submitted for publication in BioInspiration and Biomimetics. Note:
The technology described in this paper is protected under both US and
international pending patents filed by the California Institute of Technolog
Integrating Offshore Wind and Wave Resource Assessment
The aim of this paper is to review the sources of wind and wave information, the methodologies to assess offshore wind and wave energy resources, and the more relevant results at the European level as a first step to integration of the evaluation of both resources. In situ and remote sensed wind and wave data (using satellite based sensors) are done generally by distinct systems (except for SAR) but numerical atmospheric models and wind - wave models are closely related. Offshore wind resource studies using various types of data are reviewed especially in northern European seas and in the Mediterranean. The wave energy resource assessment at European and national levels is also reviewed and the various atlases are identified
The influence of humidity fluxes on offshore wind speed profiles
Wind energy developments offshore focus on larger turbines to keep the
relative cost of the foundation per MW of installed capacity low. Hence
typical wind turbine hub-heights are extending to 100 m and potentially
beyond. However, measurements to these heights are not usually available,
requiring extrapolation from lower measurements. With humid conditions and
low mechanical turbulence offshore, deviations from the traditional
logarithmic wind speed profile become significant and stability corrections
are required. This research focuses on quantifying the effect of humidity
fluxes on stability corrected wind speed profiles. The effect on wind speed
profiles is found to be important in stable conditions where including
humidity fluxes forces conditions towards neutral. Our results show that
excluding humidity fluxes leads to average predicted wind speeds at 150 m
from 10 m which are up to 4% higher than if humidity fluxes are included,
and the results are not very sensitive to the method selected to estimate
humidity fluxes
Coupled wake boundary layer model of wind-farms
We present and test the coupled wake boundary layer (CWBL) model that
describes the distribution of the power output in a wind-farm. The model
couples the traditional, industry-standard wake model approach with a
"top-down" model for the overall wind-farm boundary layer structure. This wake
model captures the effect of turbine positioning, while the "top-down" portion
of the model adds the interactions between the wind-turbine wakes and the
atmospheric boundary layer. Each portion of the model requires specification of
a parameter that is not known a-priori. For the wake model, the wake expansion
coefficient is required, while the "top-down" model requires an effective
spanwise turbine spacing within which the model's momentum balance is relevant.
The wake expansion coefficient is obtained by matching the predicted mean
velocity at the turbine from both approaches, while the effective spanwise
turbine spacing depends on turbine positioning and thus can be determined from
the wake model. Coupling of the constitutive components of the CWBL model is
achieved by iterating these parameters until convergence is reached. We
illustrate the performance of the model by applying it to both developing
wind-farms including entrance effects and to fully developed (deep-array)
conditions. Comparisons of the CWBL model predictions with results from a suite
of large eddy simulations (LES) shows that the model closely represents the
results obtained in these high-fidelity numerical simulations. A comparison
with measured power degradation at the Horns Rev and Nysted wind-farms shows
that the model can also be successfully applied to real wind-farms.Comment: 25 pages, 21 figures, submitted to Journal of Renewable and
Sustainable Energy on July 18, 201
Interannual variability of wind climates and wind turbine annual energy production
The interannual variability (IAV) of expected annual energy production (AEP)
from proposed wind farms plays a key role in dictating project financing. IAV
in preconstruction projected AEP and the difference in 50th and
90th percentile (P50 and P90) AEP derive in part from variability in
wind climates. However, the magnitude of IAV in wind speeds at or close to wind
turbine hub heights is poorly defined and may be overestimated by assuming
annual mean wind speeds are Gaussian distributed with a standard deviation
(σ) of 6 %, as is widely applied within the wind energy industry.
There is a need for improved understanding of the long-term wind resource and
the IAV therein in order to generate more robust predictions of the financial
value of a wind energy project. Long-term simulations of wind speeds near
typical wind turbine hub heights over the eastern USA indicate median gross
capacity factors (computed using 10 min wind speeds close to wind turbine
hub heights and the power curve of the most common wind turbine deployed in
the region) that are in good agreement with values derived from operational
wind farms. The IAV of annual mean wind speeds at or near typical wind
turbine hub heights in these simulations and AEP computed using the power
curve of the most commonly deployed wind turbine is lower than is implied by
assuming σ = 6 %. Indeed, rather than 9 out of 10 years
exhibiting AEP within 0.9 and 1.1 times the long-term mean AEP as implied by
assuming a Gaussian distribution with σ of 6 %, the results
presented herein indicate that in over 90 % of the area in the eastern USA
that currently has operating wind turbines, simulated AEP lies within 0.94 and
1.06 of the long-term average. Further, the IAV of estimated AEP is not
substantially larger than IAV in mean wind speeds. These results indicate it
may be appropriate to reduce the IAV applied to preconstruction AEP
estimates to account for variability in wind climates, which would decrease
the cost of capital for wind farm developments.</p
Quantitative comparison of power production and power quality onshore and offshore: a case study from the eastern United States
A major issue in quantifying potential power generation from prospective wind energy sites is the lack of observations from heights relevant to modern wind turbines, particularly for offshore where blade tip heights are projected to increase beyond 250 m. We present analyses of uniquely detailed data sets from lidar (light detection and ranging) deployments in New York State and on two buoys in the adjacent New York Bight to examine the relative power generation potential and power quality at these on- and offshore locations. Time series of 10 min wind power production are computed from these wind speeds using the power curve from the International Energy Agency 15 MW reference wind turbine. Given the relatively close proximity of these lidar deployments, they share a common synoptic-scale meteorology and seasonal variability with lowest wind speeds in July and August. Time series of power production from the on- and offshore location are highly spatially correlated with the Spearman rank correlation coefficient dropping below 0.4 for separation distances of approximately 350 km. Hence careful planning of on- and offshore wind farms (i.e., separation of major plants by > 350 km) can be used reduce the system-wide probability of low wind energy power production. Energy density at 150 m height at the offshore buoys is more than 40 % higher, and the Weibull scale parameter is 2 m s−1 higher than at all but one of the land sites. Analyses of power production time series indicate annual energy production is almost twice as high for the two offshore locations. Further, electrical power production quality is higher from the offshore sites that exhibit a lower amplitude of diurnal variability, plus a lower probability of wind speeds below the cut-in and of ramp events of any magnitude. Despite this and the higher resource, the estimated levelized cost of energy (LCoE) is higher from the offshore sites mainly due to the higher infrastructure costs. Nonetheless, the projected LCoE is highly competitive from all sites considered.</p
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