Do PGI integrated farms perform better? The case of the beef farms in Spain

European rural development policy is gaining in importance through one of its key instruments, the Protected Geographical Indications (PGI) system, which is designed to improve quality standards. Previous research has shown that PGI-certified beef farms tend to be more extensively managed operations that are better adapted to mountainous areas. This paper describes a comparative study of two production systems, one with PGI certification and one without, focusing on a number of economic variables. The results show a positive association between PGI production and profitability. In efficiency terms, non-certified farms show better pure technical efficiency scores, while PGI-certified holdings score higher on scale efficiency.

Use of STATCOM in wind farms with fixed-speed generators for grid code compliance

The increasing penetration of wind energy into power systems has pushed grid operators to set new requirements for this kind of generating plants in order to keep acceptable and reliable operation of the system. In addition to the low voltage ride through capability, wind farms are required to participate in voltage support, stability enhancement and power quality improvement. This paper presents a solution for wind farms with fixed-speed generators based on the use of STATCOM with braking resistor and additional series impedances, with an adequate control strategy. The focus is put on guaranteeing the grid code compliance when the wind farm faces an extensive series of grid disturbances.

Scour prediction and scour protections in offshore wind farms

This paper is the result of research whose main objective is to analyse different methods used for the prediction of maximum scour depth and scour extension, and for the design of scour protections in offshore wind farms located in shallow water, using medium and large diameter monopile foundations. Physical agents such as waves, currents and wind play a major role in the design of structures like offshore farms. As a result, the study has highlighted the need for introducing experience backed climate monomials such as the dimensionless wave height parameter (H0) and proposes the use of formulations that can express the extent of scour protections as a function of waves in transitional waters.

Dimensionless wave height parameter for preliminary design of scour protection in offshore wind farms

This article describes the results of an investigation aimed at the analysis methods used in the design of the protections against scour phenomenon on offshore wind farms in transitional waters, using medium and large diameter monopile type deep foundations.

Flow and wakes in large wind farms in complex terrain and offshore

Power losses due to wind turbine wakes are of the order of 10 and 20% of total power output in large wind farms. The focus of this research carried out within the EC funded UPWIND project is wind speed and turbulence modelling for large wind farms/wind turbines in complex terrain and offshore in order to optimise wind farm layouts to reduce wake losses and loads.

Simulation of wind farms in flat and complex terrain using CFD

Use of computational fluid dynamic (CFD) methods to predict the power production from wind entire wind farms in flat and complex terrain is presented in this paper. Two full 3D Navier–Stokes solvers for incompressible flow are employed that incorporate the k–ε and k–ω turbulence models respectively. The wind turbines (W/Ts) are modelled as momentum absorbers by means of their thrust coefficient using the actuator disk approach. The WT thrust is estimated using the wind speed one diameter upstream of the rotor at hub height. An alternative method that employs an induction-factor based concept is also tested. This method features the advantage of not utilizing the wind speed at a specific distance from the rotor disk, which is a doubtful approximation when a W/T is located in the wake of another and/or the terrain is complex. To account for the underestimation of the near wake deficit, a correction is introduced to the turbulence model. The turbulence time scale is bounded using the general “realizability” constraint for the turbulent velocities. Application is made on two wind farms, a five-machine one located in flat terrain and another 43-machine one located in complex terrain. In the flat terrain case, the combination of the induction factor method along with the turbulence correction provides satisfactory results. In the complex terrain case, there are some significant discrepancies with the measurements, which are discussed. In this case, the induction factor method does not provide satisfactory results.

CFD modelling of wind farms in complex terrain

Modelling of entire wind farms in flat and complex terrain using a full 3D Navier–Stokes solver for incompressible flow is presented in this paper. Numerical integration of the governing equations is performed using an implicit pressure correction scheme, where the wind turbines (W/Ts) are modelled as momentum absorbers through their thrust coefficient. The k–ω turbulence model, suitably modified for atmospheric flows, is employed for closure. A correction is introduced to account for the underestimation of the near wake deficit, in which the turbulence time scale is bounded using a general “realizability” constraint for the fluctuating velocities. The second modelling issue that is discussed in this paper is related to the determination of the reference wind speed for the thrust calculation of the machines. Dealing with large wind farms and wind farms in complex terrain, determining the reference wind speed is not obvious when a W/T operates in the wake of another WT and/or in complex terrain. Two alternatives are compared: using the wind speed value at hub height one diameter upstream of the W/T and adopting an induction factor-based concept to overcome the utilization of a wind speed at a certain distance upwind of the rotor. Application is made in two wind farms, a five-machine one located in flat terrain and a 43-machine one located in complex terrain.

Modelling wake effects in large wind farms in complex terrain: the problem, the methods and the issues

Computational fluid dynamic (CFD) methods are used in this paper to predict the power production from entire wind farms in complex terrain and to shed some light into the wake flow patterns. Two full three-dimensional Navier–Stokes solvers for incompressible fluid flow, employing k − ϵ and k − ω turbulence closures, are used. The wind turbines are modeled as momentum absorbers by means of their thrust coefficient through the actuator disk approach. Alternative methods for estimating the reference wind speed in the calculation of the thrust are tested. The work presented in this paper is part of the work being undertaken within the UpWind Integrated Project that aims to develop the design tools for next generation of large wind turbines. In this part of UpWind, the performance of wind farm and wake models is being examined in complex terrain environment where there are few pre-existing relevant measurements. The focus of the work being carried out is to evaluate the performance of CFD models in large wind farm applications in complex terrain and to examine the development of the wakes in a complex terrain environment.

Development of a wake model for wind farms based on an open source CFD solver. Strategies on parabolization and turbulence modeling

Wake effect represents one of the most important aspects to be analyzed at the engineering phase of every wind farm since it supposes an important power deficit and an increase of turbulence levels with the consequent decrease of the lifetime. It depends on the wind farm design, wind turbine type and the atmospheric conditions prevailing at the site. Traditionally industry has used analytical models, quick and robust, which allow carry out at the preliminary stages wind farm engineering in a flexible way. However, new models based on Computational Fluid Dynamics (CFD) are needed. These models must increase the accuracy of the output variables avoiding at the same time an increase in the computational time. Among them, the elliptic models based on the actuator disk technique have reached an extended use during the last years. These models present three important problems in case of being used by default for the solution of large wind farms: the estimation of the reference wind speed upstream of each rotor disk, turbulence modeling and computational time. In order to minimize the consequence of these problems, this PhD Thesis proposes solutions implemented under the open source CFD solver OpenFOAM and adapted for each type of site: a correction on the reference wind speed for the general elliptic models, the semi-parabollic model for large offshore wind farms and the hybrid model for wind farms in complex terrain. All the models are validated in terms of power ratios by means of experimental data derived from real operating wind farms.

The effect of scour protections in offshore wind farms

The installation of offshore scour protection systems in offshore wind farms allows avoid the effect of scour phenomenon around these structures. Up to date, numerous research projects have been carried out to justify the necessity of the scour protection systems and also to optimize their design. Protection systems based on riprap is frequently used due to its low cost and easy availability compared to other solutions such as geotextile bags or prefabricated concrete blocks. The sizing of these structures can be performed according to a series of recommendations that can optimize the costs associated with them, but there have been only few studies with real data up to now which have allowed identify the need for such protections. This investigation aims to assess the functionality of the scour protections adopted through the available data about their characteristics and the scour depth developed around the foundations. In this sense, this paper presents the results of a study that analyzes the functionality of scour protections in different European offshore wind farms.

Relationship among slurry characteristics and gaseous emissions at different types of commercial Spanish pig farms

This study aimed to analyse several factors of variation of slurry composition and to establish prediction equations for potential methane (CH4) and ammonia (NH3) emissions. Seventy-nine feed and slurry samples were collected at two seasons (summer and winter) from commercial pig farms sited at two Spanish regions (Centre and Mediterranean). Nursery, growing-fattening, gestating and lactating facilities were sampled. Feed and slurry composition were determined, and potential CH4 and NH3 emissions measured at laboratory. Feed nutrient contents were used as covariates in the analysis. Near infrared reflectance spectroscopy (NIRS) was evaluated as a predicting tool for slurry composition and potential gaseous emissions. A wide variability was found both in feed and slurry composition. Mediterranean farms had a higher pH (p<0.001) and ash (p=0.02) concentration than those located at the Centre of Spain. Also, type of farm affected ether extract content of the slurry (p=0.02), with highest values obtained for the youngest animal facilities. Results suggested a buffer effect of dietary fibre on slurry pH and a direct relationship (p<0.05) with fibre constituents of manure. Dietary protein content did not affect slurry nitrogen content but decreased (p=0.003) total and volatile solids concentration. Prediction models of potential NH3 emissions (R2=0.89) and CH4 yield (R2=0.61) were obtained from slurry composition. Predictions from NIRS showed a high accuracy for most slurry constituents (R2>0.90) and similar accuracy of prediction of potential NH3 and CH4 emissions (R2=0.84 and 0.68, respectively) to models using slurry characteristics, which can be of interest to estimate emissions from commercial farms and establish mitigation strategies or optimize biogas production.

Design of scour Protection Systems in Offshore Wind Farms

Scour compromises the operation of offshore facilities. This article describes the results of an investigation aimed at the analysis of different methods used in the scour protection systems design at offshore wind farms. The study is focused on transitional waters, where monopile foundations present medium or large diameters. Using the experience of offshore wind farms currently installed, a new design formula is proposed. All of this with the aim of improving a preliminary design of scour protection systems considering maritime parameters

Composition, potential emissions and agricultural value of pig slurry from Spanish commercial farms

Pig slurry is a valuable fertilizer for crop production but at the same time its management may pose environmental risks. Slurry samples were collected from 77 commercial farms of four animal categories (gestating and lactating sows, nursery piglets and growing pigs) and analyzed for macronutrients, micronutrients, heavy metals and volatile fatty acids. Emissions of ammonia (NH3) and biochemical methane potential (BMP) were quantified. Slurry electrical conductivity, pH, dry matter content and ash content were also determined. Data analysis included an analysis of correlations among variables, the development of prediction models for gaseous emissions and the analysis of nutritional content of slurries for crop production. Descriptive information is provided in this work and shows a wide range of variability in all studied variables. Animal category affected some physicochemical parameters, probably as a consequence of different slurry management and use of cleaning water. Slurries from gestating sows and growing pigs tended to be more concentrated in nutrients, whereas the slurry from lactating sows and nursery piglets tended to be more diluted. Relevant relationships were found among slurry characteristics expressed in fresh basis and gas emissions. Predictive models using on-farm measurable parameters were obtained for NH3 (R2 = 0.51) and CH4

Reports of the Director ... / Experimental Farms.

1890

Reports of the Director ... / Experimental Farms.

1894