Forecasting large and fast variations of wind power (the so-called ramps) helps achieve the integration of large amounts of wind energy. This paper presents a survey on wind power ramp forecasting, reflecting the increasing interest on this topic observed since 2007. Three main aspects were identified from the literature: wind power ramp definition, ramp underlying meteorological causes and experiences in predicting ramps. In this framework, we additionally outline a number of recommendations and potential lines of research.

No abstract

Feed-in-tariff (FIT) schemes have been widely employed to promote renewable energy deployment. While FITs may be perceived by consumers as an extra cost, renewable energies cause a noticeable price reduction in wholesale electricity markets. We analyse both effects for the case of the Spanish electricity market during 2010. In particular, we examine the level of FITs that makes savings and extra costs to be similar on an hourly basis. Results are obtained for a wide range of renewable generation scenarios. It is found that FITs with null extra costs for consumers are in the range of 50-80 e/MWh. Some of the sideeffects of a high penetration of renewable energy in the market are analysed in detail and discussed.

Two alternative paths to achieve highly-renewable electricity generation in peninsular Spain are investigated in this paper. Every transition path comprises a description of the installed and decommissioned generation and storage capacities, from 2017 to 2030, as well as a hypothesis on the evolution of the electricity demand. The electricity mix for every hour within the transition path is determined through a dispatch algorithm that prioritízes electricity from renewable energy sources. The simulation is run for 900 different combinations of time series representing the hourly capacity factors of different technologies, as well as the electricity demand. This robust approach allows the evaluation of the transition paths based on the statístícal distribution of several deflned assessment criteria, such as security of supply, C0 2 emissions or renewable share in electricity generation. The feasibility of a Spanish power system with high renewable penetration is investigated not only in a future reference year but throughout the transition path. In particular, a progressive and simultaneous phase-out of nuclear and coal power plants in the short-term is proven to be feasible. Furthermore, the results sensitívity is analyzed including scenarios with a delayed nuclear phase-out, lower hydroelectricity generation due to more frequent and severe droughts caused by climate change and higher annual increment for the electricity demand. Authors Región Spatial resolution Time series Scenario where results are simulated Time-step Aim Rasmussen et al. [27] Europe One no de 8 (2000-2007) No time reference lh Least-cost solution Eriksen et al. [6] Europe One-node-per-country network 8 (2000-2007) No time reference lh Least-cost solution Schlachtberger et al. [7] Europe One-node-per-country network 1 (2011) 95% C02 abatement lh Least-cost solution Schlachtberger et al. [49] Europe One-node-per-country network 4 (2011-2014) 95% C02 abatement lh Least-cost solution Brown et al. [50] Europe One-node-per-country network 1 (2011) 95% C02 abatement lh Least-cost solution Collins et al. [28] Europe One-node-per-country network 30 (1985-2014) 5 reference scenarios (2030) lh Scenario comparison Güs etal. [51] Europe 15 regions 1 No time reference lh Least-cost solution Brancucci et al. [5] Europe One-node-per-country network 1 (2010) 2025 lh Connolly et al.

Wind power probabilistic forecast is being used as input in several decisionmaking problems, such as stochastic unit commitment, operating reserve setting and electricity market bidding. This work introduces a new on-line quantile regression model based on the Reproducing Kernel Hilbert Space (RKHS) framework. Its application to the field of wind power forecasting

Forecasting abrupt variations in wind power generation (the so-called ramps) helps achieve large scale wind power integration. One of the main issues to be confronted when addressing wind power ramp forecasting is the way in which relevant information is identified from large datasets to optimally feed forecasting models. To this end, an innovative methodology oriented to systematically relate multivariate datasets to ramp events is presented. The methodology comprises two stages: the identification of relevant features in the data and the assessment of the dependence between these features and ramp occurrence. As a test case, the proposed methodology was employed to explore the relationships between atmospheric dynamics at the global/synoptic scales and ramp events experienced in two wind farms located in Spain. The achieved results suggested different connection degrees between these atmospheric scales and ramp occurrence. For one of the wind farms, it was found that ramp events could be partly explained from regional circulations and zonal pressure gradients. To perform a comprehensive analysis of ramp underlying causes, the proposed methodology could be applied to datasets related to other stages of the wind-topower conversion chain.

Fatigue represents a critical issue in many structural applications, and wind turbines are not an exception. Their dynamic response over the years determines the turbine's lifespan, meaning that fatigue loads have a clear impact on the Cost of Energy. Since the direct experimental determination of the loading state is complex or expensive, estimations arising from general operational signals can be explored as an indirect way to acquire knowledge of fatigue loading levels.A case study based on 10-minute aeroelastic simulations of a wind turbine dynamics is used to develop a Damage Equivalent Load estimation model using operational signals (typically recorded by SCADA systems) as inputs. The focus is on both the input selection and the model configuration, seeking the combination which reaches the lowest error. Three filters and two innovative wrappers (exploration and optimization) were considered within the selection. Linear and Artificial Neural Network models were implemented and compared. Results showed performances in Damage Equivalent Load estimation below 4% in terms of Normalized Root Mean Squared Error, which is promising as compared with related work. Additional conclusions were obtained concerning appropriate Artificial Neural Network configurations (net type, architecture and training algorithm), likewise the potential contribution of a proposed genetic algorithm.

We have determined the normal Reynolds stresses and spectra of the wind velocity over a 1:115 scale mock-up of the Bolund hill. The experiment was run in a neutral boundary layer wind tunnel using 3-component hot-wire velocimetry, 2-component particle image velocimetry, and a high-precision traversing system. Spectra have been determined at different points along transects at 2 and 5 m height above ground level. The experiment was run for 270 • wind direction and for two Reynolds numbers, Re h 1 = 4.25×10 4 and Re h 2 = 8.21×10 4 , based on the maximum height of the hill and the free wind speed at this height. Our results show how the normalized power spectral density S ii = fS ii ∕u 2 i changes over the hill. The analysis of the normalized streamwise spectrum at 2 m height, just after the escarpment, reveals that part of the energy is concentrated in the interval of normalized frequencies n h ≈ 0.01 − 0.02, which could be a signature of a weakened "flapping" phenomenon described in the literature for flows over forward facing steps. The departure of the spectra slope in the inertial subrange, from the value −5/3, was found to be correlated with the hill geometry. KEYWORDS atmospheric boundary layer, complex terrain, wind energy, wind tunnel simulation 1 INTRODUCTION The Bolund experiment, run by RISØ-DTU in 2007, is probably the most relevant test case of flow models oriented to wind energy analysis over highly complex terrains, in neutral conditions and nonaffected by Coriolis forces. 1,2 Bolund is a reference case to identify flow patterns and to validate numerical and physical models, due to the number and quality of sensors installed on the full-scale hill and the amount of numerical and physical analyses available such as literature. 1-6 Bolund is a small hill of about 130 m × 75 m × 12 m, surrounded by water with a long uniform fetch for most of the upstream directions of interest (see Figure 1-left). A large amount of periods with nearly neutral atmospheric conditions can be found in the full-scale database provided by RISØ-DTU. These characteristics convert Bolund into an ideal case for wind tunnel modeling without considering flow stratification effects.The escarpment facing westerly winds is one of the main geometric characteristics of Bolund (see Figure 1). The escarpment height varies slightly for the 200 • to 295 • wind direction interval, being roughly equal to the maximum height of the island, h = 11.73 m. Flow detachment at the escarpment has been observed in the full-scale experiment 1,7 and in wind tunnel tests. 4,8 Reproducing the flow characteristics in this region has revealed to be a challenge, particularly at lower heights, where the interaction between the turbulent inflow and the detachment dynamics is highly complex. Most of the numerical and physical models have failed to reproduce the high reduction in the mean wind speed and the high increment in the turbulent kinetic energy (TKE) found in the full-scale experiment in met mast M6 at 2 m height for 270 • wind direction, see Figure 2. ...