C.F. Ratto

Solar irradiance estimation from geostationary satellite data: I. Statistical models☆

Abstract The use of satellite data to estimate solar irradiance at ground level represents a valid alternative to ground measurements of solar radiation. The best known methods of estimating the solar irradiance at the earths surface using geostationary satellite data are reviewed. The models may be classified into statistical and physical models, depending on the approach used to treat the interaction between solar radiation and atmosphere. The main hypotheses and algorithms used in four statistical models are extensively presented and discussed. The differences between these methods are pointed out. Physical models will be examined in a second paper[1]. This second paper will include various assessments regarding the performances of the described methods and summaries of comparisons between the different models.

Mass-consistent models for wind fields over complex terrain: The state of the art☆

Abstract Among the diagnostic models for wind field simulation, mass-consistent models play an important role, thanks to the simplicity of the physics involved and their capacity to accept several measurements of wind at different points of the domain. The general procedure and mathematical supports for this kind of simulation, with particular reference to the approximation that characterize the different models developed, are analyzed. Evidently, a large number of simulations is required if one needs to know the average wind over a region, with a consequent long calculation time. Some methods reducing this time, without losing fundamental information, are described.

Proposal of a numerical procedure to select Reference Years

Abstract A procedure is presented which can be used to create, from many years of available past weather data, a Reference Year consisting in 8760 hourly values of a few chosen meteorological quantities. Such “year” corresponds to a “typical” year for the considered locality, regarding both the occurrence and the persistence of different meteorological situations, in all months. This approach is a modification of the procedure used in the production of Test Reference Years or of Design Reference Years. In this approach, the frequency distributions relative to single months in the database are compared with the long-term frequency distribution of all the months “with the same name.” Furthermore, the correlation between subsequent subsequent daily values is taken into account.

Stochastic modelling of wind velocities time series

Abstract The knowledge of wind speed time series is necessary to evaluate, for instance, the power values produced by wind turbines, in order to investigate load matching and storage requirements. The usual description of the stochastic properties of wind speed independent of its direction is here criticized and an approach based on the coupled analysis of both wind speed and direction is proposed. Two stochastic models simulating three hourly wind speed and direction time series are investigated; encouraging results are obtained with a scheme combining a Markov chain model and a Discrete Auto Regressive model of order 2 (DAR(2)). A comparison with 42 years of wind data measured at Brindisi airport, Italy, is made, showing that this compound model is able to generate direction and speed sequences that fairly agree, in the statistical sense, with the observed time series at the considered site.

Optimization of the Regional Spatial Distribution of Wind Power Plants to Minimize the Variability of Wind Energy Input into Power Supply Systems

Abstract In contrast to conventional power generation, wind energy is not a controllable resource because of its stochastic nature, and the cumulative energy input of several wind power plants into the electric grid may cause undesired fluctuations in the power system. To mitigate this effect, the authors propose a procedure to calculate the optimal allocation of wind power plants over an extended territory to obtain a low temporal variability without penalizing too much the overall wind energy input into the power system. The procedure has been tested over Corsica (France), the fourth largest island in the Mediterranean Basin. The regional power supply system of Corsica could be sensitive to large fluctuations in power generation like wind power swings caused by the wind intermittency. The proposed methodology is based on the analysis of wind measurements from 10 anemometric stations located along the shoreline of the island, where most of the population resides, in a reasonably even distribution. First ...

Functional integral methods in the theory of the Anderson model

Abstract The use of the functional integration technique applied to the problem of local moment formation in the Anderson model is reviewed in this paper. The different approximations are discussed, in order to clarify both their internal consistency and relations among them. Connection with the ordinary diagrammatic approach is made by summarizing and extending previous treatments done on this subject; and the difference between the one-field and the two-field approaches is explained in terms of the ‘unphysical diagrams’ generated by the first. The results for the magnetic susceptibility are presented for each approximation discussed in the paper, both in the strong magnetic and in the non-magnetic regime; while it is shown that no reliable approximation has been developed for the intermediate coupling situation. Finally the Kondo effect is discussed within the functional integration scheme and application of the method to the study of superconducting magnetic alloys is reviewed.

Stochastic modelling of daily global irradiation

A statistical analysis of the solar daily global irradiation for Genoa, Italy, has been carried out using a 9 year time series. The frequency distribution of the fluctuations in the daily values of the time series about the mean, normalized by the standard deviation, has been transformed into a standard Normal distribution. An Autoregressive process of order 1 has been fitted to the transformed series. The daily means and the standard deviations have been estimated by two approaches, viz. (i) Fourier expansion of the daily means and standard deviations with one and two harmonics, respectively; (ii) smoothing of the daily values of these parameters by the “monthly averages method”. For both the approaches, the Autoregressive parameter has been estimated in two ways, viz. (i) keeping it time invariant; (ii) changing it day by day during a year. The fitted model has been used to generate synthetic sequences of daily solar irradiations. All the four methods produce synthetic series which almost satisfactorily match the empirical one without showing any appreciable superiority of the one over the other method.

Statistical analysis of extreme wind speeds in the Straits of Messina

Abstract This paper illustrates the methods for the statistical analysis of extreme wind speeds, drawn up on the occasion of the preliminary design for the construction of a bridge over the Straits of Messina. The studies are based on two alternative approaches, each one constituting a verification and control element for the other, leading to sound and generally reliable assessments. With the possibility existing for further improvement, the actual quality of the results obtained suggests that the procedures established could be applied to any situation.

An assessment of a statistical method to estimate solar irradiance at the earth's surface from geostationary satellite data

A statistical model developed by Tarpley is applied to estimate solar irradiance over West Germany during November 1986. Tarpleys model and the METEOSAT data used are briefly reviewed. Daily sums and montly means of global radiation obtained fro 29 stations, uniformly distributed over the studied region, are compared with corresponding ground measurements of solar radiation provided by pyranometers. Monthly means of daily global radiation are also compared with the corresponding values obtained applying a physical method developed by Moser and Raschke.

safe_air Algorithms to simulate the transport of pollutant elements: a model validation exercise and sensitivity analysis

Abstract The safe_air model numerically simulates transport and diffusion of airborne pollutants at local and regional scales using Gaussian plume segments and/or puffs. This model is able to deal with both non-stationary and inhomogeneous conditions. safe_air Is composed of a meteorological pre-processor, the WINDS model, to build a three-dimensional (3D) wind field starting from available wind measurements, and by a pollutant dispersion simulator, the P6 model. This paper deals with two different algorithms included in P6, which allow the determination of the advection of plume elements using the 3D wind field reconstructed by WINDS. A validation exercise concerning the two cited algorithms has been performed using laboratory data from the Environmental Protection Agency wind tunnel RUSHIL experiments (flat terrain and a two-dimensional schematic hill, neutral atmospheric conditions). This paper also contains a sensitivity analysis concerning the same algorithms when the model is applied to a hypothetical emission above a very complex real orography (Regione Liguria, Italy).