1,721,165 research outputs found
Estimating the Output Gap with High-Dimensional Time Series
No full textThe output gap measures the deviation of observed output from its potential, thereby defining imbalances in the real economy that affect utilization of resources and price inflation. A novel estimator of the output gap is proposed. It is based on a dynamic factor model that extracts from a high-dimensional set of time series the common component of a stationary transformation of the individual series. The latter results from the application of a nonlinear gap filter, such that for each of the individual time series the gap filter removes from the current value the historical local maximum, which in turn defines the potential. The smooth generalized principal components are extracted and the resulting common components are aggregated into a global output gap measure. An application is presented dealing with the U.S. industrial sector, where the proposed measure is constructed using the disaggregated market and industry groups time series. An evaluation of its external validity is conducted in comparison to alternative measures
Design optimization of the phase change material integrated solar receiver: A numerical parametric study
No full textDish-Micro Gas Turbine (D-MGT) systems can be an effective way of power production (<100 kW) in rural areas having limited access to electricity. In such no fuel assisted systems, the stability of the input thermal power to the MGT is an important concern as MGT is sensitive to the temperature variations caused by the natural fluctuation of the solar flux. To reduce this effect, a novel solar receiver has been proposed integrated with a Phase Change Material (PCM) for the short-term thermal energy storage. The proposed receiver is cylindrical shaped filled with PCM, with a conical cavity on the front surface and heat transfer fluid tubes immersed in the PCM. This paper deals with the investigation of the optimum design point of the proposed receiver based on the required input parameters of the MGT. The numerical simulations have been conducted using Computational Fluid Dynamic methods to pre-evaluate the effect of many controlling parameters on the temperature, PCM liquid fraction, pressure loss and outlet thermal power of the receiver. Surface-to-Surface (S2S) radiation model has been employed along with the ray-tracing model for the constant concentrated solar flux of 500 kW/m2 on the receiver aperture surface. The influencing factors considered in this study include the high-temperature PCMs, receiver cavity dimensions, incident solar flux, hot wall thickness, tube diameter and the number of the tubes, pressure drop inside the tubes and the inlet mass flow rate. Results demonstrate the considerable effect of each variable on the receiver output parameters, and this leads to the identification of optimum design point. The result of the study offers valuable guidelines for the receiver development for further experimentation
Are GDP forecasts optimal? Evidence on European countries
No full textWe assess the accuracy of real GDP growth forecasts released by governments and international organizations for European countries in the years 1999–2017. We implement three testing procedures characterized by different assumptions on the forecasters’ loss functions. First, we test forecast rationality within the traditional approach based on a quadratic loss function (Mincer and Zarnowitz, 1969). Second, following Elliott, Timmermann and Komunjer (2005), we test rationality by allowing for a flexible loss function where the shape parameter driving the extent of asymmetry is unknown and estimated from the empirical distribution of forecast errors. Lastly, we implement the tests proposed by Patton and Timmermann (2007a) that hold regardless of the functional form of the loss function. We conclude that governmental forecasts are biased and not rational under a symmetric and quadratic loss function, but they are optimal under more general assumptions on the loss function. We also find that the preferences of forecasters change with the forecasting horizon: when moving from one- to two-year-ahead forecasts, the optimistic bias increases and the parameter of asymmetry in the loss function significantly increases
Probabilistic Performance Evaluation of Small-Scale Organic Rankine Cycle Power Plants for Waste Heat Recovery
No full textThe performance of Organic Rankine Cycles (ORC) plants is subject to uncertainties deriving from several factors. Such uncertainties are unavoidably propagated through the model to the outputs, affecting predictions of the commercial-scale performance and cost of this technology. The aim of this work is to analyse how the uncertainties associated with the performance of the expander, one of the main ORC components, propagate to the relevant thermodynamic and economic outputs and affect their final value. The analysis was performed for three different expander options (a single-stage turbine, a twin screw and a two-stage turbine) to generate a full spectrum of possible outputs rather than exact figures. Overall, a considerable variability of the output metrics was highlighted compared to the results from the deterministic analysis
Analysis of diabatic compressed air energy storage systems with artificial reservoir using the levelized cost of storage method
No full textA detailed analysis has been carried out to assess the thermodynamic and economic performance of Diabatic Compressed Air Energy Storage (D-CAES) systems equipped with above-ground artificial storage. D-CAES plant arrangements based on both Steam Turbine (ST) and Gas Turbine (GT) technologies are taken into consideration. The influence of key design quantities (ie, storage pressure, turbine inlet pressure, turbine inlet temperature) on efficiency, capital and operating costs is analysed in detail and widely discussed. Finally, D-CAES design solutions are compared with Battery Energy Storage (BES) systems on the basis of the Levelized Cost of Storage (LCOS) method. Results show that the adoption of D-CAES can lead to better economic performance with respect to mature and emerging BES technologies. D-CAES ST based solutions can achieve a LCOS of 28 €cent/kWh, really close to that evaluated for the better performing BES system. Interesting LCOS values of 20 €cent/kWh have been attained by adopting D-CAES plant solutions based on GT technology
Supercritical carbon dioxide recovery system applied to cement industries
Full text linkThe paper addresses the potential heat-to-power application of supercritical CO2 (sCO2) plants to the cement industry, thereby reducing their electricity demand and improving energy efficiency. The research was conducted as part of the European project CO2OLHEAT (G.A. 101022831), which involves the installation of a 2 MW Waste-Heat-to-Power (WH2P) skid based on a sCO2 cycle in a cement plant, the first of its kind with a MW-scale power output. The paper summarizes technologies and processes employed in the Italian cement production sector, detecting where the waste heat can be successfully extracted to feed the recovery plant without compromising the industrial process. Moreover, the paper discusses the national cement market and explores the potential advantages and limitations of integrating sCO2 recovery plants within the national cement context, considering production and energy-related data. The final finding reveals the percentage of recoverable electricity per technological class for the cement production sector in Italy with a potential application of the sCO2 recovery plant, aiming at identifying the potential market penetration of the CO2OLHEAT installation
Two-stage radial turbine for a small waste heat recovery Organic Rankine Cycle (ORC) plant
No full textLooking at the waste heat potential made available by industry, it can be noted that there are many sectors where small scale (< 100 kWe) organic Rankine cycle (ORC) plants could be applied to improve the energy efficiency. Such plants are quite challenging from the techno-economic point of view: The temperature of the primary heat source poses a low cutoff to the system thermodynamic efficiency. Therefore, high-performance components are needed, but, at the same time, they have to be at low cost as possible to assure a reasonable payback time. In this paper, the design of a twostage radial in-flow turbine for small ORC industrial plants is presented. Compared to commonly applied mono-stage expanders (both volumetric and dynamic), this novel turbine enables plants to exploit higher pressure ratios than conventional plants. Thus, the theoretical limit to the cycle efficiency is enhanced with undoubted benefits on the overall ORC plant performance. The design process involved 1D/2D models as well as 3D Computational Fluid Dynamic ones. After the design of the preliminary configuration, sensitivity analyses were carried out varying the most relevant geometric parameters for design performance improvement. Thereafter, the stages were both analyzed in off-design conditions giving their performance maps. Moreover, a stage stacking procedure was applied to obtain the overall turbine behavior
Prove di interferenza su ricevitori GPS
No full textNell'articolo vengono verificate le capacità di regsitrazione di ricevitori GPS, in singola e doppia frequenza, durante l'emissione di onde elettromagnetiche di disturbo alla stessa frequanza del segnael GPS. Durante il disturbo viene anche stimato il deterioramento dell'osservabile in termini di precisione
On the possibility of using an industrial steam turbine as an air expander in a Compressed Air Energy Storage plant
No full textSmall/medium size CAES systems (1–10 MW) could be efficiently and successfully employed for off-grid and self-consumption applications and for the delivery of ancillary services on the lower grid levels. A critical issue affecting the feasibility of such systems is related to the availability of efficient and affordable air expanders. Taking into consideration that typical CAES applications are characterized by inlet pressure levels in the range of 40–60 bar, an attractive opportunity to reduce development efforts and investment costs is to resort to the consolidated steam turbine engineering practice. In the present paper, the possibility of using existing building blocks developed to assemble industrial steam turbines to arrange air expanders for CAES applications is explored. A general model for off-design calculation capable of simulating, for a given turbine geometry, steam and air operations as well, has been developed and applied to a case study. On the basis of available information about an existing industrial steam turbine, a possible arrangement for an air expander has been set up and investigated. Results have evidenced a performance loss in terms of both power output and efficiency with respect to steam operations. Nevertheless, the air expander behavior in a wide range of operation can be considered satisfactory. Therefore, the use of industrial steam turbines technology might be considered interesting for the applications under consideration
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