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Abstract Using hourly global radiation data at Quetta, Pakistan for 10 yr, an Autoregressive Moving Average (ARMA) process is fitted. Markov Transition Matrices have also been developed. These models are used for generating synthetic sequences for hourly radiations in MJ/m 2 and that the generated sequences are compared with the observed data. We found the MTM approach relatively better as a simulator compared to ARMA modeling.

The paper deals with the preliminary design and optimization of cogenerative solar thermodynamic plants for industrial users. The considered plants are all based on proven parabolic trough technology, but different schemes have been analyzed: from a conventional configuration with indirect steam cycle and a heat transfer fluid such as synthetic oil or molten salts, to a more innovative arrangement with direct steam generation in the solar field. Thermodynamic parameters of the steam cycle have been optimized considering some constraints due to the heat requirements of the user, leading to a preliminary design of the main components of the system and an estimation of costs. Resulting net electric efficiency is about 10% for conventional synthetic oil plant, while 13% for innovative molten salts and DSG. A comparison with conventional solar thermodynamic systems for electricity production and photovoltaic power plants shows the economic and energetic benefits of the cogenerative solution. Cost of electricity for solar plant is cheaper of about 20 €/MWh than conventional solar power application. Moreover, heat recovery allows to achieve a further 50% of CO2 emission savings compared to reference solar plants for only electricity production.

Abstract A study of the economic, social-political, and environmental consequences of using renewable energy technologies (RETs, e.g., photovoltaics, wind, solar thermal, biofuels) as compared to those of conventional energy technologies (CETs, e.g., oil, coal, gas) would show that RETs are singularly consistent with a whole ethic that is implicit in the concept of sustainability. This paper argues for sustainability as an ethical, as well as a pragmatic, imperative and for RETs as an integral part of this imperative. It brings to the fore some of the specific current economic, political, and environmental assumptions and practices that are inconsistent with both sustainability and with a rapid deployment of RETs. Reflecting an emerging planetary awareness and a pressing need to come to terms with intra- and intergenerational equity, the concept of sustainability explicitly entails the right of future generations to the same opportunity of access to a healthy ecological future and the finite endowment of the Earth's resources as that of the present generation.

Abstract Hydropower plants are one of the most convenient option for power generation, as they generate energy exploiting a renewable source, they have relatively low operating and maintenance costs, and they may be used to provide ancillary services, exploiting the large reservoirs of available water. The recent advances in Information and Communication Technologies (ICT) and in machine learning methodologies are seen as fundamental enablers to upgrade and modernize the current operation of most hydropower plants, in terms of condition monitoring, early diagnostics and eventually predictive maintenance. While very few works, or running technologies, have been documented so far for the hydro case, in this paper we propose a novel Key Performance Indicator (KPI) that we have recently developed and tested on operating hydropower plants. In particular, we show that after more than one year of operation it has been able to identify several faults, and to support the operation and maintenance tasks of plant operators. Also, we show that the proposed KPI outperforms conventional multivariable process control charts, like the Hotelling t 2 index.

Abstract Various approaches to the calculation of solar radiation at the earth's surface using satellite data are reviewed. The methods range from qualitative and subjective use of hard copy satellite images at low spatial and temporal resolution to the use of high resolution digital data and spectral radiative transfer models. Operational techniques are also described. These can be either statistically or theoretically based with varying degrees of numerical complexity. The nature of the input data requirements also varies. Some methods use widely available hard copy satellite images while others are based on digital data. There is also a wide variation in the requirements for additional environmental data. Some models meet all such requirements by analysis of the satellite data. Other models need such information as precipitable water derived from upper air soundings or empirical calculations. The accuracy of various models is assessed. Accuracy increases dramatically with averaging period (hourly to monthly). Many models, even some of the more easily implemented ones, are able to match the accuracy of the models which use surface based observations of cloud or bright sunshine.