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Forecasting the output power of solar systems is required for the good operation of the power grid or for the optimal management of the energy fluxes occurring into the solar system. Before forecasting the solar systems output, it is essential to focus the prediction on the solar irradiance. The global solar radiation forecasting can be performed by several methods; the two big categories are the cloud imagery combined with physical models, and the machine learning models. In this context, the objective of this paper is to give an overview of forecasting methods of solar irradiation using machine learning approaches. Although, a lot of papers describes methodologies like neural networks or support vector regression, it will be shown that other methods (regression tree, random forest, gradient boosting and many others) begin to be used in this context of prediction. The performance ranking of such methods is complicated due to the diversity of the data set, time step, forecasting horizon, set up and performance indicators. Overall, the error of prediction is quite equivalent. To improve the prediction performance some authors proposed the use of hybrid models or to use an ensemble forecast approach. (C) 2017 Elsevier Ltd. All rights reserved.

The industrial sector is one of the biggest oil consumers in Cyprus, corresponding to 20% of the fuel consumption. A parabolic trough collector (PTC) system seems the best option to produce clean thermal energy at higher temperatures than those that can be achieved from the already widely used flat plate collectors on the island. This paper presents a simulation model built to investigate the performance of the first industrial PTC system in Cyprus, installed at the Cyprus biggest soft drinks factory. The simulation model is built in TRNSYS and is validated using data from the real PTC system installed at the factory. The results show a very good fitting between the operating parameters and the power output of the Solar Field (SF), Concrete Thermal Storage System (CTES), and the Steam Generator (SG). The average percentage relative error of the system's contribution to the process is less than 6.32% for the daily steam production and during a week did not exceed 6.45%. The novelty of this study is the development of a design tool that can be used by potential interested industries to identify the suitable system that fits their needs. All data are provided in the form of graphs and allow anyone to use as input data the thermal energy demand and required steam temperature of the industry to retrieve information about the size of a suitable system which satisfies these requirements depending on each case. The payback period for all cases examined varies from 2 to 6 years, depending on the size of the system.

Monopiles are the most commonly used foundation types for offshore wind turbines. This study investigates numerically and experimentally the effects of breaking wave impact on a monopile-type offshore wind turbine installed at different locations at the edge of a 1:25 slope. The numerical model uses a two-phase flow model based on solving the Unsteady Reynolds-Averaged Navier-Stokes (URANS) equations with using the volume of fluid method and the k-ω shear stress transport turbulence model. Typical environmental conditions from the East China Sea have been examined. The wave run-up around the monopile and the nonlinear total horizontal wave force on the monopile are examined and compared with relevant experimental data originally presented in the present paper in order to validate the accuracy of the developed numerical model. A good agreement between the experimental data and numerical predictions is observed. Moreover, the wave breaking evolution and impact kinematics are investigated numerically for the different monopile locations. The results show that there is a 23.5% interval between the maximum wave force in the breaking zone and the wave force at the beginning of breaking. The first-order energy proportion of the breaking wave force will decrease maximum 61.65%, while, the second-order and high-order energy proportion of the breaking wave force will increase maximum 25.92% and 17.57%, respectively, between the different examined monopile locations. The time of occurrence of the secondary load cycle has no great relation with the form of the breaking wave for all examined locations, and the duration time of secondary load cycle impact on the monopile lasts for approximately 16.2% of the wave period. The secondary load cycle is smaller compared to the total horizontal breaking force in a range between 16.37% and 8.5%. The pressure on the monopile increases along with the wave breaking gradually. Compared with the pressure impact on the monopile when the wave begins to break, the pressure exerted on the monopile after the wave is rolled increases by 149%.

Routine measurements of irradiance are valuable for many research fields such as energy applications. However, ground data of solar global radiation can present questionable values. In this study, a set of check procedures is used to test the quality of shortwave and longwave radiation measurements taken at two actinometric stations in Cyprus (Athalassa-inland location and Larnaca-coastal location), during the period November 2012-July 2014. The testing procedures include physically possible limits for all the radiation components and comparisons between global radiation and the sum of direct and diffuse radiation. The quality process is implemented to both the 10-min averaged irradiances, hourly irradiation and the respective daily values. This paper reviews the currently available procedures for quality assessment of the solar shortwave and longwave irradiation data. In the present study, the first level of test includes physical possible limits which are determined by the Daylight Research Group and the Baseline Surface Radiation Network of the World Meteorological Organisation (WMO). The second level of test is a semi-automated procedure that is based on the creation of an envelope in the clearness index and the diffuse to global irradiance ratio. The third level of test is based on the comparison of various radiation parameters including comparison of measured extreme values with theoretical estimations from clear sky-models. The fourth level of test of the quality control procedure refers to the analysis of daily and annual variations of the radiation parameters.

This article presents the state of the knowledge on the thermal analysis of double skin facades with integrated photovoltaic (PV) panels called the Building Integrated Photovoltaics (BIPV) in terms of the published studies carried out on these systems. The idea of integration of the PV panels by replacing building elements, increase the prospects of the renewable energy systems. Taking also into account the need to use more renewable energy systems in buildings, the investigation of the BIPV systems to improve their performance is of a great importance. The literature studies are separated into experimental and theoretical for naturally ventilated systems and mechanically ventilated with external means e.g. fan use. It is concluded that most researchers studied the systems with mechanical ventilation rather than the systems with natural ventilation because the latter are more complex in terms of the air flow behaviour in the air duct. Additionally, various researchers proposed Nu number correlations and convective heat transfer correlation under several assumptions and conditions every time, for different range or Ra number which are presented and compared in this paper.