• Energy Research

Some simplified correlations of mean hourly global and diffuse luminous efficacy on the horizontal plane for all sky conditions have been obtained for Arcavacata di Rende (Italy) and have been compared with other literature models and other experimental data measured in Geneva (Switzerland), Vaulx-en-Velin (France), Bratislava (Slovakia) and Osaka (Japan). The comparisons show that, for global efficacy, the differences among the various models are not significant, and the use of a model with a constant value of efficacy gives good predictions of global illuminance. For the prediction of diffuse illuminance the differences among the models are larger, but the use of a constant diffuse efficacy provides a good first estimate of diffuse illuminance.

Abstract To analyse the behaviour of a parabolic trough operating with nanofluids, and compare its performance to the more traditional ones using oil, a model for the thermal analysis of the system has been developed and implemented in Matlab. The simulations have been performed for a suspension of Al2O3 in synthetic oil and its characteristics compared to the corresponding basic liquid used by itself. The string has been assumed to have a length of 100 m and a concentrating surface area of 550 m2. The simulations have been carried out for different DNI (Direct normal irradiance) and variable mass flow, ensuring a temperature at the collector outlet below 400C. For a proper comparison, the following variables and efficiency indicators have been checked: power output, pumping power, thermal efficiency and overall efficiency of the parabolic trough system.

Building energy consumption constitutes a significant share of global energy demand. This study examines how a prefabricated building, often subject to challenges in maintaining comfort, can meet the nearly zero-energy building (nZEB) standards in Italy. This study fills the gap in the literature on prefabricated buildings that meet nZEB standards, proposing an innovative approach that integrates vacuum insulated panels (VIP) and photovoltaic systems with storage to optimize energy efficiency and thermal comfort. The paper examines an existing prefabricated building and assesses the most effective solutions to implement, along with their respective impacts on comfort and energy consumption. The model of the building is developed in EnergyPlus and verified with experimental data. The results indicate significant energy savings, demonstrating the feasibility of prefabricated buildings in achieving nZEB goals. In particular, if the building is equipped with solar shading, controlled mechanical ventilation, free cooling, and vacuum insulated panels, the thermal savings is 60 %. If the maximum photovoltaic power possible is installed on the roof the energy demand coverage is 63 %, which increases to 95 % with a storage system with a nominal capacity of 10 kWh. This paper aims to provide insights for designers, researchers and policymakers by exposing the potential for prefabricated solutions to meet stringent energy standards and promote sustainability in the construction industry.

Abstract Silicon based modules have been installed since the beginning of the commercial development of the PV technology, and still represent an important share of the global PV market. However, they are penalised when cells reach high temperatures, with a worsening of the conversion efficiency due to thermal drift. Several cooling techniques have been proposed to attenuate this drawback, where water- and air-based solutions have proved to be the most effective and applicable, even though issues related to deterioration of front glass optical properties and thermal shock may occur. In order to overcome these limitations, in this paper the authors report the performances of three different cooling systems operating on the PV module back surface over an acquisition period of eight months. Two systems are based on a spray cooling mechanism whereas the third exploits the forced ventilation of a cavity placed under the module. Data were monitored on the experimental set-up located on the building roof of the Department of Mechanical Engineering of University of Calabria (Italy). Results demonstrate the excellent performance of a simple spray cooling system, able to generate a monthly energy increase up to 8.6%, with a global water consumption of 2.78 m3 in the whole analysed period, whereas the employment of more complex systems based on mechanical ventilation proved to be ineffective for cooling applications.

73rd Conference of the Italian Thermal Machines Engineering Association (ATI 2018), 12–14 September 2018, Pisa, Italy In this work, the dynamic performance of a mass flow regulation system, in a concentrating solar tower plant, with unfired closed micro gas turbine, during clouds transient will be presented. The adjustment system operates with the heliostats field control system, in order to control the temperature inlet turbine. To choose the best configuration, the performance of three heliostats sizes, for four Solar Multiple, has been evaluated. The design of the solar field was carried out by means of Solar Pilot, while the numerical models have been developed in Matlab/Simulink. The results show that a particular configuration is suitable for this purpose.

Abstract Many correlations of mean hourly direct luminous efficacy for all sky, clear sky and intermediate sky conditions have been compared with experimental data measured in Arcavacata di Rende (Italy), Geneva (Switzerland), Vaulx-en-Velin (France), Bratislava (Slovakia) and Osaka (Japan). The comparisons show that, for all sky conditions, the correlations developed for one locality predict the luminous efficacy in the other localities with mean errors between −13% and 20% and root mean square errors between 15% and 35%; for clear sky conditions, the correlations developed for one locality predict the luminous efficacy in the other localities with mean errors between −7% and 14% and root mean square errors between 7% and 19%; for intermediate sky conditions, the correlations developed for one locality predict the luminous efficacy in the other localities with mean errors between −17% and 26% and root mean square errors between 20% and 41%. If the correlations with local coefficients are applied in each locality, the errors become considerably shorter. The paper gives indications on the values of the measured mean luminous efficacies and on the best models.