Comparing the performances of different cooling strategies to increase photovoltaic electric performance in different meteorological conditions

An accurate thermal model for the PV electric generation prediction: long-term validation in different climatic conditions

Seasonal performances of photovoltaic cooling systems in different weather conditions

The use of passive solutions for building envelopes represents an important step toward the achievement of more efficient and zero-energy building targets. Trombe walls are an interesting and viable option for the reduction of building energy requirements for heating, especially in cold climates. This study presents the experimental analysis of an innovative Trombe wall configuration, named a thermo-diode Trombe wall, which was specifically designed to improve the energy efficiency by providing a proper level of insulation for the building envelope. Such a design is essential in cold climates to limit the thermal losses whilst increasing solar heat gains to the heated spaces. An experimental campaign was conducted from December to March that involved monitoring the external climatic conditions and the main thermal parameters to assess the thermal performance of the proposed solution. The results demonstrated that in the presence of solar radiation, the thermo-diode Trombe wall was able to generate significant natural convection inside the air cavity, with temperatures higher than 35 °C in the upper section, by providing consistent heat gains for the indoor environment, even on cold days and for hours after the end of the daylight. The efficiency, relative to the incident solar radiation, reached 15.3% during a well-insolated winter day.

https://www.mdpi.com/1996-1073/13/9/2188/pdf

An Innovative Trombe Wall for Winter Use: The Thermo-Diode Trombe Wall

Crystalline silicon photovoltaics are a cardinal and well-consolidated technology for the achievement of energy efficiency goals, being installed worldwide for the production of clean electrical energy. However, their performance is strongly penalized by the thermal drift, mostly in periods of high solar radiation where solar cells reach considerably high temperatures. To limit this aspect, the employment of cooling systems appears a promising and viable solution. For this purpose, four different cooling systems, working on the photovoltaic (PV) panel back surface, were proposed and investigated in an experimental set-up located at the University of Calabria (Italy). Hourly electrical output power and efficiency were provided accounting for different meteorological conditions in several months of the experimental campaign. The results demonstrated that a simple spray cooling technique can provide an absolute increment of electrical efficiency of up to 1.6% and an average percentage increment of daily energy of up to 8% in hot months. More complex systems, based on ventilation or combining spray cooling and ventilation, were demonstrated not to be a viable option for PV performance improvement.

Efficiency Improvement of Photovoltaic Modules via Back Surface Cooling

Glazing surfaces strongly affect the building energy balance considering heat losses, solar gains and daylighting. Appropriate operation of the screens is required to control the transmitted solar radiation, preventing internal overheating while assuring visual comfort. Consequently, in the building design phase, solar control systems have become crucial devices to achieve high energy standards. An operation based on well-defined control strategies can help to reduce cooling energy consumption and ensure appropriate levels of natural lighting. The present study aims at investigating the effect of smart screening strategies on the energy consumption of a test building designed in the Mediterranean climate. With the aim of automatically setting the inclination of venetian blind slats, the necessary equations are analytically found out and applied. Equations obtained are based on the position of the sun with respect to the wall orientation. In the case of a cloudy day or an unlit surface, empirical laws are determined to optimize the shielding. These are extrapolated through energy simulations conducted with the EnergyPlus software. Finally, using the same software, the actual benefits obtained by the method used are assessed, in terms of energy and CO2 emissions saved in a test environment.

https://www.mdpi.com/1996-1073/13/7/1731/pdf

The Control of Venetian Blinds: A Solution for Reduction of Energy Consumption Preserving Visual Comfort

Received: 21 June 2020 Accepted: 18 August 2020 Among the new technologies for the exploitation of the solar source, double-sided photovoltaic panels represent a valid high efficiency solution. These are latest generation photovoltaic panels that allow you to capture solar radiation even from the back and to obtain a greater production of electricity compared to traditional singlesided panels. The performance of the panel is higher, with the consequent possibility of reducing the installation surface. The paper defines a calculation model to analyse performances of a double-sided photovoltaic field, for both type of orientation N-S and E-W, in order to assess the effective increase in performance compared to a traditional system. Panels are equipped with a single-axis solar tracker, which changes their inclination so that they can have the best exposure to solar radiation. The study also focuses on the optimal tracking methodology, in order to reduce the losses caused by shading. The applied technique is that of "backtracking". We have seen that backtracking is not useful for bifacial panels, but only for mono-facial. In the work, a parametric analysis is also conducted to evaluate the increase in efficiency due to distance between rows of panels.

/pdf/performance-analysis-of-a-double-sided-pv-plant-oriented-3gq5do5yvp.pdf

Performance Analysis of a Double-Sided PV Plant Oriented with Backtracking System

Received: 11 July 2019 Accepted: 20 September 2019 Linear Fresnel Plants are composed of flat mirrors that reflect direct radiation towards a fixed receiver tube parallel to the reflectors. In traditional plants, mirrors are able to rotate around a single axis. This type of solar tracking system generates high losses at its ends. In the paper a new configuration is studied in which the mirrors placed at the ends are moved around two axes. The proposed system is thus able to recover the direct radiation which, otherwise, would not reach the receiver tube. The rotation of the mirrors is managed by stepper servomotors. They allow a robust solar tracking, not influenced by external forces. The work presents the kinematic system for moving the field of mirrors actuated with open loop control. Stepper motors generate a motion by steps; in order to execute each step at the exact moment, the logic of movement is properly defined. It is necessary to know in detail the temporal position and the law of motion for each rotation to identify the driving logic of the motors. The behaviour of the \"electric motor mechanical system\" is numerically modelled, evaluating the torque and the errors in the motion.

/pdf/study-of-kinematic-system-for-solar-tracking-of-a-linear-2ysf0phuqh.pdf

Study of Kinematic System for Solar Tracking of a Linear Fresnel Plant to Reduce End Losses

Linear Fresnel plant with primary reflectors movable around two axes

In the present work, the law of motion of reflectors for a concentrating solar Linear Fresnel plant is geometrically analyzed. Firstly, a method for optimally distributing the primary reflectors on the ground is proposed. Furthermore, the mathematical procedure used to identify the law of motion that the mirrors must follow to reflect solar radiation on the absorber tube is presented. To make better use of the surface area occupied by the plant it is necessary to distance the rows of mirrors adequately so that the effects of shading and blocking between the same can be reduced. Avoiding these phenomena allows the initial costs of the plant to be reduced since the reflective material is not used in excess, thus allowing exploitation of the entire reflective surface available. In the work, using spherical trigonometry concepts, the motion law equation of the mirrors is detected. It allows the angle that they must assume in every moment of the day to be established and it has an entirely general valence: it can be applied to each plant according to its constructional characteristics and to each type of orientation. Finally, a comparison is carried out in which the main tracking differences between the plants oriented North-South and East-West are analyzed.

/pdf/law-of-motion-of-reflectors-for-a-linear-fresnel-plant-1ie6xh9cyp.pdf

Francesco Nicoletti

Papers

The Control of Venetian Blinds: A Solution for Reduction of Energy Consumption Preserving Visual Comfort

Performance Analysis of a Double-Sided PV Plant Oriented with Backtracking System

Study of Kinematic System for Solar Tracking of a Linear Fresnel Plant to Reduce End Losses

Linear Fresnel plant with primary reflectors movable around two axes

Law of Motion of Reflectors for a Linear Fresnel Plant