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European Association for the Development of Renewable Energies, Environment and Power Quality (EA4EPQ)

International Conference on Renewable Energies and Power Quality (ICREPQ’10) Granada (Spain), 23th to 25th March, 2010

Wind loads on an azimuthal photovoltaic platform. Experimental study

R. Velicu1, G. Moldovean1, I. Scalechi1 and B.R. Butuc1

1 Product Design Centre for Sustainable Development, Transilvania University of Brasov, Eroilor 29, 500036, Braşov, Romania, tel. 0268-412088, fax 0268-410525, e-mail: r.velicu@unitbv.ro, ghmoldovean@unitbv.ro, scaletzky_ivan_777@yahoo.com, bianca.butuc@unitbv.ro

Abstract. During the dimensioning stage of the embodiment design process of the azimuthal trackers for photovoltaic (PV) platforms a very important step is input load calculation. Wind load is the main load on these kinds of systems and a correct evaluation of wind load becomes significant for dimensioning. This paper presents results and conclusions from an experimental study on wind loads depending on wind velocity and functional positions of solar tracking platforms. The results are presented as graphic diagrams and can be useful for the improvement of actual standards on wind loads.

reliability but also the costs of the tracking system. Dimensions of structure and transmission of the tracking system are directly depending on the loads of the PV platform.

Key words

Experimental study, wind loads, azimuthal tracker.

1. Introduction

Fig. 1. Azimuthal tracking system - general diagram

In the actual international context, decrease of electrical consumption is a top priority at European level, as it is specified in the European directive EC 20/20/20. With this aim the renewable energy systems like PV platforms are in continuous development. They are converting solar energy into electricity by means of the photovoltaic effect.

From all the loads coming from weight, wind etc., the main load is the wind load [2]. This load is also the only one that creates reactions in the linear actuators used for positioning the α angle for altitudinal rotation of platform [3].

2. Wind load

In order to increase the efficiency of PV platforms with up to 40% [1], they can be part of dual axes tracking systems. Tracking systems are maximizing the solar radiation on the surface of panels by minimizing the incidence angle of solar ray.

Action of wind on different structures is usually evaluated either by wind pressure or by wind forces. Wind effects on buildings or specific structures depend on wind properties (medium velocity, air density, turbulences, dynamics, etc.), shape, dimensions and position of building towards direction of wind.

The dual axes tracking systems for PV platforms, using a vertical axis and a horizontal axis (fig. 1), are called azimuthal tracking systems. Rotations around the two axes (positioned by α angle for altitudinal rotation and ψ angle for azimuthal rotation) are performed by means of different kind of mechanical transmissions.

Dimensioning of the consisting mechanical transmissions and the mechanical structure itself is an important stage in the embodiment design of a tracking system for PV platforms. The dimensioning results influence the

EN 1991-1-4 standard [4] presents calculus procedures for determining wind loads acting on buildings and other specific structures.

One situation presented in EN 1991-1-4, Eurocode1 is the one of hipped roofs. This case is not proper to be used as similar to the case of wind loads on the platform of a tracking system because the values of the pressure coefficients are only considering the external pressure on

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