A Ap sin
The corrected force coefficient is calculated with relation (5).
Fig. 13. Forces on the platform for altitudinal angle variation
Figure 14 presents the resulted corrected force coefficients, for secvential ψ angles, depending on wind velocity. It can be seen that the force coefficient variation is similar with the values resulted during previous determinations (A).
11 13 15 Wind velocity [m/s]
Fig. 14. Force coefficient with wind velocity correction
Few conclusions can be drawn based on the results presented in Figures 7 ... 10 and 12.
This paper is presenting experimental results on a very small scale panel but these results (force coefficients,
F t / F n r a t i o ) s h o u l d b e s i m i l a r t o t h e c a s e o f n o r m a l P panel platforms. V
The force coefficient is higher for low wind velocity (when resulted forces are very small) and is decreasing and tending to stabilize for high wind velocity. Force coefficients are relatively close and with higher values for high tilt angles (α or ψ = 40° ... 90°). Smaller values are obtained for smaller tilt angles and rapidly decreasing with decrease of tilt angle. Values for tilt angle equal to 0° are approximately equal to 0. These values (see fig. 7) are relatively different towards the values presented in Eurocode  but closer to the values presented by .
T h e r e s u l t e d t a n g e n t i a l f o r c e , c a l c u l a t e d b y t h e F t / F n r a t i is very small for high tilt angles (α or ψ = 40° ... 90°, see fig. 10), but important in the case of small tilt angles, when the normal force is very small. o
An improvement of EN 1991-1-4 Eurocode 1 should be performed in order to cover all the situations of wind load on PV platforms tracking systems.
This paper is supported by the "PLATSOL-PV" PNII Programme, financed by the Romanian Government and by the Sectoral Operational Programme Human Resources Development (SOP HRD), financed from the European Social Fund and by the Romanian Government under the contract number POSDRU/6/1.5/S/6".
 T. Huld, M. Šuri and D. Dunlop, “Comparison of Potential Solar Electricity Output from Fixed-Inclined and Two Axis Tracking Photovoltaic Modules in Europe”, in Progress in Photovoltaics: Research and Applications, 2008, Vol. 16, pp. 47-59.
and J. Ventre, “Photovoltaic Systems ed., CRC Press, London (2004), pp. 179-  R. Messenger Engineering”, 2nd 189
 L. Ching-Yao, ”Analysis of Structural Deformation in a High Concentrated Photovoltaic System”, available at http://thesis.lib.ncu.edu.tw/.  EN 1991-1-4, Eurocode 1: “Actions on structures . General actions — Part 1-4: Wind actions”, 2004  GOST 27751-88: Part 5. Wind loads (in russian). Anexa 4, 1988  J. Cabanillas, ”The Wind and the Panacea of the Stow Position in the Solar Trackers”, www.titantracker.es  C. Coşoiu, A. Damian, R. Damian and M. Degeratu, ”Numerical and experimental investigation of wind induced pressures on a photovoltaic solar panel”, in Proceedings of the 4th IASME/WSEAS International Conference on Energy, Environment, Ecosystems and sustainable development, Algarve, Portugal, 2008, pg. 74-80  HM170 Technical data available at www.gunt.de