1 Determination of the number of VAWT blades based on power spectrum Stanisław Anweiler * Faculty of Mechanical Engineering Department of Environmental Engineering Opole University of Technology, Poland email: s.anweiler@po.opole.pl Waldemar Feadak, Wojciech Gancarski Faculty of Mechanical Engineering Department of Environmental Engineering Opole University of Technology, Poland email: wfedak7@gmail.com, wojciech.gancarski@gmail.com ABSTRACT Technology of wind exploitation has been applied widely all over the world and has already reached the level in which manufacturers want to maximize the yield with the minimum investment outlays. The main objective of this paper is the determination of the optimal number of blades in the Cup-Bladed Vertical Axis Wind Turbine. Optimizing the size of the VAWT allows the reduction of costs. The maximum power of the rotor is selected as the performance target. The optimum number of VAWT blades evaluation is based on analysis of a single blade simulation and its superposition for the whole rotor. The simulation of working blade was done in MatLab environment. Power spectrum graphs were prepared and compared throughout superposition of individual blades in the VAWT rotor. The major result of this research is the VAWT power characteristic. On the basis of the analysis of the power spectra, optimum number of the blades was specified for the analysed rotor. Power spectrum analysis of wind turbine enabled the specification of the optimal number of blades, regarding investment outlays and power output of the VAWT. KEYWORDS RES, VAWT, Cup-blade rotor, Power spectrum, Design INTRODUCTION European Union directives, as well as increased environmental awareness, together with decreasing the energy resources of the planet, are forcing us to look for non-conventional and renewable energy sources at the same time. As of today, the use of these resources for economic reasons is less profitable than obtaining energy from fossil fuels, so renewables must be subsidized or protected by the government [1]. However, this does not remove the search for more efficient solutions. Wind energy has become an important source of electricity production due to its abundance in nature and low environmental pollution. Advanced techniques have been developed to achieve as much energy as possible with the energy conversion equipment – wind turbines [2]. At present, there are two categories of modern wind turbines, namely horizontal axis wind turbines (HAWT) and vertical axis wind turbines (VAWT) , which are used mainly for electricity generation and pumping water. The main advantage of VAWT is a single moving part (the * Corresponding author