Following the growth trend and consolidation of wind power as a renewable source of energy in the global market, promising investments are likely to be made in Brazil in the next few years. Aiming to ensure profitability for prospective investors, studies on feasilibity, reliability and availability have to be carried out. This paper presents a method of calculation of the energy produced in a year by a horizontal axis wind turbine, considering failure rate and downtime. As a parameter, failure rates and downtime from countries whose climates are different from Brazil's were used. The outcomes analysis showed that the failure rates interfered significantly with the amount of energy produced in a year.