When wind passes over a hilly land, the complex terrain feature will observably change wind speed. Wind speed distribution on a hill is much different from that on a flat area. The wake produced by an upstream wind turbine generator (WTG) may affect power output of a downstream WTG. When a WTG fails, wind speed distribution over a wind farm also changes, which leads to different wind power output. This study proposes a time sequential Monte Carlo simulation technique to evaluate adequacy of a wind farm with considering the combined effect of terrain, wake and WTG reliability. A quadratic interpolation method is used to study the optimal locations of WTGs in order to maximise power output of a wind farm. A test wind farm and the IEEE reliability test system (RTS) are analysed to illustrate the models and proposed technique.