In this paper, the traditional Fault Tree Analysis (FTA) method combined with Monte Carlo simulations (MCSs) is introduced to a real micro-gird with significant clean energy penetration. Importance of different components in the microgrid is first found using the traditional FTA but cannot show a clear illustration of the system's reliability with respect to time. Using the proposed fault-tree-MCS (FT-MCS) method, a simulation program can be established with random sampling time. In this process, the contribution of each part to the whole system reliability can be clearly shown with varying time. A more accurate Mean Time to Failure (MTTF) can thus be achieved using the FT-MCS. FT-MCS is shown to combine the benefits of fault tree component hierarchy for fault propagation, as well as fault occurrence over time.