The renewable energy currently generated in the Irish system is almost entirely supplied by wind power plants. However, in the sea around Ireland there is a significant tidal energy potential. This paper provides a comparison of these two renewable energy sources, namely wind and tidal, in terms of short-term variability and its impact on the dynamic behavior of the system. With this aim, stochastic models of the short-term variability of these two energy sources are proposed. Simulation results indicate that tidal generation leads to larger frequency variations than those that are caused by wind generation. The paper also shows that the inclusion of frequency control in tidal power plants effectively mitigates such fluctuations.