The Chilean Inland Sea (CIS) has natural conditions for marine tidal energy development. Recent studies show that lunar variability in the tides should be considered, because the practical power generation varies considerably when large differences exist between spring and neap tides. Using a high resolution (similar to 1 km) 2D depth-averaged numerical model, we investigate the effect of lunar cycle variability in the CIS and this impact on tidal energy evaluation by validating a 30 days simulation. There are two highly energetic areas where currents exceed 2 m/s 50% of the time: the Chacao and Desertores Channels. Both zones are dominated by semi-diurnal tides, and tidal current amplitude shows large changes during spring and neap tides. Due to these changes power density can vary considerably in a period of 2 weeks. In the Chacao Channel, tidal-stream power is four times as large during spring tide (40 kW/m(2)) compared to neap tide (10 kW/m(2)). Tidal-stream power is only significant during spring tide in the Desertores Channel (8 kW/m(2)). This work is a contribution to understanding the tidally driven flows in an inland sea and the importance of considering the variations between spring and neap tides in tidal stream energy assessment. (C) 2019 Elsevier Ltd. All rights reserved.