Tidal power plants are connected with high upfront costs needed for construction, and therefore lack cost-competitiveness on global energy market.
Tidal power is intermittent source of energy that can only produce electricity during tidal surges which is in average around 10 hours each day. This means that in order for tidal power to be considered as a reliable source of energy needs to be accompanied with some effective energy storage solution.
Tidal power plants could lead to environmental damage in some cases as the frames of the turbines have potential to disrupt the movement of large marine animals. Also, the construction of tidal power plant can disrupt fish migration in the oceans.
Still more a theoretic source of energy, limited in real life to just a few prototype projects because technology has just started developing and needs big funds and plenty of scientific research before reaching the commercial character.