I spoke to one of the authors Esin Serin, she's a policy analyst working on UK energy and climate policy at LSE's GRI centre. There are different types of tidal energy. Their report is about one type called tidal stream energy. "Tidal stream is like wind turbines. These are installed underwater so they capture power from moving water instead of moving air… Scotland is the leader in tidal stream energy but not in tidal power overall."
Listen to the interview at BBC Radio 4