From Electricity Info yesterday:

‘Scotland’s first floating tidal power farm to be set up in Orkney. The 4MW scheme is being developed by Scottish firm Orbital Marine Power, which has created the world’s most powerful tidal turbine – the O2. The first of the two turbines is expected to be connected to the grid by the end of this year, with a view to being fully operational in early 2021. When up and running, the pioneering floating devices are predicted to generate enough electricity to power up to 3,400 homes – around a third of Orkney’s needs. The turbines are being installed at the European Marine Energy Centre (EMEC) in Orkney, a world-leading test and research facility focusing on wave and tidal power development. The scheme will be deployed at the Fall of Warness test site, off Orkney’s northern island of Eday.’

http://electricityinfo.org/news/tidal-3/

How tidal energy works

The physical capacity of tidal energy worldwide is estimated at 3 TW (3,000,000 MW) (source: IEA-OES Annual Report, 2009). With current technologies it is assumed that at least 60,000 MW of the resource are technically extractable.

The gravitational forces of the moon, and to a lesser extent the sun, on the Earth move the water of the oceans.  A tidal cycle involves water flowing into a region due to these forces, and then flowing out from that region again.  The movement of the water at a given location is cyclical and predictable.  These water flows are called tidal currents and typically there are two tides per day due to the rotation of the Earth.  Turbines placed in tidal currents will rotate and thus harness the tidal energy. Sites that are suitable for installing tidal devices can be found all over the globe.

Tidal energy is a clean, safe and reliable source of energy. It is a form of hydrokinetic power, which is harvested by capturing the energy from tidal currents and converting it into electricity.

Water rotates the blades of a submerged turbine, driving a generator that generates electricity. This electricity is then exported through a power cable to the shore. Generating electricity from tidal energy is a proven concept, and very predictable.

https://www.bluewater.com/products-technology/floating-tidal-systems/new-energy/emec/tidal-energy/

Scotland, the Saudi Arabia of tidal power?

Though their numbers might not justify comparing Scotland with the Persian Gulf in terms of overall energy potential, they do suggest that it could certainly be a Saudi Arabia for tidal power, and that the Pentland Firth could play a major role in powering the U.K [sic]. Their analysis shows that the seaway could potentially provide an average of 1.9 gigawatts of electricity at any given time, a number that equals about half of Scotland’s electrical consumption.

https://www.smithsonianmag.com/science-nature/is-scotland-the-saudi-arabia-of-tidal-power-8561364/