The seas around the coasts of Britain ebb and flow twice a day, every day; as a force of nature, tides are more reliable than the other renewable energy sources of wind and solar power.

Not surprisingly, there has been interest in tidal power in the UK for some time. But following a long review, in October 2010 the UK government decided not to proceed with any of 10 Severn estuary projects (including barrages, lagoons and other designs), saying that they looked too expensive and too risky, as they are untried in the UK.

Despite that setback, nearly six years on, tidal power projects continue to be developed. One of the highest profile developments is the Swansea Bay tidal basin, involving constructing a six-mile teardrop-shaped breakwater to create a salt-water lagoon near the port of Swansea. It promises to offer power capacity of 320 MW, driven by the difference in water height between the sea and the lagoon. The project, which would also include public amenities integrated with the structure, won planning permission in June 2015.

The sticking point at the moment may be the price of its power. Any negotiations with the UK government on that front will probably be waiting for the outcome of a government review of tidal lagoon projects, to cover value for money judgements, led by former energy minister Stephen Hendry, that is scheduled to come in autumn.

Meanwhile, work continues to develop a different technology that essentially consists of upside-down submerged miniature wind turbines. These floating installations are moored in currents of horizontally-flowing water generated by tidal forces, called tidal streams, that spin the turbine blades. Tidal streams are greatest off of the coasts of north-eastern Scotland, Northern Ireland and Wales.

A few years ago, the first prototypes began testing in real conditions; now, larger-scale units (that are still much smaller-scale than tidal lagoons) are nearing the point of installation and should provide some useful data to support a case for their commercial viability.

In May, ScotRenewables launched probably the largest of the lot, a 2 MW-capacity 550-tonne SR2000 unit, at a Belfast shipyard. The product of a £25 million effort supported by UK government, the EU and private investors, it is to be towed to a test facility in the Orkney islands later this year. ScotRenewables recently won funding to build a second unit with updated turbine design to be installed alongside it.

Also going into the same facility later this year is Sustainable Marine’s PLAT-O tidal energy platform, a 100 kW device with twin turbines. Construction of a larger 240 kW unit has reportedly begun.

This test facility is run by the European Marine Energy Centre, which seems to be a focus of floating turbine development. Two other projects in which it is involved, InToTidal and Ocean 2G, recently received EU funding. At the time, EMEC commercial director Oliver Wragg said: “It’s hard to secure private investment for real sea testing of ocean energy technologies, so grant support is vital at this stage of development.”

This article was published in the energy supplement of the July 2016 issue of Machinery magazine.