Tidal energy is coming, once hurdles vanish

The tide-based currents in the Swinomish Channel may offer a local source of reliable, predictable renewable energy. Several people have asked me whether this natural resource could be developed to power greater La Conner, including Shelter Bay and Swinomish Village.

A tidal energy system must be durable, reliable and capable of being installed and maintained cost-effectively in salt water. Doing all this has been challenging, so the engineering needed to extract energy from tidal currents hasn’t been sufficiently proven to make tidal energy commercially viable on a large scale. For now, tidal energy systems are still in the process of being proven. The most promising tidal systems are underwater turbines, which resemble wind turbines, but other design concepts also exist.

Tide energy represents an area of significant research interest. Several large-scale demonstration projects are underway in various parts of the world. Some of the relevant subsystems are available and have been long-proven. Cables that can deliver power from a saltwater-based generation system to a land-based distribution point, for instance, are readily available and are used routinely for offshore wind projects and to deliver power from mainland sources to islands (as between mainland Italy and Sardinia).

Tide turbines, unlike wind turbines, require high-cost materials that can resist saltwater corrosion, the attachment of barnacles and mussels, and the mechanical effects of tidal currents that are stronger than anticipated. Seabed conditions are inherently more difficult than typical land-based conditions for installation and maintenance.

Effects on marine wildlife need to be evaluated for each site, and environmental impact minimization requirements may vary enough from place to place to add significant custom development costs to each potential location. As tide power technologies haven’t been widely demonstrated, the process of getting a public consensus to proceed with development is likely to take longer than it would with more accepted technologies.

Although well behind traditional hydro, solar wind and geothermal, tidal power is now getting significant research attention. The MeyGen tidal array at Pentland Firth in Scotland started functioning in 2018. This project is intended to ultimately have 61 turbines on the seabed, producing up to 400 megawatts of electricity from high-speed (up to 11 mph) tidal currents. Four turbines generating 6 MW have been operating for several years.

The “Lessons Learnt” report on MeyGen, published in 2020, says that the initial project cost about $60 million, or $1 per watt, and has operated with a 34% capacity factor (in other words, the net generation is 34% of what it would be if a 6 MW plant operated 24 hours a day, 365 days a year).

Operating costs were below $2 million/year. This is very encouraging, as such costs are competitive with the installed cost of proven systems like large-scale solar, onshore wind and natural gas. The report indicates that the problems associated with installation and operation of the first four MeyGen turbines were surprisingly manageable.

Although it’s still doubtful that our slower current would be commercially viable yet, it’s possible that it might be within just a few years. It is worthwhile to anticipate that tide will become a competitive energy source. It is probably worth seeking funds now to conduct a more detailed study of the potential of the channel for tidal energy, and to begin evaluation of environmental feasibility issues.