The quest for more renewable energy continues. With water covering over 70% of the Earth, is the answer right there?

One of the things that has intrigued me for many many years, has been the relatively limited expeditions into the use of tidal energy, as another renewable source. After all, the water moves for up ot 18 hours per day, and with exceptional force. Furthermore:

• Unlike wind, tides run every day without fail
• Unlike solar, there is no impact from poor weather
• Unlike geothermal, large water currents aren’t limited to small portions of the world.

In the middle of 2017, the Australian Government announced contribution to a $5.85M research project aimed at mapping tidal energy, to identify the areas with the most potential for energy production. Indeed there are a handful of tidal generator installations found at sites around the world; the largest of which is the 254MW tidal power station in Sihwa Lake in South Korea. The Sihwa Lake installation only generates power on tidal in-flows, as the installation also deals with some contamination issues and such; however, this is more a case of “kill two birds with one stone” than a purely engineering decision. So while it remains on the fringe of renewable energy production, it’s there in proven commercial installations already, some dating as far back as the 1960s, when arguably, more unique solutions were developed rather than opting for tried and tested coal/nuclear generation.

WATER IS DENSE

One of the major benefits we see from water, is the amount of energy carried due to water being 800 times more dense compared to air. This fact helps compensate for the relatively slow speed of ocean currents, but which are readily found, compared to high speed winds which can come and go.

To put this in context, the energy contained within a water current moving at 12km/h is the same as a constant wind speed of 100km/h, for the same surface area. That’s a fairly substantial difference and one that can’t be ignored.

OCEAN VERSUS TIDAL CURRENTS

There are of course, two types of currents we can make use of: tidal and ocean; both of which potentially offer a virtually limitless source of kinetic energy.

Tidal Currents

As most people are aware, there are tidal currents which are the result of gravitational effects from the moon and sun, and the rotation of the earth. Tidal action varies around the globe, and even tidal predictions can be inaccurate to a certain degree. However, barring rare events such as very extreme weather, they happen with a good degree of regularity and predictability, and unless the moon or sun rapidly vanish, this isn’t about to change (and if it did, we’d have bigger problems to concern ourselves with anyway). Regardless of their frequency, the energy behind these tides can be tapped as a resource on the incoming and outgoing flows.

Ocean Currents

In addition to tidal currents, which ebb and flow each day, there is a complex pattern of ocean currents, circling the globe constantly; much like a large conveyor belt. These currents can be affected by winds and seasonal variations, but are constantly running one way or another. Knowledge and mapping of ocean currents is already used in the shipping industry, since sailing with the currents can reduce fuel bills or transit times (or both), while going against them is obviously going to slow things down.

WHAT’S THE IMPACT TO THE MARINE ENVIRONMENT?

We know that man-made structures quickly become havens for fish and marine life, often creating a type of artificial reef. But these will have moving parts, so steps would need to be taken to protect marine life and equipment from each other.

As with anything near or under sea water, it needs to be resistant to corrosion and marine growth. Anyone who owns a boat knows just how corrosive salt water can be to any metals, or indeed, anything at all that’s down there. Sure, plastics might not be so prone to corrosion, but marine growth will occur on just about all types of surfaces.

Without a very good maintenance schedule, any moving parts will quickly start to clog up. Any smooth parts (such as the turbine blades) will quickly become home to algae, shellfish, and more. So maintenance can be a challenge. With proper planning and design though, it could be overcome to a suitable degree.

FARADAY DEVICES

I can’t recall the precise reference, but I do remember research and development also being done on swell-driven energy. Rather than using the tidal flow, these devices bobbed up and down on the surface of the water with the swell. Using Faraday principles (i.e., magnets moving through coils to produce a current), electricity was produced. While this potentially solves many of the “moving parts in the water” type of issues, Faraday technology doesn’t tend to produce current as consistently as other methods, so it isn’t without its own challenges. However, there are constant experiments and research into these areas, to better our understanding and identify additional opportunities.

THERE IS STILL A WAY TO GO

While we’re probably not going to see a Government-sponsored consumer-level rollout of tidal energy installations any time soon, there’s so much activity in this space that it could quite possibly be the next big contributor to renewable energy for the grid. Unfortunately, at a home/DIY level, there’s probably little that can be done. Not many of us have the means, location, or knowledge to implement something like this ourselves. Nor in Australia do many of us have access to constant running, high velocity water, which some of our alpine friends may have. So while we might be best to stick with wind or solar for our own home and business renewables, there’s still opportunities for some grid-connected production.