Amongst the hustle and bustle of Tokyo city you’d be forgiven for forgetting the raw natural power that exists in Japan. For just offshore, deep in the ocean, lies a monster with ungodly strength. It has remained untouched and undisturbed for millennia. But now scientists want to harness this power to save Japan. Don’t worry, I’m not talking about Godzilla, though he may still be down there somewhere. Instead, I’m talking about deep sea turbines, as Japan is the first country to try and harness the potential of ocean currents. But why has Japan turned to the sea for power? What are the benefits? And what are the risks? Could this be an energy revolution?
Geologically speaking, Japan is one of the most fascinating countries in the world. With extensive mountain ranges, geothermal springs, volcanoes, fault lines and near-shore deep sea trenches. However, their incredible landscape has made solar farms and offshore wind turbines challenging as there isn’t the available space or suitable seabed near where energy is needed. This is also why Japanese cities are so famously cramped — the landscape boxes them in.
So, when Japan started to transition away from fossil fuel and towards renewables, they mainly went nuclear. However, since the Fukushima disaster, they have been trying to find alternatives, and recently landed on ocean currents as their carbon neutral energy of choice. You may have never heard of ocean currents as an energy source and that is because no one else has tried to harness it. Which is a shame, as it has the potential to be the ultimate climate-friendly energy supply because of how ocean currents work.
Ocean currents are powered by salinity (how salty water is). In the Poles ocean water freezes, and because ice can’t contain salt, the water around the Poles becomes saltier and therefore denser which makes it sink to the sea floor. This water is then pushed/pulled towards the equator as more water sinks in the poles and wind system around the tropic cause upwellings. Once at the surface, the water is then sucked back towards the Poles as more cold water sinks, causing this now warm water to rush in to take its place. This rotating process is known as thermohaline circulation.
These forces create giant rivers in our ocean that are way more extensive than any we have on land. Take the Kuroshio current off the East Coast of Japan. It is the ocean’s largest current and can travel at a rate of 75 miles per day and carry the equivalent water volume as 6,000 large rivers.
But, as thermohaline currents don’t rely on temperamental weather systems like wind or a clear sky, they flow with consistent power, making them an ideal energy source. What’s more, due to the nature of marine ecosystems, we can build structures within the flow of currents without causing habitat loss. In fact these structures will act as artificial reefs and have the ability to boost marine biomass and biodiversity.
So, in theory, ocean current power could be the perfect eco-energy source. Unlike solar and wind it doesn’t require expensive, giant grid-level mega-batteries to keep output consistent, which reduces its carbon footprint and the need for environmentally dubious mining. It also doesn’t cause habitat loss like solar, or impede ships like wind farms, as ocean current power is 100 m beneath the surface. What’s more, it is estimated that the Kuroshio current could provide up to 205 GW of power, which is comparable to Japan’s current total electricity production.
This is where Japan’s heavy machinery maker IHI Corp comes in. They recently completed testing of a scale prototype sub-sea turbine called Kairyu with astonishing success.
Diagram of Kairyu operation — IHI
As you can see in the pictured above Kairyu is a ‘floating’ current turbine. This means that it is anchored to the sea floor and the wing-like shape of its body can control the depth at which it ‘floats’. This makes it more akin to a subsea kite. The advantage here is that it can be maneuvered into the fastest flow of the current for optimal power (generally around 100m depth) and can easily come to the surface for maintenance. There is a turbine on each wingtip that collectively generate a total of 100 kW of power in the 3.4 mph flow of the Kuroshio current.
Kairyu shematic — IHI
IHI Corp Has tested and validated this concept and is now looking to move up to a full-scale near-production prototype. But the actual turbines are far larger than the development ones. Their turbines will be 40 m across and a single unit (two turbines on a ‘floating’ platform) will produce 2 MW making them 2,000 times more powerful than the Kairyu prototype. Once built, IHI wants to build a farm with 100 of these to produce a whopping 200 MW, enough to power 3,000 Japanese homes.
So that’s it! The perfect energy source! Case closed? Not quite.
You see, there are three problems with this tech. Noise, turbine strikes, current slowing and climate change.
Whilst manmade structures in the ocean tend not to disturb wildlife there are fears that animals can get hit by the blades and be killed or harmed. However, these turbines move far slower than wind turbines and can be engineered to turn even slower if needed, so this might not be something to worry about.
Noise on the other hand is an issue. We already know that marine mammals really struggle in the presence of excessive marine noise, which can actually cause them to beach themselves, change behaviors and disrupt feeding. So, IHI will have to do extensive work to ensure their turbines are as quiet as possible, otherwise they could have dramatic side effects.
There is also a worry that using this tech too extensively could slow these currents. This would be a significant problem as these currents provide nutrients for vast swathes of the ocean. If you slow them down it could cause substantial dead spots and crash marine ecosystems. Thankfully this would only happen if we used tens-of-thousands of these turbines in a single current. So, this isn’t an immediate problem, but it does put an upper limit on how much we can use subsea turbines.
Finally, the last problem is climate change. These currents slow down as the globe heats up due to the changing climate messing with the thermohaline mechanism. Whilst they can produce incredible power now there is a chance that these turbines will become useless in a few decades when climate change has really started to bite and currents slow to a crawl. Therefore, we need to stop climate change for this tech to be useful in the long run.
So Japan is on the verge of unlocking a brilliant new energy source that could be far more eco-friendly than any before. Yes, it does have some challenges, but with some sound engineering and our continual fight against climate change these can be solved. So who knows, maybe the future will be powered by the ocean as much as it is solar, wind or fusion.