One of the biggest challenges renewable energy faces is a little problem called intermittency. The sun and wind can provide a nearly endless supply of clean power, but… they don’t always show up exactly when we need them to.
What if there was a clean, renewable energy source that was as predictable as, say… the tides!
Tidal energy systems have been around for a while, but we haven’t seen them take off the way other renewable systems have. While experts project that tidal energy alone could power every home in the United States two times over, current tidal projects worldwide only power about a half a million homes.
But with projects in Europe, Asia, and Canada taking off, are we about to see a new wave of clean, reliable, and affordable energy?
Let’s dive into it!
If tides have one excellent quality, it’s that they are incredibly, I mean, incredibly predictable.
Humans have been able to predict tides with relative accuracy for over 2,000 years! Unless you’re Bill O’reily but I digress.
Tides are also incredibly powerful, which is why they hold so much potential. To better understand why, here’s a brief refresher on how tides work.
Tidal energy comes from the gravitational force of the Moon and to a lesser extent, the Sun.
See, any two bodies out in space exert a gravitational force on the other. The equation looks like this:
G is the gravitational constant, m1 and m2 are the mass of the two bodies, and finally we have r2, the radius or distance between the two bodies, squared in the denominator. This change in the force of gravity over distance is what we call the tidal force.
This means if two bodies are twice as far apart, the gravitational force felt between them is only 25% as strong. This is why even though the sun is way more massive, the moon exerts a larger tidal force.
So how does the tidal force cause our ocean tides? Well the strength of gravity depends on distance, and Earth has a radius of (3,958.8 miles) (6,371 km).
The side of Earth facing The Moon gets pulled harder than the other, essentially stretching the Earth, especially our oceans.
So that explains the bulge on the side closest to the moon, but what about the other side? Well, since the center of the Earth is closer to the moon than the far side, it also gets pulled harder, again resulting in a bulge. Basically, the parts of the Earth facing and opposite the moon experience the strongest tidal forces, and sides in the middle, the weakest.
Coastal areas experience high and low tides every 6 hours or so as the Earth spins, resulting in two high and low tides each day. This results in ocean water levels rising about 1-2 meters in areas of high tide.
The Sun also contributes to tides here on earth. When the sun and moon are aligned, when we see a new or full moon, their forces align and we see super high and low tides, called Spring Tides. When the Sun and Moon are 90 degrees apart, the tidal forces cancel out a bit and we have neap tides. Finally the moon’s orbit isn’t perfectly round, so it’s closer at certain points than others, not by much, but when the moon is closer in its orbit, and aligns with the sun, we get our highest tides called Proxigean Tides.
But what makes this tidal force so promising is that it’s essentially an enormous wave of energy moving across the planet every. Single. Day. Without fail.
Capturing tidal energy works a lot like capturing wind energy — basically taking wind turbines and placing them under the sea. Water is far more dense than air — over 800 times to be exact. This means that even at relatively slow current speeds, the turbines can still spin and produce electricity.
Tidal energy systems fall into two major categories.
The oldest and most common systems are Tidal Range systems — making up about 98% of tidal energy projects worldwide.
These systems use a large dam or “range” across a coastline with enormous floodgates on either side. Between the floodgates, below sea level, sits a row of enormous turbines.
As the tide rolls in, the barrage gates open. As the water flows through, the turbines, connected to generators, rotate, converting the ocean’s mechanical energy into electricity.
Once the tide reaches its highest point, the barrages close, creating a large pool of water. That water can then be released slowly, over time back out into the ocean, through the turbines to create power on demand.
In principle, these systems are very similar to Pumped Hydro Which we’ve covered in other videos. But unlike those systems, which require electric pumps to push the water back uphill, these systems rely on the planet’s natural tidal energy to pump the water in and out.
Because the turbines work in both directions, they can provide clean, reliable energy between 18 and 22 hours per day. Need power? Just open up those floodgates!
The world’s oldest Tidal Range generator, La Rance, built in northern France in 1966, produces enough electricity to power the town’s 250,000 homes and businesses.
The second type of Tidal Energy System is Called Tidal Stream. Essentially underwater wind farms. They’ve been around since the 1970s.
Large turbines connected to generators sit anchored to the sea floor, but the turbines themselves are closer to the surface. This makes them a bit more cost effective since they reduce undersea construction. Floating stream turbines are among the most powerful in the world, with individual turn capacities of 2 megawatts.
Scotland-based energy company MeyGen is developing a 398MW tidal stream project, the largest in the world. The initial phase involves four 1.5MW turbines connected to onshore power conversion units where the low voltage supply will be converted for export to the local distribution network. This initial phase will generate sufficient electricity to power 2,600 homes.
As we mentioned earlier, since water is more dense than wind, these turbines can produce the same amount of power as a similar sized wind turbine but with current speeds one-tenth the required wind speed.
At speeds as low as 1 meter per second, these turbines can equal the output of a typical wind turbine. As current speeds increase, between 2 and 3 meters per second, the turbines can access up to four times as much energy per rotor swept area as a similarly rated wind turbine.
So now that we’ve looked at how these systems work, let’s explore how they stack up to other renewables.
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A tidal range with 24 turbines has an installed capacity of 240 megawatts, or around 10 megawatts per turbine — with an annual output of around 600 gigawatt hours per year! That’s enough power to sustain over 50,000 American homes — about the number of homes in my entire city for a year. Pretty crazy.
How does this stack up to other renewables?
Most onshore wind turbines have a capacity of between 2-3 megawatts, producing roughly 6 gigawatt hours annually.
A modern day off-shore turbine comes a bit closer at roughly 8 megawatts, and the new record setting Siemens Gamesa offshore turbines coming online in 2024 produce 14.7MW.
Solar panels generally have output ratings of roughly 400 watts.
To produce the same power as those 24 tidal turbines, you would need between 80 and 120 onshore wind turbines, 15-30 off-shore turbines, and about 60,000 solar panels!
But what about efficiency?
Today’s typical solar panels, as we’ve covered on the show many times, top out around 22% efficiency. And wind turbines, often heralded as the most efficient renewable — max out around 40% efficiency.
Tidal turbines — they absolutely dunk on the others, operating around 80% efficiency! Nearly double that of wind!
At this point in the video, we like to ask — if this technology is so great — why don’t we see it everywhere? And indeed there are a couple things to consider.
First, Tidal energy plants don’t currently have the major production infrastructure that other energy sources benefit from. That means Tidal Energy systems are by far the most expensive to build — requiring the highest Capital Costs up-front.
The reason for the cost is simple. As we’ve been saying, seawater is more dense than air. And while this helps tidal turbines produce more power, it also means they need to be made from more sturdy material.
There’s also the issue of what’s called “biofouling” — basically, as the machines live underwater, they are prone to build up a variety of sea life which is great for the ocean, but can hinder the turbine’s performance. So engineers have to factor that in when constructing and maintaining this technology.
Some speculate that these base costs make Tidal Energy plants financially unviable. But what does the data say?
According to 2019 figures from the US Department of Energy, the average commercial tidal energy project costs as much as $280 per megawatt hour to build. Wind energy, by comparison, currently costs roughly $20 per megawatt hour making it one of the lowest-priced energy sources available today.
But, when it comes to energy, you can’t just look at the base cost. Instead, you need to look at what’s known as levelized cost — an economic measure that compares the lifetime costs of generating electricity across various technologies. In other words, it’s not just about how much something costs up front, but how much power it can produce over its lifetime. Levelized cost is an important factor for consumers because it is one metric by which the price of electricity.
Now — there are countless metrics to determine levelized costs, but here are some averages based on numbers from the EIA.
As you can see, depending on the technology, prices range between about $30 per mWh to about $170 per mWh.
Right now, LCOE for commercial-scale Tidal Energy projects falls between $130‒280 $/MWh for tidal energy, which would certainly put it above the competition.
But, when you factor in longevity for these facilities, things start to look a bit different.
Modern coal-fired plants have an operating lifespan of more than thirty-five years, yet environmental groups suggest that coal needs to be entirely phased out by 2040.
Wind turbines and solar panels generally come with a warranty of 20 to 25 years, and while some solar cells have reached the 40-year mark, they typically degenerate at a pace of 0.5% efficiency per year.
Tidal energy systems are inherently age resistant and have significantly longer lifespans. The average estimate for most tidal systems is 75-100 years.
And significant cost reductions in LCOE are anticipated from the current stage of deployment to the commercial target 61% for tidal energy.
By 2030 it is possible that the base case scenarios that Tidal Energy systems could come down as low as $75 per mWh.
But even at current prices, Tidal Energy systems are able to deliver power at prices equal to or less than other energy producers. Here are some current electricity rate averages for various production methods in the US.
Generation costs/kWh for new nuclear fall between 25 – 30 cents/kWh.
fossil fuel costs average between $0.05 and $0.17 per kWh.
Hydroelectric power is currently the cheapest renewable energy source, costing $0.05 per kilowatt-hour on average
wind power , which depending on the region, competes with hydroelectric, at $0.02 to $0.06 per kWh, making wind power the cheapest in some areas.
solar power $0.06 per kilowatt-hour (kWh).
electricity from a new natural gas plant is roughly 6.5 cents per KWh. Though, as we covered in our Geothermal video — lots of factors can impact the price of natural gas.
Now let’s look at tidal energy.
Estimated tidal energy from Canada’s Nova Scotia Tidal Generating Station comes in at the most expensive at around $0.66/ kWh compared to offshore wind in the region at $0.20-30/ kWh. So… not looking great.
But La Rance produces electricity at a range from $0.04 to $0.12 per kwh. Now we’re getting somewhere. And it’s been operating, as we said, since 1966!
The Sihwa tidal power station in South Korea, built in 2011, is the largest tidal range installation in the world, with an installed capacity of 254 MW. It produces electricity at $0.02 per kwh. Which puts it among the cheapest of all energy sources.
So, sure, the impact tidal energy could have on your electricity bill depends on a number of factors. But, to rule out tidal energy, saying it’s always the most expensive option — well that clearly isn’t true.
Of course, the numbers don’t tell the whole story. Remember— tidal energy produces electricity with zero carbon emissions — obviously natural gas and fossil fuels can’t make that claim, despite sometimes being cheaper.
And while other renewables may be able to produce energy at a lower price point — again, there’s that issue of intermittency and an increased need for energy storage, a problem that tidal energy just doesn’t face.
And finally, tidal energy is 100% renewable — As long as we have our sun, moon, and oceans!
But cost isn’t the only factor limiting this technology. There’s also the issue of location, location, location. Tidal systems require coastlines. Which already limits where they can be built. But, not every coastline is optimal.
See, tidal range systems benefit when the range sits around 7 meters. Any less, and the system becomes less economically feasible. The problem is that many of the areas with optimal conditions are in more remote locations where grid infrastructure may not already exist — which means larger upfront investment, and potentially impacting local environmental regions.
Still, despite these drawbacks — a number of countries have already begun to adopt tidal energy, with more projects on the horizon. As they continue to prove themselves more and more economically viable, we may start seeing more of these systems popping up along our coastlines.
But what do you think? Are tidal energy systems destined to become the next big wave in renewables? Or should we invest in other, currently proven renewables? Share your thoughts with us in the comments.