Focus On: Tidal Energy

Tidal power has always been one of our favorite ideas, and now it’s starting to evolve from cool theoretical concept to a practical source of energy.

Ocean Power Technologies is one of the front-runners here, with ongoing projects in Australia, Spain, two in the United Kingdom, Hawaii, New Jersey and two in Oregon.

Most of these are small deployments, mainly to test the technology, but the Oregon projects are noteworthy because they are slated to be full-scale, commercial power wave parks. In Coos Bay, OPT has proposed installing up to 200 of its PowerBuoys about 2.7 miles offshore, enough to generate up to 100 MW – the company says this will be the largest wave-power plant in the world.

Not far up the coast, in Reedsport, OPT expects 10 PowerBuoys offshore. It’s currently waiting for all the necessary federal permits; if it actually happens, it will be the first such commercial wave power site on the West Coast.

OPT has been testing the PowerBuoy near Atlantic City for more than two years, but the energy produced is simply dissipated. (These are big machines – see the pic above.)

Wave power is simple, in theory, but really hard to pull off. Like windmills, these systems convert kinetic energy into electricity. As the tide and waves move, the PowerBuoys move up and down, generating power.

Tide power has some key advantages over other green energy concepts. The tides, they never stop, so there’s a seemingly infinite supply here, and it could be more consistent than wind power. Plus, the tide is everywhere, so tidal power systems could be installed in a wide variety of sites.

But the sea is a very tough environment. Water and salt don’t mix well with electricity, metal and electronics, and it’s tough to send out a maintenance crew. But OPT’s systems seem to be holding up over time, so maybe we’ll see more of these. In fact, despite these not-so-trivial challenges, the main hurdle may not be the technology, but the regulatory process (see Cape Wind).

Team Effort: Supergrid

When the government really gets behind a project, sometimes it can pull off some pretty impressive work.

In this case, a continent-spanning, green “supergrid” in Europe. Nine countries are collaborating on a massive energy project that would link wind turbines, tidal energy systems, solar farms and hyrdro power sites all across the North Sea region.

The nine nations – Germany, France, Belgium, the Netherlands, Luxembourg, Denmark, Sweden and the United Kingdom – are expected to formally approve the project this month, and hope to have firm plans in place by Fall. Various estimates have pegged the cost at close to 30 billion euro.

The vision is to connect wind farms in Scotland, solar facilities and Germany and tidal power systems in Belgium and Denmark through a vast network of high-capacity, undersea DC cables. Direct current transmission lines cost more than AC, organizers say, but lose less energy over long distances.

The project has one more component that seems especially clever: all these alt-energy systems will be linked to a network of hydroelectric plants in Norway. When the wind is a’blowin’ and the waves are a’crashin’ and the sun is a’shinin’ there’s going to be plenty of juice, and the excess power can be diverted to Norway, to push water uphill. Then, when the weather is less cooperative, the water can flow downhill to power the hydro plants.

The EU has pledged to generate 20% of its power from renewable sources by 2020; that’s an ambitious target, but projects like this one could certainly help them get there.

River Power

Not that we needed it, but here’s another reason to be impressed with the creative thinking of chemists: the chemical reactions that occurs when fresh water in rivers runs into salty sea water could one day become a viable commercial power source.

Two European projects, in Holland and Norway, are testing systems to capture the energy released in estuaries, and though the concept is still in the very early stages, they estimate that the world’s estuaries could, in theory at least, put out enough power to meet 20 percent of the word’s electricity needs.

The basic idea is that when fresh water meets more concentrated salt water, the salt water, which is more concentrated, sucks in the fresh water as the two types of liquid seek equilibrium. In the process, the water becomes warmer, by about 0.1 degree C, and as we know, changing temperature requires power.

The two projects are both using specialized membranes to convert that temperature change into electricity, but with slight variations. The Dutch project captures salt particles in the process, and the salt crystals produce electrical current. The Norwegian one is trying to harness the physical force as the salt water sucks the fresh through the membrane; one researcher said the energy is comparable to the kinetic energy produced by water falling 270 meters.

Of course, there are plenty of complications, not the least of which is protecting a delicate membrane that stretches for acres and is vulnerable to tears and pollution. Oh, and one more thing. The membranes being tested are based on ones used in commercial desalination plants, which convert sea water to drinking water, But there isn’t really any design available that could be used in a commercial power plant, and there probably won’t be one available for a decade or more.

Still, I love the creative thinking that goes into finding new ways to harness the always-changing earth. And, let’s not forget that while the sun only shines in the daytime, and wind only blows when it wants to, the rivers and the tides never stop.

Making Wave Power a Reality

Here’s a quick update on tidal power.

Looks like PG&E is willing to place a bet on this emerging source of power. The California utility said last month that it would purchase power from a Canadian company that is trying to build the first U.S. commercial power plant that would transform the movement of the sea into electricity.

Finavera hopes to park eight power buoys about 2.5 miles offshore from Eureka, Calif. The so-called “wave park” is expected to be complete in 2012, and the project should put out about 2 megawatts, enough to power 1,500 homes.

But first, there are a few hoops for Finavera to jump through. First, it needs to line up enough financing for the project; having lined up PG&E as a customer will certainly help.

More importantly, the company has to perfect its AquaBuoy technology. The basic concept is fairly straightforward. The cylindrical buoys float upright in the water. A few feet stick out, but most of the device is underwater. As it rises and falls with the waves, the motion drives an internal pump that forces water through a turbine. The kinetic energy of the moving turbine is then converted into electricity and delivered to shore through an underwater cable.

Sounds simple, but there’s a lot of work involved in making this work. An earlier prototype that was deployed off the Oregon coast sunk last year. The company still doesn’t know why, and the waterlogged AquaBuoy remains on the ocean floor.

The Motion of the Ocean

What is electricity? Sure, there are plenty of ways to define this force in terms of charge or current or the interaction of particles, but unless you’ve got a solid background in physics, it’s hard to really get a handle on exactly what that means.

So here’s an interesting way to think of electricity: it’s a way to harness, store, transport and use the energy originally created by something in motion. That’s what generators do -- they turn kinetic energy into electricity. Everything starts with motion.

This is easy to see with hydroelectric power, which uses the motion of water flowing through a dam to turn a rotor; when the rotor spins inside a magnetic field, electricity is produced. But most people don’t realize that the same concept is at work in other power plants. Coal, wind and portable generators all work the same way. A lot of people don’t understand that nuclear plants are just fancy steam engines; they think it uses some kind of advanced super-scientific principle to get juice flowing directly out atoms, but in fact it uses a controlled fission reaction to release heat, which boils water. The resulting steam is used to drive a rotating turbine, which produces electricity.

So where can we find a nearly limitless source of motion? The ocean, of course. In the past week, I’ve seen two great ideas for transforming the kinetic energy of the tides and waves into electricity.

The first uses power buoys, tethered to the ocean floor. Inside the buoy, a coil of metal is attached to the tether, so it cannot rise or fall with the waves. This is surrounded by a sheath of magnets that is not tied down, and does move up and down around the coil with the tides. This motion creates electricity.

The government has approved at least four proposals to test the concept, all in Oregon.

The second idea is even more out there. It uses something called a “dielectric elastomer,” which is a fancy way of saying a high-tech, stretchy piece of plastic. Scientists know that some elastomers contract when power runs through them. Well, it turns out the process can work in reverse. Stretch out an elastomer, and it will kick out electricity.

Researchers are trying to turn this concept into a commercial power reality, using waves and tides to stretch out the elastomer. Just tie one end to the sea floor and the other to a floating buoy, and the waves will move them around all day long.

Neither idea is close to reality; one of the problems is that wind and salt water don’t mix well with power generators. Another, like offshore wind farms, is NIMBY politics. Still, this is such an elegant idea that I can’t help but hope that somebody will make it work.