The turbine is the result of research in Oxford University’s Department of Engineering Science by Professor Guy Houlsby, Professor of Civil Engineering, Dr Malcolm McCulloch, head of the electrical power group, and Professor Martin Oldfield, Emeritus Professor of the thermofluids laboratory.

The key in tidal is robust.  Tidal energy with the mass of water involved is much more forceful than the air harnessed by wind energy technologies.

Oxford University Tidal Turbine Prototype. Image Credit: Oxford University. This is the largest image.

A prototype 0.5 meter diameter turbine has already performed well in tests, proving the benefits of the blade design. The design as built and tested is a horizontal axis water turbine, to intersect the largest possible area of current. The rotor is cylindrical and rolls around its axis, catching the current. A full-scale device would measure up to 10 meters in diameter, and a series of turbines can be chained together across a tidal channel.

Oxford Tidal Turbine Graphic. Image Credit: Oxford University. This is the largest image size.

The team has calculates that a tidal site 1-kilometer in width could produce 60 Megawatts of energy.

The real beef is in the engineering – the turbine is mechanically far less complicated than anything available today, and requires fewer generators and undersea foundations, meaning it will cost less to build and maintain. The manufacturing costs are estimated to be about 60% lower and the maintenance costs 40% lower than current tidal devices.

The researchers received £50,000 in funding from the Oxford University Challenge Seed fund, managed by Isis Innovation, to build a 0.5-meter diameter prototype demonstrating the benefits of the design.  Tom Hockaday, managing director at Isis Innovation said: “This is the latest in a number of spin-outs from the Department of Engineering Science. Isis is fortunate to work with such an entrepreneurial department, particularly on technologies which have the potential to make a big impact on our energy supply.”

Tidal flow energy is a big topic in the UK because the islands of Britain, Scotland and Ireland are estimated to offer 10 per cent of the global extractable tidal resource.

Tidal currents are sub-surface, so tidal turbines have minimum visual impact, unlike wind farms or estuary barrage schemes.  Other than snagging one and getting ‘reeled in’ so to speak, they offer the best of aesthetics and practical gain.  This new approach might just send some kilowatts ashore at an enviable price.

The technology information is very thin.  But, the Oxford group has been at this for quite some time.  Now some private money is headed in bringing in commercial minded design and development.  Lets hope it works out.

Tidal across the full shoreline of the world’s oceans where flows offers current worth the investment is a very big prize.  While 10% for the UK region alone is an impressive amount there’s still 90% more out there as well.

What happens is the fresh water seeks to reduce the salinity of the seawater so it pushes through the membrane to dilute the seawater thus increasing the seawater container pressure. The pressure can be harnessed to drive mechanical devices to do work such as generate electricity.

Osmosis then isn’t the energy; it’s the means to move the water from one circumstance to another by holding the salty seawater back as fresh water moves over for dilution. It is an essentially free source of energy, but so far the capital costs are thought to be out of sight so making the prospects for investment distant.

Which is not to say development isn’t worthwhile. Rivers will always run to the sea so the source of the energy will always be available. It’s the engineering and construction costs that will need attention. There is even more than one way to use the salinity gradients to find energy, with osmosis being a part of the process each time.

Dubious? Well, the osmotic effect is used by animal bodies to recover water from the kidneys. Plants use it to maintain pressure at the needed fixed levels. The semipermeable membranes are already developed, and the salinity gradient is well known. If you have some desalination experience then you’ll know that reverse osmosis is the principle in reverse requiring pressure manipulations to function rather than producing pressure to be used for work.

There are problems strikingly similar to reverse osmosis. One being that as the fresh water moves to the salt side the salty side will dilute so reducing the pressure potential. Then there is the plugging of the membrane which would need flushing to stay functional.

SHEOPP Layout

A couple of old attempts at design are on record. The Submarine Hydro Electric Osmosis Power Plant or SHEOPP is anchored to the seafloor with fresh water piped in to drive it. The design relies on pressures by being set deep in the sea so that after generating power the fresh water is discharged and depressurized into a submarine tank. If one could deliver clean freshwater and perfect the membranes a flushing pump system wouldn’t be needed and the power output could be maximized. The practicality of this at industrial scale is dubious at best.

An Underground PRO Design

Another design is built underground. Similar to the submarine unit this also relies on “pressure retarded osmosis” a way to describe the containment of pressure until its used. This design keeps the facility on shore still below the sea surface where pressure from the sea can be used. As the osmosis takes place the pressure in the contained seawater rises. Its that flow of water that drives the generator, not the osmosis effect itself.

What Maria was seeing is the current state of development from Statkraft of Norway which is a large conglomerate involved in a wide array of businesses including hydroelectric power. Statkraft knows that Norway has a technical potential in salinity gradient of up to 12 terrawatt hours per year – that would be enough to power over a half million Norwegian homes.

Statkrafts Illustrated Osmotic Block Process Diagram

Osmotic or salinity gradient energy, if it can be made economically competitive, would be base load power; the steady reliable never stops coming power that is always there. If the engineering and design problems of getting economical facilities built are solved, there are a lot of places that could have installations built.

Statkraft Osmosis Process Diagram

Now, who would have thought that something as simple as the differential between the salinity of a river and the sea could be processed to yield a head pressure of 120 meters, a very high waterfall, and plenty to push a turbine?

Statkraft says it’s in, building a prototype at Tofte southwest of Oslo. Try the Statkraft site, its link rich with several information links with many interesting details in English.

Pentland Firth is in the UK’s far north and has been described as the “Saudi Arabia” of marine power.

The considered leading candidate is Marine Current Turbines Ltd, who confirmed that it intends to apply for a lease from the Crown Estate to deploy its “world-beating” tidal technology in Scotland’s Pentland Firth.

Atlantis Resources Corporation chief executive Timothy Cornelius said the area that the company hoped to develop in Scotland is also the Pentland Firth in the country’s north, too. The company is confident it will win a contract to build 500 underwater turbines in the sea off Scotland.

One wonders how big this Pentland Firth place is, now with so much interest.

SeaGen In Operation

Marine Current Turbines has a project underway called SeaGen deployed in May of this year, a tidal project in Northern Ireland’s Strangford Lough, the world’s first commercial-scale grid-connected tidal stream energy system. At 1.2MW capacity, SeaGen, which is in the final stages of commissioning, will generate electricity onto the grid to meet the average needs of 1000 homes. Martin Wright, Managing Director of Marine Current Turbines adds, “Harnessing the power of the Pentland Firth will be challenging and there are still substantial issues, in particular financing and grid connection, which will have to be addressed. However, the move by the Crown Estate is a significant and welcome step forward if the UK is to harness the sea’s energy potential on a truly commercial basis.”

SeaGen works in principle much like an “underwater windmill” with the rotors driven by the power of the tidal currents rather than the wind. Strangford Lough has a highly energetic tide race and so is recognized as one of the main tidal “hotspots” in UK and Irish waters.

The Aussies at Atlantis Resources Corporation have developed turbines that can generate electricity from the sea’s movement, too. The deep-water Solon turbine “is a story of a group of young Australians doing wonderful things on a global scale.” Cornelius said.

The Solon Ducted Turbine

Cornelius said, “This young guy from Townsville, in 12 months, has gone from concept to building this turbine.” The deep-water Solon turbine designed by 28-year-old Dr. John Keir is considered by many to be the world’s most efficient underwater generator.

The thrifty and frugal Scots have their naysayer in Scottish engineer Tony Trapp who told The Scotsman newspaper that tidal power was not reliable enough to generate the power levels that Atlantis is suggesting. Dr. Trapp says, “The trouble is, it isn’t the solution. Tidal and wave [power] are trivial in the world energy picture. The overall conclusion is it’s silly – it’s not a sensible use of intellect or financial resources.”

Cornelius counters saying, “The tides are completely reliable, so much so that you can predict them 20 years in advance. That is exactly the kind of information energy companies are looking for. We can be highly accurate on our outputs to the electricity grid.”

I’m with Cornelius on this. There is a huge amount of momentum in tidal flows ready for the harness if the details and economics can be worked out. It seems that the Crown Estate and Marine Current Turbines think so, too.

Now as you’ve noted, these two companies are using what can be described as conventional turbine technology of blades levering a shaft. A new take on this is a near shocker – using vortex-induced vibrations, actually making them to work in slow moving water – is counter intuitive as vortex induced vibrations are something engineers avidly seek to avoid. These vibrations are the bane of moving things; they wear, fatigue and destroy equipment and installations to great damage and harm. The idea of inducing them and pulling out the energy is just – innovative in the extreme.

A University of Michigan engineer, Michael Bernitsas, a professor in the U-M Department of Naval Architecture and Marine Engineering designed VIVACE, which stands for Vortex Induced Vibrations for Aquatic Clean Energy. VIVACE is the first known device that could harness energy from most of the water currents around the globe because it works in flows moving slower than 2 knots (about 2 miles per hour.) Most of the Earth’s currents are slower than 3 knots. Turbines and water mills need an average of 5 or 6 knots to operate efficiently. A paper on it is published in the current issue of the quarterly Journal of Offshore Mechanics and Arctic Engineering.

Vortex induced vibrations are undulations that a rounded or cylinder-shaped object makes in a flow of fluid, which can be air or water. The presence of the object puts kinks in the current’s speed as it skims by. This causes eddies, or vortices, to form in a pattern on opposite sides of the object. The vortices push and pull the object up and down or left and right, perpendicular to the current. The vortices push and pull the passive cylinder up and down on its springs, creating mechanical energy. Then, the machine converts the mechanical energy into electricity.

Professor Bernitsas estimates that array of VIVACE converters the size of a running track and about two stories high could power about 100,000 houses. Such an array could rest on a riverbed or it could dangle, suspended in the water. But it would all be under the surface. Because the oscillations of VIVACE would be slow, it is theorized that the system would not harm marine life like dams and water turbines can.

Bernitsas says VIVACE energy would cost about 5.5 cents per kilowatt-hour. Wind energy costs 6.9 cents a kilowatt-hour. Nuclear costs 4.6, and solar power costs between 16 and 48 cents per kilowatt-hour depending on the location.

Here is a hard truth and some study based facts on the power in tides and currents. “There won’t be one solution for the world’s energy needs,” Bernitsas said. “But if we could harness 0.1 percent of the energy in the ocean, we could support the energy needs of 15 billion people.

That would be a lot of power and the professor is thinking a tenth of one percent of the power available for his assertion.

It might behoove the Crown Estates to do a little further research before they commit to leases. The installed cost, the rate for kilowatt-hours to the consumers and the longevity of the initial investment with good operating cost estimates needs prime attention.

Those tides and currents aren’t likely going anywhere soon. But a bunch of capital investment will be involved for a multi decade or even longer useful lifetime. Realistically, as amazingly sensible as tide, current, wind and solar are, it will be the cost for ratepayers that matters. Great ideas need great development work and a sense of application of skills that brings more, better and cheaper. None of the resources are going to disappear or deplete. Getting it right, getting the most efficiency for the best price can take a little extra time. Harvesting systems need to get much better, and cheaper than the fueled production systems are today.

Competition has an important role here, as the best will be found and everyone will benefit. It’s a sure thing that some of the currents and tides will get into a harness.