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Nanotubes boost potential of salinity power as a renewable energy source

By

March 12, 2013

Diagram of the experimental device that sees the osmotic transport of water through a tran...

Diagram of the experimental device that sees the osmotic transport of water through a transmembrane boron nitride nanotube (Image: Laurent Joly (ILM))

In November 2009, Norwegian state owned electricity company Statkraft opened the world’s first osmotic power plant prototype, which generates electricity from the difference in the salt concentration between river water and sea water. While osmotic power is a clean, renewable energy source, its commercial use has been limited due to the low generating capacities offered by current technology – the Statkraft plant, for example, has a capacity of about 4 kW. Now researchers have discovered a new way to harness osmotic power that they claim would enable a 1 m2 (10.7 sq. ft.) membrane to have the same 4 kW capacity as the entire Statkraft plant.

The global osmotic, or salinity gradient, power capacity, which is concentrated at the mouths of rivers, is estimated by Statkraft to be in the region of 1,600 to 1,700 TWh annually. Electricity can be generated through the osmotic phenomena that results when a reservoir of fresh water is brought into contact with a reservoir of salt water through the use of a special kind of semipermeable membrane in one of two ways –either by harnessing the osmotic pressure differential between the two reservoirs to drive a turbine, or by using a membrane that only allows the passage of ions to produce an electric current.

The Statkraft prototype plant (and a planned 2 MW pilot facility) relies on the first method, using a polymide membrane that is able to produce 1 W/m2 of membrane. A team led by physicists at the Institut Lumière Matière in Lyon (CNRS / Université Claude Bernard Lyon 1), in collaboration with the Institut Néel (CNRS), have developed an experimental device that they say is 1,000 times more efficient than any previous system, significantly enhancing the commercial viability of osmotic power as a power source.

The team’s experimental device uses the second method. It consists of an impermeable and electrically insulating membrane that was pierced by a single hole through which the researchers inserted a boron nitride nanotube with an external diameter of a few dozen nanometers. With this membrane separating a salt water reservoir and a fresh water reservoir, the team measured the electric current passing through the membrane using two electrodes immersed in the fluid either side of the nanotube.

The results showed the device was able to generate an electric current through the nanotube in the order of a nanoampere. The researchers claim this is 1,000 times the yield of the other known techniques for harvesting osmotic energy and makes boron nitride nanotubes an extremely efficient solution for harvesting the energy of salinity gradients and converting it immediately into usable electrical power.

Extrapolating their results to a larger scale, they claim a 1 m2 boron nanotube membrane should have a capacity of around 4 kW and be capable of generating up to 30 MWh per year, which is three orders of magnitude greater than that of current prototype osmotic power plants.

The researchers’ next step will be to study the production of membranes made of boron nitride nanotubes and test the performance of nanotubes made from other materials.

The research is detailed in a study published in the journal Nature.

Source: CNRS (Délégation Paris Michel-Ange)

Update: This article was updated on Mar. 14, 2013, to replace the per year capacity for a 1 m2 boron nanotube membrane originally stated as "30 mWh" to "30 MWh." Our apologies for error.

About the Author
Darren Quick Darren's love of technology started in primary school with a Nintendo Game & Watch Donkey Kong (still functioning) and a Commodore VIC 20 computer (not still functioning). In high school he upgraded to a 286 PC, and he's been following Moore's law ever since. This love of technology continued through a number of university courses and crappy jobs until 2008, when his interests found a home at Gizmag.   All articles by Darren Quick
25 Comments

How much energy and money does it take to produce the nanotubes and power plant and how does it compare to the electricity and money that the nanotube power plant produces over its life?

Slowburn
13th March, 2013 @ 12:28 am PDT

This is very interesting especially when read along with today's (2012.3.13) story about Lockheed's graphene-based fresh water reverse osmosis breakthrough : http://news.yahoo.com/pentagon-weapons-maker-finds-method-cheap-clean-water-051529904--finance.html

The reverse osmosis process will produce some high salt concentration waste water along with its fresh water and the Statkraft system can be used to generate the electricity to power the reverse osmosis pumps. Now that's what you call a win-win :)

-dphiBbydt
13th March, 2013 @ 02:21 am PDT

I am a techie and this is great, if it works on a commercial scale it will have fantastic ramifications world wide both from an electrical generation perspective and a human food perspective.

If it works electricity will be renewable and cheap. Seafood will also be rare and expensive. Remember where the fresh water and the salt water mix is now call a marine estuary or a mangrove swamp. In the future it will be a power plant. Marine estuaries like mangroves are the nurseries of the oceans. No places on the planet are as important for the health of the oceans and we are now contemplating turning them into power plants. These power plants WILL destroy the mangroves and the estuaries.

Seafood is the last relatively cheap source of high quality, extremely tasty, high volume protein left on this crowded planet. All you need is a good boat, net and sonar to make a good living. You don't need to buy the land, pay land taxes, plant the crop, fertilize it, protect it from pests you just buy the combine and harvest.

We really need to think about what we are doing. When we do the cost benefit analysis on this technology through an environment assessment in whatever country has the money to build one of these plants please let us not assume that the loss to the marine ecosystem will be negligible and be made up for by the mangroves in Mexico or Bangladesh as these countries will be looking at this as a panacea too.

Up until I read this I thought the only really serious problem mankind faced was converting all our good cropland to asphalt.

Greg Riemer
13th March, 2013 @ 03:33 am PDT

"The global osmotic, or salinity gradient, power capacity, which is concentrated at the mouths of rivers, is estimated by Statkraft to be in the region of 1,600 to 1,700 TWh annually."

You often get "estimates" of the total solar power of the planet which envision every square meter of land being a solar panel (i.e. abstract total power which means nothing as far as real potential goes but makes it sound really promising). I wouldn't be surprised if the global osmotic capacity was based on every ounce of water entering the sea being run through the process. I hope this technology does well but without subsidies from governments who are easily swayed by such "estimates".

Snake Oil Baron
13th March, 2013 @ 04:08 am PDT

30 mWh per year. Thirty milliwatt-hours / year / sq.m. Really? The average household in the United States uses about 8,900 kilowatt-hours of electricity each year (easy to google). So it will require 300 sq.km of membrane to power 1 household.

splatman
13th March, 2013 @ 04:40 am PDT

Splatman, I'm thinking they meant a 30 megawatt hours per year - should the 'M' have been capitalized? Debatable, the 'k' in kWh (kilowatt hour) is not. So assuming they did mean 30 megawatt hours, then using your figures the average US household would need 8.9 sqm.

Frank McElroy
13th March, 2013 @ 05:32 am PDT

I can't imagine this ever becoming economical. This is essentially a reverse osmosis filter run in reverse (forward osmosis?) So unless your filtering the incoming fresh water down to micron levels before exposing the membrane to it, your membrane will be clogged before you know it. And filtering huge quantities of river water with fine filters would cost a fortune.

Siegfried Gust
13th March, 2013 @ 06:14 am PDT

Am I missing something here, or can you have just two tanks of water: one freshwater, one saline water? why do need a river and the sea? The amount of energy available seems to be extraordinary. I wonder what these filters cost per square metre.

David Colton Clarke
13th March, 2013 @ 08:59 am PDT

Devil is in the "dirty details" & I'm with Siegfried on this. the Nanorods are only a few dozen nanometers long, measurements similar to those are used to discribe distances on microchips. What often works on the small scale doesn't work well on a large scale & this is about as small as it gets. I doubt it will work very well on the large scale but I hope I'm wrong. If it does work it would be best implemented to reduce the cost of osmosis purification systems used to make drink water.

Matt Fletcher
13th March, 2013 @ 09:24 am PDT

Would it make a difference if such a plant were utilized on a body of water with a higher salinity, such as the Dead Sea in Israel or the Great Salt Lake in Utah?

T-Bone
13th March, 2013 @ 10:42 am PDT

As I understand the article the nano-osmo-thing is not a filter, but an impermeable membrane. However, all those little nanotubes and the connections thereto (I assume there must be some required to gather the electricity) are bound to clog up since neither salt water or fresh water are very clean in the wild. I hope they are able to scale up successfully.

Bruce H. Anderson
13th March, 2013 @ 11:46 am PDT

All of the above make good points. I would expect that if this scalable it would likely just be a great niche solution and not likely something that could power the planet. Lots of ideas that seem great as lab toys do not actually scale up very well. None the less this may be a great solution to locally power something without overwhelming the broader environment.

StWils
13th March, 2013 @ 12:11 pm PDT

@Frank McElroy

Yes, but they edited out the rest of my comment about sloppy writing and editing, making it look as if I were getting precious about one typo. So-called technical writers frequently display ignorance of high school science, and Gizmag is not immune.

splatman
13th March, 2013 @ 01:07 pm PDT

The amount of energy immediately available has little to do with the accumulated energy over time. A recent technology illustrates this very well - nano carbon super capacitors :

""The new device has a specific energy density of 85.6 Wh/kg at room temperature and 136 Wh/kg at 80 °C. These are the highest ever values for "electric double layer" super capacitors based on carbon nanomaterials.""

Newer ones approach or even exceed the “Energy Density” figures for gasoline! They recharge indefinitely!

Here we have the ability to accumulate and discharge at will, as pulsed D.C. any amount we please, without "internal resistance" loses of batteries and return by inductive coil as desired.

This will revolutionize the motor car industry world-wide, will reduce the weight of motors and wiring by virtue of higher voltages, will remove heat as an issue, will allow "Three Moving Part" power trains with lifetime guarantees, and even introduce chassis sales with interchangeable recyclable hemp (See hemp Lotus)(see hemp car bodies University of Alberta) bodies. Google the Chinese Chreos - this is what you are looking at?

Low power sources, Solar Wind, Wave, Hydro, Tidal, Geothermal Biological and Chemical as this is, are all domestic, clean, waste free, radioactive free, renewable = perpetual = eternal strengths at the very base of a nation. Be very careful with negativity - remember always: China has fathered the true Nuclear Age for mankind with their clean, waste free Thorium LFTR designs to debut in 2017, and these will "Alter Global Energy Maps Forever"

Bruce Miller
13th March, 2013 @ 04:23 pm PDT

Need this for worldwide use IE India, China, Australia, So America, awesome project for sure.

Stephen N Russell
13th March, 2013 @ 06:07 pm PDT

Could this technology possibly serve an energy storage function with lower impact and fewer challenges than as an energy source? Clearly caution would be needed with estuaries but considering the pressure differential that natural levels of salinity create a storage facility could increase this even further by increasing the salinity. Salt water and fresh water reservoirs would be much safer than large scale chemical storage solutions and the pressure gradient equivalent to several hundred meters of head would dwarf some of the pumped storage facilities we struggle to site and would not be dependent on topography. http://tinyurl.com/buuou64

MovingForward
13th March, 2013 @ 06:11 pm PDT

"1 m2 boron nanotube membrane should have a capacity of around 4 kW and be capable of generating up to 30 MWh per year"

Never mind the typo.

365 x 24 x 4 = 35040 kWh.

I'm tired, maybe I'm wrong?

Craig Jennings
13th March, 2013 @ 08:24 pm PDT

@Craig Jennings

You are correct. I missed that. These guys would fail primary school arithmetic, let alone high school science.

splatman
13th March, 2013 @ 09:53 pm PDT

@ Craig Jennings

with your quick calc they are likely working on about 85 efficiency

Colbey
13th March, 2013 @ 10:03 pm PDT

Snake Oil Baron should realize that our oil/natural gas production is heavily subsidized by the government even tho the industry is making record profits. Why? because our system of government is totally corrupt and there is no way to reform it since the foxes guard the chicken coop.

JAT
14th March, 2013 @ 07:23 am PDT

Maybe they said 30Mwh instead of 35Mwh because they assume the panels will have some downtime for maintenance. And Greg, maybe you've never seen aerial images of the mouths of the great rivers, but most of the fresh/salt water mixing is done a km or 2 (or more) out to sea. Maybe the water seeping out of the everglades is mixed in mangroves, but that has to be a very small percentage of water that flows into the sea. And maybe you've never flown over the middle portion of America, but there really is no shortage of cropland or land that could be converted to cropland. Less than 1/10 of 1% of the land is paved or has been built on.

mike65401
14th March, 2013 @ 09:25 am PDT

re; JAT

Getting tax breaks is not the same as the government handing over cash. Besides the consumer pays for all taxes on business.

Slowburn
14th March, 2013 @ 05:22 pm PDT

Some things are known to get more or less efficient as they get bigger when you extrapolate you take this into account.

Slowburn
14th March, 2013 @ 08:22 pm PDT

wow, this is HUGE. it will come down to how much a sq m will cost to make of this membrane, aswell as the infrastructure, but thats a huge output for such a small area and this is another area of resource generation that untill now has been largely overlooked interms of large scale production.

This could be a key source combined with other renewables to help shape the future independent of expensive non-renewables.

I think the biggest question, or drawback, as with alot of "new" technology, how long till this could be realisticly commercialized and brought into large scale production, im guessing probably 10-15 years and i may be optomistic. Then again im no expert on this and technology is evolving at a rapid pace, if this could be in place in 5-10 years i think that would be very good everyone.

Arahant
15th March, 2013 @ 02:42 pm PDT

Closed-loop system at the highest optimum salinity would be best because you could control the filtration and minimize contaminants. The ROI at river-sea interfaces will be orders of magnitude less efficient, nor will permits be issued as in California where desalination plants can not have dedicated sea water intakes - they can only be built adjacent to power plants where they need sea water intakes for cooling purposes to share the intake. Remember intakes have impingement and entrainment issues besides monster filtration issues to avoid contamination of the ionic membranes. Salinity gradient at 4kW/sq m is over 4x the solar radiation (typ 1000 W/sq meter) and if PV panels are around 20% efficient (200W/sq meter), then salinity gradient is roughly 20x more power per square meter, and can be compressed in spiral membrane architecture resulting in some high-density energy device as well as being base-load compared to intermittent solar and the day/night cycle.

PuraVida
14th August, 2013 @ 06:26 am PDT
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