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High-efficiency solar energy tech turns water into steam

By

November 20, 2012

Rice University graduate student Oara Neumann (left) and scientist Naomi Halas are co-auth...

Rice University graduate student Oara Neumann (left) and scientist Naomi Halas are co-authors of new research on a highly efficient method of turning sunlight into steam

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A team of researchers at Rice University has developed a new technology that uses light-absorbing nanoparticles to convert solar energy directly into steam. Even though it is already significantly more efficient than solar panels at producing electricity, the technology will likely find its first applications in low-cost sanitation, water purification and human waste treatment for the developing world.

Approximately 90 percent of the world's electricity is produced from steam turbines. Most industrial steam is produced in large, expensive boilers, but because of its very small footprint and high efficiency, this new development promises to make steam economically viable on a much smaller scale. Sterilizing medical waste and surgical instruments, preparing food and purifying water could soon become within reach of a large chunk of the developing world, that doesn't have access to the electrical grid.

The Rice technology relies on light-absorbing nanoparticles. When they are submerged and then illuminated, these particles can very quickly reach temperatures well above the boiling point of water. At this stage, they quickly dissipate heat through their very small surface area, which almost instantly results in 150°C (300°F) steam generated right at the surface of the particle. The system is so effective that it can even turn icy-cold water directly into vapor with ease.

A diagram illustrating how the light-absorbing nanoparticles turn sunlight into steam

The technology converts about 80 percent of the energy coming from the sun into steam. With the current iteration, passing the resulting steam to a turbine would generate electricity with an overall efficiency of 24 percent (compared to a solar panel's typical efficiency of around 15 percent). As the technology is further refined, the researchers say there is still room for improvement on the efficiency front.

Other potential uses could be powering hybrid air-conditioning and heating systems that run off of sunlight during the day and off of electricity at night. The system has also proved very promising in distilling water, with an experiment finding that the technology is about two and a half times more efficient than existing commercially available systems.

The project was awarded a grant from the Bill and Melinda Gates Foundation to create a small-scale system for treating human waste in areas lacking sewer systems or electricity. In the meantime, Rice engineering undergraduates have already created a solar steam-powered autoclave that can sterilize medical and dental instruments in clinics lacking electricity.

An open-access paper detailing the research efforts was published in the journal ACS Nano.

Source: Rice University

The video below illustrates the working principles behind this technology.

About the Author
Dario Borghino Dario studied software engineering at the Polytechnic University of Turin. When he isn't writing for Gizmag he is usually traveling the world on a whim, working on an AI-guided automated trading system, or chasing his dream to become the next European thumbwrestling champion.   All articles by Dario Borghino
19 Comments

The problem with heating water with a light source is getting the energy to stop in the water. I suggested something similar when I noticed that a glass of cola warms up faster than a glass lemon-lime soda when on a picnic.

If getting the radiant heat (as apposed to conducting heat) to stop in the water more efficiently makes the water heat faster adding some soot to the water in a conventional boiler might make it slightly more efficient.

Slowburn
20th November, 2012 @ 10:21 am PST

This was done in Victorian times and demonstrated at the great exhibition if my reading of the description is correct. OK, that one didn't use nano tech so that is the new thing.

There have also been several solar powered AC units built over the years.

ivan4
20th November, 2012 @ 03:35 pm PST

Desalianation? Wouldn't the salt particles bind to the nano particles and make them less efficient.

I imagine that the water used needs to be pretty clean (filtered...), unless the steam boiled other water, in that case you no longer have 90% efficiency.

abe
20th November, 2012 @ 04:55 pm PST

abe, the way I see it desalination and especially human waste treatment would involve a closed loop using pure water - steam - water and a heat exchanger to treat/desalinate.

Reason
20th November, 2012 @ 08:32 pm PST

What about just solar hot water system that actually works well? Heat the water and pass it to a holding tank. You could use a much smaller collector.

Scion
20th November, 2012 @ 09:58 pm PST

Great new idea. Desalniation by evaporation is not new, but would be now more efficient. By the way, tell me where I can buy solar panels with an efficiency of 15 % ? You can be happy if the reach 9 %. So this makes this invention even more important.

ikarus342000
21st November, 2012 @ 02:00 am PST

The technology seems interesting and cool. However, good commercial photovoltaics have an efficiency of about 20%, not 15%. And I remember a solar concentrator using a stirling engine that had an efficiency of 25-30%.

So, either the technology is much cheaper or it will end up like the aforementioned concentrator .... nowhere

ugosugo
21st November, 2012 @ 07:54 am PST

Mass produce & use for Temp emergencies or for LT power IE

EU, Russia, Iceland, Greenland, Alaska alone can use & Yukon Terr Canada.

Stephen N Russell
21st November, 2012 @ 08:05 am PST

80% efficiency! Amazing!

Sergey Jivetin
21st November, 2012 @ 09:09 am PST

"At this stage, they quickly dissipate heat through their very small surface area..."

It should read as a very high surface area. We're talking about nano-particles, they have a high surface to volume ratio, meaning the particles have more surface access area to quickly dissipate heat to the medium than if the particles were bigger.

Fretting Freddy the Ferret pressing the Fret
21st November, 2012 @ 09:51 am PST

The first issue is the availability or cost of water that is suitable for the system. Water is expensive and in some areas very hard to come by. If that water has to be processed there is another expensive barrier. As far as desalinization is concerned the issue of just what to do with all of the salt and calcium carbonate removed from salt water is a huge problem. Then the next issue is just how fast salt water destroys equipment.

If a closed loop steam system can be made it might be a way to power trains or even ships at sea. Or it might be able to spin a generator for powering homes or charging car batteries.

The catch being that victories come just a tiny inch at a time and take decades to perfect.

Jim Sadler
21st November, 2012 @ 10:37 am PST

This is interesting, and from the picture, it looks small enough that the typical household could use such a device. The key, just like ALL energy/heat producing devices is that it not only MUST be efficient, but it must also be affordable. (Affordable is in the hundreds, NOT the thousands...)

Observer101
21st November, 2012 @ 11:03 am PST

@ikarus342000,

Check out Edmund Scientific for solar cells. The more efficient units are much more expensive than the cheaper ones. You won't find panels, though, more like individual solar cells. check out http://howsolarworks.1bog.org/solar-panel-efficiency/ for more information. They have panels that claim 19% efficiency.

High quality high efficient cells are now up around 25% with a few claims of 35%. The high end claims are disputed.

The highest efficiency units tend to be concentrators, so they only work in direct sunlight. The unit in this article is a direct system. If it's cloudy where you live, you will never get a whole lot of good out of the system.

YetAnotherBob
21st November, 2012 @ 11:22 am PST

You dont put the dirty water you want cleaned or distilled into this machine. That is just stupid.

You have a primary circuit and a secondary circuit.

The primary circuit is clean and probably dosed to reduce corrosion and increase efficiency of solar collection. In fact, taking slowburns suggestion into consideration perhaps the nano-particles are suspended in solution to boost overall solar collection. perhaps the primary circuit doesnt need water at all, and instead uses a commercial heating oil with much higher flash points (such as Diphyl). then you can really get cooking without worrying about pressure.

The heat collected in the primary circuit is then feed into a heat exchanger where the energy is transferred to the secondary "dirty" fluid. you use a heat exchanger easy to clean. Also you may need to dose the clean water you make, the human body doesn't enjoy perfectly clean water.

Now if you want to make electricity with a steam turbine; to drive a turbine you need steam much hotter than 150degC, you need high pressure steam and you need very dry steam, to the point of adding superheat to mitigate the risk of condensation on the turbine blades. not that this cant be done with solar (you can easily melt steel with solar concentrators)

cm
21st November, 2012 @ 12:31 pm PST

re; Jim Sadler

Calcium carbonate has a multitude of industrial uses as does salt but admittedly salt is the only chemical extracted from the Dead Sea that the Israelis don't find it cost effective to truck nine hundred vertical feet up to ocean level they just leave it in big piles. If you would have a problem with the salt killing plants either cover the piles or put the salt back into the ocean if you can't convince somebody to haul it away at no cost to you.

Slowburn
21st November, 2012 @ 02:41 pm PST

To bypass problems with "wet" steam, use a Tesla disc turbine. Like any turbine, the Tesla design has to be made to match the working fluid that'll be run through it to optimize efficiency.

There's a very long tail of R&D on optimizing blade turbines for dry steam, not so much on optimizing Tesla's disc design, even though some very large ones had been installed decades ago for power generation.

Would have to google that to find out when and where, will leave that up to the readers. ;)

There's a source for very cheap or even free parabolic reflectors in large diameters. Old C-Band TVRO satellite dishes. The spun aluminum ones can be stripped of paint, polished then hard anodized (without a color dye). The fiberglass ones can be sanded smooth, painted then sprayed with a reflective coating like ALSA Mirrachrome (super fine aluminum suspended in alcohol) or one of the processes that uses a technique similar to applying silver to the back side of glass for making mirrors. Both of those need a clear paint coat to protect the aluminum or silver coat.

The process to make them shiny would cost more than the dish, but far less than making new dishes.

Gregg Eshelman
21st November, 2012 @ 05:08 pm PST

Looks like an old satellite tv dish with a jug strapped to the focal point. Hey that gives me an idea..... I got a few of those lying around. I don't have any nano particles, except maybe for some ball bearings... 8*)

nutcase
21st November, 2012 @ 08:01 pm PST

Heartiest congratulations to the Oara Neumann & Naomi Halas for making it a reality that solar is indeed a wonderful boon to mankind. I have no doubt that this will revolutionize our future approach on power generation.

Asoor Shyam
21st November, 2012 @ 10:35 pm PST

This is great invention! Thanks for sharing! I could remember a year ago, my eldest son had a science project on solar energy. Solar energy really amazes me so much!

Facebook User
29th November, 2012 @ 07:10 pm PST
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