(Solar) Cell a Million?

SOLAR cells were once a bespoke product, reserved for satellites and military use. In 1977 a watt of solar generating capacity cost $77. That has now come down to about 80 cents, and solar power is beginning to compete with the more expensive sort of conventionally generated electricity. If the price came down further, though, solar might really hit the big time—and that is the hope of Henry Snaith, of Oxford University, and his colleagues. As he described recently in Science, Dr Snaith plans to replace silicon, the material used to make most solar cells, with a substance called a perovskite. This, he believes, could cut the cost of a watt of solar generating capacity by three-quarters.

When light falls on a solar cell, it knocks electrons away from the cell’s material and leaves behind empty spaces called holes. Electrons and holes then flow in opposite directions and the result is an electric current.

 

The more electrons and holes there are, and the faster they flow, the bigger the current will be. Electrons, however, often get captured by holes while still inside the cell, and cannot therefore contribute to the current. The average distance an electron travels in a material before it gets captured is known as that material’s diffusion length. The larger the diffusion length, the more efficient the cell.

The silicon used in commercial solar cells has a diffusion length of ten nanometres (billionth of a metre), which is not much. Partly for this reason a silicon cell’s efficiency at converting incident light into electricity is less than 10%. Dr Snaith’s perovskite does better. It has a diffusion length of 1,000 nanometres, giving it an efficiency of 15%. And this, Dr Snaith says, has been achieved without much tweaking of the material. The implication is that it could be made more efficient still.

Perovskites are substances composed of what are known as cubo-octahedral crystals—in other words, cubes with the corners cut off. They thus have six octagonal faces and eight triangular ones. Perovskite itself is a natually occuring mineral, calcium titanium oxide, but lots of other elemental combinations adopt the same shape, and tinkering with the mix changes the frequency of the light the crystal absorbs best.

Dr Snaith’s perovskite is a particularly sophisticated one. It has an organic part, made of carbon, hydrogen and nitrogen, and an inorganic part, made of lead, iodine and chlorine. The organic part acts as a dye, absorbing lots of sunlight. The inorganic part helps conduct the electrons thus released.

It is also cheap to make. Purifying silicon requires high (and therefore costly) temperatures. Dr Snaith’s perovskite can be blended at room temperature. Laboratory versions of cells made from it cost about 40 cents per watt (ie, about half the cost of commercial silicon-based solar cells). At an industrial scale, Dr Snaith expects, that will halve again.

There are caveats, of course. The new perovskite is such a recent invention that its durability has not been properly tested. Many otherwise-promising materials fail to survive constant exposure to the sun, a sine qua non of being a solar cell. And the process of converting a laboratory-made cell into a mass-manufactured one is not always straight forward.

If it leaps these hurdles, though, Dr Snaith’s material will be a strong challenger for silicon. As solar power-generation becomes a mainstream technology over the next few years, the once-strange word “perovskite” may enter everyday language.

New technology to enable development of 4G solar cells

Professor Ravi Silva of the University of Surrey‘s Advanced Technology Institute has identified the range of combinations of organic and inorganic materials that will underpin new 4th generation solar cell technology – opening the door for more efficient, cost-effective and larger scale solar power generation.

 

Solar power – the greenest form of renewable energy – is in increasing demand across the world, with the global capacity for solar power generation now topping 100GW.

The new 4G solar cells defined by Professor Silva are a hybrid that combine the low cost and flexibility of conducting polymer films (organic materials) with the lifetime stability of novel nanostructures (inorganic materials). This ‘inorganics-in-organics’ technology improves the harvesting of solar energy and its conversion into electricity, offering better efficiency than the current 3G solar cells while maintaining their low cost base. In turn, these 3G cells offer significant cost improvements on first and second generation solar cells – based on crystalline and polycrystalline silicon – which are still responsible for over 90% of the solar power being generated today.

Along with a number of notable research institutions, the University of Surrey is part of the European Union FP7 SMARTONICS programme – a €11.6m project led by the Aristotle University of Thessaloniki. This project is currently developing the smart machines, tools and processes for large-scale production of 4G solar cells, using roll-to-roll printing technology for high throughput and cost-efficient fabrication.

Outlining the new 4G technology in his recent keynote address at the 10th International Conference on Nanoscience and Nanotechnology (NN13) in July, Professor Silva said: “These new generation materials for solar cells have been truly engineered at the nanoscale. They are designed to maximise the harvesting of solar radiation, and thereby efficiently generate electricity.”

Speaking to a packed conference hall at NN13 – part of NANOTEXNOLOGY 2013 [www.nanotexnology.com]– he also outlined the significant progress being made by the solar industry in bringing down the cost of solar electricity. In many parts of the world, it now competes with grid electricity in terms of cost, and since it requires less infrastructure, solar power can also be used in areas where conventional electricity is not an option.

Conference Chair Professor Stergios Logothetidis thanked Professor Silva for “introducing the idea and concept of 4G solar cells to the world” and added: “We believe that 4G solar cells will be the technology for future photovoltaic energy sources.”

 
Read more at: http://phys.org/news/2013-07-technology-enable-4g-solar-cells.html#jCp

One Technology That Is Already Changing the Future Of Energy

 

Daniel Burrus

Best Selling Author, Global Futurist & Innovation Expert, Entrepreneur, Strategic Advisor & Keynote Speaker

DANIEL BURRUS is considered one of the world’s leading technology forecasters and innovation experts, and is the founder and CEO of Burrus Research, a research and consulting firm that monitors global advancements in technology driven trends to help clients understand how technological, social and business forces are converging to create enormous untapped opportunities. He is the author of six books including The New York Times best seller Flash Foresight.

The accelerating change of technology we use commercially and personally is dramatically increasing the global demand for electric power. As consumers, we’re gulping power at an alarming rate, from air conditioning systems, heating systems, household appliances, and all forms of home entertainment devices to cloud computing, computers, and consumer electronics. Over the past few years, we’re also plugging in electric vehicles at an ever increasing rate. And let’s not forget the industrial power needed to churn out all these products, as well as keep the other wheels of industry turning. In fact, global electricity demand has been projected to nearly double from the year 2010 to 2030.

It’s clear we’re already close to consuming more electricity than we can generate or distribute, as manifest through the rolling black and brown outs frequently seen during summer months where peak power demand is highest. The problem is we’re adding more demand for electricity (from everything mentioned above and more) than we’re adding capacity to supply it. With that said, we still need to stay cool and to turn on lights to see at night … and we’re certainly not going to turn off our home theater and gaming systems.

So what’s the answer? Expand power generation to meet growing demand? Not so fast. Investment in electric power generation and distribution is a slow, long-term proposition, and therefore has trailed well below the increase in GDP in most developed countries. In other words, no one has the appetite (or the capital) to build enough power plants and expand the grid to meet the rising demand for electricity.

A quick point of fact: Power generation—and the grid to distribute it—has to be scaled to meet peak demand. On average, power grids operate at around 80 percent capacity, so they’re ready to cover peak demand when those hot summer days roll around. If demand rises above that peak capacity, we experience those black and brown outs.

Additionally, 75 percent of the electricity generating capacity in the United States depends on the combustion of fossil fuels. This raises a multitude of other concerns, perhaps foremost that dependence on fossil fuels for electricity is causing severe environmental and health hazards, including large emissions of toxic air pollutants and greenhouse gases.

Over the past few years, thanks to technology developments such as fracking, which were impossible just a decade ago, we can now extract natural gas in very large quantities, and that has put the United States in a position of being an exporter of energy. The good news is that natural gas is far less polluting than other fossil fuels, such as coal, and the U.S. has very large reserves. On the other hand, the United States does not have an infrastructure for capitalizing on natural gas powered vehicles, and natural gas is a fossil fuel and does have harmful emissions, even if less than the others.

When we look at renewable energy sources such as wind, solar, and waves, great strides have been taken, but until we find a way to store electricity for use at a later time, these will help but not be game changing. The good news here is that there is a technology that is already changing the game.

What if we could increase energy production without adding new capacity? What if we could use the power we already generate more efficiently, rather than have to dramatically expand power generation? Enter the work that is being done to enable smart grids, smart homes, and smart cities to help us accomplish this. But will peak power demand modeling and technology that turns lights off in empty rooms be enough? Probably not for some time. That’s where promising energy storage technology comes in as a key change accelerator to help us use the electrical power we have now more efficiently.

One of the companies leading the way is Maxwell Technologies in San Diego, California. They have developed and are manufacturing one of the most promising clean-energy power storage technologies available: ultracapacitors, which use an electro-static field to quickly capture energy and then rapidly release it when needed. Conventional batteries and advanced lithium-ion batteries that rely on a chemical reaction cannot efficiently do this because they charge slowly and discharge slowly. When batteries are asked to charge and discharge quickly—which is the case in many applications today—they begin to fail and ultimately need to be replaced.

Ultracapacitors are being incorporated (where batteries cannot) into renewable energy power generation from solar, wind, and waves to improve efficiency and reliability. Because there are many disruptions in renewable energy output from clouds, wind fluctuations, and tides that last from a few seconds to a few minutes, output can swing as much as 50 percent at any time. This variability in power supply presents issues with power grid stability, causing the grid to disconnect from the renewable energy source.

The unique quick charge/discharge ability of ultracapacitors allows renewable energy installations to quickly store power and then deliver it back to the power grid “firming” output capacity and “ride through” during short-term disruptions. This increases renewable energy utilization by 30 – 50 percent so the power grid doesn’t need to be built to such a large scale (at an incremental cost) as demand for electrical power grows. Additionally, we could further increase our use of clean energy and decrease reliance on fossil fuels for power generation.

From a very broad perspective, this is a major example of how ultracapacitors can help us use the energy we already generate more efficiently. But what about places off the grid where we waste energy every day? How about planes, trains, automobiles, trucks, and busses?

Regenerative braking systems in electric and hybrid vehicles are being used to generate and quickly store electrical energy when brakes are applied, then rapidly release it for acceleration. Conventional friction-based braking systems simply lose all this kinetic energy to heat. Ultracapacitors are being used to quickly capture and release this energy to improve fuel economy and extend battery life. Regenerative breaking systems provide an average of 7 percent fuel efficiently and would save 12 million gallons of fuel in the U.S. each year.

Conventional internal-combustion vehicles are incorporating start-stop systems that kill the engine at stoplights and stop signs, and then restart it when the accelerator is applied. Ultracapacitors are being designed into these vehicles to stabilize starter systems, electrical systems, power steering, and onboard electronics. These start-stop systems improve fuel efficiency by up to 15 percent. In the U.S. alone we could save 25.5 million gallons of fuel annually if every conventional vehicle had this type of system. Image how much energy we could save and utilize if every vehicle on the planet had a start-stop system.

Finally, let’s think at the micro-level. Small ultracapacitors can be combined with batteries in laptops, tablets, smart phones, and electronic toys to use electric power more efficiently. Unlike ultracapacitors, batteries begin to degrade when they are tasked to quickly charge and discharge, but they are great sources of long-term power. Because ultracapacitors can quickly be charged and discharged up to a million times without loss of performance, they are ideal for providing the bursts of power required by today’s electronic devices, helping them perform better and batteries last longer.

There are a multitude of other applications where ultracapacitors can—and are starting to—help us use the power we’re already generating more efficiently, instead of simply generating more power. Clean-energy ultracapacitors are a change accelerating technology that will enable energy’s future and not inhibit the dizzying rate of technological, commercial, and social change we’ve come to expect and rely on.

Meanwhile, a question: Are there obvious or obscure places you can imagine where innovative power storage technology could help us use the electrical power we have now more efficiently?

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Harvesting Energy From Carbon Dioxide Emissions

Energy: Device generates electricity from the entropy created when the greenhouse gas mixes with fresh air

By Naomi Lubick

An electrochemical cell could someday generate electricity from carbon dioxide emitted by power plants as the gas wafts into the atmosphere. Researchers demonstrate that the cell harvests energy released by the entropy created when CO₂ mixes with fresh air (Environ. Sci. Technol. Lett. 2013, DOI: 10.1021/ez4000059). The device could help power plants increase electricity output without producing additional CO₂.

Electricity From CO₂            

 A new electrochemical cell generates electricity from carbon dioxide dissolved in water solutions. When dissolved, the gas forms carbonic acid (H₂CO₃), which then dissociates into H⁺ and HCO₃^– ions. These ions adsorb selectively onto one of the two electrodes (left and right), depending on the type of membrane on the electrode (yellow and red). This process generates a current between the electrodes.            Credit: Environ. Sci. Technol. Lett

Bert Hamelers of Wetsus, a research center focused on water treatment technology in Leeuwarden, the Netherlands, and his team developed the new device based on one they created to tap energy released when seawater and freshwater mix. The previous cell consisted of electrodes coated with ion-exchange membranes. As seawater and freshwater flowed through the cell, the membranes absorbed and released sodium and chloride ions, creating a current.

Hamelers realized that the same cell design could harvest the energy released when two gases mix. To do so with CO₂, the team first mixed it with a liquid, using either deionized water or a 0.25 M water solution of monoethanolamine (MEA), which is often used to remove CO₂ from exhaust gases. In water, the CO₂ forms carbonic acid, which then dissociates into H⁺ and HCO₃^– ions. These ions act like the sodium and chloride ions in the previous entropy-harvesting device. As the solution passes through the cell, ion-exchange membranes on the cell’s electrodes absorb the ions, H⁺ on one electrode and HCO₃^– on the other. This process produces current between the electrodes.

           

                       Mixing Gases            

To harvest energy from mixing CO₂ and fresh air, researchers first must dissolve the gases in water solutions (CO₂, right; air, left). The water then passes by membranes in an electrochemical cell (rectangular block in the middle) in alternating pulses. The cell generates electricity as ions in the solutions adsorb onto and desorb from the electrodes.    Credit: Bert Hamelers/Wetsus        

Then water with dissolved fresh air flushes through the cell. Since this water is mostly ion free, the membranes release the H⁺ and HCO₃^– ions into the water, producing current in the opposite direction as before. This now ion-laden water leaves the cell and gets flushed with air. The CO₂ gas reforms and is then released. The fluidics system continually repeats this cycle, sending alternating pulses of the dissolved CO₂ and dissolved air through the cell.

With the small-scale system the researchers built in their lab, they could harvest 24% of the energy released when they used deionized water and 32% when they used MEA. At its most efficient, the lab setup generates only milliwatts of power. But with a scaled-up system, the researchers calculate that power plants could produce megawatts of power using CO₂ emissions. They estimate that flue gases from power plants worldwide contain enough CO₂ to generate 850 TWh of energy every year.

But the system has a few obstacles to overcome before it can be used in such large-scale applications, the team and outside experts say. For example, impurities in a power plant’s flue gas, such as sulfur dioxide or nitrogen oxides, could foul the cell’s membranes. The immediate problem is getting CO₂ emissions dissolved into a liquid upon exiting the stacks. With current technology, dissolving that much gas in liquid would require more energy than the researchers’ system could generate. So it will take more research to find the optimal process to dissolve CO₂ using as little energy as possible, Hamelers says.

Still, the concept is “marvelous,” says Volker Presser of the Leibniz Institute for New Materials in Germany. Now the researchers “need to envision a system that can take up tonnes and tonnes of CO₂,” over multiple cycles, he says. With such a system generating extra electricity, Presser says, coal plants could produce energy more efficiently, without emitting more CO₂.

Chemical & Engineering News

ISSN 0009-2347

Copyright © 2013 American Chemical Society

A New Hub for Solar Tech Blooms in Japan

Tilting Toward Solar in Yokohama

Photograph by Sankei via Getty Images

 

 

What appears to be an array of metal flower petals is not an art installation but part of a cutting-edge solar-power system meant to address the critical power shortage Japan now faces in the wake of the Tohoku earthquake and tsunami on March 11, 2011.

The disaster, which triggered a crippling nuclear accident at the Fukushima Daiichi plant, reignited worldwide debate about the safety of nuclear power and forced Japan to reevaluate its energy strategy.

(Related Photos: “The Nuclear Cleanup Struggle at Fukushima“)

Of Japan’s 54 nuclear reactors, 52 have been shut down for maintenance; the remaining two are set to go offline this spring. The reactors are likely to remain inoperative while Japan’s central and local governments assess which (if any) of them can be restarted, leaving the country to make up for a 30-percent loss in power generation.

(Related: “Energy-Short Japan Eyes Renewable Future, Savings Now“)

Rising electricity prices and limited supply threaten to hamper the recovery for manufacturers. So it makes sense that Solar Techno Park, the first solar-power research facility focusing on multiple technologies in Japan, is operated not by the government but by a unit of the Tokyo-based JFE, the world’s fifth-largest steelmaker. Given the energy-intensive nature of steel production, reliable power will be key to the future of Japan’s steel industry. The facility, which opened in October last year, is developing advanced technology in solar light and thermal power generation that it aims to apply both in Japan and overseas.

Located along the industrial coast of the port city of Yokohama, the Solar Techno Park aims to achieve a combined output capacity of 40 to 60 kilowatts this spring. The facility’s most notable apparatus is the HyperHelios (seen here), a photovoltaic system consisting of rows of heliostats with mirrors that follow the sun and a receiving tower. Two types of solar thermal power systems are also being developed at the park.

—Yvonne Chang

Nanoparticles Split Water, Power Fuel Cell

Si Nanoparticles Split Water, Power Fuel Cell

by Tim Palucka

Materials Research Society | Published: 29 January 2013

Generating electricity in the field to power a laptop or night vision goggles could someday be just as simple as adding water to a cartridge containing silicon nanoparticles and a base. Researchers at the University at Buffalo (SUNY) have demonstrated that nanoparticles of Si in a basic solution can split water to release hydrogen and power a portable fuel cell to produce electricity. The ability to split water on-demand without adding heat, light, or electricity to the system could be a significant advance in fuel cell technology.

“The reaction rate with these very small 10-nm Si particles is so much faster than with the relatively large 100 nm Si particles,” says Mark Swihart, whose team published their results in a recent issue of ACS Nano Letters. “Because of this fast reaction rate and the fact that there’s no delay between when you add water and when the reaction starts, it makes the technology at least practical in terms of being able to power a device instantaneously.”

 

While there was some scant evidence in the scientific literature that Si could perform this feat of splitting water to release hydrogen, it was largely ignored because the reaction rate was so slow as to be uninteresting. Using Al, Zn, or metal hydrides for this purpose looked so much more promising that Si fell by the wayside.

But Swihart and his group have been working with Si nanoparticles for more than a decade, mostly in the realm of quantum dot research. In doing so, they frequently had to use a base such as hydrazine for etching, and they noticed that hydrogen was released when aqueous hydrazine reacted with Si. Investigation showed that the hydrogen came not from decomposition of hydrazine, but from the oxidation of Si to release hydrogen from water.

Further investigation of the reaction using Si particles of different sizes, focusing on 10-nm and 100-nm-diameter particles with aqueous KOH, showed a particle size dependent liberation of hydrogen from water. But the factor of 150 increase in the reaction rate for the 10-nm-diameter particles compared to the 100-nm-particles was well in excess of the factor of 6 difference in their specific surface area. Thus, the increase in rate is much greater than expected based on increased surface area alone.

Swihart believes the difference is caused by geometry, not surface area. The 111 lattice planes etch much more slowly than other planes of Si, so crystals terminated entirely by 111 planes react slowly.  “The 10 nm particles etch isotropically—they just get smaller and go away,” he says. There’s no time for faceting to occur in this case. But the 100 nm particles undergo anisotropic etching. The faster-reacting 100 and 110 planes etch away first, leaving a particle with slower-reacting 111 planes behind in what he describes as a “hollow nano-balloon structure.” “With the bigger particles,” Swihart says, “eventually the unreactive 111 surfaces are the ones that end up being left,” thus slowing the reaction rate.

As a proof-of-concept, the research team tested a small fuel cell with a 20 stack polymer electrolyte membrane, comparing the fuel cell’s power output when fed hydrogen from the Si nanoparticle reaction versus hydrogen from a gas cylinder. Stoichiometrically, two moles of H₂ should be generated for one mole of Si. In the tests, the fuel cell powered by H₂ generated by reaction with Si produced more current and voltage than when the fuel cell was fed a stoichiometric amount of H₂ from a gas cylinder. The difference is due to additional hydrogen, beyond the stoichiometric reaction amount, that terminates the Si surfaces after fabrication of the nanoparticles.

While there is much more work to be done, Swihart believes that if this technology is ever to become practical as a portable electricity generator, the KOH (or other base) would have to be mixed in with the Si in a cartridge, so you would not have to carry around a bottle of KOH solution. Such a device would come with the instructions “just add water.” For a soldier in the field needing to power night vision goggles, water from a nearby stream could be all he needs.

 

Read the abstract in ACS Nano Letters  here.

Building design and the potential of third-generation solar cells

Ingo B Hagemann

Note To Readers: The potential of this technology IOHO gives a whole new definition to the term “Smart Building”. “Great moments are born from Great Opportunity.” (H.Brooks: 1980 “Miracle”)

Ingo B Hagemann, architect and building-integrated photovoltaic (BIPV) consultant, discusses opportunities and challenges for organic solar cells and other third-generation photovoltaic (third-gen PV) technologies in the building and construction industry.

Until now, PVs have been developed and perceived simply as systems for generating electricity, with the performance of cells being defined purely in terms of power output.

However, this is changing. In the future solar electricity production will become a by-product of multifunctional building components with integrated PV capability. Beside solar power output, the technology will be judged on other criteria, such as design and structural integration flexibility.

Organic PVs (OPVs) and dye-sensitised solar cells (DSSCs), which are collectively referred to as third-generation PV technologies (third-gen), have the potential to contribute significantly to this development. As third-gen PV technology advances in terms of performance and other factors, architecturally attractive uses of PVs in the building fabric will become more commonplace.

Unlike bulky and rigid traditional, silicon-based solar cells, third-gen PVs can be made lightweight, flexible and translucent. They can be produced in different colours and patterned, resulting in additional smart design opportunities for the integration of the PV into the building shell.

The new design features of third-gen PV correspond well with current trends in architectural design, such as an intensive use of colours, the use of (multimedia) screens and patterns for building façade designs. The technology also supports the rediscovery of the moulding of complex curving forms, which is a result and expression of contemporary architectural practice in which digital technologies are radically changing the way how buildings are conceived, designed and produced.

Printing, coating, vacuum processing and other simple, low-temperature and low-cost production processes are being developed to fabricate third-gen PVs, which will make them less costly to manufacture.

The benefits and advantages of third-gen PV for building and construction applications can be separated in to five main areas:

Good power performance under dim or variable lighting conditions

The power output of third-gen PV technologies is not so dependent on the access of direct solar radiation, compared with silicon, suggesting high performance under low light conditions such as fog, partially shaded building surface areas or indoors. This makes third-gen PV an ideal candidate for cloudy or smoggy environments such as major built up cities, where low light conditions are commonplace; in equatorial areas, where lots of clouding is caused by the Intertropical Convergence Zone (ITCZ); or in high latitudes, where overcast skies are typical. In addition, third-gen PVs can be developed for certain types of indoor applications, like powering emergency lights or motion detectors.

Power performance without cooling

Power performance without cooling means third-gen PVs can be used as an integral part of ‘sandwich’ building elements, which do not usually provide the option of back-ventilation for the integrated PV.

Sandwich elements allow for a wide variety of material combinations. Several variations are used in the building industry. Examples are structural insulated panels (SIPs), precast insulated roof systems – used often in home construction – or floor-to floor façade elements used for the bracing of curtain wall façade systems.

Together with modern construction processes using assembly line automation, prefab sandwich elements meet today’s requirements of fast installation processes and heat insulation, while allowing for high standards of accuracy.

 

Design flexibility due to low-cost materials and easy-to-handle processing technologies

The global construction industry is diverse and the types of building products and materials it uses vary considerably. Construction methods and traditions, building products and building codes differ from country to country, even region to region. Unlike standard PV modules, it is not possible to design building products – with or without integrated PV – likely to serve a market on a global scale. However as third-gen PVs could be made using more straightforward, low-temperature production methods such as roll-to-toll on flexible substrates, the financial and technological effort needed to make these cells is much lower, compared with established first- and second-gen crystal and thin-film PV cells.

Therefore third-gen PV has the potential to open up the market for building-integrated PV products that serve the needs of regional building markets.

Transparency and durability

Glass is one of the most popular and durable building materials today, allowing for buildings to be designed with large window openings to exploit natural light. Glass can be engineered to meet the increasing façade performance expectations of the building envelope, with regards to heat insulation (U-value), noise, sun protection and weather protection and durability.

Rapid developments in the field of new coatings for glass, new material combinations with glass and associated new engineering, production and construction methods ensure it will continue to be a key component in building construction. In addition glass has a relatively small impact on the environment.

Essentially, minerals are used to produce a benign product. Theoretically, glass is infinitely recyclable with no loss of quality. These features make it a first-class, ecological building product for today and tomorrow.

Flexible and lightweight

Third-gen PV made from flexible and transparent substrates and encapsulation materials can provide a product with a combination of performance characteristics that do not yet exist on the building market. So-called plastic OPV cells can be lightweight, translucent and available in different colours, such as Konarka’s Power Plastic. OPvs offer integration opportunities for all kinds of building structures where a lightweight form factor is of structural importance, such as canopies and awnings, light roof construction of factory buildings and sports stadiums.

A field of special interest for the application of this type of third-gen PV is tension membrane or pneumatic cushions structures, which have increased in importance in modern architecture. They exploit daylight, while at the same time sheltering large façade areas. At night, PV structures could be illuminated by LED lights and designed to catch the attention of the public like other multimedia façades.

These low resource-demanding structures satisfy aspects of modern and sustainable architecture and third-gen PV solar electricity production adds functionality without interfering in design elements and properties. Well-known examples of these structures – without PV – are the Allianz Arena in Munich, the façade of the Burj Al Arab in Dubai, or the Olympic Swim Stadium in Beijing, China.

Challenges

Despite these advantages, third-gen PV efficiencies lack in comparison to conventional PV. But it can be expected that further technology improvements will increase over the next few years. Low production costs will help to neutralise low efficiency issues, since there are applications for BIPV where cost is the prime concern – such as the coating of large quantities of glass or the covering of large building surface areas with one type of material only.

A bigger challenge is improving the relatively short lifetimes of third-gen PVs. Due to established cycles for the renovation of building exteriors as well as liability issues – which architects, consulting engineers and construction companies must adhere to – the lifetime of BIPV product components must achieve 20-30 years.

In conclusion, the anticipated novel design opportunities and technical performance characteristics associated with third-gen PVs make them especially attractive for architectural applications. However, it also needs to be made clear that any meaningful integration of these technologies in the building fabric will only arise from holistic planning and design approaches, which link the necessary power-engineering demands to the numerous existing and increasing requirements for building enclosures, architectural design and urban planning.

The properties desirable for a solar cell as part of an integrated structural product must be specified and consistently developed. The development of such BIPV products needs application-oriented research, to ensure products are meet practical requirements in a building.

The first- and seconnd-generation PV industry is still focused on bulk production, to benefit from mass production. But to meet the demands of an upcoming BIPV market, the low cost and flexibility of third-gen PV production provides a unique opportunity for the PV industry to make a transition to flexible production processes. Such a step would allow the PV industry to offer a structural and design flexibility for their BIPV products, which will provide architects the opportunity to create individual and alternating BIPV designs solutions

Lubricated, Nanotextured Surfaces Boost Performance of Condensers in Power and Desalination Plants

On a surface patterned with tiny pillars (white squares), and with a coating of a lubricant liquid that fills the spaces between the pillars, dome-shaped droplets of water condense but remain free to move quickly across the surface, unlike on conventional flat surfaces or ones with just the patterning, where they tend to stay stuck in place. The new surface treatment could provide a significant boost for power plants, water desalination and other applications. (Credit: Image courtesy of the Varanasi Laboratory)

ScienceDaily (Oct. 22, 2012) — Condensers are a crucial part of today’s power generation systems: About 80 percent of all the world’s powerplants use them to turn steam back to water after it comes out of the turbines that turn generators. They are also a key element in desalination plants, a fast-growing contributor to the world’s supply of fresh water. Now, a new surface architecture designed by researchers at MIT holds the promise of significantly boosting the performance of such condensers.

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The research is described in a paper just published online in the journal ACS Nano by MIT postdoc Sushant Anand; Kripa Varanasi, the Doherty Associate Professor of Ocean Utilization; and graduate student Adam Paxson, postdoc Rajeev Dhiman and research affiliate Dave Smith, all of Varanasi’s research group at MIT.

The key to the improved hydrophobic (water-shedding) surface is a combination of microscopic patterning — a surface covered with tiny bumps or posts just 10 micrometers (millionths of a meter) across, about the size of a red blood cell — and a coating of a lubricant, such as oil. The tiny spaces between the posts hold the oil in place through capillary action, the researchers found.

The team discovered that droplets of water condensing on this surface moved 10,000 times faster than on surfaces with just the hydrophobic patterning. The speed of this droplet motion is key to allowing the droplets to fall from the surface so that new ones can form, increasing the efficiency of heat transfer in a powerplant condenser, or the rate of water production in a desalination plant.

With this new treatment, “drops can glide on the surface,” Varanasi says, floating like pucks on an air-hockey table and looking like hovering UFOs — a behavior Varanasi says he has never seen in more than a decade of work on hydrophobic surfaces. “These are just crazy velocities.”

The amount of lubricant required is minimal: It forms a thin coating, and is securely pinned in place by the posts. Any lubricant that is lost is easily replaced from a small reservoir at the edge of the surface. The lubricant can be designed to have such low vapor pressure that, Varanasi says, “You can even put it in a vacuum, and it won’t evaporate.”

Another advantage of the new system is that it doesn’t depend on any particular configuration of the tiny textures on the surface, as long as they have about the right dimensions. “It can be manufactured easily,” Varanasi says. After the surface is textured, the material can be mechanically dipped in the lubricant and pulled out; most of the lubricant simply drains off, and “only the liquid in the cavities is held in by capillary forces,” Anand says. Because the coating is so thin, he says, it only takes about a quarter- to a half-teaspoon of lubricant to coat a square yard of the material. The lubricant can also protect the underlying metal surface from corrosion.

Varanasi plans further research to quantify exactly how much improvement is possible by using the new technique in powerplants. Because steam-powered turbines are ubiquitous in the world’s fossil-fuel powerplants, he says, “even if it saves 1 percent, that’s huge” in its potential impact on global emissions of greenhouse gases.

The new approach works with a wide variety of surface textures and lubricants, the researchers say; they plan to focus ongoing research on finding optimal combinations for cost and durability. “There’s a lot of science in how you design these liquids and textures,” Varanasi says.

Daniel Beysens, research director of the Physics and Mechanics of Heterogeneous Media Laboratory at ESPCI in Paris, says the concept behind using a lubricant liquid trapped by a nanopatterned surface, is “simple and beautiful. The drops will nucleate and then slide down quite easily. And it works!”

That further research will be aided by a new technique Varanasi has developed in collaboration with researchers including Konrad Rykaczewski, an MIT research scientist currently based at the National Institute of Standards and Technology (NIST) in Gaithersberg, Md., along with John Henry Scott and Marlon Walker of NIST and Trevan Landin of FEI Company. That technique is described in a separate paper also just published in ACS Nano.

For the first time, this new technique obtains direct, detailed images of the interface between a surface and a liquid, such as droplets that condense on it. Normally, that interface — the key to understanding wetting and water-shedding processes — is hidden from view by the droplets themselves, Varanasi explains, so most analysis has relied on computer modeling. In the new process, droplets are rapidly frozen in place on the surface, sliced in cross-section with an ion beam, and then imaged using a scanning electron microscope.

“The method relies on preserving the geometry of the samples through rapid freezing in liquid-nitrogen slush at minus 210 degrees Celsius [minus 346 degrees Fahrenheit],” Rykaczewski says. “The freezing rate is so fast (about 20,000 degrees Celsius per second) that water and other liquids do not crystalize, and their geometry is preserved.”

The technique could be used to study many different interactions between liquids or gases and solid surfaces, Varanasi says. “It’s a completely new technique. For the first time, we’re able to see these details of these surfaces.”

The enhanced condensation research received funding from the National Science Foundation (NSF), the Masdar-MIT Energy Initiative program, and the MIT Deshpande Center. The direct imaging research used NIST facilities, with funding from an NSF grant and the Dupont-MIT Alliance.