Should Galembeck get it right, devices that capture electricity from the air – much like solar cells capture sunlight – and using them to light a house or recharge an electric car might be possible.  Scientists already are in the early stages of developing such devices, according to a report presented at the 240th National Meeting of the American Chemical Society (ACS).

“Our research could pave the way for turning electricity from the atmosphere into an alternative energy source for the future,” said Galembeck. “If we know how electricity builds up and spreads in the atmosphere, we can also prevent death and damage caused by lightning strikes,” noting that lightning causes thousands of deaths and injuries worldwide and millions of dollars in property damage.  There’s a bunch of power up there for the taking if processes can be built for collection.

An Intense Lightning Strike Over Texas. Click image for the largest view.

The hope of harnessing the power of electricity formed naturally has tantalized scientists for centuries.  Famed inventor Nikola Tesla was among those who dreamed of capturing and using electricity from the air.  Sparks of static electricity formed as steam escaped from boilers. Workers who touched the steam even got painful electrical shocks.  Carpeting and shuffling feet can yield a shock at the faucet.

In the atmosphere electricity forms when water vapor collects on microscopic particles of dust and other material in the air.  But until now, scientists lacked adequate knowledge about the processes involved in formation and release of electricity from water in the atmosphere.  Scientists once believed that water droplets in the atmosphere were electrically neutral, and remained so even after coming into contact with the electrical charges on dust particles and droplets of other liquids. But new evidence suggested that water in the atmosphere really does pick up an electrical charge.

Galembeck a PhD is with University of Campinas in Campinas, SP, Brazil and his colleagues confirmed that idea, using laboratory experiments that simulated water’s contact with dust particles in the air. They used tiny particles of silica and aluminum phosphate, both common airborne substances, showing that silica became more negatively charged in the presence of high humidity and aluminum phosphate became more positively charged. High humidity means high levels of water vapor in the air – the vapor that condenses and becomes visible as “fog” on windows of air-conditioned cars and buildings on steamy summer days.

Galembeck explains, “This was clear evidence that water in the atmosphere can accumulate electrical charges and transfer them to other materials it comes into contact with. We are calling this ‘hygroelectricity,’ meaning ‘humidity electricity’.”
In the future, Galembeck believes, it may be possible to develop collectors, similar to the solar cells that collect the sunlight to produce electricity, to capture hygroelectricity and route it to homes and businesses. Just as solar cells work best in sunny areas of the world, hygroelectrical panels would work more efficiently in areas with high humidity, such as the northeastern and southeastern United States and the humid tropics.

Stretching the idea further, Galembeck said that a similar approach might help prevent lightning from forming and striking. He envisioned placing hygroelectrical panels on top of buildings in regions that experience frequent thunderstorms. The panels would drain electricity out of the air, and prevent the building of electrical charge that is released in lightning. His research group already is testing metals to identify those with the greatest potential for use in capturing atmospheric electricity and preventing lightning strikes.

“These are fascinating ideas that new studies by ourselves and by other scientific teams suggest are now possible,” Galembeck said. “We certainly have a long way to go. But the benefits in the long range of harnessing hygroelectricity could be substantial.”

A little simple observation illuminates the problem.  Moving air with high humidity seems to be the source.  Add in the effects of a thunderstorm and the energy gets concentrated until the atmosphere is saturated and the electrical potential grounds out – in a flash of light and clap of thunder.  The energy is a huge discharge without precise locating beforehand.

On the other hand the amount of electricity in the moist moving air is very thinly spread about.  A means to concentrate or discern the available potential – which might be quite small – needs an engineering feat of great innovation.  The power is out there, no doubt, collecting seems to be the goal.

It doesn’t seem that Galembeck and the colleagues have much new, but the understanding is growing.  What a collector might look like is purely imaginary. As far as this writer knows no functioning collector exists today.  But that doesn’t mean one can’t be designed.

The potential might be significant if a collector can be designed and return on its investment. Today that’s out there.  But if the past fifty years have made anything at all clear “out there” can be very soon indeed.  A little breeze on a hot humid day that a collector could use to power a home would cover a great deal of peak electrical demand.  It’s an idea well worth the imagineering.

PETE Solar Cell Test. Click image for more info

Melosh says in the Stanford press release, “This is really a conceptual breakthrough, a new energy conversion process, not just a new material or a slightly different tweak. It is actually something fundamentally different about how you can harvest energy.”

“Just demonstrating that the process worked was a big deal,” Melosh said. “And we showed this physical mechanism does exist; it works as advertised.”

Melosh’s group figured out that by coating a piece of semiconducting material with a thin layer of the metal cesium, it made the material able to use both light and heat to generate electricity.  Most silicon solar cells have been rendered inert by the time the temperature reaches 100º C; the “photon enhanced thermionic emission” device doesn’t hit peak efficiency until it is well over 200º C.  “What we’ve demonstrated is a new physical process that is not based on standard photovoltaic mechanisms, but can give you a photovoltaic-like response at very high temperatures,” Melosh said. “In fact, it works better at higher temperatures. The higher the better.”

And the materials needed to build a device to make the process work are cheap and easily available, meaning the power that comes from it will be affordable.

The process is called “photon enhanced thermionic emission,” or PETE and could reduce the costs of solar energy production enough for it to compete with oil as an energy source.  Because PETE performs best at temperatures well in excess of what a rooftop solar panel would reach, the devices will work best in solar concentrators such as parabolic dishes, which can get as hot as 800º C. Dishes are used in large solar farms similar to those proposed for the Mojave Desert in Southern California and usually include a thermal conversion mechanism as part of their design, which offers another opportunity for PETE to help generate electricity as well as minimize costs by meshing with existing technology.  There go all those plans for the huge arrays.  But its OK, getting to 60% efficiency changes the plans in a massive way as well.

Melosh explains how a PETE works, “The light would come in and hit our PETE device first, where we would take advantage of both the incident light and the heat that it produces, and then we would dump the waste heat to their existing thermal conversion systems. So the PETE process has two really big benefits in energy production over normal technology.”

Getting the efficiency up: Photovoltaic systems never get hot enough for their waste heat to be useful in thermal energy conversion, but the high temperatures at which PETE performs are perfect for generating usable high-temperature waste heat. Melosh calculates the PETE process can get to 50 percent efficiency or more under solar concentration, but if combined with a thermal conversion cycle, could reach 55 or even 60% – almost triple the efficiency of existing systems.  These technologies are already understood.

Its still way early – perhaps the paper published online Aug. 1 in Nature Materials is a competitive effort to get on record first.  Using a gallium nitride semiconductor in the “proof of concept” tests, the efficiency achieved in their testing was well below what they have calculated PETE’s potential efficiency to be – which they had anticipated. But the Melosh team used gallium nitride because it was the only material that had shown indications of being able to withstand the high temperature range they were interested in and still have the PETE process occur.  With the right material – most likely a semiconductor such as gallium arsenide, which is used in a host of common household electronics – the actual efficiency of the process could reach up to the 50 or 60 percent the researchers have calculated. They are already exploring other materials that might work.

Another advantage of the PETE system is that by using it in solar concentrators, the amount of semiconductor material needed for a device is quite small.  Melosh explains, “For each device, we are figuring something like a 6-inch wafer of actual material is all that is needed. So the material cost in this is not really an issue for us, unlike the way it is for large solar panels of silicon.”

That answers the questions where the cost of materials has been one of the limiting factors in the development of the solar power industry, so reducing the amount of investment capital needed to build a solar farm is a big advance.

Melosh closes with an academic’s understatement, “The PETE process could really give the feasibility of solar power a big boost. Even if we don’t achieve perfect efficiency, let’s say we give a 10 percent boost to the efficiency of solar conversion, going from 20 percent efficiency to 30 percent, that is still a 50 percent increase overall.”

The Stanford writer hits the competition with oil drum with “And that is still a big enough increase that it could make solar energy competitive with oil” while what they really need to beat is coal.  There is little oil used for power generation while coal is a major fuel source.  Getting competitive with coal would be great, burning coal is still a massive nasty effluent producer, and daylight high output solar would answer peak needs.

Taking the concept further, the PETE idea would be quite a basis to recalculate for orbital solar too.

Melosh and the Stanford team deserve some thanks for the breakout and some encouragement to keep at it.  The working prototype needs built, a bit of demonstration – seeing solar at anything in the 50% plus range is quite a feat, it’s a welcome crack in the efficiency war!

Back at the July fourth weekend, but Rick Cavallaro and the crew at fasterthanthewind.org proved a wind-powered vehicle traveled downwind faster than the wind speed.  Naysayers said it couldn’t be done, but the anarchist in this writer can’t help but spread the word.  It’s official – impossible but done.  The North American Land Sailing Association made it official July 27th, 2010 when it ratified the results.  And at better than 2.8 to 1 as well.

The achievement means physics texts, record books, and a pile of assumptions all have to be rewritten and reevaluated.  A new frontier, indeed.

Richard Jenkins wrote in part, “My heart is split between belittling idiots, and saluting eccentrics, and this downwind quest lay somewhere in the middle. These loonies were pursuing a pointless goal, doomed to failure, but there was some genuine merit in the myth and their enthusiasm . . . Traveling through zero apparent wind, with no stored power? Impossible. Why would you even attempt it?

A few months later I actually met the idiots in question and, to my surprise and concern we not only have a few mutual friends, but they seemed to be rather technically credible. But, everyone makes mistakes, and I let them off as decent people with a blinkered view of fundamentally flawed engineering . . .  A few months later they were claiming success!

There was, however, a growing momentum of technical people (who should have known better), saying that these idiots have actually proven that it is possible to travel faster than the wind going directly down wind.”

Jenkins shot the video:

The backing for the record attempts isn’t full of dopes either. The list includes JobyEnergy, Google, MetOne Instruments, and SportVision.  Some eccentric press picked it up including Wired Magazine, Popular Science, Discover, Sail Magazine, Discovery Channel, and Thin Air Designs.  Let the skeptics rest.

Cavallaro and his crew designed an innovative ultra-lightweight, aerodynamically sound cart with a 17-foot propeller that’s driven by the vehicle’s wheels. The wheels turn the prop, while the prop turns the wheels – possible thanks to an incredibly heavy-duty transmission – with the wind acting as an external power source that propels the cart faster than the wind itself.

The team set out to prove such a feat was possible and now that they’ve set a record they’ve fixed their sights on breaking it. Cavallaro hopes to reach three times the speed of the wind within a few weeks.

The counterintuitive idea that you can travel downwind faster than the wind is casus belli for aerodynamic arguments from Internet forums to college classrooms. The concept DWFTTW (Down Wind Faster Than The Wind) can cause world-renowned physicists to throw their Nobel Prizes in fits of rage.

Cavallaro explains, “If you’re on a bike and you’re going downwind, you don’t feel any wind anymore at all. You lose the power of the wind when you reach the wind speed, because there is no relative wind at that point.”   Working with a hang-gliding buddy, Cavallaro did the math and built a model to prove DWFTTW is possible.  The equations didn’t persuade anyone, “I thought people would say, ‘That’s cool,’ but they didn’t. They said, ‘Wow, you’re an idiot.’ So we decided to build a full-size one. That’s when we approached a couple of sponsors.”

Cavallaro lined up help from Google and JobyEnergy and set to work with the San Jose State University aero department on an ultralight, four-wheeled vehicle with a 17-foot-tall propeller. The vehicle is made mostly of foam and parallels the aerodynamics of a Formula 1 racecar.  The propeller is key to how it is possible to travel downwind faster than the wind. It’s also the source of the biggest misunderstandings about how the vehicle works.

Cavallaro goes on, “Skeptics think that the wind is turning the prop, and the car is turning the wheels, and that’s what makes the car go. That’s not the case. The wheels are turning the prop. What happens is the prop thrust pushes the vehicle.”

“It sounds like a perpetual motion machine – the wheels turn the prop, which turns the vehicle’s wheels, which turn the prop, which turns the vehicle’s wheels – but you’ve got the wind as an external power source,” Cavallaro said.

Building a transmission capable of transferring power from the wheels to the prop was almost as hard as convincing skeptics that the vehicle would work. It took longer than a year and a lot of trial and error to make it work. “You’ve got to come up with a transmission that can handle those loads, even though it’s not at a high horsepower,” Cavallaro said. “You break some things, and then you build bigger.”

Sometimes it’s the laws that break.  The anarchist in this writer is pleased; other laws can fall, too.  Many things, from BlackLight and cold fusion in physics on to chemistry and biology there’s a wealth of laws that need sent back to being ideas with new frontiers in their place.

Thus when research turns up ways to build panels at lower cost one perks up; there is 1.5 of an order of magnitude reduction to cover to get realistic pricing practicality.  That $20K has to get under $1K for the at risk part of the system – the panels themselves.

A Cornell University team led by William Dichtel, assistant professor of chemistry and chemical biology, has discovered a simple process for building an organic molecular framework that could pave the way for the development of more economical, flexible and versatile solar cells.  The work is described in the current issue of Nature Chemistry.

Dichtel’s strategy uses organic dye molecules assembled into a structure known as a covalent organic framework (COF). Organic materials have long been recognized as having potential to create thin, flexible and low-cost photovoltaic devices, but it has been proven difficult to organize their component molecules reliably into ordered structures likely to maximize device performance.

Stacked Covalent Organic Framework Photovoltaic Cell from Cornell

COFs are a class of materials first reported in 2005 and offer a new way to address this long-range ordering problem. Until now, the known methods for creating them had significant limitations.

Dichtel explains where his team began, “We had to develop a completely new way of making the materials in general.”  The strategy they chose uses a simple acid catalyst and relatively stable molecules called protected catechols to assemble key organic molecules into a neatly ordered two-dimensional sheet. These sheets stack on top of one another to form a lattice that provides pathways for a charge to move through the material.  The reaction is also reversible, allowing for errors in the process to be undone and corrected.

“The whole system is constantly forming wrong structures alongside the correct one,” Dichtel said, “but the correct structure is the most stable, so eventually, the more perfect structures end up dominating.” The result is a structure with high surface area that maintains its precise and predictable molecular ordering over large areas.

The Cornell team used X-ray diffraction to confirm the material’s molecular structure and surface area measurements to determine its porosity.

Once the framework is assembled, the pores between the molecular latticework could potentially be filled with another organic material to form a light, flexible, highly efficient and easy-to-manufacture solar cell.  The next step is to begin testing ways of filling in the gaps with complementary molecules.

At the core of the structure are molecules called phthalocyanines, a class of common industrial dyes used in products from blue jeans to ink pens.  Phthalocyanines are also closely related in structure to chlorophyll, the compound in plants that absorbs sunlight for photosynthesis. The compounds absorb almost the entire solar spectrum – a rare property for a single organic material.  This makes the Cornell effort extraordinary in scope.

Dichtel explains more with, “For most organic materials used for electronics, there’s a combination of some design to get the materials to perform well enough, and there’s a little bit of an element of luck. We’re trying to remove as much of that element of luck as we can.”

The structure by itself is not a solar cell just yet, but it is a model that will significantly broaden the scope of materials that can be used in COFs, Dichtel said. “We also hope to take advantage of their structural precision to answer fundamental scientific questions about moving electrons through organic materials.”

“This is the very beginning of our work,” Dichtel said.

Just so, but this work looks very good, very good indeed.

(The Cornell press release is one of the best this year as well.)

WestConnect System Map. Click image for the largest view.

The wind is packed with kinetic energy – molecules in motion that can be used to make other molecules move such as commonly seen windmill water pumps, or used to compress gas and converted into electricity.  When it blows.  When the wind is becalmed, there isn’t any energy other than the latent heat. When the NREL made its assertion one had to read the study.

Dr. Debra Lew, project manager for the study, said in her statement, “If key changes can be made to standard operating procedures, our research shows that large amounts of wind and solar can be incorporated onto the grid without a lot of backup generation.”

The situation now has it that large coal, natural gas or nuclear plants would always need to stand ready to provide backup power whenever the wind ceased to blow or clouds blocked the sun.

The NREL scientists looked at that supposition head on and found that ‘stand ready’ would be largely baseless when the parameters were optimized.  It concluded that in the West, a broad distribution of wind turbines and solar generation would essentially smooth out the supply of renewable power.  Lew explained simply, “When you coordinate the operations between utilities across a large geographic area, you decrease the effect of the variability of wind and solar energy sources, mitigating the unpredictability of Mother Nature.”

Called ‘The Western Wind and Solar Integration Study” it examines the benefits and challenges of integrating enough wind and solar energy capacity into the grid to produce 35 percent of its electricity by 2017. The study finds that this target is technically feasible and does not necessitate extensive additional infrastructure, but does require key changes to current operational practice. The results offer a first look at the issue of adding significant amount of variable renewable energy in the West and will help utilities across the region plan how to ramp up their production of renewable energy as they incorporate more wind and solar energy plants into the power grid. (Pdf download – 20.6MB)

The technical analysis performed in the study shows that it is operationally possible to accommodate 30 percent wind and 5 percent solar energy penetration. To accomplish such an increase, utilities will have to substantially increase their coordination of operations over wider geographic areas and schedule their generation deliveries, or sales, on a more frequent basis. Currently generators provide a schedule for a specific amount of power they will provide in the next hour. More frequent scheduling would allow generators to adjust that amount of power based on changes in system conditions such as increases or decreases in wind or solar generation.

Being a government animal the NREL looks at the policy issues rather than the costs to the ratepayers.  But one can infer some significant fuel costs will be taken out from the calculation when the study says integrating wind as suggested “would also decrease fuel and emissions costs by 40 percent.”  That assertion deserves some testing considering the governments record in making predictions.

The study suggests the results would come with other benefits.  Existing transmission capacity can be more fully utilized to reduce the amount of new transmission that needs to be built.   Coordinating the operations of utilities to facilitate the integration of wind and solar energy can provide substantial savings by reducing the need for additional back-up generation, such as instant on natural gas-burning plants.

And the fly in the thinking is that use of wind and solar forecasts in utility operations to predict when and where it will be windy and sunny is essential for cost-effectively integrating these renewable energy sources. Yet the meteorologists are getting quite good when only looking hours out.

When one looks at a map of the territory involved it doesn’t seem farfetched at all.  While not using the deep resources of the Midwest or the Northwest the five states when combined for managing intermittency do have what looks like a solid 35 percent or better power resource potential.

Event though the study is from a government agency, the study was undertaken by a team of wind, solar and power systems experts across both the private and public sectors.  It’s a long list of contributors.  The work is mainly an operations study, rather than a transmission study, although different scenarios model different transmission build-outs to deliver power. Using a detailed power system production simulation model, the study identifies operational impacts and challenges of wind energy penetration up to 30% of annual electricity consumption.

The NREL page links to the pdf as well as the earlier Eastern Wind Integration and Transmissions study page with a pdf link to the 17.8 MB download.

Many thoughtful people discount wind for valid reasons.  But the fact remains the energy in moving air is significant and one way to overcome the intermittency issue without having massive electron storage is to well, get organized.

Getting organized and planning things out over a big resource base has great potential that mustn’t be overlooked.

Professor Harry Atwater at his namesake research group at Caltech explains the new solar material made of tiny silicon wires could “dramatically reduce the cost of making a silicon solar cell. Instead of the expensive process of making a wafer and slicing it up with a saw, throwing away two thirds of it,” says Atwater, “We grow the material and literally peel it off. The plastic sheet is peeled off like scotch tape off a tape dispenser.”

The savings in the new cell technology is that only 2% of the cell is composed of semiconductors – the most expensive component. The other 98% is made from inexpensive plastic, which should translate into significantly lower prices for consumers compared to existing solar cell technologies.  That lower price is in inverse proportion to the rate at which the cells convert sunlight to electrical power.

Silicon Wire Photon Collector. Click image for the largest view.

Professor Atwater and his colleagues used microscale silicon wires (microwires) slightly thicker than nanowires, and poured a polymer containing light-reflecting nanoparticles into the spaces between them. The polymer scatters unabsorbed light back onto the rods and this, combined with a silver reflecting layer at the bottom of the device, allows the cells to absorb up to 85 per cent of incoming light.  But losses mostly from imperfections in the crystal structure of the microwires drive the overall efficiency below the 20 per cent achieved by the best crystalline silicon cells.

The point is that while these cells are merely as efficient as very good photovoltaic panels, they use only about a hundredth of the material. Also the new design is highly flexible: built on a bed of silicon, Atwater’s micrwire arrays can simply be peeled off and stuck pretty much wherever you want. “They could even be integrated into buildings, as components that match the shape of roof tiles,” says Atwater. He has started up a company, Alta Devices, to do just that, and has recently received research funding from the US Department of Energy.

Wire Array Structure Ready for Optical Measurements. Click image for more info.

At about the same thickness as conventional photovoltaic cells, Atwater’s new cells contain far less silicon. The team is currently working on expanding the voltage capacity and size of the cells in order to manufacture large, flexible sheets that can be manufactured inexpensively using “roll-to-roll” fabrication equipment.

The Caltech team had Dave Bullock from Wired.com in for a tour.  The article is short but the photos quite good. Over the course of nine photos one comes away with a good idea of the production process. It’s worth the click and a look.  The full paper from Nature Materials Letters is available in a pdf download.

There are two primary types of photovoltaic cells. The first is a solid silicon-based PV cell that is very efficient, but also expensive to make and relatively fragile. The second is a thin film cell, which is relatively cheap to make but not as efficient. The Caltech group’s new microwire material potentially bridges that gap, creating a photovoltaic cell that should be low cost to manufacture, but which is close to the efficiency of traditional silicon-based solar panels and perhaps not so easily broken.

This is just round one in the research.  Intuition suggests that much of the regular silicon research might well transfer to Atwater’s concept. We’ll see – this idea is worth watching and it seems Atwater’s team is looking into it as well.

Benjamin Wiley, an assistant professor of chemistry at Duke University is leading a team of chemists that have perfected a simple way to make tiny copper nanowires (CuNW) in quantity. The cheap conductors are small enough to be transparent, making them ideal for thin-film solar cells, flat-screen TVs and computer monitors, and flexible displays.  The team reported its findings online this week in Advanced Materials.

Wiley says the nanowires made of copper perform better than carbon nanotubes, and are much cheaper than silver nanowires.  The price of the materials used to synthesize 1 gram of CuNWs is $5.94, while $32.59 is needed for 1 gram of silver nanowires. The team’s paper reports it would take about $3.00 worth of CuNWs, less than half a gram, to coat 1 m² of glass.  This is a very different economic proposition.

Copper Nanowires. Click image for more info.

Currently indium tin oxide (ITO) is used as the transparent layer for the electrode in thin-film solar cells, the latest flat-panel TVs and computer screens producing images. ITO has drawbacks: it is brittle, making it unsuitable for flexible screens; its production process is inefficient; and it is expensive and becoming more so because of increasing demand.  Wind and hail would kill current photovoltaic panels by breaking the conductive layer if not the glass.  ITO works well, but coming up with a replacement is crucial.

Wiley says, “If we are going to have these ubiquitous electronics and solar cells we need to use materials that are abundant in the earth’s crust and don’t take much energy to extract.” He points out that there are very few materials that are known to be both transparent and conductive, which is why ITO is still being used despite its drawbacks.

That illustrates the importance of why Wiley’s new work showing that copper, which is a thousand times more abundant than indium, can be used to make a film of nanowires that is both transparent and conductive.

Silver nanowires also perform well as a transparent conductor, and Wiley contributed to a patent on the production of them as a graduate student. But silver, like indium, is rare and expensive. Other researchers have been trying to improve the performance of carbon nanotubes as a transparent conductor, but without much progress.

Wiley says, “The fact that copper nanowires are cheaper and work better makes them a very promising material to solve this problem.”

Wiley’s lab is the first to demonstrate that copper nanowires perform well as a transparent conductor. Other researchers have produced copper nanowires, but on a much smaller scale.  Wiley says the process will need to be scaled up for commercial use, and there are two other problems to solve as well: preventing the nanowires from clumping, which reduces transparency, and preventing the copper from oxidizing, which decreases conductivity. Once the clumping problem has been worked out, Wiley believes the conductivity of the copper nanowires will match that of silver nanowires and ITO.

Wiley and his students, PhD candidate Aaron Rathmell and undergraduate Stephen Bergin, grew the copper nanowires in a water-based solution. “By adding different chemicals to the solution, you can control the assembly of atoms into different nanostructures,” Wiley said. In this case, when the copper crystallizes, it first forms tiny “seeds,” and then a single nanowire sprouts from each seed. It’s a mechanism of crystal growth that has never been observed before.

Because the process is water-based, and because copper nanowires are flexible, Wiley thinks the nanowires could be coated from solution in a roll-to-roll process, like newspaper printing, which would be much more efficient than the ITO production process.

Wiley says, “We think that using a material that is a hundred times cheaper will be even more attractive to venture capitalists, electronic companies and solar companies who all need these transparent electrodes.”  A patent application for the process has been filed and Wiley expects to see copper nanowires in commercial use in the not-too-distant future. He notes that there is already investment financing available for the development of transparent conductors based on silver nanowires.

This is great news.  Solar panels send roof insurers into apoplexy because of the premium required to replace damaged panels taking a wide swath of the available area out of the productivity zone.  Lowering costs is critically important.  The other side also can benefit, more efficient display panels can cut the electrical energy needed to expand the human standard of living.  The Duke team’s work is much more important than a glance indicates.  The work should help in the orbital solar collector effort as well.

These microscopic planktonic organisms carry out the same chlorophyll driven photosynthesis process as green plants on land.

Proteorhodopsin Containing Bacteria. Click image for more info.

American scientists discovered in 2000 that many marine bacteria contain a gene in their genome that encodes a new kind of light-harvesting pigment: proteorhodopsin.  Proteorhodopsins are membrane-embedded, light-driven proton pump proteins that allow harvesting of energy from sunlight and are related to the pigment in the retina that enables human vision in less intense light.

Now the first direct evidence for the functioning of proteorhodopsin in native marine bacteria is being presented, based on mutational analysis in a marine bacterium. At the same time the Swedish and Spanish study shows that proteorhodopsin-mediated phototrophy, the process of acquiring energy from light, allows marine bacteria to better survive periods of starvation in nutrient-depleted ocean zones.

Pinhassi explains, “Bacteria in the surface ocean are swimming in a sea of light, and it may not be all that surprising that evolution has favored microorganisms that can use this abundant energy source.”  If one considers that a liter of seawater on average contains around a billion bacteria, many of which contain proteorhodopsin, it becomes important and worthwhile to understand the novel mechanisms for marine bacteria to efficiently use solar energy.  The activity of these bacteria play a crucial role in the global carbon cycle by determining oceanic production of CO² through respiration and determining how the fluxes of energy that are fixed by photosynthesis are channeled through marine food chains.

“Bacteria in the surface ocean are swimming in a sea of light, and it may not be all that surprising that evolution has favored microorganisms that can use this abundant energy source,” says Pinhassi.

While the first impulse on this news might not be a major jolt, the implications and the potential possibilities cause considerable fascination.  The Swedish and Spanish team has come upon methods that serve to show how the bacteria are using the genes and feeding their lives without photosynthesis.  At a decade in the knowledge inventory, the gene builders could now have new routes to harvesting solar energy.

What, where, how and when the gene can be expressed could serve organism engineering in ways yet to be dreamed of.  This is the first light on a newly discovered light to bio fuel path.  It may even give algae some competition someday.

The design is an optical innovation. After the surface lenses focuses the light with a two-dimensional lens array a secondary optic, multimode slab waveguide is used as a secondary to collect and homogenize the sunlight.

Reflective facets fabricated on the backside of the waveguide act as fold mirrors to couple sunlight into the waveguide at angles, which exceed the critical angle for total internal reflection. These facets occupy a small fraction of the total waveguide surface and enable high geometric concentrations despite decoupling loss if light strikes a subsequent coupling region.

This geometry yields a thin, flat profile for moderate concentration systems that may be fabricated by low-cost roll manufacturing. The analyses of tradeoffs show optimized designs can achieve 90% and 82% optical efficiency at 73x and 300x concentration, respectively.

Karp and his group may be in the money – for concentrator photovoltaic (CPV) to be cost-effective, the complete cost of the optics, assembly and mechanical tracking must not exceed the cost savings gained from using small area PV cells.  The team gets it; the place to shave expense is in the collection of the light, saving a big share with reduced photovoltaic cell counts.

Sunlight collected by each aperture of the arrayed primary collector is coupled into a common slab waveguide using localized injection features such as prisms, gratings or scattering surfaces. Rays that exceed the critical angle defined by Snell’s Law propagate via total internal reflection (TIR) within the waveguide to the exit aperture, typically at the edge of the slab.  TIR is a complete reflection with negligible spectral or polarization-dependent losses, which enables long propagation lifetimes.  The waveguide transports sunlight collected over the entire input aperture to a single PV cell placed at the waveguide edge. PV alignment becomes trivial since comparatively large cells are cemented to the waveguide edge(s).  Fewer PV cells reduce connection complexity and allow one heat sink to manage the entire system output.

Planar MicroOptic Solar Concentrator. Click image for more info.

As illustrated, the innovation is going beyond a lens that concentrate an area to a PV, Karp’s waveguide collects several lenses to one or more PVs.  This has to dramatically cut costs and allow budgeting for extremely efficient PVs.

The goal was to design a concentrator optic, which could be fabricated at an extremely low cost per unit area. Constraining the design to be compatible with a continuous roll process-manufacturing platform, as opposed to injection molded and assembled elements, maximizes the cost advantage of CPV.  Roll processing can perform a range of functions on rigid or flexible substrates such as embossing of refractive or diffractive structures, dielectric and metallic deposition and the joining of multiple processed layers.

The team’s paper, in the January 2010 issue of the journal Optics Express, available in a pdf download, covers in detail concentrator geometry, coupling the waveguide, optimizing the system, and the building of a prototype.  The paper also discusses the method Karp and his team use to self align the concentrator during fabrication. At 12 pages and lucid for the non-optic expert, it’s a worthwhile read.

Prototype Planar MicroOptic Solar Concentrator. Click image for more info.

The team took their prototype outdoors for testing to find the prototype system reached 90% of its maximum optical efficiency with  ± 1° angular acceptance.  The optical efficiency of the prototype system was significantly lower than the optimized simulations using custom optical elements.  Despite its relative inefficiency the experimental measurements were in close agreement with the optical model and support the notion that optimized designs would also perform with high efficiency. The team is currently pursuing variations of the basic structure to increase both concentration and optical efficiency.

The team has demonstrated self-aligned fabrication using off-the-shelf components to create a 37.5x prototype concentrator with 32.4% optical efficiency. Systems with greater than 80% efficiency are expected when using a custom lens array with a 100% fill factor and minimal aberrations.  A CPV with multimode waveguides opens a new design space for large-scale concentrator optics with the added benefits of flux uniformity and fewer PV cells in a thin, planar geometry.

OK.  That’s all real technical.  But it works, the lens array and the waveguide beneath can be roll to roll process manufactured.  Mount some photovoltaic cells along the selected edge and you have a low cost high efficiency solar panel.  One has to like this, especially if the savings can justify the cost of a solar tracking system to keep the panel squarely facing the sun.

Something has to be done about solar panel costs – it looks like Karp and his team have a very good shot at helping build a much larger market.

For a sheet of graphene to be useful as a solar collector of light photons, the sheet must be large enough. To use the absorbed solar energy for electricity the sheet can’t be made too large. Scientists find large sheets of graphene difficult to work with, and the size specification even harder to control.

The bigger the graphene sheet, the stickier it is, making it more likely to attract and attach onto other graphene sheets. Multiple layers of graphene prevent electricity production.

Indiana University at Bloomington chemists have devised an unusual solution – attach a constructed “3-D bramble patch” to each side of the carbon sheet. With a method newly devised, the IU team say they are able to dissolve sheets containing as many as 168 carbon atoms, a first, that may make large sheets of carbon available for light collection.

Graphene Sheets Built Up With Hydrocarbon Cages. Click image for more info.

The IU team’s report, online April 9, will appear in a future issue of Nano Letters.

Chemist Liang-shi Li, who led the research said, “Our interest stems from wanting to find an alternative, readily available material that can efficiently absorb sunlight. At the moment the most common materials for absorbing light in solar cells are silicon and compounds containing ruthenium. Each has disadvantages.”  Ruthenium-based solar cells can potentially be cheaper than silicon-based ones, but ruthenium is a rare metal on Earth, as rare as platinum, and will run out quickly when the demand increases.  Cost and availability loom to discourage investment.

The graphene idea has been around a while.  Chemists and engineers experimenting with graphene have come up with a whole host of strategies for keeping single graphene sheets separated. The most effective solution prior to the IU team’s paper was breaking up graphite from the top-down into sheets and then wrap polymers around them to keep them isolated from one another. But this approach makes graphene sheets with random sizes that are too large for the light absorption needed for solar cells.

Graphene in a Constructed Bramble Patch. Click image for more info.

Li and the team tried an innovative idea. By attaching a semi-rigid, semi-flexible, three-dimensional “sidegroup” to the sides of the graphene, they were able to keep graphene sheets as big as 168 carbon atoms from adhering to one another. With the new dynamic method, they could make the graphene sheets from smaller molecules built bottom-up so that they are uniform in size. To the scientists’ knowledge, it is the biggest stable graphene sheet ever made with the bottom-up approach.  Check the image below for more detail.

The sidegroup consists of a hexagon shaped carbon ring and three long, barbed tails made of carbon and hydrogen. Because the graphene sheet itself is rigid, the sidegroup ring is forced to rotate about 90 degrees relative to the plane of the graphene. The three “brambly” tails are free to whip about, with two of them tending to enclose the graphene sheet of which they are attached.  This makes up a dynamic box or cage for the graphene sheet.

But he tails don’t merely act as a cage; they also serve as a handle for an organic solvent so that the entire structure can be dissolved. Li and his colleagues were able to dissolve 30 mg of the specimens per 30 mL of solvent.  The ability to breakdown the graphene is significant as well.

Li said, “In this paper, we found a new way to make graphene soluble. This is just as important as the relatively large size of the graphene itself.”  This new know how may make all the difference for building things using graphene across a range of products.

How well does the new graphene assembly work?  To test the effectiveness of their graphene light acceptor, the scientists constructed rudimentary solar cells using titanium dioxide as an electron acceptor. The team has been able to achieve a 200-microampere-per-square-cm current density and an open-circuit voltage of 0.48 volts. The graphene sheets absorbed a significant amount of light in the visible to near-infrared range (200 to 900 nm or so) with peak absorption occurring at 591 nm.  As black as this kind of thing must be – those are good numbers.

The team is in the process of redesigning the graphene sheets with sticky ends so that they bind to titanium dioxide – a construction that will improve the efficiency of the solar cells.

Liang-shi Li’s team includes PhD students Xin Yan and Xiao Cui and postdoctoral fellow Binsong Li.  Along with grants form the National Science Foundation, the American Chemical Society Petroleum Research Fund put money into the research.

This is quite a new start for graphene as a photovoltaic solar collector material.  Kicking up the micro amp from a cm² to a meter² is 100 or 200 micro amps then is .02 amps, not a bad start at nearly a half-volt.