THE DEFINITIVE BLOG FOR EVERYTHING YOU NEED TO KNOW ABOUT THE ENVIRONMENT YOU LIVE IN, WITH REFERENCE TO LIFE, EARTH AND COSMIC SPACE SCIENCES, PRESENTED BY ENVIRONMENTAL ENGINEER DORU INDREI, ENVIRONMENTAL QUALITY AND ENERGY SPACIALIST
"Life is not about what we know, but what we don't know, craving the unthinkable makes it so amazing, that is worth dying for."Doru Indrei
Normally Oxygen is fairly tight bound to the hydrogen in water. If it can be easily removed, it has potential benefits for certain energy and fuel systems. A team of researchers at MIT has found one of the most effective catalysts ever discovered for splitting oxygen atoms from water molecules — a key reaction for advanced energy-storage systems, including electrolyzers, to produce hydrogen fuel and rechargeable batteries. This new catalyst liberates oxygen at more than 10 times the rate of the best previously known catalyst of its type.
The new compound, composed of cobalt, iron and oxygen with other metals, splits oxygen from water (called the Oxygen Evolution Reaction, or OER) at a rate at least an order of magnitude higher than the compound currently considered the gold standard for such reactions, the team says. The compound’s high level of activity was predicted from a systematic experimental study that looked at the catalytic activity of 10 known compounds.
The team, which includes materials science and engineering graduate student Jin Suntivich, mechanical engineering graduate student Kevin J. May and professor Yang Shao-Horn, published their results in Science on Oct. 28.
The scientists found that reactivity depended on a specific characteristic: the configuration of the outermost electron of transition metal ions. They were able to use this information to predict the high reactivity of the new compound — which they then confirmed in lab tests.
"We not only identified a fundamental principle that governs the OER activity of different compounds, but also we actually found this new compound" based on that principle, says Shao-Horn.Environment Clean Generations
Many other groups have been searching for more efficient catalysts to speed the splitting of water into hydrogen and oxygen. This reaction is key to the production of hydrogen as a fuel to be used in cars; the operation of some rechargeable batteries, including zinc-air batteries; and to generate electricity in devices called fuel cells. Two catalysts are needed for such a reaction — one that liberates the hydrogen atoms, and another for the oxygen atoms — but the oxygen reaction has been the limiting factor in such systems.
Fuel cells come in many varieties; however, they all work in the same general manner. They are made up of three segments which are sandwiched together: the anode, the electrolyte, and the cathode. Two chemical reactions occur at the interfaces of the three different segments. The net result of the two reactions is that fuel is consumed, water or carbon dioxide is created, and an electric current is created, which can be used to power electrical devices, normally referred to as the load.Environment Clean Generations
At the anode a catalyst oxidizes the fuel, usually hydrogen, turning the fuel into a positively charged ion and a negatively charged electron. The electrolyte is a substance specifically designed so ions can pass through it, but the electrons cannot. The freed electrons travel through a wire creating the electric current. The ions travel through the electrolyte to the cathode. Once reaching the cathode, the ions are reunited with the electrons and the two react with a third chemical, usually oxygen, to create water or carbon dioxide.
In addition, even though they have already found the highest rate of activity yet seen, they plan to continue searching for even more efficient catalyst materials. "It’s our belief that there may be others with even higher activity," Shao-Horn says.Environment Clean Generations
Jens Norskov, a professor of chemical engineering at Stanford University and director of the Suncat Center for Interface Science and Catalysis there, who was not involved in this work, says, "I find this an extremely interesting rational design approach to finding new catalysts for a very important and demanding problem."
The first "green train" in Europe to harness solar energy is running between Paris and Amsterdam.
Sixteen thousand solar panels produce 3,300 megawatts per hour of electricity.
The electricity generated on-site reduces energy losses and transportation costs.
High-speed international trains linking Paris and Amsterdam as of Monday became the first in Europe to use electricity generated by solar panels installed in a tunnel on the line.
At a cost of 15.6 million euros, project managers say the 3.6-kilometer tunnel crossing Antwerp, in northern Belgium, is fitted with 16,000 solar panels covering 50,000 square meters, roughly eight football fields.
The panels produce 3,300 megawatts per hour of electricity, or the average annual consumption of nearly 1,000 families.
The first "green train" left Antwerp on Monday for the Dutch border. While it was filled as usual with commuters and students, for a dozen or so kilometers, its engines plugged into the solar energy source fitted along the line.
The electricity produced feeds into the line's infrastructure, for lighting, signals and in-train power points, said Frederic Sacre, spokesman for Infrabel, which runs the rail network.
"By using electricity generated on-site, we eliminate energy losses and transport costs," said Steven De Tollenaere, head of project developers Enfinity, which leans on state subsidies backing energy use that meets clean climate goals.
The company hopes the project will allow it to develop new installations in the United States and other parts of the world, citing train hangars as ideal sites for such charging points in the future.
Householders own multitude of choices for enhancement that may bump up the value of their home even as improving its comfort.
Are you a home owner and thinking to improve your house completely either by repainting a room or have you thought about projects which could add aesthetic value?
Reduce your house’s heat with the help of radiant barrier as it is easy to use, safe to handle and effectual at plummeting heat loss and it can also turn back the extreme rays of the sun during the summer time and keeping the house cooler too.
Radiant barrier is a comparatively latest item for consumption that consumers are gradually becoming aware of. It has a reflective opus placed in your attic that reflects heat before it enters your home. Just by applying a coat of paint under the decking surface heat could be transferred and it also seals up the cracks and crevices in the wall.
Radiant barriers are materials installed in buildings to condense summer heat gain and winter heat loss, also to cut building heating and cooling energy usage.
The main advantage of attic radiant barrier is that it helps in reducing air-conditioning cooling in warm or hot climates. Radiant barriers generally consist of a slight sheet or veneer of an extremely reflective material, typically aluminum applied to one or double sides of a number of substrate supplies. These substrates consist of Kraft paper, plastic films, cardboard, plywood sheathing, and air infiltration barrier material.
It is expected that a radiant barrier have the potential to slab 97% of the radiant heat immersed through a roof's surface; this can result in a 30-degree cutback in attic or creep space temperature.
Spray foam insulation:It is a general and an essential thing that we insulateour homes to condense speed of heat loss. The insulation is carried by using spray foam in the opening, chink and the crevice such that there is no amend of heat linking the walls of the house and the environment.
Some of the Benefits of Spray Foam Insulation Include:
Reduction in sound diffusion, better environment, Keep Pests Outdoors, reduction in noise levels, Reduction in moisture and the development of Mold, apart from this it also has certain benefits like generating improved environment by plummeting dust, dirt, and pollen, Saving Energy structuring effectiveness & a Green Environment, produces air tight thermal seal, stops air and dampness penetration, Makes your home more comfortable, trim down capacity requirements, maintenance and wear of HVAC equipment.
Attic ventilation keeps the loft cooler in the summer and dry in the winter. Attic ventilation keeps the loft cooler in the summer and dry in the winter. Good exposure to air boosts the act of your insulation, expands the life of your HVAC unit and saves you even more money on energy bills.
Benefits of attic ventilation: it extends the life of your roof, cut downs the load on your HVAC system, stops ice damming in colder regions, and diminishes moisture build-up in the loft.
LED lighting can save more electricity than solar will produce, according to LED pioneer Roland Haitz, former chief technology officer, semiconductor products group, Hewlett-Packard (later Agilent).
"20 percent of the world's electricity that's generated is used for lighting. Three quarters of that can be saved by using LEDs; 15 percent of today's electricity consumption can be saved," he said at the Economist'sInnovation Summit.
He said that there was a lot of noise around green technology and that projects relating to solar cells and wind energy tend to get a lot of government funding. However, he believes that focusing on technologies such as LEDs could make a bigger difference. Solar energy currently accounts for 0.5 percent of the world's supply, although some have predicted that it could provide as much as 22 percent by 2050.
Haitz is in a good place to comment, as he has had the LED equivalent of Moore's Law named after him. Haitz's Law states that every decade, the cost per lumen falls by a factor of 10, the amount of light generated per LED package increases by a factor of 20 for a given wavelength of light.
Haitz says that LED lighting will be made extremely cheaply, with much better light output than the current 200 lumens per watt which are currently possible, compared with a standard 100 watt incandescent lightbulb which has an efficiency of around 17 lumens per watt.
While roofs across the world sport photovoltaic solar panels to convert sunlight into electricity, a Duke University engineer believes a novel hybrid system can wring even more useful energy out of the sun's rays.
nstead of systems based on standard solar panels, Duke engineer Nico Hotz proposes a hybrid option in which sunlight heats a combination of water and methanol in a maze of glass tubes on a rooftop. After two catalytic reactions, the system produces hydrogen much more efficiently than current technology without significant impurities. The resulting hydrogen can be stored and used on demand in fuel cells.
For his analysis, Hotz compared the hybrid system to three different technologies in terms of their exergetic performance. Exergy is a way of describing how much of a given quantity of energy can theoretically be converted to useful work.
"The hybrid system achieved exergetic efficiencies of 28.5 percent in the summer and 18.5 percent in the winter, compared to 5 to 15 percent for the conventional systems in the summer, and 2.5 to 5 percent in the winter," said Hotz, assistant professor of mechanical engineering and materials science at Duke's Pratt School of Engineering.
The paper describing the results of Hotz's analysis was named the top paper during the ASME Energy Sustainability Fuel Cell 2011 conference in Washington, D.C. Hotz recently joined the Duke faculty after completing post-graduate work at the University of California-Berkeley, where he analyzed a model of the new system. He is currently constructing one of the systems at Duke to test whether or not the theoretical efficiencies are born out experimentally.
Hotz's comparisons took place during the months of July and February in order to measure each system's performance during summer and winter months.
Like other solar-based systems, the hybrid system begins with the collection of sunlight. Then things get different. While the hybrid device might look like a traditional solar collector from the distance, it is actually a series of copper tubes coated with a thin layer of aluminum and aluminum oxide and partly filled with catalytic nanoparticles. A combination of water and methanol flows through the tubes, which are sealed in a vacuum.
"This set-up allows up to 95 percent of the sunlight to be absorbed with very little being lost as heat to the surroundings," Hotz said. "This is crucial because it permits us to achieve temperatures of well over 200 degrees Celsius within the tubes. By comparison, a standard solar collector can only heat water between 60 and 70 degrees Celsius."
Once the evaporated liquid achieves these higher temperatures, tiny amounts of a catalyst are added, which produces hydrogen. This combination of high temperature and added catalysts produces hydrogen very efficiently, Hotz said. The resulting hydrogen can then be immediately directed to a fuel cell to provide electricity to a building during the day, or compressed and stored in a tank to provide power later.
The three systems examined in the analysis were the standard photovoltaic cell which converts sunlight directly into electricity to then split water electrolytically into hydrogen and oxygen; a photocatalytic system producing hydrogen similar to Hotz's system, but simpler and not mature yet; and a system in which photovoltaic cells turn sunlight into electricity which is then stored in different types of batteries (with lithium ion being the most efficient).
"We performed a cost analysis and found that the hybrid solar-methanol is the least expensive solution, considering the total installation costs of $7,900 if designed to fulfill the requirements in summer, although this is still much more expensive than a conventional fossil fuel-fed generator," Hotz said.
Costs and efficiencies of systems can vary widely depending on location -- since the roof-mounted collectors that could provide all the building's needs in summer might not be enough for winter. A rooftop system large enough to supply all of a winter's electrical needs would produce more energy than needed in summer, so the owner could decide to shut down portions of the rooftop structure or, if possible, sell excess energy back to the grid.
"The installation costs per year including the fuel costs, and the price per amount of electricity produced, however showed that the (hybrid) solar scenarios can compete with the fossil fuel-based system to some degree," Hotz said. 'In summer, the first and third scenarios, as well as the hybrid system, are cheaper than a propane- or diesel-combusting generator."
This could be an important consideration, especially if a structure is to be located in a remote area where traditional forms of energy would be too difficult or expensive to obtain.
Hotz's research was supported by the Swiss National Science Fund. Joining him in the study were UC-Berkeley's Heng Pan and Costas Grigoropoulos, as well as Seung H. Ko of the Korea Advanced Institute of Science and Technology, Daejon.
The future of solar-powered houses is clear. People could live in glass houses and look at the world through rose-tinted windows while reducing their carbon emissions by 50 percent thanks to QUT Institute of Sustainable Resources research.
Professor John Bell said QUT had worked with a Canberra-based company Dyesol, which is developing transparent solar cells that act as both windows and energy generators in houses or commercial buildings.
He said the solar cell glass would make a significant difference to home and building owners’ energy costs and could in fact generate excess energy that could be stored on onsold.
Professor Bell said the glass was one of a number of practical technologies that would help combat global warming which was a focus of research at the ISR.
“The transparent solar cells have a faint reddish hue but are completely see-through,” Professor Bell said.
“The solar cells contain titanium dioxide coated in a dye that increases light absorption.
“The glass captures solar energy which can be used to power the house but can also reduce overheating of the house, reducing the need for cooling.”
Professor Bell said it would be possible to build houses made entirely of the transparent solar cells.
“As long as a house is designed throughout for energy efficiency, with low-energy appliances it is conceivable it could be self-sustaining in its power requirements using the solar-cell glass,” he said.
“Australian housing design tends to encourage high energy use because electricity is so cheap.
“But it is easy to build a house that doesn’t need powered cooling or heating in Queensland.”
Professor Bell said the solar cell glass was the subject of two Australian Research Council Linkage grants to QUT researchers to investigate ways to increase its energy absorption and to reduce the effects of “shadowing”, where overcast skies and shadows from trees or other buildings can cause loss of collected power.
He said the glass would be on the market a few years.
NASA has awarded the single largest prize handed down in aviation history to Team Pipistrel-USA.com for designing and demonstrating its Taurus G4 electric aircraft. Per the rules of the NASA- and Google-sponsored CAFE Green Flight Challenge, Pipistrel’s Taurus G4 covered 200 miles in less than 2 hours and did so on the electricity equivalent of less than one gallon of fuel per passenger, scoring $1.35 million for the effort.
But the cash, substantial though it may be, is only part of the story here. The CAFE (that’s Comparative Aircraft Flight Efficiency) Challenge was created to push aircraft engineers toward new, more efficient airplane designs that would perhaps usher in a new era of ultra-efficient flight, based on either electric engines or extremely efficient fuel-burning engines.
So while you can argue the day belongs to Pipistrel--and we certainly don’t mean to diminish that achievement--the CAFE Foundation and NASA are the real winners here. Consider: The challenge asked teams to average 100 miles per hour over two hours, and to do so on the equivalent of one gallon of gas. Not only did Pipistrel manage this, but so did California-based e-Genius with its electric-powered plane (for which it netted a second place prize of $120,000).
The kicker: both teams did so on just a little more than a half-gallon of fuel equivalent. That means both Pipistrel and e-Genius did twice as well as NASA and CAFE asked them to do (and Pipistrel slightly better than e-Genius, hence the distribution of prizes).
That’s pretty amazing, considering that just a few years ago engineers were still trying to figure out how to get an all-electric powered plane into the air for any considerable length of time, much less at sustained triple-digit speeds and while using very little energy.
Our jetliners aren’t going green just yet of course. But the winning teams in the CAFE Green FLight Challenge collectively spent just two years and $4 million on two aircraft that have pushed the electric airplane field forward by a considerable step. Imagine what ten years and some serious investment might do for the electric aircraft space.
When you rub your socked feet on the carpet and zap yourself on a doorknob, you're experiencing static electricity. Lightning is static electricity but on a scale your socks could never produce: It's three times hotter than the surface of the sun and could power a 100-watt bulb for more than three months [source: National Lightning Safety Institute]. Lightning has long fascinated people, motivating them to create myths about its origin and inspiring legendary experiments with electricity.
While we're all familiar with lightning, it's estimated that between one in 30 and one in 150 people around the world believe they have seen balls of lightning hovering over the ground, floating through walls and even killing people [source: National Geographic]. Stories of these glowing spheres go as far back as the Middle Ages, maybe even as far back as the Ancient Greeks. However, a recorded case didn't occur until the 18th century when Georg Richmann, a pioneer in research on electricity, was killed by what's believed to have been ball lightning.
erhaps one of the most famous ball lightning sightings was by a young Czar Nicholas, grandson to Czar Alexander II, who witnessed a flaming orb during a church service in the 19th century. But even sightings by tsars left people skeptical. Were these balls actually lightning? Perhaps otherworldly phenomena? The skepticism began to wane in 1963 when a group of scientists flying from New York to Washington, D.C., witnessed a blazing orb drift down the aisle and disappear through the rear of the plane. Looking to explain what they saw, research began.
Explanations and Theories of Ball Lightning
Ball lightning appears as glowing orbs that seem to occur during thunderstorms, usually following a lightning strike. These floating fireballs shine as brightly as a 100-watt lightbulb; can be white, yellow, orange, red or blue in color and are typically about the size of a small grapefruit, although sightings suggest they can range in size from golf ball to beach ball.
Silicon, which occurs in the ground, could be the culprit behind ball lightning.
Emanating from the fireball are little tendrils that seem to jerk the ball around as if it was under the power of a spastic puppeteer. They move slowly and erratically and are followed by smoke trails that form spirals around them. And after a moment, they disappear.
There's no scientific explanation for balls of lightning, although there are several proposed theories.
Throughout history, speculations about the cause of ball lightning have ranged from the existence of standing waves of electromagnetic radiation to plasma clouds and from short-circuiting power lines to St. Elmo's Fire. The more unusual explanations suggested mini black holes created during the big bang or a possible alien presence. While no theory has yet to explain ball lightning, a promising theory focuses on silicon.
The most popular current theory, proposed by John Abrahamson at the University of Canterbury in Christchurch, New Zealand, suggests that ball lightning is the result of a chemical reaction of silicon particles burning in the air.
When lightning strikes the ground, silicon that occurs naturally in soil combines with oxygen and carbon and turns into pure silicon vapor. As the vapor cools, the silicon condenses into a fine dust. The particles in this fine dust are attracted to each other by the electrical charge created by the lightning strike, binding together into a ball.
The glow and heat come from the chemical energy created as the silicon recombines with oxygen in the air. And once the silicon has burned out, the ball lightning disappears.
This theory also suggests materials other than silicon -- such as aluminum and iron metals -- may also cause the orbs, and that any atmospheric discharge, not necessarily lightning, may explain why ball lightning has been sighted near power poles, electrical fitters, and even active faults.
Scientists are taking this hypothesis into their labs. Researchers Antônio Pavão and Gerson Paiva of the Federal University of Pernambuco in Brazil have been working with the silicon hypothesis and believe they have verified the theory with silicon substrate and a high-voltage arc. They applied 140 amps of electricity to silicon substrate, which vaporized the substrate and sometimes produced golf ball-sized fireballs.
Eli Jerby and Vladimir Dikhtyar, of Tel Aviv University in Israel, successfully (and accidentally) recreated ball lightning with a device they call a "microwave drill." This microwave drill is made from a 600-watt magnetron taken from a conventional kitchen microwave oven and a powerful microwave beam capable of penetrating solid objects.
The tip of the drill -- a pointed rod -- aims the beam at a solid substance (silicon, glass, alumina were among the materials tried) and creates a hot spot in the solid. When the drill is pulled away from the hot spot, the drag produces a fireball resembling ball lightning.
How ball lightning seems to float through walls, however, is still up for debate.
You've probably seen calculators with solar cells -- devices that never need batteries and in some cases, don't even have an off button. As long as there's enough light, they seem to work forever. You may also have seen larger solar panels, perhaps on emergency road signs, call boxes, buoys and even in parking lots to power the lights.
Although these larger panels aren't as common as solar-powered calculators, they're out there and not that hard to spot if you know where to look. In fact, photovoltaics -- which were once used almost exclusively in space, powering satellites' electrical systems as far back as 1958 -- are being used more and more in less exotic ways. The technology continues to pop up in new devices all the time, from sunglasses to electric vehicle charging stations.
The hope for a "solar revolution" has been floating around for decades -- the idea that one day we'll all use free electricity from the sun. This is a seductive promise, because on a bright, sunny day, the sun's rays give off approximately 1,000 watts of energy per square meter of the planet's surface. If we could collect all of that energy, we could easily power our homes and offices for free.
Photovoltaic Cells: Converting Photons to Electrons
The solar cells that you see on calculators and satellites are also called photovoltaic (PV) cells, which as the name implies (photo meaning "light" and voltaic meaning "electricity"), convert sunlight directly into electricity. A module is a group of cells connected electrically and packaged into a frame (more commonly known as a solar panel), which can then be grouped into larger solar arrays, like the one operating at Nellis Air Force Base in Nevada.
Photovoltaic cells are made of special materials called semiconductors such as silicon, which is currently used most commonly. Ba¬sically, when light strikes the cell, a certain portion of it is absorbed within the semiconductor material. This means that the energy of the absorbed light is transferred to the semiconductor. The energy knocks electrons loose, allowing them to flow freely.
PV cells also all have one or more electric field that acts to force electrons freed by light absorption to flow in a certain direction. This flow of electrons is a current, and by placing metal contacts on the top and bottom of the PV cell, we can draw that current off for external use, say, to power a calculator. This current, together with the cell's voltage (which is a result of its built-in electric field or fields), defines the power (or wattage) that the solar cell can produce.
That's the basic process, but there's really much more to it. On the next page, let's take a deeper look into one example of a PV cell: the single-crystal silicon cell.
How Silicon Makes a Solar Cell
Silicon has some special chemical properties, especially in its crystalline form. An atom of silicon has 14 electrons, arranged in three different shells.
The first two shells -- which hold two and eight electrons respectively -- are completely full. The outer shell, however, is only half full with just four electrons. A silicon atom will always look for ways to fill up its last shell, and to do this, it will share electrons with four nearby atoms. It's like each atom holds hands with its neighbors, except that in this case, each atom has four hands joined to four neighbors. That's what forms the crystalline structure, and that structure turns out to be important to this type of PV cell.
The only problem is that pure crystalline silicon is a poor conductor of electricity because none of its electrons are free to move about, unlike the electrons in more optimum conductors like copper. To address this issue, the silicon in a solar cell has impurities -- other atoms purposefully mixed in with the silicon atoms -- which changes the way things work a bit. We usually think of impurities as something undesirable, but in this case, our cell wouldn't work without them.
Consider silicon with an atom of phosphorous here and there, maybe one for every million silicon atoms. Phosphorous has five electrons in its outer shell, not four. It still bonds with its silicon neighbor atoms, but in a sense, the phosphorous has one electron that doesn't have anyone to hold hands with. It doesn't form part of a bond, but there is a positive proton in the phosphorous nucleus holding it in place.
When energy is added to pure silicon, in the form of heat for example, it can cause a few electrons to break free of their bonds and leave their atoms. A hole is left behind in each case. These electrons, called free carriers, then wander randomly around the crystalline lattice looking for another hole to fall into and carrying an electrical current. However, there are so few of them in pure silicon, that they aren't very useful.
But our impure silicon with phosphorous atoms mixed in is a different story. It takes a lot less energy to knock loose one of our "extra" phosphorous electrons because they aren't tied up in a bond with any neighboring atoms. As a result, most of these electrons do break free, and we have a lot more free carriers than we would have in pure silicon. The process of adding impurities on purpose is called doping, and when doped with phosphorous, the resulting silicon is called N-type ("n" for negative) because of the prevalence of free electrons. N-type doped silicon is a much better conductor than pure silicon.
The other part of a typical solar cell is doped with the element boron, which has only three electrons in its outer shell instead of four, to become P-type silicon. Instead of having free electrons, P-type ("p" for positive) has free openings and carries the opposite (positive) charge.
Anatomy of a Solar Cell
Before now, our two separate pieces of silicon were electrically neutral; the interesting part begins when you put them together. That's because without an electric field, the cell wouldn't work; the field forms when the N-type and P-type silicon come into contact. Suddenly, the free electrons on the N side see all the openings on the P side, and there's a mad rush to fill them. Do all the free electrons fill all the free holes? No. If they did, then the whole arrangement wouldn't be very useful. However, right at the junction, they do mix and form something of a barrier, making it harder and harder for electrons on the N side to cross over to the P side. Eventually, equilibrium is reached, and we have an electric field separating the two sides.
This electric field acts as a diode, allowing (and even pushing) electrons to flow from the P side to the N side, but not the other way around. It's like a hill -- electrons can easily go down the hill (to the N side), but can't climb it (to the P side).
When light, in the form of photons, hits our solar cell, its energy breaks apart electron-hole pairs. Each photon with enough energy will normally free exactly one electron, resulting in a free hole as well. If this happens close enough to the electric field, or if free electron and free hole happen to wander into its range of influence, the field will send the electron to the N side and the hole to the P side.
This causes further disruption of electrical neutrality, and if we provide an external current path, electrons will flow through the path to the P side to unite with holes that the electric field sent there, doing work for us along the way. The electron flow provides the current, and the cell's electric field causes a voltage. With both current and voltage, we have power, which is the product of the two.
There are a few more components left before we can really use our cell. Silicon happens to be a very shiny material, which can send photons bouncing away before they've done their job, so an antireflective coating is applied to reduce those losses. The final step is to install something that will protect the cell from the elements -- often a glass cover plate. PV modules are generally made by connecting several individual cells together to achieve useful levels of voltage and current, and putting them in a sturdy frame complete with positive and negative terminals.
How much sunlight energy does our PV cell absorb? Unfortunately, probably not an awful lot. In 2006, for example, most solar panels only reached efficiency levels of about 12 to 18 percent. The most cutting-edge solar panel system that year finally muscled its way over the industry's long-standing 40 percent barrier in solar efficiency -- achieving 40.7 percent [source: U.S. Department of Energy]. So why is it such a challenge to make the most of a sunny day?
Energy Loss in a Solar Cell.
Visible light is only part of the electromagnetic spectrum. Electromagnetic radiation is not monochromatic -- it's made up of a range of different wavelengths, and therefore energy levels.
Light can be separated into different wavelengths, which we can see in the form of a rainbow. Since the light that hits our cell has photons of a wide range of energies, it turns out that some of them won't have enough energy to alter an electron-hole pair. They'll simply pass through the cell as if it were transparent. Still other photons have too much energy.
Only a certain amount of energy, measured in electron volts (eV) and defined by our cell material (about 1.1 eV for crystalline silicon), is required to knock an electron loose. We call this the band gap energy of a material. If a photon has more energy than the required amount, then the extra energy is lost. (That is, unless a photon has twice the required energy, and can create more than one electron-hole pair, but this effect is not significant.) These two effects alone can account for the loss of about 70 percent of the radiation energy incident on our cell.
The familiar sight of a rainbow represents just a sliver of the greater electromagnetic spectrum.
Why can't we choose a material with a really low band gap, so we can use more of the photons? Unfortunately, our band gap also determines the strength (voltage) of our electric field, and if it's too low, then what we make up in extra current (by absorbing more photons), we lose by having a small voltage. Remember that power is voltage times current. The optimal band gap, balancing these two effects, is around 1.4 eV for a cell made from a single material.
We have other losses as well. Our electrons have to flow from one side of the cell to the other through an external circuit. We can cover the bottom with a metal, allowing for good conduction, but if we completely cover the top, then photons can't get through the opaque conductor and we lose all of our current (in some cells, transparent conductors are used on the top surface, but not in all). If we put our contacts only at the sides of our cell, then the electrons have to travel an extremely long distance to reach the contacts.
Remember, silicon is a semiconductor -- it's not nearly as good as a metal for transporting current. Its internal resistance (called series resistance) is fairly high, and high resistance means high losses. To minimize these losses, cells are typically covered by a metallic contact grid that shortens the distance that electrons have to travel while covering only a small part of the cell surface. Even so, some photons are blocked by the grid, which can't be too small or else its own resistance will be too high.
Solar-powering a House
What would you have to do to power your house with solar energy? Although it's not as simple as just slapping some modules on your roof, it's not extremely difficult to do, either.
First of all, not every roof has the correct orientation or angle of inclination to take full advantage of the sun's energy. Non-tracking PV systems in the Northern Hemisphere should ideally point toward true south, although orientations that face in more easterly and westerly directions can work too, albeit by sacrificing varying degrees of efficiency. Solar panels should also be inclined at an angle as close to the area's latitude as possible to absorb the maximum amount of energy year-round.
A different orientation and/or inclination could be used if you want to maximize energy production for the morning or afternoon, and/or the summer or winter. Of course, the modules should never be shaded by nearby trees or buildings, no matter the time of day or the time of year. In a PV module, if even just one of its cells is shaded, power production can be significantly reduced.
If you have a house with an unshaded, southward-facing roof, you need to decide what size system you need. This is complicated by the facts that your electricity production depends on the weather, which is never completely predictable, and that your electricity demand will also vary. Luckily, these hurdles are fairly easy to clear. Meteorological data gives average monthly sunlight levels for different geographical areas.
This takes into account rainfall and cloudy days, as well as altitude, humidity and other more subtle factors. You should design for the worst month, so that you'll have enough electricity year-round.
With that data and your average household demand (your utility bill conveniently lets you know how much energy you use every month), there are simple methods you can use to determine just how many PV modules you'll need. You'll also need to decide on a system voltage, which you can control by deciding how many modules to wire in series.
You may have already guessed a couple of problems that we'll have to solve. First, what do we do when the sun isn't shining?
To take advantage of the strong winds that blow over the ocean, this gearless turbine uses a giant ring of magnets and 176-foot blades.
There’s enough wind energy along our coastlines to power the country four times over, and the race is on to build the best offshore turbines to capture it. Manufacturers worldwide are experimenting with two techniques: ever-longer blades to harness more gusts, and simplified drivetrains (including new generators) that slash the need for costly repairs at sea. GE’s upcoming machine, slated to go online in 2012, will combine both into one package.
GE created lightweight 176-foot blades—about 40 percent longer than the average—with a more aerodynamic shape. The blades will attach to a drivetrain that does away with many of the moving parts, including the gearbox, that are prone to breakage and energy loss.
A direct-drive mechanism replaces gears, and permanent magnets replace the electromagnets that require starter brushes, coils and power from the grid every time they fire up. The blades are now being tested in the Netherlands, and the drivetrain in Norway. Combining the two should result in a turbine that captures 25 percent more wind power than conventional models, so it can operate more often at its full four-megawatt potential—enough to power 1,000 homes.
Design Highlights on the Windmill
Generator: The 90-ton generator consists of a nearly 20-foot ring of magnets that spins to produce current. Its large diameter lets it create a lot of power when turning slowly, at the same 8 to 20 rpm as the blades, so it doesn’t need a gearbox to speed it up to the thousands of rpm most megawatt generators require. “Get rid of the gearbox, and now you don’t have to change the oil,” says GE engineer Gary Mercer.
Electrical Circuitry: Converters stabilize the current’s varying frequencies. Transformers boost voltage from 690 volts to more than 22,000, so current travels efficiently over long-distance lines.
Pitch Controller: To maximize lift as the wind speed changes, a controller can automatically rotate each blade anywhere from a fraction of a degree to multiple degrees per second. It can also turn the blades away from dangerously high winds to avoid power overloads or hardware damage.
Blades: Light, stiff carbon fiber replaces fiberglass at critical points in the blades, so they lose pounds and gain strength. A flat (rather than tapered) edge gives them a shape that increases lift.
How to Spin Power
1. Position the Blades
Based on data from wind-direction sensors, a yaw-drive motor turns the nacelle to face the wind. A pitch controller rotates each blade around a bearing, setting it to the best angle for the wind speed.
2. Capture the Wind
The three-bladed rotor spins in winds from 7 to 70 mph, sweeping twice the area of a football field. A 23-foot-long steel rotor shaft and two roller bearings transfer the mechanical energy to the generator.
3. Turn it into Electricity
The shaft spins the generator’s neodymium magnets inside stationary copper coils, inducing current in the coils. Circuitry adjusts the frequencies and voltage of the current and sends it off to the grid.
A Twist on Blades:The longer a turbine’s blades, the more wind it captures and the more electricity it creates. “If we could, we would just build infinitely longer blades,” Mercer says. “The problem is, blades get heavy and flexible.” That flexibility, coupled with the force from very high winds, can bend blades so much that they burden the machine or even smack the tower. So GE designed a blade that twists as it bends. It’s curved backward about eight feet, instead of extending straight out. When a gust pushes the tip up, the blade twists slightly around its curve—instantly angling itself so that it bears less of the gust’s brunt yet still captures a large part of its energy.
In December of 1942, an experiment that would change the world was taking place at the University of Chicago. After years of research and a month of construction, the world's first nuclear reactor, Chicago Pile-1, was ready for testing. Constructed of a lattice of uranium and graphite blocks stacked 57 layers high, Chicago Pile-1 bore little resemblance to today's nuclear reactors. A three person "suicide squad" was waiting to step in and shut the reactor down in case the reactor's safety features failed. Fortunately, the 50 people in attendance that day were able to share a collective sigh of relief -- as the squad was not needed. The reactor worked without a hitch, and the nuclear era was born.
Today, more than 400 nuclear power plants are located in 30 countries across the globe. Together, these plants produce 15 percent of the world's electricity and 2 percent of the world's total power supply [source: World Nuclear Association]. Nuclear power certainly has its pros and cons, but no one can deny its importance. So now that we know a little about how far nuclear power has come over the past 60 years, we're ready to take a look at the five biggest nuclear reactors on Earth, starting with a couple of reactors that might not be around much longer.
Today, more than 400 nuclear power plants are located in 30 countries across the globe. See more nuclear power pictures.
5: Isar II
Germany has long had an uneasy relationship with nuclear energy. While the country currently depends on nuclear energy for nearly 20 percent of its electricity, concerns about plant safety and nuclear waste storage have resulted in plans to close some of the country's largest reactors. Included on that list are two reactors located in Essenbach, Germany. Together the reactors, known as Isar I and Isar II, generate enough electricity to power more than 1.5 million households each year [source: Nuclear Energy Institute].
But Isar II is the reason the reactors are on this list. The reactor, commissioned in 1988, has a net installed electric capacity of 1,400 megawatts [source: E.ON]. According to E.ON, the Germany utility company that runs Isar II, creating that electricity using fossil fuels would add 12 million tons (11 million metric tons) of carbon dioxide to the environment [source: Crowley]. Perhaps that explains why some are rethinking the current plan to decommission Isar I in 2011 and its bigger brother in 2020. Read on to learn about another German reactor that's inspired more than its share of controversy.
4: Brokdorf
On the banks of the river Elbe, sheep graze lazily on fields of lush green grass, entirely unimpressed with the massive nuclear reactor located only 100 feet (30 meters) away. Brokdorf reactor, which takes its name from the surrounding city, houses more than 110 tons (100 metric tons) of uranium [source: E.ON]. Construction on the plant began in 1981, and by 1986, the plant was operational. One of the world's largest reactors, Brokdorf claimed the title of World Champion of gross annual output in both 1992 and 2005 [source: E.ON]. With an impressive net installed electric capacity of 1,410 megawatts, Brokdorf could easily recapture the title before its scheduled decommissioning in 2018 [source: E.ON].
Brokdorf's electrical capacity makes the reactor the largest in Germany. So perhaps it's fitting that, throughout the 1980s, it was also the site of the country's largest protests against nuclear power. The protests drew tens of thousands of people a day at their peak. The demonstrations often turned violent, with protestors hurling bricks, bottles and even gasoline bombs at riot police, prompting the police to respond with tear gas and mass arrests. Hundreds of injuries resulted, affecting both citizens and riot police alike. Today, the site still draws a few peaceful protestors, but as concerns rise over global warming and increasing energy costs, Germany's attitude toward nuclear power appears to be shifting. Of course, not all countries have had such a contentious relationship with nuclear power. The next reactor on our list is located in a country that gets more of its electricity from nuclear power than any other country on Earth.
3: Civaux 1 and 2
"No oil, no gas, no coal, no choice." The phrase has become a mantra explaining French support of nuclear power. As instability in the Middle East forced oil prices higher and higher throughout the 1960s, France recognized a need to move away from its fossil-fuel-burning power plants. Today, the country has 59 nuclear reactors responsible for producing 76 percent of France's electricity, and two reactors located in the city of Civaux are among its largest. Fully operational in 1999, Civaux 1 and Civaux 2 cost an estimated $4.1 billion to construct [source: Power-Technology].
While that's a hefty price tag, reactors in other countries can be much more expensive. In fact, power produced by Civaux 1 and Civaux 2 costs about as much as traditionally cheaper electricity generated from coal and natural gas. Turbines in the reactors are more than half a football field in length and weigh nearly 3,000 tons (2,722 metric tons), which helps explain how each of the Civaux reactors produces 1,450 megawatts (net) [source: Power-Technology].
The reactors have some impressive safety features as well, including the ability to shut down in only 2.15 seconds. Even so, Civaux 1 was closed for nearly a year after coolant leaks were discovered. The pipe work was replaced and the reactor was ready to come back online when regulators discovered a problem with harmful bacteria forming in the cooling circuits of similar reactors. To address the problem, engineers added an ultraviolet treatment system capable of killing the bacteria. Now both Civaux 1 and Civaux 2 are up and running, helping France to power not only its own homes and businesses but even export energy to neighboring countries.
2: Chooz B1 and 2
Like their sister reactors in Civaux, the two reactors known as Chooz B1 and Chooz B2 are part of France's series of technologically advanced N4 reactors. Among the technological innovations are computerized control rooms that provide operators detailed information about the reactors' systems, as well as very efficient steam generators and cooling pumps. Yet even with the advanced technology, Chooz B1 took only 12 years to construct. Even more impressive, the Chooz B reactors have a net installed electric capacity of 1,455 megawatts [source: Davis]. That makes the reactors the most powerful in the world in terms of individual output, capable of generating more than 5 percent of France's nuclear power [sources: Areva].
The advanced technology behind the N4 reactors caused some problems, however; like the reactors in Civaux, Chooz B1 and Chooz B2 had some problems during early operations. They shared the same faulty cooling design as Civaux 1 and 2, for instance, so the reactors were taken offline for a year as their systems were redesigned and replaced. For the time being, though, the kinks seem to be worked out and all four N4 reactors are fully operational.
And if providing a huge portion of France's electricity isn't enough, the Chooz reactors may even provide some perspective on the very nature of matter itself. In July 2009, the construction of a laboratory on the site of the Chooz B reactors was announced. The lab, designed to study the elusive neutrino, could give scientists insight into the very origins of the universe itself.
The next reactors on our list may not solve any scientific mysteries, but in terms of sheer power, they can't be beat. Read on to find out more.
1: Kashiwazaki-Kariwa
Japan's Kashiwazaki-Kariwa reactors, which were completed in 1997, won't break any records for individual output, but their combined electrical output is uncontested. The power plant, which has seven separate reactors, has a rated capacity of 8,212 megawatts. That's enough capacity to power more than 16 million households each year, providing more than 5 percent of Japan's total electricity [source: Power-Technology].
The Kashiwazaki-Kariwa reactors, like all Japanese reactors, were constructed with extensive safety mechanisms designed to withstand Japan's frequent earthquakes.
The plant extends deep into the surrounding water where it attaches to the solid ground below, providing a sturdy foundation to withstand shocks. Even so, the reactors were taken offline after a magnitude 6.8 earthquake struck the plant in July of 2007. The earthquake caused extensive damage to the plants, including fires and radiation leaks, though many expected the damage to be much worse. As of today, most of the reactors remain offline as regulators inspect the plants for further damage, though some of the reactors have received approval to resume operation.
Solar panels like these on the rooftop of Itochu headquarters in Tokyo would become more common in Japan under Prime Minister Naoto Kan's ambitious renewable energy plan. But this summer, the emphasis is on conservation.
At Tokyo's Meiji Gakuin University, professor Keiko Tanaka has been teaching classes with half as much lighting as usual and with less reliance on computers and other electricity-hogging tools. She now often gets out her chalk and eraser to use the blackboard.
But with tsunami-torn Japan's electricity system struggling, she wonders whether her fellow citizens will commit to the level of energy savings the nation needs.
"Japan is a country where 18-year-old girls take the elevator to go up a single flight of stairs because they don't want to sweat," she said. "It is a country where most toilet seats are heated, and there is an electric noisemaker in the women's toilet to mask the noise. People have really gotten used to creature comfort at very high energy costs."
Those costs are under scrutiny as perhaps never before, due to the loss of the nuclear plant Fukushima Daiichi and other grid infrastructure damage in the wake of the March 11 earthquake and tsunami. The International Energy Agency (IEA) said in a report this week that Japan "is in the midst of perhaps one of the most severe electricity shortfalls in history."
Japan has scrambled to repair infrastructure and increase its imports of liquefied natural gas (LNG), but the problem could get worse, the IEA warned, due to political backlash against nuclear energy, which before March provided one-third of the nation's electricity.
In the long run, Prime Minister Naoto Kan has indicated a push for renewables, setting a new goal of 10 million solar-powered homes by 2020, and abandoning ambitious nuclear expansion plans. But Japan—which has no fossil fuel resources of its own—faces an immediate test in the sweltering months of July and August, when air conditioning demand typically strains the grid. Japan's government says its citizens need to reduce their electricity demand this summer by 15 percent, and in Tokyo, the goal is 25 percent.
The IEA says Japan faces a challenge in meeting these goals, since—heated toilets aside—its economy already is far more energy-efficient than that of other nations. To make even greater strides, "Japan will have to undertake deep energy-efficiency and conservation measures," the IEA report concludes.
Faced with potential crisis this summer, Japan has attempted to ramp up the Cool Biz campaign it has promoted since 2005. Re-branding it Super Cool Biz, Japan is calling for offices to keep temperatures at 28°C (85°F), when summer high temperatures in Tokyo can surpass 30°C (86°F) with high humidity. Office workers are encouraged to shed their business suits in favor of sandals, khakis, and pedal pushers.
Japan's Ministry of Economy, Trade and Industry announced it planned to lead by example on energy savings—reducing the use of printers and copiers in its offices, deactivating automatic doors, reducing the number of elevators in services, and adopting early work hours.
But some advocates of saving energy already are frustrated. Taro Kono, a member of the House of Representatives in Japan's Diet, the national parliament, said he has been trying to encourage telecommuting, but the effort has fallen short of his expectations because many businesses remain unwilling to relinquish the ability to physically see what workers are accomplishing.
Japan's energy consumption per unit of GDP is 20 percent below the world average and 30 percent below that of the United States, according to the World Resources Institute's widely followed EarthTrends data. Japan's Agency for Natural Resources and Energy (ANRE) estimates that Japan improved its energy efficiency 37 percent in the past 30 years.
The IEA, in its report entitled "Saving Electricity in a Hurry," said it remains unclear how much farther small and medium-sized Japanese businesses will cut demand voluntarily. The IEA said many energy-saving measures at those companies require shifting operations to evenings and weekends—something that will require unions' approval and could disrupt many parents' schedules.
Post-Tsunami, an Anti-Nuclear Wave
Adding to Japan's electricity shortfall woes is a growing issue due to the nation's long-standing requirement that its nuclear power plants undergo routine maintenance every 13 months, with politicians in the plants' regional prefectures providing final approval before restart. The restarts typically are approved routinely, but all have been delayed since the Fukushima Daiichi disaster. More as a result of these holdups than earthquake damage, only 19 of Japan's 54 nuclear reactors are now in operation.
Kyushu Electric, which provides power to southwest Japan, received a welcome bit of news this month, when a local mayor approved its proposal to restart the reactors at its Genkai nuclear power plant in Saga prefecture. Those reactors had been shut down for maintenance since last winter.
The final decision lies with the prefecture's governor, Yasushi Furukawa, who expects to make a decision by mid-July.
Energy experts say that if Furukawa decides against a restart, other governors could follow suit—setting in motion a chain of events that could idle all of Japan's nuclear reactors within a year.
Trade and Industry Minister Banri Kaieda this week sought to reassure citizens of the reactors' safety, pledging that the government would order stress-testing at all the plants.
Renewable Energy's Rising Sun
It remains to be seen whether the stress testing in the coming weeks will succeed in reassuring Japan's citizens on nuclear plants' ability to withstand earthquakes and tsunamis, but it is clear that opponents have been able to seize on the Fukushima disaster to urge rapid expansion of alternative sources.
They have argued that Japan's rich geothermal resources—with nearly 200 volcanoes and some 28,000 hot springs—could provide more than 80,000 megawatts of generating capacity, enough to meet half of the country's electricity needs. In addition, a 2009 study published in the proceedings of the National Academy of Sciences estimated that the country's land-based wind resources could provide another half of its electricity.
Japan has aggressively sought to upgrade its solar potential—a cause taken up by Kan before he survived a no-confidence vote earlier this month.
The country has set a goal of increasing solar photovoltaics, mostly in rooftop panels, from 3,500 megawatts in 2010 to 53,000 megawatts by 2030. Beyond Kan's target of powering 10 million homes by 2020, there would be enough solar photovoltaics to power 18 million Japanese homes by 2030.
Masayoshi Son, the founder of Softbank Mobile and the country's wealthiest man, has drawn substantial attention for his plan to start a research foundation for renewable energy, bolstered by millions of his own start-up money. So far, 35 of Japan's 47 prefectures have signed on as founding members.
"The means to do this are certainly in abundance," said Andrew DeWit, a professor of public finance at Tokyo's Rikkyo University who studies the country's energy situation. "This sounds like idealistic talk, but I really think Japan, given that it's got all this pent-up demand for renewables, could see in over a year or two a truly astounding emplacement of renewable capacity."
DeWit acknowledged, however, that Japan's nuclear energy proponents will not abandon that energy source easily. "There's all kinds of rhetoric—that wind farms are too noisy, they kill birds and so on," he said. "The energy economy of this country is going to be decided over the next few months . . . The key things seem to me to be the increasing heat of summer and how disastrous this nuclear problem is."
With the future of Japan's energy supply in question, the focus for most citizens now is on cutting demand. Kazuto Tsuchiya, a student at the University of Southern California who is spending the summer with family in Suzaka in central Japan, said his relatives put off an earlier decision to buy an air conditioner.
"We are going to bear the heat of summer with round paper fans and Japanese folding fans," he said. Tschiya sees his fellow citizens neither resisting conservation nor enthusiastically embracing it.
"It's more like people think that it's 'sho ga nai' in Japanese, meaning, 'We have no choice, we have to accept,' '' he said.
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