Electric VS Fuel Cell Vehicles: 'Green' Auto Tech ExplainedBattery-powered electric cars and hydrogen fuel cell vehicles have both seen advances in their development, and one or both of these technologies may represent the future of "green" automobiles.Both technologies offer a cleaner alternative to internal combustion engines, and both use electric motors powered by electrochemical devices. But what's the difference between them? For one, electric vehicles use energy stored in a battery, whereas fuel cell vehicles have stored fuel that reacts to produce energy.The two technologies face unique challenges in achieving widespread adoption, but both are promising, experts say."They're not necessarily competing technologies they're similar and complementary," said Lawrence Drzal, a chemical engineer and materials scientist at Michigan State University in East Lansing.Electric vehiclesWhereas conventional vehicles burn fuel in an internal combustion engine, battery-powered electric vehicles don't have an engine. Instead, they use energy stored in batteries to power one or more electric motors.Electric cars have undergone a surge in popularity in recent years, but electric vehicles were already being made in the late 1800s, according to Huei Peng, a mechanical engineer at the University of Michigan who works on the design and control of clean vehicles, including electric cars. The vehicles remained popular until the early 20th century, when they had to compete with mass-produced internal-combustion-engine vehicles."After a couple of decades of competition, the internal combustion engine won, mainly because of the limitations of batteries," Peng told Live Science.Interest in electric vehicles returned during the oil energy crisis of the 1970s and 1980s, but the cars never achieved mass production. Still, electric vehicles have been making a comeback since 2008, with the introduction of fully electric cars such as the Tesla Motors Roadster (and, subsequently, the Model S), and the Nissan Leaf.Many of today's electric vehicles run on rechargeable lithium-ion batteries the same kind found in most laptops. These are replacing the cheaper lead-acid batteries used in most older models of electric vehicles.Fuel cell vehiclesFuel cell vehicles are also driven by an electric motor, but instead of being powered by a battery, they create the electricity in an onboard fuel cell, usually using oxygen from the air and stored hydrogen."Batteries and fuel cells are quite similar," said Shawn Litster, a mechanical engineer at Carnegie Mellon University in Pittsburgh who works on fuel cell design. The difference is, "with a fuel cell, you're able to decouple energy conversion from energy storage," he said.Fuel cells use a catalyst to combine two reactants, which generates a flow of electrons (aka electricity). A variety of fuels can be used to support fuel cells, but the most common is hydrogen that is produced from natural gas. When oxygen and hydrogen react, they produce only water and heat, making them "zero-emissions" vehicles (like battery-powered electric vehicles)."Probably the oldest [commercial] use of fuel cells is in the space program," said Drzal, who works on materials to make vehicles lighter and more fuel-efficient. While NASA could afford to pay virtually any price for them, for consumer vehicles, "you need fuel cells that are not only efficient, but cost-effective," Drzal told Live Science.

Electric vs. Fuel Cell ?Electric vehicles offer a promising alternative to internal-combustion vehicles because they don't directly burn fossil fuels. They are also capable of producing instant torque and smoother acceleration than conventional cars.But electric vehicles aren't necessarily more environmentally friendly than conventional combustion vehicles. If the electricity used to charge the electric vehicle comes from a coal power plant, for example, it can be dirtier than even the worst internal-combustion vehicle, Peng said. The same reasoning applies to fuel cells they're only as clean as the source of the hydrogen they use.Electric vehicles are also limited by the range they can travel on a single battery charge. For short-distance commuting, this isn't a problem, but longer trips require lengthy periods of recharging. Battery swapping in which a depleted battery is exchanged for a fully charged one is one possible solution, and Tesla Motors has begun using this option.Battery technology has improved dramatically, but "batteries are still too heavy and expensive, and don't have enough energy, which means a shorter range," Peng said. But he added that the price of batteries has come down significantly in the past 10 years.Fuel cell vehicles don't have the same range limitations as battery-powered vehicles because they can simply store more (hydrogen) fuel. The main disadvantages of today's hydrogen fuel cell vehicles are the lack of sufficient infrastructure for hydrogen refueling, and the cost of the catalysts, Litster said.Platinum is one of the most commonly used catalysts for fuel cells, but it's very expensive, Litster said. He and his colleagues are working on how to make platinum more efficient, while other researchers are developing catalysts made of lower-cost materials.While battery-powered electric vehicles may have a head start on fuel cell vehicles, both technologies are advancing rapidly. It will be interesting to see where they are five years from now, Litster said.

Cheap Holograms Could Give Rise to Glasses-Free 3D TVsLarge and affordable holographic video displays may soon be possible, which could spur the development of glasses-free 3D TVs, researchers say.The secret to developing such holographic video displays could be using acoustic waves to control the way a crystal bends light, the scientists added.Holograms are a special kind of 2D photograph that, when lit up, create the illusion of a 3D image. The pixels making up each hologram scatter light falling onto them in very specific ways, causing these light waves to interact with each other to generate an image with depth.

One potential way to create a moving holographic video instead of just a static hologram would involves displays with pixels that can alter the way they bend light. However, these pixels would have to be close to the size of the light waves they are bending, and there is currently no easy or cheap way to create such pixels.Another technique would use precisely engineered sound waves to squeeze and stretch a transparent material, changing the degree to which it bends light, or its index of refraction. This strategy, called acousto-optic modulation, could create a display that alters the way it scatters light over time, potentially generating holographic videos. However, an early prototype using this method relied on crystals of an expensive transparent material called tellurium dioxide, and could not generate images with a suitable resolution for TVs."The prototype used some of the largest crystals of tellurium dioxide every grown, these $25,000 custom pieces of equipment," said study co-author Daniel Smalley, an electrical engineer and media arts and sciences researcher at Brigham Young University in Provo, Utah.Now, scientists are developing holographic displays using common and much cheaper crystals that could generate high-resolution videos."We're using crystals that cost just $2," Smalley told Live Science.The foundations of this display are crystals of lithium niobate, a material often used in mobile phones and telecommunications networks. Under the surface of each crystal, the researchers etched a microscopic channel, or "waveguide," that serves as a tunnel for light. A metal electrode is then deposited onto each waveguide."We can use basic fabrication techniques borrowed from the semiconductor industry to make these devices," Smalley said. "This brings cost down by several orders of magnitude. Hopefully, this means we can make large holographic displays for the first time."The crystals are piezoelectric, which means that when an electric current is applied to them, they generate acoustic waves that travel like ripples across their surfaces. These acoustic waves can distort the shape of the crystals, which in turn can alter their indexes of refraction and therefore influence any light waves traveling inside them.To generate a holographic image, lasers of three colors (red, green and blue) are fired into each waveguide. The frequencies of the acoustic waves passing through each crystal determine which colors pass through and which colors are filtered out. The light waves that come out of the waveguides then interact with each other to produce a holographic image.A holographic video display would stack many of these waveguides alongside each other. Each waveguide is only a few microns wide, and they can be spaced a few dozen microns apart. In comparison, the average human hair is about 100 microns wide.The researchers suggest they can manufacture a device that can display 50 billion pixels per second. This could provide 3D images at the same kind of resolutions and frame rates seen in standard-definition TV. Now, the challenge will be to develop a computer powerful enough to provide all the data needed to generate these holographic videos, Smalley said.

Best Solar Panels for HomesSolar panels promise to lower your electricity bill by supplementing the energy you buy from the local power company. But choosing and installing solar panels can be an overwhelming task.Solar cells, which are linked together in a panel, convert sunlight into electricity via photovoltaic materials, such as silicon. When sunlight hits these materials, the light's energy is absorbed, and that energy causes electrons within the material to escape from their position in the atom of silicon or other photovoltaic material. These released electrons are captured to produce an electric current.As of the third quarter of 2014, more than 17,500 megawatts of cumulative solar electric capacity are operating in the United States, which is enough to power more than 3.5 million average American homes, according to the Solar Energy Industries Association. Residential solar panels were the fastest-growing category, with 58 percent growth during the quarter, the association reports.How much you save by using solar panels depends on your local weather they're a better deal in sunny Denver than dreary Seattle and how much electricity costs in your area."There are many systems that make great economic sense today, and these are the types of systems that are being installed in large numbers," said Tommy Cleveland, a solar energy engineer at the North Carolina State University Solar Center. "They are primarily in locations with expensive electricity rates, making the energy produced by solar systems very valuable."If you make the leap, however, it pays to get the right kind of panels. Our sister site, Top Ten Reviews, conducts in-depth reviews of solar panel technology. Here are their top three recommendations for this green technology.

#1 Kyocera KD315GX-LPBThe Kyocera KD315GX-LPB solar panel gets top marks for its high solar efficiency, which is the amount of energy converted from sunlight per unit of surface area in the panel. At 16 percent, this solar panel is not the most efficient on the market, but it ranks high. (Silicon-based solar cells like this one usually operate at an efficiency of 18 percent or lower, according to the University of Pennsylvania.) The Kyocera KD315GX-LPB panels are also durable and come with a complete five-year warranty. The company guarantees that the panels' power output will remain at 80 percent of the minimum power promised by manufacturers for at least 20 years.The panels meet industry standards for withstanding loads (it can hold up under 113 pounds per square foot of pressure from snow or ice on the roof) and can handle a beating by hailstones with a 1-inch diameter in winds of up to 51 mph.Ease of use: As with any solar panel array, you'll need to check your local regulations and permitting requirements before installing. You can mount Kyocera solar panels yourself if you're handy enough and if your local laws allow it. Experts advise against doing so unless you really know what you're doing, however."It is best to get a professional installer to install them," Cleveland told Live Science. "There is serious danger working with electricity, so someone not properly trained to install a system can easily get hurt or killed."A few notes on choosing an installer: The U.S. Department of Energy recommends approaching this step with care. Home owners should ask potential contractors about their level of experience installing both on-grid and off-grid photovoltaic systems. Most home owners will want on-grid installation, meaning your solar system is interconnected with the local power grid. Be sure the contractor you hire is licensed and certified, and that there are no legal complaints against them. Your state electrical board and the Better Business Bureau are good resources for finding this out.The Kyocera panels are easy to maintain, requiring only occasional cleaning with water and mild detergent and an annual check of the connections and hardware.Help and support: The company provides answers to frequently asked questions on its website and will respond to individual queries by phone and email. There is no online live chat option for support, a downside of this brand.#2 Canadian Solar CS6X-305MFounded in 2001, Canadian solar offers its panels in 50 countries around the globe. The company's Canadian Solar CS6X-305M model took second place in the Top Ten Reviews rankings for power, durability and visual appeal. The panels' shape is more rectangular than Kyocera's offering, which may appeal to some homeowners. The efficiency of these panels is rated at 15.9 percent, barely behind the No. 1 Kyocera model. The Canadian panels also meet industry standards for durability and are able to handle up to 113 pounds of snow per square foot. The warranty guarantees 95 percent output for one year, and 80 percent output for 25 years.Ease of use: Though the installation of this model is not significantly different than that for other solar panels, the model is advertised as self-washing. That means that with a sufficient roof angle, rain will keep dirt and dust off the solar panel surface. However, owners may still need to take a sponge and soapy water to the panels on occasion if they get particularly dirty.Help and support: Canada Solar offers support by phone and by email, and the company's website includes some information on frequently asked questions. There is no live chat or blog, making the company slightly harder to reach than competitors. Canada Solar offers a 10-year warranty on materials and workmanship.#3 Grape Solar 390WGrape Solar is a Eugene, Oregon-based company founded in 2009. It makes solar panels, largely manufactured in Asia but assembled in the United States. The Grape Solar 390W panel has an efficiency percentage of 15.21, a solid number, and can handle 50 pounds of snow per square foot. The warranty promises 90-percent power output for 10 years and 80-percent output for 25 years. Grape works with Costco and Home Depot and has a network of installers throughout the United States.Ease of use: These solar panels can be cleaned with just water, no soap necessary. Top Ten Reviews rated Grape Solar's phone-based customer service as "first rate." You can also contact the company via email or get in touch with the its technical team through a customer hotline.