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FAQ : Electricity
Is it possible to generate electricity directly from heat?
If you have a lot of heat, then you can do what power plants do -- you can use the heat to generate steam, and use the steam to spin a turbine. The turbine can drive a generator, which produces electricity. This setup is very common, but it requires a fair amount of equipment and space.
If you would like to generate electricity from heat in a simple way that has no moving parts, this usually involves thermocouples.
Thermocouples take advantage of an electrical effect that occurs at junctions between different metals. For example, take two iron wires and one copper wire. Twist one end of the copper wire and one end of one of the iron wires together. Do the same with the other end of the copper wire and the other iron wire. If you heat one of the twisted junctions (perhaps with a match) and attach the two free ends to a volt meter, you will be able to measure a voltage. Similarly, if you hook the two iron wires to a battery, one junction will get hot and the other will get cold.
Interplanetary satellites that fly toward planets such as Jupiter and Saturn are so far away from the sun that they cannot use solar panels to generate electricity. These satellites use RTGs (radioisotope thermoelectric generators) to generate their power. An RTG uses radioactive material (like plutonium) to generate heat, and thermocouples convert the heat to electricity. RTGs have no moving parts, so they are reliable, and the radioactive material generates heat for many years.
How Electricity Works?
Humans have an intimate relationship with electricity, to the point that it's virtually impossible to separate your life from it. Sure, you can flee from the world of crisscrossing power lines and live your life completely off the grid, but even at the loneliest corners of the world, electricity exists. If it's not lighting up the storm clouds overhead or crackling in a static spark at your fingertips, then it's moving through the human nervous system, animating the brain's will in every flourish, breath and unthinking heartbeat.
When the same mysterious force energizes a loved one's touch, a stroke of lightning and a George Foreman Grill, a curious duality ensues: We take electricity for granted one second and gawk at its power the next. More than two and a half centuries have passed since Benjamin Franklin and others proved lightning was a form of electricity, but it's still hard not to flinch when a particularly violent flash lights up the horizon. On the other hand, no one ever waxes poetic over a cell phone charger.
Electricity powers our world and our bodies. Harnessing its energy is both the domain of imagined sorcery and humdrum, everyday life -- from Emperor Palpatine toasting Luke Skywalker, to the simple act of ejecting the "Star Wars" disc from your PC. Despite our familiarity with its effects, many people fail to understand exactly what electricity is -- a ubiquitous form of energy resulting from the motion of charged particles, like electrons. When put to the question, even acclaimed inventor Thomas Edison merely defined it as "a mode of motion" and "a system of vibrations."
In this article, we'll try to provide a less slippery answer. We'll illuminate just what electricity is, where it comes from and how humans bend it to their will.
For our first stop, we'll travel to Greece, where inquisitive ancients puzzled over the same phenomena that zaps you when you touch a metal object after shuffling over the carpet on a cold, dry day.
How Solar Works?
We can change sunlight directly to electricity using solar cells. Every day, light hits your roof's solar panels with photons (particles of sunlight). The solar panel converts those photons into electrons of direct current ("DC") electricity. The electrons flow out of the solar panel and into an inverter and other electrical safety devices. The inverter converts that "DC" power (commonly used in batteries) into alternating current or "AC" power. AC power is the kind of electrical that your television, computer, and toasters use when plugged into the wall outlet.
A net energy meter keeps track of the all the power your solar system produces. Any solar energy that you do not use simultaneous with production will go back into the electrical grid through the meter. At night or on cloudy days, when your system is not producing more than your building needs, you will consume electricity from the grid as normal. Your utility will bill you for the "net" consumption for any given billing period and provide you with a dollar credit for any excess during a given period. You can carry your bill credit forward for up to a year.
How Power Felt Works?
You've probably had this experience: You're on the go all day and haven't had a chance to plug in your iPhone, and just when you need to make a call or check your e-mail, you see that little red icon that indicates your battery is just about to run out. It's so frustrating it actually makes you get a little hot under the collar. But wait -- maybe that's the solution. What if, instead of blowing a gasket, you could somehow convert that excess body heat into electricity and use it to power your phone or another portable device?
You've actually seen a variation of this idea before, if you're a fan of the cinematic "Matrix" trilogy, in which a giant computer network powers itself by siphoning energy from legions of comatose, unwitting human beings. We're not talking about anything that creepy, though. Small-scale thermoelectric power generation, in which body heat is harvested to power portable devices, is a concept that scientists have been looking at quite intently in recent years -- as our craving to carry power-hungry gadgetry in our pockets has continued to grow.
Recently, researchers at Wake Forest University's Center for Nanotechnology and Molecular Materials gave a boost to thermoelectric power generation's prospects when they developed a fabriclike material called "power felt," which is capable of exploiting differences between an object's heat and the room temperature to generate an electrical charge [source: Neal].
One researcher who's worked on the project envisions fashioning a jacket from power felt and using it to power an iPod, an idea that sounds pretty great for cool-weather jogging enthusiasts. But power felt doesn't just have to go in a garment. A flashlight handle swathed in power felt might be a great thing to have during an extended power outage, and a car seat made of the stuff might draw energy from your posterior to power your windows or radio. And there are other non-human energy sources that we might use it to tap, as well
How Human-scale Therm o-electric Power Generation Works?
If you're puzzled as to how your sweaty body could power an iPad on a warm summer day, think of it this way: Almost all the electricity that humans use -- about 10 trillion watts -- is generated by releasing heat energy (usually by burning fossil fuels to heat water) and then converting that heat into mechanical energy. Mechanical energy is then used to crank generators and produce electrical current. This tried-and-true method, called thermoelectric power generation, produces a lot of energy, to be sure. But it also wastes a lot of energy, because the mechanical process isn't that efficient at using heat. In fact, more than half of that heat simply escapes into the atmosphere [source: Jacques].
It would be a lot better, at least in theory, if we could find a practical way to generate electricity directly from heat itself. Scientists have long known that it's possible to do that, because when there's a difference in the temperature of the surroundings and that of an object, a conductive material between the two can use that contrast to generate electrical current, without any turbine or mechanical generator. This is known as the Seebeck effect [source: Timmer, Ozcanli].
The trick to generating and harvesting that non-mechanical electricity is to find the right conducting material. For a while, researchers have been building direct thermoelectric generators that use a metal alloy, bismuth antimony telluride, which has the ability to generate electricity from heat. But that material is expensive and it's not all that efficient [source: DOE].
That's why everyone is so excited about power felt, which -- despite its name -- isn't actually a cloth woven from wool, like the stuff they use on pool tables. Instead, power felt is
made up of plastic fibers wrapped around tiny -- and by tiny we mean one atom in thickness -- structures called carbon nanotubes, which are really, really good at conducting electricity. It's also potentially cheap to manufacture, which means we could use it all over the place
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