Wednesday, June 15, 2011

How Does Solar Energy Work?

For as long as our planet has spun 'round the sun, there's been solar energycascading down on the earth, and, for a long time -- since the 7th century B.C., when glass was used to magnify it -- humans have been working to harness it. These days, technology is a bit better, providing electricity, heating, lighting, and even flight, but the point is the same: use the sun's warm glowing warming glow for our benefit.

Solar energy vs. solar power: what's the difference?
Often used synonymously with solar energy, solar power is what you've got once the sun's energy has been converted to electricity. This can be done one of two ways: heating a liquid to produce steam and spin a generator, or through photovoltaics (but that's another post). For now, we'll concentrate on how to use the massive and largely untapped potential that exists with solar energy. But first, some basics.

What is solar energy?
Short answer: the light and heat provided by the sun. A slightly longer answer: after running the gauntlet from an average of 93 million miles away, through the various layers of atmosphere and atmospheric conditions (clouds, pollutants, dust and the like), about half of the solar energy is absorbed by water and land, with the other half reflected and re-radiated back into space. The half that makes it is absorbed by oceans, land masses and plants; in the ocean, the energy drives heat and wind-driven currents (like the Gulf Stream); on land, the energy is absorbed and creates heat, and the little bit that's left is absorbed by plants and converted to chemical energy through a process we all know as photosynthesis.

How does solar energy work?
Outside of the three scenarios above, solar energy usually requires a little human input to really work (photosynthesis, which helps grow crops for food and fuel, is a notable exception). This help can come in lots of different forms, from architecture and urban planning, which uses techniques to maximize light and heat from the sun to our benefit in our buildings, to solar thermal, the most widely used category of solar energy technology, including solar cookingwater distillation and purification and lots more, toheating water for our use and desalination.

But, by far, solar energy's most talked-about use is electricity generation. For now,photovoltaic (PV) cells and panels remain the most-used method for turning sun into electricity. Basically, photovoltaics cause photons from sunlight to knock electrons into a higher state of energy, creating electricity. Photovoltaic production has been doubling every two years, increasing by an average of 48 percent each year since 2002, making it the world’s fastest-growing energy technology.

But it's not alone in the solar world; concentrating solar systems use lenses, mirrors and tracking systems to focus a large area of sunlight into a small, concentrated beam, which is then used to generate electricity. This can be accomplished using a trough system; by allowing direct sunlight to hit troughs, the solar collectors concentrate it into a single area that boils liquid in order to make steam, which in turn moves turbines to make electricity. This up-and-coming technology can be made even more efficient with the use of a solar tower, which is just what it sounds like: a tower that uses careful sun tracking to concentrate solar energy near its top. There are various other technologies that can create solar power from solar energy, but, for now, these remain the most popular and most viable.

Advantages of solar energy
Solar's biggest advantage is that there's so much of it. The total solar energy available to the earth is approximately 3850 zettajoules (ZJ) per year, while worldwide energy consumption was 0.471 ZJ in 2004, according to the US Department of Energy. Even if you aren't a solar panel installer, you can tell that there's way more solar energy available than the world will ever need. Solar energy is also terrifically versatile; as we mentioned above, it can be used to help grow food and fuel, light, heat and modulate the temperatures in our homes, disinfect and desalinate water, and more. And, once you figure out how to best maximize the available energy, solar is the gift that keeps on giving; as long as the sun doth shine, solar energy will be available for its myriad uses.

Disadvantages of solar energy
Solar energy's disadvantages can be pretty well boiled down to one thing: cost, at least for using it as electricity. It takes a lot of land and costs a lot of cash to be worthwhile, as most types of solar cells require large surface areas to achieve average efficiency, and the silicon used in many of today's cells is also very expensive. Pollution and weather can further cut back their efficiency, which, of course, increases the cost over time.

And though solar energy will always be available on a macro scale, it isn't always available on an hour-to-hour scale, because it doesn't work when the sun isn't out (which always happens at night and sometimes happen due to weather). Storing the energy in batteries for use during these times cuts back on the efficiency further. And, of course, if you live somewhere that doesn't have good solar energy exposure, there isn't much you can do. You gotta have the sun.
Further solar power reading in TreeHugger
Together, solar energy and solar power is a huge, and hugely popular, topic here at TreeHugger. It seems like every week we're reporting the largest solar farm ever orefficiency breakthroughs for converting it to electricity. We even have a whole category dedicated to solar, but if that isn't enough to quench your thirst for sun-powered knowledge, check in with the International Solar Energy Society, the American Solar Energy Association, the Canadian Solar Industry Association and the Mexican Solar Energy Association, for starters (there's also the European Solar Thermal Industry Federation, of course). And stay tuned for more, much more, on the wonderful world of solar.

Plug in to more green knowledge with our Green Basics column, which appears Thursdays here at TreeHugger.
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