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Sierra magazine
A Short History of Bright Ideas

Renewable energy has sparked innovative thinking since the first Neanderthal basked outside A south-facing cave

By Dan Oko

Wave and Tide | Solar | Wind

London's blackened snow in Charles Dickens's A Christmas Carol was no Victorian embellishment. As early as 1662, demographer John Graunt concluded that as many as one in four deaths in the coal-choked city was the result of lung disease. Coal's environmental damage has lessened somewhat over the centuries, but the old-school fuel remains the United States' biggest source of global-warming carbon dioxide, and the preferred means of extracting it--mountaintop removal--destroys entire landscapes and poisons mountain streams.

In the meantime, the brightest minds of every generation have been intrigued by the potential of the sea, sun, and wind to provide cheap and clean power. Today's scientists are giddy over predictions that the United States could get 20 percent of its electricity from renewable sources within a decade, but they're merely the latest thinkers to be dazzled by the prospects of "alternative" energy. Here's a brief look at clean energy's past, present, and future.


Wave and Tide

In 1799, a patent for ocean energy was granted to a Parisian father and son named Girard, who envisioned harnessing the power of heavy ships rocking back and forth in a harbor.

Cost remains a barrier to many ocean-based energy technologies, but engineers at the U.K.'s University of Southampton are looking at a cheaper wave-power device called Anaconda. The 656-foot-long, 23-foot-diameter rubber tube would be anchored just beneath the sea's surface and tap wave motion to drive a turbine in its tail.

Where We've Been
Efforts to tap the power of tides trace back to Roman times. Early mills put ocean currents to work processing grain, driving lumber mills, and pumping water. By the 18th century, 500 tidal mills dotted the Atlantic coast. The Eling Tide Mill in Hampshire, England, built more than 900 years ago and reopened after a 40-year hiatus in 1980, still grinds grain into flour.

Where We Are
In 2008, the phrase "British sea power" took on new meaning. Off the coast of Northern Ireland, in a shallow 1,500-foot-wide trench known as Strangford Lough, Bristol-based Marine Current Turbines installed the world's first commercial tidal power generator. Dubbed SeaGen, the $20 million device looks like an undersea windmill. With a 1.2-megawatt capacity, it can power more than 1,000 homes.

Three years ago, in New York City's East River--actually a tidal estuary--Verdant Power installed six demonstration turbines to supply electricity to a Manhattan supermarket. Verdant hopes to expand the project to 300 turbines that could power up to 10,000 homes in the city.

Where We're Going
Existing wave systems and tidal generators use the sea's kinetic energy to produce electricity. Ocean thermal energy conversion exploits temperature differences between the ocean surface and its colder depths. The system's greatest promise is in tropical regions, where surface water temperatures reach 80 degrees Fahrenheit, while 2,000 feet below it's nearly freezing. This differential can be tapped to vaporize liquids that then drive turbines. An experimental plant at Hawaii's Keahole Point produced 50,000 watts of electricity in 1979.


Solar

In 1882, French mathematician Augustin Mouchot used a sun-driven steam engine to print 500 copies per hour of the aptly named newspaper Le Journal du Soleil.

In the Southern California community of Santa Fe Springs, a new housing development will include 511 homes constructed with unobtrusive solar roof tiles. Combined with other conservation features, the high-efficiency panels could reduce residents' utility bills by 60 percent.

Despite current cost hurdles, the U.S. Department of Energy predicts that the price of photovoltaic power will compete with traditional electricity sources within 10 years.

Where We've Been
For as long as humans have built habitations, they have used solar energy for lighting and heating. The Greek philosopher Socrates noted that "in houses that look toward the south, the sun penetrates the portico in winter." The Romans improved on this concept by covering windows and doors with glass to capture heat. By the Victorian age in England, entire "glasshouses" were affixed to the south side of country estates, circulating warm air throughout the main structure. Early U.S. settlers found ways to utilize what we now call "passive solar" energy by orienting their Southwest adobes and New England saltboxes on an east-west axis to maximize (and minimize) solar exposure.

Where We Are
In 2007, a 377-foot-tall monument to Spain's commitment to carbon-free energy appeared on the sun-drenched plains outside Seville. More than 600 steel mirrors, called heliostats, are aimed at a receiver on Solucar tower, an obelisklike contraption that powers 6,000 homes. The solar thermal electricity generating structure focuses sunlight to heat water, producing steam that spins turbines.

Lacking government incentives, solar thermal has struggled on our side of the Atlantic, but thanks to improvements in storage and efficiency, energy analysts anticipate a boom in such projects in the near future. In May, Northern California's Pacific Gas and Electric Company (PG&E) and the Google-backed start-up Bright-Source Energy announced plans to build a facility that could supply enough juice to run half a million homes starting in 2012.

Where We're Going
Future plans for solar power seem lifted from a sci-fi novel. Researchers are focused on nanotechnology, electronic paints, and even space-based sunlight aggregators. One of the most promising technologies: ultrathin film that can reduce the amount of material in solar cells by up to a hundredfold. These cells could be incorporated into household items such as window curtains. Researchers hope to improve solar-cell efficiencies, which currently range from 8 to 35 percent; solar panels on residential rooftops have an average energy-conversion rate of 15 percent. Plastic-based conductors could replace traditional silicon cells in the next few years.

Solar scientists are also betting on computerized dual-axis trackers that allow photovoltaic cells to follow the sun's path across the sky, boosting solar efficiency by up to 40 percent. PG&E and the California-based Solaren Corporation recently unveiled plans to operate a space-based "solar farm" that would beam energy to earth.


Wind

In 1745, to the delight of windmill masters everywhere, Englishman Edmund Lee introduced the fantail, a rear sail that keeps the main blades turned into the wind.

Southwest Windpower offers the Skystream 3.7, a compact wind generator that can lower an average household's utility bill by as much as 80 percent.

During peak winds, Denmark meets more than 40 percent of its electricity demand with wind power. On average, wind power provides nearly a fifth of the country's electricity.

Where We've Been
Long before the age of OPEC, the Middle East had a handle on wind power. Around the seventh century, Persians used wind-driven panemones, bundled reeds attached to an upright axis, that turned mills to grind grain and pump water. Even today on the Greek island of Crete you can find sail-based rotational pumps drawing water from wells to feed cattle.

By the 19th century, windmills had transformed into the horizontal-axis structures that we recognize today, their Dutch innovators making the devices adaptable to wind direction and designing more efficient sail shapes. Early design tweaks such as cambered blades and spoilers remain commonplace on industrial wind farms.

Where We Are
Wind power makes up a mere 1.5 percent of the electricity supply in the United States, but modern wind generators are a big deal. With towers 400 feet high and blades as long as 300 feet, a single turbine's footprint can cover a football field. The reason is simple: Double the size of a rotor and you can quadruple the electricity produced.

Big, lumbering blades are also efficient in slow winds and easier for birds to dodge. The average wind turbine installed in 2009 is almost twice as powerful as one installed even just a few years ago; manufacturing giant Siemens is promoting a turbine that sweeps 86,000 square feet of air and has the capacity to provide power for 700 homes.

Where We're Going
Wind-power designers are revisiting the eggbeater-like vertical-axis wind turbine, first conceived nearly a century ago, because it is not limited by the vagaries of wind speed and direction. Though generally less efficient than "propeller" turbines, they can be mounted closer to the ground and efficiently handle wind turbulence.

Innovative companies are exploring kites that harvest power from the jet stream. Google forged a $15 million partnership with Makani Power in 2006 to explore the energy prospects of high-altitude winds. Taking its cues from the sea, Toronto-based WhalePower designed turbine blades that mimic a humpback whale's flippers: Bumps on the blade's leading edge create vortices that enhance lift.


Illustrations by Josh Cochran; used with permission

This article has been corrected subsequent to publication.

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