Monday, February 28, 2011

Energy is power, if you've got the money

We can convert energy from one form to another, from a form that Nature provides into a form humans can use. But unless the conversion is affordable, the theoretical possibilities mean very little.

Tech to the Rescue

An early look at three technologies that may provide more energy in the future

The great thing about energy is that it's everywhere; the hard part is putting it to work in a useful fashion. What follows is a glimpse at three technologies under development that aim to tap unconventional energy sources—the motion of automobiles and the temperature and saltiness of seawater–to produce potentially vast new supplies of electricity.

Stop and Go

Getting a car moving takes a lot of energy, but when the vehicle comes to a stop most of that energy just gets dissipated. The engineers who designed hybrid gas-electric autos came up with a way to recover some of the energy lost in braking and convert it to electricity to recharge the hybrid's batteries.

But what if that converted energy could be put into the electric grid?

That's the idea behind several developments to harvest a vehicle's kinetic energy and turn drive-through lanes, parking lots and roadways into mini-power plants. The techniques vary but the idea is the same: As vehicles roll over a section of road, the device converts the force of the passing vehicle into electricity.

One company, U.K.-based Highway Energy Systems Ltd., has developed an energy-harvesting device and installed it at several sites, including airport parking garages and warehouse parking lots. The device uses moving plates that when depressed by braking vehicles use magnets to spin a generator, producing electricity. (A built-in flywheel helps maintain a consistent power level.)

A typical installation produces between 32 and 42 kilowatts an hour in continual traffic, says Peter Hughes, the system's inventor and a managing director of the company, which expects to have devices at 250 locations by summer.

In the U.S., New Energy Technologies Inc., a Columbia, Md., energy-technology company, has also demonstrated a kinetic-energy-harvesting system and plans to begin testing its latest version later this summer.

One potential problem with these systems is that they can lower the fuel efficiency of the automobile. As a result, developers intend to install them in places where vehicles are already slowing down—such as freeway off ramps, parking lots and drive-through lanes at fast-food restaurants.

Hot and Cold Oceans

The world's oceans are vast storehouses of energy, and for years scientists have been devising ways to tap the power of the seas' waves, tides and wind. Now another potential source is getting renewed attention: the difference between warm surface temperatures and the cold of the ocean depths.

Called ocean-thermal energy conversion, or OTEC, the process uses warm seawater to heat a fluid, such as ammonia, with a low boiling point, producing a vapor that turns a turbine to generate electricity. Cold water is piped from deep in the ocean to condense the vapor and keep the cycle going. Because the systems require big temperature differences—about 35 degrees Fahrenheit—the technology is best suited for coastal areas in the tropics.

The idea of ocean-thermal conversion dates to the 1880s, and the first experimental OTEC plant was built in Cuba in 1930—though it and a later plant required more power to operate than they produced. A larger, 50-kilowatt demonstration plant was built in 1979 at the Natural Energy Laboratory of Hawaii and produced about 15 kilowatts of net power.

Work on the technology slowed with the low energy prices of the 1980s and '90s, but interest in several countries has picked up recently. Lockheed-Martin Corp., whose predecessor built the Hawaii plant, in 2009 received an $8 million contract from the U.S. Navy to refine its design with the goal of building utility-scale OTEC plants.

One challenge: designing, building and deploying the 1,000-foot-long, large-diameter pipe that draws cold water to the surface. Lockheed is testing pipe designs and is aiming to begin construction on a pilot plant by 2014, says Jeff Napoliello, vice president of the company's New Ventures unit.

Where River and Sea Meet

When fresh and salt water meet, the process of osmosis creates pressure—and releases a significant amount of energy. This natural process makes the world's estuaries, where rivers meet the sea, a potentially rich source of power.

Statkraft, the state-owned Norwegian power company, in late 2009 opened the world's first osmotic power plant outside Oslo. The prototype plant, intended mainly for testing the concept, combines sea and fresh water, separated by racks of membranes; the pressure from fresh water flowing into the saltwater forces it through a turbine, generating electricity.

In the Netherlands, REDstack BV is working on a different technology that uses osmotic pressure from fresh and salt water to strip off positive and negative ions, creating a kind of battery. The company plans a 50-kilowatt pilot plant in the North-Holland province and is waiting on funding from the Dutch government.

Statkraft sees big potential in osmotic power. It estimates the technology could produce up to 1,700 terawatts of electricity globally—about half the European Union's total generation. The Statkraft plant is producing only about two to four kilowatts of electricity—about enough, the company says, to power a coffee maker. The company says its goal is to begin building commercial osmotic power plants as early as 2015.

There are many technical hurdles. Pretreating the water for use in the plants takes energy, reducing the plants' overall efficiency. Membranes are still expensive and relatively inefficient. Still, the technology "has real potential for generating base-load power in large cities at the convergence of fresh water and sea water," says Dallas Kachan, managing partner of Kachan & Co., a San Francisco consulting firm.



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