Will Clean Energy Ever Be a Reality in the U.S.? Here's What's Standing in Our Way
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Most people don't think of Texas as "a progressive, innovative state on energy," says Kapner, "but in reality it is." Solar's technological advances have evolved, rather than come through major breakthroughs, he says. Silicon is still the most common material used for photovoltaic devices, says Wladek Walukiewicz of Lawrence Berkeley Labs in California. It's not very efficient, he adds -- it converts 10 to 20 percent of the energy received to electricity--but it can be produced cheaply. The Chinese have been able to bring prices down by "the sheer power of mass production."
Some solar producers are opting for a newer technology called "thin-film" devices. These employ either a cadmium-telluride combination or a copper-indium-gallium-selenium alloy called "CIGS." They are not more efficient than silicon, says Walukiewicz, but can be produced cheaply and require far less space and thus fewer materials in the overall system.
Walukiewicz and other scientists at Lawrence Berkeley recently unveiled a photovoltaic device made from a mix of gallium nitride and indium nitride that gets 43 percent efficiency. The gallium compound is sensitive to light on the ultraviolet side of the spectrum, while the indium is sensitive to the infrared side, he explains, but if you mix the two, you get a device sensitive to visible light, and you can adjust the mix for different wavelengths. These elements are much more expensive than silicon, but the devices would be "much easier to make, much simpler."
A power grid based on renewable energy would most likely be a mix of individual sources, such as solar panels on rooftops and office and industrial buildings, and centralized generation by utilities. Utilities would have to adapt to decentralization, but "they'll still have a major role," says Ken Zweibel, as they would provide economies of scale and more reliable backup.
Decentralization requires that utilities allow "reverse metering," letting private users with solar panels pump the surplus electricity they generate back into the grid and thus reduce their bills. Some states mandate this.
How to store the electricity produced is still an issue. What do you do at night or on cloudy days? Solar-power advocates counter that it would eliminate the need for costly peak-power generation, because the most intense sun coincides with the heaviest use of air-conditioning. "Brownouts would go away," Masia says.
The flaw in that argument, Kapner say, is that there is still a high demand for air-conditioning after sundown. Electricity use peaks when people get home from work; in the Southwest, utilities run at 90 percent of peak demand at sundown, and one-third to half of that is for cooling. Kapner believes this problem could be resolved by better cooling systems and smarter grid management.
Concentrated solar-power systems can store the energy they produce as heat in tanks of molten salt, but photovoltaic devices have to rely on batteries, which are more expensive. Another possibility is using the electricity generated to pump water into mini-hydropower systems.
Storage is "not a big deal" now, says Brett Prior, but will become more crucial as renewables become a substantial part of electricity generation. "Dispatchability" is also an issue, he adds, as gas plants can be turned on and off quickly to meet demand, while solar and wind supplies are more intermittent.
Still, says Zweibel, current solar technology is "adequate to meet 10 to 20 percent of current energy needs, so we need to get on the ball." "I don't think there are any technical hurdles right now," says Walukiewicz. "Germany is not a very sunny place, but they are probably the biggest consumer of solar cells."