If solar power is ever going to take off—and the world needs it to—photovoltaic cells will have to become a whole lot cheaper to produce.

Making solar cells from silicon, the most common approach, can be expensive and relatively inefficient at turning sunlight into electricity. As semiconductor manufacturer Applied Materials chief technology officer Mark Pinto told me last year: "With solar, it's all about cost."

But there are signs of improvement, writes Richard Swanson of SunPower Corp. in this week's Science. Last year, manufacturers made 5 gigawatts of photovoltaic panels. And some of these panels required just under six grams of silicon per watt of power—down from 15 grams at the turn of the century. And that watt of power now costs around $1.40 to produce compared with $2 or more in the 1990s.

Duke Energy wants to put a power plant on your house.

Over the next year, the utility plans to spend $50 million to plop a variety of photovoltaic panels on commercial buildings, the roofs of private homes, and other property in North Carolina.

Once installed, the 10 megawatts worth of solar panels are expected to produce enough alternating-current electricity to power 1,300 homes. But the utility’s main goals for the demonstration project are to gain experience with distributed generation—putting the power plant closer to the customer—and with integrating intermittent, renewable resources like sunshine into the grid.

Munich-based Phoenix Solar AG, a German photovoltaic system installer, has committed $615 million (450 million Euros) to purchasing Solyndra's cylindrical solar cells as a core part of its future rooftop installation business. Why? "We see significant cost-savings," says chief technology officer Manfred Bächler. "We simply do not need any supporting structures or ballasts or roof penetrations," because, unlike traditional flat solar panels, the new round kind don't need any help to keep grounded when the wind blows.

In addition, the ability of the solar cylinders to collect direct, diffuse and sunlight reflected from the rooftop—as well as the ability to lay panels of them horizontal to the roof itself means more electricity can be made from a given rooftop. Further, the solar cylinders keep cooler overall, which enhances the performance of the system, Bächler says.

The amount of solar photovoltaics harnessing electricity from sunshine in the U.S. will more than double by 2013, thanks to plans to build 800 megawatts (MW) worth in California. The two vast solar farms—covering more than 12 square miles—will be among the largest ever built in the world and dwarf the current U.S. record holder: Nellis Air Force Base in Nevada with 14 MW. In fact, the total amount of solar photovoltaics connected to the grid in the entire U.S. is just 473 MW at present.

"These landmark agreements signal the arrival of utility-scale PV solar power that may be cost-competitive with solar thermal and wind energy," said Jack Keenan, chief operating officer and senior vice president for utility PG&E, which made the deal, in an announcement yesterday.