When this article says that “scientists don’t expect traditional silicon-based solar cells to become competitive with fossil fuels,” one has to ask, “Ever?” Can anyone accurately predict the future price of polysilicon or of fossil fuels?

Peter A. Kaczowka
Lenox, Mass.

Your article notes as a put-down that it would be necessary to build a 1-gigawatt nuclear-fission plant every day and a half for the next 45 years to meet anticipated global electrical demand. A similar calculation indicates that building an equivalent solar capacity would require that we coat about 60 square kilometers of desert with photovoltaic material every day and a half, plus build a massive load-leveling system.

Hugh Hixon
Phoenix, Ariz.

Research into the storage of solar power during off hours is necessary now, but when the solar-power grid is sufficiently large, we should be able to shift power around the grid so that the sunny areas can supply the nighttime areas.

William Newman
Sandy Hook, Conn.

Articles on solar cells always avoid discussing what I consider to be two crucial points. First, solar cells have a limited service life. Second, it takes a lot of energy to make a solar cell in the first place. So, you have to ask, can you get enough energy from a solar cell over its useful life to make another solar cell?

Tom Sargent
Tucson, Ariz.

Researcher Nathan Lewis says, “More energy from the sun hits the Earth in 1 hour than all the energy consumed by humans in an entire year.” So what? If it’s theoretical limits we’re talking about, there’s over 20,000 years’ worth of uranium in the oceans.

Steve Briggs
Champaign, Ill.

Aren’t they called leaves? Instead of reinventing the tree with “organic solar cells,” why not do research on harvesting electricity directly from trees?

Clarence Guidry
New Orleans, La.

This story and “Spinning into Control” (SN: 5/19/07, p. 312) should be combined. A flywheel-energy-storage device under a building roofed with solar cells is the ideal solution.

Bob Koster
North Tustin, Calif.