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Space solar power advocates may soon get their day in the sun, as different projects aimed at beaming energy to Earth from orbit begin to take shape. But at least one space power scientist worries that a U.S.-based project may be promising too much, too soon.

Last week, California regulators proposed a plan to approve a 15-year contract with the American company Solaren Corp. to supply space-based solar power to utility giant Pacific Gas & Electric (PG&E) by 2016. The Japan Aerospace Exploration Agency (JAXA) has also teamed up with a private Japanese coalition to design a solar space station for launch by the 2030s.

Such projects encourage scientists who dream of harnessing the sun's power directly, without the interruption of cloudy skies and Earth's day-night cycle. Marty Hoffert, a physicist at New York University and one of the staunchest supporters of space solar power, suggests that today's technologies allow space solar power to provide energy as cheaply as the usual solar panel arrays on Earth.

"The problem is that we're treating space solar power as something that has to compete with coal right now," said Hoffert, who gave a recent talk on beamed power at the New Jersey Institute of Technology. "Nothing can compete with coal."

Despite his enthusiasm, Hoffert remains skeptical of Solaren's plan. And he warns that failure to deliver could deal a life-threatening blow to the dream of space solar power.

A decision by the California Power Utility Commission on Solaren's plan for PG&E could come as early as Thursday, according to a Dow Jones wire report.

Harnessing the sun

Solar panels in space can receive seven times more solar energy per unit than ones on Earth and don't have to deal with weather or darkness. The challenge in harnessing that energy comes from the expensive costs of launching material into space, as well as figuring out how to beam energy back down to Earth.

Microwave beaming has long been the favored delivery option for space solar power advocates. Space power stations using this method would convert the electricity generated by solar panels into radio frequency (RF) waves for beaming down to an Earth receiver several kilometers wide.

A former NASA scientist demonstrated the RF concept last year by beaming 20 watts between two Hawaiian islands — barely enough energy to power a dim light bulb. That experiment cost just $1 million. A full-scale space solar power setup would require much bigger and more costly receivers.

Another more recent choice has arisen in the form of solid-state lasers. Such lasers now have enough power to deliver energy as a tightly focused optical beam that requires much less costly equipment in space and on the ground. But unlike RF, lasers can run into bigger problems with atmospheric interference and weather.

"Microwaves can beam through clouds, which lasers can't," Hoffert explained. "With lasers you're going to have to have receivers in desert sites that are cloud free, and maybe backup receivers in several sites."

Hoffert still favors lasers because of the lower costs required up front for a tech demonstration. By contrast, Solaren weighed its choices and decided to go with RF technology.

"Basically we chose RF because it is more efficient and has all-weather capability for the reliable delivery of electricity to our customers," said Cal Boerman, Solaren's director of energy services.

READ MORE:   Space.com