With this new impetus, engineers and start-up companies have jumped at the challenge, and while beamed power is still in its infancy, three viable options seem to be emerging. The use of radio waves to transmit electricity is perhaps the most obvious solution, since you can in principle use the same kinds of transmitters and receivers used in Wi-Fi communication. Powercast, based in Pittsburgh, Pennsylvania, has recently used this technology to transmit microwatts and milliwatts of power over at least 15 metres to industrial sensors. They believe a similar approach could one day be used to recharge small devices like remote controls, alarm clocks and even cellphones.
A second possibility, for more power-hungry devices, is to fire a finely focused infrared laser beam at a photovoltaic cell, which converts the beam back to electrical energy. It's an approach PowerBeam has adopted, but so far its efficiency is only between 15 and 30 per cent. While that could serve more power-hungry appliances, it would in practice be too wasteful.
The technology has been used to power wireless lamps, speakers and electronic photo frames that require less than 10 watts to function. Over time, as both the lasers and photovoltaic cells improve, the company hopes efficiencies of up to 50 per cent will be possible. "There's no reason we couldn't power a laptop eventually," says Graham. Unlike some other possible techniques, a sharply focused beam loses minimal energy over large distances, preserving its efficiency: "A hundred metres is no big deal."
xxx xxx on 22 Jul 08"In my personal opinion, most plants are unlikely to actually cut back because of profit factors. The smelters agreed to cut back mainly because of tight power and high power costs, but for some, supply is not much affected, only costs have gone up. But the cost of shutting down and restarting might be even higher than the increased power prices," a source from Shaanxi Tongchuan aluminum said July 11. A source from Chuangyuan aluminum said, "We also signed the agreement, but that's just a piece of paper; there is no definite ruling to say we must cut output. We have no plans to cut output at the moment or in the short term, but we may consider cutting back in the future." The Chuangyuan source also cited the power versus shutdown cost ratioand noted that in any case the company has its own power plant. "We don't expect many of the other smelters at the meeting to cut either, including Chalco ... everyone will wait and see," he said. "Domestic prices have risen slightly, but mainly affected by the rise on the LME yesterday - there seems to be little fundamental impact within China itself," an analyst from Beijing Antaike said July 11. "People are all very uncertain and maybe confused now since there are no definite details on what the cutbacks will be." A Chinese trader said domestic demand and trade activity were also expected to slow due to the Olympics, and those plants that actually shut may be able to restart in the fourth quarter, so the impact on domestic prices would be minimal.
