SunPower, a maker of solar­ panels, fell the most in six months after it cut its 2012 sales forecast. The shares have dropped 33 percent this year. Revenue for 2012 will range from $2.4 billion to $2.6 billion, SunPower said, compared with a May 3 forecast of $2.6 billion to $3 billion. Its second-quarter loss narrowed to $84.2 million, from $147.9 million.