Beacon Power Corp. (Wilmington, MA) set its planned initial public offering at eight million shares of common stock at $11 to $13 per share. In an amended prospectus filed on Thursday with the Securities and Exchange Commission, the company announced that it expects to raise about $88.1 million in net proceeds from the offering. The underwriters, led by Salomon Smith Barney, have been granted the option of buying 1.2 million more shares to cover any over-allotments.Beacon, which makes a line of energy-storage systems based on flywheel technology, is a spin-off of SatCon Technology Corp. (Cambridge, MA). However, SatCon's stake in Beacon will be reduced from 33.2 percent to 25.5 percent by the IPO. After the IPO, Beacon will have 38.5 million shares outstanding, giving it an initial market capitalization of $462.0 million, based on a price of $12 per share.Beacon says it plans to use the IPO proceeds for research and development, sales and marketing, working capital, capital spending, and acquisitions.