Shares of SunPower Corp. /zigman2/quotes/200243424/composite SPWR -2.58% sank 5.1% in premarket trading Monday, after the solar power company said it plans to sell 22 million shares of common stock to the public. The company plans to use the proceeds from the offering for general corporate purposes, which could include paying down its 0.875% convertible debt due in 2021. The offering would increase the shares outstanding by about 15%. SunPower is also offering underwriters of the offering, which are led by Goldman Sachs and BofA Securities, option to buy an additional 3.3 million shares to cover over-allotments. The stock has tumbled 35.6% over the past three months through Friday, while the S&P 500 /zigman2/quotes/210599714/realtime SPX -0.02% has gained 8.0%.