It's volatile. It's erratic. It's solar stocks, and it's not for the faint of heart. Yesterday, most of the sector slid. But today, while many stocks were making upward moves throughout the market, most of the solars came roaring back. Suntech Power ( STP) shares were gaining 4.6% by the afternoon. On Tuesday, the company said COO Johnson Chiang resigned for "personal reasons." In a press release, Suntech said that Guangchun Zhang, the company's VP of Manufacturing Technology and Quality, would look after PV operations in China. Meanwhile, CEO Zhengrong Shi would tend to certain operations in Shanghai and Japan until a new COO is found. For First Solar ( FSLR), ThinkEquity upgraded the company to buy from accumulate yesterday. Shares were swinging back and forth for most of the afternoon. The stock was changing hands up 52 cents at $150.10. In other solar stock movements: Sunpower ( SPWRA) was up 3.1% in the afternoon. Yingli Green Energy ( YGE) was up nearly 8%, or 82 cents, at $11.13.