What happened 

Shares of SunPower (NASDAQ:SPWR) fell as much as 13.6% today as investors jumped ship before a public offering of the stock hits the market. Shares closed 13.1% lower on the day. 

So what

Earlier this week, SunPower announced that it would be selling 22 million shares of stock with the potential for another 3.3 million if underwriters exercise their over-allotment option. The funds will be used for "general corporate purposes," but paying back convertible debt due in 2021 was called out as a use for the cash. 

Workers installing solar panels at solar farm.

Image source: SunPower.

What's a little strange is that the stock didn't move much on Tuesday after the share sale was announced and actually slid a little higher. But traders may be getting word that there isn't much of an appetite to pay a premium for SunPower's shares in a new offering, which could mean that the offering happens at a big discount to where shares trade. Today, those traders look to be getting ahead of that discount. 

Now what

Today's move isn't driven by news from SunPower or the solar industry overall, so it looks to be a trading phenomenon that can happen before a share offering. For long-term investors, I wouldn't be too alarmed. What will be important to watch in the coming months is how SunPower uses this cash and how its business changes after spinning off the manufacturing side of operations. There are more questions than answers today, so a cautious approach to today's drop is a wise move.