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What: Shares of solar developer First Solar, Inc. (FSLR 2.10%) fell as much as 10.3% today after being downgraded by an analyst. At 3:20 p.m. EDT, shares were still down 9.9%.

So what: Analysts at Deutsche Bank cut their rating for First Solar from buy to hold and also lowered their price target from $80 to $44. The move was made because of slow bookings, a potential delay of demand from customers as they wait for next-generation products, and industry oversupply that could lead to lower panel prices.  

Analysts have had a hard time figuring out how much demand the solar industry will have in 2017 as the U.S. and China will likely see slowing growth or even a decline. That could lead to negative earnings trends, which is the concern today.

Now what: 2017 has been a question mark for the solar industry for years, so it shouldn't be any surprise that the demand environment is uncertain. But in long run, I don't think there's any reason to change your investment thesis in First Solar. The company has one of the best balance sheets and technology in the solar industry, which in the long term will allow it to maintain a leading market position in the industry.

If you have a time horizon of five to 10 years, which you should in the solar industry, today is a buying opportunity for an industry leader, not a reason to be afraid of an analyst adjusting expectations for the next 12 months.