Barclays analyst Moses Sutton double downgraded First Solar (FSLR) to Underweight from Overweight with a price target of $49, down from $66.

The stock in premarket trading is down 5% to $55.98.

After assessing industry data on 5,000 projects, both operational and in the company's pipeline, the analyst believes First Solar's Systems business "is in trouble." This is not a bear call on U.S. Solar, and First Solar's module business is not at risk, Sutton tells investors in a research note.

However, its Systems business has lost 80% of its U.S. market share, with NextEra Energy (NEE), EDF and Invenergy gaining share, says the analyst. Sutton expects First Solar's "rapidly declining share" of the U.S. downstream project market to cause a downward re-rating of the shares.