This article is part of our Rising Star Portfolio series.

First Solar (Nasdaq: FSLR) has lost my confidence in almost every conceivable way since I purchased shares last September. I've decided to toss it from the real-money Rising Star portfolio I'm managing for Fool.com so I can focus on stocks with far brighter futures.

A long list of disappointments
I was willing to overlook the headwinds that face the solar industry overall. First Solar is hardly the only solar stock that's taken a drubbing over the course of the last six months or so. Former pick SunPower (Nasdaq: SPWR) has tumbled since I sold it more than a year ago. For more gloom, take a look at the charts of solar stocks like Trina Solar (NYSE: TSL), Suntech (NYSE: STP), and Yingli Green Energy (NYSE: YGE). This entire industry's been taking a real beating.

Uncertainty about government spending on solar buildouts has thrown shadows over the industry. Germany has been a lucrative area for solar given its position as the largest global market for solar technology, but that particular country could cut nearly 30% from subsidies that have been so helpful to the solar industry.

For American companies First Solar and SunPower, China's proven to be a major competitive difficulty. Chinese solar outfits like Trina, Suntech, and Yingli have been able to flood the market with cheap solar products, aided by the Chinese government's subsidies to the industry.

Still, some of the issues that have led to my decision are specific to First Solar. In December, I warned that First Solar was the stock I was most likely to sell from this portfolio. I took offense at the amount of compensation outgoing CEO Rob Gillette had received, and it also came to light that First Solar also threw a fair amount of money around on lobbying expenditures.

Yet still I held on, recognizing that First Solar's management style might be contrary to what I'd like to see in an investment, and a real risk to keep an eye on as time went on.

However, the outlook may really be changing for First Solar as it's been transitioning to huge solar farms from small rooftop installations. It's recently come to light that First Solar's equipment is showing some heat-related "degradation" issues, with more problems on equipment installed in hotter climates. In other words, its equipment may have weaknesses in exactly the types of places mammoth solar farms make the most sense, like sun-scorched desert.

Although First Solar's management said in its conference call it doesn't have a lot of data as of yet regarding the level of this panel performance degradation, First Solar's business evolution sounds like it's becoming riskier all the time.

Last but not least, First Solar has revealed that it's being investigated by the Securities & Exchange Commission for possible violation of Reg FD rules regarding disclosures related to its Topaz solar farm's failure to meet deadlines for U.S. Department of Energy loan guarantees.

So long, First Solar
One of my goals for this portfolio is to avoid sweating the short term, and to hold stocks for the long haul. However, if the mounting evidence seems to show a stock isn't holding up to my original thesis, or something is fundamentally changing, then there comes a point when it has to go. First Solar has reached that point for me, and then some. The portfolio's taking a major loss on this pick, but I've come to the conclusion that holding would be a far worse mistake than selling given the litany of disappointment and uncertainty.

So long, First Solar. I'll be on the lookout for brighter investment opportunities elsewhere.