Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: GT Solar (Nasdaq: SOLR) shares are down 10% in early trading today after an analyst from Credit Suisse downgraded the stock.

So what: The entire sector is under pressure today after a weak earnings report from Suntech Power (NYSE: STP) and Credit Suisse's downgrade of GT Solar, First Solar (Nasdaq: FSLR), and Trina Solar (NYSE: TSL), among others. Analyst Satya Kumar thinks "flattish" demand will lead to lower prices than expected and put downward pressure on margins.

Now what: It's been a wild ride for solar in the last few weeks as the sector rallied before earnings, saw mostly solid earnings reports, and is now on a nosedive on worries for 2011. If you've been around solar investing for long, you've heard this song and dance from analysts before. Calls for lower demand haven't really panned out in the past, and I don't think they will this time either, so I'm looking at this weakness as a buying opportunity for the whole sector. There might be more downward momentum beyond today, but in the coming weeks there will be plenty of buying opportunities.

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Fool contributor Travis Hoium owns shares of First Solar. You can follow Travis on Twitter at @FlushDrawFool, check out his personal stock holdings or follow his CAPS picks at TMFFlushDraw.

First Solar and Suntech Power Holdings are Motley Fool Rule Breakers selections. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.