Not long ago, there was a modicum of logic to their volatile movements. They rallied in 2007 as phrases like "greentech" and "clean energy" entered the popular lexicon. They rallied on as political rhetoric in the U.S. looked to solar energy as an oil alternative, as homeowners began installing solar panels and as production costs became more agreeable.

Then they kept rallying because -- well, because the momentum was there.

Come 2008, the momentum reversed. Most solar stocks fell amid reports that U.S. lawmakers, locked in partisan squabbling, might not get their act together in time to renew vital tax credits for solar installations. (Because solar panels are still more expensive than traditional energies, the tax credits offer important incentives.) Concerns about reduced subsidies in Spain and rising costs of silicon fed the declines.

For months, they kept falling -- even as valuations grew attractive once again. And they fell even further as many of the companies reported what might otherwise qualify as blowout earnings.

It was as if a bubble was bursting even before it began.

No one could say for sure why. Maybe the collapse of Chinese stocks in general was dragging down the China-based solar companies. Maybe investors who got burned decided they needed to see a real turning point before jumping back in.

But now, however, what might pass for a turning point in such a volatile corner of the market may be upon us.