Solar is so over.

The news broke early this morning, and on the other side of the ocean: Germany's No. 3 solar panel maker is bidding to enter the lucrative business of ... car manufacturing. Now, you're going to think I'm making this up, but I assure you that what follows is a true speculative deal Bloomberg reported on (with thanks to CAPS newcomer and solar skeptic Hapoalim Securities for bringing it to my attention):

What's German for chutzpah?
Solarworld AG bid 1 billion euros to buy General Motors' (NYSE:GM) Opel manufacturing sites in Germany this morning (even though Opel isn't technically for sale), its bid being conditioned on: Germany itself loaning Solarworld the cash and General Motors paying it all back. In essence, Solarworld wants GM to hand over its German sites for free -- and that ain't gonna happen. But this story is about more than just a lowball bid that GM will certainly reject. If you dig a little deeper, I think you'll agree that it sounds the death knell for the solar industry.

Solar power, green cars -- a match made in heaven?
Sure, on the surface, Solarworld's offer makes sense. Solarworld does solar power -- green energy. It wants to buy Opel to build hybrid and electric (i.e. green) cars. Plus, SW wants all of Opel's property, plant, equipment, and trained workers, for free. Hard to go wrong with terms like these. Worse comes to worst, SW could just turn around and sell Opel for a profit.

Dig a little deeper
And yet, the tenuous logic of the deal aside, the idea as a whole sounds utterly crazy. I mean, solar power is the next big thing, right? Isn't that why Suntech (NYSE:STP) and First Solar (NASDAQ:FSLR) gained like a billion percent in their first couple years post-IPO? So why would Germany's third biggest solar player diworsify away from this profit monster, and plunge into the (pardon the mixed metaphor) trainwreck that is auto manufacturing?

The answer isn't obvious, but if you think on it a bit, I suspect it will come to you: Solar power ain't what it used to be. Previously considered an industry at the front end of a capital J-curve, we're now beginning to remember that j's can be downgraded into the lower case as well.

And now, Solarworld thinks it can get better returns on its capital by building green Buicks than by manufacturing solar panels. Whether Solarworld is right or wrong about that, it doesn't sound like good news for solar pure-plays like Solarfun (NASDAQ:SOLF) or Yingli Green Energy (NYSE:YGE). Sounds to me like just one more reason Fools should adopt a skeptical stance on solar.

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This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.