I had several good discussions in response to my little alien conversation a while back. Unfortunately they all happened either offline or in the (private) FreeAllegiance/Steel Fury forums. Post in the comments next time you slackers! I know you all have Google accounts.
Anyway so something several people mentioned was, 'how could an intelligent species develop a photovoltaic cell before figuring out how bump the right two rocks together?
I see the following possible answers:
* They are in an environment unsuited to combustion (underwater, highly humid, delicate chemistry)
* They saw an example in nature
The first is so strikingly simple: underwater beings would have to find other ways of creating energy. The bouyant and tidal forces would be amazingly useful if you lived your whole life underwater. Particularly if you had an easily accessible atmosphere above the surface of your sea. But solar isn't particularly useful unless you're willing to spend enough time underwater.
The second possibility fascinates me even more. What if there was a simple animal or plant evolved to take advantage of the photovoltaic principle? It may sound far fetched, but electronic potential is a fundamental force.
One such fanciful creature: imagine colony of spores, whose natural enemy were small, slow-moving insects. Suppose a mutation emerged which resulted in the development of photovoltaic potential. In the daytime, this small potential might be enough to discourage the pests. Natural selection continues, and soon there is enough voltage developed for a sentient creature to notice and study. Perhaps given the right environment and enough time this effect could even produce theoretically perfect efficiency.
Imagine also a sentient creature who burns neither plant material nor fossil fuels because the smokey output is displeasing to a sensitive respiratory system. Such a creature would not have taken to steam powered conveniences as we humans did. When we discovered the photovoltaic principle, its output paled so far in comparison to what we could get from coal-fired steam or even the early internal combustion engine that it was not pursued with the same vigor as dirtier technology.
If we were, for some reason, unable to burn coal, how revolutionary would have been the discovery of the solar cell? In our vigor, how soon would we have discovered Cadmium Telluride? Perhaps most strikingly, would we still measure the economy of such devices to such a high standard as the one we hold now, the standard of the abundant-petroleum economy?
Essentially all the sources of energy we have at our disposal come ultimately from the pre-primordial cloud from which our solar system formed. So many elements essential to our life have come from generation after generation of stars who have fused together heavier and heavier elements. But two of the most common things in our solar system - photons and hydrogen - are really great sources of energy. It just happens to be really inconvenient way down here in our gravity well. In the scope of time the idea of painfully separating hydrogen from carbon, the idea of moving mountains to uncover rare uranium will seem just as alien as the idea of killing whales to make oil for light.