In a piece yesterday by John Wasik on Bloomberg, a cautious note is sounded about the boom in alternative energy.

He asks, are alternative energy stocks the next dot bomb?

And then suggests - amongst other options - of buying small cap index funds as a way to gain safe exposure. For some people, that may no doubt be true. Of course, every high performing industry in world history eventually reverts to the mean. Booms never do last forever.

But alternative energy is still relatively so small compared to conventional power, it's hard not to see substantial growth for some time to come. There are certain assumptions that you can make about rising environmental concerns, relative scarcity of fossil fuels and accelerating global economic growth pricing in 2 billion people from the developing world. It's also worth noting that these AEI investors are not necessarily only trying to make money - they are, at least in part, driven by SRI ethics and an intangible belief in the technology.

With oil touching $75 a barrel, I wouldn't write off alternative energy just yet.