A useful piece just published here on Motley Fool Scouting the latest IPOs.

The article mentioned 5 companies that touch on the alternative energy realm about to IPO or that just have;

i) Clean Energy Fuels Corp - a company that seeks to provide natural gas for municipal transport needs. Gas is certainly much cleaner and an environmental benefit in terms of reduced particulates. And I've got a lot of sympathy for this technology as I use it myself (liquified petroleum gas or LPG in Europe) with my old BMW. But unlike some, I would never claim this was alternative energy technology any more than including clean coal technology companies.

ii) LDK Solar - a Chinese solar wafer manufacturer, going public this week. There are plenty of Chinese solar companies already but analysts are divided on whether this party has only just got started or if it is now looking like a bubble.

iii) Yingli Green Energy - (no website I can find) another Chinese solar cell manufacturer, to IPO shortly - announced deal terms of 29 million American depositary shares at $11-$13 per share. The lead managers are Goldman Sachs and UBS.

iv) Imperium Renewables - A US-based biodiesel producer

v) China Sunergy (no website yet, to be added very shortly to AEI) - IPO'ed a couple of weeks back and makes solar cells.

In recent weeks, many have been fretting about the alternative energy bubble. But since alternative energy stocks first started to appear, arguably in the late 1990s, there have been several pullbacks or more accurately, shifts of investor focus;

Fuels cell stocks led by Ballard until 2000
Danish and German wind stocks
US-based ethanol stocks until April 2006
German solar stocks
And now it seems to be Chinese solar cell manufacturers are in vogue

So we must never fail to keep asking ourselves how long will this particular alternative energy theme last and what's next?