Google recently opened its Wikipedia competitor, styled "Knol" for unit of knowledge. I wrote a definition of cleantech to put up on Knol, and upon reflection, it's probably an overview worth passing around. Especially given that at my own sites - CleantechBlog.com and Cleantech.org - and at CNET's Green Tech Blog, we have been significant contributors to defining the sector. Without further ado, here is the definition:
Cleantech, also referred to as clean technology, and often used interchangeably with the term greentech, has emerged as an umbrella term encompassing the investment asset class, technology, and business sectors which include clean energy, environmental, and sustainable or green, products and services. (See various definitions below.)
The term has historically been differentiated from various definitions of green business, sustainability, or triple bottom line industries by its origins in the venture capital investment community, and has grown to define a business sector that includes significant and high growth industries such as solar, wind, water purification, and biofuels.