Consider the disposable diaper. It's part engineering marvel, a mechanism that takes one of the most foul side effects of parenthood and absorbs it into a small, manageable, plastic-wrapped package. But it's also part environmental catastrophe.

The average baby makes nearly 6,000 diapers dirty before becoming bathroom-trained. Waste watchers estimate that 27.4 billion disposable diapers are discarded each year in the U.S., adding as much as 3.4 million tons to dumps annually.

And that's not all. Each disposable diaper contains plastics and, in many cases, toxic chemical residues that show up in paper products, such as the chlorine used to make those diapers lily white.

We've all heard about the promise of green technology in regards to carbon emissions, the ozone layer and polar bears up on the ice cap. But, it could also save your portfolio. Recent private investment activity in this sector stands out in a depressed marketplace, suggesting that there is considerable upside potential for early investors, not to mention a future for the sector that will later be available to the public.

Four new clean technology deals were recently announced signaling that early stage private investment trend is gaining steam. Some transactions bring new participants to the table, while others reflect the commitment of repeat investments. Investment in clean technologies is robust -- a rare breed in today's market -- and the amounts are far from trivial. Further, they span all stages, from angel financing through private investment in public equity.

Where would you want to open a prototype "green" restaurant? McDonald's (MCD) has decided to do so on the south side of Chicago. The new restaurant starts with the typical standalone McDonald's unit we are used to seeing and uses "smarter design elements" to save the store 25 percent per year in utility bills.

What are the changes? The new store will use heat recovery devices to recycle cooking heat. Storm water runoff from the parking lot will be collected and used for irrigation. Plants will be stationed on the roof to provide insulation and further water control. Skylights will augment and eliminate the need for some electric lighting, and tables will be made from recycled plastic. In addition, cardboard food containers will be produced from recycled material.