There are literally hundreds of 'green' products being marketed in this era of environmental awareness. There are genuine retailers, ignorant ones and unscrupulous ones. There are extremely useful products. On the other hand there are others that don't perform as well as their manufacturers suggest. Some of them might be more wasteful of natural resources or harmful to the environment than conventional solutions.
Whether buying that solar powered car fan, upgrading your hot water heater or adding a rainwater tank it would be worthwhile to keep a few important questions in mind:
1) Most importantly - do I need it? Buying nothing requires no demand on resources compared to buying green.
2) Do I need to upgrade to green? - Is maintaining or sustaining a current system more wasteful than investing in a new efficient product?
3) What is the embodied energy of the product? What resources were required to produce it? Did it need to be shipped a long distance to get here?
4) What are the additional life-time inputs required to operate the product? e.g. water, energy, chemicals, my own time and effort
5) What is its life-cycle and warranty? Should I choose between the expensive but more durable product made of rare materials or be willing to constantly replace a cheaper model made of abundant materials?
6) Not only does it work but does it perform as well as the manufacturer suggests? Don't be beguiled by the sales pitch. Don't be afraid of asking for hard data or willing to do some rough estimations yourself. Usually the answer becomes quite obvious with a little reflection.
7) What is its payback period? Not only on the savings gained but also for the amount of resources invested in the first place
There are other things that may change in the near future that may influence you final decision such as:
1) Product price
2) Scarcity of primary resources
3) Projected price of water and electricity
Happy shopping.