Actually, the practice that's been taken on by many countries in the EU, especially the UK, is what's called Feed In Tariffs (FIT). It's also gaining momentum in the US, as in California's 2008 program which allowed anyone whose system is producing more electricity than they need to sell the excess back to the utility, thus reducing their electric bill. Please refer to the Wikipedia Article.
The biggest problem with having taxation removed from "sustainability projects and goods" is the verification process. Who's to say what is sustainable? The last 10 years has seen a boom in what's now termed "green washing". There are companies out there to verify the "truthiness" of such claims, however the process is slow, admittedly.