I'm not sure I follow. My current understanding of what I've read is we would be paying for the electricity used twice. The first time through our electric bill, the second by donating GRC to an renewable energy coin? Or are we trading a portion of GRC for the other coin, so we are holding two coins instead of one in the hopes that one may do better than another?
The current research rewards don't even come close to covering the electricity used.
If we want to be environmentally responsible a bonus should be given to more power efficient hardware. Or a environmental fee assessed and donated to a program that plants trees, or helps low income households replace inefficient appliances (save electricity and help people reduces living expense) for really old and inefficient hardware.
After reading a few comments I wonder if the energy being used is considered fungible. Most renewable energy has priority for being purchased first by the utilities. The way to be green is to use less energy so dirty energy sources are not activated. When we contrive to specifically buy 'green energy' more isn't created, someone else is just buying dirty energy.