"Indoor Cannabis production results in energy expenditures of $6 billion each year--6-times that of the entire U.S. pharmaceutical industry--with electricity use equivalent to that of 2 million average U.S. homes. This corresponds to 1% of national electricity consumption or 2% of that in households. The yearly greenhouse-gas pollution (carbon dioxide, CO2 ) from the electricity plus associated transportation fuels equals that of 3 million cars. Energy costs constitute a quarter of wholesale value.
In California, the top-producing state—and one of 17 states to allow cultivation for medical purposes—the practice is responsible for about 3% of all electricity use or 9% of household use. Due to higher electricity prices and cleaner fuels used to make electricity, California incurs 70% of national energy costs but only 20% of national CO2 emissions."
Read the full report by LBNL's Evan Mills: http://evan-mills.com/energy-associates/Indoor.html