Photo by {ryan}.

At some point in 2012, 10 cultivation centers will start growing marijuana as part of the District’s long-awaited medical marijuana program. As we’ve written before, what with application fees and security plans, it won’t be a particularly cheap undertaking. Now would-be cultivators may have one more thing to worry about — their electric bills.

A report written by a researcher at the Lawrence Berkeley National Laboratory and published in April found that growing marijuana indoors is quite the energy-intensive undertaking, so much so that it costs $5 billion a year in electricity costs, or what two million U.S. homes would use. Moreover:

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 8% 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.

From the perspective of individual consumers, a single Cannabis cigarette represents 2 pounds of CO2 emissions, an amount equal to running a 100-watt light bulb for 17 hours with average U.S. electricity (or 30 hours on California’s cleaner grid). Each four-by-four-foot production module doubles the electricity use of an average U.S. home and triples that of an average California home. The added electricity use is equivalent to running about 30 refrigerators. Processed Cannabis results in 3000-times its weight in CO2 emissions.

The majority of energy used goes into lighting, ventilation and dehumidifying, and air conditioning.

This is particularly relevant because it’s assumed that the majority of the cultivators growing for the city’s medical marijuana program will do so indoors, likely employing many of the same tools and techniques covered in the study. Considering that a 16-square-foot module that produces four plants doubles the electricity use of an average home, the 95 plants allowed under D.C. law will require some 24 modules and, well, a lot of energy. (It’s probably worth noting that Pepco wants to raise rates again.)

Of course, there are a bunch of caveats to the report, and also a number of ways that cultivators can reduce their electricity usage. Still, given that D.C. rules require that the marijuana be organically grown, it may behoove some cultivators to find a way to offset all those carbon emissions.