http://cen.acs.org/articles/91/web/2013/05/Energy-Storing-Nanomaterial-Made-Hemp.html
"Part of Mitlin’s research is finding ways to use plant waste as feedstocks for commercial materials. He thought he could transform waste from the cannabis plant (Cannabis sativa) into a carbon nanomaterial that had similar properties to graphene and with a much smaller price tag. The cannabis plant’s notorious use is for producing marijuana, but people also grow the plant to use its fibrous parts for products such as rope, clothing, oil, and plastics. The plants used for these industrial applications are referred to as hemp, and have lower levels of psychoactive compounds. Hemp is relatively inexpensive, since the plant grows rapidly in a variety of climates without the need for fertilizer and pesticides...
The team built a supercapacitor using the nanosheets as electrodes and an ionic liquid as an electrolyte. The best property of the device, Mitlin says, is its maximum power density, a measure of how much power a given mass of the material can produce. At 60 °C, the material puts out 49 kW/kg; activated carbon used in commercial electrodes supplies 17 kW/kg at that temperature."