What counts as renewable energy?

While working on a paper, I was looking through my notes about eligibility for California’s Renewable Portfolio Standard.

The California PUC has an interesting and comprehensive taxonomy of what counts as renewable energy:

• Biomass - any organic material not derived from fossil fuels, including agricultural crops, agricultural wastes and residues, waste pallets, crates, dunnage, manufacturing, and construction wood wastes, landscape and right-of-way tree trimmings, mill residues that result from milling lumber, rangeland maintenance residues, sludge derived from organic matter, and wood and wood waste from timbering operations.
• Biodiesel - Biodiesel is a type of biofuel made by combining animal fat or vegetable oil (such as soybean oil or recycled restaurant grease) with alcohol and can be directly substituted for diesel. (Source: MTC/link)
• Fuel cells using renewable fuels – electricity produced from the creation and breakdown of hydrogen. If the hydrogen source is a renewable fuel, this technology is RPS eligible.
• Digester gas - gas from the anaerobic digestion of organic wastes.
• Geothermal - natural heat from within the earth, captured for production of electric power, space heating, or industrial steam.
• Landfill gas - gas produced by the breakdown of organic matter in a landfill (composed primarily of methane and carbon dioxide), or the technology that uses this gas to produce power.
• Municipal solid waste - solid waste as defined in Public Resources Code Section 40191.
• Ocean wave - an experimental technology that uses ocean waves to produce electricity.
• Ocean thermal – an experimental technology that uses the temperature differences between deep and surface ocean water to produce electricity.
• Tidal current - energy obtained by using the motion of the tides to run water turbines that drive electric generators.
• Solar Photovoltaic - a technology that uses a semiconductor to convert sunlight directly into electricity.
• Small hydroelectric (30 megawatts or less) - a facility employing one or more hydroelectric turbine generators, the sum capacity of which does not exceed 30 megawatts.
• Solar thermal – Use of concentrated sunlight to produce heat that powers an electric generator.
• Wind - energy from wind converted into mechanical energy and then electricity.

Does anyone notice what’s missing? (Hint: it’s only the largest source of renewable energy in California, the US and the world.)