DOE Study Guide on Alternative Fuels to Know About

Ever wonder what categories of alternative fuels (something besides gasoline or diesel) are on the market, and which ones are in development? I do, and it's important to follow. Some of the race cars being tested around the world use these fuels and are testing out advanced alternative fuels and technologies. Solar race cars have been tested for years and could offer a renewable-energy powered car someday. As for now, the categories that are on the market and not just for test cars, according to Dept. of Energy, are:

Electricity
Ethanol
Biodiesel
Natural gas
Propane autogas
Hydrogen
Methanol

There isn't much methanol left, but it's still in use in small quantities. It was very big in the early 1990s, especially in fleet programs, but it eroded engines rapidly and wreaked havoc.

Here's the other categories of fuel currently under development, much of which came to be under the Energy Policy Act of 1992:

Biobutanol - an alcohol that can be produced through processing of domestically grown crops, such as corn and sugar beets, and other biomass.
Biogas - produced from the anaerobic digestion of organic matter such as animal manure, sewage, and municipal solid waste. After it is processed to required standards of purity, biogas becomes a renewable substitute for natural gas.
Biomass to Liquids (BTL) - a term describing processes for converting diverse biomass feedstocks into a range of liquid fuels.
Coal to Liquids (CTL) - processes for converting coal into liquid fuels.
Fischer-Tropsch Diesel - made by converting gaseous hydrocarbons, such as natural gas and gasified coal or biomass, into liquid fuel.
Gas to Liquids (GTL) - a process for converting natural gas into liquid fuels.
Hydrogenation-Derived Renewable Diesel (HDRD) - product of fats or vegetable oils—alone or blended with petroleum—that have been refined in an oil refinery.
P-Series - a blend of natural gas liquids (pentanes plus), ethanol, and the biomass-derived co-solvent methyltetrahydrofuran (MeTHF) that are formulated to be used in flexible fuel vehicles.
Ultra-Low Sulfur Diesel - diesel fuel with lower sulfur content enacted nationwide in 2010.

There might be other categories to consider, especially in realm of biofuels. It might already be included in the DOE's BTL category, but there's always investment, research, and development being made in algae biofuel, cellulosic ethanol, and other advanced biofuels. Synthetic fuels are also being tested, too, which are scientifically redesigned versions of gasoline and diesel with lower emissions and better efficiency.