Alternative Fuel - Carbon Neutral and Negative Fuels

Carbon Neutral and Negative Fuels

Carbon neutral fuel is synthetic fuel — such as methane, gasoline, diesel fuel or jet fuel — produced from renewable or nuclear energy used to hydrogenate waste carbon dioxide recycled from power plant flue exhaust gas or derived from carbonic acid in seawater. Such fuels are potentially carbon neutral because they do not result in a net increase in atmospheric greenhouse gases. To the extent that carbon neutral fuels displace fossil fuels, or if they are produced from waste carbon or seawater carbonic acid, and their combustion is subject to carbon capture at the flue or exhaust pipe, they result in negative carbon dioxide emission and net carbon dioxide removal from the atmosphere, and thus constitute a form of greenhouse gas remediation. Such carbon neutral and negative fuels can be produced by the electrolysis of water to make hydrogen used in the Sabatier reaction to produce methane which may then be stored to be burned later in power plants as synthetic natural gas, transported by pipeline, truck, or tanker ship, or be used in gas to liquids processes such as the Fischer–Tropsch process to make traditional transportation or heating fuels.

Carbon neutral fuels have been proposed for distributed storage for renewable energy, minimizing problems of wind and solar intermittency, and enabling transmission of wind, water, and solar power through existing natural gas pipelines. Such renewable fuels could alleviate the costs and dependency issues of imported fossil fuels without requiring either electrification of the vehicle fleet or conversion to hydrogen or other fuels, enabling continued compatible and affordable vehicles. Germany has built a 250 kilowatt synthetic methane plant which they are scaling up to 10 megawatts. Commercial developments are taking place in Columbia, South Carolina, Camarillo, California, and Darlington, England.

The least expensive source of carbon for recycling into fuel is flue-gas emissions from fossil-fuel combustion where it can be extracted for about USD $7.50 per ton. Automobile exhaust gas capture has also been proposed to be economical but would require extensive design changes or retrofitting. Since carbonic acid in seawater is in chemical equilibrium with atmospheric carbon dioxide, extraction of carbon from seawater has been studied. Researchers have estimated that carbon extraction from seawater would cost about $50 per ton. Carbon capture from ambient air is more costly, at between $600 and $1000 per ton and is considered impractical for fuel synthesis or carbon sequestration.

Nighttime wind power is considered the most economical form of electrical power with which to synthesize fuel, because the load curve for electricity peaks sharply during the warmest hours of the day, but wind tends to blow slightly more at night than during the day. Therefore, the price of nighttime wind power is often much less expensive than any alternative. Off-peak wind power prices in high wind penetration areas of the U.S. averaged 1.64 cents per kilowatt-hour in 2009, but only 0.71 cents/kWh during the least expensive six hours of the day. Typically, wholesale electricity costs 2 to 5 cents/kWh during the day. Commercial fuel synthesis companies suggest they can produce fuel for less than petroleum fuels when oil costs more than $55 per barrel. The U.S. Navy estimates that shipboard production of jet fuel from nuclear power would cost about $6 per gallon. While that was about twice the petroleum fuel cost in 2010, it is expected to be much less than the market price in less than five years if recent trends continue. Moreover, since the delivery of fuel to a carrier battle group costs about $8 per gallon, shipboard production is already much less expensive. However, U.S. civilian nuclear power is considerably more expensive than wind power. The Navy's estimate that 100 megawatts can produce 41,000 gallons of fuel per day indicates that terrestrial production from wind power would cost less than $1 per gallon.