<Ul> <Li> </Li> <Li> </Li> <Li> </Li> </Ul> <P> Such fuels are considered carbon - neutral because they do not result in a net increase in atmospheric greenhouse gases . To the extent that synthetic 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 . </P> <P> Such renewable fuels 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 . Carbon - neutral fuels offer relatively low cost energy storage, alleviating the problems of wind and solar intermittency, and they enable distribution of wind, water, and solar power through existing natural gas pipelines . </P> <P> 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 day, but wind tends to blow slightly more at night than during the day, so, the price of nighttime wind power is often much less expensive than any alternative . Germany has built a 250 kilowatt synthetic methane plant which they are scaling up to 10 megawatts . </P>

Describe two sources of earth's energy that are not produced