Carbon emission is regarded as the chief culprit of global warming, so it is necessary to lower the level of carbon dioxide in the atmosphere, aside from reducing emission of carbon dioxide and greenhouse gas. A German science team has recently developed a “multifunctional rooftop energy system” that utilizes sunlight to convert moisture and carbon dioxide in the air into synthesis gas that can be used to generate power.
Synthesis gas is similar to common hydrocarbon fuels, which are generally referred to as fuel gases mixed with carbon monoxide and hydrogen, though it can be produced through the carbon dioxide in biomass energy, renewable energy, and the atmosphere. Synthesis gas is usually used to generate power, but it can also be applied in producing drugs, plastic, and fertilizers.
ETH Zurich has targeted at this carbon neutral fuel, and is currently developing residential energy systems that are able to produce household fuels from merely sunlight and air.
The system consists of a direct carbon capture equipment, a solar redox system, and a gas-to-liquid (GTL). First, the air is sucked in, and then the extracted carbon dioxide and water are transported to the second piece of equipment, where a concentrating solar equipment would focus sunlight onto the solar reactor under a factor of 3,000 times to produce a 1,500°C high temperature. Finally, the internal cerium oxide ceramic structure would absorb the oxygen in air to produce hydrogen and carbon monoxide, which is synthesis gas.
The synthesis gas will then be transported to the third piece of equipment, where it is converted into liquid hydrocarbon fuels such as kerosene and methanol. To confirm the feasibility of the concept, researchers have laid down a small 5K watt pilot system on the rooftop of a building that produces 32ml of methanol each day under an approximate daily insolation of 7 hours.
Despite insignificant result, a calculation of the research team indicates that an expansion to an industrial scale, such as 10 major concentrating solar power plants, would derive 95,000L of fuels each day, which are more than enough for an Airbus A350 to make a round trip between London and New York.
However, it would require 45,000 km2 of solar power plants to satisfy all fuel demand of the aviation industry, and the up-front cost from these power plants would make the fuel itself much more expensive in comparison with traditional fossil fuels, thus a further increase in efficiency is required.
(Cover photo source: ETH Zurich)