Aldo Steinfield has a problem with the carbon footprint of world travelers. In his SolveForX talk Solar Syngas, he starts with a quick back of the envelope calculation. During his recent trip from Zurich to San Francisco he flew 5832 miles. The trip created a 1.4 ton carbon footprint.
Worldwide there are 50,000 flights per day carrying 3million passengers, which he estimates creates 900million tons of CO2 per year. Further, he estimates that all transportation globally creates 3.9billion tons of CO2 per year. This might account for up to fourteen percent of human carbon emissions.
Steinfeld narrows the scope of his work to aviation - there are no alternative fuels for aviation. Boeings won't be flown with batteries, he tells us in the talk. His problem statement now becomes a question of how we can drastically drop the carbon footprint from liquid hydrocarbon fuels but keep our need for driving or flying.
After a few more calculations about the amount of solar radiation hitting the earth, Aldo calculates that a square area of 160 miles per side would gather enough solar energy in a year to meet these needs. His radical proposal is to build massive solar arrays that replace the large solar collection tower with solar reactors. These solar reactors would combine water and carbon dioxide transformed by solar energy into fuel.
The two step process starts with solar reduction, introducing solar energy at a temperature of 1500 C and taking oxygen out of the mixture. The second step is to cool the reactor to 900 C, introduce water and carbon dioxide, and create the Syngas.
https://www.solveforx.com/moonshots/aldo-steinfeld-solar-syngas
Steinfield's Syngas is then converted into what he calls liquid hydrocarbons, and hopes to use as a jet fuel. As of early 2014 prototype reactors have been built that take 4 kW of solar radiation to create fuel. The current projected efficiency of solar energy to fuel creation is two percent.
Aldo calculates the efficiency by taking the heating value of fuel produced and dividing it by the solar energy input. The amount of solar energy going into a solar array is obviously massive. Long term the goal is to reach twenty percent efficiency, where Steinfield says one solar reactor will produce 4,100 gallons of kerosene per day.
This is a massive problem and Steinfield has been working on it for years if not decades. Many details still need to be finalized before the project can become a reality. One big question is where the carbon dioxide will come from - for the process to be truly sustainable the CO2 should come from atmospheric air. Aldo shows us his theoretical process of adsorption and desorption that can bring in ambient air and produce pure CO2 and H2O.
Aldo Steinfield is an incredible speaker. This SolveForX talk is fascinating because he methodically goes through the problem solving process. The basic calculations to establish the size of the problem are a great way to frame the rest of the discussion. Kyle Maxey reported last week about a recent demonstration of the sunlight-to-jet-fuel process, so the project is moving forward with great success.
https://www.solveforx.com/moonshots/aldo-steinfeld-solar-syngas