Energy

Rooftop system converts CO2, water and sunlight into kerosene

Rooftop system converts CO2, w...
The solar fuel reactor harnessing heat from concentrated sunlight to convert carbon dioxide and water into syngas
The solar fuel reactor harnessing heat from concentrated sunlight to convert carbon dioxide and water into syngas
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The solar fuel reactor harnessing heat from concentrated sunlight to convert carbon dioxide and water into syngas
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The solar fuel reactor harnessing heat from concentrated sunlight to convert carbon dioxide and water into syngas

Engineers at ETH Zurich have demonstrated a pilot system that can produce fuels from sunlight and air. The device captures carbon dioxide and water from the atmosphere and uses solar energy to convert it into syngas, which is then converted into liquid fuel that’s essentially carbon neutral.

With a clearer understanding of the damage caused by human carbon dioxide emissions, there’s plenty of work being done to transition towards electric vehicles, hydrogen power, fuel cells and other sustainable forms of energy. However, these advances will require big changes to the existing infrastructure, which can slow down their implementation.

In the meantime, synthetic fuels could be a decent solution. These are made to mimic current liquid hydrocarbon fuels but are produced from renewable sources, such as biomass, waste products or carbon already in the atmosphere. And because they replace or complement fossil fuels, they can be “dropped into” existing engines and infrastructure.

In the new study, researchers at ETH Zurich developed and tested a new system that can produce these drop-in fuels using just sunlight and air. The resulting fuel is carbon neutral, releasing only as much carbon dioxide when burned as its production removed from the air originally.

The system is comprised of three units – a direct air capture unit, a solar redox unit, and a gas-to-liquid unit. The first section sucks in ambient air, and uses adsorption to pull carbon dioxide and water out of it. These are then piped into the second unit, where solar energy is harnessed to trigger chemical reactions.

A parabolic concentrator focuses sunlight by a factor of 3,000 onto the solar reactor, creating temperatures of 1,500 °C (2,732 °F). Inside the reactor is a ceramic structure made of cerium oxide, which absorbs oxygen from the incoming carbon dioxide and water, producing hydrogen and carbon monoxide – syngas.

The syngas itself could be collected for use, or it can be funneled to the third unit, where it’s converted into liquid hydrocarbon fuels like kerosene or methanol.

To test the concept, the researchers set up a small 5-kW pilot system on the roof of a building. Running for seven hours a day in intermittent sunlight, the device was able to produce 32 ml (1.1 oz) of methanol each day.

That’s not a whole lot, but the team says it shows that the concept works and could be scaled up to commercial production. A large-scale plant could look like a solar thermal power plant, with a field of concentrators focusing sunlight onto a central tower. The team calculates that a plant using 10 of these fields, each collecting 100 MW of solar radiative power, could produce 95,000 L (25,000 gal) of kerosene per day. That’s enough to get an Airbus A350 from London to New York and back again.

To cover the entire demand of kerosene in aviation, the team calculates that around 45,000 km2 (17,375 sq miles) of solar plants would be needed. Unfortunately, high upfront costs to set up these plants would make these fuels more expensive than the fossil fuels they’re replacing, so subsidies and support would be needed to get them off the ground, which may limit their viability.

The research was published in the journal Nature. Take a tour of the system in the video below.

Fuels from sunlight and air

Source: ETH Zurich

11 comments
11 comments
greg
That's really cool and I support all avenues for finding alternative renewable approaches to transportation and everything else. I just want to make sure it is clear what just happened here though. Many people advocate syngas or hydrogen in place of battery electric vehicles. But here's the math:

that 5kW solar array could have been used to make electricity (sort of. Theyre talking solar-thermal vs solar PV, but lets assume we have resources to install one or the other for the sake of this comparison) and sent directly to an electric car, with some losses. They said they were able to get 1.1floz of basically methanol (50% as much stored energy as gasoline per unit volume) per day from their 5kW array. 1.1floz of something half as potent as gasoline would get a 50mpg (slow, boring) Prius 0.18miles. Now Based on the annual output of my home's rooftop solar array in dark, cloudy, rainy Seattle, that 5kW array would on the average day produce 14.37kWh. Very rough numbers, let take out 10% for charging losses and we're looking at 12.9kWh which if we put to the batteries of the fastest (read as: electron guzzling-est) EV in the world, the Tesla Model S Plaid, you could propel that rocketship of a vehicle 40 miles down the road compared to the.. what was it?.. 0.18 miles in the boring Prius.

Now this is still in development and I'm sure efficiency will improve. But its going to have to improve _A LOT_ to overcome that 225:1 range factor when used as automotive fuel. I'm not saying its a bad thing in the right application. But I am saying, the idea that using solar panels to make liquid or gaseous fuels for passenger vehicles is ludicrously (Tesla pun intended) wasteful.
christopher
"so subsidies and support would be needed to get them off the ground" - which is a polite way of saying "will never happen".

It's a pity that profit always comes first.
Rustgecko
There's no such thing as a free lunch.
Toddy
@greg, I think it would be a reasonable guess that if they're capable of producing methane to create methanol, and they're capable of producing longer carbon chain fuels such as kerosene, then they're also capable of producing intermediate chain length hydrocarbons such as regular octane with regular stored energy levels which then allows for keeping current internal combustion technology.

We're probably in agreement about which vehicle we'd choose given the choice between a methanol powered Prius or a Model S Plaid :) but I think the article is aiming at keeping current petrol/diesel/kerosene engines running rather than making vehicles burn novel fuels.
jerryd
There are better, easier ways. CO2, water and power driving the process with RE power on a copper, etc catalyst directly make multiple HCs including ethanol at 60% efficiency is the future. Going the syngas route just takes too many steps, losses.
The problem here is getting air CO2.
A good way is burning waste biomass, other wastes in O2 giving a clean air CO2 ready to make clean synfuels or store.
TomLeeM
I think that is both cool and green.
HoppyHopkins
"To test the concept, the researchers set up a small 5-kW pilot system on the roof of a building. Running for seven hours a day in intermittent sunlight, the device was able to produce 32 ml (1.1 oz) of methanol each day."
My off grid 4 Kw generator requires more than 100 times that amount per day just for 7 hours of daily power. Not exactly practical for small scale usefulness
Gregg Eshelman
In the USA we need something that makes a "drop in" replacement for gasoline, like isobutanol.
Karmudjun
Nice write up Michael! You could have editorialized a little - if a 5KW version produces only 1.1 oz of product in a 7 hour period, then this is the equivalent to 'teats on a mule" as Abraham Lincoln stated (when referring to his General of the Army of the Potomac).

Clearly this process is a step in the right direction. It is not ready to solve anyone's energy crisis, but it is a thought process that achieves two very important goals: 1) remove threatening levels of CO2 from the atmosphere molecule by molecule & sequester them in a useful form; 2) harness the viable light and radiation from the sun to produce something other than rising global temperatures - notably a store-able and movable energy product. When will this thinking result in realistic energy production?

I'm all for these guys thinking things through and then providing proof-of-concept, and intellectually it is a breakthrough - but the article is written from THEIR view - overhyped and incapable of making any real difference in the near future!
martinwinlow
For God's sake! What is the point in going to all this trouble to make synthetic fuel only to burn it in an engine that wastes 70%+ of the fuel's energy??!!! Wake up for crying out loud! Burn it for cooking or other processes that will make far better use of the energy but vehicles need *electric* motors not stinky fuel-based ones (and ideally batteries with about twice as much specific/volumetric energy density)!
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