Wouldn’t it be magnificent if we had a low-cost way to capture the sun’s energy and economically store it for later consumption? Actually, we do. Plant material, and its ancient forms like oil, natural gas, and coal all represent just such a scheme. As a bonus, they remove carbon dioxide from the air in the process.
Improving Nature’s Design
But researchers have long sought a way to improve upon nature’s processes. Artificial photosynthesis has great technical promise for utilizing solar power to convert carbon dioxide into fuel. Natural photosynthetic efficiency is very low, but it can result in huge accumulations of useful materials over time.
Artificial photosynthesis would speed up the process. In its simplest form, electricity produced from solar power could be used to split water into oxygen and hydrogen gas. Hydrogen could then be stored for later consumption as fuel, or it can be combined with other raw materials to produce chemicals or fuels.
Many researchers over the years have claimed breakthroughs with this sort of technology, and the media often treats these claims as “game-changing” technology. The most recent announcement comes from Cornell University startup Dimensional Energy. In a press release – Just add sun: McGovern startup converts CO2 into fuel — Cornell announced:
Dimensional Energy is pioneering artificial photosynthesis to produce green polymers and chemicals. “In industrial uses, we can capture carbon dioxide from commercial entities before it leaks into the atmosphere. We put it into our reactor, add hydrogen and sunlight. All of this goes into our machine and comes out as a useful fuel,” said David Erickson, a Cornell Atkinson Center fellow.
But here is a sampling of previous researchers making similar claims:
- In 2009, Professor Dobieslaw Nazimek at the University of Maria Curie-Sklodowska in Poland announced an artificial photosynthesis process based on the photocatalytic conversion of water and carbon dioxide into methanol.
- In 2012, a British company called Air Fuel Synthesis made an announcement that they were producing gasoline from thin air. The process combined hydrogen with carbon dioxide to make methanol, and then the methanol was converted into gasoline. It was predicted to be commercialized by 2014. It wasn’t, and the company’s website is now defunct.
- In 2015, Audi announced to great fanfare (e.g., here, here, and here) that it had conjured fuel from thin air using just water and carbon dioxide.
- Perhaps nobody has worked on this concept longer than MIT’s Daniel Nocera, who summarized the status of the technology in a 2011 paper The Artificial Leaf.
What’s the Catch?
These approaches are all technically viable. But it’s also technically viable for me to use this approach to create acetaminophen from thin air. Or just about anything containing the basic ingredients of the atmosphere like carbon, hydrogen, oxygen, and nitrogen. I could even devise a process to create DNA from thin air.
The “catch” in every one of these schemes comes by way of thermodynamic laws. These laws necessarily require that when converting water or carbon dioxide back into a fuel (like hydrogen), that it requires more energy inputs than you get back out of the fuel. For example, to produce 1 British thermal unit (Btu) of hydrogen via electrolysis may require the input of 1.5 Btus of electricity. It may require additional energy inputs to compress, store, and transport the hydrogen.
In short, there’s no free lunch. Such a process could be viable with excess solar power that might otherwise be wasted. At times, California has been producing so much excess solar electricity that it is paying neighboring states like Arizona to take it. It might be more economical to instead convert that excess electricity into hydrogen, which could later be converted back into electricity as needed — even if that means doing so at a net negative energy balance.
The real question with this type of scheme is whether it makes more economic sense to store excess electricity in another form, such as batteries or pumped hydropower. For now, take these “breakthrough announcements” with a grain of salt. Technically viable doesn’t necessarily equate to economically viable, and it isn’t clear which, if any, of these approaches will achieve lasting success.