In a new paper published on 3 June in the Proceedings of the National Academy of Sciences, Patterson and colleagues propose a novel way of potentially recycling atmospheric carbon dioxide (CO2) into synthetic fuels using renewable energy — which they suggest may be “an energy concept with no net CO2 emissions” (1).

To limit global warming to well below 1.5 to 2 degrees Celcius to prevent dangerous climate change, CO2 emissions from fossil fuel burning must be eliminated. At present, renewable energy sources cannot compete with fossil fuels. Therefore, carbon-based liquid fuels — an important medium for storing carbon removed from the atmosphere — will continue to play a crucial role in the foreseeable future, the authors write.

The team of researchers from Switzerland and Norway suggest photovoltaic cells could be used to convert solar energy into electricity, which could then be used to power hydrogen production and CO2 extraction from seawater. The resulting gasses would then be reacted to form methanol, which could be reused as a fuel — and “conveniently shipped to the end user”.

Large-scale, marine-based artificial islands of these solar farms could eventually yield zero net CO2 emissions – if enough of them are built. The so-called solar methanol islands would need to be placed in ocean areas where wave heights are less than seven meters tall and there is a low risk of hurricanes. Further, water depths must be less than 600 meters to properly moor the islands.

Therefore, the most suitable locations are shorelines along the equator with plenty of sunshine and relatively small waves, for instance, Indonesia, northern Australia, and Brazil.

The energy ‘producing’ islands were initially proposed to meet the energy requirements off-shore fish farms. However, the Norwegian researchers soon realized the approach could be re-purposed. As such, most of the technologies needed to develop these facilities already exist on an industrial scale, the authors argue, with the exception of a large scale device to extract CO2 from seawater.

Nonetheless, several challenges remain. For example, electrolysing seawater creates unwanted chlorine. Moreover, existing copper–zinc–aluminium catalysts require high pressures and temperatures – hydrogen and carbon dioxide can react to form carbon monoxide at high temperatures. And development costs must be significantly reduced to make the project economically viable.

To this end, the “ambitious” proposal is certainly a long way from being realised. But the researchers are working hard to build the first prototype and believe the effort may be worth it. They calculate that a cluster of 70 islands could potentially produce up to 1.75 tonnes of methanol per hour – which means 170,000 clusters need to be constructed to offset the emissions from long-haul transport. Moreover, they suggest using a mere 1.5 per cent of the world’s oceans for solar methanol farms could offset global fossil fuel emissions altogether.

Thus, applying the technology on a large scale in the ocean could potentially remove the need for fossil fuels altogether. And importantly, mitigate the effects of climate change over the coming decades.

(1) Patterson, B.D. et al. Renewable CO2 recycling and synthetic fuel production in a marine environment. Proceeding of the National Academy of Sciences (2019). DOI: 10.1073/pnas.1902335116

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