Could AC units be our oil wells of the future?

Air conditioning units could help mitigate climate change by capturing CO₂ and converting it into renewable hydrocarbon fuels. That’s the premise of a new article titled “Crowd oil not crude oil” published by a team of researchers from the Karlsruhe Institute of Technology.

“Imagine the renewable-electricity-powered air conditioning system in your house, apartment or office at work, besides functioning for cooling and heating, being adapted to capture carbon dioxide and water from the air,” reads the report.

“Imagine the water and carbon dioxide thus collected converted into renewable hydrocarbon fuels using existing technology and thereby creating personalised, localised and distributed, synthetic oil wells.”

Although it may sound rather speculative, the elements of such a system are already commercially available. A number of companies sell technology for:

• Capturing CO₂ directly from the air
• Generating H₂ electrochemically from H₂O or even synthesis gas by further conversion of H₂ with CO₂
• Producing a mixture of H₂ and CO by co-electrolysis of H₂O and CO₂
• Producing hydrocarbon or oxygenated fuels from CO₂ and H₂ or synthesis gas catalytically.

Based on the experimental performance of these technologies, the team calculated the amount of hydrocarbon fuels that could be captured Frankfurt’s Trade Fair Tower (or Messeturm) and its 63,000m² of office space. It estimated a production rate of liquid hydrocarbon fuels of 2,000–4,000 metric tonnes per year.

The team also looked at the potential CO₂ capture at Germany’s three largest supermarket chains. If the total network of 25,000 stores were equipped with synthesis units and the matching co-electrolysis units within one or more compact containers, about 1,000 metric tonnes of CO₂ could be captured per hour.

“Impressively, using onsite conversion this would allow provision of 3 million metric tonnes of hydrocarbon fuels per year, which is about 8 per cent of Germany’s total consumption of diesel of 38.7 million metric tonnes or 30 per cent of its total consumption of kerosene of 10 million metric tonnes.”

Finally, there is an analysis of the potential for small-scale residential CO₂ capture and conversion units. The report looked at the low-energy housing development of Vauban in Freiburg, and estimated that the 354 buildings could supply 620 metric tonnes of CO₂ per year.

Assuming a consumption of 6L hydrocarbon fuel per 100km, each of the cars in Vauban could drive 11,000km per year with the fuel synthesised by the crowd’s own production facilities. That is close to the average mileage of a car in Germany.

The report notes that despite growing awareness of the need to lower CO₂ levels, there is little appetite for large-scale CO₂ capture and storage for later use by traditional energy carriers. A distributed solution, however, would put the power in individuals’ hands.

“Perhaps more likely to gain public support is a project wherein people use renewable electricity and solar thermal or waste heat to collect CO₂ in order to recycle it into hydrocarbon fuels in their homes, apartments and offices. The products generated in these decentralised synthetic oil wells could be used to replace conventional fossil fuels or stored for later use. This could be, for example, for power generation in fuel cells or micro gas turbines at times when there is a deficit of renewable power supply, but also as a transportation fuel in the future.”

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