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CO2 as renewable energy storage vessel

Research from Det Norske Veritas (DNV) shows that CO2 could be used, amongst other things, as storage for renewable energy.

By Renewable Energy Focus staff

As part of its research into electrochemical conversion of CO2, DNV has assembled a demonstration reactor in a solar-powered trailer, where formic acid is produced from CO2 - which avoids CO2 emissions at the same time as utilising CO2.

The process of electrochemical conversion could be powered by solar, wind, hydroelectric, geothermal, tidal and thermoelectric processes, which means it can be used as a renewable electricity storage mechanism. The stored energy can be released later for end-use by oxidisation of the fuels through fuel cells or by releasing hydrogen and using it in fuel-burning engines.

DNV Research & Innovation Director Narasi Sridhar, says: "We have invested in resources and tools to analyse the CO2 value chain using electrochemical conversion as a case study. Our research demonstrates the conversion of CO2 into formic acid can be economically viable. This requires less energy per ton of CO2 than most other electrochemical conversion pathways. Also, formic acid is in demand and can also be used as chemical feedstock, steel pickling, antibacterial agents, energy storage medium, and de-icing solutions."

In the position paper Carbon Dioxide Utilization: Electrochemical Conversion of CO2 - Opportunities and Challenges, DNV describes uses of CO2 and the processes of electrochemical conversion of CO2.

Three main uses for CO2 have been identified by the risk management company:

  • As a fuel or storage medium for renewable energy;
  • As a feedstock for various chemicals; and
  • As a solvent or working fluid without converting chemically

The paper states that: "The use of CO2 to convert solar energy into biomass and, from there, to various renewable fuels is now widely supported by industry and governments as a means to secure future energy supplies and to decrease net CO2 emissions to atmosphere."

Furthermore, "second and third generation biofuels that are based on grasses and algae will increase in supply." These feedstock of course, convert CO2 into biomass and oxygen through the aid of sunlight.

Energy storage chemicals

CO2 can also be converted via chemical and electrochemical processes to other energy storage chemicals such as syngas, formic acid, methane, ethylene, methanol and dimethyl ether (DME).

Chemicals such as formic acid could be a useful storage medium for hydrogen, which again could be used in fuel cells or burnt directly, DNV says. Formic acid is currently used in leather tanning, animal feed, and bactericidal applications.

Geothermal fluid

Non-converted CO2 – so-called supercritical CO2 – could also be used as a heat transfer fluid for some geothermal applications.

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