As wind, solar, and nuclear power push the electricity grid to 95% decarbonisation, humanity discovers that the final 5% is the hardest to cross. Achieving a completely zero-carbon electricity system requires the construction of vast energy storage and transmission networks, which come at an astonishing cost. At this juncture, carbon capture and storage (CCS) emerges as a more pragmatic option: rather than pursuing absolute zero emissions, it aims to capture residual carbon emissions and offset them through engineering means.
Direct Air Carbon Capture and Storage (DACCS) represents the purest technological concept. It uses chemical adsorbents to extract carbon dioxide directly from the air, theoretically deployable anywhere without reliance on energy sources. However, the concentration of CO₂ in the atmosphere is only 0.04%, making it exceedingly thin. To capture one ton of carbon, thousands of tons of air must be processed, consuming vast amounts of energy. Currently, DACCS at the experimental scale costs between $400 and $1,000 per ton, and even if it were to drop to $200 in the future, it would still be an expensive technology. Its advantages lie in flexibility and decentralisation; however, its efficiency and cost are far from ideal.
Bioenergy with carbon capture and storage (BECCS) operates on a more natural principle. It utilises plants that absorb carbon dioxide during their growth, then burns this biomass for power generation while capturing carbon emissions from the flue gases. Since the concentration of CO₂ in combustion gases can reach 10% to 15%, hundreds of times higher than in the air, carbon capture efficiency significantly improves, with costs around $100 to $200 per ton. More importantly, it can simultaneously generate electricity. Fast-growing plants such as bamboo, elephant grass, and reeds absorb carbon rapidly during their growth phase; once harvested, burned, and captured, the land can be replanted, creating a continuous ‘negative emissions cycle’. Such power plants can operate during periods without wind or sunlight, maintaining grid stability, and represent truly ‘dispatchable’ green energy.
In comparison, DACCS is flexible but expensive, while BECCS is efficient but requires land. DACCS is suitable as a decentralised compensation method, whereas BECCS can become part of the grid, producing energy while reducing carbon. In the medium to short term, the latter is more realistically feasible. To achieve the final 5% of net zero, rather than investing astronomical sums in building super grids, it may be more prudent to allow BECCS to engineer a solution to bridge the gap.
As for energy storage, short-term power can be managed by technologies such as lithium batteries, thermal bricks, gravity storage, and flywheels; however, to address seasonal long-term fluctuations, green hydrogen and BECCS are more effective partners. Hydrogen can be stored long-term and activated quickly, while BECCS provides both power supply and carbon capture functions. Together, they form the infrastructure for ‘deep decarbonisation’.
Of course, the scientific community has yet to reach a consensus. Some experts believe that CCS is the key piece of the net-zero puzzle, but it is not yet time for large-scale promotion; others argue that as long as energy storage technology is robust enough, CCS is entirely unnecessary. However, in high-energy-consuming industries such as steel, cement, chemicals, and aviation, carbon emissions are nearly impossible to eliminate. To truly bring the planet to zero, carbon capture may be the only fallback and the last hope.
