The paradoxical result depends on the owners of a BECCS plant being financially compensated for removing carbon dioxide and arises because, as well as having a lower capital cost, an inefficient BECCS plant will remove more carbon dioxide from the air per power unit generated.

The best way to operate such a BECCS plant, the researchers say, may be in a base-load fashion, where electricity is generated constantly and dispatched to the grid on an as-needed basis, and surplus electricity is stored as hydrogen.

"The statement that this system would be more preferable from a financial perspective, even when producing more electricity than it dispatches on the grid, is likely to be counterintuitive to the power generation field," said Niall Mac Dowell of Imperial College London.

BECCS is unusual among technologies for removing carbon dioxide from the atmosphere in that it can generate electricity at the same time. From an environmental point of view, a less efficient BECCS system is better because it burns more biomass – and subsequently stores more carbon dioxide – for the same amount of energy generated.

To be widely implemented, however, a BECCS system also needs to be financially attractive. A liberalized energy market rewards power plants that generate electricity at the lowest cost to the consumer – typically efficient ones with the lowest marginal costs of energy generation. To complicate matters, the world is increasingly turning towards renewable energy, which – while exhibiting low marginal costs of energy generation – is intermittent in nature.

To analyse this financial situation, Mac Dowell and his colleague Mathilde Fajardy at Imperial took the case of a 500 MW BECCS facility that could capture carbon dioxide at an efficiency of 90%, a common benchmark. They assumed that the facility would be compensated for both the electricity it produces and the carbon dioxide it removes from the atmosphere.

By setting the power plant efficiency, how often it runs and how often it dispatches to the grid, the researchers were able to compare financial and environmental performance in different scenarios. They found that, so long as the owners of such a plant are financially compensated for removing carbon dioxide, the result will always be that a more valuable plant, compared with an efficient alternative, generates a higher return, removes carbon dioxide at lower cost and removes more carbon dioxide in total over its lifetime.

"While power generation is a valuable service, the main service that BECCS should be deployed for is carbon removal," said Mac Dowell.

The researchers stress that biomass supply chain emissions are still "a point of caution" when evaluating BECCS potential, as large-scale biomass production could itself generate high levels of carbon dioxide. "[Biomass] has to be sustainable in order for BECCS to be a viable technology," said Mac Dowell.

The study is published in Environmental Research Letters (ERL).

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