Inefficient power generation as an optimal route to negative emissions via BECCS?

Current ambitions to limit climate change to no more than 1.5 degrees C-2 degrees C by the end of the 21st century rely heavily on the availability of negative emissions technologies (NETs)-bioenergy with CO2 capture and storage (BECCS) and direct air capture in particular. In this context, these NETs are providing a specific service by removing CO2 from the atmosphere, and therefore investors would expect an appropriate risk-adjusted rate of return, varying as a function of the quantity of public money involved. Uniquely, BECCS facilities have the possibility to generate both low carbon power and remove CO2 from the atmosphere, but in an energy system characterised by high penetration of intermittent renewable energy such as wind and solar power plants, the dispatch load factor of such BECCS facilities may be small relative to their capacity. This has the potential to significantly under utilise these assets for their primary purpose of removing CO2 from the atmosphere. In this study, we present a techno-economic environmental evaluation of BECCS plants with a range of operating efficiencies, considering their full-and part-load operation relative to a national-scale annual CO2 removal target. We find that in all cases, a lower capital cost, lower efficiency BECCS plant is superior to a higher cost, higher efficiency facility from both environmental and economic perspectives. We show that it may be preferable to operate the BECCS facility in base-load fashion, constantly removing CO2 from the atmosphere and dispatching electricity on an as-needed basis. We show that the use of this 'spare capacity' to produce hydrogen for, e.g. injection to a natural gas system for the provision of low carbon heating can add to the overall environmental and economic benefit of such a system. The only point where this hypothesis appears to break down is where the CO2 emissions associated with the biomass supply chain are sufficiently large so as to eliminate the service of CO2 removal.