The Economic Accessibility of CO₂ Sequestration through Bioenergy with Carbon Capture and Storage (BECCS) in the US

Round 1

Reviewer 1 Report

Reference: land-853818

This manuscript is well written. The authors provided evidence and detail information to support the statement of the problem.

Author Response

We thank the reviewers for feedback on our manuscript. We have responded to some comments from the other reviewers.

Reviewer 2 Report

This is a well-written, authoritatively documented, and policy-relevant research article. I recommend its timely publication upon revision. I implore the authors to consider a press release through their home institutions.

Suggested changes:
The reference to pathways that can be “incrementally trialed and monitored for environmental sustainability effects” is not supported by the narrative offered in the main text. There is very little discussion of the trial and monitoring or demonstration in the paper. Instead, could this sentence reflect something about the (large) scale, (moderate) cost, or (diverse) geographic opportunities around BECCS? That seems to be a far more important finding of the paper.

A few small comments below, suggested to improve the discussion:

Technology selection: Fuels appear to be a far more lucrative market for bioenergy with CCS, as noted in recent work by LLNL and partners (“Getting to Neutral”). I recommend the authors acknowledge the emerging opportunities in fuels in the introduction and/or discussion.

45- Can you note that Mg-1 is equivalent to tonnes? That is the figure most often used in engineering and policy discussions.

Table 1 - superscripts are not properly rendered

Figure 1 - please straighten lines

Lines 330 - 339 & Figure 5 - I recommend additional narrative be added to the paper describing regional agglomeration of BECCS “hotspots” that emerge in Figure 5. I was particularly struck by the emergence of several hubs in the U.S. South and Midwest in the “10% Scenario”. These regional results could be included in the abstract, as suggested above.

Additional Figures - are the authors able to add more mapping results to the main text?

496-512 These two paragraphs seem irrelevant to the paper, I recommend removing.

Author Response

• This is a well-written, authoritatively documented, and policy-relevant research article. I recommend its timely publication upon revision. I implore the authors to consider a press release through their home institutions.
  • Response: We are grateful for the review and appreciate the suggestion.
• The reference to pathways that can be “incrementally trialed and monitored for environmental sustainability effects” is not supported by the narrative offered in the main text. There is very little discussion of the trial and monitoring or demonstration in the paper. Instead, could this sentence reflect something about the (large) scale, (moderate) cost, or (diverse) geographic opportunities around BECCS? That seems to be a far more important finding of the paper.
  • Response: I should not have included this unsupported conclusion. We revised the wording per your recommendation in lines 52-53.
• Technology selection: Fuels appear to be a far more lucrative market for bioenergy with CCS, as noted in recent work by LLNL and partners (“Getting to Neutral”). I recommend the authors acknowledge the emerging opportunities in fuels in the introduction and/or discussion.
  • Response: Thank you for this suggestion, we added this point and reference in lines 106-109.
• 45- Can you note that Mg-1 is equivalent to tonnes? That is the figure most often used in engineering and policy discussions.
  • Response: Per suggestions we have changed from “Mg^-1” to “tonnes” and “per tonne” throughout the manuscript.
• Table 1 - superscripts are not properly rendered
  • Response: We have corrected the superscripts.
• Figure 1 - please straighten lines
  • Response: We have straightened the lines.
• Lines 330 - 339 & Figure 5 - I recommend additional narrative be added to the paper describing regional agglomeration of BECCS “hotspots” that emerge in Figure 5. I was particularly struck by the emergence of several hubs in the U.S. South and Midwest in the “10% Scenario”. These regional results could be included in the abstract, as suggested above.
  • Response: Thank you for this suggestion. We have added discussion of regions where results suggest opportunities for BECCS in lines 53 and 344-345.
• Additional Figures - are the authors able to add more mapping results to the main text?
  • We have added results from the 2020 IGCC scenario. We agree that more spatial results would be informative and can add more maps if desired. Spatial results as interactive visualization will be available to readers at the link indicated in the caption.
• 496-512 These two paragraphs seem irrelevant to the paper, I recommend removing.
  • Response: We agree that these paragraphs are tangential. We have removed them.

Reviewer 3 Report

Please see the attachment.

Comments for author File: Comments.pdf

Author Response

• A table should be inserted with the average efficiency (% LHV), capital cost ($/ kWe), fixed O&M cost ($/ kWe/year), variable O&M cost ($/ MWh), discount rate (%), capacity factor, and plant economic lifetime (years) for the PC ad IGCC plants assessed in the study.
  • We have added these parameters in the text in lines 383-387 and Tables 4-7.
• A graph should be inserted showing an example breakdown of the average LCOE between capital, O&M, fuel, and CO2 transport and storage costs for the two different plants.
  • We have added Figure 7 in lines 406-402 showing LCOE cost components.
• A key contribution of this paper is the cost curves for biomass fuel delivered at the plant. However, the cost curves are only shown for LCOE and CO2 avoidance costs after the rather obscure power plant cost assessment. I propose giving the medium- and long-term biomass cost curves as a separate figure. Also, please express these costs in $/GJ (LHV). Biomass cost in $/ ton are not very useful due to the varying heating values. Ideally, these curves would be presented as stacked areas illustrating the contributions of product ion, processing, and transport at the different demand levels.
  • We agree that it’s usefully to show feedstock costs as a function of supply in GJ. I was unable to immediately create a stacked scattered curve. As an alternative we added Figure 5 showing delivered biomass feedstock quantities (exajoules) and major cost components ($ per gigajoule) modeled in the four scenarios and nine CO₂ capture levels on lines 346-349 as stacked bar charts, and referred to in the text on lines 340-342.
• In addition, the manuscript should state directly how the LCOE is calculated, including how the capital costs are annualized. For the CO2 avoidance costs, Equation 1 and Equation 2 are meaningless because the displaced emissions are not accounted for. They can be removed from the study. In addition, the wholesale rate in the US is known to be only a little more than half the required amount to cover full electricity generation costs (see the World Energy Outlook 2018), so it is not useful to compare the calculated LCOE (accounting for all costs) to the wholesale price (accounting for only half the cost).

Correct calculation of the CO2 avoidance cost (CAC) is given below. As show n, the LCOE ($/ MWh) and CO2 emissions intensity (E in ton/MWhl) of the biomass CCS plant should be compared to that of a relevant reference plant. In this case, Eccs should be negative, but it should account for the emissions involved in the biomass supply chain. In this detailed paper, one can use the generation-weighted average LCOE and emissions intensities of all the biomass plants considered in the formula below.

• We have revised the methods and results using the suggested CAC equation, as described on lines 409-424 and reported in the results section.

• The paper uses Mg, ton, and tonne as mass units, making it rat her confusing. My suggestion is to stick to ton and clearly state that the international definition of 1 t o n = 1000 kg is used.
  • Response: Per suggestions we have changed from “Mg” to “tonnes” throughout the manuscript.
• $ Mg·1 CO2 can be much more intuitively expressed as $/ tonc02.
  • Response: Per suggestions we have changed from “Mg^-1” to “per tonne” throughout the manuscript.
• In table 1, "ad" should probably be " and" in the caption, and the footnotes numbered 1-5 do not appear anywhere in the table.
  • We have made these corrections.

Round 2

Reviewer 3 Report

I think the paper is significantly improved, but there are still a couple of things that are unclear:

1. In Tables 4-7, why is the efficiency so low, particularly in the 2040 scenarios? Does this efficiency include all the losses along the full supply chain? Why are the plant capacity factors with pelletized supply considerably lower than with conventional supply?
2. In figure 7, why is the fuel cost so vastly different between the IGCC and PC plants? What is the "internal electricity offset" in the PC plant? Why is the variable O&M twice as high for the IGCC plant than the PC plant?
3. Why is the CAC of the PC plant considerably lower than the IGCC plants in figure 10, but not in figure 9? Also, I could not find the reference LCOE and CO2 emissions for the coal and gas plants assumed. Please add. 

Author Response

Please see the attachment.

Author Response File: Author Response.pdf