Author Correction: Pathway to a land-neutral expansion of Brazilian renewable fuel production

Biofuels are currently the only available bulk renewable fuel. They have, however, limited expansion potential due to high land requirements and associated risks for biodiversity, food security, and land conflicts. We therefore propose to increase output from ethanol refineries in a land-neutral methanol pathway: surplus CO2-streams from fermentation are combined with H2 from renewably powered electrolysis to synthesize methanol. We illustrate this pathway with the Brazilian sugarcane ethanol industry using a spatio-temporal model. The fuel output of existing ethanol generation facilities can be increased by 43%–49% or ~100 TWh without using additional land. This amount is sufficient to cover projected growth in Brazilian biofuel demand in 2030. We identify a trade-off between renewable energy generation technologies: wind power requires the least amount of land whereas a mix of wind and solar costs the least. In the cheapest scenario, green methanol is competitive to fossil methanol at an average carbon price of 95€ tCO2−1.

output can be increased if the total plantation area is fixed at current levels of ethanol produc-56 tion. This way, the associated negative impacts of sugarcane ethanol expansion are avoided. We 57 propose to synthesize methanol using CO 2 from the fermentation process in ethanol plants and H 2 58 produced from electrolysis powered entirely by on-site variable renewable energy sources (VRES). 59 The higher land efficiency of VRES in comparison to biomass increases the land efficiency of com-60 bined ethanol and methanol output significantly, while the almost clean CO 2 -streams from ethanol 61 fermentation allow to produce methanol from H 2 and CO 2 . This is beneficial, as methanol is much 62 easier to handle and transport than pure H 2 20 . We illustrate the land-neutral methanol pathway for Illustrating the land-neutral methanol pathway 76 We optimize power-to-methanol processes at all Brazilian sugarcane plants in a spatially and tem-77 porally explicit way that accounts for the seasonality of sugarcane production, and the variability 78 of PV and wind power at all plant sites (Fig. 1). CO 2 , H 2 , and electricity storage options are incor-79 porated to handle the temporal asynchrony of the electricity and gas streams. The entire process 80 is studied under a variety of technological assumptions in two scenarios. First, we differentiate 81 between a scenario with mixed PV and wind power generation (solar-wind scenario), and a sce-82 nario with wind power generation only (wind scenario). We do not assess a PV only scenario, 83 as it would not improve on costs or land-use efficiency over the solar-wind scenario. In contrast, 84 the wind scenario can improve on land-use efficiency -at a higher cost -due to the lower land 85 footprint of wind power. Second, we assess how varying techno-economic assumptions regarding 86 annualized electrolyzer costs, efficiency of the electrolysis, and annualized costs of PV generation 87 affect land-use, methanol cost, and system configurations (see methods and supplementary Table   88 1 for details). The production of green methanol can be easily combined with other land-efficient 89 technologies in ethanol production, as the CO 2 -streams from fermentation increase proportionally 90 to the amount of ethanol produced. We therefore also explore the implications for the feasibility 91 of the proposed pathway of ethanol production at higher land-use efficiencies. We choose methanol as the final product, as i) the process to derive it from H 2 and CO 2 is 93 comparatively simple, ii) it is a liquid fuel, easy to transport without additional infrastructure, and 94 iii) it has a variety of applications as feedstock for the chemical industry and transportation fuel. in land-use efficiency, it is more expensive under all techno-economic assumptions.

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The high land-use efficiency of the land-neutral methanol pathway is highlighted for all in-114 stallations and the two scenarios in Fig.2. The figure also illustrates that variability within the 115 scenarios is very high for the wind scenario and very low for the solar-wind scenario. This is a 116 consequence of highly variable wind conditions and comparably low heterogeneity in solar radia-117 tion between locations. There are some outliers in terms of land-use efficiency for some facilities 118 in the solar-wind scenario in the North-East and the South-East. These facilities are located close 119 to the coast where wind resources are much higher than inland, allowing for a mix of wind and PV.

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At all other locations, the wind share is very low or even 0, highlighting the low wind resources at 121 most sugarcane production sites. Facilities that have higher land-use efficiency in the solar-wind 122 scenario, however, also have low total fuel production potentials due to currently low amounts of 123 ethanol production at those sites. Lowering land-use and costs by incorporating sites with excel-124 lent wind conditions is therefore possible only for a small share of overall production, i.e. 1.5% of 125 total methanol production at 14 locations. Ethanol plants, and therefore the potential for combined  Figure 3). This implies that 158 the wind scenario is by far not cost competitive and we therefore do not discuss it in the following. 159 We emphasize here that these particular results are not generalizable but are specific to the wind storage at most times. However, if the CO 2 supply is stretched over a long period, the CO 2 stor-191 age needs time to fill up and, in some circumstances, renewable power supply will be higher than 192 the currently stored CO 2 . As storing electricity or H 2 is much more expensive than storing CO 2 ,

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To achieve the full potential of social, environmental and industrial co-benefits of the land-238 neutral methanol pathway and to make it economically competitive, a supportive land-use policy, 239 which enforces land-neutrality of Brazilian biofuel production, would have to be implemented.

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Only under such a policy could potential rebound effects from increased demand 36 be prevented.

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At the same moment, such a land-neutral policy would increase biofuel prices, making our pro- ity is exported to the electric grid. Bagasse can alternatively be used as feedstock for 2G biofuel 275 production, thus increasing the fuel output, while decreasing the electricity output of the plant. 276 We propose to upgrade existing sugarcane plants by adding a water electrolyzer, driven by VRES 277 generation, and a methanol synthesis unit which combines H 2 from the electrolyzer with CO 2 sep-278 arated from the ethanol fermentation process. We assume that the electrolyzer is not connected to 279 the electricity grid, but that it relies on electricity generated by VRES locally. This assumption is 280 justified as electricity demand for electrolysis would be substantial at large ethanol facilities. The 281 required transmission infrastructure is not available currently and building it would be very costly.

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More importantly, the generation of electricity on-site is less costly than paying wholesale market 283 prices plus grid fees. 284 We developed a linear optimization model (LP) to minimize the costs of VRES-based syn- ethanol (see Supplementary Fig. 7).

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Based on the premise of energy self-sufficiency of the installation, we assumed that the CHP 292 runs always when heat is required for the ethanol production process, but that surplus electricity is 293 not used in the electrolyzers. Currently, surplus electricity from the CHP is exported to the grid. ethanol production, as well as intra-day operation variability, is however crucial to our approach. 317 We therefore approximated the time profile of ethanol production using the CONAB statistics for Earth, the extension of these plants was measured in two different ways. In a first step, the area 347 covered by panels was measured. In a second step, the panels and the surroundings used for roads,     The proposed land-neutral methanol pathway.

Figure 2
Land-use e ciency of methanol production vs. total fuel production for all Brazilian facilities.

Figure 3
Cost-supply curves for all scenarios and costs assumptions. Upper: solar-wind scenario. Lower: wind scenario. From left to right: annualized electrolyzer cost assumptions.

Supplementary Files
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