CO₂ emission sources can be divided into diffuse sources (e.g., transport and agriculture) and point sources (e.g., factories and power production). This study uses a bottom-up approach to estimate CO₂ emissions from the following point sources in Sweden:

Industrial process plants (including iron and steel, non-ferrous metal, oil and gas refineries, lime and cement, pulp and paper, chemical, metal, and other similar plants)

Emissions data for year 2013 from the European Environment Agency’s “European Pollutant Release and Transfer Register” (European Environment Agency, 2015) was used to estimate (i) the available amount of CO₂ and (ii) the share of fossil and biogenic CO₂, for Swedish point sources, including all sources emitting 0.1 million metric tons of CO₂ per year or more. Other CO₂ sources are assumed to be negligible (except in the case of biofuels production). The concentration of CO₂ for each type of sources was estimated using (Chapel et al., 1999; Bosoaga et al., 2009) (see Table 1). For the purposes of analysis, the concentrations were divided in three ranges: low (<15 vol%), medium (15–90 vol%), and high (>90 vol%).

For biofuels plants, the CO₂ estimates are based on data gathered by Swedish Energy Agency and Energigas Sverige (2015) and Grahn and Hansson (2015) in 2012–2013. Also, the sources emitting less than 0.1 million metric tons of CO₂ per year are included in the case of biofuels since these are relatively pure and, therefore, well suited for electrofuels production. In most biofuels production processes, there is a surplus of CO₂ and the CO₂ is of high purity (Xu et al., 2010). When biogas is upgraded to transport fuel quality, a cleaning step to remove CO₂ is included, resulting in a relatively pure stream of CO₂. The CO₂ emissions from domestic biofuel production in a 2030 scenario are estimated based on biofuels production scenarios from Grahn and Hansson (2015) and on scenarios for anaerobic digestion and gasification-based biogas production from Dahlgren et al. (2013). Grahn and Hansson (2015) assessed the potential contribution of domestically produced biofuels for transport in Sweden in 2030 based on a mapping of the prospects for current and potential Swedish biofuel producers. Some of the planned biofuels production plants included in the scenario for 2030 have been canceled or put on hold and are, therefore, excluded in this study.

The 2030 scenario was constructed exclusively for biofuel plants because these represent a relatively pure stream of CO₂ of particular interest in electrofuels production, and because the use of biofuels is expected to increase in the future. For many biofuels, no extra major purification step is needed in the capture process, which leads to a relatively low capture cost. This can also be assumed for the case of biogas since CO₂ is already removed when biogas is upgraded to transport fuel quality. This can be compared to the CO₂ capture cost linked to processes requiring an extra purification step like steel and iron, ammonia, refinery, cement, and fossil or biomass combustion plants estimated at 20€₂₀₁₅–170€₂₀₁₅/ton CO₂ in the short term (10–15 years) and 10€₂₀₁₅–100€₂₀₁₅/ton CO₂ in the more long term (Damen et al., 2007; Finkenrath, 2011; Kuramochi et al., 2012, 2013; IEA, 2013). Even though it has been indicated that the cost for carbon capture represents a relatively modest share (a few percent) of the total electrofuel-production cost unless air capture is assumed (Graves et al., 2011; Tremel et al., 2015; Varone and Ferrari, 2015; see text footnote 1), using CO₂ from biofuel production represent an attractive source for electrofuel production since more pure streams will likely be used first for economic reasons and the domestic biofuel actors, representing a considerable biofuel production capacity, in order to comply with sustainability requirements need to improve their production processes in terms of CO₂ emissions.

Table 1 presents the type of CO₂ stream, typical concentration of CO₂, the range of CO₂ emissions per unit, and the amount of recoverable CO₂, for different point sources. Table 2 includes a list of all the biofuel production facilities in operation in 2015, their production capacity and associated CO₂ emissions, and the corresponding information for the biofuels plants planned by 2030. Table 3 summarizes the main assumptions used in estimating the amount of CO₂ that is available for recovery from current and future biofuels plants.

In order for CO₂ to be used to produce electrofuels, the gas needs to be separated from other substances in emissions from industrial and combustion processes, such as sulfur dioxide. The concentration of CO₂ in power plant flue gases is relatively low (<15 vol%) (Chapel et al., 1999); for process-related emissions, e.g., in the lime and cement industry, CO₂ concentrations are somewhat higher (14–33 vol%) (Bosoaga et al., 2009) (see Table 1). In this study, we assume that 90% of the CO₂ from medium- (15–90 vol%) and low- (<15 vol%) concentration CO₂ sources is recoverable (Chapel et al., 1999). Current CO₂ capture technologies do not usually capture all the CO₂ as this is too expensive and requires too much energy.

In biofuels production processes (fermentation, anaerobic digestion, gasification), relatively pure streams (>90 vol%) of CO₂ are available in latter cases due to the demand for high fuel purity in the transport sector. We assume that 100% of the CO₂ from biofuel plants is recoverable and could be converted into fuel. Approximately 54% of the biogas produced in Sweden is upgraded for the transportation sector (Swedish Energy Agency and Energigas Sverige, 2016), which means that CO₂ capturing technology already exist on several Swedish anaerobic digestion facilities. Another opportunity for anaerobic digestion-based biogas plants is to feed raw biogas to a methanation reactor, thereby combining biogas upgrading and electrofuels production (Johannesson, 2016). Biogas plants that currently do not upgrade their gas are generally small implying high costs for upgrading and currently supplying other markets than the transport sector, making them less suitable as a source of CO₂ for electrofuels production. Therefore, only CO₂ from biogas-upgrading plants is considered in this study. For simplicity, we assume that the share of upgraded biogas of total biogas production by 2030 remains at 54%.

The CO₂ emission sources have been mapped and categorized by concentration and geographical area. The geographical areas are those used for the Swedish electricity market, i.e., four price areas (SE1, SE2, SE3, and SE4) (Swedish Energy Markets Inspectorate, 2014) (see Figure 1). The electricity price areas were implemented in Sweden in order to control the transmission of electricity between regions and to promote the construction of power generation and transmission capacity in and to areas with electricity deficits. On average, the northern parts of the country (SE1 and SE2) are characterized by an excess of electricity production due to the available hydropower resources and relatively low overall power consumption. In the southern parts (SE3 and SE4), electricity consumption often exceeds production, which leads to relatively higher electricity prices in these areas (Nord Pool, 2016).

The focus in this study is on electrofuels in the form of methane, methanol, and DME since these are the most discussed electrofuels in the literature (see text footnote 1), are of interest for the relevant transport sector (shipping and trucks), and include fuels in liquid and gaseous form. The amounts of CO₂ and electricity necessary for the types of electrofuels included in this study are given in Table 4 and are based on lower heating value (LHV).

Table 4 also presents cost ranges for 2015 and 2030 estimated in the base case reference scenario in Brynolf et al. (see text footnote 1). The electricity-to-fuel efficiency of the electrofuel-production process strongly depends on the type of electrolyzer and the future development of production technologies. Alkaline electrolysers have efficiencies in the range of 43–69% today, while the most efficient electrolysers are expected to reach efficiencies above 80% based on LHV (Smolinka et al., 2011; Benjaminsson et al., 2013; Grond et al., 2013; Mathiesen et al., 2013; Bertuccioli et al., 2014; Hannula, 2015; Schiebahn et al., 2015). Combining this with the efficiency for fuel synthesis yields electricity-to-fuel efficiencies in the 30–75% range for methane, methanol, and DME, this corresponds to an electricity demand of 1.33–3.33 MWh electricity/MWh electrofuel.

Brynolf et al. (see text footnote 1) suggest costs for different electrofuels (methane, methanol, DME, gasoline, and diesel) in the span of 120€₂₀₁₅–1,050€₂₀₁₅/MWh_fuel and 100€₂₀₁₅–430€₂₀₁₅/MWh_fuel in 2015 and 2030, respectively. However, in the base case of the reference scenario representing average data, the same costs are 200€₂₀₁₅–280€₂₀₁₅/MWh_fuel and 160€₂₀₁₅–210€₂₀₁₅/MWh_fuel in 2015 and 2030, respectively. The most important factors affecting the production cost of electrofuels are the capital cost of the electrolyzer, the electricity price, the capacity factor of the unit, and the lifetime of the electrolyzer. The base case reference scenario assumes alkaline electrolyzer with a capital cost of 600€₂₀₁₅/kW_el, capacity factor of 80%, lifetime of the electrolyzer at 25 years, carbon capture cost at 30€₂₀₁₅/ton, and electricity price of 50€₂₀₁₅/MWh. A capacity factor at 80% implies that the plant is run the major part of the year. However, if electrofuels are used to balance intermittent renewable power production (i.e., there is production only when there is a surplus of power from these sources), the capacity factor will be reduced. This will not influence the estimated technical potential for production of electrofuels in Sweden in this study, but it will lead to increased electrofuel-production costs [which is further assessed in Brynolf et al. (see text footnote 1)]. In the case of a carbon capture cost at 10€₂₀₁₅/ton representing more pure streams like biofuels operation, the production cost of electrofuels is reduced by approximately 3%. In their review of the literature, Brynolf et al. (see text footnote 1) also found that the cost of capturing CO₂ generally is a minor factor in the total production cost of electrofuels representing less than 10% (when not considering CO₂ capturing from air). CO₂ can be captured from various industrial sources with costs ranging from about 10€₂₀₁₅ to 170€₂₀₁₅/ton CO₂, depending on the CO₂ concentration (Damen et al., 2006, 2007; Finkenrath, 2011; Goeppert et al., 2012; Kuramochi et al., 2012, 2013; IEA, 2013; see text footnote 1). This indicates that from an economic point of view, all CO₂ sources (except from pure air) might be of interest for electrofuel production in the future.

In Sweden, major stationary point sources currently emit approximately 50 Mton CO₂ per year. Of this, about 45 Mton CO₂ is recoverable (see Figure 2). Our analysis includes 148 facilities, with 14 U emitting more than 1 Mton CO₂/year, 88 U emitting between 1 Mton and 100 kton CO₂/year, and 47 U emitting less than 100 kton/year.

Figure 2 shows the distribution of CO₂ emissions among different types of point sources. Pulp and paper plants and heat and power plants are the two major types of point sources, corresponding to 23 Mton CO₂ (45% of the total) and 11.5 Mton CO₂ (23% of the total) per year, respectively. In total, biogenic sources account for 65% or 32 Mton of CO₂ emissions per year. The high share of biogenic CO₂ is mainly due to the extensive use of biomass in producing pulp, paper, heat, and power and from waste treatment and incineration. Emissions from biofuel production represent a small share of the current total amount of available CO₂, with approximately 0.5 Mton of recoverable CO₂ per year. According to Andreas Gundberg, Innovation manager at Lantmännen Agroetanol, CCU has already been implemented at the main Swedish ethanol producer representing approximately 90% of the total Swedish ethanol production capacity. The emissions from this ethanol production (about 100 kton/year) are included in the analysis.

Figure 3 shows the amount of CO₂ available and the corresponding potential production of electrofuels in the form of methanol at different CO₂ concentrations in Sweden in 2013 and in 2030. The majority of the CO₂ is available at low and medium concentrations, equally spread between the categories low and medium but mainly below 20 vol%. A small share of the CO₂, mainly from the biofuels industry, is available at higher, significantly more accessible, concentrations.

About 90% of the high-concentration emissions come from sources in geographic region SE3, along with about 60% of the rest of the CO₂ emission sources (see Figure 4). Anaerobic digestion and ethanol production from agricultural crops currently dominate biofuels production, and these are mostly located in densely populated areas (producing biogas from digestion of sewage sludge and food waste) or in proximity to agricultural operations (farm-based ethanol and biogas production), which are mainly found in southern Sweden. However, electricity prices in the southern parts are currently less favorable than further north where hydropower resources and lower demand create an excess of electricity while the transmission capacity to the southern industrial and population centers is limited.

The projected large-scale introduction of biofuels based on lignocellulosic feedstocks should entail higher shares of high-concentration CO₂ emissions in the northern regions, SE1 and SE2, if plants are located near feedstock resources.

The biofuels sector is expected to grow significantly in Sweden during the coming years in order to achieve national climate and transport targets. Figure 5 illustrates the current and estimated amount of CO₂ available for electrofuels production from different biofuel production technologies and a minor share of others sources available by 2030 in Sweden based on Dahlgren et al. (2013) and Hansson and Grahn (2013). Only CO₂ from the production of upgraded biogas is included. In 2030, the CO₂ originates mainly from gasification, anaerobic digestion, and fermentation-based biofuels production (utilizing both cereals and lignocellulosic biomass and considering recent implementation plans). In 2030, these sources could potentially yield 2.2 Mton CO₂ for electrofuels production (approximately 5.5 times the amount currently available). The largest increase in production capacity is expected with the large-scale implementation of a variety of biomass-gasification-based biofuels, such as synthetic natural gas, DME, or methanol from lignocellulosic biomass. Ethanol produced from lignocellulosic feedstocks could also potentially generate large amounts of highly concentrated biogenic CO₂.

Using all the currently recoverable CO₂ from the point sources identified in this study to produce electrofuel in the form of methane would yield approximately 224 TWh per year. This corresponds to approximately 2.5 times the current Swedish demand for transportation fuels [approximately 85 TWh per year in 2014 (Swedish Energy Agency, 2015b)]. For electrofuels with lower conversion efficiencies (e.g., methanol and DME), production could instead cover about twice the current demand. Producing 224 TWh per year of electro-methane requires about 448 TWh of electricity (assuming 2 MWh_el/MWh_fuel), which corresponds to three times the current Swedish electricity generation [149 TWh (Swedish Energy Agency, 2015a)].

The high-concentration sources, represented mainly by biofuel plants, suffice to provide only about 2% of the current demand for transportation fuels (corresponding to 1.5–2/year, see Figure 6). Converting the high-concentration emissions to electrofuels would require about 3–4 TWh of electricity (2–3% of the current national production). In 2030, the potential production of electrofuels in the form of methane, methanol, and DME from high-CO₂ sources is 8–11 TWh (see Figure 6). This corresponds to approximately 9–13% of the current demand for transportation fuels and would require about 15–21 TWh of electricity (10–14% of current electricity production).

Table 5 shows the requirements for meeting the current Swedish fuel demand for (non-air) transport with electrofuels in the form of methanol. As seen in Table 5, about half of the recoverable CO₂ (23 Mton) would be needed to supply the entire current Swedish road transport demand with electrofuels in the form of methanol (assuming a conversion factor of 0.275 ton CO₂/MWh methanol). The corresponding amount of CO₂ needed to satisfy the entire fuel demand from heavy trucks and all domestic and international shipping currently bunkering in Sweden is estimated to be about 5 and 6 Mton CO₂, respectively. This implies that in the case of large-scale introduction of electrofuels for road transport (including heavy trucks), heavy trucks only, or shipping in Sweden, the supply of CO₂ is not a limiting factor.

However, meeting the entire current road transport demand with electrofuels would require about 164 TWh_el of electricity (with methanol at 1.93 MWh_el/MWh_fuel). This would more than double the current demand for electricity. To meet the current Swedish fuel demand for passenger cars (at about 41 TWh) (Swedish Government Official Reports, 2013) with electrofuels in the form of methanol would require approximately 11 ton CO₂ and 79 TWh_el of electricity. For comparison, if the entire passenger car fleet were replaced by electric vehicles, the increased demand for electricity would be approximately 10 TWh (based on Swedish Government Official Reports, 2013).

Using electrofuels for the heavy truck sector and for shipping bunker fuel sold in Sweden would require about 35 and 41 TWh_el, respectively. For comparison, in 2014, domestic power generation was 150 TWh (SCB, 2016). Further, the goal is to increase domestic generation from renewable sources by about 30 TWh by 2020, compared to 2002 figures and current production of renewable electricity is approximately 85 TWh (SCB, 2016). Large-scale introduction of electrofuels would require a major increase in the supply of electricity from renewable energy sources.