The Potential of Biomethane in Replacing Fossil Fuels in Heavy Transport : A Case Study on Finland

sustainability Article The Potential of Biomethane in Replacing Fossil Fuels in Heavy Transport—A Case Study on Finland Anna Pääkkönen 1,2,*, Kalle Aro 3, Pami Aalto 3, Jukka Konttinen 1and Matti Kojo 3 1Faculty of Engineering and Natural Sciences, Tampere University, Korkeakoulunkatu 8, 33720 Tampere, Finland 2MAB Powertec Oy, Finlaysoninkatu 7, 33210 Tampere, Finland 3Faculty of Management and Business, Tampere University, Kanslerinrinne 1, 33100 Tampere, Finland *Correspondence: [email protected] Received: 10 July 2019; Accepted: 25 August 2019; Published: 30 August 2019   Abstract: Electrification is a frequently discussed solution for reducing transport related carbon dioxide emissions. However, transport sectors such as aviation and heavy-duty vehicles remain dependent on on-board fuels. Here, biomethane is still a little exploited solution, and the case of heavy-duty vehicles is particularly underappreciated despite the recent technical advances and potentially notable emission reductions. This paper discusses the potential of biomethane in heavy-duty road transport in the case of Finland, where the utilization rate is low compared to the technical potential. To this end, the potential of biomethane production through both anaerobic digestion and gasification was calculated in three scenarios for the heavy-duty transport fleet, based on the literature values of biomethane potential and truck class fuel consumption. The authors find that approximately half of the heavy-duty transport in Finland could be biomethane fueled by 2030. The estimated production costs for biomethane (81–190 € /MWh) would be competitive with the current consumer diesel price (152 € /MWh). Utilizing the total biomethane potential in heavy-duty transport would furthermore decrease the respective carbon dioxide emissions by 50%. To accelerate the transition in the heavy-duty transport sector, a more comprehensive political framework is needed, taking into account both production and consumption. Keywords: renewable transport fuels; biomethane; carbon emission reduction; heavy-duty transport; transition; Finland; anaerobic digestion; wood gasification 1. Introduction The transport sector is responsible for 14% of global CO 2 emissions [ 1 ]. This share is set to increase further with economic growth in the developing countries [ 2 ]. In 2015, approximately half of total oil end use worldwide (49.7%) was for transport [ 3 ]. At the same time, reducing the utilization of fossil fuels in all sectors is essential to reduce the emissions of CO 2 and other greenhouse gases (GHGs) in order to combat global warming. Several European countries are considering bans on fossil fuelled passenger vehicles. Norway aims to achieve such a ban by 2025 alongside severe emission reductions for all vehicle classes by 2030 [ 4 ]. Similar plans also exist in France, Ireland, Sweden, Germany, and the UK, while in Finland the issue was discussed in connection with the 2019 parliamentary elections. The electrification of transport is a frequently discussed solution for reducing GHG emissions in this sector. For passenger and medium-duty vehicles, electrification will be the most efficient emission reduction technology, assuming a high share of renewable low carbon power in the electric energy system. However, aviation, shipping, and a significant part of heavy-duty transport will remain dependent on on-board, high energy density transportable fuels for a considerable time to come [ 5 , 6 ]. In this article, we focus on the provision of low-carbon fuels for heavy-duty transport. While this is a Sustainability 2019,11, 4750; doi:10.3390/su11174750 www.mdpi.com/journal/sustainability Sustainability 2019,11, 4750 2 of 19 global policy challenge, it is typically a more acute need for countries with low population density or with long distances between major concentrations of raw materials and sites of production and consumption. One study suggests that, in particular, countries where heavy truck-trailer combinations are widespread require solutions since such combinations are difficult to electrify even with high battery capacity [ 7 ]. Electric road systems, for their part, require very high investments and are unlikely to be able to serve all traffic needs [7]. In short, because it is unlikely that one solution for delivering low-carbon heavy transport will be applicable across all countries [ 6 , 7 ], several options need to be explored, including gaseous fuel solutions. Particularly in the European context, the considerable, yet largely unexploited technical potential of biomethane, or upgraded biogas, is one such option with several raw material streams available [8,9]. 1.1. Background Biomethaneiscurrently emergingasoneviablesolutionfortheheavy-dutytransportsector[ 10 – 12 ], with comprehensive reviews of its benefits and constraints [ 13 , 14 ], and of the required heavy-duty vehicle fleet [ 15 ]. The European biomethane market comprises 90% of the global supply [ 16 ] and has grown seven-fold since 2000 [ 17 ]. Production can be doubled by 2030 [ 8 , 17 , 18 ]. The global potential is also promising. Using energy plants for the production of biogas has a better energy output per unit area than using the same plant-based raw material for producing liquid biofuels—which is so far remains the preferred solution in several countries around the world owing to its relative compatibility with vehicles using oil-based fuels. While in this respect it is possible to view biogas as a renewable fuel with a great deal of potential, its competitiveness can further be enhanced by also using the associated CO2for commercial applications in numerous sectors [19]. For the use of biogas in transport, biomethane can be either pressurized (200 bar) or liquefied. Unlike hydrogen (H 2 ), which is constrained by costs, availability of vehicles and deficiencies in the transport and storage infrastructure [ 20 ], biomethane can be used in existing systems where natural gas methane (CH 4 ) is utilized. Suitable gas fuelled heavy traffic vehicles are commercially available, including so-called dual fuel (diesel/NG diesel for ignition and as a fuel) and spark ignition engines (only NG) [ 10 , 11 ]. The scenario of the Natural and Bio Gas Vehicle Association Europe (NGVA) expects the number of methane fuelled trucks to increase from 9000 to 480,000 by 2030, reaching a 25% market share, while liquefied natural gas (LNG) vehicles would take up a 10% share of the market [21]. The main constraint in promoting gas fuelled heavy trucks is the approximately 30–40% higher purchase price compared with fossil fuelled trucks [10], depending on the equipment [22–24]. A life cycle assessment has found that biomethane solutions, when used to power Euro6 buses, generally have a lower environmental impact than their main competitors—including liquid biodiesels—in terms ofglobal warming, stratosphericozone depletion, photochemicaloxidant formation, acidification potential, and eutrophication potential [ 14 ]. Kalinichenko et al. [ 19 ] find crop-based biogas to provide a greater amount of vehicle fuel energy than the biodiesel or ethanol options. According to Hijazi et al. [ 25 ] and Baldino et al. [ 8 ], the raw material used for producing biomethane is crucial to the environmental sustainability of the fuel. Differences exist, for example, between crop-based and animal manure-based raw material, while the storing, management and production technologies also have a role. Livestock manure offers the greatest technical potential of biomethane in the EU compared with other raw materials, constituting 43% in the transport use case [8,25]. The use of biomethane for transport has to compete with its use for power and heat, where biogas is more cost-efficient than in the transport sector when considering conceivable financial incentive structures [ 8 ]—while biogas can also be used to produce chemicals. However, the current incentives typically prioritize low carbon power production, not the heat or transport sectors. The existing transport sector incentives focus mostly on electric vehicles, which in Ireland, for example, enjoy sixteen-fold incentives compared to a natural gas vehicle operating on biomethane [ 26 ]. Moreover, since the transport case requires more complex infrastructure than the heating case, for example, Sustainability 2019,11, 4750 3 of 19 filling stations, higher incentives would be natural [ 26 ]. Great energy efficiency and environmental benefits exist in the transport use case [ 9 ], including minimization of particle emissions and reduction of emissions in agriculture [26]. In the EU context, biomethane-based transport is at its most advanced in the case of Sweden, with half of biogas production used for transport [ 19 ]. Börjesson et al. [ 11 ] focus on the system level (per vehicle km), bypassing the question of the actual number of vehicles. Ammenberg et al. [ 27 ] address the demand side actors and policies as well as the supply and distribution side through expert interviews in Stockholm County in Sweden. Biogas was found to have potential for buses and taxis, while utilization for heavy fuel transport was only mentioned as a future possibility. In addition, Lönnqvist et al. [28] explored the potential for biogas produced in anaerobic digestion (AD) in Stockholm County based on a survey of key actors. Jensen et al. [ 29 ] examined three biogas production scenarios in Denmark with a focus on commercial light and heavy-duty vehicle utilization, using three different technology assumptions for AD biogas production and assuming a 100% share for biomethane fuelled heavy-duty vehicles. Uusitalo et al. [ 30 ] found biogas a potent transport fuel in Finland in view of its cost-effectiveness (calculated from the point of view of the gas grid owner), as well as GHG and particle emission reductions, but they did not directly examine the heavy-duty transport sector. 1.2. Scope of the Paper This article breaks new ground by examining biomethane solutions in the context of heavy-duty transport, which so far has been little studied. Finland is presented as a typical case within a larger group of countries [ 31 ], wherein the heavy-duty transport sector is relatively large [ 32 ], showing a growing trend [ 33 ] (Countries meeting these criteria include, for example, France, Poland, Portugal and Spain) and in particular, where truck-trailer combinations are widespread [ 7 ]. Crucially, no studies have been published that include a vehicle class analysis of this case. The transport sector accounts for 20% of Finland’s GHG emissions [ 34 ], while the country’s exports consist predominantly of transport intensive commodities, including forest, chemical and metal industry products as well as machinery and vehicles. The presence of the forestry industry in Finland enables the production of liquid or gaseous biofuels from the industry’s side-products. Consequently, liquid biofuels are a key part of the national energy and climate strategy, where biogas is also mentioned [ 35 ]. Yet the large-scale production of liquid biofuels is associated with much-discussed problems. Production from forest-based biomass may become limited by the availability of suitable raw material, and may have negative implications for the carbon sink, while the large-scale use of crop-based raw materials risks competing with food production [8,20]. NG vehicles so far represent a niche sector in Finland, numbering only 3600 in 2017 [ 36 ]. However, Finland’s techno-economic potential for biogas is large, estimated at 10 TWh [ 37 ], making it larger for the transport use case than Sweden, the current leader, and twelfth largest in the EU [ 8 ]. Finland’s 2016 Energy Strategy foresees the gasification of woody biomass for producing transport fuel as part of the 40% target for renewable fuels by 2030 [ 35 ]. The key constraints for the low utilization rate of the biogas potential include limitations in the distribution network and economic feasibility [ 38 ]. Moreover, Huttunen et al. [ 39 ] identify inadequate policy cohesion resulting from conflicting political targets and policy instruments. Winquist et al. [ 40 ] find some improvement in the recognition of biogas and the related benefits in recent policy documents, also outside of the energy sector. However, actual objectives and measures to promote biogas usage remain very generic. At the same time, significant additional potential exists for increasing biogas production from forest residues and agricultural by-products that could further improve Finland’s raw material base. In the case of Sweden, Börjesson found that the realization of similar potential requires improved political guidance and regulation for this production not to conflict with environmental goals [ 41 ]. Moreover, for both Sweden and Norway, a need has been identified to co-ordinate the regulatory system and to provide subsidies to enable the most environmentally advantageous use of biogas [42,43]. Sustainability 2019,11, 4750 4 of 19 This paper seeks to contribute to this debate by first assessing how high a share of Finland’s heavy-duty transport could be biomethane fuelled. Drawing upon a pilot study on the potential of AD biogas for heavy traffic in Finland [ 44 ], this study uses an illustrative vehicle fleet model and calculates three different scenarios for a biomethane fuelled heavy-duty transport fleet. The biomethane potential was estimated based on the values in the existing literature of available raw material from AD processes as well as from woody biomass gasification. In addition, an estimate of CO 2 -emission reduction/ton is provided. In light of the results, this paper also discusses the respective constraints for biomethane production, delivery infrastructure and policies. Our primary research questions are: (1) How large a share of heavy-duty road transport could the techno-economic potential of biomethane cover? (2) What would be the cost of biomethane utilization for the heavy-duty truck fleet? (3) How much transport related CO2(and other) emissions could be avoided? The biomethane potential suitable for the heavy-duty transport sector was found to be 7.4 TWh annually, which is substantial in the context of Finland. Depending on the priority order of vehicle classes, domestic biomethane could fuel as many as 66% of the vehicles in the current heavy vehicle fleet. Utilizing the entire potential of biomethane in the heavy-duty transport sector was found to halve the sector’s GHG emissions as well as its NO x -emissions, regardless of the scenario chosen. Economic analyses conducted to ascertain the theoretic magnitude of the financial investments required conclude that biomethane production (81–190 € /MWh) would be competitive with the current consumer price for diesel (152 € /MWh). However, limited fuelling and delivery infrastructure, in addition to the small number of gas operated vehicles currently in use, imply that additional investments will also be required over and above biomethane production alone. Biogas has remained a niche technology in Finland, as both production and usage levels have remained low. The biogas production chain is characterized by a high level of uncertainty stemming from political incoherence between targets and means, as well as a low level of local co-operation. A more comprehensive and cross-sectoral framework is required to address obstacles to production and demand simultaneously, and to trigger a transition in heavy-duty road transportation in Finland. The results provide insights beyond Finland to other EU Member States by adjusting the vehicle classes, availability of biomethane and features of biogas policy-making according to the respective characteristics of each case. 2. Methods, Materials and Assumptions A case study on biomethane solutions in the heavy-duty transport sector in Finland is reported here. Single case studies are particularly useful in little explored areas such as those discussed herein. They can generate observations to be subsequently explored in other typical cases [ 31 ]—in this context, heavy transport intensive countries with a relatively high biomethane potential, of which there are many in the EU. As suggested above, Finland is a somewhat difficult case in this group owing to the dominant role of the forest industry and, hence, a vested interest in liquid biofuels [ 45 ], while the widespread use of truck-trailer combinations curtails the prospects for electrification and necessitates considering several options, including biomethane. In other words, if biomethane solutions are found to be readily applicable in Finland, it is reasonable to expect the same for other cases in this group of countries. However, prospective comparisons must recognize the regional and local variation in the raw material, the distance to production sites and the effectiveness of transport [ 14 , 19 , 46 , 47 ]. Yet the authors expect the procedures used to be replicable and the results to be applicable to other countries in this group after adjustment for vehicle class, raw material base, and transport conditions. The observations in this paper concern the production and potential of biomethane, its use in the heavy-duty traffic fleet in three different scenarios and the respective policy needs. All calculations represent theoretical process values. In addition, the authors calculated the amount of biomethane potential for gasification. The analysis of the constraints and required policies for the implementation of biogas solutions in Finland draws upon the literature available. Sustainability 2019,11, 4750 5 of 19 2.1. Assumptions on the Production of Biomethane AD processes can utilize residual biomaterial such as municipal bio-waste, sewage sludge or agricultural residues, resulting mainly in CH 4 (50–70 vol-%) and CO 2 (30–50 vol-%). Prior to utilization as a transport fuel, CO 2 and other impurities must be removed by means of chemical or physical absorption, membrane separation, adsorption on a solid surface, cryogenic separation or chemical conversion [ 48 – 50 ]. In biomass gasification, the main product is H 2 (40–50 vol-% of the dry product gas) that can be utilized directly as a transport fuel or further reacted catalytically or biologically with CO or CO 2 to form CH 4 . Other gasification products include CO (typically 21 vol-%), CO 2 (15 vol-%) and CH 4 (10 vol-%) [ 47 , 51 ]. Commercial projects for transport fuel production via biomass gasification include GoBiGas in Sweden and GAYA in France [ 52 ] (Figure 1). Due to limitations of space, we do not consider power-to-gas technologies here, which can also be used to produce biomethane. Sustainability 2019, 11, x FOR PEER REVIEW 5 of 19 2.1. Assumptions on the Production of Biomethane AD processes can utilize residual biomaterial such as municipal bio-waste, sewage sludge or agricultural residues, resulting mainly in CH 4 (50–70 vol-%) and CO 2 (30–50 vol-%). Prior to utilization as a transport fuel, CO 2 and other impurities must be removed by means of chemical or physical absorption, membrane separation, adsorption on a solid surface, cryogenic separation or chemical conversion [48–50]. In biomass gasification, the main product is H 2 (40–50 vol-% of the dry product gas) that can be utilized directly as a transport fuel or further reacted catalytically or biologically with CO or CO 2 to form CH 4 . Other gasification products include CO (typically 21 vol- %), CO 2 (15 vol-%) and CH 4 (10 vol-%) [47,51]. Commercial projects for transport fuel production via biomass gasification include GoBiGas in Sweden and GAYA in France [52] (Figure 1). Due to limitations of space, we do not consider power-to-gas technologies here, which can also be used to produce biomethane. Figure 1. Simplified production paths for biomethane. In 2017 there were 71 biogas production sites in Finland. Total production including collection from landfill sites was approximately 700 GWh [53], of which only 30 GWh was used as transport fuel. As of 2018, a mere 708 gas fuelled vehicles ran on natural gas (NG) only, and 2925 on both NG and petrol. Most of these vehicles were passenger vehicles. Only 18 NG and 75 dual fuel trucks were registered. In 2017, there were altogether 3,099,566 cars, vans and trucks in Finland [36]. The potential for the expansion of the fleet of gas fuelled vehicles is considerable. In this paper it is assumed that all the biomethane available to be used solely for heavy-duty transport, originating from both AD of waste material and gasification of woody biomass. Furthermore, based on [37], the techno-economic biomethane potential from AD in Finland is estimated to be 10 TWh. The amount of available woody biomass for transport fuels is expected to be 4 Mm 3 by 2030 according to the Finnish Government’s estimate as calculated by the Ministry of Employment and the Economy for the country’s 2016 Energy Strategy [35]. In addition, it is assumed that the wood contains 30% of moisture, higher heating value (HHV) is 20 MJ/kg and average mass 238 kg/m 3 [54]. The amount of syngas from woody biomass can be calculated based on cold gas efficiency η G [47]: 𝜂𝑀 󰇗𝐿𝐻𝑉  𝑀 󰇗𝐿𝐻𝑉  (1) where M g is the mass flow of product gas, LHV g is the lower heating value of the product gas, M b is the mass flow of wood, and LHV b the lower heating value of wood. In this study, η G = 0.7 based on [47,55]. The amount of available biomethane from wood gasification for its part is based on typical wood syngas composition (dry basis) (Table 1). Figure 1. Simplified production paths for biomethane. In 2017 there were 71 biogas production sites in Finland. Total production including collection from landfill sites was approximately 700 GWh [ 53 ], of which only 30 GWh was used as transport fuel. As of 2018, a mere 708 gas fuelled vehicles ran on natural gas (NG) only, and 2925 on both NG and petrol. Most of these vehicles were passenger vehicles. Only 18 NG and 75 dual fuel trucks were registered. In 2017, there were altogether 3,099,566 cars, vans and trucks in Finland [ 36 ]. The potential for the expansion of the fleet of gas fuelled vehicles is considerable. In this paper it is assumed that all the biomethane available to be used solely for heavy-duty transport, originating from both AD of waste material and gasification of woody biomass. Furthermore, based on [ 37 ], the techno-economic biomethane potential from AD in Finland is estimated to be 10 TWh. The amount of available woody biomass for transport fuels is expected to be 4 Mm 3 by 2030 according to the Finnish Government’s estimate as calculated by the Ministry of Employment and the Economy for the country’s 2016 Energy Strategy [ 35 ]. In addition, it is assumed that the wood contains 30% of moisture, higher heating value (HHV) is 20 MJ/kg and average mass 238 kg/m 3 [ 54 ]. The amount of syngas from woody biomass can be calculated based on cold gas efficiency ηG[47]: ηG= . MgLHVg . MbLHVb (1) where M g is the mass flow of product gas, LHV g is the lower heating value of the product gas, M b is the mass flow of wood, and LHV b the lower heating value of wood. In this study, ηG =0.7 based on [ 47 , 55 ]. The amount of available biomethane from wood gasification for its part is based on typical wood syngas composition (dry basis) (Table 1). Sustainability 2019,11, 4750 6 of 19 Table 1. Typical wood gasification product gas composition [ 47 , 51 ] and lower heating values (LHV) of the gas components. Compound Vol-% LHV (kJ/mol) H247 241.8 CO221 - CO 15 283 CH410 802.3 CxHy4 N23 - sum 100 The LHV of the syngas was calculated as a weighted average based on the gas composition and LHV of each of the gas components (Table 1). For gases, the volume fraction equals the molar fraction. Syngas typically contains contaminants such as tars, solid particles and acids, which must be removed before further processing. Cleaning methods usually include cyclones, wet scrubbers and catalytic steps [ 56 , 57 ]. H 2 and CO as well as CO 2 from the syngas can be further reacted to CH 4 . The overall reactions can be simplified as Equations (2) and (3): 3H2+CO –>CH4+H2O (2) 4H2+CO2–>CH4+2H2O (3) Both reactions are exothermic (e.g., demand heat). The conversion of CO and CO 2 (Equations (2) and (3)) was assumed equal to 1 [ 58 ]. Methanation of CO and CO 2 include several reactions [ 52 , 59 ], however the overall reactions were found to be sufficient for the purposes of this study. Since the amount of H 2 in the syngas (Table 1) does not suffice for reacting all the CO and CO 2 from the syngas, we preferred the methanation of CO (Equation (2)). Any excess H 2 left from (Equation (2)) would then be utilized in CO 2 methanation (Equation (3)). Several methods for methanation exist, including fixed and fluidized bed reactors, structured reactors, as well as slurry reactors [ 52 ]. A more detailed description of the CO and CO 2 methanation technologies can be found in [ 52 , 59 ]. The LHV of methane is 802.3 MJ/kmol. For the sake of simplicity, the energy losses from gas purification and pressurization were ignored. 2.2. Assumptions Regarding Heavy-Duty Traffic: Vehicle Model and Scenarios The travelling distance estimates for the three existing commercial manufacturers of gas fuelled heavy-duty vehicles vary between 1000 and 1600 km [ 22 – 24 ]. The total energy consumption of trucks in Finland (2017) was 14.1 TWh [ 60 ], which exceeds the biomethane potential available (10 TWh). In order to examine the most effective scenario for biomethane in heavy-duty transport, the heavy transport trucks were divided into three vehicle classes, namely: Light duty (LD) including delivery vans, refuse collection vehicles and other single unit trucks <18 t Medium duty (MD) including semi-trailer combination vehicles >18 t <60 t Heavy duty (HD) including all articulated vehicles >60 t In 2017, the combined mileage of all the heavy-duty vehicles in Finland was 3,369,642,891 km [ 60 ] and was expected to increase 6% from the 2012 levels by 2030 [ 61 ]. The number of vehicles and the mileage of each vehicle class are presented in Table 2. [62] Sustainability 2019,11, 4750 7 of 19 Table 2. Number of vehicles and average mileage of the vehicle classes [62]. Truck Class Number of Vehicles Mileage per Vehicle (km/a) LD 65,616 19,476 MD 5652 80,060 HD 18,123 73,358 The potential number of biomethane fuelled trucks was examined in three scenarios with different classes of target vehicles. The number of vehicles in each scenario was calculated on the basis of maximum quantities of biomethane theoretically available. The target vehicle class in scenario I was LD trucks. First, the number of LD trucks that could be run with biomethane was calculated based on mileage (Table 2) and fuel consumption (Table 3). If the available volume of biomethane were to exceed the needs of the maximum number of LD trucks (Table 2), the next target class would be MD trucks. Were some biomethane potential still to remain, it would be used for as many HD trucks as possible. Table 3. Average truck diesel consumption (kWh/100 km) [60,63]. Highway Freeway Truck Class Empty Load Full Load Empty load Full Load LD 173 207 207 283 MD 246 374 306 498 HD 335 553 424 770 The target truck class in scenario II was HD, then MD and as many LD trucks as possible and in scenario III, the share of biomethane fuelled vehicles was divided equally between all classes (%). The vehicle fuel consumption and theoretical amount of biomethane fuelled heavy transport vehicles was based on the relevant literature. Average fuel consumption (Table 3) of the chosen vehicle classes was based on diesel truck measurements by [63] and statistical data by [60]. The average energy (kWh/100 km) consumption per vehicle class was calculated as: De* (bf* cfr,e +bh* ch,e)+Df*(bfr * cfr,f +bh* ch,f) (4) where D is the mileage fraction (empty or full load), b is the road fraction (highway or freeway), and c is the fuel consumption [l/100 km]. The subscript e indicates empty load, f full load, fr the freeway, h highway, and d diesel. Empty running average 28% of total mileage was based on [ 64 ]. For the sake of simplicity, it was assumed that for the rest of the mileage the trucks run on full load. The trucks were assumed to be driving 80% highway, 20% freeway [ 65 ]. The average consumption for biomethane trucks was assumed to be 18% higher than for diesel fuelled trucks [ 11 ]. However, gas truck manufacturers claim that the fuel economy of gas fuelled trucks equals that of diesel equivalents [ 23 ] or exceeds it [ 24 ]. However, preferring to err on the side of caution, we assumed a lower efficiency for biomethane trucks. 2.3. Assumptions Concerning Economic and Emission Saving Analysis Our estimate for the overall costs of transforming the heavy transport fleet to biogas is tentative. A detailed calculation regarding the production and distribution costs as well as CO 2 savings of biomethane in the whole transport fleet in the Swedish context can be found in [ 11 ], while these results can be expected to be largely applicable to the Finnish case. According to the International Renewable Energy Agency (IRENA) [ 12 ], the main constraint regarding biomethane as a transport fuel is currently the production cost, which mainly depends on the feedstock used. Here, this study proceeded from the expected biogas potential (10 TWh) of Finland Sustainability 2019,11, 4750 8 of 19 and for AD production facilities followed the IRENA estimate [ 66 ] of the investment costs to vary between 2640–5540 € /kW. For wood gasification plants, the chosen values refer to the experiences of the GoBiGas plant in Gothenburg, Sweden [ 47 ], with 8250 € /kW of gas production capacity. Since this is a pilot plant, the cost will most likely decrease once the technology matures. Yet again to err on the side of caution, this more conservative reference value was chosen. Plant investment costs refer to overnight building costs. Gas filling stations are assumed to be located by the plant site and are included in the overnight costs of the plants. For both types of biomethane plants (AD and gasification), the yearly operational hours were assumed to be 8000 h. The yearly share of investment costs was calculated based on the annuity method with the assumption of 4% investment interest and plant lifetime of 20 years. Based on [ 11 ], the assumed production costs for AD biomethane is approximately 57 €/MWh and for gasification biomethane 72–114 €/MWh, depending on the gasification technology chosen (direct or indirect gasification). The equivalent diesel fuel price was calculated from consumer diesel price (1.4 € /L) [ 67 ], energy content of diesel (11.5 MWh/t), and diesel density (0.08 kg/L). Since the calculations are based on assumptions in the literature, a sensitivity analysis for investment and production costs was performed by changing one parameter at a time by ± 30% in order to calculate whether investment or operational and fuel costs affect the overall costs of biomethane more. The amount of CO 2 -equivalent and NO x emissions for diesel trucks (Table 4) were based on emissioncalculations data byVTT, theTechnicalResearchCentreofFinlandLtd.[ 60 ], using standard EN 16258. The amount of CO 2 -equivalent emissions for each vehicle class was determined by substituting energy consumption in Equation (4) with emissions. As a rough estimate, the CO 2 emission of biomethane vehicles can be expected to be approximately 80% less than that of diesel trucks, depending on the calculation method used (ISO vs. RED) [ 11 ]. The NO x emissions of biomethane fuelled vehicles are reported to be 86% lower [ 10 ] than those of diesel fuelled vehicles, while the fine dust emissions and noise levels are also lower for gas fuelled vehicles [ 12 ]. The total CO 2 and NO x emissions for scenarios I-III were determined on the basis of the number of biomethane and diesel fuelled trucks in each scenario. Table 4. Average NO x and CO 2 -equivalent emissions for the truck classes running with diesel [g/km] [60]. NOx[g/km] CO2-eqv. [g/km] Highway Freeway Highway Freeway Truck Class Empty Load Full Load Empty Load Full Load Empty Load Full Load Empty Load Full Load LD 2.2 2.8 3.4 4.5 402 507 531 815 MD 4.3 5.3 6.9 9.7 630 962 965 1662 HD 4.7 6.5 8.3 14.0 834 1319 1298 2376 2.4. Limitations of the Methodology Limitations of the methodology stem mainly from the vehicle class categorization. As each of the three vehicle classes examined includes a fairly wide range of vehicles, a more detailed analysis could be provided by sub-dividing the vehicle classes into more specific analytical units. Moreover, the assumptions regarding average mileages, loading levels (full/empty) and relative shares of highway and freeway do not fully reflect the differences in the use of different types of heavy vehicles. Light delivery trucks, for example, often operate within a certain area and could have more predictable routes in their operations than the other types of vehicles considered here. Therefore, it can be expected that the share of freeway use is higher in the case of such vehicles than the average value would suggest. Another limitation is utilizing the average values for fuel consumption and emissions. These are heavily dependent on the driver’s behavior, such as time of idling and might in reality differ greatly from the average value. However, as heavy-duty transportation systems consist of a diverse range of actors and vehicles with different operating logics, it is feasible to expect the chosen approach to Sustainability 2019,11, 4750 9 of 19 usefully indicate the benefits from transitioning the heavy-duty vehicle fleet into running on renewable resource based gaseous fuels such as biomethane. Finally, it should be kept in mind that the amounts of biomethane available through both AD and wood gasification are purely theoretical—the actual available amounts are dependent on many contingencies such as the interest of farmers in collecting agricultural side streams (for the related, possible policy incentives, see below). 3. Results and Discussion In this section, the availability of biomethane and potential number of trucks in the three scenarios examined are discussed in relation to current biomethane policies. In addition, recommendations for policy measures to enhance biogas utilization in the heavy truck fleet are presented. 3.1. Amount of Biomethane Available According to [ 37 ] the energy consumption of a biogas plant itself is 24% of the energy content. Consequently, the biomethane from AD available for use as transport fuel (10 MW minus the plant energy need) is 7.4 TWh. The amount of biomethane available from wood gasification was based on an estimate of 4 Mm 3 of wood [ 35 ] with a moisture content of 30%. The mass of 4 Mm 3 of wood was calculated to be 952,000 t, with a total LHV of 3509 GWh. The LHV of product gas from gasification was calculated Equation (1) to be 2456 GWh. The calculated amount of total biomethane available (CH 4 directly from gasification and from CO plus CO 2 methanation reaction Equations (2) and (3) resulted in 2147 GWh of energy. Therefore, the total amount of biomethane available for heavy duty transport would be 9.5 TWh. 3.2. Vehicle Class Scenarios Calculations of the vehicle class scenarios were based on the current number of trucks and average mileages (Table 2) as well as the average energy consumption calculated for each vehicle class. The energy consumption of biomethane fuelled trucks per vehicle class Equation (4) with the assumed 18% lower efficiency [ 11 ] would result in 257 kWh/100 km (LD trucks), 454 kWh/100 km (MD trucks) and 675 kWh/100 km (HD trucks). The numbers of trucks in each class and the respective average energy consumption for the examined scenarios are presented in Figure 2and compared to the current heavy-duty transport vehicle fleet. Sustainability 2019, 11, x FOR PEER REVIEW 9 of 19 3.1. Amount of Biomethane Available According to [37] the energy consumption of a biogas plant itself is 24% of the energy content. Consequently, the biomethane from AD available for use as transport fuel (10 MW minus the plant energy need) is 7.4 TWh. The amount of biomethane available from wood gasification was based on an estimate of 4 Mm 3 of wood [35] with a moisture content of 30%. The mass of 4 Mm 3 of wood was calculated to be 952,000 t, with a total LHV of 3509 GWh. The LHV of product gas from gasification was calculated Equation (1) to be 2456 GWh. The calculated amount of total biomethane available (CH 4 directly from gasification and from CO plus CO 2 methanation reaction Equations (2) and (3) resulted in 2147 GWh of energy. Therefore, the total amount of biomethane available for heavy duty transport would be 9.5 TWh. 3.2. Vehicle Class Scenarios Calculations of the vehicle class scenarios were based on the current number of trucks and average mileages (Table 2) as well as the average energy consumption calculated for each vehicle class. The energy consumption of biomethane fuelled trucks per vehicle class Equation (4) with the assumed 18% lower efficiency [11] would result in 257 kWh/100 km (LD trucks), 454 kWh/100 km (MD trucks) and 675 kWh/100 km (HD trucks). The numbers of trucks in each class and the respective average energy consumption for the examined scenarios are presented in Figure 2 and compared to the current heavy-duty transport vehicle fleet. Figure 2. Number of trucks and energy consumption of vehicle classes for the scenarios. Note: for scenarios I-III the number of trucks and energy consumption in vehicle classes represent biomethane fuelled trucks with 18% higher energy consumption. In scenario I, the available biomethane (9.5 TWh) would suffice for all the LD trucks (65,616) and MD trucks (5652) currently in traffic (Table 2), as well as 46% of HD trucks (8400). In scenario II, the available biomethane (9.5 TWh) would suffice for all the HD trucks currently in traffic (18,123; Table 2) and for 26% of the MD trucks (1450). With HD trucks preferred in this scenario, no biomethane would be available for LD trucks. In scenario III, the biomethane would suffice for a 66% share of trucks currently in traffic (Table 2) divided between the three classes (LD 43,744, MD 3768, and HD 12,082). Assuming that up to 35% of heavy transport in Finland could be electrified [7], in principle the entire volume of the country’s heavy traffic could either run on biomethane or be electrified. 3.3. Economic and CO 2 Savings Analysis The overall costs of transforming the heavy-duty transport fleet to run on biomethane are difficult to estimate since, for example, the price of gas fuelled trucks depends on the accessories. The lack of gas fuelled vehicles and fuelling infrastructure also hampers cost estimation. Gas fuelled trucks may be up to 30%–40% more expensive than diesel fuelled trucks [10]. The availability of used gas trucks is currently limited, while renewing the whole truck fleet in Finland within a short timeframe is unrealistic. However, by investing in the fuelling station network and promoting investments in gas fuelled vehicles, a large share of the fleet could be gas fuelled in 10 to 20 years. Figure 2. Number of trucks and energy consumption of vehicle classes for the scenarios. Note: for scenarios I-III the number of trucks and energy consumption in vehicle classes represent biomethane fuelled trucks with 18% higher energy consumption. In scenario I, the available biomethane (9.5 TWh) would suffice for all the LD trucks (65,616) and MD trucks (5652) currently in traffic (Table 2), as well as 46% of HD trucks (8400). In scenario II, the available biomethane (9.5 TWh) would suffice for all the HD trucks currently in traffic (18,123; Table 2) and for 26% of the MD trucks (1450). With HD trucks preferred in this scenario, no biomethane would be available for LD trucks. Sustainability 2019,11, 4750 16 of 19 7. Liimatainen, H.; van Vliet, O.; Aplyn, D. 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