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Synthetic fuel production costs by means of solid oxide electrolysis cells
Energy xxx (2014) 1e10
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Synthetic fuel production costs by means of solid oxide electrolysis cells Iva Ridjan*, Brian Vad Mathiesen, David Connolly Department of Development and Planning, Aalborg University, Denmark
a r t i c l e i n f o
a b s t r a c t
Article history: Received 11 November 2013 Received in revised form 21 February 2014 Accepted 1 April 2014 Available online xxx
The purpose of this paper is to provide an overview of fuel production costs for two types of synthetic fuels e methanol and methane, along with comparable costs for first and second generation biodiesel, two types of second generation bioethanol, and biogas. When analysing 100% renewable systems, the intermittent nature of renewable energy sources needs to be taken into consideration, so flexible solutions that can provide an option for regulating the energy system by balancing and storing excess electricity are essential. Coupled with the limitations of biomass resources and the need for the sustainable use of it, the solution that fits both concerns needs to be prioritized. The model analysed in this article is a 100% renewable scenario of Denmark for 2050, where the data for the transport sector has been changed to estimate the fuel production costs for eight different fuel pathways. The results confirm that synthetic fuel pathways reduce the demand for biomass, while simultaneously increasing the flexibility of the energy system by enabling a high share of wind energy. The most interesting finding is that the production costs of synthetic fuels are comparable with petrol production costs once the associated CO2 emissions are included. Ó 2014 Elsevier Ltd. All rights reserved.
Keywords: Synthetic fuels 100% Renewable energy system Flexible system Biomass scarcity Transport
1. Introduction Over the decades emissions from the transport sector have been increasing while no significant renewable energy penetrations have been implemented. Due to the many different modes in the transport sector, flexible solutions that can be implemented in the existing infrastructure, completely adapted to liquid fuels, would be preferred. While there is a large potential for electric vehicles for personal cars, other modes of transport such as trucks and ships require fuels in a liquid or gaseous form. The focus traditionally has been on biofuels such as bio-diesel and bio-ethanol, as the only recommended supplements for the liquid fuel production [1]. The reason why biomass is interesting for the transport sector is that it can be converted to fuels with a high energy density. Implementation of biofuels raised discussions about their actual effect on the environment [2], such as the risk of interfering with food production, deforestation, and changes in land-use [3]. The comparison of biofuel emissions and their fossil equivalents was analysed in Ref. [4] which has raised the question of the sustainability of these
* Corresponding author. E-mail addresses: [email protected] (I. Ridjan), [email protected] (B.V. Mathiesen), [email protected] (D. Connolly).
fuels. However, there are many uncertainties on how to calculate lifecycle emissions for biofuels, which caused concerns on the accuracy of the real results [5]. Recent research in 100% renewable energy systems heightened the need to consider fuels in which you can limit the use of biomass when including the transport sector in the energy system analysis [6]. When switching to renewable sources their intermittent nature needs to be taken into consideration. The implementation of sources such as wind and solar energy requires balancing capacity that can enable extensive penetration into the grid. Electrolysers can convert electrical energy to chemical energy in the form of fuels, which enables electrolysers to substitute fossil energy in different ways. In combination with carbon from biomass conversion in the heat and power sector it enables production of liquid or gaseous fuels that can be either used in other energy sectors that require high energy density fuels or reused for power generation. The benefit of converting electricity into a form of liquid/gas fuel via electrolysis provides flexibility in terms of system regulation. There are different types of electrolysers that can be used in the process of synthetic fuel production: alkaline, PEM (polymer exchange membrane) and SOEC (solid oxide electrolysis cell). The reason why alkaline and PEM electrolysers are not the one of interest is because of their lower efficiency compared to the solid oxide electrolyser cells, along with the fact that they can only be
http://dx.doi.org/10.1016/j.energy.2014.04.002 0360-5442/Ó 2014 Elsevier Ltd. All rights reserved.
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used for steam electrolysis. However, these electrolysers could be a possible transition solution as solid oxide electrolyser cells are still not commercially available. Even though the SOECs are still not commercialized the technology has been demonstrated and tested in a period of 9000 h [7]. The high operation temperature of SOEC (>800 C) results in faster reaction kinetics, which reduces the need for expensive catalyst materials. The SOEC could potentially operate in reverse as a fuel cell (SOFC) and therefore provide more options for balancing the energy system. The advantage of SOEC compared to other electrolyser technologies is that it conducts oxygen ions so they enable CO2 electrolysis. SOEC can also generate synthetic gas by conducting co-electrolysis, the combined electrolysis of carbon dioxide and steam. However, this process is more complicated than separate steam and CO2 electrolysis, and overall reaction pathway is not clearly defined [8]. Throughout this paper the term synthetic fuel will refer to a fuel that does not include the use of fossil fuel in the production process, and instead it is produced by combined use of electrolysers with carbon source. The carbon source can come either through: the recycling of CO2 from a stationary energy-related/industrial process, or from the biomass gasification. The CO2 recycling or biomass “boosting” (upgrading the energy content of biomass with hydrogen) for renewable fuel production would open the door to renewable energy in the transport sector, which was previously not accessible in the form of liquid fuels, with the exception of biofuels. Moreover this way of fuel production enables flexible fuel choice, as produced syngas can be converted to various liquid or gaseous fuels. One of the main advantages of some synthetic liquid fuels such as methanol and DME (dimethyl ether), is that implementation requires a limited change in the infrastructure: these typically include alterations of the vehicles and existing fuelling stations to a new type of fuel. The synthetic fuel production is still at an early stage of development when combining renewable sources and CO2 recycling. However, the George Olah Renewable Methanol Plant in Iceland has started the production of methanol via carbon recycling from a geothermal power station, using a technology called ETL (Emission to Liquid) [9]. Biomass gasification to fuels is already demonstrated in Sweden and there are a few projects planned for its commercialization. The BioDME project has already demonstrated the production of bio-DME and bio-methanol from the gasification of black liquor in 2011 [10]. The first commercial biomass to methanol plant, which gasifies biomass residues, will be inaugurated in Hagfors, Sweden and plans to start production in 2014/2015 [11]. Methane production from forest biomass is a key focus in the Bio2G project and a plant is planned in the Öresund region [12]. Two more methanol plants, based on wood gasification and black liquor gasification are planned to be built by Rottneros Biorafinery AB [13]. Therefore, although the hydrogenation of CO2 and biomass are relatively new concepts for the production of fuels, there are already a number of large-scale plants either in operation or at the planning phase. In this paper eight different fuel production pathways are analysed in the 100% renewable energy system and their fuel production costs are compared. The three synthetic fuel pathways (biomass hydrogenation, CO2 hydrogenation and co-electrolysis) were analysed both for methanol and methane production, while the other three pathways (biodiesel e 1st and 2nd generation, bioethanol e 2nd generation with and without C5 sugar utilization and biogas) are analysed as separate cases. The synthetic fuel pathways using CO2 recycling process (CO2 hydrogenation and co-electrolysis) analysed in this article use CO2 emissions from the biomass combustion in the heat and power sector as their carbon source. The scenarios of the energy system have been allocated the same names as pathways implemented in the transport sector. The
infrastructure costs, such as building new gas networks for transporting gaseous fuels, CO2 or syngas, were not included in the cost calculation because the aim of the article is to give an overview of the fuel production costs and not the overall implementation costs of these fuels in the system. The flexibility of the different pathways is compared with the level of wind energy integration as the determining factor and the sensitivity analysis of biomass use is conducted to highlight the importance of conscientious use of biomass in the future energy systems. The objective of this paper is to determine the fuel production price for different synthetic fuels and their competitors by providing an overview of all production chain elements that are forming the fuel price. The study provides the enhanced knowledge of the production chain components and related costs which enabled the more detailed modelling of synthetic fuels in the energy system. The focus of this study is narrowed in order to get the clear picture of the production costs and the competitiveness of the newly proposed fuels. The present study confirms previous findings [14] and contributes by giving the insight of the fuel price formation. 2. Methodology The model analysed in this article is taken from the Danish 100% renewable scenario for 2050 [6] where the data for the transport sector has been changed in order to get the overview of costs for different renewable fuels that can be implemented. The obtained results include the costs of the production units, fuel handling costs, associated CO2 emissions costs, and the feedstocks needed for the production. All the analysed scenarios are 100% renewable energy systems. The scenarios have been analysed using the energy system analysis tool EnergyPLAN [15] to analyse different fuel types in the energy system. EnergyPLAN was chosen because it includes the balancing of the system in its fuel costs calculations. This aspect was important because electrolysers enable high share wind integration; therefore the costs are more accurate when including balancing costs. All scenarios were analysed with technical optimization, meaning that the fuel consumption is minimized. This is important due to the level of biomass resource used in the scenarios. The system in all scenarios was balanced in terms of CEEP (critical excess electricity production) and the gas balance, so the scenarios could be comparable. The balancing of the gas grid includes import and export, utilisation of gas storage and regulation strategies to minimise the exchange of gas to and from the system. The model operates in a way that it reduces the demand for natural gas with the produced biogas and/or syngas so the output is a biogas/syngas grid instead of a natural gas grid due to the analysis of 100% renewable systems. The scenarios vary depending on the pathways implemented in the transport sector, but in terms of primary energy supply the variations are mainly the ability to integrate wind capacity and the biomass demand for fuel. All the scenarios have closed self-sufficient energy systems. Many previous studies have been carried out using EnergyPLAN such as analysing high shares of intermittent sources particularly wind power on the system [16], DH and CHP [17], analysis of alternative transport technologies [18e20] and analysis of 100% renewable energy systems [6,21e24]. The tool is a free-ware software that is updated regularly so it can implement the newest technologies in energy systems. The latest updates are new facilities of waste-to-energy technologies in combination with geothermal and absorption heat pumps, new costs data, different biomass conversion plants such as biogas, biomass gasification, biodiesel and ethanol plants, new facilities for grid gas (natural gas/ bio/syngas) and additional grid stabilisation options. Furthermore,
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synthetic gas and liquid fuel production modelling is now enabled for different types of pathways. It is possible to directly model biomass hydrogenation, CO2 hydrogenation, co-electrolysis and biogas upgrade to methane. The produced syngas can be converted to synthetic jet-fuel, methanol and DME through the chemical synthesis option. Detailed description of the model and possible applications can be found at [25].
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The Co-electrolysis pathway is using combined process of steam and CO2 electrolysis called co-electrolysis, and the produced synthetic gas can afterwards be catalysed into various types of fuel (see Fig. 3). The produced syngas from this process has 2:1 hydrogen to carbon monoxide ratio which is the desired ratio for further conversion to methanol; however this does not exclude the possibility of conversion to other types of fuels as there are no barriers to do that.
2.1. The synthetic fuel pathways 2.2. Biofuel pathways and biogas The fundamental difference between synthetic fuel pathways is in the carbon source. Biomass hydrogenation uses direct input of biomass in the gasification process, and the produced gas is later on boosted with hydrogen produced from steam electrolysis. CO2 recycling pathways (CO2 hydrogenation and co-electrolysis) do not require any direct biomass input, instead they use emissions from the biomass used in the heat and power sector combined with electrolysis. This section will give a short overview and flow diagrams of three synthetic fuel pathways. The biomass hydrogenation pathway is using biomass gasification as a base process for synthetic fuel production. The syngas produced from this process is boosted by hydrogen from steam electrolysis (see Fig. 1) and later on converted by chemical synthesis to the desired fuel output. This way of producing fuel from a biomass resource enables the integration of the wind in the system due to the electricity related to hydrogen production, which is needed for the biomass upgrading process and concurrently lowers the need for biomass. The CO2 recycling pathways enable a strong connection between energy sectors by using recycled CO2 from the heat and power sectors to produce transport fuels. The principal objective of these pathways is to create a transport fuel without direct biomass input, by combining the electrolysis process with a carbon source provided by biomass used in other parts of the energy system. The syngas produced in both pathways consists of different amounts of carbon dioxide, carbon monoxide and hydrogen depending on the process of production. The fuel production by CO2 hydrogenation pathway combines hydrogen from the steam electrolysis with recycled carbon dioxide from a stationary source to form a syngas. The produced syngas can be subsequently converted by chemical synthesis to chosen fuel output (see Fig. 2).
Four biofuel pathways were analysed along with the biogas pathway in the paper as a comparison to synthetic fuel pathways. The biofuel pathways are chosen according to the existing technology and due to their current contribution as the most exposed renewable replacement for fossil fuels. Biogas was analysed as an alternative to synthetic production of methane as only gaseous fuel that was consider in synthetic fuel pathways. The first generation biodiesel is used for analysis as it is the most commonly produced biofuel in Europe. It is based on a chemical modification of vegetable oil by transesterification in order to produce a fuel that can be used in existing diesel engines. The analysed biodiesel is based on the production from energy crops [26]. The second generation biodiesel represents the production by BTL (biomass-to-liquid process). The biomass is firstly gasified; afterwards the produced gas is cleaned and converted to longchained alkanes by Fisher-Tropsch synthesis. The alkanes are subsequently treated by thermal cracking to produce the desired fuel [27]. Two second generation bioethanol scenarios were analysed, one without and one with the C5 sugar utilization. Both technologies are commercially available, however a research focus is to improve the process with the C5 sugar fermentation [27]. The main reason for using both scenarios is due to the cost differences. The modelled second generation bioethanol uses straw as a biomass resource which is fermented after the biomass pre-treatment. The process finishes with the purification that delivers the end ethanol product. The produced by-products are lignin and molasses which have high value and can become the important part of the production as they can be used for further conversion. Biogas is modelled according to [28], where biogas is produced by using animal manure treated in an anaerobic process. The biogas
Fig. 1. The well-to-tank conversion processes for the biomass hydrogenation pathway.
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Fig. 2. The well-to-tank conversion processes for the hydrogenation of CO2 pathway.
plant is a centralized biogas plant with a daily input of manure and organic waste of 1000 tonnes (80e90% of animal manure and 10e 20% organic waste from industry) [28]. The manure goes through an anaerobic process resulting in biogas that afterwards can be used for different purposes. The output biogas is in this analysis completely upgraded into methane with hydrogen from water electrolysis. 3. Components of the fuel production chains and economy The components of the fuel production chains are the key for understanding the calculations of the fuel costs that is the outcome of this analysis. This section will provide a short description of all
the system components that form the price in different pathways (see Table 1). The section also provides the main economic data for the calculations of fuel production: the investment costs of production units, feedstock expenses and fuel handling costs (see Table 2 and Table 3). All the investment costs in the plants are based on the specifications of the production units, lifetime and fixed operation and maintenance costs. The biofuel scenarios present commercially available technologies for biodiesel and bioethanol production. First generation biodiesel is the simplest scenario as it uses direct conversion of biomass in the bio-refinery to produce biodiesel from the energy crops (grass or corn). The process is characterized by a high efficiency. The total price is based on the investment costs of the biodiesel plant, biomass
Fig. 3. The well-to-tank conversion processes for the co-electrolysis pathway.
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Table 1 Components and feedstock used in the production cycle. Biodiesel/Biodiesel 2nd generation
Bioethanol 1/ Bioethanol 2
Carbon source
Biomass
Biomass
Bioenergy plant Resource
Biodiesel plant Energy crops (grass or corn)/ Straw or wood incl. pellets
Bioethanol plant Straw or wood incl. pellets
Electricity source Electrolysis Fuel synthesis
Biogas hydrogenation
Biomass hydrogenation
CO2 hydrogenation
Co-electrolysis
Biomass gasification
CO2 emissions from biomass CHP plant
CO2 emissions from biomass CHP plant
Offshore wind SOEC Chemical synthesis
Offshore wind SOEC Chemical synthesis
Biogas plant Manure
Gasification plant Straw or wood incl. pellets
Offshore wind SOEC Chemical synthesis
Offshore wind SOEC Chemical synthesis
expenses and the fuel handling costs. The second generation biodiesel process is based on BTL technology and the cost of this technology is higher than the first generation biodiesel plant [25]. The process is modelled with a biomass to fuel efficiency of 39% and the fuel price is formed by adding the fuel handling costs to investment costs of biodiesel plant and biomass expenses. The second generation bioethanol production from straw is more complicated than the production of first generation bioethanol from food. Bioethanol production uses both electricity and steam for the production process and the biomass used for steam production is added when calculating the total biomass consumption for the pathway. The bioethanol scenario which includes the utilisation of C5 sugar is modelled the same as the scenario without the C5 sugar utilisation, apart from the costs. The cost of the production plant without sugar utilisation is taken from Refs. [26], while the cost of a new fermentation technology which utilises with C5 sugars is from Ref. [27]. In the biogas scenario analysed, biogas is produced from animal manure, hence no biomass costs are associated with the production as the manure is considered free. The costs calculated for the biogas production involve operation and investment costs for the biogas plant and the cost for biogas upgrade to methane by hydrogen from water electrolysis. The hydrogen is produced by using wind power to run the dissociation of oxides in electrolysis. Therefore the overall production costs of biogas involve investment costs of wind turbines, electrolysers needed for hydrogen production as well as the synthesis plant investment. The fuel costs by using biomass hydrogenation pathway consist of costs for the biomass gasifier, wind turbine costs, electrolyser investments and the synthesis plant. Biomass gasifier costs used in this analysis correspond to the costs for low temperature gasification, based on the Pyroneer gasifier [28]. The biomass goes through three main components of the gasifier: a pyrolysis chamber, a char reactor and a recirculating cyclone. The biomass is converted into synthetic gas, which can be further used for hydrogenation to
produce methanol or methane as a substitute to fossil fuels. The efficiency of the process used in the analysis is 83% for the conversion of biomass to syngas. In case of CO2 recycling pathways an analysis was conducted with the post-combustion CCR (carbon capture and recycling) process, due to the fact that this method is more established for CO2 capture than the others. The electricity demand for CO2 sequestration is calculated from the specified factors for electricity needed for extracting CO2 (TWh/Mton) and extracted CO2 per produced synthetic gas (Mton/TWh). The hydrogen needed in all pathways was provided by high temperature electrolysis with SOEC (Solid Oxide Electrolyser Cells). The SOECs are powered by offshore wind capacities and their electricity demand is calculated from the ratios of hydrogen per fuel output and electrolyser efficiency. In the case of co-electrolysis the ratio of hydrogen and CO2 per fuel output was used. The efficiency used for the steam electrolysis is 73% and for co-electrolysis is 77% and both efficiencies include the assumed energy losses in the production of 10% and 5% extra for the gas storage. The investment costs of SOEC include local grid reinforcement to connect electrolysers to the transmission system [29]. The costs for the synthesis plant in the analysis are for methanol production from synthesis gas, in a pressurized catalytic process [26]. The catalyst used for this process is copper-based and the operating temperature of the process is approximately 200e 300 C. In the case of methane production the same costs were assumed. 3.1. Analysis uncertainties Uncertainties in this paper are mainly due to the maturity of the technologies and the long-term investment predictions. The cost calculations for technologies that are still at the R&D level are very uncertain and highly dependent on the technological development. Therefore investment costs for SOECs are based on predictions and
Table 2 Investment costs for plants included in the analysis. Type
Unit
Investment (MV/unit)
Lifetime (years)
O&M (% of investment)
Source
Biomass gasifier Biogas plant Biodiesel plant 1st generation Biodiesel 2nd generation Bioethanol plant 1 Bioethanol plant C5 sugar Fuel synthesis plant SOEC electrolyser Offshore wind 2015 Offshore wind 2050
MWsyngas TWh/year MWbio input MWbio input MWbio input MWbio input MWfuel ouput MWe MWe MWe
0.316 392 0.27 1.89 1.82 0.435 0.55 0.28 3.1 2.1
25 20 20 20 20 20 20 15 20 30
7 6.96 1 3 3.69 7.68 3.48 3 3.5 3.21
[28] [28] [26] [27] [26] [27] [26] [29] [28] [28]
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Table 3 Additional costs for feedstock, fuel handling and CO2 sequestration.
CO2 sequestration Straw or wood incl. pelletsa Green energy crops (grass or corn)a Fuel handlinga a
Unit
Costs
Source
V/t V/GJ V/GJ V/GJ
30 5.7 7.5 4
[30] [31] [31] [31]
Adjusted to 2010 prices.
today’s available stack costs. All synthetic fuel pathway calculations of resources needed for the fuel production processes were based on chemical reactions and energy balances, therefore the different energy densities of the chemical reaction components can cause variations of the results. The bioethanol plants produce food by-products during the production of bioethanol. It is possible that the income of the food by-product would influence the costs of ethanol if accounted like that. The actual value of this by-product is currently very uncertain therefore it was not included in the analysis; however this could be used in the future calculations when certain cost value can be signed to the by-product. It is assumed that none of the other pathways produce by-products of significant value. 4. Results The fuel production costs were calculated for the same demand in all scenarios (32.15 TWh/year, which is the forecasted demand for transport fuels in Denmark in 2050) that has been met by different fuels. In the case of synthetic fuel pathways two different fuel types were analysed, methanol as a liquid and methane as gaseous fuel. First and second generation biodiesel, two bioethanol pathways and biogas costs were calculated as separate scenarios. The calculated fuel price per GJ of produced fuel can be seen on Fig. 4 for biofuels, biogas and petrol (as a base of comparison) and in Fig. 5 for synthetic fuels. Fig. 6 and Fig. 7 show the breakdown of costs for biofuels, biogas and synthetic fuels to the production units, feedstock and fuel handling costs, together with the CO2 emissions cost. It can be seen that the first generation biodiesel scenario have the lowest production costs, while the synthetic fuel pathways
have the highest costs along with second generation biodiesel, biogas hydrogenation and both bioethanol scenarios. The results vary due to the complexity of the different scenarios, their ability to integrate wind power production, technology costs and the amount of biomass used for the fuel production. The biodiesel scenario uses 33.5 TWh of biomass to produce enough biodiesel to cover demand, which is approximately 70% of its total production costs. For second generation biodiesel the production plant cost is higher, accounting for around 20% of the total. Moreover, the biomass used in this scenario is double compared to the first generation biodiesel due to the lower efficiency of the process. In the case of the bioethanol scenarios, it is clear that the technology with C5 sugar utilisation is cheaper simply due to the price of the bioethanol production plant. The bioethanol pathways use the most biomass resources: 89 TWh of biomass is needed to cover the whole transport demand. The biogas costs are highly connected to the investment in biogas plants, which accounts for 35% of the total fuel costs, and wind power which accounts for 38% of the total. The high share of wind is due to the upgrading of biogas to methane with hydrogen so it can be used in the transport sector. In the case of synthetic fuel scenarios, specifically in relation to CO2 recycling pathways the production costs of methanol are higher than in case of methane. This can be explained by the ratio of hydrogen for the methanol and methane production which is directly connected with the amount of electricity needed for the steam electrolysis to provide hydrogen. It can be seen that, which proves their concept of electricity to fuel conversion. The biomass hydrogenation for methane is more expensive because of the biomass to hydrogen ratio, which is opposite than in the case of CO2 recycling pathways. Even though the methane production uses 7.3 TWh less biomass, the electricity penalty for the hydrogen production is higher than the biomass savings. It is interesting to note that all synthetic fuel scenarios are not far off the production costs of petrol when the CO2 emission costs are accounted. This finding is very important as it puts the synthetic fuels in the competitive position to today’s fossil fuel. 4.1. Sensitivity analysis The sensitivity analysis was conducted with three biomass price levels (see Table 4) due to the uncertainties of the fuel costs in the
Fig. 4. Calculated fuel production costs for biofuels, biogas and petrol.
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Fig. 5. Calculated fuel production costs for synthetic fuels.
long term planning. Moreover the biomass price level was changed because some of the analysed fuels are directly connected to the biomass input. Fig. 8 shows the correlation between biomass consumption and fuel output for each pathway that has fuel production based on biomass resources. This figure is quite revealing compared to the previous ones as it shows directly the biomass consumption per scenarios. The sensitivity analysis shows that biomass prices influence the most pathways with a high share of biomass in their production process (see Fig. 9). As it can be seen from previous figures all biofuel scenarios apart from biogas are highly dependent on biomass, as it is the base of their process. The biomass hydrogenation pathway is sensitive to biomass price change but not to the same extent as biofuel scenarios due to the lower share of biomass
in the overall fuel production price. On the contrary CO2 recycling pathways are not influenced by changes in biomass prices because there is no direct input of biomass in the production therefore the biomass price sensitivity analysis was not conducted for these pathways. As synthetic fuel scenarios are not as sensitive to biomass price changes, another sensitivity analysis was carried out to investigate the influence of investments in offshore wind on the fuel production costs. As the scenarios in the analysis use the investment costs for 2050, to conduct a sensitivity analysis the offshore wind investment costs for 2015 were taken for comparison. It can be seen that the price of the fuels is drastically higher for CO2 recycling pathways in case of offshore wind investment prices for 2015, which was expected due to the fact that wind share in the
Fig. 6. Shares of the production components in forming the fuel price for biofuels and biogas.
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Fig. 7. Shares of the production components in forming the fuel price for synthetic fuels.
Table 4 Biomass prices for sensitivity analysis. V/GJ
Straw or wood incl. Pellets
Energy crops
Low price level Medium price level High price level
4.3 5.7 8.3
5.4 7.5 11.8
production cost is 67% (see Fig. 10). The pathways with lower share of wind in the production process are not so sensitive to the price change. 5. Conclusion The present study was designed to determine the fuel production prices for different renewable fuels that can be produced in
order to meet the demand in transport sector that cannot be met by electrification. The reason for the development of synthetic fuels is due to the limited biomass resource available, which will become an important aspect of 100% renewable energy systems. The results show the breakdown of the production costs based on the components of the production process, the biomass consumption for different fuel pathways and the fuel production cost. The study has shown that the pathways that have higher share of biomass in their production process are not as flexible in terms of wind integration and the fuel output as other proposed scenarios. However, the production costs for some of these pathways are the lowest due to the simplicity of the process and the high conversion rate (as is the case for first generation biodiesel). The synthetic fuel pathways enable the wind integration which varies from lowest for the biomass hydrogenation pathways to highest for CO2 recycling
Fig. 8. Biomass consumption per fuel output for the biomass based scenarios.
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Fig. 9. Production costs sensitivity analysis to biomass prices for biomass based scenarios (scenarios without direct biomass consumption were not included).
Fig. 10. Production costs sensitivity connected to offshore wind investment for scenarios with wind integration (scenarios without wind integration were not included).
pathways. Moreover this way of fuel production enables flexible fuel choice, which was shown by the production of both methanol and methane. The synthetic fuel pathways have higher production costs due to the technologies that they use for the production process, yet they are still lower than the costs of second generation bioethanol. The major finding was that the production costs of synthetic fuels are comparable with petrol production costs when the associated CO2 emissions are accounted for. Taken together, these results suggest that these fuels have a potential to be a future fossil fuel replacements in the transport sector. If the certain recommendation is to be given on which pathway should be implemented, a further research needs to be undertaken by identifying the efficiency of different vehicles and their driving range depending on the used fuel. This can give a more holistic view of the pathways. In the long term perspective, the final
decision will also depend on the availability of biomass resources, the types of biomass resources and their land-use, the biomass costs, the technological development, demonstration of facilities on a large-scale and the infrastructure costs. Acknowledgements The findings in this article result from a research project Coherent Energy and Environmental Analysis (CEESA) carried out at Aalborg University and funded by The Danish Council for Strategic Research. The research was also supported financially by the ForskEL research program on Development of SOEC (2011-1-1069). A preliminary version of the paper was presented at the SDEWES 2013 conference in Dubrovnik, Croatia, and therefore we wish to thank the audience for their contributions during the discussions.
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References [1] European Commission. Renewable Energy: Progressing towards the 2020 target. Available from: http://eur-lex.europa.eu/LexUriServ/LexUriServ.do? uri¼COM:2011:0031:FIN: EN:PDF; 2011. [2] Dallemand JF, Leip A, Rettenmaier N. Biocarburants liquides pour le transport: de défi d’une correcte évaluation du bilan environnemental. In: Pollution Atmosphérique e Numéro Spécial. Anonymous; 2009. p. 89. [3] Eickhout B, Born G, Notenboom J, Mv Oorschot, Ros J, Dv Vuuren, et al. Local and global consequences of the EU renewable directive for biofuels: testing the sustainability criteria; 2008. [4] Koper M, Berg MVD, Hamelinck C. BOLK II Air polluting emissions from bioenergy supply chains e Final Report. Available from: http://www.rivm.nl/ bibliotheek/digitaaldepot/BOLK_II_LCA_Final.pdf; November, 2009. [5] Gallagher E. The Gallagher review of the indirect effects of biofuels production. East Sussex, UK: Renewable Fuels Agency Ashdown House; 2008. [6] Henrik Lund (Edt.), Frede Hvelplund, Brian Vad Mathiesen, Poul A. Østergaard, Per Christensen, David Connolly, Erik Schaltz, et al. Coherent Energy and Environmental System Analysis (CEESA). [7] Tietz F, Sebold D, Brisse A, Schefold J. Degradation phenomena in a solid oxide electrolysis cell after 9000 h of operation. J Power Sources 2013;223: 129e35. [8] Stoots CM, O’Brien JE, Condie KG, Hartvigsen JJ. High-temperature electrolysis for large-scale hydrogen production from nuclear energy e experimental investigations. Int J Hydrogen Energy 2010;35:4861e70. [9] George Olah renewable methanol plant. Carbon Recycling International; 2012. [10] BioDME. Production of DME from biomass and utilisation of fuel for transport and industrial use. Available from: http://www.biodme.eu/ [accessed 06.20.13]. [11] Gillberg BO. World’s first commercial scale biomethanol plant in Hagfors Sweden. Hagfors, Sweden. Available from: http://www.varmlandsmetanol.se/ dokument/History%20March%2012.pdf; March 2012. [12] Möller BF. Gasification development at E.ON. Sweden. Available from: https:// www.ecn.nl/fileadmin/ecn/units/bio/Biomassa/Syngas_and_SNG/ Gasification_2010/Gasification_development_at_E.on.pdf; 2010. [13] Rottneros AB. Hallvarsson & Halvarsson annual report 2011. Sweden; 2011. Available from: http://www.rottneros.com/afw/files/press/rottneros/ Rottneros_Annual%20Report2011.pdf. [14] Ridjan I, Mathiesen BV, Connolly D, Dui c N. The feasibility of synthetic fuels in renewable energy systems. Energy 2013;57:76e84. [15] Aalborg University. EnergyPLAN: advanced energy system analysis computer model. Available from: http://energy.plan.aau.dk/ [accessed 06.14.12].
[16] Connolly D, Lund H, Mathiesen BV, Leahy M. Modelling the existing Irish energy-system to identify future energy costs and the maximum wind penetration feasible. Energy 2010;35:2164e73. [17] Lund H, Münster E. Modelling of energy systems with a high percentage of CHP and wind power. Renew Energy 2003;28:2179e93. [18] Lund H, Munster E. Integrated transportation and energy sector CO2 emission control strategies. Transp Policy 2006;13:426e33. [19] Mathiesen BV, Lund H, Nørgaard P. Integrated transport and renewable energy systems. Util Policy 2008;16:107e16. [20] Lund H, Kempton W. Integration of renewable energy into the transport and electricity sectors through V2G. Energy Policy 2008;36:3578e87. [21] Lund H, Mathiesen BV. Energy system analysis of 100% renewable energy systemseThe case of Denmark in years 2030 and 2050. Energy 2009;34:524e31. [22] Mathiesen BV, Lund H, Karlsson K. 100 renewable energy systems, climate mitigation and economic growth. Appl Energy 2011;88:488e501. [23] Connolly D, Lund H, Mathiesen BV, Leahy M. The first step towards a 100% renewable energy-system for Ireland. Appl Energy 2011;88:502e7. [24] Mathiesen BV, Lund H, Karlsson K. The IDA climate plan 2050. The Danish Society of Engineers and Aalborg University; 2009. Available from: http://ida. dk/News/Dagsordener/Klima/Klimaplan2050/Sider/Klimaplan2050.aspx. [25] Department of Development and Planning, Aalborg University, Lund Henrik. EnergyPLAN, Advanced energy planning systems analysis computer model e documentation version 11.0. Denmark. Available from:, http://www.energyplan.eu/ wp-content/uploads/2013/06/EnergyPLAN-Documentation-V11-2013.pdf; 2013. [26] Danish Energy Agency. Alternative drivmidler i transportsektoren (Alternative Fuels for Transport). Available from: http://www.ens.dk/; 2012. [27] FORCE Technology, Department for Biomass & Waste, Evald A, Hu G, Hansen MT. Technology data for advanced bioenergy fuels. Denmark. Available from:, http://www.ens.dk/sites/ens.dk/files/info/tal-kort/ fremskrivninger-analyser-modeller/teknologikataloger/technology_data_for_ advanced_bioenergy_fuels.pdf; June, 2013. [28] Danish Energy Agency, Energinet. Technology data for energy plants. Generation of Electricity and District Heating, Energy Storage and Energy Carrier Generation and Conversion. Maj; 2012. [29] Mathiesen B, Ridjan I, Connolly D, Nielsen M, Hendriksen P, Mogensen M, et al. Technology data for high temperature solid oxide electrolyser cells, alkali and PEM electrolysers. Department of development and planning, Aalborg University; May, 2013. [30] Energistyrelsen (Danish Energy Authority), Danish Energy Agency, Energinet.dk. Technology data for energy plants. Copenhagen, Denmark; 2010/6. [31] Danish Energy Agency. Forudsætninger for samfundsøkonomiske analyser på energiområdet (Assumptions for socio-economic analyses for energy); 2011.
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Contents lists available at ScienceDirect
Energy journal homepage: www.elsevier.com/locate/energy
Synthetic fuel production costs by means of solid oxide electrolysis cells Iva Ridjan*, Brian Vad Mathiesen, David Connolly Department of Development and Planning, Aalborg University, Denmark
a r t i c l e i n f o
a b s t r a c t
Article history: Received 11 November 2013 Received in revised form 21 February 2014 Accepted 1 April 2014 Available online xxx
The purpose of this paper is to provide an overview of fuel production costs for two types of synthetic fuels e methanol and methane, along with comparable costs for first and second generation biodiesel, two types of second generation bioethanol, and biogas. When analysing 100% renewable systems, the intermittent nature of renewable energy sources needs to be taken into consideration, so flexible solutions that can provide an option for regulating the energy system by balancing and storing excess electricity are essential. Coupled with the limitations of biomass resources and the need for the sustainable use of it, the solution that fits both concerns needs to be prioritized. The model analysed in this article is a 100% renewable scenario of Denmark for 2050, where the data for the transport sector has been changed to estimate the fuel production costs for eight different fuel pathways. The results confirm that synthetic fuel pathways reduce the demand for biomass, while simultaneously increasing the flexibility of the energy system by enabling a high share of wind energy. The most interesting finding is that the production costs of synthetic fuels are comparable with petrol production costs once the associated CO2 emissions are included. Ó 2014 Elsevier Ltd. All rights reserved.
Keywords: Synthetic fuels 100% Renewable energy system Flexible system Biomass scarcity Transport
1. Introduction Over the decades emissions from the transport sector have been increasing while no significant renewable energy penetrations have been implemented. Due to the many different modes in the transport sector, flexible solutions that can be implemented in the existing infrastructure, completely adapted to liquid fuels, would be preferred. While there is a large potential for electric vehicles for personal cars, other modes of transport such as trucks and ships require fuels in a liquid or gaseous form. The focus traditionally has been on biofuels such as bio-diesel and bio-ethanol, as the only recommended supplements for the liquid fuel production [1]. The reason why biomass is interesting for the transport sector is that it can be converted to fuels with a high energy density. Implementation of biofuels raised discussions about their actual effect on the environment [2], such as the risk of interfering with food production, deforestation, and changes in land-use [3]. The comparison of biofuel emissions and their fossil equivalents was analysed in Ref. [4] which has raised the question of the sustainability of these
* Corresponding author. E-mail addresses: [email protected] (I. Ridjan), [email protected] (B.V. Mathiesen), [email protected] (D. Connolly).
fuels. However, there are many uncertainties on how to calculate lifecycle emissions for biofuels, which caused concerns on the accuracy of the real results [5]. Recent research in 100% renewable energy systems heightened the need to consider fuels in which you can limit the use of biomass when including the transport sector in the energy system analysis [6]. When switching to renewable sources their intermittent nature needs to be taken into consideration. The implementation of sources such as wind and solar energy requires balancing capacity that can enable extensive penetration into the grid. Electrolysers can convert electrical energy to chemical energy in the form of fuels, which enables electrolysers to substitute fossil energy in different ways. In combination with carbon from biomass conversion in the heat and power sector it enables production of liquid or gaseous fuels that can be either used in other energy sectors that require high energy density fuels or reused for power generation. The benefit of converting electricity into a form of liquid/gas fuel via electrolysis provides flexibility in terms of system regulation. There are different types of electrolysers that can be used in the process of synthetic fuel production: alkaline, PEM (polymer exchange membrane) and SOEC (solid oxide electrolysis cell). The reason why alkaline and PEM electrolysers are not the one of interest is because of their lower efficiency compared to the solid oxide electrolyser cells, along with the fact that they can only be
http://dx.doi.org/10.1016/j.energy.2014.04.002 0360-5442/Ó 2014 Elsevier Ltd. All rights reserved.
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used for steam electrolysis. However, these electrolysers could be a possible transition solution as solid oxide electrolyser cells are still not commercially available. Even though the SOECs are still not commercialized the technology has been demonstrated and tested in a period of 9000 h [7]. The high operation temperature of SOEC (>800 C) results in faster reaction kinetics, which reduces the need for expensive catalyst materials. The SOEC could potentially operate in reverse as a fuel cell (SOFC) and therefore provide more options for balancing the energy system. The advantage of SOEC compared to other electrolyser technologies is that it conducts oxygen ions so they enable CO2 electrolysis. SOEC can also generate synthetic gas by conducting co-electrolysis, the combined electrolysis of carbon dioxide and steam. However, this process is more complicated than separate steam and CO2 electrolysis, and overall reaction pathway is not clearly defined [8]. Throughout this paper the term synthetic fuel will refer to a fuel that does not include the use of fossil fuel in the production process, and instead it is produced by combined use of electrolysers with carbon source. The carbon source can come either through: the recycling of CO2 from a stationary energy-related/industrial process, or from the biomass gasification. The CO2 recycling or biomass “boosting” (upgrading the energy content of biomass with hydrogen) for renewable fuel production would open the door to renewable energy in the transport sector, which was previously not accessible in the form of liquid fuels, with the exception of biofuels. Moreover this way of fuel production enables flexible fuel choice, as produced syngas can be converted to various liquid or gaseous fuels. One of the main advantages of some synthetic liquid fuels such as methanol and DME (dimethyl ether), is that implementation requires a limited change in the infrastructure: these typically include alterations of the vehicles and existing fuelling stations to a new type of fuel. The synthetic fuel production is still at an early stage of development when combining renewable sources and CO2 recycling. However, the George Olah Renewable Methanol Plant in Iceland has started the production of methanol via carbon recycling from a geothermal power station, using a technology called ETL (Emission to Liquid) [9]. Biomass gasification to fuels is already demonstrated in Sweden and there are a few projects planned for its commercialization. The BioDME project has already demonstrated the production of bio-DME and bio-methanol from the gasification of black liquor in 2011 [10]. The first commercial biomass to methanol plant, which gasifies biomass residues, will be inaugurated in Hagfors, Sweden and plans to start production in 2014/2015 [11]. Methane production from forest biomass is a key focus in the Bio2G project and a plant is planned in the Öresund region [12]. Two more methanol plants, based on wood gasification and black liquor gasification are planned to be built by Rottneros Biorafinery AB [13]. Therefore, although the hydrogenation of CO2 and biomass are relatively new concepts for the production of fuels, there are already a number of large-scale plants either in operation or at the planning phase. In this paper eight different fuel production pathways are analysed in the 100% renewable energy system and their fuel production costs are compared. The three synthetic fuel pathways (biomass hydrogenation, CO2 hydrogenation and co-electrolysis) were analysed both for methanol and methane production, while the other three pathways (biodiesel e 1st and 2nd generation, bioethanol e 2nd generation with and without C5 sugar utilization and biogas) are analysed as separate cases. The synthetic fuel pathways using CO2 recycling process (CO2 hydrogenation and co-electrolysis) analysed in this article use CO2 emissions from the biomass combustion in the heat and power sector as their carbon source. The scenarios of the energy system have been allocated the same names as pathways implemented in the transport sector. The
infrastructure costs, such as building new gas networks for transporting gaseous fuels, CO2 or syngas, were not included in the cost calculation because the aim of the article is to give an overview of the fuel production costs and not the overall implementation costs of these fuels in the system. The flexibility of the different pathways is compared with the level of wind energy integration as the determining factor and the sensitivity analysis of biomass use is conducted to highlight the importance of conscientious use of biomass in the future energy systems. The objective of this paper is to determine the fuel production price for different synthetic fuels and their competitors by providing an overview of all production chain elements that are forming the fuel price. The study provides the enhanced knowledge of the production chain components and related costs which enabled the more detailed modelling of synthetic fuels in the energy system. The focus of this study is narrowed in order to get the clear picture of the production costs and the competitiveness of the newly proposed fuels. The present study confirms previous findings [14] and contributes by giving the insight of the fuel price formation. 2. Methodology The model analysed in this article is taken from the Danish 100% renewable scenario for 2050 [6] where the data for the transport sector has been changed in order to get the overview of costs for different renewable fuels that can be implemented. The obtained results include the costs of the production units, fuel handling costs, associated CO2 emissions costs, and the feedstocks needed for the production. All the analysed scenarios are 100% renewable energy systems. The scenarios have been analysed using the energy system analysis tool EnergyPLAN [15] to analyse different fuel types in the energy system. EnergyPLAN was chosen because it includes the balancing of the system in its fuel costs calculations. This aspect was important because electrolysers enable high share wind integration; therefore the costs are more accurate when including balancing costs. All scenarios were analysed with technical optimization, meaning that the fuel consumption is minimized. This is important due to the level of biomass resource used in the scenarios. The system in all scenarios was balanced in terms of CEEP (critical excess electricity production) and the gas balance, so the scenarios could be comparable. The balancing of the gas grid includes import and export, utilisation of gas storage and regulation strategies to minimise the exchange of gas to and from the system. The model operates in a way that it reduces the demand for natural gas with the produced biogas and/or syngas so the output is a biogas/syngas grid instead of a natural gas grid due to the analysis of 100% renewable systems. The scenarios vary depending on the pathways implemented in the transport sector, but in terms of primary energy supply the variations are mainly the ability to integrate wind capacity and the biomass demand for fuel. All the scenarios have closed self-sufficient energy systems. Many previous studies have been carried out using EnergyPLAN such as analysing high shares of intermittent sources particularly wind power on the system [16], DH and CHP [17], analysis of alternative transport technologies [18e20] and analysis of 100% renewable energy systems [6,21e24]. The tool is a free-ware software that is updated regularly so it can implement the newest technologies in energy systems. The latest updates are new facilities of waste-to-energy technologies in combination with geothermal and absorption heat pumps, new costs data, different biomass conversion plants such as biogas, biomass gasification, biodiesel and ethanol plants, new facilities for grid gas (natural gas/ bio/syngas) and additional grid stabilisation options. Furthermore,
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synthetic gas and liquid fuel production modelling is now enabled for different types of pathways. It is possible to directly model biomass hydrogenation, CO2 hydrogenation, co-electrolysis and biogas upgrade to methane. The produced syngas can be converted to synthetic jet-fuel, methanol and DME through the chemical synthesis option. Detailed description of the model and possible applications can be found at [25].
3
The Co-electrolysis pathway is using combined process of steam and CO2 electrolysis called co-electrolysis, and the produced synthetic gas can afterwards be catalysed into various types of fuel (see Fig. 3). The produced syngas from this process has 2:1 hydrogen to carbon monoxide ratio which is the desired ratio for further conversion to methanol; however this does not exclude the possibility of conversion to other types of fuels as there are no barriers to do that.
2.1. The synthetic fuel pathways 2.2. Biofuel pathways and biogas The fundamental difference between synthetic fuel pathways is in the carbon source. Biomass hydrogenation uses direct input of biomass in the gasification process, and the produced gas is later on boosted with hydrogen produced from steam electrolysis. CO2 recycling pathways (CO2 hydrogenation and co-electrolysis) do not require any direct biomass input, instead they use emissions from the biomass used in the heat and power sector combined with electrolysis. This section will give a short overview and flow diagrams of three synthetic fuel pathways. The biomass hydrogenation pathway is using biomass gasification as a base process for synthetic fuel production. The syngas produced from this process is boosted by hydrogen from steam electrolysis (see Fig. 1) and later on converted by chemical synthesis to the desired fuel output. This way of producing fuel from a biomass resource enables the integration of the wind in the system due to the electricity related to hydrogen production, which is needed for the biomass upgrading process and concurrently lowers the need for biomass. The CO2 recycling pathways enable a strong connection between energy sectors by using recycled CO2 from the heat and power sectors to produce transport fuels. The principal objective of these pathways is to create a transport fuel without direct biomass input, by combining the electrolysis process with a carbon source provided by biomass used in other parts of the energy system. The syngas produced in both pathways consists of different amounts of carbon dioxide, carbon monoxide and hydrogen depending on the process of production. The fuel production by CO2 hydrogenation pathway combines hydrogen from the steam electrolysis with recycled carbon dioxide from a stationary source to form a syngas. The produced syngas can be subsequently converted by chemical synthesis to chosen fuel output (see Fig. 2).
Four biofuel pathways were analysed along with the biogas pathway in the paper as a comparison to synthetic fuel pathways. The biofuel pathways are chosen according to the existing technology and due to their current contribution as the most exposed renewable replacement for fossil fuels. Biogas was analysed as an alternative to synthetic production of methane as only gaseous fuel that was consider in synthetic fuel pathways. The first generation biodiesel is used for analysis as it is the most commonly produced biofuel in Europe. It is based on a chemical modification of vegetable oil by transesterification in order to produce a fuel that can be used in existing diesel engines. The analysed biodiesel is based on the production from energy crops [26]. The second generation biodiesel represents the production by BTL (biomass-to-liquid process). The biomass is firstly gasified; afterwards the produced gas is cleaned and converted to longchained alkanes by Fisher-Tropsch synthesis. The alkanes are subsequently treated by thermal cracking to produce the desired fuel [27]. Two second generation bioethanol scenarios were analysed, one without and one with the C5 sugar utilization. Both technologies are commercially available, however a research focus is to improve the process with the C5 sugar fermentation [27]. The main reason for using both scenarios is due to the cost differences. The modelled second generation bioethanol uses straw as a biomass resource which is fermented after the biomass pre-treatment. The process finishes with the purification that delivers the end ethanol product. The produced by-products are lignin and molasses which have high value and can become the important part of the production as they can be used for further conversion. Biogas is modelled according to [28], where biogas is produced by using animal manure treated in an anaerobic process. The biogas
Fig. 1. The well-to-tank conversion processes for the biomass hydrogenation pathway.
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Fig. 2. The well-to-tank conversion processes for the hydrogenation of CO2 pathway.
plant is a centralized biogas plant with a daily input of manure and organic waste of 1000 tonnes (80e90% of animal manure and 10e 20% organic waste from industry) [28]. The manure goes through an anaerobic process resulting in biogas that afterwards can be used for different purposes. The output biogas is in this analysis completely upgraded into methane with hydrogen from water electrolysis. 3. Components of the fuel production chains and economy The components of the fuel production chains are the key for understanding the calculations of the fuel costs that is the outcome of this analysis. This section will provide a short description of all
the system components that form the price in different pathways (see Table 1). The section also provides the main economic data for the calculations of fuel production: the investment costs of production units, feedstock expenses and fuel handling costs (see Table 2 and Table 3). All the investment costs in the plants are based on the specifications of the production units, lifetime and fixed operation and maintenance costs. The biofuel scenarios present commercially available technologies for biodiesel and bioethanol production. First generation biodiesel is the simplest scenario as it uses direct conversion of biomass in the bio-refinery to produce biodiesel from the energy crops (grass or corn). The process is characterized by a high efficiency. The total price is based on the investment costs of the biodiesel plant, biomass
Fig. 3. The well-to-tank conversion processes for the co-electrolysis pathway.
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Table 1 Components and feedstock used in the production cycle. Biodiesel/Biodiesel 2nd generation
Bioethanol 1/ Bioethanol 2
Carbon source
Biomass
Biomass
Bioenergy plant Resource
Biodiesel plant Energy crops (grass or corn)/ Straw or wood incl. pellets
Bioethanol plant Straw or wood incl. pellets
Electricity source Electrolysis Fuel synthesis
Biogas hydrogenation
Biomass hydrogenation
CO2 hydrogenation
Co-electrolysis
Biomass gasification
CO2 emissions from biomass CHP plant
CO2 emissions from biomass CHP plant
Offshore wind SOEC Chemical synthesis
Offshore wind SOEC Chemical synthesis
Biogas plant Manure
Gasification plant Straw or wood incl. pellets
Offshore wind SOEC Chemical synthesis
Offshore wind SOEC Chemical synthesis
expenses and the fuel handling costs. The second generation biodiesel process is based on BTL technology and the cost of this technology is higher than the first generation biodiesel plant [25]. The process is modelled with a biomass to fuel efficiency of 39% and the fuel price is formed by adding the fuel handling costs to investment costs of biodiesel plant and biomass expenses. The second generation bioethanol production from straw is more complicated than the production of first generation bioethanol from food. Bioethanol production uses both electricity and steam for the production process and the biomass used for steam production is added when calculating the total biomass consumption for the pathway. The bioethanol scenario which includes the utilisation of C5 sugar is modelled the same as the scenario without the C5 sugar utilisation, apart from the costs. The cost of the production plant without sugar utilisation is taken from Refs. [26], while the cost of a new fermentation technology which utilises with C5 sugars is from Ref. [27]. In the biogas scenario analysed, biogas is produced from animal manure, hence no biomass costs are associated with the production as the manure is considered free. The costs calculated for the biogas production involve operation and investment costs for the biogas plant and the cost for biogas upgrade to methane by hydrogen from water electrolysis. The hydrogen is produced by using wind power to run the dissociation of oxides in electrolysis. Therefore the overall production costs of biogas involve investment costs of wind turbines, electrolysers needed for hydrogen production as well as the synthesis plant investment. The fuel costs by using biomass hydrogenation pathway consist of costs for the biomass gasifier, wind turbine costs, electrolyser investments and the synthesis plant. Biomass gasifier costs used in this analysis correspond to the costs for low temperature gasification, based on the Pyroneer gasifier [28]. The biomass goes through three main components of the gasifier: a pyrolysis chamber, a char reactor and a recirculating cyclone. The biomass is converted into synthetic gas, which can be further used for hydrogenation to
produce methanol or methane as a substitute to fossil fuels. The efficiency of the process used in the analysis is 83% for the conversion of biomass to syngas. In case of CO2 recycling pathways an analysis was conducted with the post-combustion CCR (carbon capture and recycling) process, due to the fact that this method is more established for CO2 capture than the others. The electricity demand for CO2 sequestration is calculated from the specified factors for electricity needed for extracting CO2 (TWh/Mton) and extracted CO2 per produced synthetic gas (Mton/TWh). The hydrogen needed in all pathways was provided by high temperature electrolysis with SOEC (Solid Oxide Electrolyser Cells). The SOECs are powered by offshore wind capacities and their electricity demand is calculated from the ratios of hydrogen per fuel output and electrolyser efficiency. In the case of co-electrolysis the ratio of hydrogen and CO2 per fuel output was used. The efficiency used for the steam electrolysis is 73% and for co-electrolysis is 77% and both efficiencies include the assumed energy losses in the production of 10% and 5% extra for the gas storage. The investment costs of SOEC include local grid reinforcement to connect electrolysers to the transmission system [29]. The costs for the synthesis plant in the analysis are for methanol production from synthesis gas, in a pressurized catalytic process [26]. The catalyst used for this process is copper-based and the operating temperature of the process is approximately 200e 300 C. In the case of methane production the same costs were assumed. 3.1. Analysis uncertainties Uncertainties in this paper are mainly due to the maturity of the technologies and the long-term investment predictions. The cost calculations for technologies that are still at the R&D level are very uncertain and highly dependent on the technological development. Therefore investment costs for SOECs are based on predictions and
Table 2 Investment costs for plants included in the analysis. Type
Unit
Investment (MV/unit)
Lifetime (years)
O&M (% of investment)
Source
Biomass gasifier Biogas plant Biodiesel plant 1st generation Biodiesel 2nd generation Bioethanol plant 1 Bioethanol plant C5 sugar Fuel synthesis plant SOEC electrolyser Offshore wind 2015 Offshore wind 2050
MWsyngas TWh/year MWbio input MWbio input MWbio input MWbio input MWfuel ouput MWe MWe MWe
0.316 392 0.27 1.89 1.82 0.435 0.55 0.28 3.1 2.1
25 20 20 20 20 20 20 15 20 30
7 6.96 1 3 3.69 7.68 3.48 3 3.5 3.21
[28] [28] [26] [27] [26] [27] [26] [29] [28] [28]
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Table 3 Additional costs for feedstock, fuel handling and CO2 sequestration.
CO2 sequestration Straw or wood incl. pelletsa Green energy crops (grass or corn)a Fuel handlinga a
Unit
Costs
Source
V/t V/GJ V/GJ V/GJ
30 5.7 7.5 4
[30] [31] [31] [31]
Adjusted to 2010 prices.
today’s available stack costs. All synthetic fuel pathway calculations of resources needed for the fuel production processes were based on chemical reactions and energy balances, therefore the different energy densities of the chemical reaction components can cause variations of the results. The bioethanol plants produce food by-products during the production of bioethanol. It is possible that the income of the food by-product would influence the costs of ethanol if accounted like that. The actual value of this by-product is currently very uncertain therefore it was not included in the analysis; however this could be used in the future calculations when certain cost value can be signed to the by-product. It is assumed that none of the other pathways produce by-products of significant value. 4. Results The fuel production costs were calculated for the same demand in all scenarios (32.15 TWh/year, which is the forecasted demand for transport fuels in Denmark in 2050) that has been met by different fuels. In the case of synthetic fuel pathways two different fuel types were analysed, methanol as a liquid and methane as gaseous fuel. First and second generation biodiesel, two bioethanol pathways and biogas costs were calculated as separate scenarios. The calculated fuel price per GJ of produced fuel can be seen on Fig. 4 for biofuels, biogas and petrol (as a base of comparison) and in Fig. 5 for synthetic fuels. Fig. 6 and Fig. 7 show the breakdown of costs for biofuels, biogas and synthetic fuels to the production units, feedstock and fuel handling costs, together with the CO2 emissions cost. It can be seen that the first generation biodiesel scenario have the lowest production costs, while the synthetic fuel pathways
have the highest costs along with second generation biodiesel, biogas hydrogenation and both bioethanol scenarios. The results vary due to the complexity of the different scenarios, their ability to integrate wind power production, technology costs and the amount of biomass used for the fuel production. The biodiesel scenario uses 33.5 TWh of biomass to produce enough biodiesel to cover demand, which is approximately 70% of its total production costs. For second generation biodiesel the production plant cost is higher, accounting for around 20% of the total. Moreover, the biomass used in this scenario is double compared to the first generation biodiesel due to the lower efficiency of the process. In the case of the bioethanol scenarios, it is clear that the technology with C5 sugar utilisation is cheaper simply due to the price of the bioethanol production plant. The bioethanol pathways use the most biomass resources: 89 TWh of biomass is needed to cover the whole transport demand. The biogas costs are highly connected to the investment in biogas plants, which accounts for 35% of the total fuel costs, and wind power which accounts for 38% of the total. The high share of wind is due to the upgrading of biogas to methane with hydrogen so it can be used in the transport sector. In the case of synthetic fuel scenarios, specifically in relation to CO2 recycling pathways the production costs of methanol are higher than in case of methane. This can be explained by the ratio of hydrogen for the methanol and methane production which is directly connected with the amount of electricity needed for the steam electrolysis to provide hydrogen. It can be seen that, which proves their concept of electricity to fuel conversion. The biomass hydrogenation for methane is more expensive because of the biomass to hydrogen ratio, which is opposite than in the case of CO2 recycling pathways. Even though the methane production uses 7.3 TWh less biomass, the electricity penalty for the hydrogen production is higher than the biomass savings. It is interesting to note that all synthetic fuel scenarios are not far off the production costs of petrol when the CO2 emission costs are accounted. This finding is very important as it puts the synthetic fuels in the competitive position to today’s fossil fuel. 4.1. Sensitivity analysis The sensitivity analysis was conducted with three biomass price levels (see Table 4) due to the uncertainties of the fuel costs in the
Fig. 4. Calculated fuel production costs for biofuels, biogas and petrol.
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Fig. 5. Calculated fuel production costs for synthetic fuels.
long term planning. Moreover the biomass price level was changed because some of the analysed fuels are directly connected to the biomass input. Fig. 8 shows the correlation between biomass consumption and fuel output for each pathway that has fuel production based on biomass resources. This figure is quite revealing compared to the previous ones as it shows directly the biomass consumption per scenarios. The sensitivity analysis shows that biomass prices influence the most pathways with a high share of biomass in their production process (see Fig. 9). As it can be seen from previous figures all biofuel scenarios apart from biogas are highly dependent on biomass, as it is the base of their process. The biomass hydrogenation pathway is sensitive to biomass price change but not to the same extent as biofuel scenarios due to the lower share of biomass
in the overall fuel production price. On the contrary CO2 recycling pathways are not influenced by changes in biomass prices because there is no direct input of biomass in the production therefore the biomass price sensitivity analysis was not conducted for these pathways. As synthetic fuel scenarios are not as sensitive to biomass price changes, another sensitivity analysis was carried out to investigate the influence of investments in offshore wind on the fuel production costs. As the scenarios in the analysis use the investment costs for 2050, to conduct a sensitivity analysis the offshore wind investment costs for 2015 were taken for comparison. It can be seen that the price of the fuels is drastically higher for CO2 recycling pathways in case of offshore wind investment prices for 2015, which was expected due to the fact that wind share in the
Fig. 6. Shares of the production components in forming the fuel price for biofuels and biogas.
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Fig. 7. Shares of the production components in forming the fuel price for synthetic fuels.
Table 4 Biomass prices for sensitivity analysis. V/GJ
Straw or wood incl. Pellets
Energy crops
Low price level Medium price level High price level
4.3 5.7 8.3
5.4 7.5 11.8
production cost is 67% (see Fig. 10). The pathways with lower share of wind in the production process are not so sensitive to the price change. 5. Conclusion The present study was designed to determine the fuel production prices for different renewable fuels that can be produced in
order to meet the demand in transport sector that cannot be met by electrification. The reason for the development of synthetic fuels is due to the limited biomass resource available, which will become an important aspect of 100% renewable energy systems. The results show the breakdown of the production costs based on the components of the production process, the biomass consumption for different fuel pathways and the fuel production cost. The study has shown that the pathways that have higher share of biomass in their production process are not as flexible in terms of wind integration and the fuel output as other proposed scenarios. However, the production costs for some of these pathways are the lowest due to the simplicity of the process and the high conversion rate (as is the case for first generation biodiesel). The synthetic fuel pathways enable the wind integration which varies from lowest for the biomass hydrogenation pathways to highest for CO2 recycling
Fig. 8. Biomass consumption per fuel output for the biomass based scenarios.
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Fig. 9. Production costs sensitivity analysis to biomass prices for biomass based scenarios (scenarios without direct biomass consumption were not included).
Fig. 10. Production costs sensitivity connected to offshore wind investment for scenarios with wind integration (scenarios without wind integration were not included).
pathways. Moreover this way of fuel production enables flexible fuel choice, which was shown by the production of both methanol and methane. The synthetic fuel pathways have higher production costs due to the technologies that they use for the production process, yet they are still lower than the costs of second generation bioethanol. The major finding was that the production costs of synthetic fuels are comparable with petrol production costs when the associated CO2 emissions are accounted for. Taken together, these results suggest that these fuels have a potential to be a future fossil fuel replacements in the transport sector. If the certain recommendation is to be given on which pathway should be implemented, a further research needs to be undertaken by identifying the efficiency of different vehicles and their driving range depending on the used fuel. This can give a more holistic view of the pathways. In the long term perspective, the final
decision will also depend on the availability of biomass resources, the types of biomass resources and their land-use, the biomass costs, the technological development, demonstration of facilities on a large-scale and the infrastructure costs. Acknowledgements The findings in this article result from a research project Coherent Energy and Environmental Analysis (CEESA) carried out at Aalborg University and funded by The Danish Council for Strategic Research. The research was also supported financially by the ForskEL research program on Development of SOEC (2011-1-1069). A preliminary version of the paper was presented at the SDEWES 2013 conference in Dubrovnik, Croatia, and therefore we wish to thank the audience for their contributions during the discussions.
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References [1] European Commission. Renewable Energy: Progressing towards the 2020 target. Available from: http://eur-lex.europa.eu/LexUriServ/LexUriServ.do? uri¼COM:2011:0031:FIN: EN:PDF; 2011. [2] Dallemand JF, Leip A, Rettenmaier N. Biocarburants liquides pour le transport: de défi d’une correcte évaluation du bilan environnemental. In: Pollution Atmosphérique e Numéro Spécial. Anonymous; 2009. p. 89. [3] Eickhout B, Born G, Notenboom J, Mv Oorschot, Ros J, Dv Vuuren, et al. Local and global consequences of the EU renewable directive for biofuels: testing the sustainability criteria; 2008. [4] Koper M, Berg MVD, Hamelinck C. BOLK II Air polluting emissions from bioenergy supply chains e Final Report. Available from: http://www.rivm.nl/ bibliotheek/digitaaldepot/BOLK_II_LCA_Final.pdf; November, 2009. [5] Gallagher E. The Gallagher review of the indirect effects of biofuels production. East Sussex, UK: Renewable Fuels Agency Ashdown House; 2008. [6] Henrik Lund (Edt.), Frede Hvelplund, Brian Vad Mathiesen, Poul A. Østergaard, Per Christensen, David Connolly, Erik Schaltz, et al. Coherent Energy and Environmental System Analysis (CEESA). [7] Tietz F, Sebold D, Brisse A, Schefold J. Degradation phenomena in a solid oxide electrolysis cell after 9000 h of operation. J Power Sources 2013;223: 129e35. [8] Stoots CM, O’Brien JE, Condie KG, Hartvigsen JJ. High-temperature electrolysis for large-scale hydrogen production from nuclear energy e experimental investigations. Int J Hydrogen Energy 2010;35:4861e70. [9] George Olah renewable methanol plant. Carbon Recycling International; 2012. [10] BioDME. Production of DME from biomass and utilisation of fuel for transport and industrial use. Available from: http://www.biodme.eu/ [accessed 06.20.13]. [11] Gillberg BO. World’s first commercial scale biomethanol plant in Hagfors Sweden. Hagfors, Sweden. Available from: http://www.varmlandsmetanol.se/ dokument/History%20March%2012.pdf; March 2012. [12] Möller BF. Gasification development at E.ON. Sweden. Available from: https:// www.ecn.nl/fileadmin/ecn/units/bio/Biomassa/Syngas_and_SNG/ Gasification_2010/Gasification_development_at_E.on.pdf; 2010. [13] Rottneros AB. Hallvarsson & Halvarsson annual report 2011. Sweden; 2011. Available from: http://www.rottneros.com/afw/files/press/rottneros/ Rottneros_Annual%20Report2011.pdf. [14] Ridjan I, Mathiesen BV, Connolly D, Dui c N. The feasibility of synthetic fuels in renewable energy systems. Energy 2013;57:76e84. [15] Aalborg University. EnergyPLAN: advanced energy system analysis computer model. Available from: http://energy.plan.aau.dk/ [accessed 06.14.12].
[16] Connolly D, Lund H, Mathiesen BV, Leahy M. Modelling the existing Irish energy-system to identify future energy costs and the maximum wind penetration feasible. Energy 2010;35:2164e73. [17] Lund H, Münster E. Modelling of energy systems with a high percentage of CHP and wind power. Renew Energy 2003;28:2179e93. [18] Lund H, Munster E. Integrated transportation and energy sector CO2 emission control strategies. Transp Policy 2006;13:426e33. [19] Mathiesen BV, Lund H, Nørgaard P. Integrated transport and renewable energy systems. Util Policy 2008;16:107e16. [20] Lund H, Kempton W. Integration of renewable energy into the transport and electricity sectors through V2G. Energy Policy 2008;36:3578e87. [21] Lund H, Mathiesen BV. Energy system analysis of 100% renewable energy systemseThe case of Denmark in years 2030 and 2050. Energy 2009;34:524e31. [22] Mathiesen BV, Lund H, Karlsson K. 100 renewable energy systems, climate mitigation and economic growth. Appl Energy 2011;88:488e501. [23] Connolly D, Lund H, Mathiesen BV, Leahy M. The first step towards a 100% renewable energy-system for Ireland. Appl Energy 2011;88:502e7. [24] Mathiesen BV, Lund H, Karlsson K. The IDA climate plan 2050. The Danish Society of Engineers and Aalborg University; 2009. Available from: http://ida. dk/News/Dagsordener/Klima/Klimaplan2050/Sider/Klimaplan2050.aspx. [25] Department of Development and Planning, Aalborg University, Lund Henrik. EnergyPLAN, Advanced energy planning systems analysis computer model e documentation version 11.0. Denmark. Available from:, http://www.energyplan.eu/ wp-content/uploads/2013/06/EnergyPLAN-Documentation-V11-2013.pdf; 2013. [26] Danish Energy Agency. Alternative drivmidler i transportsektoren (Alternative Fuels for Transport). Available from: http://www.ens.dk/; 2012. [27] FORCE Technology, Department for Biomass & Waste, Evald A, Hu G, Hansen MT. Technology data for advanced bioenergy fuels. Denmark. Available from:, http://www.ens.dk/sites/ens.dk/files/info/tal-kort/ fremskrivninger-analyser-modeller/teknologikataloger/technology_data_for_ advanced_bioenergy_fuels.pdf; June, 2013. [28] Danish Energy Agency, Energinet. Technology data for energy plants. Generation of Electricity and District Heating, Energy Storage and Energy Carrier Generation and Conversion. Maj; 2012. [29] Mathiesen B, Ridjan I, Connolly D, Nielsen M, Hendriksen P, Mogensen M, et al. Technology data for high temperature solid oxide electrolyser cells, alkali and PEM electrolysers. Department of development and planning, Aalborg University; May, 2013. [30] Energistyrelsen (Danish Energy Authority), Danish Energy Agency, Energinet.dk. Technology data for energy plants. Copenhagen, Denmark; 2010/6. [31] Danish Energy Agency. Forudsætninger for samfundsøkonomiske analyser på energiområdet (Assumptions for socio-economic analyses for energy); 2011.
Please cite this article in press as: Ridjan I, et al., Synthetic fuel production costs by means of solid oxide electrolysis cells, Energy (2014), http:// dx.doi.org/10.1016/j.energy.2014.04.002