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Fostering renewable energy provision from manure in Germany – Where to implement GHG emission reduction incentives
Energy Policy 110 (2017) 471–477
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Fostering renewable energy provision from manure in Germany – Where to implement GHG emission reduction incentives
MARK
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Katja Oehmichena, , Daniela Thräna,b a b
Deutsches Biomasseforschungszentrum gGmbH (DBFZ), Leipzig, Germany Helmholtz Centre for Environmental Research, Leipzig, Germany
A R T I C L E I N F O
A B S T R A C T
Keywords: Biogas Life cycle assessment Greenhouse gas emissions Mitigation potential Manure
Livestock production makes up a major share of agriculture sector and the manure it produces significantly contributes to greenhouse gas emissions. One option to lower these emissions significantly is using the manure to produce biogas which is used to generate power. Our model calculations show, that per kWh power from manure-based biogas –about 1.448 kg of CO2 eq. of greenhouse gas (GHG) emission can be avoided due to the improved manure management and the substitution of electricity from the grid under actual German conditions. This form of utilization is supported under the German Renewable Energy Act; however, only the minor share of the manure is processed so far. Thus the question arises as to whether instruments in agricultural policy or instruments in energy policy are better to unlock this remaining potential. The elaborated allocation shows, that both sectors cause a comparable amount of GHG emissions reductions, at around 50% each. However, based on expected developments, the relevance of agriculture-related emissions is slated to increase. This leads to the conclusion that implementing instruments in both agricultural and energy policies would make sense.
1. Introduction Livestock production is a significant sector in German agriculture and makes up 3% of the global production (FAOSTAT, 2016). This production is characterized by a tremendous demand for feedstock and the production of enormous amounts of excrement in the form of liquid or solid manure and slurry - currently estimated at 139 M tons per year (Thrän et al., 2014). This excrement contains significant amounts of nitrogen and other nutrients so that it is typically spread directly on farmland as fertilizer. Excrement is produced on a continuous basis, however, because it can only be re-used as a fertilizer during certain times of the year, large storage capacities for manure are necessary (Verordnung über die Anwendung von Düngemitteln, 2012). These storage facilities are often open silos where the stored manure produces relevant amounts of methane which cause 1% of the overall German GHG emissions (Haenel et al., 2014). There are a few possibilities to reduce these emissions. One of them is producing biogas from manure which can reduce the GHG emissions from manure storage and provide a renewable energy carrier as well. If the renewable energy carrier is used as a substitute for fossil fuels, additional GHG emissions are saved. So far, about 3000 biogas plants have been installed at farm sites in Germany, mainly under the Renewable Energy Act (Scheftelowitz and Thrän, 2016). These biogas plants provide renewable energy and
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combined heat and power (CHP). Because only about 48% of the animal waste produced nation-wide is currently utilized in biogas plants (Thrän et al., 2014), more than one hundred thousand farms, with varying amounts of livestock (cattle and pigs), provide additional potential for biogas production. There is a clear need to further reduce GHG emissions through manure management as stipulated by the ambitious targets set by the Paris agreements. These aim to reduce national greenhouse gases by 80–95% in Germany by 2050 (in comparison to 1990). But this requires further incentives and begs the question of how to design these incentives in an appropriate way: Since biogas production from manure supports greenhouse gas emissions reduction in both the energy and in the agriculture sector, the relevance of these two effects needs to be taken as a basis for developing enhanced support instruments. Against this background, the main research question of this paper is: How many GHG emissions can be reduced through the use of manure for electricity production via biogas? Which sectoral allocation of the reduction effects can be derived from the quantification and in which sector are incentives relevant?? Most studies on the reduction of GHG emissions are concerned either with the mitigation effects of improved manure management, from the point of view of disposal (Riaño and García-González, 2015; Rodhe
Corresponding author. E-mail address: [email protected] (K. Oehmichen).
http://dx.doi.org/10.1016/j.enpol.2017.08.014 Received 22 December 2016; Received in revised form 31 July 2017; Accepted 2 August 2017 0301-4215/ © 2017 Published by Elsevier Ltd.
Energy Policy 110 (2017) 471–477
K. Oehmichen, D. Thrän
Inventory are described below for the present case of biogas production from manure.
et al., 2015; Costa et al., 2015; Clemens et al., 2006; Kirchmeyr et al., 2015), or with the mitigation effects of electricity production from biogas, from the point of view of substitution (Gronauer and Bachmaier, 2007; Horschig et al., 2016; DBFZ, 2011; Majer et al., 2015). To quantify the mitigation potential, we have merged both effects and we have elaborated on an appropriate method for assessing the GHG emissions from using manure in biogas plants in Germany and the associated GHG mitigation effects under the actual support schemes over the last seven years. We also discuss options for further developing the promotion of biogas plants.
2.1.2. Boundaries Setting the system boundaries is one of most essential issues for carrying out a life cycle assessment. The system boundaries define the framework in which the assessment takes place and determine which energy material flows are taken into account in the assessment. In the present case a ‘cradle to gate’ life cycle has been analyzed. The ‘cradle to gate’ life cycle means that all flows of materials and energy which are necessary for the operation of the biogas plant and the production of electricity from manure based biogas have been taken into account. The assessed life cycle starts with the transport of the manure (in case that the manure is not generated on site) and ends with the transformation of manure based biogas to electricity at the combined heat and power (CHP) plant and the subsequent feed of the produced electricity into the electricity grid. Contrary to the ‘cradle to gate’ life cycle for the biogas processes a ‘gate to gate’ life cycle has been chosen for the provision and use of manure from animal husbandry production. This means that only transport expenditures and direct manure emissions at the biogas plant has been calculated. Whereas upstream processes associated with livestock breeding such as, for example expenditures from crop cultivation for animal feed were not considered. Because the goal of livestock breeding is not the production of excrements (such as manure) but the production of milk and meat, from which the manure results as a waste product. That's why the life cycle emissions of manure are zero until the place of the production. At the same time not included, are on the one hand emissions from the transport and the field application of the digestate. In particular, nitrous oxide emissions from spreading the digestate can have an influence on the GHG balance sheet, the amount of these emissions depends mainly on the method of digestate spreading and on the technique the digestate has been incorporated into the soil. On the other hand, the fertilizing effect of the digestate and the associated substitution of synthetic fertilizer are not taken into account. Climate relevant emissions resulting from the energy-intensive production of synthetic nitrogen fertilizers can be avoided in this manner. This approach seems to contradict the fact that the avoided emissions from the conventional manure storage are included in the life cycle assessment. Since due to the anaerobic digestion of the manure the improved manure management is directly linked to the supply of the manure (the manure is not stored after production, but is placed in the digester in a timely manner), the emissions avoided are to be located within the boundaries of the GHG assessment. Due to the negligible impact the GHG emissions associated with construction and demolition of the biogas plant and the CHP were not considered. On the basis of these assumptions, the system boundaries of this assessment include the major stages of the manure based biogas system: (i) manure provision, (ii) the production of biogas by anaerobic digestion of manure, (iii) using the produced biogas in a combined heat and power (CHP) plant to produce electricity and heat and (iv) feed the electricity into the grid (see Fig. 1). These steps are further detailed in the life cycle inventory (LCI) as described in the following chapters.
2. Method To answer the question regarding the GHG emissions from using manure in biogas plants in Germany and the associated GHG mitigation effects, GHG emissions from manure based biogas systems have been analyzed, calculated and assessed with regard to their reduction potential for both farm based manure management and the substitution of fossil fuels for power generation. There are different methodological approaches for the investigation of lifecycle GHG emissions from products or services. The assessment of lifecycle GHG-emissions is often part of a life cycle assessment (LCA). LCA is an appropriate method for evaluating the GHG performance of a manure based biogas system compared to a fossil reference system. Requirements for conducting an LCA are detailed in the international standards ISO 14040 (ISO 0, 1404, 2006) and ISO 14044 (ISO 4, 1404, 2006). According to these standards, the analysis covers the complete product life cycle from the production of the raw material to the final disposal of the product after the use phase, including all pre-products and energy carriers used. Using the selected LCA-based approach, we were able to extrapolate the mitigation potential for the entire amount of liquid manure used in Germany. This calculation is based on the specific GHG savings from a case study that compared a typical manure based biogas system with reference data on the GHG emissions released as part of conventional electricity production in Germany. The methodology employed in the evaluation of the GHG emissions is described in the following sections. 2.1. Goal and scope The first step of the LCA method - the definition of the goal and scope – includes a description of the underlying questions of the case study, the system boundaries under consideration, the definition of the functional unit, the allocation procedures, the life cycle impact assessment (LCIA) and the types of impact (ISO 14040, 2006). 2.1.1. Aim and scope of the study The principal aim of the study is to estimate the GHG emission mitigation effects associated with use of manure from livestock breeding, with regard to two aspects (i) mitigation of GHG emissions due to an improved manure management and (ii) replacing electricity from the German electricity grid by producing electricity from manure based biogas. To achieve the stated goals a LCA is performed according to the standards ISO 14040 and ISO 14044, using the software Umberto 5.5 and the database Ecoinvent (Ecoinvent v2.1, 2009) for background data. The primary steps by conducting a LCA, the setting of the system boundaries, the definition of the functional unit and the Life Cycle
2.1.3. Function and functional unit The main objective of this GHG assessment is to calculate the GHG Fig. 1. System boundaries.
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generated with (KTBL, 2015). The anaerobic digester is fed with 8500 t*a−1 of cattle slurry and 2100 t*a−1 of pig slurry. Biogas production is around 167,572 m3CH4*a−1 and the biogas plant is operated for 8000 h*a−1. It's assumed that the biogas consists of 56% CH4. During the production of biogas, methane can leak into the atmosphere. According to (Vetter and Arnold, 2010; Vogt, 2007), methane leakages from the digester were assumed to be 1% of the total methane produced. The biogas is conveyed to an Otto engine that generates around 75 kW of electrical energy. The key parameters for the CHP plant are the electrical efficiency in the amount of 35% which corresponds to a quantity of 580,987 kWh*a−1 electricity which is fed into the grid, and the thermal efficiency in the amount of 43%. Unburned methane emissions from the combustion are assumed to be 0.5% of the total methane contained in the biogas. The amount of electricity demand of the biogas plant was estimated to be 58 MWh*a−1 and was assumed to be supplied from the German electricity grid. The electricity consumption of a biogas plant depends on various parameters like type of substrate and fermentation and the management of the biogas plant. Due to the high share of manure and the associated higher demand for stirring a power consumption of 10% of the produced electricity at the CHP plant which is more in the upper range of a bandwidth (FNR, 2008). Also about 10% is the portion of the heat produced at the CHP plant, which is usually used internally in the process for heating the fermenter. In the majority of time only a small fraction of the residual heat can be used for external heating purposes by substituting fossil energy based heat. In the present study a share of 30% has been assumed. It should be pointed out, that the utilization of heat for external purposes increases when the system is connected to a larger object or to a heating grid. Depending on the retention time of the substrates in the fermenter, high residual methane emission can be produced by post-fermentation processes of the digestate in the digester storage tanks. In case of an uncovered storage tank climate relevant emissions in excess of 44 gCO2eq.*kWh−1 can be assumed (Gronauer and Bachmaier, 2007). In order to reduce these GHG emissions the digestate is stored in closed tank. For that reason, no GHG emissions concerning biogas digestate were considered. The produced electricity is fed into the electricity grid.
emissions associated with the production of electricity from manurebased biogas and to compare the result with a reference system in order to determine GHG mitigation effects due to replacing electricity from the German production mix. To compare the life cycle GHG emissions of both systems, it is important to pay attention to the functional equivalency. This means in this regard systems, the biogas system from manure and the fossil fuel based reference system, provide the same functionality defined as functional unit. The main product of the examined processes is the electricity (kWh) that is fed into the grid. Thus 1 kWh of electricity is the functional unit which all the relevant environmental effects (in this study exclusively the GHG emissions) are based on. 2.1.4. Co-products and credits The calculation defines the main product as - electricity generated from biogas. The additional products, which are generated during the process, are called co-products. Co-products are (i) avoided emissions by improved manure management and (ii) external heat from the combined heat and power plant. If biogas has converted to electricity at CHP plant always heat as a by-product has been released. There are different methods used to proportionately allocate the environmental impacts to the main product and the co-products (ISO 14040, 2006); the credit method was chosen for the present study. By applying the credit method, the influence of the co-products can be read directly in a bar graph. At a glance it can be estimated where the balance could be improved through increased use of the co-products. In the credit method, all of the emissions are initially attributed to the main product (in this case the main product is electricity from biogas CHP unit). Credits are given for co-products. The overall GHG balance is calculated by deducting the credits from the calculated emissions. 2.1.5. Life cycle impact assessment (LCIA) methodology and types of impacts The present assessment of manure based biogas production only considers the impact category global warming potential (GWP). Within the category GWP the greenhouse gases relevant for manure based biogas plants are carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O). The global warming potential of greenhouse gases is expressed in kg of carbon dioxide equivalents (CO2eq). To convert a specific methane mass to kg CO2eq, the methane weight is multiplied by 25 and the nitrous oxide mass is multiplied by 298 (based on a period of 100 years according to IPCC 2007) (Eggleston et al., 2006). The CO2 emissions from biogas combustion are not included in GHG calculation, according to the IPCC biogenic CO2 emissions are considered to be offset by the CO2 sequestration during plant growth.
2.2.2. Calculating the credits from improved manure management In terms of manure management, we assumed that manure is stored in open storage systems on farms without biogas plants, and that conventional manure storages produce inevitable climate-relevant emissions in the form of methane (CH4) (Haenel et al., 2014). By introducing manure as a substrate in a biogas plant early on, the stated GHG emissions can be largely avoided (Dämmgen and Webb, 2006). Thus, it can be assumed that the emissions would occur in all reference scenarios of manure digestion. They are calculated as follows: Two factors are decisive for calculating emissions from manure storage and thus, in determining a credit factor: (i) the maximum animal specific methane producing capacity (B0) and (ii) the methane conversion factor (MCF). The MCF describes the proportion of methane that is actually produced by B0 in various storage systems. Varying information regarding the level of these parameters has been published and provide data on these factors (Friehe et al., 2013; KTBL, 2013; UBA, 2014); the values for the specific methane producing capacity range from 8 to 17 m3CH4/m³manure for pig and cattle slurry. The range of methane conversion factors differ from 10 to 25% depending on the type of storage system (e.g. slurry storage with/without a floating cover) (Friehe et al., 2013; KTBL, 2013; UBA, 2014). To derive the GHG credits shown in Table 1 average values for B0 have been assumed. The values used for MCF serve as the basis for calculating Germany's National Inventory Report (Haenel et al., 2014). The calculation shows that the specific GHG reduction potential from pig manure is almost twice as high as from cattle. Based on these figures, and taking the proportion of the different manure types from 2012 into consideration (80% cattle slurry; 20% pig slurry)
2.2. Life cycle inventory analyses (LCI) The next step is to compile a list of the material and energy flows that enter and leave the system. This LCI contains all flows in and out of the product system, including raw resources and materials, energy flows, water and emissions to air, water and soil. The data for the LCI come from (KTBL, 2015; BioGrace, 2014). The following sections describe in detail the databases and assumptions used to calculate the avoided emissions through improved manure management, and to calculate the reference system, with a clear focus on biogas production. 2.2.1. Inventory of biogas production and biogas use in combined heat and power (CHP) plant A case study is used to illustrate the GHG performance of manure based biogas production and subsequent electricity production. The data and configuration of the biogas plant and the CHP do not come from a specific existing site, but a constructed farm model which represents a typical average manure based biogas plant in Germany. The following assumptions for the key parameters of the biogas plant were 473
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Table 1 Typical values and calculated GHG savings. Animal manure
B0
MCF %
m³CH4/m3 slurry Cattle slurry Pig slurry a
14 17
17 25
GHG savings kgCH4/m3 slurry
kgCO2 eq/m3 slurrya
1.71 3.06
42,84 76,5
Conversion factor of 25 g CO2 per g CH4.
(Scheftelowitz and Thrän, 2016) an average GHG emission of 49.6 kgCO2 eq*m3−1 manure has been determined. The credit factor is calculated using these parameters as well as the overall yield of 158.8 kWh of biogas per m³ manure input as described in Table 1.
Fig. 2. Specific GHG emissions of the German electricity mix 2008–2014 in g CO2eq*kWh−1 el (Icha, 2015).
2.2.3. Calculating the credits for external heat use The use of residual heat for external purposes from cogeneration is taken into account by way of a credit. To calculate the amount of the credit, it is necessary to define a fossil reference system. It has been assumed, that the heat from biogas CHP replaces the German heat mix, a production mix of natural gas and fuel oil boilers. According to this, heat from biogas plants substitutes 70% of heat from natural gas and 30% of heat from oil fuel (Thrän et al., 2013). Thus a credit of 86.7 g CO2 eq is assigned to each MJ of residual heat from CHP for external use (Table 2). The processes used in the provision of the German heat mix determine the environmental impact per MJ of useful heat this means the energy which is available to the end user. To account for the loss that arises when the heat is transported from the biogas CHP plant to the end user, the amount of heat from the biogas CHP plant was reduced by 10% before the credit was calculated.
The overall mitigation potential resulting from the use of manure can be calculated based on this analyzed specific mitigation potential and the overall input quantities of manure for biogas production (Scheftelowitz and Thrän, 2016) from 2008 to 2014.
3. Results 3.1. Specific GHG emissions Based on the methodology and assumptions described in Section 2, the following areas have been analyzed in terms of their greenhouse effect: (i) the GHG emissions linked with the demand and use of electricity from the grid for biogas production, (ii) the biogas digester as methane leakage (iii) the CHP plant as methane leakage (iv) credit for the avoided emissions from an improved manure management and (v) credits for the external use of residual heat from biogas CHP plant. The results of the calculation of the GHG emissions are illustrated in the three graphs in Fig. 3 and explained below: Graph (A) emissions from the energy demand for biogas plant and from digester and CHP as methane leakage; Graph (B) credits for avoided emissions from improved manure management and external use of heat from biogas CHP and Graph (C) sum and overall emissions. The demand and source of electricity for the operation of the biogas plant and methane losses from biogas digester have the greatest impacts on GHG emissions from the operation of the biogas plant and CHP unit as shown in Fig. 3, Graph (A). The source of electricity is an important parameter because the electricity from the grid is very emission intensive due to the high proportion of fossil fuels in the German electricity mix (Icha, 2015). Methane slip accounts for 52 g CO2eq*kWh−1 using the leakage rate estimated to be 1% of the methane production (Vetter and Arnold, 2010). The described methodology for GHG assessment produces credits for the positive effects of the production of electricity from manure based biogas. These credits take into consideration the improved manure management by using manure as a biogas substrate and the external use of residual CHP heat. The values for the calculated credits are shown in Fig. 3, Graph (B). The credit for the external use of CHP heat is 141 g CO2e/kWh electricity. The amount of this credit mainly depends on thermal efficiency of the CHP plant, the fraction of the external use of the heat, and the chosen reference system. The credit for the avoided GHG emissions from an improved manure management amounts to the largest share of the overall credit. This value basically depends on the following factors: (i) type of manure (the avoidance potential of manure is much higher than that of solid manure; see Table 2), (ii) the proportion of manure in the substrate mix, and (iii) the biogas yield from the type of manure used. The overall GHG emissions are calculated as the sum of emissions
2.3. Mitigation effects of electricity production from manure based biogas in Germany from 2008 – 2014 The annual GHG savings for the years 2008 – 2014 are calculated based on the information on the development of biogas production in Germany (Scheftelowitz et al., 2014), the use of manure in biogas plants during this period (Scheftelowitz and Thrän, 2016) and the associated substitution and GHG avoidance effects described above. In order to make a point about how much GHG emissions can be saved by electricity from manure-based biogas compared to the generation of electricity from fossil sources, the definition of a reference system is necessary analog to the calculation of the heat credits. The GHG emissions of this reference system can then be used to classify the results. It is assumed that the electricity from the manure based biogas CHP plant replaces electricity from the German electricity mix. The amount of the specific emissions associated with the production of the electricity mix mainly depends on the proportion of fossil fuels in the fuel mix. The specific GHG emissions of the German electricity mix from 2008 to 2014 are shown in Fig. 2 (Icha, 2015). To calculate the credits for external CHP heat use, it is assumed that the German heat mix has not changed in the years 2008–2014. According to this, the values of Table 2 are valid. Table 2 Specific GHG emissions from the German heat mix in gCO2eq*MJ−1 of heat (Thrän et al., 2013).
German heat mix GHG emissions
Heat from natural gas 70%
Heat from oil fuel 30%
Emissions from 1 MJ of German heat mix
Unit
79.3
85
86.7
gCO2 eq./ MJ
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Fig. 3. Specific GHG emissions for manure-based biogas production in gCO2eq*kWh−1 el.
brought into the digester to be anaerobic digested. The remaining part of the savings results from substituting the German electricity mix. With regard to the development of the different shares during the last seven years, we clearly see an increasing relevance in GHG savings from manure management. This is not surprising because the substituted electricity is characterized by a lower GHG emission burden and a savings decrease as a result of the general support for generating power from renewable energy sources.
(Graph A) and the given credits (Graph B). The result is presented in the sum column in Fig. 3 Graph (C) and shows the significant influence of the credits, in particular the credits for the avoided emissions due to the use of manure as biogas substrate and the associated improved manure management, on the overall emissions. The value of the overall emissions is −839 CO2eq*kWh−1el. This means that the plants under consideration emit −839 g of CO2 equivalents in order to produce 1 kWh of electricity from manure based biogas and to feed it into the power grid.
4. Discussion 3.2. Total GHG mitigation
When electricity is generated through the production of biogas from manure, major GHG reductions can be achieved, namely in two sectors: the energy sector by substituting fossil fuels, and the agricultural sector by avoiding climate-related emissions through manure storage. Our calculation shows for the actual German conditions a specific reduction of 1.448 kg of CO2 eq. per kWh power generated from manure based biogas. Using this exemplary calculation as a basis, we can estimate the overall GHG emission reduction potential of 3.5 M t of CO2 eq through manure utilization. But this is only the minor share of the potential which has been exploited with the implemented mechanism of the Renewable Energy Act (Thrän et al., 2014) while the remaining potential is difficult to assess due to the comparably high number of small farms (Scheftelowitz and Thrän, 2016). Hence, the question arises what kind of additional instruments can be implemented to unlock this huge climate gas reduction potential. Looking at the major reduction effects, we see that over 50% of the savings are due to the fact that the manure is not stored conventionally but quickly brought into the digester and fermented. The remaining part of the savings results from substituting the German electricity mix. Emission reduction goals are set from the German government for both sectors. With regard to the current and expected development the emission reduction in the power provision sector is expected to progress much faster in the years to come, what also leads to the conclusion, that the agricultural sector should encourage the power production from manure based biogas much stronger in the future. One way to support the use of manure in biogas plants is to apply
Fig. 4 shows the estimated GHG reduction from the years 2008–2014 when manure was used in biogas plants. While about 1.9 million tons of CO2eq were avoided in 2008, 3.7 million tons - nearly twice as much emission - were saved in 2014 by increasing the use of manure. The upper part of the bar indicates the amount of emissions that were avoided through improved manure management as a percentage of total GHG reductions. Thus, over 50% of the savings are due to the fact that the manure is not stored conventionally but quickly
Fig. 4. Total GHG mitigation from manure-based biogas production in tCO2eq*a−1.
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Funding
the principles of the European Union's Common Agricultural Policy (CAP). Here sustainability and environmental concerns have been anchored which differ in two aspects: (i) ensuring a sustainable way of farming by avoiding environmentally harmful agricultural activity (the “polluter pays principle”) and (ii) providing incentives for environmentally beneficial public goods and services (the “provider gets principle”) (Integrating Environmental Concerns into the CAP, 2016). According to the “polluter pays principle”, the costs for complying with common rules and standards for preserving the environment and landscape would have to be borne by the farmers. These common rules and standards are mandatory and form the very basis for ensuring that agricultural activity is undertaken in a sustainable way; however, they do not contain measures for decarbonisation. Appropriate incentives must be provided in order to engage farmers voluntarily in improving the environment beyond what is mandatorily required. According to the “provider gets principle”, the voluntary commitment of farmers to the environment should be compensated. Under the Common Agricultural Policy, this takes the form of agri-environmental payments which provide farmers with an incentive to go beyond the reference level in terms of environmental protection. Such agri-environmental payments are meant to cover the costs of the voluntary environmental performance and to compensate for income losses. Due to the fact, that improved manure management is associated to waste disposal matters, the implementation of mentioned incentive mechanism should be regulated on farm level to ensure technical measures, but also on regional level to ensure sustainable use of the residues from biogas production in agricultural systems. The related support schemes should implemented in the agricultural support roles. Additionally measures need to be taken to ensure a system oriented and efficient energy provision from the produced biogas. This will be more important in the future, when electricity from biogas can compensate gaps from a more fluctuating power energy provision from wind and solar not only for the power provision in general but also with specific wins on regional level (Trommler et al., 2016). Depending on the situation of the Energy transition the related instruments can be implemented on national or regional scale. Having an agricultural based support schemes implemented, in Germany the role of the EEG for biogas from manure could be reduced to incentives for flexible power provision under the consideration of the regional frame conditions.
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Entwicklung der spezifischen Kohlendioxid- Emissionen des deutschen Strommix in den Jahren 1990 bis 2014. Umweltbundesamt. Integrating environmental concerns into the CAP, 2016. Agriculture and rural development. URL 〈http://ec.europa.eu/agriculture/envir/cap/index_en.htm#polluter〉. abgerufen am-10-07. ISO 14044,2006. Umweltmanagement - Ökobilanz - Anforderungen und Anleitungen (ISO14044:2006), Deutsche und Englische Fassung EN ISO 14044:2006, 10/. ISO 14044, 2006. Umweltmanagement - Ökobilanz - Anforderungen und Anleitungen (ISO 14044:2006), Deutsche und Englische Fassung EN ISO 14044:2006, 10/. Kirchmeyr, Franz; Majer, Stefan; Emily, Nicholas; Scheidl, Stefanie: D 5.2 Assessment of GHG reduction potentials due to the use of animal excrements and organic waste streams as biogas substrates and the replacement of industrial chemical fertilisers by digestate, BIOSURF, 2015. KTBL, 2015. Online Anwendung - Wirtschaftlichkeitsrechner Biogas: Kuratorium fürTechnik und Bauwesen in der Landwirtschaft e.V. (KTBL), Darmstadt. KTBL: Faustzahlen Biogas. 3. Auflage. Aufl. : KTBL, 2013 — ISBN 978-3-941583-85-6. Majer, Stefan, Oehmichen, Katja, Kirchmeyr, Franz, Scheidl, Stefanie: D5.3 | Calculation of GHG emission caused by biomethane, BIOSURF, 2015. Riaño, B., García-González, M.C., 2015. Greenhouse gas emissions of an on-farm swine manure treatment plant – comparison with conventional storage in anaerobic tanks. J. Clean. Prod. Carbon Emiss. Reduct.: Policies Technol., Monit., Assess. Model. Bd. 103, 542–548 (S). Rodhe, Lena K.K., Ascue, Johnny, Willén, Agnes, Persson, Birgitta Vegerfors, Nordberg, Åke, 2015. Greenhouse gas emissions from storage and field application of anaerobically digested and non-digested cattle slurry. Agric. Ecosyst. Environ. Bd. 199, 358–368 (S). Scheftelowitz, M., Daniel-Gromke, J., Rensberg, N., Denysenko, V., Hildebrand, K., Naumann, K., Ziegler, D., Witt, J., 2014. U.A.: Stromerzeugung aus Biomasse (Vorhaben IIa Biomasse) (preliminary report). Deutsches Biomasseforschungszentrum, Leipzig. Scheftelowitz, Mattes, Thrän, Daniela, 2016. Unlocking the energy potential of manure—an assessment of the biogas production potential at the farm level in Germany. Agric. Bd. 6 (Nr. 2), 20 (S). Thrän, Daniela, Pfeiffer, Diana, Adler, Philipp, Brosowski, André, Erik, Fischer, Herrmann, André, Majer, Stefan, Oehmichen, Katja, u, a., Thrän, Daniela, Pfeiffer, Diana (Hrsg), 2013. Methodenhandbuch Stoffstromorientierte Bilanzierung der
5. Conclusion and policy implications Biogas production and conversion to electricity under the Renewable Energy Act has introduced a significant reduction in GHG emissions in Germany. However this is limited and additional instruments are necessary. The allocation of the GHG emission reduction potential to the two related sectors, energy and agriculture, can be used as a basis to identify policy fields in which additional instruments should be implemented. The results show, that the implementation of instruments in both agricultural policies and in energy policies might be appropriate. Because the reductions of GHG emissions from conventional manure storage and the production of a renewable energy carrier which can also be used in operation of farms can be a vital component in the decarbonisation of the agricultural sector. The results from the German case study also provide conclusions for other countries that have a significant amount of livestock breeding and which are faced with an energy transition towards renewables. Depending on the emission intensity of the national electricity mix, the GHG savings in some countries by using manure to produce energy in the agricultural sector may be greater than the energy sector. Following the “polluter pays principle”, the incentives for energy production from manure should be implemented in the agricultural sector. Only the system related services of the power generation from biogas are relevant for the energy sector.
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UBA: Berichterstattung unter der Klimarahmenkonvention der Vereinten Nationen und dem Kyoto-Protokoll 2014. Nationaler Inventarbericht zum Deutschen Treibhasugasinventar 1990-2012: Umweltbundeamt, 2014. Verordnung über die Anwendung von Düngemitteln, 2012. Bodenhilfsstoffen, Kultursubstraten und Pflanzenhilfsmitteln nach den Grundsätzen der guten fachlichen Praxis beim Düngen (Düngeverordnung - DüV). Bd. Neugefasst durch Bek. v. 27.2.2007 I 221; zuletzt geändert durch Art. 5 Abs. 36 G v. 24.2 I 212. Vogt, Regine, 2007. Basisdaten zu THG-Bilanzen für Biogs-Prozessketten und Erstellung neuer THG-Bilanzen. Institut für Energie- und Umweltforschung, Heidelberg.
Klimagaseffekte, Schriftenreihe des BMU-Förderprogramm„ Energetische Biomassenutzung“. Leipzig DBFZ: Thrän, Daniela; Pfeiffer, Diana (Herg.) (ISBN ISSN 2192-1806). Thrän, Daniela, Krautz, Alexander, Scheftelowitz, Mattes, Lenz, Volker, Liebtrau, Jan, Daniel-Gromke, Jaqueline, Zeymer, Martin, Nelles, Michael, 2014. Auswirkungen der Gegenwärtig Diskutierten Novellierungs-Vorschläge für das EEG-2014. Osnabrück. Trommler, Markus, Dotzauer, Martin, Barchmann, Tino, Matthischke, Steffi, Brosowski, André, Keil, Annette, Gerigk, Ulrich, Lange, Clemens, 2016. U.A.: RegioBalance Bioenergie-Felxibilisierung als regionale Ausgleichsoption in deutschen Stromverteilernetzen. DBFZ Deutsches Biomasseforschungszentrum gGmbH, Leipzig.
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Fostering renewable energy provision from manure in Germany – Where to implement GHG emission reduction incentives
MARK
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Katja Oehmichena, , Daniela Thräna,b a b
Deutsches Biomasseforschungszentrum gGmbH (DBFZ), Leipzig, Germany Helmholtz Centre for Environmental Research, Leipzig, Germany
A R T I C L E I N F O
A B S T R A C T
Keywords: Biogas Life cycle assessment Greenhouse gas emissions Mitigation potential Manure
Livestock production makes up a major share of agriculture sector and the manure it produces significantly contributes to greenhouse gas emissions. One option to lower these emissions significantly is using the manure to produce biogas which is used to generate power. Our model calculations show, that per kWh power from manure-based biogas –about 1.448 kg of CO2 eq. of greenhouse gas (GHG) emission can be avoided due to the improved manure management and the substitution of electricity from the grid under actual German conditions. This form of utilization is supported under the German Renewable Energy Act; however, only the minor share of the manure is processed so far. Thus the question arises as to whether instruments in agricultural policy or instruments in energy policy are better to unlock this remaining potential. The elaborated allocation shows, that both sectors cause a comparable amount of GHG emissions reductions, at around 50% each. However, based on expected developments, the relevance of agriculture-related emissions is slated to increase. This leads to the conclusion that implementing instruments in both agricultural and energy policies would make sense.
1. Introduction Livestock production is a significant sector in German agriculture and makes up 3% of the global production (FAOSTAT, 2016). This production is characterized by a tremendous demand for feedstock and the production of enormous amounts of excrement in the form of liquid or solid manure and slurry - currently estimated at 139 M tons per year (Thrän et al., 2014). This excrement contains significant amounts of nitrogen and other nutrients so that it is typically spread directly on farmland as fertilizer. Excrement is produced on a continuous basis, however, because it can only be re-used as a fertilizer during certain times of the year, large storage capacities for manure are necessary (Verordnung über die Anwendung von Düngemitteln, 2012). These storage facilities are often open silos where the stored manure produces relevant amounts of methane which cause 1% of the overall German GHG emissions (Haenel et al., 2014). There are a few possibilities to reduce these emissions. One of them is producing biogas from manure which can reduce the GHG emissions from manure storage and provide a renewable energy carrier as well. If the renewable energy carrier is used as a substitute for fossil fuels, additional GHG emissions are saved. So far, about 3000 biogas plants have been installed at farm sites in Germany, mainly under the Renewable Energy Act (Scheftelowitz and Thrän, 2016). These biogas plants provide renewable energy and
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combined heat and power (CHP). Because only about 48% of the animal waste produced nation-wide is currently utilized in biogas plants (Thrän et al., 2014), more than one hundred thousand farms, with varying amounts of livestock (cattle and pigs), provide additional potential for biogas production. There is a clear need to further reduce GHG emissions through manure management as stipulated by the ambitious targets set by the Paris agreements. These aim to reduce national greenhouse gases by 80–95% in Germany by 2050 (in comparison to 1990). But this requires further incentives and begs the question of how to design these incentives in an appropriate way: Since biogas production from manure supports greenhouse gas emissions reduction in both the energy and in the agriculture sector, the relevance of these two effects needs to be taken as a basis for developing enhanced support instruments. Against this background, the main research question of this paper is: How many GHG emissions can be reduced through the use of manure for electricity production via biogas? Which sectoral allocation of the reduction effects can be derived from the quantification and in which sector are incentives relevant?? Most studies on the reduction of GHG emissions are concerned either with the mitigation effects of improved manure management, from the point of view of disposal (Riaño and García-González, 2015; Rodhe
Corresponding author. E-mail address: [email protected] (K. Oehmichen).
http://dx.doi.org/10.1016/j.enpol.2017.08.014 Received 22 December 2016; Received in revised form 31 July 2017; Accepted 2 August 2017 0301-4215/ © 2017 Published by Elsevier Ltd.
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Inventory are described below for the present case of biogas production from manure.
et al., 2015; Costa et al., 2015; Clemens et al., 2006; Kirchmeyr et al., 2015), or with the mitigation effects of electricity production from biogas, from the point of view of substitution (Gronauer and Bachmaier, 2007; Horschig et al., 2016; DBFZ, 2011; Majer et al., 2015). To quantify the mitigation potential, we have merged both effects and we have elaborated on an appropriate method for assessing the GHG emissions from using manure in biogas plants in Germany and the associated GHG mitigation effects under the actual support schemes over the last seven years. We also discuss options for further developing the promotion of biogas plants.
2.1.2. Boundaries Setting the system boundaries is one of most essential issues for carrying out a life cycle assessment. The system boundaries define the framework in which the assessment takes place and determine which energy material flows are taken into account in the assessment. In the present case a ‘cradle to gate’ life cycle has been analyzed. The ‘cradle to gate’ life cycle means that all flows of materials and energy which are necessary for the operation of the biogas plant and the production of electricity from manure based biogas have been taken into account. The assessed life cycle starts with the transport of the manure (in case that the manure is not generated on site) and ends with the transformation of manure based biogas to electricity at the combined heat and power (CHP) plant and the subsequent feed of the produced electricity into the electricity grid. Contrary to the ‘cradle to gate’ life cycle for the biogas processes a ‘gate to gate’ life cycle has been chosen for the provision and use of manure from animal husbandry production. This means that only transport expenditures and direct manure emissions at the biogas plant has been calculated. Whereas upstream processes associated with livestock breeding such as, for example expenditures from crop cultivation for animal feed were not considered. Because the goal of livestock breeding is not the production of excrements (such as manure) but the production of milk and meat, from which the manure results as a waste product. That's why the life cycle emissions of manure are zero until the place of the production. At the same time not included, are on the one hand emissions from the transport and the field application of the digestate. In particular, nitrous oxide emissions from spreading the digestate can have an influence on the GHG balance sheet, the amount of these emissions depends mainly on the method of digestate spreading and on the technique the digestate has been incorporated into the soil. On the other hand, the fertilizing effect of the digestate and the associated substitution of synthetic fertilizer are not taken into account. Climate relevant emissions resulting from the energy-intensive production of synthetic nitrogen fertilizers can be avoided in this manner. This approach seems to contradict the fact that the avoided emissions from the conventional manure storage are included in the life cycle assessment. Since due to the anaerobic digestion of the manure the improved manure management is directly linked to the supply of the manure (the manure is not stored after production, but is placed in the digester in a timely manner), the emissions avoided are to be located within the boundaries of the GHG assessment. Due to the negligible impact the GHG emissions associated with construction and demolition of the biogas plant and the CHP were not considered. On the basis of these assumptions, the system boundaries of this assessment include the major stages of the manure based biogas system: (i) manure provision, (ii) the production of biogas by anaerobic digestion of manure, (iii) using the produced biogas in a combined heat and power (CHP) plant to produce electricity and heat and (iv) feed the electricity into the grid (see Fig. 1). These steps are further detailed in the life cycle inventory (LCI) as described in the following chapters.
2. Method To answer the question regarding the GHG emissions from using manure in biogas plants in Germany and the associated GHG mitigation effects, GHG emissions from manure based biogas systems have been analyzed, calculated and assessed with regard to their reduction potential for both farm based manure management and the substitution of fossil fuels for power generation. There are different methodological approaches for the investigation of lifecycle GHG emissions from products or services. The assessment of lifecycle GHG-emissions is often part of a life cycle assessment (LCA). LCA is an appropriate method for evaluating the GHG performance of a manure based biogas system compared to a fossil reference system. Requirements for conducting an LCA are detailed in the international standards ISO 14040 (ISO 0, 1404, 2006) and ISO 14044 (ISO 4, 1404, 2006). According to these standards, the analysis covers the complete product life cycle from the production of the raw material to the final disposal of the product after the use phase, including all pre-products and energy carriers used. Using the selected LCA-based approach, we were able to extrapolate the mitigation potential for the entire amount of liquid manure used in Germany. This calculation is based on the specific GHG savings from a case study that compared a typical manure based biogas system with reference data on the GHG emissions released as part of conventional electricity production in Germany. The methodology employed in the evaluation of the GHG emissions is described in the following sections. 2.1. Goal and scope The first step of the LCA method - the definition of the goal and scope – includes a description of the underlying questions of the case study, the system boundaries under consideration, the definition of the functional unit, the allocation procedures, the life cycle impact assessment (LCIA) and the types of impact (ISO 14040, 2006). 2.1.1. Aim and scope of the study The principal aim of the study is to estimate the GHG emission mitigation effects associated with use of manure from livestock breeding, with regard to two aspects (i) mitigation of GHG emissions due to an improved manure management and (ii) replacing electricity from the German electricity grid by producing electricity from manure based biogas. To achieve the stated goals a LCA is performed according to the standards ISO 14040 and ISO 14044, using the software Umberto 5.5 and the database Ecoinvent (Ecoinvent v2.1, 2009) for background data. The primary steps by conducting a LCA, the setting of the system boundaries, the definition of the functional unit and the Life Cycle
2.1.3. Function and functional unit The main objective of this GHG assessment is to calculate the GHG Fig. 1. System boundaries.
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generated with (KTBL, 2015). The anaerobic digester is fed with 8500 t*a−1 of cattle slurry and 2100 t*a−1 of pig slurry. Biogas production is around 167,572 m3CH4*a−1 and the biogas plant is operated for 8000 h*a−1. It's assumed that the biogas consists of 56% CH4. During the production of biogas, methane can leak into the atmosphere. According to (Vetter and Arnold, 2010; Vogt, 2007), methane leakages from the digester were assumed to be 1% of the total methane produced. The biogas is conveyed to an Otto engine that generates around 75 kW of electrical energy. The key parameters for the CHP plant are the electrical efficiency in the amount of 35% which corresponds to a quantity of 580,987 kWh*a−1 electricity which is fed into the grid, and the thermal efficiency in the amount of 43%. Unburned methane emissions from the combustion are assumed to be 0.5% of the total methane contained in the biogas. The amount of electricity demand of the biogas plant was estimated to be 58 MWh*a−1 and was assumed to be supplied from the German electricity grid. The electricity consumption of a biogas plant depends on various parameters like type of substrate and fermentation and the management of the biogas plant. Due to the high share of manure and the associated higher demand for stirring a power consumption of 10% of the produced electricity at the CHP plant which is more in the upper range of a bandwidth (FNR, 2008). Also about 10% is the portion of the heat produced at the CHP plant, which is usually used internally in the process for heating the fermenter. In the majority of time only a small fraction of the residual heat can be used for external heating purposes by substituting fossil energy based heat. In the present study a share of 30% has been assumed. It should be pointed out, that the utilization of heat for external purposes increases when the system is connected to a larger object or to a heating grid. Depending on the retention time of the substrates in the fermenter, high residual methane emission can be produced by post-fermentation processes of the digestate in the digester storage tanks. In case of an uncovered storage tank climate relevant emissions in excess of 44 gCO2eq.*kWh−1 can be assumed (Gronauer and Bachmaier, 2007). In order to reduce these GHG emissions the digestate is stored in closed tank. For that reason, no GHG emissions concerning biogas digestate were considered. The produced electricity is fed into the electricity grid.
emissions associated with the production of electricity from manurebased biogas and to compare the result with a reference system in order to determine GHG mitigation effects due to replacing electricity from the German production mix. To compare the life cycle GHG emissions of both systems, it is important to pay attention to the functional equivalency. This means in this regard systems, the biogas system from manure and the fossil fuel based reference system, provide the same functionality defined as functional unit. The main product of the examined processes is the electricity (kWh) that is fed into the grid. Thus 1 kWh of electricity is the functional unit which all the relevant environmental effects (in this study exclusively the GHG emissions) are based on. 2.1.4. Co-products and credits The calculation defines the main product as - electricity generated from biogas. The additional products, which are generated during the process, are called co-products. Co-products are (i) avoided emissions by improved manure management and (ii) external heat from the combined heat and power plant. If biogas has converted to electricity at CHP plant always heat as a by-product has been released. There are different methods used to proportionately allocate the environmental impacts to the main product and the co-products (ISO 14040, 2006); the credit method was chosen for the present study. By applying the credit method, the influence of the co-products can be read directly in a bar graph. At a glance it can be estimated where the balance could be improved through increased use of the co-products. In the credit method, all of the emissions are initially attributed to the main product (in this case the main product is electricity from biogas CHP unit). Credits are given for co-products. The overall GHG balance is calculated by deducting the credits from the calculated emissions. 2.1.5. Life cycle impact assessment (LCIA) methodology and types of impacts The present assessment of manure based biogas production only considers the impact category global warming potential (GWP). Within the category GWP the greenhouse gases relevant for manure based biogas plants are carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O). The global warming potential of greenhouse gases is expressed in kg of carbon dioxide equivalents (CO2eq). To convert a specific methane mass to kg CO2eq, the methane weight is multiplied by 25 and the nitrous oxide mass is multiplied by 298 (based on a period of 100 years according to IPCC 2007) (Eggleston et al., 2006). The CO2 emissions from biogas combustion are not included in GHG calculation, according to the IPCC biogenic CO2 emissions are considered to be offset by the CO2 sequestration during plant growth.
2.2.2. Calculating the credits from improved manure management In terms of manure management, we assumed that manure is stored in open storage systems on farms without biogas plants, and that conventional manure storages produce inevitable climate-relevant emissions in the form of methane (CH4) (Haenel et al., 2014). By introducing manure as a substrate in a biogas plant early on, the stated GHG emissions can be largely avoided (Dämmgen and Webb, 2006). Thus, it can be assumed that the emissions would occur in all reference scenarios of manure digestion. They are calculated as follows: Two factors are decisive for calculating emissions from manure storage and thus, in determining a credit factor: (i) the maximum animal specific methane producing capacity (B0) and (ii) the methane conversion factor (MCF). The MCF describes the proportion of methane that is actually produced by B0 in various storage systems. Varying information regarding the level of these parameters has been published and provide data on these factors (Friehe et al., 2013; KTBL, 2013; UBA, 2014); the values for the specific methane producing capacity range from 8 to 17 m3CH4/m³manure for pig and cattle slurry. The range of methane conversion factors differ from 10 to 25% depending on the type of storage system (e.g. slurry storage with/without a floating cover) (Friehe et al., 2013; KTBL, 2013; UBA, 2014). To derive the GHG credits shown in Table 1 average values for B0 have been assumed. The values used for MCF serve as the basis for calculating Germany's National Inventory Report (Haenel et al., 2014). The calculation shows that the specific GHG reduction potential from pig manure is almost twice as high as from cattle. Based on these figures, and taking the proportion of the different manure types from 2012 into consideration (80% cattle slurry; 20% pig slurry)
2.2. Life cycle inventory analyses (LCI) The next step is to compile a list of the material and energy flows that enter and leave the system. This LCI contains all flows in and out of the product system, including raw resources and materials, energy flows, water and emissions to air, water and soil. The data for the LCI come from (KTBL, 2015; BioGrace, 2014). The following sections describe in detail the databases and assumptions used to calculate the avoided emissions through improved manure management, and to calculate the reference system, with a clear focus on biogas production. 2.2.1. Inventory of biogas production and biogas use in combined heat and power (CHP) plant A case study is used to illustrate the GHG performance of manure based biogas production and subsequent electricity production. The data and configuration of the biogas plant and the CHP do not come from a specific existing site, but a constructed farm model which represents a typical average manure based biogas plant in Germany. The following assumptions for the key parameters of the biogas plant were 473
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Table 1 Typical values and calculated GHG savings. Animal manure
B0
MCF %
m³CH4/m3 slurry Cattle slurry Pig slurry a
14 17
17 25
GHG savings kgCH4/m3 slurry
kgCO2 eq/m3 slurrya
1.71 3.06
42,84 76,5
Conversion factor of 25 g CO2 per g CH4.
(Scheftelowitz and Thrän, 2016) an average GHG emission of 49.6 kgCO2 eq*m3−1 manure has been determined. The credit factor is calculated using these parameters as well as the overall yield of 158.8 kWh of biogas per m³ manure input as described in Table 1.
Fig. 2. Specific GHG emissions of the German electricity mix 2008–2014 in g CO2eq*kWh−1 el (Icha, 2015).
2.2.3. Calculating the credits for external heat use The use of residual heat for external purposes from cogeneration is taken into account by way of a credit. To calculate the amount of the credit, it is necessary to define a fossil reference system. It has been assumed, that the heat from biogas CHP replaces the German heat mix, a production mix of natural gas and fuel oil boilers. According to this, heat from biogas plants substitutes 70% of heat from natural gas and 30% of heat from oil fuel (Thrän et al., 2013). Thus a credit of 86.7 g CO2 eq is assigned to each MJ of residual heat from CHP for external use (Table 2). The processes used in the provision of the German heat mix determine the environmental impact per MJ of useful heat this means the energy which is available to the end user. To account for the loss that arises when the heat is transported from the biogas CHP plant to the end user, the amount of heat from the biogas CHP plant was reduced by 10% before the credit was calculated.
The overall mitigation potential resulting from the use of manure can be calculated based on this analyzed specific mitigation potential and the overall input quantities of manure for biogas production (Scheftelowitz and Thrän, 2016) from 2008 to 2014.
3. Results 3.1. Specific GHG emissions Based on the methodology and assumptions described in Section 2, the following areas have been analyzed in terms of their greenhouse effect: (i) the GHG emissions linked with the demand and use of electricity from the grid for biogas production, (ii) the biogas digester as methane leakage (iii) the CHP plant as methane leakage (iv) credit for the avoided emissions from an improved manure management and (v) credits for the external use of residual heat from biogas CHP plant. The results of the calculation of the GHG emissions are illustrated in the three graphs in Fig. 3 and explained below: Graph (A) emissions from the energy demand for biogas plant and from digester and CHP as methane leakage; Graph (B) credits for avoided emissions from improved manure management and external use of heat from biogas CHP and Graph (C) sum and overall emissions. The demand and source of electricity for the operation of the biogas plant and methane losses from biogas digester have the greatest impacts on GHG emissions from the operation of the biogas plant and CHP unit as shown in Fig. 3, Graph (A). The source of electricity is an important parameter because the electricity from the grid is very emission intensive due to the high proportion of fossil fuels in the German electricity mix (Icha, 2015). Methane slip accounts for 52 g CO2eq*kWh−1 using the leakage rate estimated to be 1% of the methane production (Vetter and Arnold, 2010). The described methodology for GHG assessment produces credits for the positive effects of the production of electricity from manure based biogas. These credits take into consideration the improved manure management by using manure as a biogas substrate and the external use of residual CHP heat. The values for the calculated credits are shown in Fig. 3, Graph (B). The credit for the external use of CHP heat is 141 g CO2e/kWh electricity. The amount of this credit mainly depends on thermal efficiency of the CHP plant, the fraction of the external use of the heat, and the chosen reference system. The credit for the avoided GHG emissions from an improved manure management amounts to the largest share of the overall credit. This value basically depends on the following factors: (i) type of manure (the avoidance potential of manure is much higher than that of solid manure; see Table 2), (ii) the proportion of manure in the substrate mix, and (iii) the biogas yield from the type of manure used. The overall GHG emissions are calculated as the sum of emissions
2.3. Mitigation effects of electricity production from manure based biogas in Germany from 2008 – 2014 The annual GHG savings for the years 2008 – 2014 are calculated based on the information on the development of biogas production in Germany (Scheftelowitz et al., 2014), the use of manure in biogas plants during this period (Scheftelowitz and Thrän, 2016) and the associated substitution and GHG avoidance effects described above. In order to make a point about how much GHG emissions can be saved by electricity from manure-based biogas compared to the generation of electricity from fossil sources, the definition of a reference system is necessary analog to the calculation of the heat credits. The GHG emissions of this reference system can then be used to classify the results. It is assumed that the electricity from the manure based biogas CHP plant replaces electricity from the German electricity mix. The amount of the specific emissions associated with the production of the electricity mix mainly depends on the proportion of fossil fuels in the fuel mix. The specific GHG emissions of the German electricity mix from 2008 to 2014 are shown in Fig. 2 (Icha, 2015). To calculate the credits for external CHP heat use, it is assumed that the German heat mix has not changed in the years 2008–2014. According to this, the values of Table 2 are valid. Table 2 Specific GHG emissions from the German heat mix in gCO2eq*MJ−1 of heat (Thrän et al., 2013).
German heat mix GHG emissions
Heat from natural gas 70%
Heat from oil fuel 30%
Emissions from 1 MJ of German heat mix
Unit
79.3
85
86.7
gCO2 eq./ MJ
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Fig. 3. Specific GHG emissions for manure-based biogas production in gCO2eq*kWh−1 el.
brought into the digester to be anaerobic digested. The remaining part of the savings results from substituting the German electricity mix. With regard to the development of the different shares during the last seven years, we clearly see an increasing relevance in GHG savings from manure management. This is not surprising because the substituted electricity is characterized by a lower GHG emission burden and a savings decrease as a result of the general support for generating power from renewable energy sources.
(Graph A) and the given credits (Graph B). The result is presented in the sum column in Fig. 3 Graph (C) and shows the significant influence of the credits, in particular the credits for the avoided emissions due to the use of manure as biogas substrate and the associated improved manure management, on the overall emissions. The value of the overall emissions is −839 CO2eq*kWh−1el. This means that the plants under consideration emit −839 g of CO2 equivalents in order to produce 1 kWh of electricity from manure based biogas and to feed it into the power grid.
4. Discussion 3.2. Total GHG mitigation
When electricity is generated through the production of biogas from manure, major GHG reductions can be achieved, namely in two sectors: the energy sector by substituting fossil fuels, and the agricultural sector by avoiding climate-related emissions through manure storage. Our calculation shows for the actual German conditions a specific reduction of 1.448 kg of CO2 eq. per kWh power generated from manure based biogas. Using this exemplary calculation as a basis, we can estimate the overall GHG emission reduction potential of 3.5 M t of CO2 eq through manure utilization. But this is only the minor share of the potential which has been exploited with the implemented mechanism of the Renewable Energy Act (Thrän et al., 2014) while the remaining potential is difficult to assess due to the comparably high number of small farms (Scheftelowitz and Thrän, 2016). Hence, the question arises what kind of additional instruments can be implemented to unlock this huge climate gas reduction potential. Looking at the major reduction effects, we see that over 50% of the savings are due to the fact that the manure is not stored conventionally but quickly brought into the digester and fermented. The remaining part of the savings results from substituting the German electricity mix. Emission reduction goals are set from the German government for both sectors. With regard to the current and expected development the emission reduction in the power provision sector is expected to progress much faster in the years to come, what also leads to the conclusion, that the agricultural sector should encourage the power production from manure based biogas much stronger in the future. One way to support the use of manure in biogas plants is to apply
Fig. 4 shows the estimated GHG reduction from the years 2008–2014 when manure was used in biogas plants. While about 1.9 million tons of CO2eq were avoided in 2008, 3.7 million tons - nearly twice as much emission - were saved in 2014 by increasing the use of manure. The upper part of the bar indicates the amount of emissions that were avoided through improved manure management as a percentage of total GHG reductions. Thus, over 50% of the savings are due to the fact that the manure is not stored conventionally but quickly
Fig. 4. Total GHG mitigation from manure-based biogas production in tCO2eq*a−1.
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Funding
the principles of the European Union's Common Agricultural Policy (CAP). Here sustainability and environmental concerns have been anchored which differ in two aspects: (i) ensuring a sustainable way of farming by avoiding environmentally harmful agricultural activity (the “polluter pays principle”) and (ii) providing incentives for environmentally beneficial public goods and services (the “provider gets principle”) (Integrating Environmental Concerns into the CAP, 2016). According to the “polluter pays principle”, the costs for complying with common rules and standards for preserving the environment and landscape would have to be borne by the farmers. These common rules and standards are mandatory and form the very basis for ensuring that agricultural activity is undertaken in a sustainable way; however, they do not contain measures for decarbonisation. Appropriate incentives must be provided in order to engage farmers voluntarily in improving the environment beyond what is mandatorily required. According to the “provider gets principle”, the voluntary commitment of farmers to the environment should be compensated. Under the Common Agricultural Policy, this takes the form of agri-environmental payments which provide farmers with an incentive to go beyond the reference level in terms of environmental protection. Such agri-environmental payments are meant to cover the costs of the voluntary environmental performance and to compensate for income losses. Due to the fact, that improved manure management is associated to waste disposal matters, the implementation of mentioned incentive mechanism should be regulated on farm level to ensure technical measures, but also on regional level to ensure sustainable use of the residues from biogas production in agricultural systems. The related support schemes should implemented in the agricultural support roles. Additionally measures need to be taken to ensure a system oriented and efficient energy provision from the produced biogas. This will be more important in the future, when electricity from biogas can compensate gaps from a more fluctuating power energy provision from wind and solar not only for the power provision in general but also with specific wins on regional level (Trommler et al., 2016). Depending on the situation of the Energy transition the related instruments can be implemented on national or regional scale. Having an agricultural based support schemes implemented, in Germany the role of the EEG for biogas from manure could be reduced to incentives for flexible power provision under the consideration of the regional frame conditions.
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5. Conclusion and policy implications Biogas production and conversion to electricity under the Renewable Energy Act has introduced a significant reduction in GHG emissions in Germany. However this is limited and additional instruments are necessary. The allocation of the GHG emission reduction potential to the two related sectors, energy and agriculture, can be used as a basis to identify policy fields in which additional instruments should be implemented. The results show, that the implementation of instruments in both agricultural policies and in energy policies might be appropriate. Because the reductions of GHG emissions from conventional manure storage and the production of a renewable energy carrier which can also be used in operation of farms can be a vital component in the decarbonisation of the agricultural sector. The results from the German case study also provide conclusions for other countries that have a significant amount of livestock breeding and which are faced with an energy transition towards renewables. Depending on the emission intensity of the national electricity mix, the GHG savings in some countries by using manure to produce energy in the agricultural sector may be greater than the energy sector. Following the “polluter pays principle”, the incentives for energy production from manure should be implemented in the agricultural sector. Only the system related services of the power generation from biogas are relevant for the energy sector.
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