A method to calculate efficiency of energy crop production including sun energy,

direct and indirect energy for cultivation, processing, and conversion into fuel is

demonstrated using rape and derived fuels as an example. Every production and

conversion step is a process and calculated separately. The overall efficiency

includes energy input and output of all processes. The process efficiency of rape

cultivation reaches in Finland up to 1100 %. However, the overall energy efficiency of

rape methyl ester (RME) is 1 to 2 ‰ only. The production of biogas from manure of

dairy fed by rape meal results in a process energy efficiency of 33 to 41 %, but the

overall energy efficiency of RME and biogas together is only 1.2 to 2.5 ‰. In

contrast, thermal or photovoltaic solar collectors improve overall efficiency 1 to 3

orders of magnitude compared to fuel production from rape. Competition for

cultivation area and the low photosynthetic efficiency limit the feasibility of fuel

production from energy crops. As a measure for sustainability of renewable fuel

production, the energy surplus of energy conversion from insolation to fuel per

resident and square meter is proposed

Schäfer, Winfried

English

Organic Eprints

The 5th International Scientific Conference on Sustainable Farming Systems                    E C O M I T    82SUSTAINABILITY, OVERALL AND PROCESS EFFICIENCY OF ENERGY CROPS  Schäfer, W. MTT Agrifood Research Finland, Vakolantie 55, 03400 Vihti, Finland, E-mail winfried.schafer@mtt.fi  Abstract A method to calculate efficiency of energy crop production including sun energy, direct and indirect energy for cultivation, processing, and conversion into fuel is demonstrated using rape and derived fuels as an example. Every production and conversion step is a process and calculated separately. The overall efficiency includes energy input and output of all processes. The process efficiency of rape cultivation reaches in Finland up to 1100 %. However, the overall energy efficiency of rape methyl ester (RME) is 1 to 2 ‰ only. The production of biogas from manure of dairy fed by rape meal results in a process energy efficiency of 33 to 41 %, but the overall energy efficiency of RME and biogas together is only 1.2 to 2.5 ‰. In contrast, thermal or photovoltaic solar collectors improve overall efficiency 1 to 3 orders of magnitude compared to fuel production from rape. Competition for cultivation area and the low photosynthetic efficiency limit the feasibility of fuel production from energy crops. As a measure for sustainability of renewable fuel production, the energy surplus of energy conversion from insolation to fuel per resident and square meter is proposed.  Introduction Agricultural machinery and buildings cause up to 40% of production cost. The high costs of technical input forces to specialisation of farm production by splitting animal and crop production located at different areas or even continents, narrow crop rotations, and dependency from fossil fuels and counteracts to sustainable farming principles and green house gas mitigation. In short, the entropy of modern farming systems increases. However, a physical and technological approach and engineering proficiency may contribute to the aims of sustainable farming also in respect of energy crop issues.  The crop scientist focuses his research on high quantity and quality of yield based on a sustainable tilth. The engineer is interested in maximisation of the process efficiency. He interprets the crop scientist’s approach as maximisation of photosynthesis’ efficiency. Odum (1996) developed an excellent logical framework for energy accounting based on sun energy input. Although the methodology is further developed and applied worldwide (e.g. Bastianoni et al. 2007, Jiang et al. 2007, Rótolo et al. 2007,  Ukidwe & Bakshi  2007), the methodology seems to be quite unknown to European decision makers in the field of environmental and agricultural sciences. One reason may be that applied thermodynamics in environmental accounting requires more scientific skills than life cycle analysis (ISO 14040) which is easily to accomplish by simple spreadsheet calculations. Objective of this paper is to support the assessment of energy crop production in terms of sustainability and energy efficiency applying basic engineering sciences methods in energy accounting. Figure 1 shows the theoretical approach.  Material and methods  The engineer quantifies the sustainability of energy crop production by means of the overall efficiency ηO that is the energy output divided by the energy input of all processes involved: The 5th International Scientific Conference on Sustainable Farming Systems                    E C O M I T    83  Figure 1: Simplified model of energy crop production. The model shows all the exergy flows directly or indirectly needed for the process and the partial efficiencies of the backward steps to the original solar exergy source. (Bastianoni et al. 2007, modified).  []1i in1 ii i in1 ii i O ) K P (S A ) η S (A η−= =⎟ ⎟⎠⎞⎜ ⎜⎝⎛+ + ⋅ ⋅ ⎟ ⎟⎠⎞⎜ ⎜⎝⎛⋅ ⋅ = ∑ ∑  A denotes the area, S the solar energy, P the energy input of crop cultivation, K the energy input of fuel conversion, ηi the technical efficiency of photosynthesis and i the member of crop rotation. The crop scientist concerns for ηi and to some extent for P while K and P is of engineers and partially animal production scientist’s interest. Please note that the global solar-radiation intensity is limited like the cultivation area too. The equation is applicable for farm level, national level, and worldwide. However, it does not take into consideration the energy saving potential of crop fibre for heat insulation.  The calculation of the process energy efficiency includes the process energy input and the free energy (exergy) before and after processing. The engineer considers photosynthesis, cultivation, and conversion each as process. E.g., the process efficiency of buring biomass for heat production depends only on incinerator efficiency and on energy input for transport of biomass and ash. Additional treatment like pelleting, extraction of oil, anaerobic digestion, ethanol fermentation etc. raises the energy input considerably. The production of ethanol from corn renders always a negative exergy balance due to the thermodynamic laws (Patzek 2004).  Crop processing generates usually different products. Some are suitable for energy production others for fibre production, human nutrition or animal feed. This fact causes a methodological problem, called allocation. The process energy for rape crop production may be allocated to seed, straw, and roots. The process energy input for extraction, refining, and esterification of rapeseed oil has to be split between   SunCropPrecipi- tation   Pasture   Phyto-planktonPhyto- - planktonPhyto-planktonGeochemicalcycle Forest   Animals    Kerogen Kerogen Kerogen Peat     Manure    Oi  Oi Oil  Coal   Diesel  IronSteelMachinery Iron The 5th International Scientific Conference on Sustainable Farming Systems                    E C O M I T    84rape methyl ester (RME), meal, and glycerine, the by-product of esterification of rape oil. Depending on the allocation method, the process energy balance may diverge in a wide range.  Results and discussion Table 1 shows a chain of processes of rape production and processing, their efficiencies and the resulting cumulated overall efficiency derived from different sources (Elsayed et al. 2003, Bugge 2000, Schäfer 1996).   Table 1: Energy input, energy output, process efficiency and overall efficiency of rape production and rape processing in Finland.   The results show that the high process energy efficiency of the rapeseed cultivation fosters common acceptance of rape as energy crop. Even under Finnish climate conditions, exergy of rape crop exceeds up to 11-times the energy input for production and exergy of seed up to 3.7 times. Conversion of rapeseed into fuel decreases the energy surplus. Rape methyl ester (RME) delivers still 1.2-fold the energy input for cultivation and conversion. The whole rape crop (root, straw, seed) contains 3 to 6 ‰ of the overall energy input, RME 1 to 2 ‰ only. Animal production Process Input kWh m-2 a -1 Output kWh m-2 a -1 Process- efficiency  % Overall  efficiency % crop cultivation direct  and  indirect energya) 0.3 - 0.8 root straw  seedb)  3.3 - 6.3 262 - 366 262 - 366 262 - 366 787 - 1100photo- synthesis  sun light  1000 root straw  seedb)  1.1 - 2.1 1.1 - 2.1 1.1 - 2.1 0.11 - 0.21 0.11 - 0.21 0.11 - 0.21  0.33 - 0.63 incineration  straw seed  2.2 - 4.2  calorific heat  1.76 - 3.78  80 - 90  0.18 - 0.38oil and meal production seed energy  1.1 - 2.1 0.1 oil. meal total 0.64 - 1.21 0.46 - 0.89 1.1 - 2.1 52.9 - 55.1c) 38.7 - 40.3d) 91.7 - 95.5e) 0.06 - 0.12c)0.05 - 0.09d)0.11 - 0.21e)bio-refinery  seed  energyf) 1.1 - 2.1 0.1 - 0.2 RME meal 0.64 - 1.21 0.46 - 0.89  84.6 - 95.5e) 0.11  -  0.21e)milk production meal direct and indirect energy 0.46 - 0.890.2g) milk h) manure heat, CH4 total 0.09 - 0.18 0.16 - 0.31 0.21 - 0.40 14.1 - 16.5 17.1 - 19.1 22.6 - 25.2 53.9 - 60.7 0.01 - 0.020.02 - 0.030.02 - 0.040.05 - 0.09anaerobic digestion manure heat and power 0.16 - 0.310.03 - 0.15biogasi) effluenti) 0.08 - 0.15 0.08 - 0.15 33.3 - 41.7 33.3 - 41.7 0.01 - 0.02 0.01 - 0.02power production  biogas 0.08  -  0.15 power heat 0.03 - 0.05 0.05 - 0.10 33.3 66.7 <0.01 <0.01 thermal collector sun energy manufacture 1000 2.3j)  heat  600 - 800  60 - 80  59.9 - 79.8 photovoltaic collector sun energy manufacture 1000 6 - 11k)  power  100 - 150  10 - 15  9.9 - 14.9 a)Direct and indirect energy input of Finnish agriculture is 0.83 kWh m-2 a-1, of which 0.34 kWh m-2 a-1 fossil fuels, of which 0.07 to 0.14 kWh m-2 a-1 diesel/RME (LAMPINEN et al. 2006, NYHOLM et al. 2005, ELSAYED et al. 2003, BUGGE 2000, SCHÄFER et al. 1986). b)Seed yield 160 to 310 g m-2; allocation of energy output: 1/3 seed, straw, and root respectively. c)In respect of oil. d)In respect of meal. e)In respect of oil/RME and meal. f)Oil extraction 416 Wh kg-1 seed; esterification 476 Wh kg-1 seed (CAMPA®- BIODIESEL GMBH & CO. KG 2006, http://www.campa-biodiesel.de/cadeunof/cadnumw3.htm). g)Estimated. h)Allocation: milk 20.2%; manure 34.4%; heat 40.4%; methane 5% (HORN et al. 1994). i)Allocation: 50% each.  j)Mass 15 kg m-2; estimated energy input for production 3.9 kWh kg-1; depreciation 25 years. k)KNAPP et al. 2000. The 5th International Scientific Conference on Sustainable Farming Systems                    E C O M I T    85converts rape meal feed into manure, which is suitable for anaerobic digestion together with glycerine. The biogas augments the overall efficiency additionally 0.2 to 0.5 ‰. Rape cultivation requires a 4 to 7-year crop rotation. This and the low overall efficiency make it difficult in Finland to achieve energy self-sufficiency on-farm replacing diesel fuel by RME. The technical efficiency of the photosynthesis limits the maximum energy yield and reaches up to 5 % of the insolation input in the tropics and up to 0.8 % in Finland (Lampinen & Jokinen 2006). Mainstream production renders better photosynthesis efficiencies in terms of increased biomass yield on expense of lower cultivation efficiencies because of high energy input triggered by mineral fertilisers and chemicals. Due to photosynthesis’ low efficiency, even a double biomass yield improves the overall efficiency only marginally. Vice versa, 20 to 56 % lower energy input in organic crop production (Mäder et al. 2002) increases only marginally the overall efficiency.    By comparison, the efficiency of a photovoltaic collector is 165 to 248-fold better than the conversion efficiency of biomass or biogas produced from rapeseed and rape straw into electric power. The efficiency of the thermal collector exceeds heat production from burning the rape crop 157 to 443-fold. However, storage and continuous production of power and heat from sun energy is very limited. For that reason, the storage of sun energy in liquid carbon hydrates is subject of present research. Future biotechnology produces hydrogen and liquid carbon hydrates by CO2 and H2O (Centi et al. 2006, Gattrell et al. 2007) or thermo-chemical processes (Abu-Hamed et al. 2007, Jeong et al. 2007) powered by sun energy.  A measure for sustainability of renewable energy is the ratio between energy yield from sun energy conversion and energy consumption per capita and square meter of a nation’s surface area. If we succeed, to convert insolation with an overall efficiency of e.g. 0.1% (bio-mass, solar technique etc.) into all types of energy needed, the surface area is not sufficient to cover the present energy consumption. Countries of high population density prove the most severe energy deficit, table 2.  Table 2: Sustainability of energy consumption assuming 0.1% overall conversion efficiency of insolation. (aEnergy and Environment Data Reference Bank (EEDRB), 2003.  http://iaea.org/inisnkm/nkm/aws/eedrb/data/FI-encc.html#c1, bŠúri M. et al. 2007, PVGIS © European Communities, 2001-2008) Country  BG CZ H  PL SK  SLO  FIN  L Surface areaa 1000 km2  110.9 78.9 93.0 312.7 48.9 20.3 304.5  2.6Populationa 106 capita  7.8 10.2 10.1 38.2 5.4 2.0 5.2 0.5Total energy consumptiona MWh capita-1 year-1 33.0 28.3 31.9 27.7 43.5 45.5 68.6  116.2Insolationb MWh m-2 a-1  1.3 1.0 1.2 1.0 1.1 1.2 0.8 1.0Sun energy yield  MWh capita-1 year-1  18.7 8.0 11.2 8.3 10.1 12.0 49.1  5.9Sustainability %  67.7 28.2 35.1 29.9 26.7 27.6 71.6  5.1  Conclusion Energy crop production is captivating with many win-win situations: environmentally neutral bio-fuels replace polluting fossil fuels, farmers get better prices for energy The 5th International Scientific Conference on Sustainable Farming Systems                    E C O M I T    86crops, the agrochemical industry gains from intensification of energy crop production, and turn over of power industry grows due to increasing energy consumption to produce agrochemicals and to process biomass into fuel. As a following, the state tax income improves too. However, better prices for mainstream energy crops may trigger export of environmental pollution at the expense of food production because higher overall efficiency in tropical countries favours the import of organic raw material for bio fuel production.  Yet, high process efficiencies of technical processes to convert biomass into fuel justify the production of renewable energy from organic waste and residues. Thus, agriculture policy should not focus on energy crop production but on production of high quality food environment-friendly. The overall efficiency of energy production from energy crops will never be competitive with solar techniques.  Solar collectors replace fossil fuels for heat production outside agriculture already now sustainably and more efficient. Research on solar-technical processes to produce liquid carbon hydrates from methane, carbon dioxide, and water powered by solar energy without diversion into photosynthesis offers much a greater potential than research on energy crop production.  Consequently, humankind has two ways only to warrant sustainable energy supply for the future: The first challenge is to increase the overall efficiency of techniques to convert sun energy into fuel and electric power by means of improved process efficiencies. Probably cheaper and more rapidly to achieve, is the second way: energy saving.  One kernel of grain or oil seed has the potential to generate up to 50 kernels and more cultivated on fertile land. No hedge fond guarantees a similar interest rate. That means the entropy of seed is very low, compared to the thermal energy content. Thus, why humankind should burn its food?   References Abu-Hamed T., Karni J., Epstein M. 2007. The use of boron for thermochemical storage and distribution of solar energy. Solar Energy 81: 93–101.  Bastianoni S., Facchini A., Susani L., Tiezzi, E. 2007. Emergy as a function of exergy. Energy 32: 1158–1162.    Centi G., Perathoner S. 2006. Converting CO2 to fuel: A dream or a challenge? The 232nd ACS National Meeting, San Francisco, CA, September 10-14, 2006, http://oasys2.confex.com/acs/232nm/techprogram/P990579.htm (12.01.2007). Ekbladh, G.; Grönlund, E.; Ingemarson, F.; Karlsson, L.; Nilsson, S. and Strid Eriksson, I. Doherty, S. and Rydberg, T., Eds. 2002. Ecosystem properties and principles of living systems as foundation for sustainable agriculture – Critical reviews of environmental assessment tools, key findings and questions from a course process. Ecological Agriculture – 32, Centre for Sustainable Agriculture, Swedish University of Agricultural Sciences, Uppsala, 84 p. Elsayed M., Matthews R., Mortimer N. 2003. Carbon and energy balances for a range of biofuels options. Project report number B/B6/00784/REP, Department of Trade and Industry Sustainable Energy Programme URN, 03/836, Resources Research Unit, Sheffield Hallam University, United Kingdom. Final Report for the Energy Technology Support Unit. Report No. 21/3, 27 p.  http://oasys2.confex.com/acs/232nm/techprogram/P990579.htm  (12.01.2007). The 5th International Scientific Conference on Sustainable Farming Systems                    E C O M I T    87Bugge J. 2000. Note: Rapeseed oil for transport 1: energy balance and CO2 balance. The Danish Energy Agency's Model for Economic And Environmental Assessment Of Biofuels, DK-7760 Hurup Thy,  http://oasys2.confex.com/acs/232nm/techprogram/P990579.htm  (12.1.2007). Gattrell M., Gupta N., Co A. 2007. Electrochemical reduction of CO2 to hydrocarbons to store renewable electrical energy and upgrade biogas. Energy Conversion and Management 48:1255–1265.       van Horn H., Wilkie A., Powers W., Nordstedt R. 1994. Components of dairy manure management systems. J. Dairy Sci. 77: 2008-2030. Tae-Young Jeong, Gi-Cheol Cha, Ik-Keun Yoo and Dong-Jin Kim 2007. Hydrogen production from waste activated sludge by using separation membrane acid fermentation reactor and photosynthetic reactor. International Journal of Hydrogen Energy, 32: 525-530. Jiang M.M.,  Chen B., Zhou, J.B.  Tao F.R., Li Z., Yang Z.F., Chen G.Q.  2007. Emergy account for biomass resource exploitation by agriculture in China. Energy Policy 35: 4704–4719. Kauppa- ja teollisuusministeriö, 2007. Energiakatsaus 2/2007, 39s. Knapp E., Jester T.  2000. An empirical perspective on the energy payback time for photovoltaic modules. American Solar Energy Society Solar 2000 Conference, Madison, Wisconsin June 16-21, 2000, http://oasys2.confex.com/acs/232nm/techprogram/P990579.htm (12.01.2007). Lampinen A. Jokinen E. 2006. Suomen maatilojen energiatuotantopotentiaalit. University of Jyväskylä, bio- ja ympäristötieteiden laitos. Research reports in biological and environmental sciences 84: 1-160. Mäder P., Fließach A., Dubois D., Gunst L. Fried P., Niggli U. 2002. Soil fertility and biodiversity in organic farming. Science 296: 1694-1697. Odum, H.T. 1996. Environmental Accounting, Emergy and Decision Making. John Wiley, NY, 370 pp. Patzek T. 2004. Thermodynamics of the corn-ethanol biofuel cycle. Critical Reviews in Plant Sciences 23: 519-567. Pimentel, D., Rodrigues , Wang T., Abrams R., Goldberg K., Staecker H., Ma E., Brueckner L., Trovato L., Chow C., Govindarajulu U., Boerke S. 1994. Renewable Energy: Economic and Environmental Issues. BioScience, 44: 536-547. Ukidwe N.U.,  Bakshi B.R. 2007. Industrial and ecological cumulative exergy consumption of the United States via the 1997 input–output benchmark model. Energy 32: 1560–1592. Schäfer W., Luomi, V. Palva, T. Parmala, S. Ahokas, J. 1986. Kasviöljyt dieselmoottorin polttoaineena. VAKOLAn tutkimusselostus 42:1-37. SFS-EN ISO 14040 Ympäristöasioiden hallinta. Elinkaariarviointi. Periaatteet ja pääpiirteet Environmental management. Life cycle assessment. Principles and framework (ISO 14040:2006) 49 s.      

Sustainability, overall and process efficiency of energy crops

Abstract

Similar works

Full text

Available Versions

Organic Eprints

Jukuri