Farming Systems Design 2007 - International Environmental ...

Farming Systems Design 2007
Field-farm scale design and improvement
efficiency of the energy chain (from solar energy to mechanical energy). While PV reaches 4.9%,
hydrogen attains 0.9 % and ethanol 0.04 % only. This values correspond to 43.5 toe/ha for PV, 8.3
toe/ha for hydrogen and 0.38 toe for ethanol respectively.
If we consider oil from rapeseed instead of ethanol from wheat, we can analyse that i) the energy
balance is better (only 0.33 MJ of non renewable energy for 1 MJ delivered energy), ii) the yield
per ha is lower (1370 litres of oil for 3.3 t grain instead of 2550 litres of ethanol for 9 t grain), iii) the
energetic content is higher (37.2 MJ/kg instead of 26.8) (ADEME 2002 and 2006). Finally, the
renewable energy produced is not better with 34.1 GJ/ha vs 34.8 for ethanol.
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This study may appear very theoretically hence the presented technologies are subject of
continuous development. However, the aim is to show the gap between bio fuel from energy crops
and PV fuel. Such large differences of efficiencies show clearly where to set priorities for the long
term research. Research on solar-technical processes to produce thermo chemical fuels (Abu-
Hamed et al. 2007) or liquid carbon hydrates from methane, carbon dioxide and water powered by
solar energy without diversion into photosynthesis (Gattrell et al. 2007, Centi & Perathoner 2006)
offers much a greater potential than research on energy crop production.
Setting the priority for one or the other of these two pathways may have a strong impact either on
economics or on environmental issues, or even on food resources and social aspects. For
example, production of PV energy needs only 1 % of the area provided for energy crops and the
saved 99 % of the area compensate more than the lower yield of organic farming area in terms of
food quantity per ha. Organic farming plus PV energy production reduce not only energy
consumption for food production but also reduce environmental pollution.
Another advantage of PV energy is that it can be produced not only on the poorest arable lands
but also on the roofs of the buildings, whether they are agricultural, industrial, or urban. Installation
of solar panels in mountain areas improves the efficiency of PV because of lower temperature and
reduces competition for better lands.
Presently, the energy of one hour insolation reaching the earth would be enough to cover the
annual energy consumption of the world. One challenge for research is to use solar energy as
directly as possible with the minimum of transformations. Therefore, the direct technical use of sun
energy allows i) to satisfy the food needs of the humanity, ii) to reduce inputs with strong negative
impacts on the environment and on human health, iii) to reserve a part of arable land for the
production of non alimentary agricultural products (fibres, drugs, feedstocks).
The agricultural sector in Europe consumes more energy than it produces. The major part of
biomass produced for feedstocks and food remains energetically unused. Organic waste is the
right source for biofuel production hence it requires only energy for conversion and storage. We
suppose that the progress based on research and development will not impugn these conclusions.
Abu-Hamed T. et al 2007: The use of boron for thermochemical storage and distribution of solar energy.
Solar Energy 81 (2007) 93–101.
ADEME 2006, Energy and GHG balances of biofuels and conventional fuels. Convergences and
divergences of main studies, Study realized for ADEME by ECOBILAN, 18p.
ADEME 2002, Bilans énergétiques et gaz à effet de serre des filières de production de biocarburants en
France. Note de synthèse (décembre 2002). ADEME-DIREM-PRICE WATERHOUSECOOPERS, 19p.
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,
Elsayed M. et al 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, Un.Kingdom. Final Report for the Energy Technology
Support Unit. Report No. 21/3, 27 S. http://www.dti.gov.uk/files/file14925.pdf?pubpdfdload=03%2F836
Gattrell M. et al 2007. Electrochemical reduction of CO2 to hydrocarbons to store renewable electrical
energy and upgrade biogas. Energy Conversion and Management 48:1255–1265.
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