MACHINERY SYSTEMS IN TROPICAL
AGRI-FOOD CHAINS
Francesco Garbati Pegna
Lesson 2
Energy
ENERGY
Energy is the capacity of a physical system to perform
work
(a system possesses energy if it has the ability to do work)
According to the law of conservation of energy, the total energy of a system
remains constant, though energy may transform into another form.
Forms of Energy
. mechanical
Potential / Kinetic (movement)
. gravitational
. electromagnetic
. nuclear
. thermal
. electrical
. electromagnetic radiation
In the SI the unit of energy is the Joule that is the amount of energy transferred
to an object by the mechanical work of moving it 1 m against a force of 1
Newton.
ENERGY
Almost all energy available on our planet comes directly or
indirectly from the sun :
• hydraulic energy,
• wind energy,
• chemical energy of fossil fuels (coal, petrol and natural gas) and of
biomasses (i.e. wood)
• energy of waves.
• tidal energy comes from the gravitational fields of Sun, Moon and Earth
geothermal energy and nuclear energy instead date back to the formation
of Earth (they don’t derive from transformation of sun energy).
Agriculture needs energy inputs, in various and different forms
Agriculture is itself an energy conversion process, namely the conversion of
solar energy through photosynthesis to food energy for humans and feed for
animals.
Primitive agriculture involved little more than scattering seeds on the land and
accepting the scanty yields that resulted.
Modern agriculture requires an additional energy input at all stages of agricultural
production such as direct use of energy in farm machinery, water management,
irrigation, cultivation and harvesting.
Post-harvest energy use includes energy for food processing, storage and in
transport to markets.
In addition, there are many indirect or sequestered energy inputs used in
agriculture in the form of mineral fertilizers and chemical pesticides, insecticides and
herbicides.
http://www.fao.org/docrep/003/X8054E/x8054e05.htm
This energy can be measured and for each agricultural process an
energy balance can be drawn
Agricultural inputs and outputs can be expressed in terms of energy
Energy input and outputs can be used to assess energy efficiency and
environment impact of an agricultural process.
An energy balance is based on total non-renewable energy consumed by the
process and on the gross energy stored in the process products; the balance can
be used to determine also the energy efficiency of a process.
Energy inputs include sources of direct energy (i.e. fuel, food, etc.) together with
the energy consumed to obtain all other material inputs, from the extraction of
raw materials to the final product available at the entrance of the farm, (farm
equipment, fertilizers, pesticides etc.). Energy output is the energy of agricultural
products, byproducts and other useful outputs (i.e. heat) obtained from the
process. Energy balance is usually expressed per unit of land surface (i.e. MJ/ha)
or of product (i.e. MJ/t).
Energy efficiency is used to compare two different processes or alternatives on an
energy-use point of view and is expressed in the form of an I/O ratio
Energy analysis provides a relevant view of the specificity of
agriculture, as a user and a producer of energy simultaneously.
This distinctive feature makes agriculture play a specific role in
CO2 cycles, thanks to the phenomenon of photosynthesis. With
forestry and some other human activities utilizing renewable
energies, agriculture is the only human occupation which may
produce more energy than it had consumed.
Ralph C. Martin, Rod MacRae, 2014, Managing Energy, Nutrients, and Pests in Organic Field Crops
Bernadette Risoud, 2000, Energy efficiency of various French farming systems: questions to sustainability
Risoud, 2000
Each input can be quantified in terms of energy …
Risoud, 2000
… and operations
It is possible to calculate energy inputs and outputs for a certain process
(i.e. cultivation)
Also other parameters can be calculated for agricultural inputs
besides energy
Energy balance and energy efficiency can be used as indicators
but they are not directly linked to the economic balance of a
process since a process can have a good energy balance and a
poor economic balance (i.e. forestry in some cases) and vice versa
(i.e. production of off-season vegetables in greenhouses, of high
tech wines, etc.), but the variation of energy efficiency in a single
process always directly affects its economic balance
EXERCISES
(choose one):
1 – Compare an energy balance and an economic balance for an
agricultural process and explain when the energy balance can be
useful
2 - Understand what Life Cycle Analysis is and how it can be useful
for agriculture,
Make a short Presentation