Annex
A.1:
Indicators of energy use in agriculture
FAO has initiated work on the development of energy
indicators of sustainable agriculture. The definition for the basic indicator is
the energy utilized in agriculture on a yearly basis expressed as a ratio of
energy inputs and agricultural production as well as in absolute terms. This is
measured in unit of Joules per tonne of agricultural products, and its purpose
is to provide a measure of energy intensity in agriculture.
The development of this indicator is highly relevant to
sustainable development. Energy is essential for most human activities,
including agriculture. Too little energy makes it difficult to obtain decent
productivity and meet food requirements. Too much energy signifies waste, global
warming, and other stress on the environment. The indicator can guide policies
and investments regarding (i) energy requirements in all stages of agricultural
production in order to measure agricultural productivity and, (ii) energy
efficiency, to reduce energy intensity. The indicator is relevant to promote an
increase in agricultural production with a parallel increase in energy
efficiency. The indicator is closely related to the energy indicators under
consumption and production patterns. It is also linked to environmental
indicators such as land condition change and emissions of greenhouse gases.
Total energy consumption in agriculture derives from the
energy inputs in all stages of agricultural production and processing, that is
land preparation, mechanization, fertilization, irrigation, harvesting,
transport, processing, and storage. Each of these stages uses different forms of
energy (mechanical, electrical, thermal) which can be aggregated in equivalent
units. Total agricultural production is an established concept and needs no
further elaboration.
Annual energy inputs for each stage in agricultural
production and processing are determined
and converted into equivalent units such as terajoules
(TJ) and aggregated as total energy. Annual agricultural production figures are
collected for all products. The obtained values are then compared for the same
year, and can be tracked over time to see how changes in both terms affect their
ratio. At present, no international targets exist or apply. At the national
level targets could be developed, depending on the country's range of
agricultural products.
Agricultural production is affected by factors other
than energy inputs (for example, climate, availability of other inputs). These
factors are less distorting if comparative values are collected for consecutive
years. Data for energy use in agriculture at the present time are not considered
to be very reliable. Special surveys could generate sound data, but would be
expensive, and may not be a priority for statistical agencies. The indicator
could be expanded to include non-commercial energy inputs, such as human and
animal power. Human power quantification methodologies might need to be further
elaborated. The relevance of this alternative to sustainable development is
questionable.
Data are needed on energy inputs for different
agricultural activities and on agricultural production. Some data are available
for most countries, although reliable and comprehensive statistics to enable
time-series analysis are elusive. Energy balances are prepared by energy
ministries or other competent national authorities. Agricultural production
figures are available from agriculture ministries. FAO has processed and
compiled considerable data in both energy and production at the international
level.
A.2: Bioenergy terminology and database29
Bioenergy systems are complex and any final energy use
can be supplied by different technologies using many kinds of biomass as fuel
(Figure A.1). For instance, either sugar (food product) or alcohol (usually for
energy) can be produced as a main product from sugarcane, but in both processes
an important amount of bagasse is yielded. Bagasse is a solid lignocellulosic
by-product, which can be used to produce either heat and electricity by direct
combustion, or more alcohol, using acid or enzymatic hydrolysis. Fuelwood can be
derived from different sources, both native and planted forests, as well as from
by-products of forest industries (sawmills, particle board plants, etc.) and is
used by different sectors, such as households, rural industries and commercial
activities. This intrinsic complexity is relevant and should be properly
considered when a bioenergy database is created.
Figure A.1:
Generic Bioenergy System
Table A.1 lists a biofuel classification, which
recognizes the basic site where biomass production occurs. The groups on the
supply side deal with important sub-divisions, which identify the origin of
biofuels. On the user side, a variety of fuels can be produced for each group.
Listed on the right side of Table A.1 are the different types and qualities of
primary, secondary and even tertiary fuels which can be used for heat,
electricity and power generation. The secondary and tertiary fuels are often
derived from raw biomass produced from different supply sources after the
application of more or less complex transformation processes. Brief definitions
of the main terms adopted are listed in Table A.2.
Table A.2:
Definition of Biofuel Classifications
1st level |
2nd level |
Brief definition |
Woodfuels |
Direct
Woodfuels |
Wood used directly or indirectly as fuel, produced
for energy purposes |
|
Indirect
Woodfuels |
Mainly solid biofuels produced from wood
processing activities |
|
Recovered
Woodfuels |
Wood used directly or indirectly as fuel, derived
from socio-economic activities outside the forest sector |
|
Wood-derived
fuels |
Mainly liquid and gaseous biofuels produced in
forest activities and the wood industry |
Agrofuels |
Fuel crops |
Growing plants for the production of
biofuels |
|
Agricultural by-products
|
Mainly residues from crop harvesting and other
kinds of by-products from agricultural activities left in the
field |
|
Animal
by-products |
Basically excreta from cattle, horses, pigs and
poultry |
|
Agroindustrial
by-products |
Several kinds of materials, produced chiefly in
food processing industries, such as bagasse and rice husks |
Municipal
by-products |
Solid and liquid municipal
residues |
Detailed
definitions
- Biofuels: organic primary and/or secondary fuels derived from biomass which can be used for the generation of thermal energy by combustion or by using other technology. They comprise both purpose-grown energy crops, as well as multipurpose plantations and by-products (residues and wastes). The term "by-products" includes the improperly called solid, liquid and gaseous residues and wastes derived from biomass processing activities. There are three main biofuel categories: Woodfuels, Agrofuels and Municipal wastes.
- Woodfuels: include all types of biofuels derived directly and indirectly from trees and shrubs grown in forest and non-forest lands. Woodfuels include biomass derived from silvicultural activities (thinning, pruning etc.) and harvesting and logging (tops, roots, branches, etc.), as well as industrial by-products derived from primary and secondary forest industries which are used as fuel. They also include woodfuels derived from ad hoc forest energy plantations. Taking into account the available database, it is interesting to classify woodfuels into four groups: Direct woodfuels, Indirect woodfuels, Recovered woodfuels
and Wood-derived fuels, as defined as follows.
- Direct Woodfuels:
consists of wood directly removed from Forests (natural forests and plantations; land with tree
crown cover of more than 10% and area of more than 0.5 ha);
- Other Wooded Lands (land either with a tree crown cover of 5-10% of trees able to reach a height of at least 5 m at maturity in situ; or crown cover of more than 10% of trees not able to reach a height of 5 m at maturity in situ, and shrub or bush cover); and Other Lands to supply energy demands and includes
both inventoried (recorded in official statistics) and non-inventoried
woodfuels. Direct woodfuels can be divided into primary and secondary fuels,
depending on whether they are directly burned or are converted into another
fuel, such as charcoal, pyrolysis gases, pellets, ethanol, methanol, etc.
- Indirect Woodfuels:
usually consists of industrial by-products, derived from primary (sawmills,
particle boards, pulp and paper mills) and secondary (joinery, carpentry) wood
industries, such as: sawmill rejects, slabs, edging and trimmings, sawdust,
shavings and chips bark, etc. They preserve essentially the original structure
of wood and can be used either directly or after some conversion to another
biofuel.
- Recovered Woodfuels:
refers to woody biomass derived from all economic and social activities
outside the forest sector, usually wastes from construction sites, demolition
of buildings, pallets, wooden containers and boxes, etc., burned as they are
or transformed into chips, pellets, briquettes, powder, etc.
- Wood-derived fuels:
refers to woodfuels produced in the forest sector, which require several
thermochemical processes before use. They do not preserve any trace of the
original wood's physical structure, as is the case with black liquor and
methanol produced from wood.
- Black liquor: is the
alkaline-spent liquor obtained from the digesters in the production of
sulphate or soda pulp during the process of paper production, in which the
energy content is mainly derived from the content of lignin removed from the
wood in the pulping process.
- Agrofuels: fuel obtained as a product of agriculture biomass and by-products. It covers mainly biomass materials derived directly from fuel crops and agricultural, agroindustrial and animal
by-products.
- Fuel crops: is employed to describe species of plants cultivated on fuel plantations or farms to produce raw material for the production of biofuel. The fuel crops can be produced on land farms (manioc, sugar cane, euphorbia, etc.), on marine farms (algae) or in fresh water farms (water hyacinths). The land-produced fuel crops can also be classified under: sugar/starch crops, oil
crops and other energy crops. Sugar/starch
crops: are crops planted basically for the production of ethanol (ethyl alcohol) as a fuel mainly used in transport (on its own or blended with gasoline). Ethanol can be produced by the fermentation of glucose derived from sugar-bearing plants (like sugar-cane) or starchy materials after hydrolysis. Oil crops: cover oleaginous plants (like sunflower, rape, etc.) planted for direct energy use of vegetable oil extracted, or as raw material for further conversion into a diesel substitute, using trans-esterification processes. Other energy
crops: include plants and specialized crops more recently considered for energy use, such as: elephant grass (Miscanthus), cordgrass and galinggale (Spartina spp. and Cyperus longus), giant reed (Arundo donax) and reed canary grass (Phalaris arundinacea).
- Agricultural by-products:
are mainly vegetal materials and by-products derived from production,
harvesting, transportation and processing in farming areas. It includes, among
others, maize cobs and stalks, wheat stalks and husks, groundnut husks, cotton
stalks, mustard stalks, etc.
- Agroindustrial
by-products: refer to food processing by-products, such as sugar-cane
bagasse, rice/paddy husks and hulls, coconut shells, husks, fibre and pith,
ground nut shells, olive pressing wastes, etc.
- Animal by-products: refer to dung and other excreta from cattle, horses, pigs, poultry and, in principle, humans. It can be dried and used directly as a fuel or converted to biogas by fermentation. Biogas: is a by-product of
the anaerobic fermentation of biomass, principally animal wastes by bacteria.
It consists mainly of methane gas and carbon dioxide.
- Municipal By-products:
refer to biomass wastes produced by the urban population and consist of two
types of products: solid municipal by-products and gas/liquid municipal
by-products produced in cities and villages.
- Solid municipal biofuels:
comprise by-products produced by the residential, commercial, industrial,
public and tertiary sectors that are collected by local authorities for
disposal in a central location, where they are generally incinerated
(combusted directly) to produce heat and/or power. Hospital waste is also
included in this category.
- Gas/liquid municipal
biofuels: correspond to biofuels derived principally from the anaerobic
fermentation (biogas) of solid and liquid municipal wastes which may be
land-fill gas or sewage sludge gas.
The most commonly used types of woodfuels are fuelwood and charcoal, which can be burned in both
traditional and modern energy systems for cooking, heating or power. These main
woodfuels can be recognized under this category (fuelwood and charcoal) even
when other fuels, such as chips, wood powder, pellets, briquettes, methanol,
ethanol, pyrolysis gases, producer gas, etc., can also be derived from the
previously mentioned main supply sources.
- Fuelwood: includes "wood in the rough" in small pieces (fuelwood), chips, pellets and/or powder derived from forests and isolated trees, as well as wood by-products from the wood products industry and from wasted wood products. When needed, fuelwood can be prepared into more convenient fuels, such as chips and pellets. Chips: wood that has been deliberately reduced to small pieces from wood in the rough, or residues suitable for energy purposes. Wood pellets: can be considered as a fuel derived
from the auto-agglomeration of woody material as the result of a combined
application of heat and high pressure in an extrusion machine.
- Charcoal: refers to a
solid residue derived from the carbonization, distillation, pyrolysis and
torrefaction of wood (from the trunks and branches of trees) and wood
by-products, using continuous or batch systems (pit, brick and metal kilns).
It also includes charcoal briquettes, made from wood-based charcoal which,
after crushing and drying, is moulded (often under high pressure), generally
with the admixture of binders to form artefacts of even shapes.
Parameters and Units
Energy sources and commodities may be measured by their mass or weight or still volume, but the essential factor is the energy content related to these sources and commodities. That energy worth must be evaluated in terms of energy parameters, always using standard units. This standardization in the recording and presentation of original units is a primary task of energy and forestry statisticians before quantities can be analyzed or compared. It is recommended that for international reporting, and as far as possible in national accounting procedures, energy and forestry statistics should use the International System of Units, officially abbreviated to SI. Two basic relationships for bioenergy evaluation are introduced as follows, keeping in mind that both the heating value and density depend mainly on the moisture of the biofuel.
(1)
(2)
- Mass: most solid
biofuels, such as wood and agrofuels, are measured in units of mass, as are
many liquid fuels. The principal units of mass used to measure energy
commodities include the kilogram and the metric ton. The metric tonne is the
most widely adopted.
- Volume: units of volume are original units for most liquid and gaseous, as well as some solid, fuels (woodfuel, charcoal, etc.). The basic SI units of volume are the litre and the kilolitre, which is equivalent to the cubic metre. The stere or stacked volume, usually considered as equal to 0.65 solid cubic meter, has been widely used in the past when measuring the woodfuel volume. Current preference is to measure timber and fuelwood using solid volume units, usually in cubic meter. One
advantage of measurements by volume is the relatively small influence of the
moisture content of the wood on the measurement results. The more water per
unit weight, the less fuelwood. Therefore, it is imperative that the moisture
content be accurately specified when fuelwood is measured by weight.
- Density: the density of
wood, i.e., the weight per unit of volume, varies widely between different
wood species and types. The density of an air-dried hardwood, such as mahogany
or ebony, is around 1 000 kg/cum. The air dried density of a really
lightweight wood, such as balsa, is as low as 160 kg/cum. The usual species
used for fuelwood are around 500 and 600 kg/cum.
- Moisture: the amount of
water in biofuel affects, in a decisive manner, the available energy of every
biofuel. Two methods (dry and wet basis) are commonly used to specify the
moisture content, depending on the adopted basis used to account for the water
mass. It is important to distinguish between them, especially when the
moisture content is high.
(3)
(4)
The wet weight refers to the burned condition and the dry weight refers to wood
after a standardized drying process. It is important to state on which basis the
moisture content is measured.
- Ash content: another
important factor of the biofuel energy content is the ash content, always
measured on the dry basis, which refers to the solid residue remaining after
the complete combustion. While the ash content of fuelwood is generally around
1%, some species of agrofuels can register a very high ash content. This
affects the energy value of the biofuels since the substances that form the
ashes generally have no energy value. Thus dry woodfuels with a 4% ash content
will have 3% less energy than biomass with a 1% ash content.
- Heating value (or calorific value): biofuel is essentially a material for burning as fire or as a thermal source of energy. The amount of thermal energy stored can be measured through the heating value or calorific value of fuels. The higher heating value (HHV), or gross calorific value (GCV), measures the total amount of heat that will be produced by combustion. However, part of this heat will be locked up in the latent heat of the evaporation of any water existent in the fuel during combustion. The lower heating value
(LHV), or net calorific value (NCV), excludes
this latent heat. Thus, the lower heating value is that amount of heat which
is actually available from the combustion process for capture and use. The
higher the moisture content of a fuel, the greater the difference between GCV
and NCV and the lesser the total energy available, as shown in Figure A.2.
Figure A.2:
Effect of moisture (wet basis) on heating value
Charcoal - When
statistically recording the conversion from fuelwood (or woodfuels) to charcoal,
three principal aspects must be dealt with: wood density, moisture content of
the wood, and the means of charcoal production. The yield of charcoal from
fuelwood, using different types of kiln, is presented in Table A.3. (165 kg
of charcoal is produced from one cubic meter of fuelwood).
Table A.3: Fuelwood required for charcoal production (m3/ton of charcoal)
Kiln
type |
Fuelwood
moisture (%, dry basis) |
|
15 |
20 |
40 |
60 |
80 |
100 |
Earth kiln |
10 |
13 |
16 |
21 |
24 |
27 |
Portable steel kiln |
6 |
7 |
9 |
13 |
15 |
16 |
Brick kiln |
6 |
6 |
7 |
10 |
11 |
12 |
Retort |
4.5 |
4.5 |
5 |
7 |
8 |
9 |
Agrofuels - The energy
values of agricultural by-products are determined by its moisture content and
its ash content. Data for these energy sources are rarely collected directly but
are derived from crop/waste or end-product/waste ratios. Bagasse is used as a
fuel mostly for the sugar industry's own energy needs, but surpluses are sold to
the public grid in many sugar-producing countries. Table A.4 presents data for
typical agricultural by-products.
Table A.4:
Energy data for selected agricultural by-products
Product |
Moisture |
Approx. Ash
content |
LHV |
|
(%, dry basis) |
(%) |
(MJ/kg) |
Bagasse |
40-50 |
10-12 |
8.4-10.5 |
Groundnut shells |
3-10 |
4-14 |
16.7 |
Coffee husks |
13 |
8-10 |
16.7 |
Cotton husks |
5-10 |
3 |
16.7 |
Coconut husks |
5-10 |
6 |
16.7 |
Rice hulls |
9-11 |
15-20 |
13.8-15.1 |
Olives (pressed) |
15-18 |
3 |
16.7 |
Oil-palm fibres |
55 |
10 |
7.5-8.4 |
Oil-palm husks |
55 |
5 |
7.5-8.4 |
Corncobs |
15 |
1-2 |
19.3 |
Rice straw and husk |
15 |
15-20 |
13.4 |
Wheat straw and husk |
15 |
8-9 |
19.1 |
The main factors to be used for bioenergy accounting
cover several kinds of biofuels and considering the usual information available
from primary data sources. The objective here is to obtain the energy worth of a
mass or volume flow of some biofuel, so expressions (1) and (2), already
presented above, must be used. However, taking into account the substantial
variations in heating value and volume with moisture, it is advisable to express
the values of biofuels in a dry and without ash basis, especially for accounting
in energy balances. Table A.5 presents values for density and the heating
value for typical moisture content.
Table A.5:
Basic parameters in accounting biofuels
Biofuel |
Primary Data |
Density |
LHV |
Moisture |
|
|
(kg/cum) |
(MJ/kg) |
(%, dry basis) |
Direct Woodfuels |
Volume |
0.725 |
13.8 |
30 |
Charcoal |
Mass, volume |
|
30.8 |
5 |
Indirect Woodfuels |
Mass, volume |
0.725 |
13.8 |
|
Recovered Woodfuels |
mass, volume |
0.725 |
|
|
Wood-derived fuels |
mass |
- |
|
|
Black liquor |
mass |
|
|
|
Methanol |
mass |
|
20.9 |
0 |
Non-forest Biofuels |
mass |
- |
|
|
Ethanol |
mass |
|
27.6 |
0 |
Agricultural by-products |
mass |
(see Table 4) |
Animal by-products |
mass |
- |
13.6 |
|
Agroindustrial by-products |
mass |
- |
|
|
Bagasse |
mass |
- |
8.4 |
40 |
Municipal wastes |
mass |
- |
19.7 |
- |
A.3:
Recommendations to promote Photovoltaics for Sustainable Agriculture and Rural
Development
The following is a package of recommendations arising
from the FAO study directed at promoting cooperation between institutions from
the energy, agricultural and rural development sectors with the aim to use the
opportunities that PV systems offer in contributing to Sustainable Agriculture
and Rural Development (FAO, 2000a). These recommendations are the result of an
assessment of the experiences collected in this study, enriched with other
discussions and inputs. They are intended to provide a set of activities for
different stakeholders involved in the process of PV electrification and rural
development. It is clear that the main responsibility for action lies with
national development authorities. The role of technical cooperation agencies
such as FAO is to support these national efforts.
Policy
and planning
- National governmental policies need to be established
to promote the important role that renewable energies in general, and solar
photovoltaic systems, in particular, can play in achieving sustainable
agriculture and rural development;
- these policies should guide the establishment of
plans, programmes and targets of the agricultural, energy and environmental
sectors, and should also create the appropriate environment and the necessary
regulatory and normative context for the role of the private sector and
non-governmental institutions;
- synergies as identified when PV applications are
promoted simultaneously in various sectors of rural society, should be built
into policies and programmes;
- policies in the electricity sector should establish
the role of independent power producers and the rules to be followed by both
power producers and purchasers;
- policies and programmes should also establish the nexus with international efforts to reduce CO2
emissions and fulfil the goals and targets of the Climate Change Convention
and the Kyoto Protocol;
Research
and development
- Research is further needed to assess the
replicability of promising PV applications and the conditions under which they
are successful;
- further research efforts are required for the
optimization of PV systems for agricultural use (panels, electronics,
applications and end-uses), in order to develop optimized services or product
packages, e.g. optimized irrigation systems (panels, electronics, pumps and
drip-irrigators) for economic irrigation and fertilization;
- such efforts should be accompanied by assessment of
the life cycle technical and economic behaviour of theses PV systems, and by
the development of accompanying training and dissemination programmes;
- other areas of continued research and development are
low energy consuming appliances (such as affordable low energy consumption
refrigerators) and PV/diesel and PV/wind hybrid energy systems;
- research should also include the development of
quality standards, e.g. for agricultural applications, in combination with
mechanisms to implement these standards;
Finance
- Rural and agricultural development banks should
include PV systems as eligible for loans;
- innovative financing channels should be explored,
including the possibility of applying the CDM to PV systems; it is expected
that investments in productive uses (agriculture) of PV will be easier to
finance than Solar Home Systems because of the income generated by the former;
- as for many other products, equal access to credit by
women is required, which would increase their chances to use PV for household
and income generating opportunities;
- private sector investments can and should be
attracted for financing of PV electrification programmes; international donor
funds, soft terms loans and other seed capital can be used as a leverage for
such private sector investments.
Demonstration, implementation and marketing
- Demonstration and promotion are required for PV
applications such as drip-irrigation, cattle watering, PV electric fences and
aquaculture applications, to be integrated in agricultural development
programmes;
- demonstration and promotion of small PV systems for small cottage industry activities are needed to increase the awareness and knowledge of PV contribution to micro-enterprise development. A possible and innovative approach could be based on PV powered
micro-enterprise development zones or business
incubator, through the installation of multi-purpose or multi-service PV
units, that can deliver power for income generating activities and common
access to phone/fax/web;
- demonstration projects, not done in isolation, but as
an intrinsic component of an implementation plan, should include all main
stakeholders, including the private sector and government; results of these
demonstration efforts should be made public;
- subsidies, when necessary, should be transparent,
targeted and time-framed within a gradual phase-out plan; otherwise subsidies
should be limited to those PV applications for basic social services such as
education, health care, etc.;
Training/information/education/awareness
- Agriculture and other rural extension services should
become agents to identify potential PV applications; information and training
in this field is required;
- training packages are required for preparing PV
installation, operation, maintenance and repair services, but also in the use
of PV for various agricultural applications, e.g. improved irrigation
techniques;
- particular attention should be given to information
and training of women, as main users especially of household systems, and
academic curricula at all levels should be prepared and incorporated into
educational programmes.
Institutions
- The complex institutional set-up behind SARD needs to
be "energized" by the institutions dealing with energy, in general, and with
PV systems, in particular;
- to this end, intersectoral efforts are required to
bring closer the plans, programmes and policies identified above; this
involves the agriculture, energy, health, education and environmental sectors
in particular;
- such intersectoral collaboration is critical since
small renewable energy systems can have a significant and durable impact on
rural development if applied in "packages" in, for instance, agriculture and
social services (e.g. communication, education, health care);
- synergies as identified when PV applications are
promoted simultaneously and in an integrated approach in various sectors
should be built into collaborative implementation and marketing strategies;
- there is a scope for developing a plan for action for
the integration of rural energy delivery programmes with micro-enterprise
development programmes; mutual benefits could be gained: PV electricity rural
markets can become a source and stimulus for both Energy Service Companies and
for small "electrified" entrepreneurial activities;
- since PV systems normally require more involvement of
the end-user than conventional grid electricity, the involvement of farmers'
and other end-users' organizations in all phases of PV programme design and
implementation is critical; failure to achieve ownership will most probably
lead to failure of the programme.