Felichesmi Selestine Lyakurwa
Mzumbe University, Tanzania, United Republic of
E-mail: felichesmi@gmail.com
Submission: 15/04/2016
Revision: 23/06/2016
Accept: 02/07/2016
ABSTRACT
Energy
access has a significant contribution to the social, economic and environmental
dimensions of human development. The access to clean and safe energy can
improve the human health and quality of ecosystems by reducing the extent of
pollution caused by use of inefficient cooking equipment’s and processes, and
by slowing environmental degradation. In this paper, Monte Carlo simulation was
applied to evaluate the amount of crop residues available which provided the
basis for the quantity of energy that can be generated from the crop residues
and animal wastes in Tanzania. The amount of crop residues and animal wastes
was estimated from the agricultural statistical data obtained from the Food and
Agriculture Organization of the United Nations (FAO) from 1961 - 2012. The
analysis revealed the bioenergy potential of crop residues in Tanzania to be
5,714TJ in 2012, which is extremely larger than the installed electric energy
generation capacity of 1.564TJ in 2013. Besides, the estimation of renewable energy
potential of live animals indicated the ability to generate 1,397TJ/year if
exploited. Thus, effective utilization of crop
residues and animal wastes without compromising the amount required for the
soil fertility and animal feeds can contribute greatly to the access of safe
and clean energy for sustainable development of the rural and urban areas of
Tanzania.
Keywords: Energy, Monte Carlo, Crop residues, Animal wastes,
Tanzania
1. INTRODUCTION
Sustainable development in the
world, especially developing countries of Africa and Asia are challenged by
access to reliable and clean energy, greenhouse gas emissions (GHG) and high
price of fossil fuels (FELIX; GHEEWALA, 2011; SONG, et al., 2014; ZHAO et al.,
2016). The world energy council (WEC) documented that, about 1.2 billion of the
world population have access to energy and if crucial actions are not taken the
number will decrease to 500 million by 2050 (WEC, 2015).
Development of abundant energy
sources from both renewable and non-renewable can provide safe, affordable,
reliable and environmental friendly energy that spur the economic growth,
social development and universal energy access in developing countries (TAULO, 2015; ISMAIL; KHEMBO, 2015; RAYA, et al., 2016).
To date, agriculture residues have
been ascertained to be a potential renewable energy source in different
countries of the world, whereby systematic studies were conducted to probe the
competing uses of crop residues at the national level (GÓMEZ, et al., 2010;
DUKU, et al., 2011; SONG, et al., 2014; MONFORTI, et al., 2015).
For example, the biomass energy
accounts for 92% of the total energy consumption in Tanzania, and projected to
dominate the national energy balance. The renewable energy sources such as
fuel-wood and agricultural residues used to meet rural energy needs in Tanzania,
accounts for the 80% of the rural energy requirements, while commercial
energies such as kerosene, electricity and liquefied petroleum gas contributes
about 1% of the national energy consumption (SHEYA; MUSHI, 2000; FELIX;
GHEEWALA, 2011).
Besides, the energy balance of Tanzania
indicates an energy shortage, when comparing the installed capacity for
electricity production (700MW) and the electricity demand (900MW) which calls a
need for development of renewable energy technologies. An interesting story is
that, to date, majority of the people especially those residing in the rural
areas of Africa depends on wood, animal dung and charcoal for cooking, lighting
and warming their bodies.
A simple hypothesis can be,
developing countries do not have appropriate technology for value adding on the
raw wood/charcoal/animal dung to a more advanced source of energy which is
environmental friendly and safe or scientists in africa are thinking of too big
technologies that are inappropriate to our geography and forget simple
technologies like making an energy efficient “cooking stove”, “briquettes
charcoal”.
Despite the wide use of bioenergy
resources in developing countries, including Tanzania, yet information about the
supply and the energy potential of agriculture (crop and animal) residues, have
not been quantified. Thus, developing a method that can be used to quantify the
energy potential of agriculture residues is critical for efficient energy
planning and appropriate use of energy resources.
Nevertheless, the traditional
bioenergy (i.e., dung, charcoal and firewood) used in Tanzania like other
developing countries for domestic (cooking), crop drying, heating of bricks,
tobacco production, fish smoking and others, are characterized by low
investment, simple technology, large human labour inputs and low energy
efficiencies.
The use of traditional bioenergy for
various domestic uses by rural and urban population causes the majority of
people to suffer from chronic respiratory diseases, difficulty in breathing and
stinging eyes, in which young children and their mothers suffer most, and many
dies because of indoor air pollution (FELIX; GHEEWALA, 2011).
Hence, developing biogas
technologies so as to convert biowaste into renewable energy can improve
livelihood of the rural poor, who constitute more than 80% of the population
and reduce human health and environment problems. Comparing with the European
and Asian countries that have abundant experience on exploitation of
agriculture residues (HU; CHEN, 2013; SONG, et al., 2014; MONFORTI, et al.,
2015), Tanzania national level studies about utilization of biomass energy is
still at an infant stage, and also the competing uses of agriculture residues
are uncertain.
Over the past several years,
bioenergy technology has been applied to generate energy from agriculture
residues with the use of various types of equipment in different countries
around the world (GÓMEZ, et al., 2010; FERREA, et al., 2011; SONG et al. 2014).
Many studies have been conducted to
quantify crop residues available, the energy potential and environmental impact
(soil fertility) of crop residue use, that set a solid foundation for the
intensive use of agriculture residues (HOU et al., 2009; NZILA et al., 2010; DUKU
et al., 2011; MORENOA et al., 2012).
The residue to product ratio (RPR)
ratio has been widely used to estimate crop residues generated from different
crops (GEHRUNG; SCHOLZ, 2009; BI et al., 2010; BENTSEN et al., 2014; MONFORTI et
al., 2015). However, many studies have not considered the uncertainty of crop
residues caused by difference in growing conditions, field management and
climate, which is seldom to be considered for accurate estimation of crop
residues.
In most cases, considering the
uncertainty of crop residues, guarantees timely provision of quality
information about availability and energy potential of agriculture residues
needed for the national energy planning, review of energy policy and effective
natural resources management.
To date, several methods have been
established to estimate agriculture residues available from crops and animal
wastes. Scarlat et al. (2010) and Monforti et al. (2013) established regression
models that determine the causal relationships between straw production and
grain yields for the main crop residues, used to estimate the total energy
available.
The Monte Carlo simulation have been
widely applied to establish the amount of agriculture residues under
uncertainty, system optimization, risk management and sensitivity analysis (DEBOYS,
2004; JONES, 2008; WOINAROSCHY, 2008). The advantage of Monte Carlos technique
over the others is its ability to simulate the uncertainty of repeated random
sampling from independent input variables based on the previously known
probability distributions. Besides, the simulated results can be presented by
histograms whereby all necessary statistical parameters are obtained.
Despite the importance of residues
for bioenergy production, yet only few studies conducted to explore the
availability of crop residues in Tanzania and none of them considered the
uncertainty of crop residues or evaluated the energy potential of crop residues
and animal wastes. Hence, the objective of the present study is to assess the
bioenergy potential of crop residues and animal wastes, and evaluate what would
be the contribution of biomass energy to the national energy balance.
2. MATERIALS AND METHODS
2.1.
Data collection
The assessment of energy potential
of crop residues and animal wastes were built on the statistical data obtained
from the food and agriculture organization of the united nations (FAO, 2015).
Crop residues can be classified as field or process residues, such that the
former refers to residues left in the field after grain harvest and the later
constitute byproducts generated in the course of grain processing (COOPER;
LAING, 2007; BI et al., 2009; SONG et al. 2014).
This study has considered corncob
and rice husks to be process residues and others were considered to be field
residues. The number of live animals and crop production were taken as averages
over a period of fifty one (51) years, 1961-2012 (FAO, 2015). The assessment
covers the animal and crop production from all regions of Tanzania as
documented in the faostat database by 2015 (FAO, 2015).
Considering more than 70% of Tanzanians
are agriculturalists, over sixteen number of crops are grown in the area such
that the majority of the crops constitutes food crops than cash crops such as
coffee, sisal and tea to mention a few (Figure
1).
Figure 1: Crop yields in Tanzania
1961 – 2012
Source:
FAO, 2015
Despite the availability of sixteen
crops grown in Tanzania, yet this study have computed crop residues and energy
potential of ten (10) crops including wheat, rice, paddy, maize, cassava,
tubers, sugar cane, beans, seed cotton, oil seeds and sisal. Similarly, the
energy content of animals wastes were calculated for the four (4) live animals
such as cattle, sheep, goats, pigs and poultry (chicken and ducks). The
selection of the crops and animals in this study were based on the number,
quantity of crops’ yield and animal production with respect to their energy
potential. The residue to product ratio (RPR) technique was applied to estimate
the quantity of residues generated in each year. The rpr of different crops and
their respective heating values and standard coal equivalents were obtained
from various published literatures (suppoting information SI.1). Besides, the
quantity of manure produced by each live animal per day, energy recovery,
biomethane potential and heating values of the animal wastes were collected
from published literatures (SI. 1).
2.2. The
energy potential of crop residues and animal wastes
2.2.1. Computation
of energy potential of crop residues
The quantity of crop residues can be
established in different ways based on their potential including technical,
theoretical, economic, implementation and sustainable biomass potentials (BIOAMASS
ENERGY EUROPE, 2010). The theoretical method is usually the most convenient
means for estimation of energy potential as it takes into consideration all the
biomass available for various uses e.g., soil nutrient cycling, fodder and
energy which can be obtained from the crop production statistics.
Considering the nature of developing
countries, not all biomass can be collected and used for energy production due
to economic, social, environmental and political concerns. The technical
potential is the fraction of theoretically available biomass which are
technically recoverable (KEMAUSUOR et al. 2014) and can be used to indicate the
optimal renewable energy potential of crop residues without jeopardizing the
environment, animal feed and soil quality. This paper therefore, adopted the
technical and theoretical concept in establishing the energy potential of crop
residues that provide a clue of renewable energy (MJ) to be added into the
national energy balance if at all exploited.
The amount of crop residues were
computed according to OKELLO et al. (2013) with improvements by considering the
uncertainities. The Monte Carlo simulations that has been developed as a
standard software of crystal ball oracle was employed to simulate different
values of residue product ratios (RPR) of each crop so as to absorb variations
that can affect the quantity of residues generated.
A probability distribution of rpr of
the collected data for different crops (Table 1) was simulated and defined as
an independent variable to the model. The fitted probability distribution of RPR
for each crop and modeling parameters are shown (figure 2), which set a solid
foundation for the monte carlo simulation analysis. The amount of crop residues
generated were defined as a forecast variables according to model (equation. 1)
and rpr probability displayed in Figure 2. Considering the simulation results
are influenced by sample numbers, 2000 repeated trials were specified so as to
improve the simulation accuracy. The random sampling for monte carlo simulation
stops automatically as the accumulated sample number reaches the pre-defined
standard.
Table 1: Rpr of crops for
different crops derived from published historical data (SI. 1)
Crop |
Quantity (kg/year) |
RPR |
Wheat |
14,145,327.12 |
0.67 – 2.70 |
Rice, paddy |
15,386,186.92 |
0.56 – 1.53 |
Maize |
12,501,760.77 |
0.55 – 2.37 |
Cassava |
79,210,839.23 |
0.50 –1.00 |
Tubers, nes |
20,379,872.14 |
0.50 – 1.00 |
Sugar cane |
741,346,675.38 |
0.10 – 0.52 |
Beans dry |
6,456,299.23 |
1.5 – 1.7 |
Seed cotton |
4,956,671.92 |
2.22 –1.55 |
Oil seeds,
nes |
5,843,554.81 |
2.10 – 2.0 |
Sisal |
6,586,075.96 |
2.40 – 4.70 |
The
energy potential of crop residues were computed according to the method
proposed by Jiang et al. (2012)
with some improvements. The energy potential of crop residues is presented by
eq. 1.
|
(1) |
Where, Epi is the energy potential of crop residues, Qi represents crop production
(kg/year), Ɛi presents the standard coal conversion
ratio, LHV is the low heating value
of the standard coal (BLANCO; LAL, 2009), n
presents number of crops, and i is
the reference crop.
Figure
2: Probability distribution of crop residues for different crops in Tanzania
2.2.2. Computation
of energy potential of animal wastes
Animal waste refers to livestock
garbages such that the quantity of wastes produced depends on the amount of
fodder consumed, fodder quality and animal weight. Considering the limited
number of studies conducted to estimate the energy potential of animal wastes
in africa, the energy potential of animal wastes was calculated according to
the method proposed by Kemausuor et al. (2014) with the assumption that the
quantity of manures produced (kg/day) by livestock in Ghana is equivalent to
that in Tanzania. Though this assumption is not always valid to all
geographical locations but can provide an indication of the energy potential of
animal wastes in Tanzania.
3. RESULTS AND DISCUSSION
3.1.
The amount of crop residues
The study revealed a significant
difference in the quantity of crop residues that can be generated from the ten
crops studied in Tanzania from 1961-2012 (Table 2). Sugar cane has been
established to have the highest amount of crop residues (229,817,469.37
kg/year) followed by cassava which can generate about 59,408,129 kg/year of
crop residues, while dry beans has the least amount crop resudes generated
i.e., 9,343,326.58 kg/year.
Considering the existing strong
correlation between the amount of crop residues that can be collected compared
to the amount of renewable energy to be generated, great effort has to be given
to the exploitation of renewable energies from sugar cane and theafter cassava
which is widely grown in many regions of tanzania.
It has been documented that various
projects have been initiated to produce clean and safe energy from sisal for
several years in tanzania without success (TERRAPON-PFAFF et al. 2012),
the findings of this study challenges the energy policy makers and planners to
see the possibility of generating clean and safe energy from the sugar cane.
Table 2: Amount of crop residues
generated from crop yields
Crop |
Yield
(kg/year) |
RPR |
Crop residues
(kg/year) |
Wheat |
14,145,327.12 |
1.678 |
23,735,858.90 |
Rice, paddy |
15,386,186.92 |
1.04 |
16,001,634.40 |
Maize |
12,501,760.77 |
1.46 |
18,252,570.72 |
Cassava |
79,210,839.23 |
0.75 |
59,408,129.42 |
Tubers, nes |
20,379,872.14 |
0.75 |
15,284,904.11 |
Sugar cane |
741,346,675.38 |
0.31 |
229,817,469.37 |
Beans dry |
6,456,299.23 |
1.6 |
10,330,078.77 |
Seed cotton |
4,956,671.92 |
1.885 |
9,343,326.58 |
Oil seeds, nes |
5,843,554.81 |
2.05 |
11,979,287.36 |
Sisal |
6,586,075.96 |
3.55 |
23,380,569.66 |
3.2. The
energy potential of crop residues
Based on the average biomass yield
from different crops and conversion efficiency i.e., thermal values of each
type of crops grown, the energy potential of crop residues of tanzania from
1961-2012 has been estimated. The results revealed that the total bioenergy
potential of crop residues in Tanzania reached 5,714 TJ in 2012 (Table 3),
which is extremely larger than the installed electric energy generation
capacity (1564 MW) of TANZANIA in 2013 (GERMAN ENERGY DESK, 2013).
In addition, the results indicated
that sugar cane has the highest energy potential (2,966.4 TJ/year), followed by
cassava with the renewable energy potential of 845 TJ/year, while seed cotton
has the lowest energy potential (148.4 TJ/year). So the difference in energy potential
of various crop residues provides a sign of priority areas for the energy
investments in Tanzania.
Besides, the results have
demonstrated the need for the government to exploit the available crop residues
since even crops with the least energy generation capacity e.g., seed cotton (Table
3) can remove completely the existing problem of the energy access in the rural
areas of tanzania and support the governments’ efforts of turning our economy
into industrialized economy.
Table 3: Energy potential of
crop residues available in Tanzania
Crop |
Crop
residues (kg/year) |
Conversion
ratioa (ɛi) |
Equivalent
standard coal (kg/year) |
Energy
potential (mj/year) |
Energy
potential (tj/year) |
Wheat |
23,735,858.9 |
0.500 |
11,867,929.4 |
347,374,295.0 |
347.3 |
Rice, paddy |
16,001,634.4 |
0.429 |
6,864,701.1 |
200,929,802.9 |
200.9 |
Maize |
18,252,570.7 |
0.529 |
9,655,609.9 |
282,619,702.1 |
282.6 |
Cassava |
59,408,129.4 |
0.486 |
28,872,350.9 |
845,093,710.8 |
845.0 |
Tubers, nes |
15,284,904.1 |
0.486 |
7,428,463.3 |
217,431,123.6 |
217.4 |
Sugar cane |
229,817,469.3 |
0.441 |
101,349,503.9 |
2,966,499,982.0 |
2,966.4 |
Beans dry |
10,330,078.7 |
0.543 |
5,609,232.7 |
164,182,243.2 |
164.1 |
Seed cotton |
9,343,326.5 |
0.543 |
5,073,426.3 |
148,499,188.7 |
148.4 |
Oil seeds, nes |
11,979,287.3 |
0.529 |
6,337,043.0 |
18,548,5248.9 |
185.4 |
Sisal |
23,380,569.6 |
0.521 |
12,181,276.7 |
356,545,971.8 |
356.5 |
Source
of convertion ratioa: USDA
(2006)
3.3. The
energy potential of animal wastes
Over the past several decades,
animals were considered to be the main source of nutrients to human being and
soil fertility with a little attention to the energy potential of their wastes.
The present study revealed a significant contribution of animal wastes to the
tanzania electric energy grid such that a total of 1397TJ of energy could be
generated from the live animals in 2012 (Table 4).
Table 4: Energy potential of
animal wastes available in TANZANIA
Animal |
Plive (heads)a |
Yman (kg/head/d)b |
ƞbrec |
Cts (gts/100g)b |
Biogas (m3/d) |
Biogas (m3/year) |
Ɛn (MJ/year) |
Cattle |
1368174 |
12 |
0.2 |
12 |
86687544 |
31640953680 |
1139074332 |
Sheep |
3541011 |
1.2 |
0.2 |
25 |
4674135 |
1706059373 |
61418137 |
Goats |
8350005 |
1.5 |
0.2 |
25 |
13777509 |
5028791000 |
181036476 |
Pigs |
280786 |
3.6 |
0.5 |
11 |
1223104 |
446433072 |
16071590 |
Poultry |
10874 |
0.02 |
0.5 |
25 |
598 |
218313 |
7859 |
Source: Fao (2015) and kemausuor et al. (2014)
The number of live animals (plive), manure production (yman),
solid concentration (ctc),
recovery (ƞrec), methane
conversion factor (µ) (0.036GJ/m3)b, biomethane potential (ybmp) m3/kgts
(0.22)b and energy potential (ɛn).
Out of the five live animals kept in
Tanzania, cattle was found to have the highest energy potential (1,139,074,332 MJ/year),
followed by goats with the energy potential of 181,036,476 MJ/year while
poultry has the lowest energy potential of 7859 MJ/year. The findings have
demonstrated that, the existing problem of energy access to many regions of Tanzania
can be eliminated completely if more priority will be given to energy
generation from crop residues and animal wastes so long as the amount of animal
wastes required for the soil fertility and animal feed is maintained.
In addition, the results awakes
policy makers and energy planners to restore the biogas production plants that
were built in various manufacturing industries and community centres such as CAMATEC
in ARUSHA and Minja Ufundi in Mwanga Districts of Tanzania just to mention a
few.
4. CONCLUSION
The
amount of crop residues, animal wastes, energy potential of crop residues and
animal wastes have been evaluated and quantified. The results demonstrated that
proper utilization of crop residues and animal wastes for the generation of
renewable energy in rural and urban areas of Tanzania can increase
significantly energy access and reduce fossil energy consumption. Besides,
appropriate use of crop residues and animal wastes for the energy generation
has great contribution towards improved livelihood of rural population, human
health and alleviation of the global warming.
5. ACKNOWLEDGEMENT:
This
study was supported by VRIL-UOS/IUC - Mzumbe University, Project 3: Natural
Resources Management.
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