Logistics issues of biomass: The storage problem and
the multi-biomass supply chain
Athanasios A. Rentizelas
*
, Athanasios J. Tolis, Ilias P. Tatsiopoulos
Department of Mechanical Engineering, Sector of Industrial Management and Operational Research,
National Technical University of Athens, 9 Iroon Polytechniou Street, Zografou 15780, Athens, Greece
Received 19 November 2007; accepted 7 January 2008
Abstract
Biomass is a renewable energy source with increasing importance. The larger fraction of cost in biomass energy generation originates from the
logistics operations. A major issue concerning biomass logistics is its storage, especially when it is characterized by seasonal availability. The biomass
energy exploitation literature has rarely investigated the issue of biomass storage. Rather, researchers usually choose arbitrarily the lowest cost storage
method available, ignoring the effects this choice may have on the total system efficiency. In this work, the three most frequently used biomass storage
methods are analyzed and are applied to a case study to come up with tangible comparative results. Furthermore, the issue of combining multiple
biomass supply chains, aiming at reducing the storage space requirements, is introduced. An application of this innovative concept is also performed
for the case study examined. The most important results of the case study are that the lowest cost storage method indeed constitutes the system-wide
most efficient solution, and that the multi-biomass approach is more advantageous when combined with relatively expensive storage methods.
However, low cost biomass storage methods bear increased health, safety and technological risks that should always be taken into account.
# 2008 Elsevier Ltd. All rights reserved.
Keywords: Logistics; Biomass storage; Multi-biomass; Biomass supply chain; Energy exploitation; Agricultural biomass
Contents
1. Introduction . ................................................................................ 888
2. Previous literature on biomass storage ............................................................... 888
3. The biomass supply chain........................................................................ 888
3.1. Typical layout . . . ........................................................................ 888
3.2. Characteristics . . . ........................................................................ 889
4. The multi-biomass approach . . . ................................................................... 890
4.1. Advantages . ............................................................................ 890
4.2. Limitations . ............................................................................ 890
5. Case study description . . ........................................................................ 890
5.1. The problem ............................................................................ 890
5.2. Biomass supply chain description . . . ........................................................... 891
5.2.1. Collection and loading ............................................................... 891
5.2.2. Transport. ........................................................................ 891
5.2.3. Unloading and storage ............................................................... 891
6. Results and discussion . . ........................................................................ 892
7. Conclusions. . ................................................................................ 893
References . . ................................................................................ 894
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Renewable and Sustainable Energy Reviews 13 (2009) 887–894
* Corresponding author. Tel.: +30 210 7722383; fax: +30 210 7723571.
E-mail address: arent@central.ntua.gr (A.A. Rentizelas).
1364-0321/$ – see front matter # 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.rser.2008.01.003
1. Introduction
Biomass is one of the renewable energy sources on which
policy makers are greatly based upon to reduce the greenhouse
gas emissions. One of its main advantages is that it is a very
versatile energy source, generating not o nly electricity but also
heat and biofuels to be used in the transportation sector. It is
also one of the few renewable energy sources that may be stored
and can generate energy on-demand. The academic community
has also been very interested in the energy exploitation of
biomass. Several studies have been performed to forecast the
contribution of biomass in the future energy supply, both at a
regional and at a global level [1–3]. All of these studies
conclude to the fact that biomass usage will be increased
significantly in the years to come. Nonetheless, there is no
consensus on the maximum level biomass exploitation could
achieve.
One of the most important barriers in increased biomas s
utilization in energy supply is the cost of the respective supply
chain and the technology to convert biomass into useful forms
of energy. It is therefore natural that many attempts have been
made to date to simulate and optimize a specific biomass supply
chain on the understanding that significant cost reductions
could originate from more efficient logistics operations. Most
of the research work performed concerns simulation models of
the biomass supply chain, focusing on various aspects of the
logistics operations.
The cost of producing short rotation forestry was
investigated by using spreadsheet models in ref. [4], focusing
mainly on the operations of biomas s production, collection and
storage. An analytic supply chain modeling for 5 biomass types
was performed in ref. [5], concluding that 20–50% of biomass
delivered cost is due to transportation and handling activities.
Similarly, very analytical supply chain simulation models for
forest [6], cotton [7] and Miscanthus giganteus biomass [8]
have been developed. GIS has also been employed in several
studies [9,10] to calculate the exact transportation distances for
supplying specific amounts of energy crop feedstock across a
state, taking into account the spatial variability in their yield.
2. Previous literature on biomass storage
The stage of biomass storage is a very critical link on the
respective supply chain. In most cases of the relevant research
work low cost storage solutions are chosen, without examining
the positive effect that more sophisticated (and more costly)
solutions may have. Many researchers assume on-field biomass
storage [5,8,11]. Both ambient and covered on-field storage has
also been examined [12]. The method of on-field storage has the
advantage of low cost but on the other hand, biomass material
loss is sign ificant and biomass moisture cannot be controlled
and reduced to a desired level, thus leading to potential
problems in the power plant technological devices. Further-
more, health and safety issues exist, such as the danger of
spores and fungus formation [5,13] and self-ignition due to
increased moist ure. Finally, the farmers may not allow on-farm
storage of the biomass for a significant time period, as they may
want to prepare the land for the next crop [11].
Several authors consider the use of intermediate storage
locations between the fields and the power plant [5,14,15]. For
all biomass fuels in which the use of intermediate storage has
been modelled, the fuel has to be transported twice by road
transport vehicles (first from farm/forest to the intermediate
storage facility and then from storage to the power station). This
fact wi ll result in a higher delivered cost than a system in which
there is only one road transport movement (directly from farm/
forest to power station). Using an intermediate storage stage
may add in the region of 10–20% to the delivered costs, as a
result of the additional transportation and handling costs
incurred [5].
Finally, the option of settling the storage facil ity next to the
biomass power plant has also been examined in the relevant
literature [15,16]. On the latter case, an innovative storage
layout with biomass drying capability using dumped heat from
the power plant was presented. This concept aims at reducing
faster the biomas s moisture content and prevents material
decomposition as well as fungus and spores formation. Using
storage facilities attached to the power plant is the only viable
case of accelerating the drying proce ss of the biomass, as
dumped heat may be used without n eed for extra energy
consumption.
It is obvious that the biomass supply chain literature has not
paid to the issue of biomass storage the attention it deserves. In
most cases the lowest possible cost solution is adopted, without
examining the effect this solution may have on the total system
cost. This work aims at comparing three biomass storage
solutions found in the literature, in terms of total system cost.
The concept of multi-biomass is also adopted in its simplest
form: two locally available biomass types are considered, as
this concept may lead to significant system cost reduction [14].
The analysis is performed by examining a case study, in order to
come up with some tangible results.
3. The biomass supply chain
3.1. Typical layout
A typical biomass supply chain is comprised of several
discrete processes. These processes may include ground
preparation and planting, cultivation, harvesting, handling,
storage, in-field/forest transportation, road transportation and
utilization of the fuel at the power station.
Considering the typical locations of biomass fuel sources
(i.e. in farms or forests) the transport infrastructure is usually
such that road transport will be the only potential mode for
collection and transportation of the fuel. Other factors that
favour the use of road transport include the relatively short
distances over which the fuel is transported and the greater
flexibility that road transport can offer in comparison with other
modes. Other transportation means, such as ship or train may be
considered when long distance biomass transport is examined
[17]. However, this is not the case in this work, where emphasis
is placed on locally existing biomass types.
A.A. Rentizelas et al. / Renewable and Sustainable Energy Reviews 13 (2009) 887–894888
The activities required to supply biomass from its production
point to a power station [5] are the following:
Harvesting/collection of the biomass in the field/forest.
In-field/forest handling and transport to move the biomass to
a point where road transport vehicles can be used.
Storage. Many types of biomass are characterized by seasonal
availability, as they are harvested at a specific time of the year
but are required at the power station on a year-round basis; it
is therefore necessary to store them. The storage point can be
located in the far m/forest, at the power station or at an
intermediate site.
Loading and unloading of the road transportation vehicles.
Once the biomass has been moved to the roadside it will need
to be loaded to road transportation vehicles for conveyance to
the power station. The biomass will need to be unloaded from
the vehicles at the power station.
Transport by road transportation vehicles. There are varying
opinions in the literature on whether it is more economical to
use heavy goods vehicles [5,8] or agricultural/forestry
equipment [15] for biomass transport to the power station.
Ultimately, it appears to be a matter of the average transport
distance, biomass density, the carrying capacity and
travelling speed of the respective vehicles, as well as their
availability.
Processing biomass to improve its handling efficiency and the
quantity that can be transported. This may involve increasing
the bulk density of biomass (e.g. processing forest fuel or
coppice stems into wood chips) or unitising the biomass (e.g.
processing straw or Miscanthus in the swath into bales).
Processing can occur at any stage in the supply chain but will
often precede road transport and is generally cheaper when
integrated with the harvesting.
In the present work, a relatively simple but typical biomass
supply chain design has been adopted. The requirement of
developing a generic supply chain model for examining several
biomass types and also the multi-biomass approach, including
any combination of biomass types, led to the supply chain
design that is presented in Fig. 1.
3.2. Characteristics
The biomass suppl y chain presents several distinctive
characteristics that diversify it from a typical supply chain.
First of all, agricultural biomass types are usually characterized
by seasonal availability [18] . The period when these biomass
types are available is very limited and is determined by the crop
harvesting period, the weather conditions and the need to re-
plant the fields. Since most of the biomass-to-energy
applications to date concern single biomass use, there is a
need of storing very large amounts of biomass for a significant
time period, if year-round operation of the power plant is
desired. The limited time frame for collecting a large amount of
biomass leads also to significant seasonal need of resources,
both equipment and workforce. This seasonal demand may
increase the cost of obtaining these resources, while leading to
suboptimal utilization of resources, particularly of the storage
space. The problems introduced by the seasonality of biomass
availability may be avoided, if a biomass that is available year-
round is used, which is very rare in practice. The multi-biomass
approach may smooth significantly these problems and this is
why this approach is examined here.
Another characteristic of the biomass supply chain is that it
has to deal with low-density materials. As a result, there is
increased need for transportation and handling equipment, as
well as storage space. This problem is enhanced by the low
heating value, which is partly due to the increased moisture of
most agricultural biomass types. The low density of biomass
increases further the cost of collection, handling, transport and
storage stages of the supply chain [5].
Finally, several biomass ty pes require custom ized collec-
tion and handling equipment, leading to a complicated
structure of the supply chain. For example, there are different
requirements on handling and transportation equipment and
storage space configuration if biomass is procured in the forms
of sti ck s or chips [5]. Therefore, the form in which the biomass
will be procured often determines the investment and
operational costs of the respective bioenergy exploitation
system, as it affects the requirements and design of the biomass
supply chain.
Fig. 1. Generic biomass supply chain design.
A.A. Rentizelas et al. / Renewable and Sustainable Energy Reviews 13 (2009) 887–894 889
All of the abovementioned factors lead to increased supply
chain cost and require significant attention in designing a
biomass power plant, in order to reduce their negative impact to
the financial yield of the entire system. The multi-biomass
approach aims at reducing the impact of these factors.
4. The multi-biomass approach
The concept of multi-biomass utilization has been rarely
dealt with by researchers up to now, despite the advantages that
such an approach is expected to have. For example, in ref. [17]
the need for widening the operational window of biomass
logistics is acknowledged, e.g. by combining multiple biomass
chains, to minimize the share of capital costs.
The research that has been performed on the multi-biomass
concept has been very limited to date. For example, the
simultaneous use of straw and reed canary grass has been
investigated [14]. The conclusion the researchers reached was
that the specific combination led to a total system cost reduction
of about 15–20% compared to a single-biomass case, despite
the increased production cost of reed canary grass compared to
straw. Anot her interesting work examined the case of utilizing
six biomass sources, including municipal solid waste [16].In
this research, the criterion for the technical capability of using
the biomass mix was the Lower Heating Value of the mix. The
cost of producing energy using all the available biomass types
in a certain region was determined [19]. Finally, a case study for
utilizing multiple forest biomass types for local district heating
applications, using GIS for logistics modeling was presented
[20].
4.1. Advantages
The advantages that one may expect from using multipl e
biomass sources lie mainly on the total system cost reduction.
Significant savings can be realized in the stage of storage, as the
inflow of biomass throughout the year may be smoother and the
storage space required may be reduced. Furthermore, additional
cost savings could be expected from smoother resource
requirements at the biomass supply chain, both equipment
and labor. The example of ref. [14], where a 15–20% cost
reduction was obtained simply by using two biomass sources
instead of one is indicative of the cost reduction potential of the
multi-biomass approach.
4.2. Limitations
A major reason for the limited research on the multi-biomass
approach up to now is mainly the difficulties and limitations
introduced by this approach. The logistics can become quite
complex, especially when a variety of biomass streams are
involved. Organizational aspects, variations in availability,
storage and backup fuel, especially in winter months, are issues
that require more detailed study, according to ref. [21].
One of the main technical challenges of the multi-biomass
approach is the ability of the available energy conversion
technology to use a fuel mix comprised of several biomass
types with varying fuel characteristics, or a fuel that will vary its
characteristics according to the season of the year. There is no
absolute solution to this issue. Several energy conversion
technologies are tolerant to the variability of fuel character-
istics, whereas others are extremely sensitive even to small fuel
characteristics variations (e.g. pyrolysis). However, in ref. [21]
the existence of technologies capable of coping with
simultaneous use of biomass types with varying fuel properties
or contamination level is acknowledged. Furthermore, there
exist several families of biomass types that have very similar
characteristics and fuel properties (e.g. woody biomass types,
several cereal biomass types, etc.). In this work, it is assumed
that a suitable technology will be considered to use the fuel mix
that may result from the locally available biomass sources of
the case study region.
Another issue stemming from the multi-biomass approach
concerns the equipment for handling and processing the several
biomass sources. Most biomass types can be processed into
numerous forms, each one potentially requiring different
equipment for handling, loading, unloading, transport and fuel
feeding. It is essential for the multi-biomass approach that all
the potential biomass sources may be processed in a form that
will allow the use of only one type of handling and feeding
equipment or that will require small, inexpensive and easily
made modifications and customizations. Otherwise the
advantage of using multiple biomass types on the capital cost
reduction of the equipment may be wiped out. Therefore, the
multi-biomass approach requires that the biomass types
examined may have a similar form that will allow using the
same equipment for all of them.
5. Case study description
5.1. The problem
The model developed is implemented for the case study of a
municipality of the prefecture of Thessaly, Greece. Thessaly is
one of the most appropriate cases for implementing the model,
since it is the largest plain in Greece, in which a large number of
different crops exist. The availability of many biomass types is
a prerequisite for the examination of the impact of the multi-
biomass approach.
The heat consumer is considered to be the local community
of Farkadon. The reasons for choosing this specific community
is its size (about 2000 inhabitants), which makes it ideal for the
typical biomas s energy applications, and its geographical
position. The co-generation power plant is centralized, and is
considered to be an independent producer, as all the electricity
produced is supplie d to the national grid. The heat generated is
used mainly for domestic and public sector applications, for
space heating or space cooling, by using absorption chillers.
Therefore, a tri-generation application is considered. The
ultimate target is to build a biomass-to-energy exploitation unit
that will operate on heat-match mode.
The results provided in this work concern the biomass
supply chain. However, these results have been obtained by
applying the global optimization conce pt on a system-wide
A.A. Rentizelas et al. / Renewable and Sustainable Energy Reviews 13 (2009) 887–894890
base. Therefore, for each case examined the whole bioenergy
exploitation system is optimized. The system comprises of the
biomass supply chain (upstream), the energy exploitation unit
(power plant) and the energy products distribution supply chain
(downstream), namely electricity, heat and cooling.
The cases examined in this work refer to the following
biomass types:
1. Cotton stalks.
2. Almond tree prunings.
The optimum biomass mix has been determined for each
scenario examined. These biomass types are among the ones
locally prevailing in the region around the case study
municipality. In order to perform the case study, raw statistical
data for biomass availability at the case study region has been
obtained and has been processed with GIS software to attach
the appropriate geographical information.
5.2. Biomass supply chain description
In this paragraph, the supply chain design adopted for the
case study examined is presented. The biomass supply chain
may be analyzed to the discrete stages of collection, loading,
transport, unloading, handling and storage. These stages are
described in more detail.
5.2.1. Coll ection and loading
The model used has the ability of investigating a multi-
biomass supply chain. The complexity introduced by the many
potential collection methods and forms for each biomass type is
enormous. For this reason, only one collection method and one
form for each biomass type has been considered in the case
study. The biomass types will be converted either to chips or
chopped form. The characteristics of each biomass type are
introduced parametrically in the model. The input data used for
biomass are displayed in Table 1.
The biomass types considered do not have significant
alternative use and specific market price currently in Greece.
Actually, farmers often have to pay to dispose this type of
agricultural residues. Therefore, it has been assumed that they
may be available at a very low price. The prices shown in
Table 1 include also the loading cost to the transportation
vehicles.
5.2.2. Transport
There are two possible means for performing the biomass
transport:
1. Using trucks from a 3PL (third party logistics) company.
2. Using the farmers’ equipment (tractors and platforms).
In the current work, it has been assumed that chartered
trucks will be used. The reason is that the extended usage
period, resulting from adopting the multi-biomass approach,
will probably conflict with the availability of farmer’s
equipment, since it might be needed for other agricultural
processes. The data used for the transportation stage of the
supply chain are presented in Table 2. Technical data for trucks
have been adopted from ref. [8].
Transport cost is a function of the travel distance and the
travel time. Travel distance affects mainly the fuel consumption
of transportation vehicles, whereas travelling time affects
mainly the proportion of depreciation, insurance, maintenance
and labour allocated to the specific trip. Travelling time
includes the round-trip time, since no return load is available, as
well as the loading and unloading waiting time. Each biomass
type is assumed to be collec ted and transported at a constant
rate during the whole availability period of the specific type.
Due to the low density of all biomass types, the capacity of the
transportation vehicles will ultimately be limited by the volume
and not by the weight of the cargo. The travelling distance has
been calculated from the Euclidean distance multiplied by a
tortuosity factor equal to
ffiffiffi
2
p
, to account for the windings of the
rural road infrastructure.
5.2.3. Unloading and storage
Biomass is transporte d from the fields to the storage facility,
which is assumed to be attached to the biomas s CHP plant. The
first type of storage assumed is closed warehouse with biomass
drying capability, by hot air injection (scenario WD). Hot air is
generated by dumped heat of the CHP plant and is supplied
from the warehouse floor through appropriate canals and grids.
The biomass storage using hot air helps to avoid quality
degradation of the biomass due to infections, fermentation and
Table 1
Characteristics of two prevailing biomass types in the case study region
Cotton
stalks
Almond tree
prunings
Residue yield (t/ha)
a
5.47 6.21
Residue availability factor (%)
a,b
70 90
Biomass remaining for energy exploitation (t/ha) 3.83 5.59
Moisture wet (%)
a
30 40
HHV (MJ/dry kg)
a,b
18.1 18.4
Density (kg/m
3
) 200 300
Availability of biomass October–
November
December–
February
Purchasing price (s/t wet)
c
20 30
a
Source: [19].
b
Source: [16].
c
Biomass purchasing price includes also loading costs.
Table 2
Transportation vehicles characteristics
Max biomass purchasing distance (km) 40
Weight capacity of truck (kg) 25,000
Volume capacity of truck (m
3
) 100
Mean speed of empty vehicle (km/h) 50
Mean speed of loaded vehicle (km/h) 40
Mean truck fuel consumption (l/km) 0.3
Purchasing cost of truck (s) 120,000
Truck insurance and maintenance cost (s/yr) 10,000
Service life of truck (yr) 7
Drivers’ shift duration (h) 8
Drivers’ hourly pay rate (s)12
A.A. Rentizelas et al. / Renewable and Sustainable Energy Reviews 13 (2009) 887–894 891
