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Case Studies of Energy Storage with Fuel Cells and Batteries for Stationary and Mobile Applications

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In this paper, hydrogen coupled with fuel cells and lithium-ion batteries are considered as alternative energy storage methods. Their application on a stationary system (i.e., energy storage for a family house) and a mobile system (i.e., an unmanned aerial vehicle) will be investigated. The stationary systems, designed for off-grid applications, were sized for photovoltaic energy production in the area of Turin, Italy, to provide daily energy of 10.25 kWh. The mobile systems, to be used for high crane inspection, were sized to have a flying range of 120 min, one being equipped with a Li-ion battery and the other with a proton-exchange membrane fuel cell. The systems were compared from an economical point of view and a life cycle assessment was performed to identify the main contributors to the environmental impact. From a commercial point of view, the fuel cell and the electrolyzer, being niche products, result in being more expensive with respect to the Li-ion batteries. On the other hand, the life cycle assessment (LCA) results show the lower burdens of both technologies.
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challenges
Article
Case Studies of Energy Storage with Fuel Cells and
Batteries for Stationary and Mobile Applications
Nadia Belmonte 1, Carlo Luetto 2, Stefano Staulo 3, Paola Rizzi 1, * and Marcello Baricco 1
1Department of Chemistry, Centre for Nanostructured Interfaces and Surfaces (NIS), University of Turin,
10125 Torino, Italy; nadia.belmonte@unito.it (N.B.); marcello.baricco@unito.it (M.B.)
2Tecnodelta Srl., 10034 Chivasso, Italy; carlo.luetto@tecnodeltaimpianti.com
3Stones Sas., 10093 Collegno, Italy; stones.staulo@gmail.com
*Correspondence: paola.rizzi@unito.it; Tel.: +39-011-670-7565
Academic Editors: Annalisa Paolone and Lorenzo Ulivi
Received: 31 January 2017; Accepted: 20 March 2017; Published: 22 March 2017
Abstract:
In this paper, hydrogen coupled with fuel cells and lithium-ion batteries are considered as
alternative energy storage methods. Their application on a stationary system (i.e., energy storage
for a family house) and a mobile system (i.e., an unmanned aerial vehicle) will be investigated.
The stationary systems, designed for off-grid applications, were sized for photovoltaic energy
production in the area of Turin, Italy, to provide daily energy of 10.25 kWh. The mobile systems, to be
used for high crane inspection, were sized to have a flying range of 120 min, one being equipped
with a Li-ion battery and the other with a proton-exchange membrane fuel cell. The systems were
compared from an economical point of view and a life cycle assessment was performed to identify
the main contributors to the environmental impact. From a commercial point of view, the fuel cell
and the electrolyzer, being niche products, result in being more expensive with respect to the Li-ion
batteries. On the other hand, the life cycle assessment (LCA) results show the lower burdens of
both technologies.
Keywords:
fuel cell; battery; life cycle assessment; integrated power system; unmanned aerial
vehicle (UAV)
1. Introduction
Energy is one of the keys to the development of nations and society. Civilization is dependent on a
constant, consistent supply of energy; globally, the demand for energy has been increasing consistently
in parallel with growth in population and economic consumption [
1
]. Stringent energy-related
problems have led to an increased interest in renewable energy sources. Due to the intermittent nature
of those sources, the energy production varies significantly according, for example, to the hour of the
day and the period of the year. Therefore, it is necessary to store the produced energy allowing its use
after production. The criteria for the selection of solutions for the storage of renewable energy are still
under debate, both for stationary and mobile applications [2].
Hydrogen is considered as an energy carrier and its chemical energy can be converted into
electricity through a chemical reaction by a fuel cell. Therefore, coupling energy storage systems
with renewable energy sources through an electrolyzer, which can transform electric energy into
hydrogen chemical energy, is considered as a highly sustainable process of exploitation of energy [
3
5
].
A good storage system should also be useful if the system is located in a remote off-grid area [
6
8
],
like mountainous regions [
9
] or small islands [
10
], as an alternative to the less-efficient and less
environmentally-friendly diesel generators that are normally used in these contexts [
11
13
]. For the
same type of applications, Li-ion batteries are also used coupled with renewable energy sources.
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Challenges 2017,8, 9 2 of 15
The tradeoff between batteries and fuel cells is an issue not only for stationary applications,
but also for mobile ones, as shown in the literature about PEMFCs (proton exchange membrane
fuel cells) and electric vehicles [
14
,
15
]. The choice of one of these technologies for a specific application
can be made taking into account different factors, such as the hydrogen source, the electricity mix or
the price of the fuel, or specific application-related issues, like the weight of the system. This is the
case of small and mini unmanned aerial vehicles (UAVs), also known as drones. Due to an increased
interest in these devices [
16
19
], a large number of efforts have been dedicated to the estimation and
optimization of the flying range [20,21].
Since the currently commercialized drones are battery fed, increasing the size of the battery
could represent the easiest solution. According to some authors, however, this is not a viable
solution, as the weight of the battery becomes a limiting factor [
22
]. Studies on other portable power
applications
[23,24]
concluded similarly that, for shorter operational times, the battery system is best,
while for longer operational times the fuel cell is preferred from a weight perspective. Another explored
option is the use of a fuel cell: in this case, in fact, the only limit to the flying range is given by the
amount of fuel onboard. Hydrogen and methanol both represent valid alternatives as fuels for the
PEM fuel cell. In both cases, the power supply system of the device becomes more complicated with
respect to the use of batteries, requiring a fuel tank (for liquid methanol, or compressed hydrogen gas),
auxiliary components, and in the case of the use of methanol, a reformer unit. In particular, the presence
of a reformer unit determines the addition of extra weight and auxiliary components not necessary in
the case of a hydrogen-powered system.
Since it is not possible to find a general solution for the energy storage, specific case studies,
such as those aforementioned, have to be considered. However, when comparing batteries and fuel
cells for different stationary and mobile applications, some general benefits and drawbacks can be
outlined. For this reason, two alternative energy storage systems will be investigated in this work, i.e.,
Li-ion batteries and hydrogen coupled with PEM fuel cell-based technologies. The two technologies
will be considered for both a stationary and a mobile application. In particular, the stationary system
is a family house designed to have two days of self-sufficiency, while the mobile application is a
coaxial octocopter having a flying time of 120 min. A cost analysis will be shown, evidencing the main
contributions to the final cost of the considered devices. In addition, both systems will be investigated
focusing on the energy and materials used for their production, through a life cycle assessment tool.
Both energy storage technologies showed low environmental burdens if compared to other
components of the same system. Batteries have lower costs than fuel cells, and require less auxiliary
components. On the other hand, fuel cell-based systems showed a better adaptability to long operating
times. Starting from results on specific applications, it will be possible to obtain a wider overview of
the advantages and issues of the use of both technologies.
2. Systems Description
2.1. Stationary Application: Family House Energy Storage
A family house with 3–4 inhabitants, located in the area of Turin, Italy, was considered. This area
was chosen since it offers a great multiplicity of different scenarios, going from the grid-connected
urban area, to small, but still grid-connected villages, up to the remote mountain lodges, located in the
alpine chain, which cannot rely on grid connection. In all of these scenarios the application of a system
coupling renewable energy production and storage would lead to an improvement. In the case of
mountain lodges, this scenario will benefit from energy efficiency and self-sufficiency while, in urban
areas, the renewable energy system will help in meeting peak electrical load demands, thus reducing
risks of blackout phenomena.
Photovoltaics are the most widely applicable solution for renewable energy production in
this area. For an estimation of the energy production, the irradiation data for Turin in winter,
summer, and spring/autumn have been considered. The average daily irradiation has been obtained,
Challenges 2017,8, 9 3 of 15
as explained in detail in [
25
], and power curves were calculated. To estimate the electricity consumption
by the family house, load curves were estimated considering commercial electrical appliances.
In Figure 1, the estimated power consumption and production curves for the winter months are
reported as a function of time. The colored areas represent the system working. In the green area,
the electricity production exceeds the amount required by the load. This excess is used to recharge the
batteries, in the case of the battery-based system, and to produce hydrogen through electrolysis, in the
case of the fuel cell-powered system. In the red area, no or little electricity is produced with the solar
panels, thus, the storage system intervenes.
Challenges 2017, 8, 9 3 of 15
by the family house, load curves were estimated considering commercial electrical appliances. In
Figure 1, the estimated power consumption and production curves for the winter months are
reported as a function of time. The colored areas represent the system working. In the green area, the
electricity production exceeds the amount required by the load. This excess is used to recharge the
batteries, in the case of the battery-based system, and to produce hydrogen through electrolysis, in
the case of the fuel cell-powered system. In the red area, no or little electricity is produced with the
solar panels, thus, the storage system intervenes.
Figure 1. Average electricity production from photovoltaics during winter months compared with
the energy consumption for the same season. The area in green represents the produced energy that
is not directly used by the household and is stored (through hydrogen production or battery
charging), while in the red area the stored energy is used by the household.
On the basis of these considerations, both systems were sized for being self-sufficient for two
days in the worst conditions, i.e., with the irradiation data of December. The two systems, the
schemes of which are reported in Figures 2 and 3, differ in the storage unit, which is represented by
a battery pack in one case, and an electrolyzer coupled with a fuel cell system in the other case.
As the average daily consumption of the examined household was estimated to be 11 kWh with
3 kW maximum load, a fuel cell with a 3 kW nominal power output will be considered. The hydrogen
necessary for two days of self-sufficiency is produced by an electrolyzer. In order to produce the
necessary amount of hydrogen during the sunny hours of one day, a nominal power input of 5 kW
is considered. Hydrogen will be stored at 30 bar, which is the pressure released by the electrolyzer,
into type I aluminum tanks with an internal volume of 50 L. For two days of self-sufficiency 10 tanks
are needed, but since standard cylinder bundles are composed of 12 tanks, two additional cylinders
are added to the system. The hydrogen-based system needs an additional photovoltaic array because
of the electrolyzer power requirements. A simplified scheme of this system is shown in Figure 2.
Figure 1.
Average electricity production from photovoltaics during winter months compared with the
energy consumption for the same season. The area in green represents the produced energy that is
not directly used by the household and is stored (through hydrogen production or battery charging),
while in the red area the stored energy is used by the household.
On the basis of these considerations, both systems were sized for being self-sufficient for two days
in the worst conditions, i.e., with the irradiation data of December. The two systems, the schemes of
which are reported in Figures 2and 3, differ in the storage unit, which is represented by a battery pack
in one case, and an electrolyzer coupled with a fuel cell system in the other case.
As the average daily consumption of the examined household was estimated to be 11 kWh with
3 kW maximum load, a fuel cell with a 3 kW nominal power output will be considered. The hydrogen
necessary for two days of self-sufficiency is produced by an electrolyzer. In order to produce the
necessary amount of hydrogen during the sunny hours of one day, a nominal power input of 5 kW
is considered. Hydrogen will be stored at 30 bar, which is the pressure released by the electrolyzer,
into type I aluminum tanks with an internal volume of 50 L. For two days of self-sufficiency 10 tanks
are needed, but since standard cylinder bundles are composed of 12 tanks, two additional cylinders
are added to the system. The hydrogen-based system needs an additional photovoltaic array because
of the electrolyzer power requirements. A simplified scheme of this system is shown in Figure 2.
Challenges 2017,8, 9 4 of 15
Challenges 2017, 8, 9 4 of 15
Figure 2. Scheme of the fuel cell-based stationary system.
The battery-based system, the scheme of which is reported in Figure 3, is composed of 12
batteries, with 12 V and 150 Ah.
Figure 3. Scheme of the battery-based stationary system.
It is noteworthy that both systems schematized in Figures 2 and 3 have the possibility of being
connected to the grid, if available. This gives the possibility of conferring the extra energy produced
to the grid, as well as getting this back during the night hours.
2.2. Mobile Application: UAV
In recent years the use of UAVs, traditionally related to military operations, has been gaining
interest for civilian applications in different fields [2426]. Among these, one particularly promising
application is structure health monitoring [27,28]. Video inspection performed by drone can also be
a valid tool for the periodical inspection of lifting equipment and cranes. These inspections are, in
fact, normally carried out by disassembling and putting on the ground the components to be
inspected, but this procedure is expensive and time-consuming.
For this application the drone must have a flying time of at least 120 min and a high stability to
allow image acquisition. Stability requirements lead to the choice of a coaxial octocopter [29]. As far
as the flying range is concerned, two power alternatives are considered: the Li-ion battery
traditionally used for these devices [24,30] and a PEM fuel cell, as successfully demonstrated in
previous works [3133]. The latter is not a conventional PEM fuel cell, but a lightweight one, suitable
for aerospace applications [34], for which weight is a crucial issue. This also determines the need for
limiting the number of auxiliary components necessary for the fuel cell to operate, which means air-
cooling (no cooling liquid circuit necessary), and dry-type membranes, that do not need to be
humidified. A simplified representation of the UAV fuel cell-based system is shown in Figure 4.
Aside from this PEM fuel cell-powered device, a commercial Li-ion battery-powered device was
considered.
Figure 2. Scheme of the fuel cell-based stationary system.
The battery-based system, the scheme of which is reported in Figure 3, is composed of 12 batteries,
with 12 V and 150 Ah.
Challenges 2017, 8, 9 4 of 15
Figure 2. Scheme of the fuel cell-based stationary system.
The battery-based system, the scheme of which is reported in Figure 3, is composed of 12
batteries, with 12 V and 150 Ah.
Figure 3. Scheme of the battery-based stationary system.
It is noteworthy that both systems schematized in Figures 2 and 3 have the possibility of being
connected to the grid, if available. This gives the possibility of conferring the extra energy produced
to the grid, as well as getting this back during the night hours.
2.2. Mobile Application: UAV
In recent years the use of UAVs, traditionally related to military operations, has been gaining
interest for civilian applications in different fields [2426]. Among these, one particularly promising
application is structure health monitoring [27,28]. Video inspection performed by drone can also be
a valid tool for the periodical inspection of lifting equipment and cranes. These inspections are, in
fact, normally carried out by disassembling and putting on the ground the components to be
inspected, but this procedure is expensive and time-consuming.
For this application the drone must have a flying time of at least 120 min and a high stability to
allow image acquisition. Stability requirements lead to the choice of a coaxial octocopter [29]. As far
as the flying range is concerned, two power alternatives are considered: the Li-ion battery
traditionally used for these devices [24,30] and a PEM fuel cell, as successfully demonstrated in
previous works [3133]. The latter is not a conventional PEM fuel cell, but a lightweight one, suitable
for aerospace applications [34], for which weight is a crucial issue. This also determines the need for
limiting the number of auxiliary components necessary for the fuel cell to operate, which means air-
cooling (no cooling liquid circuit necessary), and dry-type membranes, that do not need to be
humidified. A simplified representation of the UAV fuel cell-based system is shown in Figure 4.
Aside from this PEM fuel cell-powered device, a commercial Li-ion battery-powered device was
considered.
Figure 3. Scheme of the battery-based stationary system.
It is noteworthy that both systems schematized in Figures 2and 3have the possibility of being
connected to the grid, if available. This gives the possibility of conferring the extra energy produced to
the grid, as well as getting this back during the night hours.
2.2. Mobile Application: UAV
In recent years the use of UAVs, traditionally related to military operations, has been gaining
interest for civilian applications in different fields [
24
26
]. Among these, one particularly promising
application is structure health monitoring [
27
,
28
]. Video inspection performed by drone can also be a
valid tool for the periodical inspection of lifting equipment and cranes. These inspections are, in fact,
normally carried out by disassembling and putting on the ground the components to be inspected,
but this procedure is expensive and time-consuming.
For this application the drone must have a flying time of at least 120 min and a high stability
to allow image acquisition. Stability requirements lead to the choice of a coaxial octocopter [
29
].
As far as the flying range is concerned, two power alternatives are considered: the Li-ion battery
traditionally used for these devices [
24
,
30
] and a PEM fuel cell, as successfully demonstrated in
previous works
[3133]
. The latter is not a conventional PEM fuel cell, but a lightweight one,
suitable for aerospace applications [
34
], for which weight is a crucial issue. This also determines
the need for limiting the number of auxiliary components necessary for the fuel cell to operate,
which means air-cooling (no cooling liquid circuit necessary), and dry-type membranes, that do not
need to be humidified. A simplified representation of the UAV fuel cell-based system is shown in
Figure 4. Aside from this PEM fuel cell-powered device, a commercial Li-ion battery-powered device
was considered.
Challenges 2017,8, 9 5 of 15
Challenges 2017, 8, 9 5 of 15
Figure 4. Scheme of the PEM fuel cell-based UAV.
Simplified schemes of the battery-based and the fuel cell-based drones are reported in Figures 5
and 6, respectively.
Figure 5. Simplified scheme for the battery-powered UAV.
The dashed arrow in Figure 6, going from the gas tanks to the fuel cell represents the hydrogen
flow, which is regulated by the control electronics. The auxiliary components of the fuel cell system,
such as air compressor, blower and solenoid valves, require a power supply of about 22 W. For this
reason, an extra power must be supplied to the system, aside from the 728 W required by the drone
engines (common to both systems). Thus, the two systems, although designed for the same
application and size, are slightly different in the amount of power effectively supplied to the engines.
As a consequence, considering 1 kW power, the battery-based system has a slightly longer flying
time, with respect to the fuel cell system.
Figure 6. Simplified scheme for the fuel cell-powered UAV.
Unlike for the stationary application, for the mobile application the hydrogen production aspect
has not been examined. However, considering a small electrolyzer producing 400 nl/h with a power
supply equal to 2.8 kW, the amount of hydrogen necessary for the fuel cell-powered drone running
for 120 min can be produced in about 250 min, with a total energy consumption of 11.8 kWh.
3. Cost Analysis
Cost can be a deciding factor in the choice between two different systems for applications. In
order to identify which solutions are more competitive and the impact of the energy storage solution
on the total cost of the system, a cost analysis has been performed for both stationary and mobile
Figure 4. Scheme of the PEM fuel cell-based UAV.
Simplified schemes of the battery-based and the fuel cell-based drones are reported in
Figures 5and 6, respectively.
Figure 5. Simplified scheme for the battery-powered UAV.
The dashed arrow in Figure 6, going from the gas tanks to the fuel cell represents the hydrogen
flow, which is regulated by the control electronics. The auxiliary components of the fuel cell system,
such as air compressor, blower and solenoid valves, require a power supply of about 22 W. For this
reason, an extra power must be supplied to the system, aside from the 728 W required by the drone
engines (common to both systems). Thus, the two systems, although designed for the same application
and size, are slightly different in the amount of power effectively supplied to the engines. As a
consequence, considering 1 kW power, the battery-based system has a slightly longer flying time,
with respect to the fuel cell system.
Challenges 2017, 8, 9 5 of 15
Figure 4. Scheme of the PEM fuel cell-based UAV.
Simplified schemes of the battery-based and the fuel cell-based drones are reported in Figures 5
and 6, respectively.
Figure 5. Simplified scheme for the battery-powered UAV.
The dashed arrow in Figure 6, going from the gas tanks to the fuel cell represents the hydrogen
flow, which is regulated by the control electronics. The auxiliary components of the fuel cell system,
such as air compressor, blower and solenoid valves, require a power supply of about 22 W. For this
reason, an extra power must be supplied to the system, aside from the 728 W required by the drone
engines (common to both systems). Thus, the two systems, although designed for the same
application and size, are slightly different in the amount of power effectively supplied to the engines.
As a consequence, considering 1 kW power, the battery-based system has a slightly longer flying
time, with respect to the fuel cell system.
Figure 6. Simplified scheme for the fuel cell-powered UAV.
Unlike for the stationary application, for the mobile application the hydrogen production aspect
has not been examined. However, considering a small electrolyzer producing 400 nl/h with a power
supply equal to 2.8 kW, the amount of hydrogen necessary for the fuel cell-powered drone running
for 120 min can be produced in about 250 min, with a total energy consumption of 11.8 kWh.
3. Cost Analysis
Cost can be a deciding factor in the choice between two different systems for applications. In
order to identify which solutions are more competitive and the impact of the energy storage solution
on the total cost of the system, a cost analysis has been performed for both stationary and mobile
Figure 6. Simplified scheme for the fuel cell-powered UAV.
Unlike for the stationary application, for the mobile application the hydrogen production aspect
has not been examined. However, considering a small electrolyzer producing 400 nl/h with a power
supply equal to 2.8 kW, the amount of hydrogen necessary for the fuel cell-powered drone running for
120 min can be produced in about 250 min, with a total energy consumption of 11.8 kWh.
3. Cost Analysis
Cost can be a deciding factor in the choice between two different systems for applications. In order
to identify which solutions are more competitive and the impact of the energy storage solution on the
Challenges 2017,8, 9 6 of 15
total cost of the system, a cost analysis has been performed for both stationary and mobile applications.
The estimated costs of the main components for the two stationary systems are reported in Table 1,
and their distribution and total prices are shown in Figure 7.
Table 1. Costs of the main components for the stationary systems.
System Component Cost ()
Fuel cell
Fuel cell system 30,000
Type I gas tanks 7500
PV (photovoltaic) panels 5500
Auxiliary components 7000
Battery
Li-ion batteries 18,000
PV panels 3500
Auxiliary components 3500
Challenges 2017, 8, 9 6 of 15
applications . The estimated costs of the main components for the two stationary systems are reported
in Table 1, and their distribution and total prices are shown in Figure 7.
Table 1. Costs of the main components for the stationary systems.
System
Component
Cost (€)
Fuel cell
Fuel cell system
30,000
Type I gas tanks
7500
PV (photovoltaic) panels
5500
Auxiliary components
7000
Battery
Li-ion batteries
18,000
PV panels
3500
Auxiliary components
3500
Figure 7. Total costs and cost distributions for the two alternatives of the stationary systems.
As can be seen from Figure 7, although the total costs are very different for these solutions, the
price distribution among the components is similar, with the energy storage unit representing more
than half of the total cost for both systems. The reason is two-fold: on one hand, the high number of
batteries required by the battery-powered system to guarantee two days of self-sufficiency gives a
significant rise to the price, while, on the other hand, the high cost of the electrolyzer + PEM fuel cell
system is, nowadays, fixed by the low market penetration of these devices. The use of gas cylinders
gives another significant contribution to the cost of the hydrogen technology system.
Different trends can be observed in the case of the selected mobile application, for which the
costs are reported in Table 2, and their distribution among the components is summarized in Figure 8.
Table 2. Costs of the main components for the mobile systems.
System
Component
Cost (€)
Fuel cell
Fuel cell system
13,200
Engines and structure
5800
Type III gas tanks
2200
Auxiliary components
3200
Image acquisition system
2600
Battery
Li-ion battery
1000
Engines and structure
5800
Auxiliary components
1600
Image acquisition system
2600
Figure 7. Total costs and cost distributions for the two alternatives of the stationary systems.
As can be seen from Figure 7, although the total costs are very different for these solutions,
the price distribution among the components is similar, with the energy storage unit representing more
than half of the total cost for both systems. The reason is two-fold: on one hand, the high number of
batteries required by the battery-powered system to guarantee two days of self-sufficiency gives a
significant rise to the price, while, on the other hand, the high cost of the electrolyzer + PEM fuel cell
system is, nowadays, fixed by the low market penetration of these devices. The use of gas cylinders
gives another significant contribution to the cost of the hydrogen technology system.
Different trends can be observed in the case of the selected mobile application, for which the costs
are reported in Table 2, and their distribution among the components is summarized in Figure 8.
Table 2. Costs of the main components for the mobile systems.
System Component Cost ()
Fuel cell
Fuel cell system 13,200
Engines and structure 5800
Type III gas tanks 2200
Auxiliary components 3200
Image acquisition system
2600
Battery
Li-ion battery 1000
Engines and structure 5800
Auxiliary components 1600
Image acquisition system
2600
Challenges 2017,8, 9 7 of 15
Challenges 2017, 8, 9 7 of 15
Figure 8. Total costs and cost distributions for the two alternatives of the mobile system.
In this case, the PEM fuel cell is responsible for about half of the total cost of the fuel cell-powered
drone, while the battery in the battery-powered system has a much lower impact, not only if
compared to the fuel cell of the fuel cell-based mobile system, but also to the previously-presented
battery-based stationary application. This is simply due to the different number of batteries required
by the two applications. In the case of the UAV, a single battery is enough for a single run while, for
the stationary application, 12 batteries are necessary to guarantee two days of self-sufficiency. The
impact of the engines and structure of the drone to the total cost of the drone, as well as that of the
control and image acquisition part, is quite different for the two systems, even if the absolute cost is
obviously the same. This result indicates a very different contributions of the two energy storage
methods to the total cost of the drone.
In the case of the battery-based drone, 52% of the total price is due to the engines and structure.
This can be attributed to the use of carbon fiber. The production of this material is, in fact, energy-
and capital-intensive. Therefore, a large effort is being done to develop new production technologies
of carbon fiber, in order to significantly reduce manufacturing costs [35]. Structure and engines
represent 21% of the total price of the fuel cell-powered UAV. In this case, however, the type III gas
tanks are partly made of carbon fiber and contribute to 8% of the total price of the system, suggesting
the need of an improvement in composite tank manufacturing [36].
The systems examined for the two applications show the same main critical aspect from a cost
point of view: the higher impact of the fuel cell with respect to Li-ion batteries. In fact, the latter
represents a mature technology already commercialized on a large scale. In particular, in the case of
selected applications, battery-powered drones are already available at different prices and sizes,
while for stationary application kits containing batteries, photovoltaic panels, and controllers can be
purchased in a variety of power options.
The commercial situation of fuel cell technology is, at present, quite different, these products not
yet being commercialized on a large scale. Their production process, which still needs improvement
[37], makes them quite expensive. If there is a market for PEM fuel cells for stationary use (e.g., small-
scale CHP), when PEM fuel for mobile and aerospace applications are considered, the prices increase
significantly. This is due to the use of lightweight materials and to a significantly lower diffusion on
the market of this type of fuel cell, when compared to similar systems for stationary applications.
4. Life Cycle Assessment
Life cycle assessment (LCA) is an important tool to evaluate the environmental impact of a
product, as described by the ISO 14040/14044 methodology [38,39]. LCA has been already carried out
on stationary energy-storage systems on both battery-based [40,41] and fuel cell-based systems [42
44]. The novelty of this study is given by a comparison between the two different solutions, sized for
the same conditions for the stationary application. As far as the UAV is concerned, to our knowledge,
no previous LCA studies have been reported.
Figure 8. Total costs and cost distributions for the two alternatives of the mobile system.
In this case, the PEM fuel cell is responsible for about half of the total cost of the fuel cell-powered
drone, while the battery in the battery-powered system has a much lower impact, not only if compared
to the fuel cell of the fuel cell-based mobile system, but also to the previously-presented battery-based
stationary application. This is simply due to the different number of batteries required by the two
applications. In the case of the UAV, a single battery is enough for a single run while, for the stationary
application, 12 batteries are necessary to guarantee two days of self-sufficiency. The impact of the engines
and structure of the drone to the total cost of the drone, as well as that of the control and image acquisition
part, is quite different for the two systems, even if the absolute cost is obviously the same. This result
indicates a very different contributions of the two energy storage methods to the total cost of the drone.
In the case of the battery-based drone, 52% of the total price is due to the engines and structure.
This can be attributed to the use of carbon fiber. The production of this material is, in fact, energy- and
capital-intensive. Therefore, a large effort is being done to develop new production technologies of
carbon fiber, in order to significantly reduce manufacturing costs [
35
]. Structure and engines represent
21% of the total price of the fuel cell-powered UAV. In this case, however, the type III gas tanks are
partly made of carbon fiber and contribute to 8% of the total price of the system, suggesting the need
of an improvement in composite tank manufacturing [36].
The systems examined for the two applications show the same main critical aspect from a cost
point of view: the higher impact of the fuel cell with respect to Li-ion batteries. In fact, the latter
represents a mature technology already commercialized on a large scale. In particular, in the case
of selected applications, battery-powered drones are already available at different prices and sizes,
while for stationary application kits containing batteries, photovoltaic panels, and controllers can be
purchased in a variety of power options.
The commercial situation of fuel cell technology is, at present, quite different, these products not
yet being commercialized on a large scale. Their production process, which still needs improvement [
37
],
makes them quite expensive. If there is a market for PEM fuel cells for stationary use (e.g., small-scale CHP),
when PEM fuel for mobile and aerospace applications are considered, the prices increase significantly.
This is due to the use of lightweight materials and to a significantly lower diffusion on the market of this
type of fuel cell, when compared to similar systems for stationary applications.
4. Life Cycle Assessment
Life cycle assessment (LCA) is an important tool to evaluate the environmental impact of a
product, as described by the ISO 14040/14044 methodology [
38
,
39
]. LCA has been already carried out
on stationary energy-storage systems on both battery-based [
40
,
41
] and fuel cell-based systems [
42
44
].
The novelty of this study is given by a comparison between the two different solutions, sized for the
same conditions for the stationary application. As far as the UAV is concerned, to our knowledge,
no previous LCA studies have been reported.
Challenges 2017,8, 9 8 of 15
4.1. Goal and Scope
The goal of this study is to obtain an overview of the potential environmental impacts of the
described systems, identifying the main bottlenecks associated with the manufacturing process of
corresponding components. The functional unit of an LCA study is the reference to which all of the
inputs and outputs are related, thus allowing a comparison among different systems. In this study the
systems examined have different applications and sizes, so a functional unit of 1 kW power supplied
has been chosen.
4.2. Inventory
The data used for this LCA study have been taken from the Ecoinvent database [
45
].
Components and materials composing the systems are listed in the Tables 36(left column),
together with data taken from Ecoinvent (right column) to model them. All elements are rescaled on
the basis of the system being examined, as explained later in detail.
4.2.1. Inventory for the Stationary Systems
The inventory for the fuel cell-based stationary system has been grouped in Table 3
Table 3. Inventory for the fuel cell- based stationary system.
Components Data from Ecoinvent
Polycrystalline silicon solar panel (32 ×0.25 kW) Polycrystalline silicon solar panel (0.21 kW)
PEM Fuel cell (3 kW) PEM fuel cell (2 kW)
Alkaline electrolyzer (5 kW) PEM fuel cell (2 kW)
Inverter (3 kW) Inverter (2.5 kW)
Solar controller Electric scooter controller
Auxiliary Components for the Fuel Cell System
Aluminum gas tanks (12 ×50 l) Drawing of a wrought aluminum alloy (1 kg)
Plastics (6 kg) Molding of bottle grade PET granulate (1 kg)
Steel (356.4 kg) Galvanized steel (1 kg)
Connection cables (145 m) Connector cable for computer (1 m)
Li-ion batteries for startup (3.6 kWh) Li-ion battery for electric vehicle
Brass (0.6 kg) Brass (1 kg) + Brass casting
Steel (1.1 kg) Stainless steel (1 kg) + average metal working
for manufacturing of a chromium steel product
Steel (0.6 kg) Chromium steel pipe (1 kg)
The PEM fuel cell in Ecoinvent [45], with a nominal power output of 2 kW, has been rescaled on
the 3 kW PEM fuel cell of the fuel cell system. Due to the unavailability of data on alkaline electrolyzers,
this device has been modeled with the same rescaled PEM fuel cell, as discussed in [
25
]. The inventory
for the battery-based stationary system has been grouped in Table 4.
Table 4. Inventory for the battery-based system.
Components Data from Ecoinvent
Polycrystalline silicon solar panel (20 ×0.25 kW) Polycrystalline silicon solar panel (0.21 kW)
LiFePO4batteries (22 kWh) LiMn2O4battery for electric vehicle (2 kWh)
Inverter (3 kW) Inverter (2.5 kW)
Solar controller Electric scooter controller
Auxiliary Components for the Fuel Cell System
Steel (222.7 kg) Galvanized steel (1 kg)
Connection cables (100 m) Connector cable for computer (1 m)
Challenges 2017,8, 9 9 of 15
Even though the photovoltaic panels present in Ecoinvent [
45
] have a lower watt-peak with
respect to those reported in the datasheet of the panels considered for this study, they comprise of the
same number of cells. It is, thus, reasonable to consider the use of a similar amount of materials for
their manufacturing.
4.2.2. Inventory for the Mobile System
The inventory for the fuel cell-based UAVs is shown in Table 5.
Table 5. Inventory for the fuel cell-based mobile system.
Components Data from Ecoinvent
PEM Fuel cell 1 kW PEM fuel cell 2 kW
Engines and structure
Copper production (1.6 kg) + wires drawing
PAN fiber production (2.92 kg)
Aluminum production (0.3 kg) + impact extraction
Gas tanks
Aluminum production (1.45 kg) + sheet rolling
PAN fiber production (1.21 kg)
Liquid epoxy resin production (0.81 kg)
Auxiliary Components for Fuel Cell System
Printed circuit board Printed wiring board for power supply unit
Stainless steel Chromium steel production (secondary) (0.33 kg) + Impact extrusion
Plastics Polyethylene production (0.3 kg) + Injection molding
Copper Copper production (0.17 kg)
Titanium Titanium production (0.17 kg)
Brass Brass casting (0.07 kg)
Air filter Polyethylene fleece (0.05 kg)
Since data on carbon fiber (CF) were not available in Ecoinvent [
45
], polyacrylonitrile (PAN)
production was considered, which is used as a precursor to obtain carbon fiber. Being that PAN is
a precursor, the conversion processes of the former into carbon fiber is not accounted for and, thus,
the impact of this process will be underestimated. According to a manufacturer [
46
] the energy input
for CF production from PAN is 72 MJ/kg, while the production of PAN requires 69.3 MJ/kg [
47
].
According to another study [
48
], the energy input for the overall process of CF production ranges from
286 to 704 MJ/kg. These energy input data give an idea of the potential environmental impacts of the
associated processes: from these values it seems that the impact of CF production is three times higher
than that of PAN fiber (or even more, according to Duflou et al. [
48
]). For copper, titanium, and brass,
due to their low amount, only production has been considered because the contribution of further
processing is negligible. The inventory for the battery-based UAVs is shown in Table 6.
Table 6. Inventory for the battery-based mobile system.
Components Data from Ecoinvent
Li-ion battery 1.5 kWh LiMn2O4battery for electric vehicle 2 kWh
Engines and structure
Copper production (1.6 kg) + wire drawing
PAN fiber production (2.92 kg)
Aluminum production (0.3 kg) + impact of extraction
Auxiliary Components for Battery System
Printed circuit board Printed wiring board for power supply unit
Challenges 2017,8, 9 10 of 15
4.3. LCA Results
LCA was performed by means of the commercial software Sima Pro 8.2 (PRéSustainability,
Amersfoort, The Netherlands) [
49
]. The impact assessment method chosen was Impact
2002+ [
50
]. Global warming potential (GWP) and non-renewable energy have been considered as
impact categories.
The impact assessment results for the stationary and mobile systems are reported in
Figures 9and 10, respectively.
Challenges 2017, 8, 9 10 of 15
4.3. LCA Results
LCA was performed by means of the commercial software Sima Pro 8.2 (PRé Sustainability,
Amersfoort, The Netherlands) [49]. The impact assessment method chosen was Impact 2002+ [50].
Global warming potential (GWP) and non-renewable energy have been considered as impact
categories.
The impact assessment results for the stationary and mobile systems are reported in Figures 9
and 10, respectively.
Figure 9. Impact distribution for the main components of the stationary systems for global warming
potential and non-renewable energy.
Figure 10. Impact distribution for the main components of the mobile systems for global warming
potential and non-renewable energy.
LCA results show similar trends for stationary and mobile applications. As can be noticed in the
Figures 9 and 10, both fuel cell and battery-based systems have low environmental burdens. In fact,
for the stationary application, the GWP is 1% and 3%, for the battery-based and fuel cell-based
systems, respectively, whereas it is 5% and 29%, respectively, for the mobile application. These values
are rather low, if compared to GWP of other components for the same systems. For example, in the
case of the stationary application, photovoltaic panels provide 85% and 31% of the GWP for the
battery-based and fuel cell-based systems, respectively. For the mobile systems, the engine and
structure of the UAV result in 58% and 12% of the GWP for the battery-based and fuel cell-based
systems, respectively.
Although a direct comparison with previous studies is not easy due to the different methods for
impact assessment used, similar battery-based stationary systems investigated by Balcombe et al. [51]
and Kabakian et al. [40] confirm the dominating impact of the solar panels with respect to batteries.
No detailed LCA studies on stationary systems coupling PV and fuel cells are available. In a study
Figure 9.
Impact distribution for the main components of the stationary systems for global warming
potential and non-renewable energy.
Challenges 2017, 8, 9 10 of 15
4.3. LCA Results
LCA was performed by means of the commercial software Sima Pro 8.2 (PRé Sustainability,
Amersfoort, The Netherlands) [49]. The impact assessment method chosen was Impact 2002+ [50].
Global warming potential (GWP) and non-renewable energy have been considered as impact
categories.
The impact assessment results for the stationary and mobile systems are reported in Figures 9
and 10, respectively.
Figure 9. Impact distribution for the main components of the stationary systems for global warming
potential and non-renewable energy.
Figure 10. Impact distribution for the main components of the mobile systems for global warming
potential and non-renewable energy.
LCA results show similar trends for stationary and mobile applications. As can be noticed in the
Figures 9 and 10, both fuel cell and battery-based systems have low environmental burdens. In fact,
for the stationary application, the GWP is 1% and 3%, for the battery-based and fuel cell-based
systems, respectively, whereas it is 5% and 29%, respectively, for the mobile application. These values
are rather low, if compared to GWP of other components for the same systems. For example, in the
case of the stationary application, photovoltaic panels provide 85% and 31% of the GWP for the
battery-based and fuel cell-based systems, respectively. For the mobile systems, the engine and
structure of the UAV result in 58% and 12% of the GWP for the battery-based and fuel cell-based
systems, respectively.
Although a direct comparison with previous studies is not easy due to the different methods for
impact assessment used, similar battery-based stationary systems investigated by Balcombe et al. [51]
and Kabakian et al. [40] confirm the dominating impact of the solar panels with respect to batteries.
No detailed LCA studies on stationary systems coupling PV and fuel cells are available. In a study
Figure 10.
Impact distribution for the main components of the mobile systems for global warming
potential and non-renewable energy.
LCA results show similar trends for stationary and mobile applications. As can be noticed in the
Figures 9and 10, both fuel cell and battery-based systems have low environmental burdens. In fact,
for the stationary application, the GWP is 1% and 3%, for the battery-based and fuel cell-based systems,
respectively, whereas it is 5% and 29%, respectively, for the mobile application. These values are rather
low, if compared to GWP of other components for the same systems. For example, in the case of the
stationary application, photovoltaic panels provide 85% and 31% of the GWP for the battery-based
and fuel cell-based systems, respectively. For the mobile systems, the engine and structure of the UAV
result in 58% and 12% of the GWP for the battery-based and fuel cell-based systems, respectively.
Although a direct comparison with previous studies is not easy due to the different methods for
impact assessment used, similar battery-based stationary systems investigated by Balcombe et al. [
51
]
and Kabakian et al. [
40
] confirm the dominating impact of the solar panels with respect to batteries.
Challenges 2017,8, 9 11 of 15
No detailed LCA studies on stationary systems coupling PV and fuel cells are available. In a study by
Bauer et al. [
15
] in a comparison between battery and fuel cell electric vehicles, both batteries and fuel
cells resulted in having lower environmental burdens for GWP with respect to the glider of the vehicle
(i.e., the vehicle without drivetrain). Even if the structure of the drone and the glider of the vehicle
in [
15
] are different in the materials used and in weight with respect to the battery/fuel cell, a similar
trend can be observed in Figure 10, as the structure of the UAV represents the largest contribution to
the total impact, especially in the case of the battery system.
The impact of the batteries is mainly given by the electrode manufacturing [
52
],
although distribution of the impacts between anode and cathode depends on the battery chemistry [
53
].
The environmental performance of batteries can be enhanced by improving the manufacturing
process, for example, by reducing or replacing some elements, like gallium used for the resistors [
54
],
or improving recycling and recovery of materials [55].
Similar considerations can be outlined in the case of fuel cells, where the largest contribution
to the environmental impact is given by the platinum group metals. The impact of platinum group
metals, although their small amount, lies mainly in their extraction process, as suggested in previous
studies [56,57] and confirmed by the impacts flowchart shown in Figure 11.
Challenges 2017, 8, 9 11 of 15
by Bauer et al. [15] in a comparison between battery and fuel cell electric vehicles, both batteries and
fuel cells resulted in having lower environmental burdens for GWP with respect to the glider of the
vehicle (i.e., the vehicle without drivetrain). Even if the structure of the drone and the glider of the
vehicle in [15] are different in the materials used and in weight with respect to the battery/fuel cell, a
similar trend can be observed in Figure 10, as the structure of the UAV represents the largest
contribution to the total impact, especially in the case of the battery system.
The impact of the batteries is mainly given by the electrode manufacturing [52], although
distribution of the impacts between anode and cathode depends on the battery chemistry [53]. The
environmental performance of batteries can be enhanced by improving the manufacturing process,
for example, by reducing or replacing some elements, like gallium used for the resistors [54], or
improving recycling and recovery of materials [55].
Similar considerations can be outlined in the case of fuel cells, where the largest contribution to
the environmental impact is given by the platinum group metals. The impact of platinum group
metals, although their small amount, lies mainly in their extraction process, as suggested in previous
studies [56,57] and confirmed by the impacts flowchart shown in Figure 11.
Figure 11. Environmental impacts flowchart for the PEM fuel cell.
As can be seen in Figures 9 and 10, for both hydrogen-based systems, a significant impact is
given by the gas tanks (62% for the stationary system and 49% for the mobile one). It must be pointed
out that due to the different application requirements, different types of tanks have been chosen for
the systems: Type I aluminum tanks [58] for the stationary system and Type III (aluminum liner
wrapped with carbon fiber [58]) for the mobile application, due to the stringent weight issues.
Although different, both gas cylinders types have high environmental burdens, mainly associated
with the production of the materials they are made of. In the case of the Type III tank, one of the main
contributors is the PAN fiber production. However, the last step of PAN conversion into carbon fiber
has not been considered in this study, as previously reported in paragraph 4.2.2. In other studies, the
Figure 11. Environmental impacts flowchart for the PEM fuel cell.
As can be seen in Figures 9and 10, for both hydrogen-based systems, a significant impact is given
by the gas tanks (62% for the stationary system and 49% for the mobile one). It must be pointed out that
due to the different application requirements, different types of tanks have been chosen for the systems:
Type I aluminum tanks [
58
] for the stationary system and Type III (aluminum liner wrapped with
carbon fiber [
58
]) for the mobile application, due to the stringent weight issues. Although different,
both gas cylinders types have high environmental burdens, mainly associated with the production
Challenges 2017,8, 9 12 of 15
of the materials they are made of. In the case of the Type III tank, one of the main contributors is
the PAN fiber production. However, the last step of PAN conversion into carbon fiber has not been
considered in this study, as previously reported in paragraph 4.2.2. In other studies, the contribution of
carbon fiber was considered [
46
48
]. In [
46
] the authors report that the production of carbon fiber from
PAN is a very energy-intensive process, involving the thermosetting of PAN fibers into an oxidizing
atmosphere at 200–300
C and carbonizing them at 1000–1700
C, leading to 80% of the total impact
for carbon fiber production. Both the liner of the Type III tanks and the Type I tanks for the stationary
system are made of aluminum. The main contribution to the environmental impact of this material is
the electrical energy consumption, the most critical step being the electrolytic smelting of bauxite [
59
].
Furthermore, in this study, primary aluminum was considered, which is much less environmentally
friendly than secondary aluminum [59].
5. Conclusions
In order to compare the battery and fuel cell-based technology for energy storage in stationary
and mobile applications, the results of LCA and cost analysis have been normalized per kWh energy
supplied and they are summarized in Figure 12. The mass of the storage system, cost, and global
warming potential are reported, together with the corresponding impact of the energy storage on
the system.
Challenges 2017, 8, 9 12 of 15
contribution of carbon fiber was considered [4648]. In [46] the authors report that the production of
carbon fiber from PAN is a very energy-intensive process, involving the thermosetting of PAN fibers
into an oxidizing atmosphere at 200300 °C and carbonizing them at 10001700 °C, leading to 80% of
the total impact for carbon fiber production. Both the liner of the Type III tanks and the Type I tanks
for the stationary system are made of aluminum. The main contribution to the environmental impact
of this material is the electrical energy consumption, the most critical step being the electrolytic
smelting of bauxite [59]. Furthermore, in this study, primary aluminum was considered, which is
much less environmentally friendly than secondary aluminum [59].
5. Conclusions
In order to compare the battery and fuel cell-based technology for energy storage in stationary
and mobile applications, the results of LCA and cost analysis have been normalized per kWh energy
supplied and they are summarized in Figure 12. The mass of the storage system, cost, and global
warming potential are reported, together with the corresponding impact of the energy storage on the
system.
Figure 12. Results normalized per kWh energy supplied for the different examined systems.
Both systems examined, whether for stationary or mobile use, present similar advantages and
drawbacks. For both stationary and mobile systems presented, the battery-based systems are simpler
than the fuel cell-based ones, requiring fewer auxiliary components. The latter requires a power
supply that determines a reduction in the overall system efficiency, since this power is not used for
the household or the flying range. The fuel cell systems are, thus, oversized to compensate this extra
consumption (and efficiency of the electrolyzer, in the case of the fuel cell-based stationary system).
Systems using battery storage can benefit from a wide commercial diffusion of Li-ion batteries and
correlated devices for the chosen application (for example, the already assembled micro-UAVs, as
well as kits containing battery packs, solar panels, controllers, and an inverter for stationary off-grid
applications), which makes the prices more attractive. On the other hand, as soon as the amount of
energy to be stored increases, new batteries have to be added, which means additional costs and the
Figure 12. Results normalized per kWh energy supplied for the different examined systems.
Both systems examined, whether for stationary or mobile use, present similar advantages and
drawbacks. For both stationary and mobile systems presented, the battery-based systems are simpler
than the fuel cell-based ones, requiring fewer auxiliary components. The latter requires a power
supply that determines a reduction in the overall system efficiency, since this power is not used for
the household or the flying range. The fuel cell systems are, thus, oversized to compensate this
extra consumption (and efficiency of the electrolyzer, in the case of the fuel cell-based stationary
system). Systems using battery storage can benefit from a wide commercial diffusion of Li-ion batteries
Challenges 2017,8, 9 13 of 15
and correlated devices for the chosen application (for example, the already assembled micro-UAVs,
as well as kits containing battery packs, solar panels, controllers, and an inverter for stationary off-grid
applications), which makes the prices more attractive. On the other hand, as soon as the amount of
energy to be stored increases, new batteries have to be added, which means additional costs and the
increasing weight of the system. In stationary applications weight is not an issue. However, in UAV
applications the weight of the additional battery might not be compatible with the features of a drone
and become a limiting factor.
In FC-based systems, given the maximum power output of a fuel cell (and its fuel consumption),
the only limiting factor is the amount of hydrogen to be stored. The main drawback of fuel cell-based
systems is, at present, represented by their high cost, which is about double that of a battery-based
system of the same size and for the same applications. Fuel cell-based systems are more complex and
require a larger number of auxiliary components for their operation, which means additional weight.
This has to be taken into account, especially when considering mobile applications.
LCA results have shown that both battery and fuel cells have low environmental burdens with
respect to other components of the same systems.
Acknowledgments:
This work was performed in the framework of the Piedmont Regional projects “STERIN” and
“Dron-Hy”, financed by FINPIEMONTE, POR-FESR Asse I, AttivitàI.1.3 Innovazione e P.M.I., Polo “Architettura
Sostenibile e Idrogeno” and Polo “Polight”, respectively.
Author Contributions:
Nadia Belmonte performed cost and Life cycle assessment analysis and drafted the paper;
Carlo Luetto and Stefano Staulo defined the size and auxiliaries of the investigated systems; Paola Rizzi and
Marcello Baricco coordinated the activities and finalized the text.
Conflicts of Interest: The authors declare no conflict of interest.
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