Journal of Transportation Technologies, 2012, 2, 144-149
http://dx.doi.org/10.4236/jtts.2012.22015 Published Online April 2012 (http://www.SciRP.org/journal/jtts)
Solar-Electric Boat
Giuseppe Schirripa Spagnolo, Donato Papalillo, Andrea Martocchia, Giuseppe Makary
Department of Electronic Engineering, University “Roma Tre”, Roma, Italy
Received February 4, 2012; revised March 2, 2012; accepted March 15, 2012
ABSTRACT
The aim of this paper is the design of a Solar-Electric Boat for tourists’ transport along the coast, in the rivers, in the
lakes. Our idea is to define the project guidelines for the realization of a zero impact boat. This paper illustrates the
practical new technologies (naval architecture small craft design, mechanical and electrical design), rational design and
engineering approach, safety and reliability methods used in solar boats. In our project, the boat is powered by lith-
ium-ion batteries that can be charged at any time by the photovoltaic generator placed on a flat top structure. The pro-
ject is designed for brief trip around coast, where the public transport becomes very polluting during summer. Starting
from the consideration that this boat is used during sunny weather, it is possible to know the boat’s energy demand and
proceed with the design of a suitable electric boat and of the energy storage/management system. It is also proposed an
innovative management of charge/discharge of the batteries. With this management, we have optimized the use and
prolonged the time of life of the batteries during the navigation and the control of the real autonomy of it.
Keywords: Solar-Electric Ship; Electric Propulsion; Photovoltaic; Lithium-Ion Batteries
1. Introduction
Many protected areas in the world are facing the growth
of tourism pressure; the same problem is present in the
areas of naturalistic interest. Tourism is seen as a viable
financial option for protected areas with the tourism
concessions, through private sector partnerships, that per-
mitted to gaining momentum and that allows the over-
arching goal of preservation and conservation to remain
with the state. However, without appropriate planning or
best practices in place, tourism concessions can lead to
such problems as waste, habitat destruction and the dis-
placement of local people and wildlife. In other words,
tourism brings economic benefits to countries, but there
are usually substantial socio-economic and environmen-
tal costs associated with it. The inherent conflict between
protecting ecosystems and cultural heritage on one hand
and providing public use programs and related infra-
structure and visitor services in protected natural and
cultural areas on the other hand is as old as the modern
conservation movement [1]. Similar problems exist with
the tourism on coastal environments [2].
Tourists’ transport along the coast, in the rivers, in the
lakes, can be performed on route well-defined and car-
ried out with boats that sail at low speed. Therefore,
starting from the design of a hull that minimizes the drag,
In this paper it will be illustrate a “system” for tourist
navigation with an “exclusively” electric boat propelled
[3-5]. The ship is powered by direct solar energy. Our
boat uses solar cells that transform the solar energy into
electrical energy, which is stored temporarily in lith-
ium-ion batteries, and used to drive the boat through
electric motors (permanent magnet synchronous motors)
and drive systems [6,7]; electric propulsion offers effect-
tive maneuverability, precise and smooth speed control,
reduced engine room, low noise and low pollution rates.
Solar-electric boats are recommended solution for
tourist navigation in areas where combustion engines are
prohibited (lake, protected areas, etc.).
Actually many solar-electric boats are available [8-10],
unfortunately these boats have a sporadic use.
This paper wants to represent a base to design a so-
lar-electric boat. It desires to be a reference for control-
ling of the charge-discharge batteries and for checking
the real autonomy of navigation.
2. Ship Environment
2.1. The Catamaran
For our project we consider a ship with the following
characteristics.
 Catamaran
 Maximum speed: 15 km/h (~8 kts)
 Cruising range: 5 hours
 Length over all: 14.00 m
 Width: 5.50 m
 Draft at full load: 0.9 m
Besides we consider that:
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G. SCHIRRIPA SPAGNOLO ET AL. 145
 The ship is equipped with two 8 kW permanent
magnet synchronous motors;
 Normal cruising speeds equal to 8 km/h (~4 kts);
 Boat travels for about 200 days per year (about 1000
hours of navigation for year);
 Average electrical power required during the cruise
11 kW (average electrical energy consumption for
year 11 MWh).
Not all ships are suitable targets for the integration
with photovoltaic generating system. A solar-electric
ship must have sufficient deck space. For the project we
have chosen a catamaran. In our boat a flat top structure
is proposed (see Figure 1) in order to maximize the area
available for putting up a photovoltaic array.
2.2. Batteries
For our ship, we assume that the average electrical power
necessary during the cruise is 11 kW and the maximum
peak power is 22 kW.
To get a system that can ensure a reliable transport, we
must assume that the energy, used during the cruise (5 h),
must be entirely taken from the batteries; for designing in
safety, we have to hypothesize that the photovoltaic sys-
tem doesn’t supply energy. Therefore, the daily energy
consumption that the batteries have to provide is equal to
the average power (11 kW) for half cruise time (2.5
hours), while in the other half, we consider an emergency
situation during which, is required the maximum power
(22 kW) to ensure the fastest return journey to the harbor.
With all these hypotheses, the total storage battery ca-
pacity has to be >82 kWh. Figure 2 shows the electrical
load during a typical day without return in emergency.
Furthermore, we have to hypothesize the necessity to
charge the batteries during the docking time. To fulfill
Figure 1. Caramaran boat and available area for photo-
voltaic array.
Figure 2. Daily load.
this task, an access to the industrial grid connection (400
V), on the pier, is necessary. Rectifying the grid tension
is possible to ensure an effective DC voltage of 550 V.
For our project, we have chosen the batteries Valence
U27-36XP model.
Specifications of Battery model U27-36XP
Voltage (Vo) 38.4 V
Normal Capacity 45 Ah
Weight 19.6 kg
Dimension 306 × 172 × 225 mm
Standard discharge (Vcoff , Id) 30 V, 90 A
Standard charge (Vch, Ich) 43.8 V , 45 A
DC internal resistance 25 mΩ
If, we consider a system structure of four battery banks
(BM1, BM2, BM3 and BM4), as mentioned earlier, the
BMx bank must be compatible with the charging voltage
of 550V, so we need a series of N batteries:
Batt ch
550 13NV


Buso Batt
DC 499VN


The maximum necessary current for a return in emer-
gency of the boat is:
Bus
22 kW/DC44 A.
In conclusion we have considered a system made by
52 batteries (four battery banks), with these features:
 Total weight: 52 × 19.6 kg ≈ 1020 kg
 Volume: 0.306 × 0.172 × 0.225 × 52 ≈ 0.6 m3
 Maximum electrical energy storage ≈ 90 MWh.
The weight of the electric drive system is lower and
more efficient to distribute in the hull than a classical
system, therefore the drive unit is small and the batteries
can be distributed somewhat flexibly and it is possible to
divide them between the catamaran hulls. Comparing the
whole weight of electric system with diesel systems, in-
cluding all batteries, PV array, generators, fuel and the
electric system comes out either heavier, lighter, de-

G. SCHIRRIPA SPAGNOLO ET AL. 146
pending on the assumptions of fuel, or the same. Not
surprisingly, since the technology is not being manufac-
tured in high volume, the first cost of the electric system,
including installation is higher than the equivalent diesel
one, for about 30%, but it must be considered that prices
are very likely to come down with time.
Another advantage of the electric system is to have
“instant power”. There is no need to wait for the engine
to warm up; there is no gearbox to engage, it’s sufficient
to turn on and go. Instant reverse is available too; one
can go from full power forward to full reverse in an in-
stant for a very abrupt emergency stop.
2.3. Photovoltaic Generating System
In our boat the area available for laing a photovoltaic
array is about 55 m2. On this area, it is possible to install
42 Sanyo’s HIT Power 225 A solar module; every single
panel has a dimensions of 1.580 mm × 798 mm × 46 mm,
Maximum Power Voltage (Vmp) 43.4 V, Maximum
Power Current (Imp) 5.21 A, which leads to a Maximum
Output Power (WPmax) 225 W in Standard Test Condi-
tions.
We configure the connection of the panels in this way:
6 strings of 7 panels in series, providing an output
maximum power voltage of 304 V, and maximum power
current of 31.26 A.
The yearly average electrical energy from photovoltaic
array is given by the following equation
DC1 23 4mN
PQWKKKK (1)
 DC P is the photovoltaic energy [kWh/year].

N
W is the photovoltaic array energy output at stan-
dard radiation; in our case:
max max
0.225 kW42 panels9.450 kW
P
P .
 m Q is the yearly average flux of solar radiation; in
this work we consider a global horizontal irradiation
of 1500 kWh/m2/year.
 1
K
is a coefficient for compensating temperature
effect. Operating temperature increases when module
where placed in the sun. When operating temperature
increases, power output decreases (due to the proper-
ties of the conversion material—this is true for all so-
lar modules). For our photovoltaic panel 10.9K

is
a good approximation.
 2
K
is the coefficient that take account of the stain
and wear, factor that worsen with the passage of time.
A typical value of 2
K
can be estimated with 0.96.
 3
K
is the coefficient that take account of DC circuit
losses. Typical solar electric systems require more
than one module to be connected to another one. The
wires used to connect the modules create a slight re-
sistance in the electrical flow, that decrease the total
power output of the system, similar to low pressure
water flowing through a long water hose. In addition,
slight differences in power output from module-to-
module reduce the maximum power output available
from each module. A typical value of the losses is
0.95.
 4
K
is the coefficient that take account of the losses
of the DC-DC converter, in order to be converted for
the DC power from the solar modules to the usable
one (battery charge, motors, etc.). The conversion
DC-DC decreases approximately of 0.95.
With these considerations, the energy from our 42
Sanyo’s HIT Power 225 A solar module will be about 11
MWh; the photovoltaic array is able to furnish all the
energy necessary to the navigation. In other words, the
boat is driven by two electric motors powered “exclu-
sively” with rechargeable batteries. The energy stored in
the batteries derives through renewable energy sources.
The photovoltaic array is sized to provide, on average in
a year, all the energy required by the boat.
The boat is grid connected to a harbor; it can put in
grid the energy produced in excess and to furnish, when
necessary, the energy for the recharge of the batteries.
3. Power Management System (PMS)
The PMS is used for the right managing of the energy
aboard. Our idea is to provide the master with the real
autonomy of navigation and the real power from the bat-
tery.
In our system, a storage device (battery bank) is used
for balancing the mismatch between the available energy
by the photovoltaic array and power required by motors
and ship instruments. Both the powers that flow in and
out of the storage device have to be designed accurately
and controlled for a global energy management strategy.
In particular, since the lithium-ion batteries decrease the
storage capacity with aging, is not possible for the cap-
tain to know the instant energy available for the naviga-
tion, by measuring the output voltage of the battery.
Figure 3 shows the battery capacity changes with the
charge/discharge cycles.
Figure 3. Valence U27-36XP capacity retention.

G. SCHIRRIPA SPAGNOLO ET AL. 147
For a safety and reliable navigation, it is necessary to
know the real autonomy of navigation, which means to
know the real energy storage within the battery banks.
It is often important in fact to provide accurate infor-
mation regarding the remaining capacity of the battery.
Some batteries provide a “fuel gauge” that gives an indi-
cation of the charge level of the battery [11].
Figure 4 shows the setup of solar-electric boat. The
Figure 4. Topology of solar-electric boat.
proposed system is composed by a photovoltaic array,
four battery banks, a boost converter, a reversible in-
verter, three inverters, a charge control, a discharge con-
trol, and a computer to manage the energy flows (energy
management controller).
In our system, the maximum necessary current is about
44 A. This current can be supplied by a single battery
bank for one hour. Our chosen battery can be fully dis-
charged without damage [12]. To know the real stored
energy, we fully discharge a package of batteries. Sub-
sequently, the energy for the load it is provided by an-
other package of batteries. In this way, while a battery
bank supplies the necessary power, the discharged bat-
teries are under charge by the photovoltaic array or by
the grid. Measuring the energy flow toward the batteries
and from the batteries, cycle for cycle, it is possible to
determine the real stored energy.
3.1. Photovoltaic MPPT Control
MPPT control technology is widely used in the applica-
tion of solar power generation [13]. As shown in Figure
5, the output voltage of photovoltaic array can be deter-
mined in such way that the corresponding power is the
maximum out-power. If the working point is on the left
of the maximum power point: dd 0PV; and if the
working point is on the right of the maximum power
point: dd 0PV

.
According the characteristics of Figure 5, the control
process of the perturb and observe method is that: First,
set up a photovoltaic array operation voltage, then gener-
ate some periodic disturbance to the photovoltaic cell by
adjusting the duty cycle of the boost converter, then
compare the photovoltaic output power with the previous
one, if the output power increases, that means it works on
the left of maximum power point, and we should con-
tinue to maintain the disturbance direction to increase the
Figure 5. Output characteristic curve of photovoltaic array
strings.

G. SCHIRRIPA SPAGNOLO ET AL. 148
output voltage; otherwise, if the output power decreases,
that means it works on the right of the maximum power
point, the disturbance direction will be away from the
maximum power point, thus it should change the distur-
bance direction to decrease the output voltage of photo-
voltaic array. When the cycle is complete the system is
adjust, so finally, the maximum power point will be
found [14].
3.2. Charge and Discharge Controllers
Charge controller, through the information received by
the management control, sends the energy that comes
from the photovoltaic array, to the fully discharged bat-
tery bank. During the charge process, charge controller
measures the flow of incoming energy in the battery bank.
When the battery bank is completely charged, the energy
flow is sent to another fully discharged battery bank. In
the eventuality that there are no fully discharged battery
banks the energy flow is sent to the loads through the
discharge controller; in alternative, the energy flow is
sent to the grid if it is connected. The discharge control
carries to discharge fully a single battery bank at a time.
During the discharge process the discharge control
measures the energy flow and management control com-
pares this with one memorized during the preceding
charge. Through this comparison is possible to establish
the aging of the battery and to determine the real storable
energy.
3.3. Management Control
The principal assignment of the management control
system is to determine the real available energy for the
navigation and to furnish information on the ship auton-
omy. To realize this assignment, the system preserves
information of the flows of energy and manages the
complete discharge/charge of the battery banks.
The performances of all electrical systems are moni-
tored by the management control. It manages the dis-
charge of the single battery bank one at a time. With this
management strategy we check the battery life and limit
the number of charge/discharge. In our system, the sizing
of battery capacity has been select in such a way that,
with an opportune control, at most only one cycle of
charge/discharge could be done during the navigation.
Considering that our batteries bear 2000 complete dis-
charges with a loss within the 20% (see Figure 3), the
time life of the batteries will be greater than 10 years.
4. Conclusions
The design of a Solar-Electric Boat for tourists’ transport
along the coast, in the rivers, in the lakes has been pre-
sented. With our system, it is possible to replace the
standard fuel engine with an electric one, by accepting a
loss in power, and without changing the weight and the
dimension of the boat.
Our boat has greater price in comparison to an equiva-
lent boat equipped with traditional propulsion. Currently
to manufacture a solar-electric boat there are extra cost
due to photovoltaic plant, battery bank and management
control system. These additional costs are partially com-
pensated by reduction of operation costs; in solar-electric
boat there is no consumption of fuel and the costs of
maintenances are relatively lower. In our boat, the initial
additional cost is about of 50,000$. On the other hand,
the annual saving on the exercise is estimable in 5000$;
within ten years the extras costs are amortized. Besides,
the great advantage of the use of renewable energy pro-
duces indirect socio-economic advantages; ecosystem
preservation, reduction of CO2, NOx and SOx emission,
etc.
In this paper we have proposed an innovative man-
agement of charge/discharge for battery. With this man-
agement, we have optimized the batteries life, and during
the navigation we have a real time control of the naviga-
tion autonomy. Besides we have designed ship with zero
pollution and very low running costs; all the necessary
energy for the navigation has origin by renewable.
Electricity produced by photovoltaic is safer and more
environmentally benign than conventional sources of
energy production. However, there is environmental,
safety, and health issues associated with manufacturing,
using, and disposing of photovoltaic equipment. The
manufacturing of electronic equipment is energy inten-
sive.
The electricity produced is higher than the one neces-
sary to manufacture the photovoltaic modules and the
energy break-even point is usually reached in a period
from three to six years.
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