Large-scale solar powered ship
Figure 1: Horizontal solar panels can capture direct solar energy while vertical panels can capture reflected sunlight
Introduction
With the depletion and increasing cost of traditional fossil fuels,
solar energy is a promising alternative technology for the shipping industry.
Solar power not only has the potential to reduce the cost of energy spent by
current ships but also improve ships’ navigability, particularly in the open
sea where there is a large amount of solar energy readily available. The
surface of solar panels that a cargo ship requires in order to capture the
solar energy necessary for its operation must be six to eight times larger than
the surface of the ship’s hull. This will ensure the ship can navigate
autonomously during the day and night at the same speed today’s cargo ships
sail. Therefore, a solar energy system is needed that allows solar panels to be
placed beyond the ship’s own surface area.
My solution is a telescopic structure that can expand and decrease its
size when needed. This design will enable a ship to navigate both the open sea
– in calm sea conditions it can sail with the extended solar structure – as
well as ports, narrow rivers and channels, during which time the structure can
be adjusted to fit a ship’s measurements.
To be able to expand and reduce the size of the structure that carries
the solar panels, a telescopic structure was designed that has solar panels
arranged horizontally and vertically. the horizontally arranged solar panels
would capture direct energy from the sun while the vertically arranged solar
panels would allow diffused solar energy and sunlight reflected from the sea water
to be captured. Solar energy reflected in the open sea is an important source
of energy (we consider this energy to be nearly 50% of the direct solar energy
of the sun in the open sea), which can be added to the direct solar energy used
in principle by the horizontally arranged panels.
Figure 2: Solar panels will be organised in a telescopic structure allowing navigation on the open sea and in ports
If the support structure of the solar panels is very large, this type of
ship also has as an option to have two floats attached to the sides of the hull
in order to support the structure’s own weight, taking the form of a Trimaran
species. where side floats only fulfill the function of supporting the weight
of the structure of the solar panels and no loads are carried on said floats.
Although these floats would increase the ship’s resistance in a
semi-folded position, it would also improve the lateral stability of the ship,
allowing it to navigate the high seas better during storms and easily maneuver
through shallow water depths.
Solar panel efficiency
At this time the maximum efficiency of commercial solar panels is approximately
20 to 21%. There are space-use solar cells with efficiencies of the order of 35
to 40%, however, they would be very expensive to use in this type of ship. The
maximum efficiency that a multi-juncture or tandem solar cell could have is
68.2%. Solar cells composed of silicon quantum dots, which have the potential
to reach efficiencies of the order of 40-50%, are currently under development.
Laboratories around the world are working on new types of solar cells, how the called Phonovoltaic Solar Cell that have the theoretical potential to reach efficiencies close to the Carnot Limit of 95%. So,
it can be expected that at some point 50% efficiency will be reached, if not
exceeded.
Therefore, for the calculations in this article, we will consider solar
panels with an efficiency of 50%.
Speed and characteristics
As an example, we will consider the application of this form of solar-powered
propulsion system to a Panamax-type vessel of 50,000dwt with a total maximum length
of about 250m, a maximum width of 32m and a draft of 12m. However, this type of
telescopic layout of solar panels may also be applied to larger ships such as post-Panamax
ships or smaller vessels where it is justified.
Figure
3: Solar panels in a fully folded position
For a vessel of these dimensions, the maximum width of the support
structure of the solar panels would be 256m (making it eight times larger than
the maximum width of the ship), 250m long (equal to the maximum length of the
vessel), with the height of the vertical solar panels 128m (half the width of
the horizontal panels). For calculation purposes, we consider the hours of
sunshine per day with a standard radiation of 1,000W/m2 at a south latitude of
35° (the position of Buenos Aires or Cape Town) is 6.5h/day for an average
summer day and 2.5h/day for a winter day in open sea conditions.
Consider also that the vertical solar panels that capture diffuse and sea-reflected
surface solar energy have an energy radiation of the order of 50% of the direct
solar energy of the sun. That is, that the vertically arranged solar panels will
generate around 50% of the energy generated by the horizontally arranged panels,
for a general situation of the ship, although this diffuse reflected solar
energy will depend on the position of the ship and the vertical panels relative
to the sun.
As stated previously, the solar panels used in this ship will have a
maximum efficiency of 50%, generating an estimated 13,000kW of energy per day
during the summer and 5,000kW of energy on a typical winter day.
Further factors to be considered in this scenario include:
- The extra advance resistance generated by the ship’s pontoons and the sail resistance of the vertical solar panel as well as the structure of the horizontal solar panels.
- The vessel’s two electric motors coupled to two propellers and direction of different turns, which generates an improvement in propulsion efficiency with respect to the use of a single propeller of 5-8%.
- The vessel and its pontoons will be coated with silicone paints, which have 4-8% less resistance than the conventional paints that are primarily used today.
- The overall efficiency of the electrical system of both motors and electric batteries is of the order of 80%.
Given all of the above, we expect the ship to have an average speed of
16.5knots (equal to 30,55km/h) on a summer day and 12.5knots (equal to
23,15km/h) on a winter day. This calculation is only to estimate what such a
ship could achieve in the future with a solar cell efficiency of 50%. However,
the efficiencies of marine solar cells today are lower than the values considered
in these calculations.
Operation at higher speeds
This type of ship will have to carry electric accumulators to store the
solar energy generated by the solar panels during the day for the night.
Additionally, a sufficient amount of electric batteries are needed to guarantee
the ship will have energy stored for at least four or five days of operation in
case the ship has to go through an area of storms or cloudy days. If a greater speed
is needed, the batteries carried by the ship can be recharged while at port.
During its operation, the ship will be able to draw on the energy
generated by the solar panels and the energy from the electric accumulators,
allowing the ship to obtain a greater speed than a vessel which only relies on
the energy generated by the solar panels.
Another interesting application that ships powered by solar energy may
have is the generation of surplus electrical energy at sea that could then be
used in coastal areas on land. Such ships could replace floating solar parks,
which can be difficult to tie to the sea floor and struggle to withstand the
swell of a strong storm.
If we use a solar boat to generate energy with solar energy that
radiates over the seas or the oceans offshore, it will be easier and more
convenient than doing it with floating solar parks.
In addition, these power-generating ships in their offshore operation
may function as electric power recharging stations for ships that need more
electrical power for operation, either because they are winter days with little
solar radiation at sea or because they need higher speed of transport of the
loads that the vessel can give it with the solar panels that it carries with
this type of solar panel carrier structures.
Loading and unloading
In this type of solar ship, when the structure that holds the solar
panels is folded, the telescopic structure and its solar panels will be folded
on top of the ship and above the loads that will be placed on the ship’s hull,
whether bulk cargo or containerised cargo.
To be able to load and unload a special telescopic crane bridge would be
required for loading and unloading. Current port cranes would be incapable of
performing this task correctly because the upper part of the ship is covered by
the solar panels and its support structure when it is folded.
The crane bridge would have a main carriage that moves longitudinally
along the ship’s hull and transversely across the width. It can be seen in
schematic form in Figure 4, illustrating how the crane bridge will load and
unload while moored.
Figure
4: The telescopic crane bridge
Construction of the first
ships powered partially by solar energy
From another point of view, looking to the future, one possibility is
that solar powered boats will begin to be used after electrically powered boats
start to be manufactured from rechargeable electric batteries, as these types
of boats are less complex to manufacture than fully solar powered boats as
proposed in this article. The ships that are currently beginning to be
manufactured powered by lithium batteries and recharged in the ports, how
current electric cars are recharged, have a cost of the recharge energy
purchased by the ship from the systems of recharges at a price that ranges
between 120 to 150 u$s/MWh, but if we take into account that today the
cost of wholesale production of solar energy in a photovoltaic park in a sunny
area of a desert it does not exceed 15 or 30 u$s/MWh and although in
the open sea the direct solar radiation is a little lower than in a desert in
the future it will surely be convenient that the electric boats that are
currently being manufactured are add as many solar panels as possible to
self-consume your own generated energy and thus decrease the costs of the
energy purchased to propel it to external electrical energy sources to the
boat, starting slowly to manufacture the solar powered boats how we propose in
this article.
One way to start building this type of ship with the solar panels that exist today, which as we said have a lower efficiency than those considered in the calculations we did, is to make a solar ship with a smaller support structure for the solar panels without the side floats, which are the ones that generate the most navigability complications for this type of boats, reducing the solar energy generated by the ship but also reducing the complexity of construction and operation of the telescopic structure and making a partial solar energy propulsion, that is, propelled partially to solar energy with the current panels that have an efficiency of the order of 20-21% and the rest of the energy necessary to move the ship would be recharging the ship's electric batteries with recharging sources external to the ship.
This type of ships powered partially by solar energy could start to
build in the manner indicated in the figure below, where it is seen that the
surface of the solar panels is less than the vessel intended to operate 100%
solar energy but also surely easier to build and test on the first ships that
want to be manufactured with this telescopic solar panel support system.
Figure 5: Design that would have the first solar boats built partially with solar energy without a large horizontal structure and without its side floats.
Conclusion
The increase in the cost of fossil fuels in recent years due to the increasing depletion of its world reserves, forces us to look for alternative fuels, where solar energy, due to the abundance of obtaining it, especially in the open seas and oceans, and with its ever-increasing cost reduction and improvements in the efficiency and in the useful life of its collection equipment and accumulation of the electrical energy generated, it can be a very important alternative to consider.
Although the use of solar energy in cargo ships has certain technical difficulties such as the addition of the telescopic structure proposed here to increase the surface area for capturing the solar energy that the ship will need for its operation, which may add inconveniences in navigation compared to traditional ships; given the high cost of fossil fuels, it allows us to think that the use of solar energy in the propulsion of ships will be able to effectively replace the use of traditional fuels, and in addition, significantly reduce the cost of operation and value end of the freight of the transported loads.
Furthermore, considering the other alternatives currently being studied to replace fossil fuels on ships that are primarily the use of electric batteries or hydrogen, which would recharge on ships as they currently recharge on electric cars; we also believe that the direct use of the solar panels on the ships themselves, will grant them greater autonomy to reach greater distances traveled without the need for energy recharges and a lower cost in their operation since it consumes the energy produced by their own solar panels and not the purchase of electrical energy from sources external to the ship is necessary.
Although the use of solar energy in cargo ships has certain technical difficulties such as the addition of the telescopic structure proposed here to increase the surface area for capturing the solar energy that the ship will need for its operation, which may add inconveniences in navigation compared to traditional ships; given the high cost of fossil fuels, it allows us to think that the use of solar energy in the propulsion of ships will be able to effectively replace the use of traditional fuels, and in addition, significantly reduce the cost of operation and value end of the freight of the transported loads.
Furthermore, considering the other alternatives currently being studied to replace fossil fuels on ships that are primarily the use of electric batteries or hydrogen, which would recharge on ships as they currently recharge on electric cars; we also believe that the direct use of the solar panels on the ships themselves, will grant them greater autonomy to reach greater distances traveled without the need for energy recharges and a lower cost in their operation since it consumes the energy produced by their own solar panels and not the purchase of electrical energy from sources external to the ship is necessary.
Therefore, we believe that the telescopic structure that carries solar panels that we propose in this project so that ships can be propelled by solar energy will be able to have a great implementation in large-load transport vessels both in the present and in the future and surely we believe that its implementation will be progressive over time, starting to use small and medium-sized structures and as navigability problems and the weight that this structure generates improve, larger and larger structures will be implemented until trying to generate 100% of the energy that these ships consume with their own solar panels to reduce as much as possible the cost of the energy consumption of these ships and reduce the cost and value of the freight of the cargoes transported.
International Publications of this Project
This Large-Scale Solar Powered Ship project was published by the prestigious naval engineering magazine "The Naval Architect" in January 2020 which is edited by the Royal Institution of Naval Architects (R.I.N.A.) of the United Kingdom.
Project status
At this time, a patent application for the telescopic structure of the ship’s solar panels has been filed, and we are seeking interested industry parties in hopes of being able to build this project.
If you are interested in this project you can contact me by email:
Martín-Giordano@hotmail.com.
