How much fuel does the Burgus catamaran save?

Solar modules on board

Roman Rubanovich, NENCOM

In 2021, we participated in the construction of a tourist catamaran for the Burgas municipality. We were tasked with developing a photovoltaic (PV) backup power system for the critical loads of the ship.

After three years of successful vessel operation, we gathered detailed statistics and updated our article «Solar energy for a catamaran» with new data. During this period, the photovoltaic system produced 9 MW·h of electrical energy, which accounted for 80% of the total consumption on the critical line. The remaining 20% was provided by the diesel generator and shore power.

Data from the monitoring system

As usual, we posted a link to this article on our Facebook page, which drew a lot of attention to this unconventional project. Among the comments was one that said, «Compared to fuel, this is 0.0001% of the energy».

We asked the author of this comment to show the complete calculation, not just the result, as it would be beneficial for everyone. However, the commenter refused to provide the computations, suggesting that we take care of it ourselves. Fine, let’s evaluate.

Share of solar energy

The catamaran’s engines use diesel fuel to convert the energy from its combustion into mechanical energy for the vessel’s movement. The efficiency of the diesel engine is around 40%.

Photovoltaic modules use photons of light to convert solar energy into electricity, which powers the critical loads on board the ship. The efficiency of the solar modules is around 20%.

Construction of the catamaran

According to information from the shipbuilding company «Galera 07», the Burgus catamaran consumes about 100 liters of diesel per hour at a cruising speed of 9 knots. It operates an average of 5 hours a day, 120 days a year. Thus, the catamaran’s engines have consumed about 180 thousand liters of diesel fuel over 3 years of operation.

The energy density of diesel fuel is about 10 kW·h per liter. It turns out that over 3 years, the catamaran’s engines consumed ~1 800 MW·h of fuel energy, providing ~720 MW·h of mechanical energy for the vessel’s movement.

During the same time, the catamaran’s PV system, as stated in our article, produced 9 MW·h of electrical energy to power the critical loads on board the vessel, which constitutes 1.25% of the mechanical energy of the engines.

The commentator’s estimate of 0.0001% differs from the actual value in 12.5 thousand times. If we take the benefit of the correct comment as 100%, then mathematically, the benefit of such a comment amounts to a negligible 0.008%. But in reality, this comment is very important as it allows our followers to learn more about the operation of photovoltaic systems.

Why do we compare the amount of electrical energy produced by the PV system with the mechanical energy of the catamaran’s engines, rather than with the energy of the burned fuel?

Because fuel is the source of energy for the engines we need for movement, just as the Sun is the source of energy for the PV system, which we need for producing electricity.

Previously, we mentioned that the efficiency of solar modules is around 20%. This means that to produce 9 MW·h of electrical energy, we «spent» 45 MW·h of solar energy, which already accounts for 2.5% of the energy of the consumed fuel.

The key difference in such consumption is that:

1. The Sun is an inexhaustible source of energy on a human scale;

2. The Sun is a free source of energy (even the delivery is free);

3. By using solar energy, we do not disrupt the thermal balance of the planet.

Fuel savings

We can also calculate how much additional fuel the catamaran’s diesel generator would have consumed if our PV system were not present.

To produce 9 MW·h of electrical energy at 40% efficiency, the generator would require 22.5 MW·h of fuel energy. We already know that the energy density of diesel fuel is about 10 kW·h per liter. This means we would need to burn an additional 2 250 liters of fuel, costing around 2 800 €, not to mention the significant increase in maintenance costs for the generator.

It turns out that our PV system not only fulfills its main task — uninterrupted power supply for the critical loads of the ship, but also returns the investments made in it every day, even though such a task was not set at all.

Furthermore, as we wrote in the article, by replacing the small AGM batteries with LFP batteries of higher capacity, the performance of the PV system will increase significantly. In this case, according to our estimates, the system will generate no less than 14 MW·h of electrical energy over a similar three-year period, which will account for about 2% of the mechanical energy of the engines.

The potential of photovoltaics

Since we are already doing calculations, let’s also estimate how much energy the PV system could produce if the solar modules were installed as a canopy over the catamaran’s hull, as shown in this photo:

Solar catamaran © Mobicat

In the case of the Burgus catamaran, taking into account the additional surfaces on the sides, we could utilize about 140 m², installing 70 solar modules of 440 Wp each. Thus, the installed capacity of the PV system would be 30.8 kWp, which is exactly 7 times greater than the current system (4.4 kWp).

This «floating power station» could produce more than 100 MW·h over 3 years, providing about 15% of the total energy needed by the vessel for both movement and operation of electrical appliances. Of course, in this case, our catamaran would require hybrid engines, but there are no problems with that. The solar catamaran Mobicat, for example, is completely electric.

Photovoltaics in water transport — a very promising direction. It can be particularly advantageous when used on ferries and water taxis; during pauses between trips, the energy reserve in the batteries will be automatically replenished, unlike fuel, which unfortunately does not appear by itself in the tanks.

We at NENCOM are advocates of electric transport. Thanks to the rapid development of technologies in this area, the efficiency of movement on electric drive is constantly increasing. The efficiency of modern synchronous permanent magnet motors (PMSM) is 94-97%, while the overall efficiency of the best production diesel engines is in the range of 40-45%.

The weak link in the electric propulsion system is the batteries, whose energy density, although increasing year by year, still significantly lags behind that of combustible fuels. However, for projects like the Burgus catamaran, this disadvantage could be compensated by using fully submerged foils, which reduce hydrodynamic resistance by 80%.

Hydrofoils © Candela

Modern PMSM are so compact and reliable that they can be integrated directly into the hydrofoils of an electric boat or catamaran. This technology significantly reduces energy consumption, increases speed, and provides passenger comfort through an active stabilization system.