Solar energy for a catamaran

Uninterruptible power supply for critical loads

Roman Rubanovich, NENCOM

We build solar power plants of various types and for different purposes: grid-tied, off-grid, and hybrid systems, for self-consumption and for selling electricity, suitable for private homes, offices, warehouses, factories, hotels, farms, yachts, and ships.

This time, we received an order from the shipbuilding company «Galera 07», which was developing a tourist catamaran for 100 passengers for the Burgas municipality. The catamaran will be equipped with two diesel engines with a total power of 544 kW (740 hp), as well as a 35 kW diesel generator to power electrical devices.

Contents

Task
Construction
Launching into the water
Testing
Journey home
Mysterious island
Videos
Three years later

Task

Our task is to create a backup power system for critical loads such as lighting, radar, echo sounder, navigation, radio communication, steering system, fire alarm, pumps, and more. Some of these require alternating current (AC) with a voltage of 230 V, while others need direct current (DC) with a voltage of 24 V.

In order to save fuel during normal operation and to extend the duration of autonomous operation in the event of generator failure during daylight hours, it is necessary to install photovoltaic (PV) modules that will convert solar energy into electrical.

The customer provided us with a 3D model of the ship with the planned layout of the solar modules — in the bow section, on the sides of the captain′s bridge and on the «wings» above it, as well as on the arch at the rear of the vessel:

We agreed on the technical specifications and system components with the customer, taking the allocated budget into account, and began the design process.

Construction

As soon as the aluminum body of the catamaran was ready, we arrived for inspection and to plan the installation work. Vertically, the ship is divided into three levels: the upper open deck, the main enclosed deck, and two hulls beneath it.

The length of the catamaran is 20 meters

The right hull houses one of the two engines and a generator, while the left hull contains the second engine and a freshwater storage tank.

The width of the catamaran is 7.8 meters

We started installing the equipment in July, so we literally had to sweat while working inside the hull of the ship, which was heated by the sun. The process was complicated by the fact that other teams involved in the construction of the vessel were also working alongside us, and we often had to wait our turn to access the necessary areas. We could cool off and take a break in the shade under the catamaran, where we discovered the culinary creations of an unknown artist:

Live fish and lobsters

Roasted pig

After the installation of insulating materials, it was much more pleasant to be inside the ship, and work became more enjoyable. On the main deck, directly beneath the captain′s bridge, there is a technical room where we were set to install the components of the photovoltaic system (in the center of the photo):

In this technical room, we installed equipment from the Netherlands company Victron Energy, which is perfectly suited for marine applications: five BlueSolar MPPT charge controllers (one for each group of PV modules) and a MultiPlus battery inverter with a power rating of 5 kV·A.

Solar charge controllers reduce the voltage generated by the photovoltaic panels to a level suitable for charging batteries, while proportionally increasing the current. Essentially, they are step-down DC-DC converters with a MPPT (maximum power point tracking) function.

The bidirectional inverter MultiPlus features a built-in charger, so it not only converts the direct current from batteries and solar modules into alternating current at 230 V, but it can also charge the batteries from shore power or a generator.

In the lower left corner of the photograph, there is a separation transformer, that is essential for ensuring electrical safety on board and for protecting against galvanic corrosion when connecting the vessel to shore power. Victron Energy manufactures isolation transformers and galvanic isolators for marine applications, but in our case, the transformer was delivered and installed by the contractor responsible for the main power system of the catamaran.

According to the requirements of the Bulgarian Register of Shipping (BRS), battery banks must not be installed in the same room as switching devices due to the potential for sparking. A separate ventilated compartment is provided for them behind a wall. Despite the few centimeters of distance between the batteries and other equipment, it was forbidden to breach the integrity of this wall, so the cables (both power ones with a cross-section of 95 mm², and the thinner, used for balancing and monitoring the voltage and temperature of the batteries) took a long route through the captain′s bridge above the technical room.

In our projects, we typically use durable, safe, and efficient lithium iron phosphate (LiFePO₄ or LFP) batteries. However, in this case, due to budget constraints, we opted for lead-acid Victron batteries type AGM (absorbent glass mat). We installed six 12-volt batteries with a capacity of 240 A·h each, grouping them into three strings of two batteries to achieve a nominal voltage of 24 V. The total energy reserve in the batteries is 17.3 kW·h, which, with a recommended depth of discharge of 50% for this type of battery, means about 8.6 kW·h of usable energy. The lifespan of AGM batteries typically ranges from 2 to 4 years, depending on operating conditions, after which they can be replaced with similar ones or more durable LFP batteries.

The aluminum sheet to the left of the batteries displays the alloy index used for the vessel: EN AW-5083-H111. This alloy, known for its very high corrosion resistance, is primarily utilized in shipbuilding and the chemical industry. Even with prolonged exposure to saltwater, the mechanical properties of aluminum 5083-H111 remain intact. Additionally, the alloy maintains exceptional strength after welding.

To convert solar energy into electricity, we used ten photovoltaic standard-sized Longi modules with a power rating of 370 Wp each, installing them on the front (3), the arch (3), and on the sides of the captain′s bridge (2+2). Additionally, on the wings and above the captain′s bridge we installed four compact Victron Energy modules rated at 175 Wp each. Thus, the total peak power of the solar panels amounted to 4.4 kWp.

Considering potential dynamic loads, we increased the number of mounting points: instead of four for each module, we used 16 for the standard modules and 12 for the compact modules.

Mass-produced solar modules have an area of about 2 m², which can sometimes pose a challenge for non-standard installations. Victron offers over 10 different sizes of PV modules (starting from very small 20-watt units measuring 44 × 35 cm), allowing for the selection of the optimal option for any yacht, boat, camper or caravan.

Victron Energy 175 Wp modules

Victron Energy also manufactures inverters and charge controllers of various power ratings, enabling the construction of both mini-systems for applications such as travel, telecommunications or street lighting, as well as powerful commercial systems for supplying energy to manufacturing facilities, offices or agriculture.

So, the catamaran is painted and ready to be launched into the water for the completion of installation work and testing of all systems. The aluminum hull and bronze propellers are additionally protected from galvanic corrosion by zinc sacrificial anodes (to the right in the photo).

Launching into the water

The complex operation of transporting the ship to the sea began, accompanied by road police and representatives from the network operator who managed the disconnection of power lines along the route.

The «wings» above the captain′s bridge had to be temporarily dismantled to pass under the high-voltage power lines. Navigating the narrow bridge over the river required precise maneuvering.

Finally, two powerful cranes gently lowered the catamaran onto the surface of the Black Sea

© Sky Pictures Bulgaria

After the launch, the installation and adjustment of various systems on the catamaran continued for several more days.

We reinstalled the solar modules above the captain′s bridge and also on the arch at the rear of the vessel.

It is important to note that the catamaran was entirely designed and built by Bulgarian specialists — employees of the Varna shipbuilding company «Galera 07» and numerous contracting companies. The project manager is captain Andrey Stanev:

Andrey Stanev on the captain′s bridge

The project also involved specialists from the Varna «Technical university» and the Bulgarian scientific «Ship hydrodynamics centre», located in Varna.

Thus, Bulgaria as a whole, and particularly the city of Varna, possesses all the necessary technical and human resources for the design and construction of vessels, including those powered by hybrid systems and fully electric ones.

Our team is inspired by the trust placed in NENCOM to design and build the emergency power system with photovoltaic modules for the catamaran. This is a significant responsibility and a unique experience for us.

The cost of this «floating solar power station» in 2021 amounted to 29 870 lv (15 270 €), including design, delivery, installation, commissioning and VAT.

Testing

The construction and testing process of the catamaran was conducted under the supervision of the Bulgarian Register of Shipping. The vessel confirmed a design speed of 13 kn (knots), while the actual maximum speed reached 14 kn (26 km/h):

© Sky Pictures Bulgaria

All systems operated correctly during the tests, the ship was approved by the acceptance commission, certified and registered under the name «Burgus».

© Sky Pictures Bulgaria

Journey home

On August 28, 2021, our «solar» catamaran set off on its maiden voyage from Varna to Burgas, its base location. We monitored its movement through Marine Traffic (MMSI 207836540).

© Sky Pictures Bulgaria

It was a sunny day, and throughout the voyage, the photovoltaic system generated power exceeding 3 kW, covering the consumption of all critical loads with a big reserve.

© Sky Pictures Bulgaria

For remote monitoring and management of our system, we installed on board a communication center Cerbo GX, and for local monitoring of all parameters, we integrated a display GX Touch into the dashboard on the captain′s bridge:

The monitoring system allows for separate observation of the performance of each of the five groups of solar modules and the status of the batteries:

Monitoring of the lead-acid batteries is made possible by the battery monitor, which is connected to Cerbo GX and transmits data to the portal.

Since some critical loads are powered by direct current from the batteries, we installed a BatteryProtect to prevent deep discharge.

© Burgas Municipality

After 6 hours of sailing, the «solar» catamaran arrived ceremoniously at Burgas port, where it remained the center of attention for journalists and the public for several more days.

The mysterious island

The catamaran «Burgus» runs regular trips from Burgas port to Saint Anastasia Island. Formed from ancient volcanic rocks, this island holds many stories and secrets.

© Burgas Municipality

Here stands a medieval monastery that survived not only pirate raids and fires but was also turned into a prison for 43 political prisoners in the early 20th century. Their escape to the Soviet Union was depicted in the film «On a Small Island» (1958) by director Rangel Valchanov.

Another notable chapter in the island’s cinematic history is the filming of «The Island» (2011) directed by Kamen Kalev, starring Laetitia Casta and Thure Lindhardt in the leading roles.

In the romantic drama, presented at the Cannes Film Festival, the couple faces unexpected challenges to their love on the mysterious Bulgarian island, adding a unique atmosphere to this mystical location.

© Burgas Municipality

Today, the island is a cozy space where visitors can explore a museum, attend concerts, enjoy local cuisine and even stay overnight. The journey to the island by catamaran takes just 25 minutes.

Videos

We present to your attention some interesting videos featuring our «solar» catamaran. First, the music video «Your name is a woman», filmed on the catamaran Burgus and the island of Saint Anastasia:

Secondly, an engaging video with time-lapse elements, shot and edited by our friend Petar Petrov from «Sky Pictures Bulgaria», which condenses the entire process of designing, building, and testing the catamaran into just 14 minutes:

Thirdly, an informative feature by Maritime Global about the Burgus catamaran, highlighting its specifications:

Three years later

Sufficient time has passed to confidently state that our system not only met expectations but also exceeded them. Serving essentially as a backup power source, the photovoltaic installation has effectively become the primary source of electricity on board.

During three years of operation, the total consumption of critical loads on the catamaran amounted to 11.2 MW·h, of which only 2.2 MW·h (20%) was supplied by the generator and shore power.

In the screenshot below, taken on August 28, 2024, the distribution of energy sources over the last 24 hours, 7 days, 30 days and 365 days is displayed:

The diagram shows that over the last 365 days, the consumption from the generator and shore network remains at the same 20% as over the past three years. We have not observed any significant signs of system degradation during this period, and a recent visual inspection of the equipment on site also confirmed that all components are in excellent condition.

In sunny weather, the system is fully autonomous, as the energy produced by the PV modules completely covers the current consumption, and the batteries do not discharge. Only in cloudy weather is the lack of PV generation supplemented by the energy reserves from the batteries, which manage to recharge during the catamaran’s stops between trips.

In fact, our system can be fully autonomous year-round, and the small consumption from shore power and the generator is due to the need to maintain a certain energy reserve in the batteries (around 80%) in case of generator failure. Our settings allow the batteries to discharge more deeply only in the absence of external power.

In addition, the size of the battery compartment in the catamaran allows for the installation of LFP batteries with much larger capacities. This can significantly increase the ship’s power autonomy not only directly (by increasing the energy reserve in the batteries) but also indirectly (due to the higher efficiency of LFP technology).