Frequently Asked Questions

The Concept
Solar powered boat is a matured technology that is rapidly developing worldwide. Now there are more than 50 solar boat manufacturers worldwide. The milestones achieved by some solar boat manufacturers around the world.
  1. World’s largest solar boat – MS Turanor Planet solar Launched in 31st March 2010 (First ever solar vehicle to circumnavigate the world).
  2. World’s first marine zero emission sea bus – La Rochelle Sea bus passenger solar ferry built by Alternatives energies of France in 1998.
  3. World’s Fastest Trans-Atlantic crossing – Sun 21, is a 14 meter catamaran boat built by MW-Line.
  4. World’s First vessel to cross Atlantic using solar energy- C60 is built by Grove solar boats.
Solar Boats are 100% eco-friendly and avoids the pollution (Air, Water & Noise) caused by conventional boats. It also provides a viable boating solution, with zero operating cost and low maintenance cost. They also have lower cost of ownership if the initial cost, operating cost and cost of pollution are factored in. For large solar boats the breakeven period is around 6 years.
Solar power is mainly used for the boat propulsion and operation of auxiliary equipment’s like fire pump, bilge pump, lights, wiper motor, horn, GPS etc. Thus the solar boats have zero operating cost.
Solar powered boats design is completely different from that of a conventional boat. Solar boat is designed based on the functional & performance needs. Some critical factors needed to consider in solar boat construction is that:

1) Boat is almost always catamaran for lower propulsion power
2) Hull shape needs to be optimized
3) Boat should be light weighted
4) Propeller design needs to be optimized
5) Flow to propeller, clearances, shaft bearing, and rudder needs to be optimized

These are aimed to reduce the propulsive power so that it can be powered by the sun. Hence utmost care should be given from right from the concept design stage. To convert the conventional boats to solar powered ones, these most critical rules are compromised and hence it is not viable to convert conventional boat to solar powered.
Endurance or range of a solar boat depends on the energy storage in your battery and energy produced from solar modules flowing to battery. On a sunny day with clear sun, the range will be increased. It also depends on the environment like wind speed, current, waves etc. which will affect the propulsion power.

Solar ferries are usually designed for 6-8 hours range on a sunny day.
It depends on the size of the battery bank. Most of the large solar boats are designed for recharging in 6 hours. In our 75 passenger solar ferry (#IndiasFirstSolarFerry) 50 kWh battery bank is used and it will take 5-6 hours to recharge this battery bank.
At night when vessel is docked, we can use the utility grid to charge the battery bank, which can help to start the vessel with full battery capacity in the morning.
License required to operate a solar boat are similar to the conventional boats. Rules in operating a conventional boat are applicable to solar powered boats also.
Compared to a conventional fuel operated vessel, solar boats are easy to operate. The twin propulsion system, and joy stick control system makes it convenient for the operator. Electric propulsion can be started from dead start easily compared to normal engine that require to heat up during a cold start.

Electric propulsion does not need a gear arrangement for the RPM control. However, proper training should be given to the boat driver on various controls & monitoring systems, to take the proper decision.
Solar ferry is equipped with two independent motors (with 100% redundancy) & battery bank. The independent propulsion systems provide a better safety & redundancy. Under normal conditions the motors run at 50% of load. In an emergency situation where one of the motor stops, we can use the alternate propulsion system which have an independent battery bank & solar modules.
Over time, all solar cells have a tendency to degrade slightly under the sun’s rays. Crystalline panels have a much slower degradation factor than thin film and will therefore continue to produce energy for a longer period of time. Warranties will reflect this: crystalline panels are often guaranteed for 80% performance in 20 years – an average degradation of 1% per year.
We build our boats in fiberglass and composite whose life is of course based on the maintenance and usage (a horizon of 20-30 years is very realistic). The electric drive contains little or no wear parts and requires no lubrication. Lithium batteries announce about 2500 cycles and last about 7 years (5 years warranty). Solar panels do not wear out and their performance are guaranteed at least 20 years. However a six-monthly check up of panel connectors and yearly check of solar panels is appropriate. Solar modules need to be cleaned every day by rinsing with fresh water.
This again depends on battery bank size. A 50 kWh battery bank used in 75 Pax Solar ferry would cost nearly 50 lakhs after a period of 5 years (mostly 7 years)
Yes! Don’t think that solar boats work only on sunny days. Whether its sun, cloud, rain or night it works, but endurance varies. During a cloudy day, the production from the solar module decreases but production is not zero. If you want extended range during night or cloud we can increase battery bank or provide intermediate charging from grid.
No. Car batteries are designed for short bursts of high power to crank an engine. Solar boats need batteries which give a steady power for a long time. For solar ferries we use lithium iron magnesium phosphate batteries.
We need lithium ion battery instead of the lead acid battery due to the following reasons:

  1. Deep discharge capability: Lithium ion batteries can deep discharge up-to 80-85% when compared to lead acid battery for optimum life cycle.
  2. More lifetime: Lithium Ion battery can give extended life time up to 5- 7 years compared to sealed lead acid battery which is to replace every two years.
  3. Better safety: Lithium ion battery have better safety when compared to normal lead acid battery
  4. Individual cell monitoring: Battery management system can help to monitor the voltage of individual cellin battery modules.
  5. The CAN Bus allows the information to be passed to battery management system which can help inmonitoring the different parameters of battery bank.
  6. Less weight & high energy density of lithium ion battery bank provides greater flexibility in solar boatdesign.
Battery bank is protected from deep discharge beyond 80% with help of automatic cut- off arrangement, which remove electrical loads from the battery bank.
Solar boats are designed to match the performance of conventional boats. So the propulsion system required to attain the speed should be chosen properly. All our large solar boats are designed for maximum cruise speed of 7.5 knots though the operating cruise speed would be in range of 6 knots. In case of our 75 Pax solar ferry to achieve a service speed of 5.5 knots, only 16 kW power is required, but in actual the boat is equipped with 40 kW propulsive power which provides 100% redundancy in adverse conditions.
Photovoltaic cells will produce energy from sunlight. This energy will be stored in the battery, and enables the boat to move at night. During a cloudy day, the production from the solar module decreases but production is not zero. But if the sky is overclouded for a long period then then the endurance and speed will be reduced. If you want extended range during night or cloud we can increase battery bank or provide intermediate charging from grid.
Similar to the Conventional boat having a fuel gauge to check the fuel level, solar ferries have monitoring system mounted which shows battery SOC (State of charge), battery temperature, battery voltage which help us to know we are safe to take the boat.

Like any other vehicle it’s always safe to check the battery and other systems are in proper condition, before starting the voyage.
Economic Analysis
It’s common to compare the price of solar boats with a conventional boat. This is because people think placing solar modules on top of conventional boats can make it solar powered boat.

To manufacture a solar/electric boat there are extra cost due to photovoltaic plant, battery bank, high-efficient motors and management control system. This entire system makes the solar boats more reliable. It will be clear to anyone that the lithium batteries are six to eight times costlier than normal lead acid batteries. Lithium batteries are used because they have a discharge depth of 80% compared to normal FLA batteries which makes boat more efficient

These additional costs are partially compensated by reduction of operation costs; in solar-electric boat there is no consumption of fuel and the cost of maintenance is relatively lower.
A conventional 75 passenger ferry that has to be build with similar ergonomics and safety standards under classification society approval would cost about 150 lakhs. With a two 50 HP main engine and consumption of 15 litres diesel per hour on average, and total of 150 litres per day (engines are running all the time). At current price of diesel that amounts to ₹7500 per day and ₹26 lakhs per year (350 days running).

Lubricating oil can be taken as 10% of fuel cost, which is ₹2.6 lakhs per year. Maintenance cost for engines is another 5%, ₹1.3 lakhs per year.
Total operating cost per year is ₹30 lakhs (excluding labour and other expenses that are same in both). These are expected to grow each year at 10%.

For solar ferry an operating cost that comes is in sixth year is replacement of battery bank. This is ₹30 lakhs for 50kWh system. A daily grid charging cost of ₹400 (@ ₹10/ unit) and total of ₹ 1.4 lakhs per year expected to grow at 10% per year.

The total cost of ownership of a conventional ferry and that of a solar ferry is listed in the two graphs.

If we were to compare the total cost of ownership between the two boats, see graph on the left.

The graph shows that although solar boats have higher upfront costs, the total cost of ownerships is lower. This boat has a break-even period of six years.

The total cost of a conventional ferry and that of a solar ferry is listed in the two graphs on top. It clearly shows that from after second year, solar ferry boat saves money for the client. If we were to compare the total cost of ownership between the two boats, see graph below. If one were to factor the cost of pollution and uncomfortable journey by conventional ferry then the savings would be even greater.