Case Study of 75 Pax Solar Boat
Mission: To transport 75 passengers across a 1.1 nautical miles (2 km) backwater stretch of Kerala at 5.5 knots average speed in a solar ferry built under class. The energy storage size is to be designed for sunny condition to reduce the cost (reduce size of battery bank).
For providing comfortable seating for 75 passengers and 3 crew, a catamaran with deck area of 15 m length and 5.5 breadth is sufficient. However after multiple iteration it was found that about 19.5 kW (18 kW for propulsion) solar panel power is needed to provide good energy management. For this purpose the boat size was defined as 20 m length and 7 m breadth.
Solar boats are better boats than conventional boats because they: do not pollute water, do not release, harmful emissions in air, are very silent and comfortable for passengers, have lower cost of ownership (high initial cost but low operating cost)A solar boat design process is completely different from that of a conventional boat so much so that it can be termed as “solar boat design philosophy.” It starts with defining functional and performance needs. Normally such functional and performance specifications are made to match conventional boats. Solar boats are very effective in passenger boats where the propulsion power needed is less (unlike high speed boats, tugs, trawlers, cargo vessels).A successful solar boat requires two different but critical focus areas
Some key points of solar boat design are;
- Optimisation of Energy management It is challenging to design solar ferries that run over 6 hours daily and almost every day in a year, compared to solar cruise boats that run 3 hours daily and 200 days in a year.
- the propulsion power needed for a solar passenger boat compared to a conventional boat is half in case of comparable composite boat and less than one-third of a steel boat.
- The total energy available during the day from solar panel depends on the location and weather condition. Locations closer to equator receives more solar energy than those far away and bright sunny day receives more energy from sun than a cloudy day.
- “Is the solar boat worth the high price?” The resounding answer is “YES”.Large solar ferries are usually four times costlier than a conventional single hull steel ferry. However if one raises the ergonomics and safety standards (built under classification society) of the conventional boat to that of solar ferries the ratio is close to three. The consumable cost (fuel and lubes) is usually INR 20-25 lakhs (USD 32-40000) for a large conventional ferry compared to zero for solar ferries. Diesel engines and steel hull structure have higher maintenance compared to electric motors and FRP hull. The total operating costs of a conventional ferry comes to about INR 25-30 lakhs (USD 40-48000) per year. In addition if we add the carbon credit, govt. subsidy, and then do an economic analysis, the break-even period is usually six years (see case study). If we were to add the cost of pollution for conventional ferries the break-even period is even lower.
White Paper on Solar Boats published by NavAlt Solar and Electric Boats is giving full details about this project.