I had the opportunity to speak about solar electric boats during a panel discussion on mobility, attended by ministers and senior officials from over 35 Asia-Pacific members states of International Solar Alliance (ISA). I introduced Navalt as a marine technology company specialising in the design and manufacture of solar electric boats for public transport, tourism, fishing and other applications. Since I was explicitly asked how we reduce cost, enhance reliability, manage public perception, and overcome adoption barriers, I structured my explanation accordingly.
When addressing cost, it is important to discuss about CAPEX (capital expenditure) and OPEX (operating expenses). Both are primarily influenced by energy cost – either the cost of storing energy (CAPEX) or consuming it (OPEX). Our approach to reducing these involved three design strategies:
- Weight reduction – We replace traditional materials like steel and wood with composites (such as GRP) and aluminium, along with structure optimisation. For example, a 75-passenger ferry traditionally weighting 35 tonnes can be halved to about 17 tonnes with this step.
- Hull shape optimisation – By refining the underwater hull shape, we reduce the drag and thus energy consumption by up to two-thirds.. For the above ferry, the power needed to cruise at 6 knots drops from 45 kW to just 15 kW.
- Maximising Solar energy contribution – Increasing boat size (while keeping the weight low) allows for a large solar plant. On the 75-passenger ferry operating at 6 knots, approximately 70% of the energy needs can be met by solar power, with the rest from the grid.
These combined measures enable smaller battery size and help keep CAPEX relatively low. Currently, solar ferries cost about 20-30% more to build than their diesel counterparts, primarily dies to the nascent scale of production compared with millions of electric vehicles on road. We anticipate that at a production scale of thousands of boats, this cost gap will disappear, bringing solar and diesel ferries to price parity.
From an OPEX perspective, a typical 75 passer diesel ferry consumes about 100 litres of fuel daily, roughly 100 USD in energy cost. In contrast, the solar ferry costs only around 3 USD daily- about 1/30th of the energy cost – owing to the efficiencies described above. This is supported by operational experience with over 35 solar boats running across India.
Regarding reliability, solar ferry utlise marine-grade systems designed for high robustness and redundancy. Unlike buses, where passengers can disembark quickly, boat emergencies require particularly reliable systems, including dual independent power trains and energy storage, engineered for continuous duty over 4000 annual operating hours.
To address public perception, solar ferries must meet or exceed diesel ferry functionality; they cannot be slower or have shorter range. In fact, solar ferries offer enhanced passenger experience – zero noise, vibration or smell of fuel – while being larger, more comfortable and more spacious. Importantly they produce no air or water pollution.
The main barrier to adoption remains scale. Larger production volumes will reduce costs and encourage widespread uptake. The second issue is especially crucial for island nations with smaller markets, where the logistics cost for transporting large boats-often 20-25% of boat price, as in the Maldives example-are substantial. Localising boat manufacturing and shipping only propulsion systems globally could reduce logistics cost to about 5%. However, this depends on the local boat building ecosystem, which can be challenging for small island countries.
We are already building solar ferries for countries such as the Maldives, Israel, Seychelles, and Canada. I hope more countries with abundant waterways take inspiration and transition to solar electric boats for public transport and tourism, contributing to a sustainable and clean maritime future.
Sandith Thandasherry 