Just one glance at the boat pulling into Ocean Terminal last month was enough to tell you were looking at something revolutionary. The Turanor PlanetSolar is the largest solar-powered boat ever built and is helping to prove the practical value of harnessing energy from the sun. Its round-the-world odyssey marks a milestone. So far, it has travelled 38,000 kilometres, free of any incident, and more importantly, free of any pollution - no emissions into the air or water, and no noise. The only obstacle in the way of this wonderfully clean transport is cost. The price of designing and building the boat was more than HK$135 million. But while the PlanetSolar may not be commercially viable, there should be a bright, sunlit future for the technology behind it. Beyond cost, there are two drawbacks to the sun-powered ship. First, its light-sensitive panels can be used for a mere 20 years - and they contain silicon and other heavy metals that are non-biodegradable and could therefore be harmful to the environment. The panels could be recycled but, again, at an unaffordably high cost. In other words, after 20 years, the panels will end up in landfills. Secondly, the PlanetSolar's dependence on weather conditions prevents the ship from taking the most direct route. It has to avoid cloudy areas which increases costs. It also means that, as PlanetSolar left Tsim Sha Tsui with 22,000 kilometres to go, it was impossible to know when it would reach its final destination of Portugal. To perfect the technology, the energy storage system must be improved. Like a camel that stores water for its journey, the ship can travel for a certain distance before becoming 'thirsty' for sunlight. Currently, PlanetSolar can store about 60 days' worth of energy, equivalent to 1,200 kilowatts. Though a ground-breaking achievement, it is only a small measurement in terms of the great distances across oceans. A solution would be to develop hybrid ships, combining solar power and traditional fossil fuels. Raphael Domjan, the boat's Swiss designer, says the ship is an extreme experiment. Ship-makers should focus on hybrid boats, using fossil fuel as a back-up source to power the vessel when there is no sunlight, Domjan adds. I believe hybrid boats could be the future of sea transport. It's only a matter of time before renewable energy becomes more affordable than fossil fuels. Why not plan ahead and make the change now?