There is more energy to harvest at sea. True, water craft have stronger resistance to overcome but on balance, it means that energy independent electric boats are more common than their equivalents on land or in the air and they have lessons for both. The good weather/ bad weather duo of solar and wind generation are well established in the form of small propeller-type wind turbines on the stern of yachts and motor sailers coupled with solar decking but this has been too weak to charge traction batteries: it assisted with hotel services, navigation lights and so on. However, more efficient photovoltaics combined with up to three kilowatts from the propeller reversing in tidestreams when the boat is moored and when it is under sail provide ample electricity for traction batteries and there is further to go. Propellers need optimising for the particular compromise of thrust and generation chosen.
In addition, combining mechanical thrust such as sails with sun and wind harvesting to make electricity is particularly realistic at sea.
One of the finest designers of energy independent electric boats is Naval DC with sister company Soel Yachts. Owner David Czap has sold traditional Polynesian sailboats that travel on solar power when the wind drops and SoelCat solar boats with two crew for heavy cargo or 24 passengers. He says, "With an installed battery capacity of 2 x 60kWh, the SoelCat 12 sustains a maximum speed of up to 15 kts for one hour in an emergency. "Break-even point" in sun is 6.5 kts without battery or 24 hours with battery. The solar array can even achieve 13MWh yearly around the equator!"
The Sun Flyer pure electric aircraft with solar wings is sold on the promise of $100,000 in aviation fuel saved in training a pilot. The marine equivalent is SoelCat 12 saving more than $126,000 for a typical 300-day operational profile per year. With no fuel other than sunlight, it can operate in remotest areas and be used as a mobile AC power station providing 6kVA of AC inverter power.
David Czap is a key speaker at the world's first conference on "Energy Independent Electric Vehicles" 27-28 September at the Technical University of Delft, leader in solar racing boats and many of the next EIV technologies. The TU Delft speaks on "Highly Efficient Solar Powered Vessels on Seas" and on "The Future of Photovoltaics for Energy Independent Vehicles". Amazingly, for inland waterways, TU Delft's all-solar craft have hydrofoils and electronically driven wings optimising on stability, maneuverability, and efficiency and now they are addressing seagoing needs.
Organiser of the event Raghu Das CEO of analysts IDTechEx says, "Learn about 6D motion harvesting producing kW levels in small boats. Toyota, which has marine interests, talks on its progress towards energy independent vehicles. International Windship Association covers quasi-independent ships.
Today, the largest ships each currently emit toxic gases and particulates equivalent to up to millions of cars but they can become energy independent electric vehicles emitting nothing. We reveal the huge choice of technologies that can be combined to achieve this from drag reduction by wave power altering the hull attitude and by air lubricating hulls to Flettner rotors harvesting low-level wind and solar roads generating huge amounts of electricity as decking: TNO SolarRoad is a speaker. Indeed, Kitenergy Italy, Kitepower Netherlands and Kitemill Norway reveal how kites and tethered drones aboard the ship will generate megawatts from the more consistent, stronger winds higher up. The UK University of Bolton even describes research on piezo/PV sails potentially making electricity from rain, sun and wind!"
Top image source: Soel Yachts