Dr Peter Harrop
There is more energy to harvest at sea. True, watercraft 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 maximum speed of up to 15kt for one hour in emergency. ‘Break-even point’ in sun is 6.5kt 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.
Dr Peter Harrop is the chairman of IDTechEx.