Unlike some other proposals for reviving the use of sails in commercial shipping, the EnergySail from Eco Marine Power (EMP) can harness the power of the wind and sun at the same time, for high-efficiency transport on the high seas.
Made of either high strength steel or carbon fiber, the EnergySail is a rigid sail sitting on a rotating pole, mounted on the deck of a ship. Solar panels embedded in the sail, along with panels mounted on the deck, are used to augment the power usually provided by auxiliary generators. When conditions get rough, the sails can be lowered and stored out of harm's way.
When the ship is sitting in port, the EnergySails can also be used to collect energy. It'll be stored in a battery and used for zero-emissions operation of its electrical systems. EMP is also planning a version of the sails capable of collecting solar power when lowered.