Reducing the amount of fuel that giant cargo ships burn is a very important goal. 

One interesting approach is using giant kites, but another is a combo of wind and solar power, the Sun Sails by Solar Sailor. A few months ago Warren wrote:"The 30 metre long sails, festooned in photovoltaic panels are expected to catch enough wind to reduce fuel costs by between 20% and 40%, whilst those PV cells will provide the ships with 5% of their electricity. A computer automatically angles the sails for maximum wind and solar efficiency, and if all goes to plan the sails will have recovered their initial cost within four years."