"Defence chiefs are turning to the benefits of energy-efficient technology, with this latest move towards installing LED lighting on two destroyers expected to allow for energy consumption reductions of 80 per cent on present levels."
http://www.rapidonline.com/latestnews.aspx?id=800471202&tier1=Industry&title=US+warships+to+be+fitted+with+energy-efficient+LED+lighting I assume it will be an energy reduction on power used for lighting only.
"A boat the size of the Auriga Leader needs about 400 kilowatts of energy while at port,while a larger vessel like an oil supertanker needs about eight megawatts (enough juice to power 5,500 homes!) to pump its cargo of oil off the ship."
http://inhabitat.com/auriga-leader-cargo-ship-gets-power-from-solar-panels/