Ships return to renewable energy power

Since the earliest days of sailing, boats and ships have been powered by renewable energy. At first, the motive energy came from muscles manipulating oars. I would have said human muscles, but boats predate modern humans. Almost a million years ago, Homo erectus settled several Indonesian islands that couldn’t have been reached without boats.

Boats with sails aren’t known to be that ancient; the first evidence of their existence starts around 7,000 years ago. Recreational sailboats, and various types of boats with oars, are still commercially viable.

On commercial and military ships, bigger an...