A company of U.S. Marines recently conducted a remarkable three-week patrol through southern Afghanistan, replacing hundreds of pounds of spare batteries in their packs with roll-up solar panels the size of placemats to power their battle gear.

By allowing the troops to recharge their radios, GPS devices and other equipment, the green technology freed the Marines of India Company from constant resupply by road and air. And by carrying fewer batteries, they carried more bullets.

The...