An Italian professor worked out a floating solar system on water, see more from the link.
http://news.yahoo.com/italian-engineer-invents-floating-solar-panels-155245586.html;_ylt=Amotpedm0y2RQTWJqSwJKsbzUc0F;_ylu=X3oDMTE2MjFyZjd0BG1pdAMEcG9zAzEEc2VjA01lZGlhU2VhcmNoUmVzdWx0c0liWEhS;_ylv=3

The flat panels are winged by reflectors and sit on raft-like structures which are anchored to the lake bed with a pylon, with water cooling at the back of the module. So the efficiency is expected to be higher than conventional system. But it may cause other problems, like the growth of aquatic life, the impaction to the biology under the water surface. What do you think?