Generally, energy conversion systems would require a degree in mechanical engineering, with a specialty on power systems.
Photovoltaic systems would probably be covered in an electrical engineering, although perhaps, one might find it in a mech. program.
Some universities may offer a program in alternative energy engineering.
Rensselaer Polytechnic Institute (RPI) had a Environmental and Energy Engineering program, but that was restructured such that energy engineering part was moved into Mechanical Engineering.
Here are the mechanical and environmental curricula (links subject to change)
http://www.eng.rpi.edu/mane/ug_curriculum_meche.cfm
http://www.cee.rpi.edu/env_engineering.cfm
Some innovative research at RPI into alternative energy sources.
Student in accelerated BS/PhD program at RPI works on PEM Fuel Cells.
http://www.rpi.edu/about/inside/issue/v2n17/fuel.html
Rensselaer Student Invents Alternative to Silicon Chip
http://soenews.rpi.edu/update.do?artcenterkey=706
http://www.eng.rpi.edu/lemelson/finalist_Huang.cfm
U. Wisconsin
http://www.engr.wisc.edu/me/ - UWisc - Mech Eng.
http://sel.me.wisc.edu/ - UWisc - Solar energy lab
http://www.engr.wisc.edu/ep/ - UWisc - Eng. Phys.
Univ. Illinois Urbana-Champaign
http://www.mechse.uiuc.edu/ - Mech Eng.
http://www.mechse.illinois.edu/content/courses/index.php - Mech Eng courses.
One may have to tailor one's major, e.g. a joint Mechanical and Civil/Environmental course program.
One should start with universities in one's state, and see what they have to offer. Compare to other programs that appear to offer what one would like.