Solar energy, like most product fields, is multidisciplinary. It involves EE’s, ME’s, ChemE’s, and scientists of several types, all performing different roles. You could enter any of those fields (or others still!) and go into solar energy. So the question is really what in particular excites you about solar energy enough to want to do that one particular thing as a career? Or, alternately, what talents and interests do you possess that would make one of those fields easier and more enjoyable than the others?