You're interested in civil and photovoltaic, but might do biomedical engineering? lol!
Anyways, as a single degree, first year is the same throughout almost all (if not all) engineering discliplines. First semester involves math, physics, computing, and engineering design. Second semester involves math, mechanics (the mech version is 1/2 statics and 1/2 dynamics, the civil version is 3/4 statics and 1/4 dynamics), materials and/or chem, engineering design 2 or some other elective.
Second year you start to differ a bit.
There's more math.
Mech/aero/mtrn/naval/manufac engineers do subjects like mechanics of solids, thermodynamics, fluid mechanics.
Civil/environmental do subjects like soil mechanics (i think?), water mechanics.
Electrical engineers do electrical subjects and maybe some more physics subjects.
Third year and onwards you get into the core subjects of your degree (eg mechanical systems, robotics, aero, naval courses, etc)
As a double degree you would do the same subjects, but you would do commerce subjects too.
