It would be possible but probably not feasible unless you had a lot. IIRC the cells in calculators are 2v 15ma which is 0.03w each. To make 60w you'd need 2000 of them. That'd be a lot of work, soldering 4000 tiny wires coming out of them and would most likely be very expensive. Although if you have a very cheap source then it could possibly be feasible. Another issue to think about would be mounting them since they're pretty fragile.