Solar power does not make DS1 move, directly. Solar power, from solar panels on DS1, makes electricity. Different parts of the thruster have to receive certain voltages of electricity to work properly.
Electricity energizes the plasma in the main chamber of the thruster.
A flow of electrons, which is electricity, is also necessary to shoot into the plasma to make ions of the atoms in the plasma, as well as to neutralize them once they have left DS1. The solar panels also provide electricity to other parts of DS1.