Practice Solar Panel added by Going Green DLC, is required in the workshop if you plan on running the Solar Panel Development program. Each panel can be used by up to four prisoners. Maximum program Capacity is 20, so it is recommended to place five of these in the workshop.
Prisoners participating in the Solar Panel Development program will tinker with the solar panel, causing them to gradually damage it. The same prisoners will then repair it back to normal. This is the only object that prisoners can damage without the intervention and punishment of a guard.
Note that, unlike actual Solar Panels, this object can only be placed indoors, despite the fact that the workshop can be located outside.