Why Install it in the slab? A solar panel is not a load bearing structure. You cannot use it for structural purposes. That is simply a bad decision because solar panels are costly and hence they need to be kept safe from damage. We can install them above the slab though if we wish to.
But again, slabs are horizontal and it's foolish to install a horizontal solar panel. You'll never see it that way anywhere except for at the equator. That is because sunlight mostly falls at a slant and to grab maximum intensity, the solar panel has to be perpendicular to the sun rays which will never be horizontal. Beyond the tropics, sunlight will never fall vertical ever in a year. So, no chance of installing a solar panel in the slab. Only if there's a non load bearing slab cast to hold the solar panel, then it might be possible but that too is a bad idea because it will unnecessarily add to building cost, time and weight.