In a diesel generator, if you increase the load, you have to supply more fuel to keep the engine-generator turning at the same speed. Accordingly, if you electrically disconnect the generator, the engine has to burn less fuel or it will overspeed.

With a solar array, if E amount of energy is hitting the panel, some is turned to electricity, some is reflected, some is turned to heat, some passes through it, etc.... Presumably E-X(generatedkw) is going somewhere like reflected light and heating.

If the array is generating 5kw of power and it is suddenly disconnected from the grid, what happens to that 5kw of energy? A shade doesn't extend and the sun doesn't dim, so E is still striking the surface. I would think that 5kw has to "go" somewhere, probably in the form of heat, but I've never heard of a panel getting brighter/hotter/whatever if it's "unplugged" compared to plugged in. Or maybe it does? 5kw of energy (~1.5 tons) would probably be a noticeable heat or light increase, I would think.

ELI15: Where does the energy go, or what happens?