How much energy does one inch of solar panel give?

We can calculate that out!

The sun gives us 1366 watts per meter squared (roughly) 90% of this is absorbed coming into the atmosphere. That leaves us 136 watts.

One meter is 39.3 inches per meter so we have 136 watts per 39.2 square inches, which is about 3.4 watts of available energy. Solar cells are about 20% at best so we would see about 680 miliwatts from this panel (at best).

The ratings of panels is somewhat misleading though. The panel would provide this much to a short circuit condition. You would see about 300 miliwatts of useable power at .6 vdc.