How to estimate solar panel output as a function of solar radiation
Normally Solar panels are rated with the power output when irradiated with 1kW/m^2 - this is close to the max solar irradiance at noon on a clear day.  You seem to be mixing up energy (kWh) with power (kW).

The current output of a PV cell will be fairly linear with the intensity of solar radiation.  The voltage will reduce with temperature but if you keep the cell cool the power will then be proportional to the intensity of radiation.

This assumes that the sunlight falls on the cell at 90 degrees - as the sun moves across the sky that cannot be maintained unless you have a tracking PV array.  If not there will be a Cosine correction that will need to be applied.

The total amount of energy you get per day from a cell will depend upon how long the light is present i.e. how long the day is which will vary with latitude and season and how clear the air is (e.g are there clouds).

The link you gave has a map showing the integrated average energy per day for various locations.

This graph shows how the current output of a PV cell varies with light intensity and voltage.