We have equipped our transmission electron microscope (accelerating voltage up to 300 kV) with a cathodoluminescence (CL) system that covers a wavelength range of 180 — 1800 nm and temperatures from 10 K upwards. This contribution shows how this system can be utilized to study the initial damage process due to electron irradiation in Cu(In,Ga)Se2 thin solar films. This damage leads essentially to atomic defects that cannot structurally be imaged in the transmission electron microscope, but influence the luminescence spectra. We analyse in-situ the spectral evolutions with electron dose of Cu(In1-xGax)Se2 with [Ga]/([Ga]+[In]) ratio x ranging from x=0 to x=1 and interpret the defect formation kinetics with a first model. The obtained results indicate that the films with equal Ga and In concentration are the least radiation sensitive. The voltage dependence of the damage rate indicates that the damage arises essentially due to displacement by electron knock-on (in the voltage range 150 — 300 kV).