  We study the evolution of electric currents during the emergence of magnetic
flux in the solar photosphere and the differences exhibited between solar
active regions of different Hale complexity classes. A sample of 59 active
regions was analyzed using a method based on image segmentation and error
analysis to determine the total amount of non-neutralized electric current
along their magnetic polarity inversion lines. The time series of the total
unsigned non-neutralized electric current, $I_{NN,tot}$, exhibit intricate
structure in the form of distinct peaks and valleys. This information is
largely missing in the respective time series of the total unsigned vertical
electric current $I_z$. Active regions with $\delta$- spots stand out,
exhibiting 1.9 times higher flux emergence rate and 2.6 times higher
$I_{NN,tot}$ increase. The median value of their peak $I_{NN,tot}$ is equal to
$3.6\cdot10^12$ A, which is more than three times higher than that of the other
regions of the sample. An automated detection algorithm was also developed to
pinpoint the injection events of non-neutralized electric current. The
injection rates and duration of these events were higher with increasing
complexity of active regions, with regions containing $\delta$-spots exhibiting
the strongest and longest events. These events do not necessarily coincide with
increasing magnetic flux, although they exhibit moderate correlation. We
conclude that net electric currents are injected during flux emergence, but are
also shaped drastically by the incurred photospheric evolution, as active
regions grow and evolve.
