  We present an observational analysis of the electron thermal energy budget
using data from Parker Solar Probe. We use the macroscopic moments, obtained
from our fits to the measured electron distribution function, to evaluate the
thermal energy budget based on the second moment of the Boltzmann equation. We
separate contributions to the overall budget from reversible and irreversible
processes. We find that an irreversible thermal energy source must be present
in the inner heliosphere over the heliocentric distance range from 0.15 to 0.47
au. The divergence of the heat flux is positive at heliocentric distances below
0.33 au, while beyond 0.33 au, there is a measurable degradation of the heat
flux. Expansion effects dominate the thermal energy budget below 0.3 au. Under
our steady-state assumption, the free streaming of the electrons is not
sufficient to explain the observed thermal energy density budget. We conjecture
that the most likely driver for the required heating process is turbulence. Our
results are consistent with the known nonadiabatic polytropic index of the
electrons, which we measure as 1.18 in the explored range of heliocentric
distances.
