  We investigated incompressible and compressible magnetohydrodynamic (MHD)
energy cascade rates in the solar wind at different heliocentric distances. We
used in situ magnetic field and plasma observations provided by the Parker
Solar Probe (PSP) mission and exact relations in fully developed turbulence. To
estimate the compressible cascade rate, we applied two recent exact relations
for compressible isothermal and polytropic MHD turbulence, respectively. Our
observational results show a clear increase of the absolute value of the
compressible and incompressible cascade rates as we get closer to the Sun.
Moreover, we obtained an increase in both isothermal and polytropic cascade
rates with respect to the incompressible case as compressibility increases in
the plasma. Further discussion about the relation between the compressibility
and the heliocentric distance is carried out. Furthermore, we compared both
exact relations as compressibility increases in the solar wind and although we
note a slightly trend to observe larger cascades using a polytropic closure, we
obtained essentially the same cascade rate in the range of compressibility
observed. Finally, we investigated the signed incompressible and compressible
energy cascade rates and its connection with the real cascade rate.
