  We determine the entire electrical current density vector in a geometrical 3D
volume of the inner penumbra of a sunspot from an inversion of
spectropolarimetric data obtained with Hinode/SP. Significant currents are seen
to wrap around the hotter, more elevated regions with lower and more horizontal
magnetic field that harbor strong upflows and radial outflows (the
intraspines). The horizontal component of the current density vector is 3-4
times larger than the vertical; nearly all previous studies only obtain the
vertical component and thus strongly underestimate the current density. The
current density and the magnetic field vectors form an angle of about 20
degrees. The plasma beta at the 0 km level is larger than 1 in the intraspines
and is one order of magnitude lower in the background component of the penumbra
(spines). At the 200 km level, the plasma beta is below 0.3 nearly everywhere.
The plasma beta surface as well as the surface optical depth unity are very
corrugated. At the borders of intraspines and inside, the magnetic field is not
force-free at deeper layers and nearly force free at the top layers. The
magnetic field of the spines is close to being potential everywhere. The
dissipated ohmic energy is five orders of magnitudes smaller than the solar
energy flux and thus negligible for the energy balance of the penumbra.
