  We consider $\Lambda$=0 three dimensional gravity with asymptotically flat
boundary conditions. This system was studied by Ashtekar and Varadarajan within
the second order formalism -with metric variables- who showed that the
Regge-Teitelboim formalism yields a consistent Hamiltonian description where,
surprisingly, the energy is bounded from below and from above. The energy of
the spacetime is, however, determined up to an arbitrary constant. The natural
choice was to fix that freedom such that Minkowski spacetime has zero energy.
More recently, Marolf and Pati\~no started from the Einstein-Hilbert action
supplemented with the Gibbons-Hawking term and showed that, in the 2+1
decomposition of the theory, the energy is shifted from the
Ashtekar-Varadarajan analysis in such a way that Minkowski spacetime possesses
a negative energy. In this contribution we consider the first order formalism,
where the fundamental variables are a so(2,1) connection $\omega_a{^I}_J$ and a
triad $e_a^I$. We consider two actions. A natural extension to 3 dimensions of
the consistent action in 4D Palatini gravity is shown to be finite and
differentiable. For this action, the 2+1 decomposition (that we perform using
two methods) yields a Hamiltonian boundary term that corresponds to energy. It
assigns zero energy to Minkowski spacetime. We then put forward a totally gauge
invariant action, and show that it is also well defined and differentiable.
Interestingly, it turns out to be related, on shell, to the 3D Palatini action
by an additive constant in such a way that its associated energy is given by
the Marolf-Pati\~no expression. Thus, we conclude that, from the perspective of
the first order formalism, Minkowski spacetime can consistently have either,
zero, or a negative energy equal to -1/4G, depending on the choice of
consistent action employed as starting point.
