  In solar flares, energy is released impulsively and is partly converted into
thermal energy of hot plasmas and kinetic energy of accelerated nonthermal
particles. Despite numerous efforts, no consensus on quantifying this energy
balance has yet been reached. We aim to understand the reasons for the
contradicting results on energy partition obtained by various recent studies.
We considered five recent studies that address the thermal-nonthermal energy
partition in solar flares. Their results are reviewed, and their methods are
compared and discussed in detail. The main uncertainties in deriving the energy
partition are identified as (a) the derivation of the differential emission
measure (DEM) distribution and (b) the role of the conductive energy loss for
the thermal component, as well as (c) the determination of the low-energy
cutoff for the injected electrons. The bolometric radiated energy, as a proxy
for the total energy released in the flare, is a useful independent constraint
on both thermal and nonthermal energetics. In most of the cases, the derived
energetics are consistent with this constraint. There are indications that the
thermal-nonthermal energy partition changes with flare strength: in weak
flares, there appears to be a deficit of energetic electrons, while the
injected nonthermal energy is sufficient to account for the thermal component
in strong flares. This behavior is identified as the main cause of the
dissimilar results in the studies we considered. The changing partition has two
important consequences: (a) an additional direct (i.e. non-beam) heating
mechanism has to be present, and (b) considering that the bolometric emission
originates mainly from deeper atmospheric layers, conduction or waves are
required as additional energy transport mechanisms.
