  One of the key problems in solar flare physics is the determination of the
low-energy cut-off; the value that determines the energy of nonthermal
electrons and hence flare energetics. We discuss different approaches to
determine the low-energy cut-off in the spectrum of accelerated electrons: (i)
the total electron number model, (ii) the time-of-flight model (based on the
equivalence of the time-of-flight and the collisional deflection time); (iii)
the warm target model of Kontar et al.~(2015), and (iv) the model of the
spectral cross-over between thermal and nonthermal components. We find that the
first three models are consistent with a low-energy cutoff with a mean value of
$\approx 10$ keV, while the cross-over model provides an upper limit for the
low-energy cutoff with a mean value of $ \approx 21$ keV. Combining the first
three models we find that the ratio of the nonthermal energy to the dissipated
magnetic energy in solar flares has a mean value of $q_E=0.57\pm0.08$, which is
consistent with an earlier study based on the simplified approximation of the
warm target model alone ($q_E=0.51\pm0.17$). This study corroborates the
self-consistency between three different low-energy cutoff models in the
calculation of nonthermal flare energies.
