  The energy of the thermal flare plasma and the kinetic energy of the
non-thermal electrons in 14 hard X-ray peaks from 9 medium-sized solar flares
have been determined from RHESSI observations. The emissions have been
carefully separated in the spectrum. The turnover or cutoff in the low-energy
distribution of electrons has been studied by simulation and fitting, yielding
a reliable lower limit to the non-thermal energy. It remains the largest
contribution to the error budget. Other effects, such as albedo, non-uniform
target ionization, hot target, and cross-sections on the spectrum have been
studied. The errors of the thermal energy are about equally as large. They are
due to the estimate of the flare volume, the assumption of the filling factor,
and energy losses. Within a flare, the non-thermal/thermal ratio increases with
accumulation time, as expected from loss of thermal energy due to radiative
cooling or heat conduction. Our analysis suggests that the thermal and
non-thermal energies are of the same magnitude. This surprising result may be
interpreted by an efficient conversion of non-thermal energy to hot flare
plasma.
