  Solar flare activity in cycle 24 is studied. Satellite observations of x-ray
fluxes from GOES-15 and UV emission lines from the SDO/EVE experiment are used.
The most powerful flares of cycle 24 in classes X9.3 and X8.2 in September 2017
are compared with powerful flares in classes M5-X6.9. The times at which the
fluxes in the 30.4 and 9.4 nm lines and in the 0.1-0.8 nm x-ray range begin to
increase are compared for 21 of the large flares. The total energies arriving
at the earth from flares in the 30.4 and 9.4 nm lines and in the 0.1-0.9 nm
x-ray range, $E_{30.4}$, $E_{9.4}$, and $E_{0.1-0.8}$, from 25 flares during
2011 and 2012 are calculated. It is shown that the calculated energies of the
flares in the analyzed lines from SDO/EVE and in the x-ray range from GOES-15
are closely interrelated.
