Based on X-ray (1-8 Å) flux data for 1972-1995 the integral spectra of solar flare energy were computed. It has been shown that the spectral index β of the integral energy spectrum (IES) vanes systematically with the 11-year cycle phase. The interval of $\beta$ 수식 이미지-variations (0.47 <β<1) is characteristic of UV-Cet stars. The maximum energy of the X-ray flares does not exceed 10 32 erg.