The Sun has an absolute magnitude of about M = 4.8.
What is the power of the Sun?

        We know that a star of absolute magnitude M = 0 
        produces about 4 x 10^(28) Watts.  The power
        of the Sun must be


           power (Sun)           0.4 * [ 0 - M(Sun) ]
         -----------------  =  10
           power (M=0 star)
        
                                 0.4 * [ -4.8 ]
                            =  10

          
                            =  0.012


        So, with a little algebra,


           power (Sun)      =  0.012 * power(M=0 star)

                            =  0.012 * 3 x 10^(28) Watts

                            =  3.6 x 10^(26) Watts