The Burning Sun — William J. Benning

The adventure continues for Billy Caudwell, the teenage First Admiral of the Universal Alliance Fleet. The Bardomil Empress, eager to avenge the defeat of her Imperial Fleet at the hands of Billy Caudwell, acquires a weapon that can generate super-charged solar flares and incinerate entire planets. Having tested the weapon, the Empress discovers a strategic territorial weakness in Billy's Alliance and launches the solar flare weapon at Planet Earth as a diversion to a full-scale assault on the Alliance. Billy Caudwell, still trying to stay on top of his dangerous double life, now has to protect Earth and save the Alliance from annihilation. And, as if that's not enough, Billy also has girl troubles