Energy materials are at the heart of various renewable energy technologies that are revolutionizing our future. I will touch upon two renewable energy applications where the fundamental understanding of novel materials from first-principles is of crucial importance. In the area of photovoltaics, we have developed a large-scale time dependent density functional theory which can predict electronic excitations from first-principles. Using this method, we have studied the fundamental physical problems underlying photoexcitation in organohalide perovskites. Next, I will present a computational strategy to rapid screen and design novel catalysts for fuel cell applications. We have developed a multiscale method to predict catalytic activity of core/shell nanoparticles for oxygen reduction reaction.