I'm a little disappointed in the responses, particularly that this thread was moved to "Homework-Grade K-12" category as it is almost certainly too advanced a subject for even university bachelors degree level.
I was hoping to see something along the lines of advanced optics: large-source fresnel diffraction plate engineering, staged coherent radiation sources, synchrotron sources, beamed energy, sub-wavelength wave manipulation, maybe even waveguides based on distantly-separated quantum-entangled optical apertures.
Nothing I've investigated can provide industrial power levels to Earth at a cost that competes with nuclear fission. Too bad considering how much energy is given off by the Sun. Enough to power millions of civilizations like ours. It's the most abundant source of energy in the universe, the most reliable, the most long-lasting, the highest capacity, and seemingly the least accessible.
Ergo, I present it as a Grand Challenge.