The most powerful force is Electromagnetism, no? I mean its the force that keeps atoms together, or am I being a dumbass? Again, scepti has a point. As a viable energy source the sun(big ball of helium & hydrogen, not a reflection.) would be most, uh, viable. Technically not a force, but still a means to collect & harness energy. If there were solar panels across 169x169 miles in the Mojave desert it could satisfy all energy requirements across both Americas(or something. I'll check & edit later).