The flow of energy starts in in you arms. You put your hands together, and use your arms to move your hands back and forth, this is kinetic energy. Your hands rubbing together causes the molecules to bump into each other, this is friction. As the molecules bump into each other they begin to move faster, and the fast movements of the molecules is what creates heat.
Answer:
The sun provides more than enough energy to meet the whole world's energy needs, and unlike fossil fuels, it won't run out anytime soon. As a renewable energy source, the only limitation of solar power is our ability to turn it into electricity in an efficient and cost-effective way.