Solar Energy
Solar energy is one of the most renewable and abundant forms of energy ever in existence. The only thing more powerful are solar system destroying super novas and other similar star caused phenomenon. The only problem is harnessing that energy and putting into something useful.
Plants have been harnessing solar energy effectively for billions of years and have converted that energy into nutrients and other compounds that are used by every living and non-living thing on the planet. Humans evolved because of solar power as did every other creatures on Earth. No sun, no life, but now we can use that power for other uses, such as powering this computer and providing transportation.
Solar energy is one of the most useful renewable energy sources available. It is constantly shining somewhere and if that somewhere is a solar panel or solar collector then those photons are being harnessed. If there is nothing like a solar array anywhere around that energy will be converted to heat when it strikes the ground or turned into chlorophyll when it strikes a plant.