First, the resources. Pretty much all available energy on the earth comes from energy radiated by the sun. Straight sunlight offers heat and light. Some of that is captured by plants, which can in turn be eaten or burned for light and heat. The plant eaters (human or otherwise) can be put to work or eaten. Some of the sunlight evaporates water, which rises into the atmosphere and then falls as rain. Some of this rain lands on very high places and converges as gravity pulls it into streams and rivers that run towards lakes and oceans. The mechanical energy offered by running water is essentially stored sunlight. Meanwhile, differences in temperature because of the uneven distribution of sunlight (owing in part to the shape, tilt, and rotation of the earth) causes air to circulate, meaning winds are stored sunlight too. As are waves (which are driven by winds). And, of course, fossil fuels are reserves of stored sunlight, derived from biological depositions which have been accumulating for millions upon millions of years.