Lets take a snapshot of human civilisation many thousands of years ago, lets say at that point in time when the human population numbered a thousand, physically and mentally they are almost identical to you and I. The total energy available to them was limited to that which they could harvest from the sun, either radiant heat or energy derived from their food. That would be about 2000 kcal each per day, now the best that even Einstein or James Watt could make of that would be gather enough food for some of tomorrow, shelter in a cave or maybe make some very rudimentary tools like a flint knife to make some basic clothes and help with the food gathering, not much really and thats the way things stayed until Humans learned to domesticate fire, at that stage more energy was available and cooked food releases more energy than uncooked food, it enabled small steps to be taken in releasing more of the earth's resources, metals were now available, hunting became easier, and the first attempts at agriculture were made, the first consumer goods began to appear, agriculture meant that villages appeared .....................
Today in the western world we have an average of 140,000 kcal available per capita everyday and that enables us to have cars and planes and hospitals and housing estates and TV and computers and ..................... None of this would be possible without that 140,000 kcals of energy per day although if we adjusted our technologies we could do the same things with about 80,000 kcals or maybe a little less. The developing worlds citizens have an average of 55,000 kcals per capita available to them every day.
Our medium term, the next 40 years, goal should be to meet in the middle. Renewable energy can meet that budget of 80,000 kcals per capita per day.