According to the Energy Information Administration, just 1.6% of total U.S. energy production came from solar in 2018, while wind power accounted for 6.6%. The biggest challenge facing renewable sources has been energy storage, since solar arrays only generate electricity when the sun is shining, and wind turbines only work when the wind is blowing. The U.S. electrical grid requires a steady, consistent stream of energy, and that's one of the main reasons why fossil fuels still provide nearly two-thirds of our power each year. Large-scale batteries are the solution, and recent price drops in the cost of energy storage mean that renewable sources could soon threaten fossil fuels from an economic perspective.

For cavemen, a high-volume trade day might have looked a bit different than what we’ve come to expect.