We can withdraw stored energy from plants. One method results in liquid ethanol. This ethanol can readily be used in the auto industry and has even been used to power airplane jet engines
In 2003, we used about 4.4e20 Joules of primary energy (>70% from fossil fuels). Experimentally, we’ve cultivated switch grass such that 1000 gallons of ethanol can be made each year from an acre of land (or 2.2e11 Joules per hectare). Assume that a production efficiency of 3 to 1 or 3 Joules of ethanol produced requires 1 Joule of energy to account for planting, harvesting, and producing. Thus, to produce our primary energy requirements, we need dedicate the production of 2.7e9 hectares. This is almost twice the area of Russia. But, we’re already using all available land on earth.
Where will we obtain our energy after we’ve exhausted the supply of fossil fuels.