The chart shows how much caloric energy input is required to get one calorie of human food.
This chart comes from http://environ.andrew.cmu.edu/m3/s3/all_ene_sys.htm
For coastal fishing, it takes about one calorie of energy input to catch one calorie of fish, but it takes ten times more energy input via fuel, equipment, and other expenses to catch fish on the high seas away from home. Range-fed beef requires about half the energy input via cattle herding expenses, and transportation to market expenses, as is available from eating the cattle. However, in the upper right corner, we see that feedlots’ beef energy costs in calories are ten times the return in human food calories. The most efficient way to create human food is by growing wet rice in Indonesia where a unit of energy put into rice production results in fifty times as much food energy for human consumption. Low-intensity potatoes, which appears to mean planting the potatoes in some good location, doing nothing, and then harvesting and eating them gives about twenty times the food energy as it takes to grow them. But, intensively grown potatoes means cultivating them using modern farm machinery for tilling the soil, irrigating it, planting the potato starters, fertilizing the crop, spraying with insecticides, weeding, harvesting the crop, cleaning and packaging it and sending it to a market, which gives about two calories of food for all of the input.
This chart indicates the US food system in 1970 was using eight calories of energy to produce one calorie of human food. Most of that energy was coming in the form of the fossil fuels used to operate farm equipment, making fertilizer, bringing water to the plants, hauling produce to the market, and retailing expenses.
World peak oil, coal, gas, nuclear production are peaking out before 2030 and because those are non-renewable energy sources when they are gone, they are gone forever. Only the pollution created by our consuming them will remain. But there is hope if solar, wind, and geothermal, projections turn out to be accurate. The chart at the top of this page illustrates the linkage between energy and food; thus if the production of food were to drop as the fossil fuels do in this illustration the human population would be forced to drop back to 1870 levels by 2090. People born today are expected to live for eighty years and that would be a decade beyond the drop of fossil energy to near zero. But, if fossil fuel is no longer providing the energy to make human food the only energy available to make those people’s food will have to come from solar, wind and geothermal sources. The graph shows a huge increase in those sources of energy production. That will require a realization by our planners and a willingness to commit to create these sources of energy and make them available before a worldwide famine sets in. If they don’t foresee the problem and react to it vigorously the world population will follow the green line to near zero. And that’s assuming there are no major wars. But in such a super stressful time there will be wars so things will get even worse.
Creating robots specifically designed to make solar energy farms would make it possible for energy production to be used for food production.