Desumaiden:
Solar energy might be able to provide us with electricity, but you can't use solar panels to produce enough food to feed 7 billion people.
Yes you can, because the vast majority of energy used for agriculture is used in the production of
ammonia, for fertilizer. Ammonia is a chemical (NH4) which has no carbon atoms in it. No hydrocarbons are needed to produce ammonia. Although natural gas is used at present, the gas is used as a
hydrogen donor. Any source of hydrogen would do, such as
water.
During the 1950s, ammonia was made using electricity and
water, until there was a widespread natural gas infrastructure, at which point gas was used to make the ammonia. As always, there was a gradual transition based upon currently-available resources.
I should also point out here, that ammonia is liquid at modest temperatures, and is suitable as a vehicle fuel (it burns in internal combustion engines). Thus, ammonia could also be used to power tractors and transportation equipment. Of course, there are many other options also.
Oil is not a magical substance which has irreplaceable chemical properties. I realize some people here treat oil as some kind of magical thing and there's NO POSSIBLE WAY to do anything without it, but in fact, it's an ordinary chemical, and there are lots of substitutes. For example, people here repeatedly denied that it was even possible to run a truck using overhead wires, but it's obviously straightforward to do so and has already been done. People here denied you can run a ship using woodchips, but that was already common before 1920. Lots of peak oilers claim that fertilizer can only be made out of gas, but in fact, it can be made from any source of hydrogen, and that was already common before 1960.
There are obvious substitutes for
all uses of oil. Oil can even be manufactured. Oil was used first because it was cheap and convenient, that's all. It's straightforward to make or obtain plasticky substances (silicones), ammonia (NH4), energy, electricity, and vehicle fuels using sources other than oil or fossil fuels.
-Tom S