I enjoyed the following short clip from AEI about power and energy, even though (like many pieces of its type) it confuses the two concepts as well as their separate units.
The picture above shows how hard it is to concentrate literal horsepower to operate something as big as a combine. That's quite a harness-full of horseflesh (or are they mules?) for one driver to control! Life gets a lot easier if you can use a concentrated source of energy like fossil fuel and an internal combustion engine. Well, of course, it's easier in some ways and more complicated in others.
The video claims that a horse, though only seven times as heavy as a man, has 100 times his power (i.e., his ability to apply energy to a useful task in a given time period). That calls for a lot of oats, obviously -- all the little plant cells industriously working away to use sunlight to combine water and carbon dioxide into high-energy molecules that can be burnt in the horse's metabolic furnace.