Why is the human body unable to convert the sun's energy to carbohydrates?

The human body is unable to convert the sun's energy to carbohydrates because it has no photosynthetic structures.

Plants do have such structures, called chloroplasts, which contain chlorophyll, which is a photosensitive chemical which transforms energy from light into chemical energy to help break water into hydrogen and oxygen, and break carbon dioxide into carbon and oxygen, so they can re-combines into assemblages of carbon, hydrogen, and oxygen, otherwise known as carbohydrates.