Can people live off the sun's energy?

No. At the very least you need water to combat the dehydrating effect of perspiration.

You also need proteins to maintain your body. Then you need carbohydrates, fat, vitamins and spore elements to get the process of maintenance (and growth) going. And you need to breathe good air.

Answer:

Not directly - that is you can't stand in a field like a photo cell and recharge

Indirectly however you live entirely off the sun's energy. It drives the photosynthesis in plants which you eat or eat animals that eat the plants, powers the hydologic cycle which makes rain and rivers, oceans and lakes, warms the ocean for currents to bring food to fish, created the oil gas and coal which fuels our economy and heats our homes. Even the sun's gravitational energy creates tides in the earths core which (along with the decay of radioactive elements formed in the destruction of previous suns) keep the core warm.

Answer:

The term 'breatharianism' is used by some to mean the practice of living off the prana (life energy) of light from the sun.

The sages of India in ancient times were said to have perfected the ability to keep the body alive for years by directly absorbing the energy of the sun, through supernatural tantric and yogic practices learned under the guidance of an accomplished guru. Theoretically this could still be done, but an ordinary person would never be able to achieve this.