From National Geographic:
The total power needs of the humans on Earth is approximately 16 terawatts,” he said. (A terawatt is a trillion watts.) “In the year 2020 it is expected to grow to 20 terawatts. The sunshine on the solid part of the Earth is 120,000 terawatts. From this perspective, energy from the sun is virtually unlimited.
On how to catch solar energy, their pros and cons:
There are two main ways to harness it. The first is to produce steam, either with parabolic troughs like the ones in Nevada or with a field of flat, computer-guided mirrors, called heliostats, that focus sunlight on a receiver on top of an enormous “power tower.” The second way is to convert sunlight directly into electricity with photovoltaic (PV) panels made of semiconductors such as silicon.
Each approach has its advantages. Right now steam generation, also known as concentrating solar or solar thermal, is more efficient than photovoltaic—a greater percentage of incoming sunlight is converted into electricity. But it requires acres of land and long transmission lines to bring the power to market. Photovoltaic panels can be placed on rooftops at the point where the power is needed.