Solar energy is a plentiful energy source, radiance energy coming from sun is at the order of 85,000 to 120,000 TW, while current world energy consumption is around 18 TW (IEA, Key Energy Statistics, 2014; Coimbra, Photovoltaic and Photothermal Energy Production: Future of Energy, 2014).
For electricity, solar energy technologies are broadly divided into photovoltaic cells (direct PVs) (direct conversion to electricity: photons to electrons); solar thermal power (using heat, also known as concentrated solar power) and other technologies (solar Stirling engines etc.).
Conventional PV cells have a very low efficiency, only 20%, but multi-junction cells, which absorb photons from different parts of the solar spectrum have efficiencies around 40% (however, they are 100 times more expensive than conventional PV cells).
Solar thermal power has an intermediary step, where solar energy is transformed first into thermal energy than into electrical energy. Mirrors can heat either a central liquid transforming it into steam or a working fluid, usually a high-temperature oil, in small tubes.
The biggest problem with solar energy is its variation, season to season, day to day, morning to evening. Daily variations can be somewhat balanced because daily electricity consumption roughly coincides with higher solar radiance, however storage is a must for long term development of the technology (Coimbra, Photovoltaic and Photothermal Energy Production: Future of Energy, 2014).