Technology
A variety of technologies have been developed to take advantage of the sun’s energy. The two most commonly used are solar thermal electric generation (STEG) and photovoltaic systems (PV).

STEG systems use the sun’s rays as a heat source. There are various technologies that are considered STEG but the most common type is the parabolic-trough, which concentrates the sun's energy with long U-shaped mirrors tilted toward the sun, focusing sunlight on a pipe containing oil, which is then used to boil water in a conventional steam generator to produce electricity.

PV systems convert sunlight directly into electricity. In addition to being used to power calculators, watches and other mobile or off-grid devices, they are also commonly used in small behind-the-grid applications such as roof-tops of office buildings or parking garages.  Utility scale power generation is also becoming more common. When sunlight is absorbed by semiconductors, the solar energy knocks electrons loose from their atoms, allowing the electrons to flow through the material to produce electricity.

Market / Advantages
Globally, STEG and PV comprise about 8,000 MWs but have grown rapidly (+45%) over the past few years.  The US and Europe are the leaders in installed capacity and have committed, among other countries, to growing global solar power generation through government supported mandates and financial incentives.

The thermal energy generated by STEG systems can be stored or combined with conventional fossil fuels to enable operation during the night and in cloudy weather or to shift power output to peak demand periods. It can deliver power on demand, and its power generation methods resemble those already used by the nation's power industry.

Solar PV systems can eliminate the need to build expensive new power lines to remote locations. Grid connected PV systems typically boost electricity output during times of high demand for air conditioning power.

Issues
Although both have received strong government support, they remain some of the more expensive of the renewable technologies (on a cost of energy basis).  However, storage and material innovations may reduce energy cost in the foreseeable future and may make solar competitive with fossil fuel generation in high solar resource areas in the foreseeable future.
 
STEG systems require large amounts of water for traditional cooling of the steam turbines and are typically located in sunny and arid regions where water is scarce.  

The variability of power generated from PV panels can be extreme because of sudden drops from cloud cover.  Also, power output may be reduced when the panels are not directly facing the sun.