There are really two "types" of solar energy and they are defined most simply by the way they're used. Active solar energy is solar energy that is used to either create electricity through the photovoltaic process or to create heat through the solar thermal process. Passive solar energy is the simple absorption of heat or light - think of getting out of a cold pool and lying on hot pavement in direct sunlight - very useful and very simple.
Active solar energy is also useful - and much more controllable - but very complicated. Solar Photovoltaic (PV) and Solar Thermal energy are the overlapping components of sunlight. Most of the familiar solar modules only use the visible components (the bright part) of the sunlight and most Solar Thermal modules only use the invisible, or Infrared (the warm part) component of sunlight. In fact, the bright part is bad for solar thermal panels and the warm part is bad for PV panels - but that's a different article.
Now, comparing the two technologies, PV is the more complicated process. It requires semiconductor material and some means of protecting and insulating the semiconductor material. It also requires highly specialized manufacturing processes to grow the Silicon ingots and slice them into solar cells, then solder them together so the electricity can flow out of them. Solar thermal, while becoming more complicated and more efficient, can be a simple as a tank of water with pipes leading to the nearest tap.
In short, solar PV should be used for anything that doesn't involve intentionally creating heat - solar thermal should be used for any heating process. The reason for this is that even at its best, solar PV can only convert 18% of the energy it receives into electricity and then that electricity has to be turned into heat by forcing electrons through a resistor and causing it to get hot. A very expensive process considering that solar PV costs about $8 per watt and it takes 2000 watt hours to heat one 30 gallon tank of water. Solar thermal, on the other hand, transfers as much as 95% of the infrared energy in receives directly into hot water - at about $4 per watt installed. One solar thermal module can heat water better than 10 of the same sized PV modules!
[Photo: Rajput Sun Symbol, T Taylor and L Ramsey]