What's needed in a solar setup is dictated by what it is going to be used for. The method of power generation also plays a factor.
Assuming the actual generation is already taken care of:
If the system is setup just to generate power to feed into the grid (see Solar and Grid?), then usually only an inverter is required. If you want to power a house, then you probably need batteries and an inverter.
The best way to understand what will be each type of setup is to know a little about the components that may make it up.
Solar 'Generator' or Converter:
These were discussed in Solar Basics. What matters here is the type of power they put out, either AC or DC. Mains power is AC, at ~110V or ~240V.
Solar Panels put out DC.
Converters using heat engines or fluid boiling can put out either AC or DC. The output is dictated by the type of generator installed.
However, it is important to note that if power storage is required, DC is the appropriate type of power. DC is needed to charge batteries, and batteries produce DC power.
Required if power storage is needed. This is the case in most systems, except those feeding straight into the grid.
Different types of batteries exist - simplified: wet cells or sealed / gel cells. The battery for a setup depends upon certain factors like charge and discharge cycle.
A reasonable article on batteries can be found here.
An inverter converts DC to AC. They also usually contain a transformer, to change the voltage to the required level. Whether an inverter is needed depends upon the type of power generated and the use.
Solar panels produce DC, thus an inverter is needed to power normal appliances or feed into the grid. If a lighting circuit was the only intended use however, an inverter is often not needed. These solar powered lighting circuits are set up to use the DC power provided by solar panels.
When using heat engines or fluid boiling, it can be simplified to: Storage means DC production and an inverter, no storage means AC production and no inverter.
Solar power is most commonly used in the following ways or setups:
Of course, every solar power setup requires a solar converter (panels, heat engine or fluid boiling).
The standard basic solar system for powering a house consists of a solar converter (most often solar panels), batteries and an inverter.