A photovoltaic array is the name given to a collection of photovoltaic panels all connected and located on one place. An array is built to ensure that the energy needs of a building can be met - it is easier with more panels.
PV is a form of solar power. Rather than simply using the energy of the sun to heat water, which was the model for thermal solar power, PV is more ambitious. PV cells convert the sun's energy into electricity within the cell itself. They are much more versatile, and can provide a good amount of the electricity needed to run a household or business. A converter turns the DC power they create into AC power, which is stored in a battery located within the premises.
One PV panel is often not sufficient to power a home or a business. It is vitally important to maximise the amount of sunlight used, especially is areas of the world that don't see so much sun (like the UK!) In order to do this, an array is constructed, out of several panels. A photovoltaic array is usually fixed onto a south facing roof, and is designed to maximise the amount of roof that is covered.
Photovoltaic systems (PV system) use solar panels to convert sunlight into electricity. A system is made up of one or more photovoltaic (PV) panels, a DC/AC power converter (also known as an inverter), a racking system that holds the solar panels, electrical interconnections, and mounting for other components. Optionally it may include a maximum power point tracker (MPPT), battery system and charger, solar tracker, energy management software, solar concentrators or other equipment. A small PV system may provide energy to a single consumer, or to an isolated device like a lamp or a weather instrument. Large grid-connected PV systems can provide the energy needed by many customers. The electricity generated can be either stored, used directly (island/standalone plant), or fed into a large electricity grid powered by central generation plants (grid-connected/grid-tied plant), or combined with one or many domestic electricity generators to feed into a small grid (hybrid plant). Systems are generally designed in order to ensure the highest energy yield for a given investment.