Introduction

Individual solar cells create relatively low voltage,  typically of around 0.5V. Several cells are combined within a a laminate with the cells effectively wired in series. The laminate is covered in a weatherproof housing and installed in a frame to form a photovoltaic module or panel. The panel will typically develop around 15 volts or more when under a load (e.g. while charging a 12-volt battery). Open circuit voltage could be higher, perhaps 20 volts or more.

If  panels are connected (electrically) in series,  it is possible to obtain very high output voltages.  In fact, a number of panels can be connected to form a PV string. Moreover, two or more strings can be fed to an inverter to create a PV array. Inverters are used to convert the DC current from the modules to AC.

PV systems can be designed to operate as a stand alone installation or to be connected to an electrical grid. In the latter case, their output may be used on site or or exported depending on the local power demand. PV systems can also be integrated with other generation plants (e.g. diesel generators) to form hybrid systems. In all these systems, electrical energy can also be stored for later local use or transmission to distant users by using batteries and other devices. 

In its simplest form, a  PV system has its cells or panels directly connected to DC electrical equipment. The obvious shortcoming of this approach is the lack of an energy supply when there is no sunlight. In practice such direct use is limited to powering small batteries, cell phone chargers, pocket calculators and similar small portable equipment.

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