The electricity generated by a PV module is in the form of direct current (d.c.). Transformation of direct current to alternating current (a.c.) required by many common appliances and for grid-connection is achieved with an inverter.

The efficiency of inverters is generally greater than 90%, when the inverter is operating above 10% of its rated output, and can peak as high as 96%. Inverters connected directly to the module (as opposed to through a battery) incorporate a Maximum Power Point Tracker (MPPT), which continuously adjusts the load impedance such that the inverter is always extracting the maximum power from the system.

Inverters fall into two-main categories: self-commutated and line-synchronised. The first can operate independently, being activated solely by the input power source; the line-synchronised inverters are triggered directly from the grid. Utilities require that inverters connected to the grid must contain suitable control and protection to ensure that systems are installed safely and do not adversely affect the power quality.

Traditionally, one inverter was used for the whole array. Now separate inverters may be used to connect each 'string' of modules or even mounted on the back of individual modules ('a.c. modules'). String inverters and a.c. modules are likely to be increasingly used in the building-integrated PV market because they permit easy system expansion, independent operation and easier installation.

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