A Solar inverter or PV inverter is a type of electrical inverter that is made to change the direct current (DC) electricity from a photovoltaic array into alternating current (AC) for use with home appliances and possibly a utility grid.

Solar inverters may be classified into three broad types:
Stand-alone off grid inverters - used in isolated systems where the inverter draws its DC energy from batteries charged by photovoltaic arrays and/or other sources, such as wind turbines, hydro turbines, or engine generators. Many stand-alone inverters also incorporate integral battery chargers to replenish the battery from an AC source, when available. Normally these do not interface in any way with the utility grid, and as such, are not required to have anti-islanding protection.

Grid tie inverters - these match phase with a utility-supplied sine wave. Grid-tie inverters are designed to shut down automatically upon loss of utility supply, for safety reasons. They do not provide backup power during utility outages.

Battery backup grid tie inverters - These are special inverters which are designed to draw energy from a battery, manage the battery charge via an onboard charger, and export excess energy to the utility grid. These inverters are capable of supplying AC energy to selected loads during a utility outage, and are required to have anti-islanding protection.

Solar Terms (Glossary)

Stand-alone off grid inverters
Typically ranging in size from 500 watts to 5000 watts, off-grid inverters serve remote cabins, homes, barns and other facilities with no access to the public utility grid. Electricity from solar modules or wind turbines is stored in large battery banks from which the inverter draws power when needed.

Grid tie inverters
A grid-tied inverter or utility intertie inverter converts DC current from solar modules into AC current and feeds the user's electricity needs directly. To the extent that the solar modules produce more than the user requires, excess power is pushed by the inverter in the public utility grid where it is purchased by the utility company according to local rules and regulations. Grid-tied systems use the utility grid, as the storage bank, drawing from the grid when necessary and pushing into the grid when there is excess power.

These inverters are designed to typically operate between 200 and 600 volts DC, requiring that solar modules be grouped into strings that combine to reach this voltage window. As a result, gridtied inverters are also called string inverters. At these voltages, electricity is very dangerous and should be managed in a careful manner.

Because grid-tied inverters cannot handle storage systems such as batteries, grid-tied systems are subject to the weaknesses of the local grid. When the grid goes down the grid-tied solar energy system will also go down.

Battery backup grid tie inverters
Dual function inverters work both as an off-grid and grid-tied inverter in one box, allowing battery storage for use when the grid goes down, and also pushing power to the grid when the batteries are full and the solar panels are producing excess electricity. These inverters are typically used where there is an unreliable grid that goes down for extended periods of time or in situations where even a short grid blackout is intolerable.

These systems are called Grid-Tied Battery Backup systems and are the most expensive choice for customers wishing to go solar. They necessarily require the expense of both the off-grid and grid-tied systems.