Understanding the Types of Solar Inverters

Understand the Solar Inverter

Solar Inverter  is an electrical device that can convert the variable direct current (DC) output from solar photovoltaic systems into alternating current (AC) with the appropriate voltage, frequency, and phase for use by AC devices, and is also used for exporting to the grid when connected to the grid. In addition to converting DC to AC, solar inverters can also provide anti-islanding effects and maximum power point tracking.

If the power output of a solar system exceeds the local demand for electricity, the grid-connected system can export electricity to the grid. Regulations require that if the grid itself is out of power, the distributed generator connected to the grid (such as solar) must automatically shut down, a function called anti-islanding. This is done to protect utility workers and perhaps to restore grid power to avoid electric shock.

The output of solar panels varies with solar radiation levels and their operating temperatures. Under a given set of environmental conditions, the panel current will vary with voltage, from the maximum current (Isc) at short-circuit conditions to the maximum voltage (Voc) at open-circuit conditions, following the characteristic IV curve shown in the figure. A  solar electric inverter  with maximum power point tracking (MPPT) obtains the maximum possible energy from the photovoltaic array by continuously sampling the output of the solar panel and setting a resistor (load) that always produces the maximum power.

Types of Solar Inverters

Standalone: 

Typically used in applications far from the grid, where solar is used to charge batteries, which are then converted to AC for local use only. This type of solar inverter typically includes a battery charging controller and does not require anti-islanding.

Grid-connected: 

The power of the solar light inverter is used locally with the grid, or if there is excess power it can be output to the grid. The sine-wave AC phase must match the grid-supplied power, and anti-islanding is also required.

String Inverter: 

An inverter that can convert the DC outputs of multiple panels that are electrically in series. Micro-inverters: A type of solar inverter that can convert the DC output of a single solar panel or two solar panels, and multiple micro-inverters are combined into one system. Power Optimizer: Separates MPPT functionality from DC-AC conversion, MPPT occurs at the panel level, and each solar panel has a separate optimizer unit. The DC output of the optimizer is combined into a single inverter for conversion to AC.