Selecting a Grid-Tie Inverter

Inverters are perhaps the most important component in your renewable energy system. They are the device that converts you battery voltage (DC-direct current) into something you can use, specifically AC (alternating current). There are generally two types of inverters that are used with renewable energy systems: (1) modified sine-wave Inverter (or modified square-wave) and (2) pure or true sine-wave inverter.

Cost wise, modified sine-wave inverters are less expensive, however, their usefulness is limited to supplying AC loads including linear and switching power supplies used in electronic equipment, transformers, and motors. This is because a modified sine wave is a synthesized, stepped wave form that approximates a sine wave but it does fully mimic one. Most computer-based electronics are specifically designed to convert pure sign-wave AC signal into DC.

To operate most electronic-based appliances such as desk-top computers, a pure sine-wave inverter is needed. Grid-tie inverters are required to match voltage and frequency, which includes producing a pure sign wave. Only inverters marked as “Grid Interactive” are permitted to be connected to the utility grid. This labeling is only applied after the inverter has complied to UL 1741, inverters, Converters, Controllers, and Interconnection System Equipment for Use with Distributed Energy Resources. Green Team Direct sells several different makes of grid-tie inverters (interactive inverters) from leading manufacturers such as OutBack, Xantrex, Enphase, and SMA (Sunny Boy).

Selecting a grid-tie inverter is not as easy as selecting it based solely on the maximum output power rating annotated on the unit, although it is one of the factors. Keep in mind that stand alone inverters are rated at the maximum power that the inverter can supply the AC loads. Grid-interactive inverters are rated at the maximum DC input. Depending on the solar array characteristics and assuming grid-tie connection, a properly size inverter is capable of producing the power requirements needed, capable of handling the maximum expected input DC voltage, and produce a current capable of meeting the minimum DC voltage required ensuring the inverter “turns on”.