Solar inverters or photovoltaic (PV) inverters are electrical devices that convert the direct current (DC) produced by a PV cell or array into alternating current (AC). Although the DC outputs from a PV module are variable, the AC currents are sinusoidal and suitable for the commercial power grid or off-grid. Most solar inverters include wired or wireless communications capabilities along with a real-time microcontroller. Through maximum power point tracking (MPPT), the controller maximizes the DC outputs from PV devices. Some solar inverters also provide battery energy storage and use advanced peripherals. For example, some solar DC-AC inverters are designed to read an analog-to-digital converter (ADC) and adjust the pulse-width modulation in a single clock cycle.
Types of Solar Inverters
There are three main types of solar inverters: stand-alone, grid tie, and battery back-up. Stand-alone products draw their DC power from a battery that is charged by PV arrays. They typically do not interface with the commercial electrical grid. By contrast, grid tie devices are designed to convert DC to AC that is compatible with the utility grid. Finally, battery backup inverters draw DC energy from a battery, manage the battery’s charge, send excess power to the grid, and supply AC power during utility outages. Applications for each of these product categories include solar power, renewable energy, grid power, off-grid power, and power generation.
Solar inverters differ in terms of DC input, AC output, and general specifications. DC input parameters include recommended PV power, maximum DC voltage, operating DC voltage range, and maximum usable DC input current. AC output parameters cover maximum output power, nominal AC output voltage, utility AC voltage range, maximum AC current, maximum utility feedback current, operating frequency range, total harmonic distortion (THD), and power factor. General product specifications for solar inverters include maximum efficiency, consumption during operation and in standby, enclosure type, weight, ambient temperature range, and cooling technology.
Protection types, approvals and certifications, and features are important to consider when selecting solar inverters. For example, some products feature ground fault protection, DC reverse polarity, islanding protection, and surge protection. Typically, anti-islanding protection is achieved in accordance with published standards such as UL 1741 from Underwriters Laboratories and IEEE 1547 from the Institute of Electrical and Electronics Engineers. In the United States, the Federal Communications Commission (FCC) sets standards for electromagnetic interference (EMI). Features for photovoltaic inverters include battery charging and the use of a true or pure sine wave.