What Is a Hybrid Inverter?

If you’re a homeowner contemplating a jump onto the solar train, it’s good to know a solar array consists of more than just photovoltaic (PV) panels. Some systems, even those tied to the grid, include batteries to store energy. If your system has a battery pack, you need a controller to keep the batteries charged and prevent overcharging.

Every system also needs an inverter, a device that converts the DC power generated by the panels and stored in the batteries to grid-friendly AC power. It also functions as a transformer, stepping up the voltage in batteries (12 to 48V) to the standard on the grid (120 to 240V).

In the early days of solar development, inverters were bulky and inefficient, producing choppy AC signals sensitive electronic equipment couldn’t use. We used to have one of those. Because our dryer had electronic controls, it wouldn’t work unless the generator (which produced its own 120V signal) was on.

While addressing such deficiencies, manufacturers went further, turning inverters into multitasking control systems for ever more complex PV systems. These are known as hybrid inverters.

What Is a Hybrid Inverter?

Think of it as one that multitasks. It provides the interface between the panels, the battery and the grid. Depending on type, it can operate in four modes:

• Basic grid-tie mode: Converts the DC current from solar panels into AC current compatible with that supplied by the power company.
• Battery storage mode: Converts AC current from the grid to DC current for charging the battery.
• Backup mode: During a power outage, a grid-tied inverter can automatically switch to backup mode and supply the panel with power from the battery.
• Off-grid mode: Can simultaneously supply power to the panel and charge the backup battery.

One significant advantage of hybrid inverters over conventional ones is the ability to operate “in reverse.” That means it can convert AC current to DC, the opposite of what an inverter normally does. So during a period of extended cloudiness, when the panels aren’t charging the batteries, the inverter uses grid power to charge them.

How Does a Hybrid Inverter Work?

A standard grid-tie inverter converts DC power to AC, and transforms the voltage from the PV array and the battery to the grid voltage.

It converts from DC to AC via a system of transistors that switch on and off to reverse the current direction at a frequency of 60Hz (cycles per second). The AC signal then passes through a transformer coil that induces a current in a second coil next to it by magnetic induction.

The ratio of the number of turns in the coils determines the voltage ratio, which makes it easy to accurately produce the grid voltage.

A hybrid inverter can also convert AC power to DC and step down the voltage to charge batteries using grid power. The conversion from AC to DC is called rectification, and the electronic components that do it are called diodes.

Before rectification, the voltage needs to be reduced. An easy way to do this is directing the signal through the same transformer, but in reverse.

Hybrid inverters typically have four connection ports. One comes from the PV array, one goes to the electrical panel, and two connect to the batteries, one as input and the other as output.

Internal electronics monitor electric usage and provide yet another benefit. A hybrid inverter can switch from grid power to the battery to operate the electrical system during periods of peak usage, when the grid is overloaded and electricity most expensive.

Types of Hybrid Inverters

Not all hybrid inverters include all the features discussed above. A wide selection of models are available, each with its own maximum power output, battery compatibility and voltage range for battery charging. They basically fall into three main types:

• Solar storage: This type you would use for an off-grid situation. It can supply power from the PV array to the panel and charge batteries.
• Solar storage and back-up power: You’ll need this one if you’re tying your solar energy system to the grid. It can do everything a solar storage hybrid inverter can do, and it has all the electronics needed to feed electricity back to the power company.
• Battery energy storage system (BESS): This comes with a lithium-ion battery pack in the same housing. It can be as large as a refrigerator, but most are much smaller. The Tesla Powerwall is about four feet high, two-and-a-half feet wide and six inches deep.

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