How Does a Solar Inverter Work?

How does a solar inverter work to deliver AC electricity after taking in a solar array’s DC current? Here, below, is the answer and more.

In your search for solar inverter information, you’re probably asking yourself this: how does a solar inverter work? Do different inverters operate differently? And so on. This article is meant to answer all these and other solar inverter questions — in a way that you’ll find straightforward and easy to grasp.

How Does a Solar Inverter Work?

A solar inverter system is mainly composed of an inverter, solar panels, and (most often) storage batteries together with the charge controller. The inverter converts the DC power to useful AC power. On the other hand, the charge controller regulates the battery charging.

The basic solar inverter operation is pretty simple: when there is surplus power from the solar panels, the excess energy is stored in batteries. When the power is insufficient, power is taken from the batteries. That way, the inverter ensures a steady supply of power even when there solar panels are not generating electricity.

Different types of solar inverters may work differently, though—and fit different purposes. For instance, some connect directly to the grid, and may or may not use battery storage. Grid-connected solar inverters are able to sell surplus power to the utility company, while non-grid inverters can only use power that is stored in batteries. Read more below.

Solar Inverter Working Principle

Let’s now see how PV inverters manage to give an AC output or, in other words, the working principle of solar inverter devices. Seen from the outside, a PV inverter may look like a simple box. However, inside there are several electronic circuits that work together to make the conversion from DC to AC happen.

Solar Inverter Components

Different types of PV inverters may use different components to achieve the DC-AC conversion. Below are some of the main solar inverter components that help to convert DC to AC:

• Diodes
• Transformers (in transformer-based inverters)
• Capacitors and inductors
• MOSFETs or IGBTs
• Monitoring software

The Solar Inverter working

The solar inverter working, based on the mentioned components, involves rapidly switching direct current within a circuit to produce an alternating current. In order to achieve that, high-frequency switching devices are used. These are usually either MOSFETs (metal-oxide-semiconductor field-effect transistor) or IGBTs (insulated-gate bipolar transistors).

Capacitors and inductors, on the other hand store energy in the form of electric charge and electric field, which is then released when needed to smooth the output that results from the switching action. Diodes, when used in solar inverter technology, mainly provide a path for inductive load currents, while transformers change voltage to the required level.

Finally, the monitoring software found in virtually every inverter today serves to monitor inverter operation and detect faults before (or when) they occur. Different inverters, as mentioned earlier, may use different ways to produce AC power: more about that next.

Working of Solar Inverters by Type

The working principle of solar inverter devices mostly depends on whether they’re transformer-based or transformerless, pure sine wave or modified sine wave, and if it’s a single phase or 3 phase solar inverter. In order to understand these differences, let’s take a peek at each type of solar inverter, how it works, and more.

Solar Inverter Transformer vs. Transformerless

Simply put, a transformer-based solar inverter uses an isolation transformer to convert voltage as needed. A transformerless inverter doesn’t use one and relies on electronic components. As you might expect, this can result in some advantages and disadvantages for each type: more about these inverters below.

Transformer-Based Solar Inverter

This is the traditional or standard solar inverter. It uses a regular transformer for the DC to AC conversion, along with several electronic components such as capacitors and transistors. One of its main advantages is that it provides electrical isolation between the input and output circuits, resulting in higher electrical safety.

But a transformer based solar inverter are is more expensive than transformerless inverter. This is because the transformer itself is an expensive component. In addition, the transformer adds weight and bulk to the inverter, making it larger and less convenient to install.

Another disadvantage is that the transformer can introduce power losses. These losses are typically around 2-3%, but can be as high as 5%. This means that the inverter will be less efficient than a transformerless inverter, in addition to producing a characteristic hum during operation.

Transformerless Inverter

Transformerless solar inverters are a newer type of the device. Instead of physical transformers, these use semiconductor devices to change DC to AC as well as voltage to the required level. That has several advantages over transformer-based inverters.

First, transformerless inverters are more efficient because they don’t lose energy in the transformation process. Second, transformerless inverters are smaller and lighter than transformer-based inverters, making them easier to install. They are also less expensive, seeing that they do not use a transformer.

Most TL inverters today also come installed with MPPT, which makes them quite effective when it comes to power delivery. Transformerless solar inverters lack the isolation safety that transformers provide, though, which can be a concern. However, modern models come equipped with technologies to deal with that.

Pure Sine Wave Inverter vs. Modified

The waveform of a PV solar inverter output also determines how it works. The two most common types of waveforms are pure sine wave and modified sine wave. Although rare, you may also come across square wave inverters. Learn more about the 3 types of inverters and how they work below.

Pure Sine Wave Inverter

The output of a pure sine wave solar inverter is a perfect sine wave. This is the same kind of waveform produced by utility companies (sometimes even better). Pure sine wave inverters are more expensive than other types of inverters (and more complex), but they’re also more efficient and have better power quality.

A pure sine wave inverter for solar system is the best choice for a backup power system: it provides clean, reliable power for all of your sensitive electronics. They are most suitable when it comes to powering sensitive appliances or motorized equipment like pumps and fans.

Modified Sine Wave Inverter

The output of a modified sine wave solar inverter assumes a staircase shape. This type of waveform is less expensive than a pure sine solar inverter, but it’s also less efficient and has lower power quality. Modified sine wave inverters are, therefore, typically used in applications where power quality is not as important.

The main advantage of modified sine wave solar inverters is that they’re usually less expensive than pure sine wave inverters. However, their modified waveform can cause some electronic equipment to operate less efficiently or generate more heat. Generally, they’re usable in low power applications.

Square Wave Solar Inverter

The solar inverter output voltage in this case makes abrupt changes from peak positive to peak negative, producing a square waveform. This type of waveform is the most basic and cheapest to produce. But just like the modified sine wave types, these inverters can make many electrical appliances to overheat or operate less efficiently.

Single Phase vs Three Phase Solar Inverter

A solar inverter is also either a single or 3 phase device. The single phase solar inverter only has one input voltage, while a 3 phase solar inverter has three. Single phase inverters are most commonly used in residential solar systems because they’re less expensive and more than sufficient for powering a home. Three phase solar inverters are typically used in commercial solar systems or very large residential systems.

Single Phase Solar Inverter

A single phase solar inverter is the most basic and common type. It produces single phase output from the solar array current, making it well suited for small loads such as those in a home or small office. The downside of using a single phase solar inverter is that they can only power certain types of equipment.

Three Phase Solar Inverter

A 3 phase solar inverter is more complex than a single phase solar inverter and works by producing three different output currents from the DC input. These produce more power and are best suited for larger loads such as those in an industrial setting. As you can expect, the three phase solar inverter is usually more expensive and complex to design and build.

Conclusion

The working that’s responsible for solar inverter DC to AC conversion can take various forms and require different components. Generally, the solar inverter technology today includes the use of semiconductor devices. Different inverter working principles have different advantages and disadvantages. These are outlined in this post. Use the information to find the most appropriate type of inverter for your solar energy system.