The inverter is a fundamental part of every solar or back-up power installation. Hence, understanding this piece of equipment is important in ensuring you choose the right inverter for your application. In this article, we’re taking you into the world of inverters - giving you a basic understanding of what inverters are, and describing the different types of inverters.

Understanding inverters

Before discussing what inverters are, it is important to first understand that there are two types of electricity – alternating current (AC) and direct current (DC).

At home, appliances are designed to run off of an AC supply. AC electricity is received from electrical outlets. However, electricity received from solar panels and batteries is DC electricity. In order to power appliances and other electrical equipment from renewable sources or battery banks, an inverter is used to invert DC electricity into AC electricity.

An inverter typically consists of a number of electronic switches known as IGBT’s (insulated-gate bipolar transistors). The opening and closing of these switches is controlled. The IGBT’s can open and close exceptionally fast, and in pairs, to control the flow of electricity. By controlling the path which the electricity takes and how long it flows in the different paths, AC electricity is then produced from the DC source.

Inverters explained

Inverter applications

Typical applications of solar inverts include:

  • Uninterruptible power supplies
  • As a building block of a switched mode power supply
  • As standalone inverters

Different types of inverters

A hybrid solar system stores excess solar energy and can also provide back-up power during load shedding. This is ideal for residential use. For businesses (which primarily operate during daylight hours), a grid-tied solar system is still the most economical choice.

In grid-tied and hybrid solar systems, the panels are connected directly into the inverter. The inverter then plugs into the building’s electrical box or (DB board). Functions typically performed by grid-tied and hybrid inverters include:

  • Monitoring power usage
  • Grid synchronisation
  • Uses an alternative source of power (batteries or solar panels)
  • Synchronises between power sources (uses another source if one is depleted)

1. Pure Sine Wave

When purchasing an inverter, you always want the current wave to be as “true” or “pure” as possible. Pure sine wave inverters can be used on all electronic equipment and typically will not have any side effect. Features of pure sine wave inverters include the fact that they deliver quality power output, they are quieter than modified sine waves, and they are ideal for modern appliances.

A pure sine wave inverter, however, is more expensive than a modified sine wave inverter.

2. Modified sine wave

Modified sine wave inverters output lower quality power and are only compatible with certain appliances. As such, they can be used for simple systems that don’t have any delicate electronics or audio equipment. Although some equipment may seem to be working fine with a modified sine wave inverter, they may actually run hotter and their lifespan may also be affected.

Pure vs modified sine wave

Grid-tied inverters (used for energy efficiency)

String inverters are the least expensive option for use in grid-tied systems. With this type of inverter, there are large groups of panels wired together into strings. However, shade on one panel can affect the entire string. If the system is partially shaded, the efficiency of string inverters drops dramatically.

With the provision of building a system in full sunlight, a great option will then be the string inverter - saving money, without sacrificing quality or efficiency. However, if there is shade or other obstructions to the system, consider string inverters with individual power optimizers on each panel.

Power optimizers allow the inverter to control the output of each panel independently. So if one panel gets shaded, the rest of the panels in the array will continue to produce at full strength. Optimizers also allow for the monitoring of the system on a per-panel basis.

Many string inverters can function with or without power optimizers. These are simply an extra cost to add the monitoring and shade mitigation functionality.

Another option for grid-tied systems is the micro-inverter. The concept of micro-inverters is simple: attach an inverter to every panel. There are two main instances where micro-inverters should be used:

• When starting with a small system, with a view of expanding down the road.

• When importance is placed on monitoring and optimizing each panel independently.

When pairing a micro-inverter with a panel, a self-contained single-panel solar energy system is created. Each will produce power, regardless of how many panels there are. This eliminates the need to rewire and re-balance panel strings when adding on to the system down the road. This is a more expensive option than string inverters, however, the overall yield is slightly higher.

Hybrid inverters (used for load shedding)

The most versatile option is the hybrid inverter. These accept DC and AC power, and various solar power applications are possible with hybrid variations. Here are a few advantages of hybrid inverters:

  • Affordable for its functionality
  • Powers loads by using energy sources in the most efficient way
  • Ideal choice for both business and residential use

To illustrate how hybrid inverters work, take for example a home that runs 1000 watts of power. In the event that solar panels can only produce half of this, the inverter will pull the remaining energy required from the battery. In the instance where there is no battery capacity available, the inverter then draws the remaining energy required from the grid.

Most modern hybrid inverters have the battery charger and connection built-in, making the future addition of a battery much easier. However, hybrid inverters are more expensive, when compared to grid-tied inverters.

Off-grid inverters

Off-grid systems are typically used where there is no municipal connection. These systems are made up of the same equipment as a hybrid system, but have large battery banks. Furthermore, they are typically designed to operate for at least 3 days without any sun light. Solar power generated from panels charge the batteries directly. Off-grid inverters then invert the DC electricity from the batteries into AC electricity.

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