Solar Inverters Introduction

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What is a solar inverter?

A solar inverter is an essential part of a grid-connected solar system. Solar panels generate DC electricity, which must be converted to alternating current (AC) electricity to be used in homes and businesses. This is the primary role of the solar inverter. Without a solar inverter, you cannot use the solar electricity generated. Solar inverters come in many varieties and sizes, where the size or power rating of the inverter is measured in kilowatts (kW). The two main types are string solar string inverters and microinverters, which are described in the next section.

Types of solar inverters

Choosing the best type of inverter for a solar energy system depends on various factors, including system size, installation location, budget, and specific requirements. Here's a breakdown of each type of inverter and considerations for selecting the most suitable option:

1. String Solar Inverters

String solar inverters are the most common type of inverter available and are the most affordable option for people looking for a basic solar system without battery storage. These inverters are available in a huge range of sizes and brands and are generally very reliable if installed correctly in an appropriate location. In a standard string inverter system, the solar panels are linked together in strings of 3 to 14 or more solar panels connected together in series. The DC electricity from the strings is brought to the solar inverter via a high-voltage DC cable. The inverter then converts the DC power to AC power, which can be used in the home or fed into the electricity grid.

• Advantages:

  • Cost-effective for small to medium-sized systems.

  • Simplified installation and maintenance due to centralised placement.

  • Best for installations with unshaded panels and consistent sun exposure across all panels.

• Considerations:

  • Vulnerable to performance degradation if a single panel in the string is shaded or malfunctioning.

  • Not suitable for complex roof design with multiple aspects.

  • Efficiency may be impacted by partial shading or panel mismatch.

2. Microinverters

Microinverters can offer several benefits over string solar inverters, especially for those with complex rooftops and severe shading issues from trees of roof-mounted obstacles. In a microinverter system, each panel has a small microinverter attached to the rear side of the panel. The panel still produces DC but is converted to AC on the roof, then fed to the electrical switchboard, and finally to your home appliances or the grid. Microinverters enable each panel to work independently and are well suited to complex roofs or locations with shading from trees or rooftop obstacles.

• Advantages:

  • Optimized energy production, especially in installations with shading or panel-level differences in performance.

  • Greater system design flexibility as panels can be oriented in different directions or have varying tilt angles.

  • Easy to upgrade - New panels of a different type or voltage can be added at any time to increase solar capacity and boost power.

• Considerations:

  • Higher initial cost compared to string inverters, primarily due to the need for one microinverter per panel.

  • Increased complexity in installation, as each microinverter needs to be mounted on or behind its respective panel.

3. Hybrid Inverters

Hybrid inverters are solar inverters that can be used for home battery storage and backup power. They function the same as solar inverters and generally look very similar, with inputs for solar panel strings. However, they also feature battery connections and controls, plus most hybrid inverters provide emergency or backup AC power. See more information in the hybrid inverter section below.

• Advantages:

  • Provides greater energy independence through battery storage integration.

  • Enables self-consumption optimisation by storing excess solar energy for use during periods of low solar generation or high grid demand.

  • Provides backup power during grid outages and can operate in off-grid mode.

• Considerations:

  • Higher upfront cost compared to standard string or microinverters, especially when including battery storage.

  • More complex system design and integration, particularly when combining solar, storage, and the necessary load metering equipment.

How to select the right inverter for your needs

When choosing between string, micro, or hybrid inverters, it's essential to understand your specific needs, budget constraints, and system requirements. Consider factors such as shading, panel orientation, energy storage requirements, and backup power needs to determine the best fit for your household. Consulting with a qualified solar installer or system designer can also provide valuable insights and recommendations based on your individual circumstances.

Regular shading of solar panels can be a big problem, resulting in panel failure. Fortunately, there are advanced string inverter systems with small power optimisers attached to the back of each solar panel. Much like microinverters, power optimisers can monitor and control each panel individually and ensure every panel is operating at maximum efficiency under all conditions.

Where should a solar inverter be located?

Solar inverters are very sophisticated equipment that must operate in extreme outdoor environments for up to 10 hours a day. To prolong the life of a solar inverter and improve its efficiency, it should be mounted in a sheltered location and out of direct sunlight.

The ideal location is in a garage or undercover area near the electrical switchboard. However, in reality, a well-covered location is not available, and it will need to be installed on an external wall. This is okay, but the inverter should still be positioned to avoid direct sunlight if possible, especially during summer. Sunny, west-facing walls should be avoided, but if this is the only option, then a suitable sun cover or simple awning will help prevent overheating and improve efficiency. Also, some manufacturers may not cover a warranty claim if the inverter was installed in a very exposed sunny location. Micro inverters mounted under the solar panels do not suffer from this problem but can still be affected by extreme temperatures and high humidity.

Hybrid inverters for battery storage

Hybrid inverters are essentially two inverters in one and are used for both solar and battery storage. Learn more about hybrid inverters and the many different hybrid inverters and energy storage systems available, including well-known hybrid inverters from SolarEdge, Goodwe, Redback and SMA. Most hybrid inverters are designed to work with lithium battery systems, which can be of the same brand or from an alternative battery manufacturer. However, the battery system must be compatible and approved to work with the inverter.

Battery backup and emergency power

Hybrid inverters generate power the same way as common string solar inverters but have battery connections and other features built-in to enable energy storage for later use. This ability to store energy enables most hybrid systems to operate as a backup power supply during a blackout, similar to a UPS system. During a blackout, some hybrid inverters can also operate in off-grid mode for a prolonged amount of time, provided there is enough solar energy to recharge the energy during the day. However, dedicated off-grid solar systems should be designed and installed with specialised off-grid inverters that can handle larger surge loads.