Solar panels output Direct Current (DC). As DC electricity is not compatible with common household appliances nor fed into the mains grid, it first needs to be converted to Alternating Current (AC). The conversion is performed by solar inverters, also known as grid-tied inverters.
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How inverters for solar power systems work
Solar inverters are key components in solar energy systems, converting the direct current (DC) electricity generated by solar panels into alternating current (AC) electricity, which is used in homes and businesses. Here’s a step-by-step look at how they work:
DC Input: Solar panels capture sunlight and convert it into DC electricity. This current is fed into the solar inverter.
Conversion: Inside the inverter, electronic components such as transformers and capacitors transform the DC electricity into AC electricity. This process is necessary because most household appliances and the electrical grid use AC power.
Smoothing and Filtering: The inverter smooths and filters the AC electricity to ensure it is clean and free of distortions. This ensures the power quality is suitable for all electrical devices and systems.
Synchronisation with Grid: The inverter ensures that the converted AC electricity is synchronised with the frequency and voltage of the electrical grid. This allows any excess energy produced by your solar panels to be fed back into the grid, potentially earning you a feed-in tariff from your energy retailer.
Monitoring and Protection: Modern inverters often include monitoring systems that track energy production and performance. They also have built-in protection mechanisms to prevent damage from issues like overvoltage, short circuits, or overheating.
In essence, solar inverters are the bridge between your solar panels and the electrical system in your home or business, ensuring that the renewable energy you produce is usable and efficient.
- Solar panels convert the sun’s energy into DC electricity
- The DC electricity is channelled into a solar inverter that converts it to 240V 50Hz AC electricity.
- The 240V AC electricity can be used to power home appliances
- Surplus electricity is fed back into the main grid.
- Click here for more information on home grid connect solar
Types of solar inverters
There are 3 main solar inverter types for grid-tied: string, micro, and central. This article discusses the basics of what each inverter is, and each type’s advantages and disadvantages; followed by some technical information on how grid-tied inverters work in general.
String inverters
A solar string inverter is a type most commonly used in home and commercial solar power systems. It is a large-ish box that is often situated some distance away from the solar array. Depending on the size of the installation, there may be more than one solar string inverter present. All modern string inverters incorporate Maximum Power Point Tracking (MPPT) technology.
How a string inverter works
Conversion process
DC collection from solar panels
- Solar panels generate DC electricity, with voltage and current depending on irradiance, temperature, and the panel’s electrical characteristics.
- Panels are connected in series to form a string, which increases the voltage while keeping the current constant.
- Multiple strings can be connected in parallel to the inverter.
Maximum Power Point Tracking (MPPT)
- MPPT is a power electronics algorithm within the inverter that adjusts the voltage and current to ensure the panels operate at their maximum power point (MPP).
- The MPP is affected by:
- Irradiance levels (more sunlight = higher power output)
- Temperature (higher temperatures reduce panel voltage)
- Shading and soiling (partial shade can significantly reduce power output)
- The inverter continuously adjusts the operating voltage to find the MPP, extracting the highest possible energy from the solar array.
DC to AC conversion (Inversion)
- The inverter contains IGBTs (Insulated-Gate Bipolar Transistors) or MOSFETs that rapidly switch on and off to convert DC into an AC waveform.
- The inverter uses pulse-width modulation (PWM) to approximate a sinusoidal waveform, which is then smoothed using filters.
Synchronisation with the grid
- The inverter matches the frequency and phase of the grid (typically 50 Hz in Australia).
- It ensures that voltage, frequency, and phase alignment meet grid standards.
- If the grid fails (e.g., blackout), anti-islanding protection disconnects the inverter to prevent back-feeding.
Benefits of a String Inverter
High efficiency (97–99%)
- Modern string inverters have high conversion efficiency, making them a reliable choice for large-scale residential and commercial solar systems.
Lower cost compared to microinverters
- String inverters are more cost-effective than microinverters since a single unit handles the entire array, reducing the number of components needed.
- Lower upfront cost means a shorter payback period.
Simpler installation & maintenance
- Since only one or a few inverters are used in a system, installation is straightforward.
- Easier troubleshooting and maintenance, as all DC-to-AC conversion happens in a single location.
Scalability for larger systems
- Ideal for medium-to-large-scale solar setups where panel orientation is consistent.
- Multiple MPPT inputs allow different panel orientations to be managed within a single inverter.
Reliable and proven technology
- String inverters have been around for decades, with well-established safety and operational standards.
- Less risk of firmware issues compared to newer modular solutions.
Grid compliance features
- Supports reactive power control (volt-VAR response) to help stabilise the grid.
- Integrated anti-islanding protection ensures safe disconnection during a blackout.
Advanced monitoring capabilities
- Most modern string inverters come with Wi-Fi, Ethernet, or 4G connectivity, allowing real-time performance tracking via mobile apps.
Compatible with DC optimisers
- When combined with DC optimisers (like SolarEdge or Tigo), a string inverter can offer panel-level optimisation, reducing the impact of shading and panel mismatch.
Limitations of String Inverters
Performance affected by shading
- Since all panels in a string operate at the same current, a shaded or underperforming panel reduces the output of the entire string.
- Solutions:
- Optimisers (such as Tigo or SolarEdge) mitigate this issue by adjusting the voltage at the panel level.
- Microinverters (alternative to string inverters) offer panel-level MPPT.
Limited flexibility in system design
- All panels in a string must have a similar orientation and tilt for optimal performance.
- Multiple MPPT inputs help in cases where panels face different directions.
DC voltage safety concerns
- High DC voltage (often 600V to 1000V in residential and commercial systems) poses a fire risk if wiring is damaged or improperly installed.
Efficiency drops at low power
- String inverters typically operate at 97-99% efficiency, but performance declines when solar generation is low (e.g., early morning or late afternoon).
Lifespan and maintenance
- String inverters have a typical lifespan of 10-15 years, shorter than solar panels (25+ years).
- Requires active cooling (fans or heat sinks), which can degrade over time.
Additional considerations
- Reactive power control: Some modern inverters support volt-VAR control, which helps stabilise grid voltage.
- Remote monitoring: Many string inverters have Wi-Fi or 4G connectivity, allowing users to monitor system performance via an app.
- Hybrid functionality: Some newer models integrate battery storage compatibility, offering hybrid operation.
Microinverters
A microinverter consists of a small box located on the back of or situated very close to a solar panel. Its role is to convert the DC electricity produced by a single solar panel. Unlike string inverters, each microinverter works independently to convert energy and deliver it to the home, grid, or battery storage. The world’s leading microinverter brand is Enphase.
How a microinverter works
Conversion process
DC to AC conversion at the panel level
- Each solar panel has its own dedicated microinverter, which converts the panel’s DC output to AC immediately.
- The AC output from all microinverters is combined and fed into the electrical panel or grid.
Maximum Power Point Tracking (MPPT) per panel
- Each microinverter has an independent MPPT algorithm, ensuring each panel operates at its optimal voltage and current.
- Unlike string inverters, where a weak panel affects the whole string, microinverters allow each panel to perform individually.
Grid synchronisation
- Microinverters match the grid frequency and voltage just like string inverters.
- They include anti-islanding protection, preventing power export during a grid outage.
Modular expansion
- Additional solar panels can be added without worrying about string voltage limitations, making microinverters highly scalable.
Benefits of microinverters
Eliminates single-point failure
- In a string inverter system, if the inverter fails, the whole system shuts down.
- With microinverters, the failure of one unit only affects one panel, keeping the rest of the system operational.
Superior performance in shaded or mismatched conditions
- Since each panel operates independently, shading, dirt, or panel degradation on one module does not reduce the output of the entire system.
- Ideal for roofs with multiple orientations, shading issues, or mixed panel types.
Flexible system design
- No need to match panel voltages in a string.
- Panels can be installed on different roof angles and orientations without affecting system performance.
Better monitoring & diagnostics
- Microinverters provide panel-level monitoring, allowing users to detect issues with individual panels, not just the whole system.
- Many brands (like Enphase) offer app-based monitoring for real-time performance tracking.
Improved safety – No high DC voltage
- String inverters operate at high-voltage DC (600V-1000V), posing fire and electrocution risks.
- Microinverters convert DC to AC immediately at panel level, reducing these risks significantly.
Easier system expansion
- Adding more panels is simple since each panel has its own inverter.
- No need to worry about matching string sizes or voltage limits.
Longer warranty
- Microinverters often come with 20-25 year warranties, compared to 10-15 years for string inverters.
Limitations of microinverters
Higher upfront cost
- Microinverters are more expensive than string inverters since each panel requires an individual inverter.
Increased complexity & maintenance
- Installing and servicing multiple microinverters is more time-consuming than a single string inverter.
- Troubleshooting a failed microinverter requires access to the rooftop, unlike string inverters, which are typically ground-mounted.
More points of failure
- Having multiple electronic components on the roof increases potential failure points.
- Microinverters are exposed to heat and weather, which may shorten their lifespan compared to string inverters installed in a protected location.
Slightly lower efficiency at scale
- While individual MPPT improves performance, microinverters generally have slightly lower conversion efficiency (96-98%) compared to top-tier string inverters (97-99%).
Central inverters
A central inverter is a large-scale version of a string inverter, designed for commercial and utility-scale solar installations. Instead of multiple smaller inverters, a single high-power inverter (ranging from 100 kW to multi-megawatts) converts the DC electricity from multiple solar panel strings into AC power.
How a central inverter works
Conversion process
Multiple string inputs → DC bus
- Hundreds to thousands of panels are grouped into multiple strings, each connected to DC combiner boxes.
- These combiner boxes consolidate the DC power and feed it into the central inverter’s DC bus.
DC to AC conversion
- The inverter converts high-voltage DC (typically 600V-1500V) to three-phase AC power suitable for grid transmission.
- Uses Insulated Gate Bipolar Transistors (IGBTs) to regulate voltage and frequency.
Maximum Power Point Tracking (MPPT) at central level
- A central inverter typically has fewer MPPT channels (1-6) compared to string or microinverters.
- If one section of the solar array is shaded, all panels connected to that MPPT channel are affected.
Grid synchronisation & power factor control
- Advanced grid-support features like voltage control, reactive power compensation, and frequency regulation.
- Ensures compliance with grid codes for utility-scale solar farms.
Benefits of central inverters
Lowest cost per watt
- More cost-effective than string or microinverters for large-scale projects.
- Economies of scale reduce cost per kW compared to deploying thousands of smaller inverters.
High efficiency (98-99%)
- Utility-grade central inverters are among the most efficient in the industry, often reaching 99% peak efficiency.
- Fewer conversion stages compared to microinverter-based systems.
Simplified large-scale deployment
- Fewer components mean simpler system design and wiring compared to managing thousands of individual inverters.
- Suitable for flat, open-field solar farms where panel orientation is consistent.
Advanced grid management
- Provides reactive power support, voltage control, and grid frequency stabilisation.
- Ensures compliance with Australian grid codes for high-voltage transmission.
Lower maintenance per kW
- A single unit is easier to monitor and maintain than thousands of microinverters.
- Remote monitoring and diagnostics reduce on-site maintenance costs.
Limitations of central inverters
Single point of failure
- If the central inverter fails, the entire system goes offline, leading to significant downtime.
Limited MPPT capabilities
- Since MPPT is applied to large groups of panels, partial shading or panel mismatch reduces efficiency.
- Performance suffers in sites with varying sun exposure.
Large physical size & cooling requirements
- Central inverters require dedicated climate-controlled enclosures with active cooling systems (air or liquid-cooled).
- High installation space requirements and infrastructure costs.
High DC voltage risks
- Operates at 1000V-1500V DC, increasing the risk of arc faults and electrical hazards.
- Requires strict safety protocols and protective gear for maintenance.
When to choose a central inverter?
- Utility-scale solar farms (e.g., 1 MW+ projects)
- Large commercial solar systems with uniform sun exposure
- Sites where cost per kW is a primary concern
- Projects requiring advanced grid integration
Which is the best type of inverter?
While the most suitable solar inverter type will be dependent on the installation scenarios; generally speaking 3-phase string inverters offer the widest range of applications in terms of residential to large commercial installations.
5 key factors to consider when selecting a solar inverter
1. System size & inverter capacity
- Ensure the inverter’s rated capacity (kW) matches the total solar panel array’s output.
- In Australia, inverters are often undersized relative to panel capacity (e.g., 6.6 kW of panels with a 5 kW inverter) to maximise STC rebates and system efficiency.
- For commercial or utility-scale systems, consider whether multiple string inverters or a central inverter is more suitable.
2. Efficiency & MPPT capabilities
- Choose an inverter with high efficiency (≥97%) to reduce energy losses.
- More Maximum Power Point Trackers (MPPTs) improve performance in systems with multiple orientations or partial shading.
- Microinverters provide individual MPPT per panel, while string and central inverters have limited MPPT inputs.
3. Grid compatibility & compliance
- Ensure the inverter meets Australian grid standards (AS/NZS 4777.2:2020) for voltage and frequency compliance.
- Some inverters offer grid support features like reactive power control and frequency regulation for Virtual Power Plants (VPPs).
- Hybrid inverters should support battery integration if future energy storage is planned.
4. Warranty & manufacturer reliability
- Look for inverters with at least a 10-year warranty (some premium brands offer up to 15-20 years).
- Choose reputable brands with a proven track record, local support, and availability of spare parts.
- Consider failure rates—central inverters have a single point of failure, while string and microinverters offer redundancy.
5. Environmental & installation considerations
- Check the IP rating (e.g., IP65/IP66 for outdoor use) to ensure durability in harsh weather conditions.
- Consider cooling mechanisms—fanless inverters last longer with less maintenance.
- Ensure the inverter location allows for proper ventilation and easy access for monitoring and servicing.
| Feature | Central Inverter | String Inverter | Microinverter |
|---|---|---|---|
| Typical Power Size | 100 kW – 5 MW+ | 3 kW – 100 kW | 200W – 800W (per panel) |
| Cost per kW | Lowest | Medium | Highest |
| MPPT Control | Limited (1-6 MPPTs) | Multiple MPPTs | Individual per panel |
| Shading Tolerance | Low | Moderate | High |
| Efficiency | 98-99% | 97-99% | 96-98% |
| Scalability | Best for large solar farms | Best for residential & commercial | Best for complex roof layouts |
| Monitoring Level | System-wide | String-level | Panel-level |
| Installation & Maintenance | Requires large space & cooling | Easy for small systems | More complex |
| System Expansion | Less flexible | Flexible | Highly flexible |
| Grid Support Features | Best | Good | Limited |
World-leading inverters
Energy Matters has partnered with some of the world’s largest inverter manufacturers to help you select the right inverter for your needs. Check out our recommended products page to find out more about the inverters available for Australian homes, businesses, and commercial applications.
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