One of the major things to consider when installing solar is the size of your solar inverter. You might have heard about ‘undersizing’ and ‘oversizing’ your solar PV system, but what does that mean?
Solar inverter sizes are rated in watts (W) based on the inverter’s maximum output. Broadly, inverter capacity should be equivalent to the system’s capacity, but it’s common practice to oversize the solar array (ie. a smaller inverter) for efficiency gains. However, this should always be within the recommended ratio.
This is the reason why you may see a ‘mismatch’ between inverter size and solar panel capacity – for example, a 6.6kW system advertised with a 5kW inverter. It’s critical for an oversized system to remain within the correct ratio, as this not only impacts efficiency, but also your eligibility for government solar incentives.
You’ll also need to consider your region’s export limits when choosing an inverter for grid-connected solar. Some solar inverter brands may be compatible with export limiting, but this isn’t a solution for all brands or regions.
We’ve created this guide to help you better understand solar inverter sizing, ensuring you get the most out of your investment.
Read on to learn more!
Table of Contents
How Does Solar Inverter Sizing Work?
Solar inverter sizing is rated in watts (W). As a general rule of thumb, your solar inverter wattage should be about the same as your solar array’s total capacity, within the optimal ratio. For example, a 6.6kW array typically uses a 5kW inverter.
It is important to get the sizing right so your solar inverter can carry the load or handle the power of the solar system you’re attaching to it. Choosing the right solar inverter size also ensures you can get the optimal performance from your solar system.
Incorrect inverter size may result in loss of power or inefficiency in your system. If your system is too large, you may not be eligible to export power to the grid, or you may need to limit your inverter.
However, within the recommended window, it’s possible to deviate from an ‘exact match’ and even benefit from improved performance. You can learn more about oversizing your solar array below.
Are All Solar Inverters The Same Size?
No, solar inverters are not the same size, as the size you need will depend on the generation capacity of your solar array. There is no one-size-fits-all inverter, as the size affects the unit’s efficiency and larger inverters are more expensive.
How to Calculate The Solar Inverter Size You Need
The easiest way to calculate the solar inverter size you need is to check the DC rating. Typically, the DC rating is the same as the AC output.
Another figure you can look at when determining the inverter size you need is the array-to-inverter ratio. This refers to the relationship between the DC rating and AC power output.
To get the array to inverter ratio, you must divide the array’s DC rating by the inverter’s maximum AC output.
|DC Rating||AC Output||Calculation||Array-To-Inverter Ratio|
|3 kW||3,000 W||3,000 (DC) ÷ 3,000 (AC)||1|
|5 kW||3,800 W||5,000 ÷ 3,800||1.32|
|8 kW||5,000 W||8,000 ÷ 5,000||1.6|
Most solar systems fall between 1.15 to 1.25 array-to-inverter ratio. As long as you fall below the 1.33 recommended maximum array-to-inverter ratio, then your solar system is working optimally.
What Are The Most Common Solar Inverter Sizes?
The most common solar inverter sizes are as follows:
|Solar Inverter Size (AC)||Equivalent Solar Array Size (DC)||Maximum Solar Array Size (DC)|
|4 kW||4 kW||5,320 W|
|5 kW||5 kW||6,650 W|
|6 kW||6 kW||7,980 W|
|8 kW||8 kW||10,640 W|
|8.2 kW||8.2 kW||10,906 W|
|9 kW||9 kW||11,970 W|
|10 kW||10 kW||13,300 W|
|10.2 kW||10.2 kW||13,566 W|
Oversizing Your Solar Array
Oversizing the solar array, sometimes called ‘overclocking the inverter’, means using a lower wattage inverter relative to the PV system’s capacity. This is a common practice when installing a solar PV system, as it offers efficiency and performance benefits.
The kW figure you see when buying a solar panel is the unit’s maximum DC rating. Most of the time, solar panels are actually operating below that rating, which is one reason people opt to undersize their solar inverter compared to the array.
Many solar inverter manufacturers actively endorse overclocking, and it’s completely safe for the inverter. You don’t need to worry about working the inverter too hard, since they’re most efficient when running at a high capacity. Any additional power above the inverter’s capacity is ‘clipped’ and this doesn’t cause any damage to the unit.
While this may sound like a waste, oversizing a solar array within the correct ratio actually maximises overall power generation over the course of the day. This is because the level of daylight fluctuates from dawn to dusk.
The goal of oversizing the solar array (and installing a smaller inverter) is to minimise the number of hours that the inverter is running at low efficiency. A lower capacity inverter will reach the optimal zone sooner and stay there longer, generating more power, even when ‘clipping’ occurs midday.
Most Australian states also impose an export limit of 5kW for grid-connected solar, meaning that higher-capacity inverters may be ‘export limited’. This provides a disincentive to install a higher capacity inverter unless your PV system has the infrastructure to capitalise on greater output, such as solar battery storage.
An additional benefit is that a smaller inverter is less expensive. Between upfront hardware savings and increased efficiency, your solar payback period will be reduced compared to a higher capacity inverter.
How Much Can You Oversize Your Solar Array?
You can oversize your solar array up to a ratio of 1.33, or 33% larger than the inverter size. For instance, a 5kW inverter can be used for a solar PV system up to 6.6kW in capacity.
This regulation is set by Australia’s Clean Energy Council to ensure all solar installations can effectively offset current and future carbon emissions. If this is exceeded without solar battery storage, you won’t qualify for STCs under the Small-scale Renewable Energy Scheme (SRES), Australia’s national solar incentive.
However, this restriction doesn’t apply if you’re also installing DC-coupled solar battery storage. You’ll still want to ensure your inverter is the most efficient choice, though.
Since many regions of Australia cap energy exports to the grid at 5kW or disallow inverters above 5kW for grid-connected solar, this is an additional consideration when choosing your solar inverter size.
Undersizing Your Solar Array
Undersizing a solar array (or oversizing the inverter) means using a solar inverter that’s bigger than the recommended wattage for your solar system. Homeowners sometimes ask about getting a larger inverter to expand their solar PV system in the future or avoid overloading it, but this is rarely recommended.
How Much Can You Undersize Your Solar Array?
While undersizing a solar array isn’t recommended, remaining within a 33% ratio will still allow you to qualify for STCs under the Small-scale Renewable Energy Scheme (SRES).
How to Choose The Right Size Solar Inverter for Your Solar System
The following points need to be considered before you choose your size and start the solar inverter installation process:
The Size of Your Solar System
The size of your solar system or array is the main determining factor in the size of your inverter. This is because the inverter converts the array’s DC electricity into your home’s AC requirement.
Typically, manufacturers indicate the inverter size recommended for their solar array, and this should be about the same within a ratio of 33%. For instance, a 6.6 kW array could theoretically be paired with a 6,600-watt inverter. However, oversizing the array is a common practice for maximum efficiency, and a 6.6kW solar PV system typically comes with a 5kW inverter.
How Much Sunlight You Get
The typical climate and sunlight available throughout the day will impact the ideal inverter capacity. The positioning of your solar PV system will also affect the solar inverter size you need to purchase. Consider the orientation of your house or building, plus the angle, tilt, and position of your mount on the roof.
This is especially true if planning to oversize your solar array, as fluctuations in sunlight throughout the day and timing of peak generation is a key factor to consider.
Network Operator Requirements
Network operators may have export limits on grid-connected solar systems. This means a higher-capacity inverter may be export limited via the connected energy meter. Inverters which exceed capacity restrictions may also be eligible for a feed-in tariff, which is a key factor in the financial viability of solar energy.
For this reason, you’ll want to understand your state’s export limits when choosing a solar inverter. If your solar PV system is geared towards self-consumption and battery storage, this may not be a priority, but those aiming to sell energy back to the grid will want to abide by the limits.
What Is the Most Common Solar Inverter Size for Home?
In Australia, the most common solar inverter size for the home is 5 kW or 6.6 kW. Some homeowners opt for 2 kW or 3 kW inverters for very small solar arrays.
What Size Inverter Do I Need for a 6.6 KW Solar System?
The typical solar inverter size for a 6.6kW solar system is 5kW. Oversizing the solar array maximises efficiency and a 5kW inverter meets export limit restrictions present in most Australian states.
This article is published in good faith and for general informational purposes only. JFK Electrical does not make any warranties about the ongoing completeness and reliability of this information. Always seek personalised advice on solar energy to ensure any recommendations suit your property and scenario.
John Lyons, the owner of JFK Electrical Solar & Air, started his career in the electrical industry in 1997. With years of experience gained in the industry across multiple continents, he relocated to Australia and decided to specialise in solar and air conditioning. After deciding he wanted to be closer to his family, John began his own local electrical business in Mandurah, using his extensive knowledge and training in the industry. At JFK, John’s number one goal is to provide tailored solutions to his customers. And thanks to his experience and commitment to his customers, JFK Electrical is now one of the most trusted local businesses in Mandurah for solar and electrical services.