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Inverter under-sizing v.s. Inverter over-sizing

Blog updated on 28th February 2024

Understanding Inverter Sizing for Optimal Solar Performance

When it comes to solar power systems, the efficiency and longevity of your investment significantly depend on the correct sizing of your solar inverter. Inverter sizing, whether undersized or oversized, plays a pivotal role in the overall system performance, affecting not only the energy yield but also the economic benefits of your solar installation. Let’s delve into the nuances of inverter sizing to ensure you make an informed decision tailored to your solar energy needs.

The Strategic Advantage of Undersizing Your Solar Inverter

Undersizing, often referred to as ‘overclocking,’ has become a widely accepted practice in the Australian solar market. This approach involves installing a solar panel array with a higher capacity than the inverter. According to the Clean Energy Council guidelines, it’s permissible to oversize your solar power system by up to 133%. For instance, pairing a 5kW inverter with 6.6kW of solar panels maximizes the system’s efficiency without necessitating a larger, more expensive inverter. This strategy not only optimizes the use of Small-scale Technology Certificates (STCs) but also ensures a better value by reducing the cost per watt of your solar system.

Oversizing Your Inverter: A Future-Proofing Strategy?

While undersizing focuses on immediate efficiency and cost-effectiveness, oversizing your inverter might seem like a prudent choice for future expansions. However, an oversized inverter may not always guarantee optimal energy extraction, especially if the solar panel array does not match its capacity. It’s essential to discuss with your installer the potential impacts of inverter sizes on your system’s energy yield over time. A thorough understanding will help you balance between the upfront costs and the long-term benefits, ensuring your solar investment is sound and future-proof.

Making the Right Choice for Your Solar System

Choosing between undersizing and oversizing your solar inverter requires a careful evaluation of your specific energy needs, future expansion plans, and financial considerations. It’s crucial to ask the right questions and gather comprehensive insights to strike the perfect balance in your solar investment. Whether you lean towards undersizing for immediate efficiency gains or consider oversizing for future scalability, the key is to ensure your solar power system delivers optimal performance and maximum savings over its lifespan.

As renewable sources of energy are gaining popularity through the rise of a “green conscience” and the support of the government through incentives, the average size of a solar power system is also getting bigger. Only five years ago, most households were buying 3kW solar power systems which are approximately 12 panels.  Now, a 6.6kW solar system size has become the most commonly requested system size for new buyers as well as those looking to replace their older systems.

There are a few reasons for the increased system size demands which mainly revolve around the substantial decrease in the manufacturing cost of solar systems which consequently made solar panels much more affordable than they were only a few years ago. 

The cost of solar power systems keeps falling as a result of which bigger systems are becoming more affordable. More panels mean more STCs (the Federal Government’s ‘rebate’) which consequently means a bigger point of sale discount for the customer.

A 6.6kW is a great size for anyone thinking about adding a battery to their solar system. Solar suppliers and their customers have done their research and over the years have worked out that a 6.6kW provides a better value.  A 6.6kW system size essentially means 6.6kW of solar panels installed on the roof with a 5kW inverter.

The efficiency of the inverter drives the efficiency of a solar panel system because inverters convert Direct Current (DC) (as produced by the solar panels), into Alternating Current (AC) (as used by the electric grid). This leads many to wonder what effect over-sizing or under-sizing an inverter will have on overall system efficiency. This article sheds some light on this issue, hopefully helping shoppers to make better decisions in regards to their current or future solar photovoltaic installation.

Inverter under-sizing – sometimes referred to as ‘overclocking’ – has actually become a common and widely accepted practice in Australia.

You may be wondering how this panel to inverter combination came to being. According to the Clean Energy Council guidelines as well as the network distributors (the companies that own the poles and lines), this panel to inverter ratio is completely legitimate. The rule is that you are allowed to have your solar power system over-sized by 133%. This means that you can get an inverter with 5kW capacity and add 6.6kW of solar panels (5kW x 133% = 6.6kW).

Insights and Benefits of a 6.6kW solar system size

Maximizing STCs: The 6.6kW Advantage

One of the reasons 6.6kW solar systems are soaring in popularity is their ability to optimize Small-scale Technology Certificates (STCs) without necessitating an upgrade from a 5kW to a 6kW inverter. What does this mean for you? A savvy savings of a few hundred dollars, and from a ‘value for money’ vantage point, a reduction in the cost per watt of your solar system.

The Economic Logic Behind 5kW Inverters

Contrary to what one might assume, 5kW inverters aren’t as pricey as their 6kW counterparts. This economic sweet spot is further sweetened by the extensive array of 5kW single-phase inverters available, driving competitive pricing. Noteworthy network distributors, such as Western Power, often impose a 5kW inverter limit but greenlight panel oversizing up to 133% of the inverter’s capacity. A simple math would reveal: 5kW×133%=6.6kW5kW×133%=6.6kW.

More Power, More Savings

In essence, the 6.6kW solar system offers unparalleled value, granting you more energy for every dollar spent. The strategy of solar inverter under-sizing (or, viewing from another angle, solar panel array oversizing) isn’t just a fleeting trend in Australia – it’s a well-established practice prioritized over inverter oversizing.

Inverter Efficiency: The Operational ‘Window’

The heart of a solar system, the inverter, thrives within a defined operational ‘window’ (typically outlined in its specifications). As the energy input from the panels oscillates, the inverter’s prowess in converting DC electricity to AC fluctuates. However, as long as this input remains within this predefined window, the inverter operates at its peak.

When Might an Installer Suggest an Undersized Inverter?

There are scenarios where your installer might lean towards an undersized inverter. This is especially the case if your location, climate, or the orientation of your panels predicts lower solar irradiation. Sometimes, this means installing more panels that sync with a smaller inverter. Yet, even under ideal conditions, under-sizing the inverter can boost the system’s overall performance.

Over-sizing Inverters: A Future-Forward Thought or a Misstep?

While an inverter with a capacity exceeding your solar panel array might sound promising for future expansions, it’s not always the best choice. An oversized inverter might not extract the maximum energy yield from your system, especially if the size difference is substantial. Inverters can handle power inputs lower than their nominal capacity, but there’s a threshold. It’s crucial to engage in a candid conversation with your installer about how different inverter sizes might impact your energy yields over the next 5-10 years. Weigh these insights against the price tags of different system configurations to make an informed decision.

Your Solar Investment: Asking the Right Questions

Before you finalize your solar system choice, ensure you’re armed with the right questions. How would your energy output vary with an oversized inverter compared to a ‘right-sized’ or undersized one? A comprehensive understanding will ensure you strike the perfect balance in your solar investment.

Get Best Solar Expert Advice

Reach out to Austra Solar for the best deals on solar inverters.

Phone: 1300-237-588