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6kW Solar Systems – The Most Popular in Australia

Australian homeowners and business owners install various sizes of solar energy systems. But 6kW solar systems have been the go-to choice for domestic solar installations in the solar industry in recent years.

There are also 6.5kW and 6.6kW solar systems installed in many homes. This type of solar system is the most common choice for the Australian solar market. Its capacity for generating solar electricity matches the electricity usage of most Australian households. Although there is some variance between different systems in terms of efficiency and constant output.

The reason for the increasing popularity of such solar system installations is simple. Electricity prices in Australia are rising, and the cost of installing a solar energy system is decreasing. Solar technology has become more advanced and more efficient.

On top of that, there are still generous federal and state incentives for homeowners. These encourage people to adopt renewable energy alternatives for the future. The feed-in-tariff (FiT) also provides payment for excess electricity exported by households to electricity retailers.

But back to the 6kW solar system.

What does the 6kW refer to?

The most common solar systems installed by Australian homeowners are either 6kW, 6,5kW or 6.6 kW. A 6kW solar system produces from 17 to 27kW/h of electricity (annual averaged daily output). The output varies depending on location, type of panel, season, and other factors.

The average Australian household consumes around 20kW/h per day (annual averaged daily consumption).

This is why the 6kW, 6.5kW and 6.6kW options have become popular.

Years ago, when people first started installing solar energy systems, a 3kW system was the norm. Then it became a 5kW system. Now, with advances in solar technology and lower prices, the 6.6kW is rapidly becoming the new norm.

This size of the system also makes battery storage or battery backup systems more feasible. More people are becoming interested in having solar battery storage as part of their solar energy system nowadays.

TIP: A 6.6kW solar energy system allows you to maximise the number of STCs (Small-scale Technology Certificates) you get. These are created as part of the federal solar rebate.

Why is the inverter only 5kW?

Yes, this is something that confuses many people. There are a couple of reasons why a 5kW inverter is often used with a 6.6kW solar energy system.

  • A 5kW inverter is cheaper and pre-approved for grid connection
  • Greater choice of 5kW inverters on the Australian market
  • Many electricity distributors allow 5kW inverters to be ‘oversized’ by133% (6.6kW)

So a 5kW inverter can handle a 6.6kW solar energy system easily.

There are 6kW inverters available. They are more expensive, there is less choice of brands, and they are not pre-approved for connection to the grid.

Under the AS/NSZ 4777 standard, most distribution network service providers (DNSPs) allow single-phase inverters up to 5kW or 3-phase inverters up to 30kW.

It’s possible to get an inverter larger than 5kW approved for grid connection. But there’s a lot more red tape involved, and unless you’re going to run a commercial system, it’s generally not worth the hassle.

Inverter size is measured in kilowatts (kW). The rating is the maximum capacity of solar-generated electricity the inverter can safely handle.

There is a simple rule:

  • The maximum output of the inverter must be equal or greater than 75% of the solar panel array maximum output.
  • This explains the ‘oversizing’ mentioned earlier. The maximum output of the solar panel array can be 133% of the maximum rating of the inverter.

Who regulates this?

The Clean Energy Council stipulates the rule for the size of inverters and solar panel arrays. To claim your STCs (Small-scale Technology Certificates) your solar PV system must comply with the CEC regulations.

How many solar panels do I need for a 6kW system?

Solar panel size varies as does their output and efficiency. Then there are physical factors like location, shade, and roof orientation which all affect the output of a solar energy system. It’s rare for a system to crank out 100% of its theoretical output consistently. A figure of about 75% is more reasonable.

The average domestic 6kW solar PV system installed in Australia, using solar panels rated at 275-300 watts, will need 22-24 panels.

How much space does that take up?

Panels vary in size, but the average is about 1.7m2. So you’ll need around 40m2 of space for a typical 6kW solar energy system.

How much solar electricity can I generate using a 6kW system?

The amount of electricity you generate will vary. The time of day, season, geographical location, and efficiency of the components in the solar energy system all affect the output.

On average, a 6kW solar energy system in Australia generates about 24 kW/h of electricity per day. This is more than the average domestic consumption per household in Australia.

TIP: You’ll receive a payment based on the feed-in-tariff (FiT) for any excess electricity you export to the power grid. But you should aim to use as much of your solar-generated electricity as you can.

Try to use the electricity during the day. This will avoid paying daylight peak-tariffs when the electricity you purchase from the grid is the most expensive. Think about running your air-conditioning, pool pump, and other appliances using solar electricity you generate. That’s the most effective use of your solar energy system.

What’s the price of a 6kW solar energy system?

Solar system pricing varies according to the brand, quality of components and the exact configuration of the solar energy system you buy. But as a guide: expect to pay from $5,000 to $9,000 to have a system installed. Usually, all prices quoted already take into account the solar panel rebate from the government.

How long is the payback period for 6kW solar systems?

Your solar installer should give you a full payback analysis before you go ahead with the installation. Typically, the system will pay for itself in 4-5 years. This assumes that the system design is a good quality one, optimised for your location and level of electricity consumption.

Another way to look at it is this: you can choose to finance the purchase of your solar energy system. When the savings on your energy bills are enough to cover the monthly financing cost, the system will pay for itself from day one.

Why do some people advise installing a 6.6kW system?

The 6kW solar energy system has been the most common for domestic installations for some time now. But you can install a system with greater capacity, a 6.6kW system. This is based on the capacity of the solar array (the solar panels) not the inverter.

Why do this?

CEC regulations for domestic solar energy systems state you can have a system with a 5kW inverter and 6.6kW capacity of solar panels. This is 133% × the inverter’s maximum capacity.

You should do this to maximise the STCs you can claim. The number of STCs created for your system is based on the capacity of the solar panels, not the capacity of the inverter.

So you get more of a ‘rebate’ because you have more solar panels. You get the best value for your money this way!

With a good feed-in-tariff, the maximum solar array capacity of 6.6kW will give you the best payback period. It will also maximise your income from the excess solar electricity exported to the local electricity retailer or DNSP.

Why ‘oversizing’ your solar energy system is a good idea

Oversizing is when your solar panels have a greater output capacity than the inverter used in the system. We explained before that a 5kW inverter can handle 133% of its maximum capacity in solar panels (6.6kW).

It’s perfectly safe to do. Most solar arrays don’t continually produce their peak output. This is because of factors such as sub-optimal tilt angle, weather, dirt, poor efficiency, system losses, and temperature. On a typical hot day (25°C) a solar panel will lose about 10% of its peak power output capacity. If you have 20+ solar panels in your solar array, that’s quite a drop in efficiency.

By ‘oversizing’, you’re making sure that your 5kW inverter is working optimally for most of the time.

And remember, some Australian DNSPs don’t allow inverters larger than 5kW to be connected to the power grid. So you want to maximise its capacity and performance.

Is a 6.6kW system more expensive than a 6kW system?

Yes, but not much more. Expect to pay around $200 more for a 6.6kW solar installation. You’re probably buying two extra 300-watt solar panels to make a 6.6kW system. It’s not a big difference in price. But the difference in output efficiency is worth the extra investment.

The difference in the system cost is negligible because the extra work your solar installer needs to do in the installation process is minimal. They are already on site, and the solar inverter is the same as used in a 6kW system. So the extra system size only involves installing a couple more solar panels and some extra cabling.

How do I get a quote for a 6.6kW solar energy system?

Solar energy system prices are not cheap. But it’s a smart investment. Whether you pay for it in cash or choose to finance it, make sure your installer and all the system components are CEC approved.

Get quotes from multiple solar retailers or solar installers before making your final decision. Be sure to get a full payback period analysis from the installer. Ensure the system you buy and the solar company comply with all CEC regulations. This is important so you can qualify for the federal and any state-level solar rebates or similar financial incentives.

It’s important to choose a quality solar power system that is covered by a comprehensive product warranty and workmanship warranty. A quality system will give you years of free electricity and require minimal maintenance.

You won’t regret getting a home solar energy system when you begin to see the massive savings on your electricity bills!