Can I Use A 5kw Inverter For Installing 6.5kw Of Panels?

In this article we will first be addressing the question of the ability of the inverter to handle excess power. Then we will take a look at what is said by the Australian regulations about the oversizing practice, and hopefully some changes that are imminent. We will finally see if it supersizing your solar is a good idea given your situation.

Inverter Capability

Manufacturers of inverters specify what the maximum input capacity is on their specification. It is often expressed in amps and volts instead of watts. For example, SMA, document a very conservative maximum input. However, when their technical support team is called, they explain away this limit. They increase the limit, and supporting documentation is sent. All inverters, in short are worth their salt, are able to handle input power that is a lot higher than an electrician would ever try to connect. This is due to the fact that electricians take a conservative approach when it comes to Australian regulations.

Limitations To Regulations

The reason that solar in Australia has been successful is due to the Renewable Energy Credits programme from the federal government. The credits get paid proportionally on how much renewal energy that will be produced by a system, or most importantly, how much carbon is going to be offset within a 15 year period. A financial incentive of around $5,000 will be attracted by a 6.5kW solar system under the programme. There are strict regulations mandating the way systems must be installed to ensure the success of this program. The body responsible for coming up with regulations and standards for promoting renewable energy is the Clean Energy Council. The clear thinkers at the Clean Energy Council understand that a 5KW of solar panels operates only at 5000w whenever the temperature is at 25 degrees, the sun is shining at a 90-degree angle towards the panels, and there is 1000w worth of irradiation. In other words: hardly ever. In order to get good use from your inverter, it is clearly a good idea to oversize. However, by how much? The panel capacity, according to the CEC, shouldn’t be over 33 percent of the inverter’s nominal output before the production of your panel starts to get wasted, and there is a misuse of the payout of the Renewable Energy Credit.

Energex Limitations

Why not buy a 6kW inverter then? If your house runs on a single phase (like most households do), then Energex will just approve an inverter up to 5kW.

If your home has 3 phase, an application can be submitted by use to Energex to get a large system. Processing can take a couple of months and it might or might not be approved. Also, because the most common sizes of inverters used are 10kW and 5kW inverters, inverters in this range are un-proportionally expensive.

Limitation Of Nominal Output

You might have noticed we mentioned maximum output and nominal output. So what is the difference between the two?

Maximum output is the amount your inverter outputs on a day that is perfect (within tolerance). A majority of 5kW inverters have a 500W maximum output. If your panel array is oversized, a 5000w inverter reaching 5100w is not unusual.

Nominal output is basically a joke. It is merely whatever the manufacturer of the inverter decides to label it in order to meet the thresholds of a specific power authority. Thanks to SMA, the solar giant, a nominal output is 4.6kW from Germany’s regulation, despite that the inverter can run at 5000W easily.

That is important due to the fact that CEC only allows for a system to be oversized by a maximum of 333 percent of its nominal output. So what that means is the SMA 5kW inverter, which is made in Germany, and all who have followed the same path, are limited to just 1.33 x 4.6kw = 6.118kW.

Inverters like SolarEdge, on the other hand, have a complete 5.0kW nominal output. Those inverters are able to manage 6.6kW of panels, providing you with 500W more for your money.

It is that annoying “nominal output” leaving many companies such as Appolo Solar marketing a 6.5kW of panel on the Sungrow 5Kw inverter having a 4.6kw nominal output. They cannot technically claim the $5,000 renewable energy credits on those jobs.

People at the Clean Energy Council currently are working on getting this outdated rule updated. Hopefully we will be able to update this information later in 2016. Then we can use the maximum rather than nominal output, or have a solution that is more nuanced.

Your Investment

The Inverter manufacturer is fine with your panel array being oversized, and it is considered to be financially responsible by the Clean Energy Council. However, does your roof need that big of a system. We often recommend a 6.5kW system if you have a pool or electric hot water system, or your bills is more than $500 per quarter.