Installers need to keep up to date on standards for inverters to get the most out of systems, writes Clean Energy Council general manager installation integrity Sandy Atkins.

On September 30 last year Australia Standards released an update to AS/NZS4777.1, the standard affecting installation requirements for the grid connection of energy systems via inverters.

The standard had a six-month transition period which ended at the end of March. This means the standard is now live and all installers need to ensure they are up to speed with the changes.

The scope of the standard has broadened quite a bit. It now covers off systems that are up to 200kVA, up from 30kW in the existing version.

Some of the key changes in this version are:

  • The standard relates to any inverters regardless of the energy source, whether the technology is a battery, wind, hydro, PV, or something else.
  • The rating limit for single-phase systems in an individual installation is 5kVA. For system sizes greater than 5kVA, the output shall be balanced across all phases unless specifically approved by the electricity distributor.
  • “Multiple mode inverter” has been defined and installation requirements specified.

There are too many changes to list in full in this column. The CEC ran a webinar last year on the changes. Our webinars are recorded for viewing later, so logging in to the CEC installer area is a good first step if you are not up to date with everything.

Power quality issues for solar power systems

The CEC technical team has been fielding calls lately in regards to systems not operating to their full potential. After some investigation it was determined that the voltage at the inverter terminals is too high and the inverters were going into what is called a “power quality response mode”.

Without trying to make things too confusing, last October all inverters had to be compliant to the new inverter product standard (AN/NZS 4777.2). This standard defines different types of power quality response modes. The main power quality response mode is volt/watt. This mode reduces the power output of the inverter when the voltage at the inverter’s terminals rises above a specified value.

It is possible that this can be an issue with the utility’s supply voltage but it is also an issue we can introduce as part of the design. AS/NZS 4777.1 has a requirement that the cables from the point of supply through to the inverter terminals shall not have a voltage rise of greater than 2%. This is quite a tight requirement, making cable selection extremely important. More often than not we don’t touch the mains cables so we only have influence over the inverter AC cable.

It is common for electricians to usually look at the current-carrying capacity of the cable and not to properly consider voltage rise. So yes, in some situations you may be able to us a 2.5mm2 cable to handle the current of a 5kVA inverter. But in this case you could only run it 6 metres to keep the voltage rise on that section of cable to 1% (remember that the mains cable will have some voltage rise also). Even a 6mm2 cable with a 5kVA inverter can only run 14 metres to stay under the 1% threshold.

It is really important that the cable sizing is picked up at the design stage. It is too late once the system has been installed and the inverter does not perform. The only ways to fix voltage rise are to run a bigger cable or reduce the current in the cable – which means removing panels.

AS/NZS 4777.1 Appendix C has a great explanation on this along with the calculations on how to comply with this.

Battery enclosures in Clean Energy Council guidelines

Last year the Clean Energy Council published the first Australian guidelines for the installation of grid-connect energy systems with battery storage.

More recently there has been a lot of discussion around the enclosure requirements for batteries. The intention behind the guidelines around the enclosure requirements is to prevent unauthorised people from accessing live parts of the battery system – whether that means children or overly-enthusiastic retired engineers.

There are battery systems where the installer gets the battery cells and makes the system themselves. Therefore the enclosure in this case is required to go around the battery cells to prevent access to the battery terminals. And there are other pre-manufactured battery systems where the manufacturer packages the battery cells in their own enclosure, with the terminals under a cover that can only be accessed by a tool.

For installers, the thing to note is that these pre-manufactured systems have adequately restricted access to the live parts by way of the manufacturer’s enclosure. So unless this enclosure does not actually restrict the access to the live sections, installers are not required to build an additional enclosure.