Energy

Designing homes to conserve energy and use it efficiently, from sources that cause least environmental harm.

Inverters

Household grid supply in New Zealand is alternating current (AC) and most household appliances work on AC electricity. An inverter is required to convert the DC electricity from photovoltaic generation or battery storage, to AC.

On this page:

  • Requirements for provision of AC or DC power
  • Inverter types
  • Installation

The inverter can supply AC current at any voltage or frequency by transformers, switches and control circuits.

Requirements for provision of AC or DC power

Electricity supply to buildings must be provided as:

  • AC at 240 V and 50 Hz for single-phase power for most household applications and wiring circuits
  • AC at 415 V and 50 Hz for three-phase power for permanently wired and heavy load systems
  • DC if there are appliances with a DC supply.

There are losses each time power is converted from AC to DC and vice versa.

Inverter types

Several options are available:

  • True sine wave inverters produce voltage equal to or better than the grid supply. They may incorporate a battery charger, which allows a generator or CHP unit to be used to charge up the batteries when natural charging conditions are poor.
  • Modified sine wave inverters are less complicated but they may not successfully run some appliances, and they may produce a hum. These are not recommended for an average house with many electronic appliances and are not very common now.
  • Grid-connected inverters allow for a connection to the grid, they may incorporate a battery charger and they can provide back-up power if the grid power fails.
  • AC coupled inverters are designed for use for a micro-grid, i.e. a property with several houses or a remote rural settlement with no national grid connection.

Some inverters can be programmed to start a generator if the battery voltage gets too low or household power demand goes above a pre-set level.

Grid-connected inverters must be AS/NZS 4777 compliant and allow for a connection to the grid. They range from small 250 watt micro inverters that sit under each individual solar panel, up to single units of many kWs to allow larger 10 kW wind generators and solar arrays to be grid-connected.

Most inverter/chargers can connect to a home WiFi system, allowing performance to be checked remotely with a smartphone or computer.

Installation

Installation is covered in AS/NZS 4777.1:2016 Grid connection of energy systems via inverters Part 1: Installation requirements.

Inverters should:

  • be mounted above the floor and on a wall or shelf
  • have ventilation or cooled air flow
  • be protected from sunlight
  • be easy to access for emergency operation
  • have a switch or fuse to isolate the inverter from the electrical systems
  • be in close proximity to the batteries.

They must also be:

  • protected from dust
  • protected from overheating
  • electrically isolated in case of an emergency
  • protected from damage by lightning
  • connected to the batteries with large cables, as there may be substantial current flows, voltage drops and heat dissipation.

The system will need to be installed by a registered electrician, and a certificate of compliance will be required that covers the scope of the installation and confirms its compliance with AS/NZS 4777.2:2015 Grid connection of energy systems via inverters Part 2: Inverter requirements.

 

Updated: 20 September 2019