Grid-connected systems

Grid connection provides back-up if micro-generation doesn't meet your electricity needs all of the time. You also have the opportunity to sell any excess electricity if you're connected to the grid.

The most common form of grid-connected micro-generation is solar photovoltaics (PV). These use solar panels to convert sunlight to electricity. Wind and hydro generation are also used.

Usually, a grid-connected micro-generation system is designed carefully so it just covers your electricity needs.

Any excess you generate may be able to be sold, but bear in mind, you are likely to be selling it for less than it cost to generate.

As with stand alone systems, it's almost always cheaper to use less electricity than it is to generate your own. Even with a grid-connected system it makes good economic sense to make your house as efficient as possible.

Selling electricity back to the grid

Owners of grid-connected systems may be able to sell surplus electricity to an electricity retailer. This means that when the system is generating more electricity than is needed, for example, during the day when no one is home, the owner could be paid for the surplus. Each electricity retailer has their own terms and conditions for buying excess electricity. The price that they offer per kilowatt hour (kWh), called the ‘buy-back' price, will also vary.

Connecting to the grid

Connection to the local electricity network is via an inverter. The inverter converts direct current (DC) into grid-compatable alternating current (AC). A special meter needs to be installed to separately measure the electricity you export.

Applying for a grid connection

In order to install a grid-connected system an application to the local electricity lines company (sometimes called the ‘network' or ‘distribution' company) needs to be made. This is the company that manages and maintains the lines that deliver electricity to your house.

Local lines companies:

• Can charge you up to $200 for a connection (for a generator less than 10 kW)
• Can charge $60 to carry out any onsite inspections of the installation prior to its commissioning
• Must take no longer than 30 working days to process your application.

Check out more information in the 2007 government regulations.

You can find out which network company is serving your area by visiting the Electricity Networks Association of New Zealand website.

Grid-connection standards

Grid-connected inverters must comply with your local network company's connection standards and safety requirements. You may be able to view these standards and requirements on the company's website. AS4777 is one standard that has been adopted by some New Zealand lines companies.

Network companies are likely to approve your installation sooner if you use a compliant grid-connected inverter. Compliance with the standard assures the network company that issues around safety, fault protection and power quality are dealt with.

When choosing an inverter, make sure:

• It's compatible to connection with the grid and complies with the requirements of your network company
• Local support and servicing are available.

Connecting to the grid made easy

Some companies can offer a ‘one-stop-shop' service. This will take care of connecting your micro-generation to the network, designing and installing your system, and liaising with the network company and electricity retailer. This can make the process easier for homeowners and businesses interested in micro-generation. Ask your system designer or installer if they can arrange your network connection for you.

Case studies

A Canterbury tourist lodge uses wind to generate electricity, and sell it back into the grid - read case study

More information

Use the following links to find out more about:

• Efficiency first - by reducing your energy requirements, you'll reduce the amount (and cost) of generation you'll need.
• Stand alone power systems (SAPS) are off-grid electricity generation systems that may include photovoltaics, micro wind turbines or micro hydro, batteries and a back-up generator
• Choosing energy options explains what you should consider when deciding on the best generating options for your location
• Solar photovoltaics (PV) convert the sun's rays to electricity.
• Micro hydro for households is typically less than 5 kW
• Micro wind energy refers to the use of micro wind turbines typically less than 10 kW
• Micro-generation is one form of distributed generation, which refers to local electricity generation connected to lines networks, rather than the natioal grid.  
• More about use New Zealand's use of renewable energy.
• Find out more about grid-connected systems on the Sustainable Electricity Association of New Zealand website.