Energy

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

Distributed generation (DG)

Find out about:

  • how a distributed generation (DG) system works
  • requirements for a DG system
  • considerations and limitations of DGs
  • buy-back arrangements.

How a distributed generation system works

With distributed generation systems, the property owner or a group of property owners generate their own power and are also connect into the national grid network. The self-generated power is used by the owner(s), but if more power is generated than being used, the excess may be supplied to the national grid through an import/export meter, and a credit is given for the power that has been supplied.

Grid-connected, distributed generation system 
Grid-connected, distributed generation system

 Security of supply is generally provided by connection to the local electricity network.

 

The on-site generation is provided by the same means as the stand-alone systems and include:

Requirements for a DG system

Self-generated systems typically generate less than 15 kW. They must be installed in accordance with AS 4777 and its associated standards to meet the requirements of the electricity distributor being supplied.

In the Electricity Governance (Connection of Distributed Generation) Regulations 2007, the government specified that there should not be undue barriers or timing constraints to hinder a DG connection as long as is the system was compliant with relevant standards.

Considerations and limitations

The mains wiring design and installation for self-generated systems is similar to a normal grid-supplied installation but there are additional mains cable and main board design considerations, such as the inclusion of two-pole lockable isolation.

A disadvantage of distributed generation systems is that the self-generated power supply stops if the national grid fails as the self-generated system must disconnect from the grid so it does not cause lines somewhere else from becoming live during a grid failure.

This situation can be overcome by incorporating a control system that activates the grid connection when the mains power is available but provides power from a battery bank via the inverter when the grid fails.

Schematic of a typical grid-tied system 
Schematic of a typical grid-tied system

 

 

Schematic of an alternative grid-tied system with grid credit meter and generator back-up 
Schematic of an alternative grid-tied system with grid credit meter and generator back-up

 

 

Schematic of an alternative grid-tied system with grid credit meter but without generator back-up 
Schematic of an alternative grid-tied system with grid credit meter but without generator back-up

 

 

Buy-back arrangements

Grid-connected systems are able to export surplus electricity to the grid by arrangement with an electricity retailer. This involves agreement about how the flow in and out of the property will be metered, and the price that will be paid for electricity fed into the grid.

In mid 2008, the best offer in New Zealand was a one-for-one buy-back scheme i.e. the retailer paid the same rate as they charged for electricity taken from the grid, and included the lines portion of the kWh/hr charge.

More information