Small-scale distributed generation (DG) in New Zealand, particularly photovoltaic (PV)
generation, has been growing steadily over the past few years. In the last year alone to 31 March
2016, installed PV generation of all capacities has grown by a factor of about 1.6 to reach 37
MW. Approximately 90% (33 MW) of this installed PV capacity is made up of small-scale,
single phase residential grid-tied systems with ratings below 10 kW. This corresponds, on
average, to approximately 300-400 new PV systems being installed each month within low
voltage (LV) distribution networks.
Traditionally, the flow of power in electricity distribution networks has been largely
unidirectional. However, distributed generation introduces reverse power flows into the LV
network when the power produced by DG systems is greater than what can be consumed
locally. This introduction of reverse power flows and the dynamic behavior of DG system
inverters can negatively impact the electricity network, causing issues such as over-voltage,
phase imbalance, overloading of conductors and transformers, and create unique safety
challenges. As such, each DG connection application received by electricity distribution
businesses (EDBs) presently needs to be carefully considered for its impact on the electricity
network. The resourcing demand imposed by larger numbers of connection applications, and
the difficulty of technical assessment including congestion evaluation, are likely to increase
substantially as DG uptake intensifies. This has prompted the Electric Power Engineering
Centre (EPECentre) via its GREEN Grid programme, with the assistance of the electricity
industry based Network Analysis Group (NAG), to develop a small-scale inverter based DG
connection guideline for New Zealand EDBs. This has been developed on behalf of the
Electricity Engineers’ Association (EEA) specifically for the connection of inverter energy
systems (IES) of 10 kW or less.
This paper summarizes key aspects of this guideline. This includes a streamlined connection
application evaluation process that enables EDBs to efficiently categorize DG applications into
three groups. These groups vary from those with minimal or moderate network impact that can
be auto-assessed, to those most likely to cause network congestion that require manual
assessment. These categories are determined by looking at the DG hosting capacity specific to
the LV network that the DG is connecting to. For two of these categories, mitigation measures
for connection, are prescribed. It is also shown how DG hosting capacity can be used to simply
evaluate LV network congestion in order to satisfy Electricity Industry Participation Code
(EIPC) Part 6 requirements. Key technical requirements for all IES, appropriate for New
Zealand conditions, are also summarized