Trading in the New Zealand wholesale electricity market (NZEM) pool began on 1 October 1996. The New Zealand pool market was the first one to use two elements of what has since become the North American standard market design, with locational marginal pricing and ancillary service cooptimization, but it was implemented in a physical and regulatory environment that differs markedly from that in North America. This article reflects on 20 years of experience with New Zealand's 1996 market design, assesses its points of difference from other jurisdictions, and speculates on some possible future directions.

Globally, renewable generation is growing rapidly, and the next few decades are likely to see many consumers adopting new grid-connected technologies such as electric vehicles, photovoltaics and energy management systems. However, these 'greener' and smarter' changes could create significant challenges for power quality, safety and other aspects of grid management. We describe how New Zealand is an ideal research environment for combining smart grid capability with integration of high levels of renewables, as it already has around 80% renewable generation, and advanced metering infrastructure in over 62% of households. Challenges for achieving a greener, smarter grid identified in the GREEN Grid research programme include managing the increased variability in supply, especially from the growing use of wind and solar generation; the potential for power quality and congestion issues from high levels of small scale distributed generation; the need for increased frequency keeping and instantaneous reserves as variability increases; and the relatively low level of consumer engagement in demand response which could ideally assist with variability. In this paper we describe the methodology and approach used in the research programme, and note some initial findings that may help address these issues, including the benefits of geographically distributed wind farms to reduce overall wind variability; the development of a hosting capacity tool for small scale distributed generation; a proposal for new ancillary services to help manage (and cover the costs of) increased variability; and the increased use of hot water cylinders for demand response. As the research programme continues to move forward with developing mechanisms for managing a smart green grid, the findings are likely to have widespread relevance to other nations that are seeking high levels of renewable generation.

High voltage direct current (HVDC) grids may be protected from dc faults through the application of HVDC circuit breakers. Recent advances in dc circuit breaker technologies may allow faults in the dc grid to be cleared without a permanent loss of power to the connected ac grids. The requirements for the protection have yet to be fully defined; especially where half-bridge modular multilevel converter (MMC) controls are concerned. This paper investigates integrating dc circuit breakers with half-bridge MMC converters, specifically looking to at how to recover from a pole-to-pole fault. The fault response of the converter to a fault is analyzed in depth. This analysis highlights key stages in the converter response to a dc fault, allowing the MMC fault currents to be predicted. This analysis is then verified in PSCAD simulations and the power flow recovery is shown. The converter controls are investigated, improvements made to the power flow recovery, and the need for arm current controllers highlighted.

Residential rooftop-mounted solar photovoltaic (PV) panels are being installed at an increasing rate, both in New Zealand and globally. There have been concerns over possible issues such as overvoltage and overcurrent. These PV systems are mostly connected at low voltage (LV). This study presents a case study of simulating the entire LV network from a single utility, comprising 10,558 11 kV-415 V transformers and their associated distribution feeders. These results are also presented by network type. Various solar PV penetration levels are added to the model and the power-flow results are presented. From these results, possible maximum limits of solar PV penetration are investigated and measures to alleviate overvoltage problems are simulated. The effect of using PV inverters with voltage regulation is simulated. Results show that some minor overvoltage problems can be expected in the future, particularly in urban areas. However, in most cases the overvoltage would not be much higher than the statutory limit of 1.06 p.u.

This paper examines combinations of photovoltaic (PV) generation plus battery energy storage for islanded electricity systems from energetic and economic perspectives, using hourly solar resource data, and 17 household-scale demand profiles, for Christchurch, New Zealand. Optima for normalised storage, expressed as a proportion of annual demand, and for energy returned on energy invested (EROEI), occurred at energy penetrations ranging from 2.50 to 4.00. The ratio of maximum to minimum daily demand predicted optimal storage capacity and EREOI. Improved optimal EROEI values occurred following reductions in embodied energy and at lowered penetrations with longer battery lifetimes. Energy spillage at the optimal penetrations was spread relatively evenly over the year, with the exception of several weeks during winter, and final discharge depths averaged 3.1%. Economic optima, expressed as net present cost, occurred at energy penetrations ranging from 3.00 to 5.00. Reductions in PV panel and battery capital costs, and a longer battery lifetime, reduced the penetrations at which economic optima occurred, and in some cases these coincided with energetic optima. It is suggested that both energetic and economic optima need to be evaluated in the planning process, and that the role of secondary loads be investigated in future research programmes.

Responding to the global challenges of maintaining energy security while combatting climate change, the New Zealand government has issued a target of generating 90% of the country’s electricity needs from renewable sources by 2025. With much of New Zealand’s generation already provided by hydro, geothermal and wind, questions remain as to whether this target should be achieved by more widely adopting solar photovoltaics (PV) into the energy mix. Following from previous GREEN Grid research into the uptake of solar PV in New Zealand, this paper considers the economics of PV generation at a variety of scales: residential rooftop; commercial rooftop; and ground-mount utility. For each scale, discounted cash-flows were used to assess system costs and financial returns, and levelized cost of energy used to compare with other sources of generation. In the case of residential generation, there is a significant difference in the value of energy which is locally consumed versus that which is grid-exported. Consequently the value of PV to a household depends on the consumption patterns of a particular household. To understand the value across different households, typical residential load profiles were found by clustering load profiles from over 2,000 houses, and resulting representative load profiles used to estimate financial returns based on the energy consumption patterns. The paper concludes that PV is now a commercially attractive investment for some types of households, but that household load makes a major difference to the returns. In the commercial sector PV is also commercially attractive to the company making the investment in some cases, and for both residential and commercial, returns are very sensitive to discount rate, location, and type of retail tariff. However for both residential and commercial, improving energy efficiency is a lower cost option than PV, and should be considered first. At the utility scale PV is not yet commercially attractive, even excluding transmission and distribution charges and opportunity cost of land. However if the cost of PV continues to fall,

This paper presents a preliminary economic study on the feasibility of using electric vehicles (EVs) to provide demand response, carried out as part of the GREEN Grid project. A mathematical model is developed to track the charge cycle of an EV battery, and this in turn provides estimates of the cost associated with battery life degradation under different scenarios. Three case studies are presented in this paper: the first investigates the potential cost saving for the EV owner by confining the charging of an EV battery to the night tariff period; the second investigates the financial gain associated with regulating the charging of an EV battery based on spot prices; and the third investigates the possible economic benefit for the EV owner of participating in the electricity market by buying energy at low prices and selling at high prices. The first case also includes the situation of just a battery being used to store energy during the night to run a household during the day. Results show that it is most economical to charge an EV during the night (Case 1), but that it varies considerably depending on the region in New Zealand. Regulating the charging rate depending on the spot price (Case 2) provides a small benefit. Using the EV to trade energy (Case 3) is, in most cases, uneconomic given the degradation of battery life. The variation of Case 1 also shows that at current battery costs, it is not economic to store energy during the night for use during the day. Given that there will be other costs associated with these activities, such as the charger equipment capable of both importing and exporting energy from the grid, the economics do not appear to favour use of EVs for demand response provision, except for the case of simply adjusting the time of charging to suit the tariff.

The GREEN Grid project is investigating the impact of solar power generation from photovoltaics (PV) connected to the low and medium voltage distribution networks. One of the goals of this research is to provide guidelines for adoption of PV in New Zealand, and modelling tools and techniques for distribution companies to better understand its impact on power quality within their networks. While collecting data from PV sites around New Zealand and considering how modelling in the distribution network should be conducted, the question of just how much PV is installed in New Zealand was asked. This paper presents the findings of a survey of 12 distribution company areas covering about 80% of New Zealand’s population. It discusses the findings in the international context, and how PV might develop in the future in New Zealand. To obtain some idea of the adoption of PV in the future, and what the eventual installed capacity of PV might be, the Bass Diffusion Model, used to study new product diffusion, has been applied to the uptake data.