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The following options for improving energy efficiency were explored:

Photovoltaic-ready house (installing cabling only)

Electricity-generating photovoltaic (PV) panels are rapidly falling in price, making them increasingly affordable for domestic application. Homeowners who are interested in future proofing their new house - or wanting self-generation immediately - are advised to install the necessary electrical cabling from their roof to their fuse box (or similar) at the time of construction. This saves money later on, as internal wall access is simplified and no remedial work is required. Having a solar-ready house may also be beneficial in terms of future sales.


Installation cost estimates were based on estimates from several PV installers in late 2016.

3kW grid-connected photovoltaic system fully installed

Photovoltaic (PV) systems are the most popular renewable-based technology for providing electricity to private residences in New Zealand. It is likely that they will only get more popular with time due to their wide applicability, falling price, low maintenance and high reliability. Grid-connected (i.e. grid-tied) installations are by far the most common PV system type in New Zealand, as they are considerably simpler and cheaper than alternatives. A fully set up medium-sized (i.e. 3kW) good quality system, which has the potential to generate about a third of a typical household's needs, cost around $10,000 in late 2016.

Ideally, renewably generated electricity should be used on site. This is due to electricity retailers paying considerably less for the excess electricity exported back to the grid than they charge for supplying.

However, there is currently a lot of uncertainty about: 

  • what tariff electricity retailers will award for excess electricity produced (known as the buy-back or feed-in price)
  • charge for supply
  • just how much electricity can be used immediately on site, which will vary by individual household
  • additional fees charged by some lines companies for households with grid-connected PV systems. 

It is therefore very difficult to estimate the likely lifetime financial returns of installing a system. For a rough cost-benefit estimation for individual households, use these web resources to carry out an assessment for your circumstances:

Correctly-sized heat pump

This is one of the easiest ‘upgrades' of all and yet costs nothing to achieve! Space heating accounts for about a third of the energy needs of New Zealand homes, with heat pumps being the number one space heater specified. Correct heat pump sizing is critical to both efficiency and performance and results in quieter running and lower lifetime maintenance. In overseas studies, inefficiencies of up to 35% result from incorrect sizing.


A search for a robust, New Zealand-relevant method for sizing all heater types was carried out. Key influences such as local climate, number of external walls of the room being heated, building construction details and room volumes all had to be considered in the calculation method. 

4 Energy Star dishwasher and washing machine

Although dishwashers and washing machines only account for about 2% of the energy use in New Zealand homes, this can be reduced even further. However, the extra price difference is considerable from the units sampled. At present, for the limited numbers of dishwashers and washing machines on the Australia-NZ Energy Star directory, it seems that it is not cost effective to buy 4-star energy-rated appliances due to the price difference. However, purchasing the appliances in a sale may change this.


The comprehensive Australian energy-rating site was used to determine the performance of various appliances.

For the dishwasher - assume that an inefficient 2 Energy Star dishwasher is being replaced by a 4 Energy Star dishwasher, and it is used every day with 10+ settings. This upgrade will save around $70 a year to operate. The break-even price difference between the two dishwasher types is just under $300.

For the washing machine - assume that an 8 kg model is chosen and a 2 Energy Star washing machine is being replaced by a 4 Energy Star washing machine. This upgrade will save around $170 a year to operate. The break-even price difference is just over $700. Lifetime savings for all the examples are based on an electricity charge of 30 c/kWh.

4 Energy Star fridge/freezer

Fridge/freezers are the biggest consumers of energy of all the household appliances, accounting for about 10% of household energy use. Their efficiency decreases as the surrounding temperature increases, so they should be located away from heat sources and direct sunlight. Choose a new fridge/freezer that is sized appropriately for the household. Ideally, they also should be placed so that they have a 75 mm gap all around for better ventilation.


It was assumed that only one fridge/freezer unit is replaced per house. An average-sized unit (at just under 400 litres in volume) was used for the comparison. A 2-door, 1.5 Energy Star fridge/freezer was compared to a 3.5 Energy Star fridge/freezer of a similar capacity. The Australia-NZ Energy Star directory was used to determine the standardised energy use of representative fridge/freezers to determine the average energy savings (of 43%). This saving was then reduced by 20% to better reflect actual performance as the standardised external temperatures are more representative of Australian conditions. The retail prices of 380-litre energy-efficient fridge/freezers listed on were compared with a group of similar capacity low-efficiency fridge/freezers. No significant price difference could be found. Lifetime savings are based on an electricity charge of 30 c/kWh.

Energy-efficient lighting

Ideally, all lighting installed in homes should be energy efficient, as well as meeting targets for appropriate colour representation, glare and utility. As nearly 10% of energy used in homes is from lighting, large ongoing savings are possible by shifting to more efficient lamps. BRANZ suggests that only lamps with an efficiency of greater than 40 lumens/watt is specified and used in homes. Thus, incandescent or halogen lamps should be substituted if possible in almost all situations, since very little of their energy use is converted to visible light. LED and fluorescent-style lamps are both more energy efficient and longer lasting and are dropping in price. In addition, they come in a wide range of styles and fittings to match the surrounding decor.


There have been no recent New Zealand studies on what is specified in homes in terms of lamp type. Building consent documentation is seldom specific enough to determine this either. The NZ Rightlight website (now EECA Energywise: Lighting) was used to establish the total lifetime costs of a wide variety of lamps i.e. the initial purchase price plus running costs plus replacements. Using the BRANZ/CRESA report Lighting in New Zealand homes, a model house representing a more traditionally set-up house was developed then upgraded to an energy-efficient version providing the same amount of lighting over the same period of time. The traditional house was artificially lit by incandescents (46% of the total lighting energy) and halogens (42%) but also CFLs (10%) and fluorescents (2%). The upgraded house was lit by CFLs (80%) and LEDs (20%). The upgrade resulted in a 51% reduction in energy use as well as a 50% reduction in total costs. Lifetime savings are based on an electricity charge of 30 c/kWh.

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