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Energy efficiency

Up-Spec provides actual data for a range of performance improvements for new homes related to energy efficiency.

The following options for improving energy efficiency were explored:

  • Photovoltaic-ready house (installing cabling only)
  • 3kW grid-connected photovoltaic system fully installed
  • Correctly sized heat pump
  • All lighting is energy efficient

Photovoltaic-ready house (installing cabling only)

Electricity-generating photovoltaic (PV) panels have fallen 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.

Approach

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

3 kW 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.

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.

Approach

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.

Energy-efficient lighting

Around 13% of the energy consumed in New Zealand homes is used by lighting and all lighting installed should be energy efficient. BRANZ recommends using LED rather than incandescent or other lamps in homes. Incandescent lamps (which have a wire filament that is heated until it gives off light) are basically the same today as when they were invented over 100 years ago. Most of their energy output is radiated as heat rather than light. In comparison, LEDs are typically 75–80% more efficient.

Approach

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. Research was carried out to establish the total lifetime costs (the initial purchase price plus running costs plus replacements) of a wide variety of lamps. Using the BRANZ/CRESA scientific paper Lighting in New Zealand homes [PDF, 148KB], 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.

More information

Updated: 04 December 2023