First year Zero Energy results

Zero Energy House

Zero Energy achieved

For Shay and Jo to achieve Zero Energy for their project required generating as much energy onsite via renewable sources as was used in the home. Zero Energy is measured over a calendar year and in 2013 – the first year after Shay and Jo’s house was completed – the house-wide monitoring system recorded all energy generated and used.

The results for this first year were:

  • Energy used: 2,361 kWh.
  • Energy generated: 5,387 kWh.
In the first year, the Zero Energy House generated more than double the energy used.

In that first year, the Zero Energy House generated more than double the energy used. This substantial difference is, in part, because the house was designed and built to be Zero Energy even after Shay and Jo had a family. For most of 2013 it was just the two of them living in the home, so energy use was lower than it is now, when they share the house with their two children.

The couple estimated that, once the house was full, energy use would increase by 40% to around 3,200 kWh, which is still less than what the photovoltaic system (PV) generates. This surplus capacity was intentionally planned, as Shay and Jo wanted extra renewable energy available in the future to allow them to charge an electric car – which they began doing in 2018.

Energy use results

<p>Minimising energy use is a key goal in planning for Zero Energy as it reduces the amount of energy that needs to be generated, which in the case of the Zero Energy House meant a smaller PV array. Shay and Jo’s consumption of 2,361 kWh in 2013 was around 25% of the energy used in a typical Auckland home<sup>1</sup>. Reducing energy use by nearly 75% was achieved by focusing on three key areas:</p>

  1. Eliminating heating. The typical Auckland home uses around 30% of its energy to keep people warm in winter. Through passive design and an efficient building envelope the Zero Energy House eliminated the need for heating altogether, cutting consumption by 30%.
  2. Solar water heating. Water heating takes up another 30% of the typical Auckland home’s energy consumption. By using solar water heating for most of their hot water needs, Shay and Jo cut their energy consumption by another 25%.
  3. Energy & water-efficient fittings. The remaining 20% of energy savings came from fittings used in the house. These included LED lighting and energy-efficient appliances as well as water-efficient taps and shower heads that reduced hot water use and therefore the energy needed to heat that water.

<p>The chart below compares the energy profile of the Zero Energy House (ZEH) (using data from September to December of 2013<sup>2</sup>) against that of a typical Auckland home (using data from the BRANZ Household Energy-use Project (HEEP)<sup>3</sup>.</p>


  • Monitoring system. This is the house-wide monitoring and control system, which records energy and water use, along with thermal performance. In addition, it provides building automation and control via a web interface and smartphone app of many areas of the house, e.g., heated towel rails, garage door, lighting.
  • Solar hot water (SHW) control & pump. This is the energy used by the solar water heating system controller (controls when the pump runs) and pump (circulates a heat exchange fluid to the solar collectors on the roof where it is heated before returning it to heat the cylinder).
  • Lighting. The low use here compared with a typical home is due to all-LED lighting.
  • Rain and greywater. This refers to the pumps used to run these water systems. The rainwater pump moves water from the rainwater tank into the home. This water is used for washing clothes, flushing toilets, and outside taps.
  • Hot water cylinder & heating. These two items indicate the biggest areas of savings. Hardly any electricity is used to power the hot water cylinder as the house relies mostly on solar water heating. And, for the reasons mentioned previously, there is no need to heat the home in order to keep it warm.
The 5,387 kWh generated by the PV panels roughly matches the performance modelled during design.

Energy generation results

The 5,387 kWh generated by the PV panels in 2013 roughly matches the performance Shay and Jo had modelled during the design stage, with some variation month to month.

The chart below shows monthly patterns of energy generation and use compared with what was predicted during design. The four data series are:

  • Generation. The light green line indicates energy generated by the PV system each month. The peak month for generation was January with 660 kWh, while the lowest was June with 269 kWh.
  • Generation (predicted). The dark green line indicates modelled performance of the PV system prior to installation. Over the year, the PV system performed slightly better than expected.
  • Consumption. The light brown line indicates monthly use of energy, with peak use in June of 250 kWh and lowest use in January of 129 kWh.
  • Consumption (predicted). The dark brown line shows modelled energy use. As mentioned above, this model is based on a full house. While every month in 2013 saw generation exceed consumption, this modelled line shows that once the house is full, Shay and Jo can expect an energy deficit during winter months and will need to top up with energy from the grid.

The shaded brown area indicates the total amount of energy used over the year. The shaded green area indicates the surplus energy generated from the solar PV system that is not required for use in the home and can be exported to the grid.

Achieving Zero Energy allowed Shay and Jo to reduce reliance on energy sources that generate carbon dioxide and to reduce the costs of running their home. In fact, over the first year they ended up making a profit on energy. And, with the amazing results of their first year of occupation, their house was certified as Net Zero Energy by the Living Future Institute. One of the most important lessons from their energy results, though, is that Shay and Jo’s energy model helped them plan not only for their immediate circumstances but for their future circumstances too. The Zero Energy House was Zero Energy then and continues to be Zero Energy today, even though the family has doubled in size.

Footnotes
  1. Building Research Association New Zealand (BRANZ). (2006). Energy use in New Zealand households: Report on the year 10 analysis for the household energy end-use project (HEEP). p17.
  2. While Shay and Jo have total house-level energy consumption recorded for all of 2013, some of the circuit-level monitoring devices were not activated until September, hence circuit-level data is only available from then until December.
  3. BRANZ (2006).

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