Drawing on modelling data, we explain the difference between ZNC, ZNE and NB homes from a construction, cost, sustainability and liveability perspective.
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Solar photovoltaic (PV) can achieve different things in homes. Factors like the energy efficiency of the home can impact how a solar PV system performs and how much solar PV is required.
When talking about what solar PV can achieve, terms such as zero net carbon (ZNC), zero net energy (ZNE) and no bills (NB) are sometimes used, and often confused.
This article is the first in a two-part series. In this article, we draw on modelling data to explain what these terms ZNC, ZNE and NB mean from a construction, cost, sustainability and liveability perspective.
In article two, we expand on these terms and explain how you can get these most out of your solar PV with energy-efficient home design.
We analysed 3 homes (a 2 bed, 3 bed and 6 bed) ranging in size from 115m2 to 295m2. Each home was assessed against multiple scenarios to achieve ZNC, ZNE and NB.
The modelling was based on the typical behaviours of a 4-person household. An assumed plug-in appliance load was also used. In all scenarios, solar PV sizing was specified assuming a north facing orientation with no shading.
Below is an overview and breakdown of different types of homes and varying solar PV outcomes. These home types are based on common scenarios currently seen or discussed within the Victorian market.
Standard home with solar
Up to 3kW
A 6-star NatHERS rated home with standard appliances and a solar PV system on the roof up to 3kW
Customers who like renewable energy or are interested in reducing their bills, carbon footprint or energy use, but may not have the capital to purchase the other options.
No solar energy-efficient home
No solar PV
A home with a minimum 7-star NatHERS rating, efficient appliances, and no solar PV system
Anyone who wants an energy-efficient home and to reduce their bills, carbon footprint or energy use.
It also suits people who want to focus on liveability with a more comfortable home.
Zero Net Carbon (ZNC) Home
From 4–5kW for efficient homes and 4.2–11.5kW for standard homes
A home that produces enough renewable energy to offset the emissions produced during the operation of the home
Any new home buyer who is:
Zero Net Energy (ZNE) Home
From 4–5kW for efficient homes and from 7–15kW in standard homes
A home that produces enough renewable energy to offset the annual energy use of the operation of the home
Any new home buyer who:
No Bills (NB) Home
From 10–12kW for the efficient electric homes and from 13–22kW for the standard home
A home that produces no net energy bills in its operation
Any new home buyer who wants to have:
No Bills (NB) battery home
A home that produces no net energy bills in its operation and stores energy for the home to use when needed
Any new home buyer who wants:
A Standard home with solar is a 6-star NatHERS rated home with standard appliances (including 5 W/m2 lighting), and up to 3kW of solar. This could be either mixed fuel or an all-electric home.
Solar PV size of up to 3kW is assumed as that keeps it below the ZNC, ZNE and NB range.
A No solar energy-efficient home achieves a 7-star NatHERS rating or above and includes energy-efficient appliances.
While you can have both energy-efficient mixed-fuel and all-electric homes, the home analysed in this scenario was a 7-star NatHERS rated electric with highly efficient appliance choices and light power density of 2W/m2. There is no solar PV on the roof.
A ZNC home produces enough renewable energy to offset the homes operational emissions on an annual basis. The amount of solar PV required to achieve ZNC typically ranges between 4–5kW for an energy efficient home, and between 4.2–11.5kW for less efficient homes.
A ZNE home produces enough renewable energy to offset the homes operational energy on an annual basis. The home can be either an energy-efficient home (requiring 4–5kW of solar PV) or a standard home (requiring 7–15kW of solar PV).
The NB home produces no net energy bills in its operation. In some instances, where a battery is installed, the home also stores energy for use as needed.
For homes that do not include energy efficiency features, the solar PV size will range from 11.5kW to 22kW. By including energy efficiency features, the solar PV size range is reduced to between 10–11.5kW.
When assessing what you would like to achieve from a solar PV system, it is important to ensure that your aims are realistically achievable. For example, that you have enough room on the roof for the panels required or that you’re not exceeding grid constraints, such as the 5kW export limit.
With that in mind, solar PV can contribute to lower energy bills and improve the overall sustainability of a home.
Including a mix of solar PV and energy-efficient features in a new home achieves the best overall benefits for home buyers. This combination also creates homes that are future proof, efficient and resilient.
Read more on how energy-efficient design and solar PV work together.