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For the standard home, including or adding solar photovoltaic (PV) is a relatively cost effective way to reduce the home’s ongoing utility bills, whilst also benefiting the environment. But when combined with energy-efficient home design, the way you use solar PV changes – requiring a smaller system and achieving even better cost and emissions savings.
This is the second article in a two-part series on solar PV. In this article we explain how solar PV and energy-efficient design can work together to make things more cost effective and more efficient for both builder and home buyer.
For background on the benefits of solar PV and the types of things that solar PV can achieve in the home – including Zero Net Carbon (ZNC), Zero Net Energy (ZNE) and No Bills (NB) – read Understanding solar photovoltaic..
Installing extra solar panels on a roof does not always provide as big a benefit as homeowners expect. This is due to several factors, like local electricity network export caps of 5kW, the lower income on exports versus imports, or because the home itself has high energy requirements.
By coupling solar PV with a high performing thermal envelope and energy-efficient appliances you reduce the number of panels required, as the home consumes less energy. You also get a more comfortable home and cost savings that aren’t susceptible to price fluctuations, the same way solar PV savings are.
In addition to an enhanced thermal envelope, a whole-of-home approach to design will reduce a home’s overall annual energy use, cost, and greenhouse gas emissions with little additional construction cost. Read more about the positive impacts of a whole-of-home approach.
To better demonstrate the benefits of combining solar PV with energy-efficient design, we analysed 3 homes with various configurations, from a standard home to an all-electric energy efficient home.
The data demonstrates the impact of different designs on the amount of solar PV needed to achieve the status of a Zero Net Carbon Home (ZNC), Zero Net Energy Home (ZNE) and No Bills Home (NB).
You can read more about what these mean and the cost versus benefit of different solar PV outcomes in Understanding solar photovoltaic.
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.
A solar PV export cap of 10kW was assumed for the NB homes. However, some areas on the grid have an export cap of 5kW.
A. Standard electric
B. Standard mixed fuel
C. Energy-efficient (using a whole-of-home approach)
Annual performance without solar
NB with 10 kWh battery
*The energy use indicated to achieve the ZNE shows the annual energy use of the home, not the solar PV system. A negative number indicates that on an annual basis the home produces more energy than it uses. This is because it is not possible to have half a solar PV panel.
**An export cap of 10kW had to be assumed as it was otherwise not possible to achieve a NB home with the available roof space. It should be noted that in some areas a 5kW export cap applies.
A. Business as usual (BAU) electric
B. Business as usual (BAU) mixed fuel
C. Energy-efficient (using a whole-of-home approach
A. Business as usual (BAU) electric
No solar WoH
By building homes that include enhanced energy efficiency measures, builders can install moderate sized solar PV systems to boost the cost and energy outcomes of the home. Builders can also have homes that achieve ZNC and ZNE status, whilst still ensuring the solar PV system fits on available roof space and doesn’t exceed export restrictions, that in turn affect the income from the feed in.
ZNC is very achievable in all situations but in the absence of energy-efficient design, ZNC is not necessarily an appealing product to home buyers.
When it comes to ZNE, the analysis showed that achieving a ZNE and ZNC requires the same amount of solar in all-electric scenarios.
To achieve ZNE in mixed fuel homes, almost double the amount of solar PV was needed when compared to achieving ZNC; making ZNC the better option for mixed fuel homes. This is because gas has a lower emission intensity than electricity in Victoria at present; however, the gas homes use a lot more energy at the end use point than their electric counterparts.
A combination of constraints make achieving NB status difficult or, in some instances, impossible. These include:
Additionally, NB homes can lead to dissatisfied customers, who may behave differently to the modelled energy use such as time of use and assumed plug in load versus actual.
The following additions can make NB status more achievable: