Future household energy self-sufficiency challenge
In my recent book, Net Zero Suburbia, I investigated the ability for suburban living to be in control of its energy production, storage and use, as a way to reduce expensive grid load and return prosperity to the suburbs, as these places are currently under extreme financial stress.
The easiest way to generate domestic energy is by solar, and to determine whether solar generation is feasible to cover household energy needs, it is crucial to analyse current capabilities and explore future technological advancements that can support such outcomes.
A typical Australia home consumes around 20kWh of electricity per day, whether this is supplied via the grid or solar. In South East Queensland, households can expect approximately 5.5 hours of peak solar energy per day. Achieving 5.5 peak sun hours every day is unrealistic due to seasonal variations, cloud cover, and suboptimal roof orientations. Consequently, to ensure year-round energy coverage a 13.5kW solar array maybe required for self-sufficiency.
A 13.5kW system could, in theory, generate over 55kWh per day. However, solar installers typically apply a 75% efficiency ratio when selecting inverters, meaning that the system's practical output would be around 44kWh per day. It is also estimated that about one-third of all days achieve full solar potential within this region, while the remaining days produce varying levels of energy, dropping potential generation to around 30-35kWh per day. This output should suffice for the typical household usage, including during winter months.
Sizing energy storage batteries are the next tricky part of the equation. For the average, it is likely that 60% of this energy is consumed at night when solar power is unavailable. This suggests that a 12-15kWh of battery storage, might be the ideal solution, provided there is no EV charging demand. To account for winter degradation in solar generation then a system of a 13.5kW solar array with 16-20kWh of battery storage for increased winter energy demand is potentially ideal for total energy independence while remaining connected to the grid.
Adding an EV with an average daily commute of 50-70km requires approximately 13.5kWh of additional electricity. Depending on charging habits, some of this demand could be met by unused daytime solar generation or battery reserves. However, to account for the unpredictability of travel, it is prudent to consider additional generation capacity. This would necessitate larger battery storage of 25-30kWh.
A 13.5kW system, comprising 31 x 440-watt panels, would require an estimated 63m2 of roof space. This is feasible even considering the complexities of Australian hip and gable roofs. Typically, the roof area for single-storey homes in Australia equals the built footprint, averaging around 240m2, offering ample space for PV installations.
The roofs seen in suburban developments are typically designed using load-bearing outer walls and truss-type frames to span the internal space. Traditional climate-responsive Queensland homes, as well as more modern flat or skillion roof designs, provide ample accessible area for PV installation.
A system of this scale would cost between $30,000 and $40,000 AUD, which includes government rebates (not tax credits) applicable only to solar PVs, as there are currently no incentives available for battery storage in Australia. Batteries used for solar energy storage are similar to Electric Vehicle (EV) technology, typically offering a 10-year warranty, while PV panels are rated for up to 25 years.
As EVs age and battery technology undergoes real-world testing, they have shown minimal degradation beyond 10 years. However, their long-term cycle rates remain uncertain, making it difficult to guarantee performance beyond a decade. The replacement cost for batteries in 2024 is estimated at 60-65% of the initial system cost, highlighting the importance of longevity. Fortunately, battery production costs have decreased by 90% over the past decade, and as electrification continues to scale up, future replacement costs are expected to decrease further.
Image: Grid connected Self-sufficient Home Solar and Battery System
While remaining connected to the grid, such a system (despite its expense) would provide near 100% self-sufficiency under current climatic conditions. However, with global temperatures approaching a 1.5°C average rise, further increases to +3.0°C could necessitate greater cooling demands, potentially increasing household energy consumption and capacities of solar array and storage systems.
For example, in January 2025, a coastal residential development within this region experienced three consecutive days of sustained heat above 35°C. This is already an abnormal pattern, as historical records indicate that the area typically experiences only about two days per year above 35°C, let alone three in a single month[1]. According to the Climate Council's predicted heat map for this suburb, if no action is taken to mitigate rising temperatures, days exceeding 35°C will become a regular occurrence. Combined with rising average temperatures in the low to mid-30s, this will lead to a significant increase in electricity demand for cooling.
Calculating this additional energy demand, it could take anywhere between 6 to 12 kW to power up to four split-cycle air conditioners running for an 8-hour period[2]. Requiring additional investment in solar generation and battery storage. This serves as further evidence of how in Australia we are under specifying the system needed for today as well as into the future, and this process continues to drain further wealth from suburbia, and developing a lifestyle that may not be resilient to climate change.
It’s time that governments and developers start becoming accountable for the loss of wealth being extracted from the suburbs, why should the everyday Australian punter carry this burden because of poor policy implementation.
[1] Refer to historical data for this area - https://www.eldersweather.com.au/climate-history/qld/caloundra
[2] Based on estimates from a regional HVAC supplier - https://www.hhaircon.com.au/general-news/split-system-air-conditioner-running-costs/