title: "Scenario guide: retiree on a fixed income — 5 kW PV + 8 kWh battery"
description: "How a retired Perth couple might approach battery sizing on a fixed income — balancing budget, usage patterns and rebate timing."
lastUpdated: "27 Feb 2026"
Scenario guide: retiree on a fixed income
This is an illustrative scenario based on typical Perth household data, not a specific customer story.
Home profile
Occupants: 2 adults (retired)
Cooling/heating: Small reverse-cycle split system, used moderately
Hot water: Electric storage on timer (runs at 10 am)
Daily usage: ~12-16 kWh, with mornings and evenings as peak periods
Solar: 5 kW PV (existing, installed 3-5 years ago)
Battery: 8 kWh usable capacity
Backup: Essential-circuits only (lights, fridge, modem)
Goal: Reduce electricity bills on a fixed income without over-investing
How this typically plays out
Retirees often have a different usage pattern from working families. More energy is used during the day, while solar is producing, which means a smaller battery is usually enough. The battery's main job is covering the evening gap between solar production ending and bedtime.
Daytime advantage: Because retirees are home during the day, more appliances run during solar hours. This naturally increases self-consumption without needing a large battery. Running the dishwasher, washing machine, and vacuum during 10 am-2 pm maximises direct solar use.
Right-sized battery: An 8 kWh battery matches the typical evening load of 6-8 kWh (from 5 pm to 10 pm). Oversizing to 13 kWh would add $3,000-4,000 to the cost with diminishing returns, since the smaller daytime gap means less surplus to store.
Budget consideration: At current prices, an 8 kWh AC-coupled battery typically costs $8,000-$10,000 before rebates. After the WA rebate ($1,040 for 8 kWh) and federal STCs (~$2,554 in H1 2026), the net cost drops to roughly $4,400-$6,400. On typical savings of $600-900/year, the payback period is 5-8 years, well within the battery's 10-year warranty.
Winter: Shorter solar days mean the battery may not fully charge. A forced-charge window on off-peak rates (if available) can top up the battery cheaply on cloudy days.
Key takeaways
Don't oversize the battery. Match it to your actual evening load, not the biggest option available. For most retired couples, 8-10 kWh is enough.
Daytime usage is your advantage. Being home during solar hours means you naturally consume more solar directly, reducing what needs to go through the battery.
Rebate timing matters on a fixed budget. Both the WA state rebate and federal STCs are declining, so locking in current rates improves the financial case.
Essential-circuits backup covers lights, fridge and modem during summer storm outages, without the cost of whole-home backup.
