What is the right battery size for a solar sharer plan? Compare total battery savings over a 15-year lifespan against simply investing that same money, using a “real” (inflation-adjusted) return, since that keeps everything in today’s dollars. A fair benchmark is beating what the money would earn going toward a mortgage instead, historically around 2% real return; using a 2.5% target builds in some safety margin.
The calculation accounts for:
- Capacity fading to roughly 70% by year 15 (so ~85% average usable capacity)
- VPP payments (~$150/year plus $1/kWh of capacity)
- NSW’s VPP incentive, worth up to ~$1,000 for larger batteries
- Installed costs, which drop per kWh as battery size increases
- Electricity prices assumed flat for 8 years, then 20% lower for the remainder, to account for possible future price falls
The result:
plotting battery savings against the investment-return benchmark shows the two lines crossing at just over 28 kWh. The point where a battery still beats parking the money elsewhere. Chase a higher return (say 4%) and the ideal size drops to about 22 kWh; accept a lower one (2%) and it climbs to around 31 kWh. Push for a 5% return, though, and no battery size gets there.
On backup power:
A battery charged fresh every day from a free window is often already sitting on a useful reserve if the grid goes down. So a dedicated backup buffer matters less than with batteries charged the traditional way. Sizing up by just ~5% is enough to guarantee power for essentials during an outage, though for many households, that extra cost isn’t worth it if blackouts are rare.
For a typical household using around 6,500 kWh a year, roughly 28 kWh comes out as the financial sweet spot, bigger than most people would guess. Since rebates are generally a once-per-property deal, erring larger tends to be the safer mistake to make.
Why Choose UNIfied?
At UNIfied Energy, we’re committed to making your electrification journey seamless. We help Australian households and businesses:
- Reduce energy bills and operating costs
- Lower carbon emissions and confidently adopt sustainable practices.
Contact UNIfied Energy today or call 1300 817 847 to achieve greater savings in these precarious times and start your journey of clean energy living.
