Bigger Battery Capacity

Why larger home battery capacity helps futureproof your energy storage investment

Considering installing a home solar battery? These are the main reasons that we are finding HEG customers are installing, on average, 20kWh of batteries at their home, and why 40kWH+ home batteries in Tasmania have become common. Note: Tiered battery rebate changes and rebate reductions from 1st May 2026 onwards may affect the economic viability of larger batteries.

Bigger is… cheaper

Bigger batteries cost less the more you add. This is because the rebate is based on the usable storage capacity of an installed battery system and, because there is only a small marginal cost to add extra batteries once the battery electrician has installed the first battery and connected it to your switchboard, the price of additional battery labour and materials doesn’t increase much compared to the first one. This is especially true with “stacked” brick-like batteries.

One bite of the… rebate

This Commonwealth Government rebate only applies once per site. If you decide to add more batteries next year, for example, they will be at their full cost i.e. the rebate won’t apply again. This is encouraging households to invest in a capacity that is appropriately sized, rather than installing a small battery system to test the waters.

Learning from the past

16 years ago, it was common for household solar installs to be 2kW or 3kW in size. Recently, our typical solar install range has been 8kW to 12kW per household because that offsets the majority of a typical power bill. We feel batteries will be the same… 10kWh of storage doesn’t seem large any more, especially with individual battery modules being about 10kWh, and you can string a few of them together to achieve closer to 40kWh. 

Time of Use Tariffs and Load Shifting

Most energy retailers in Tasmania offer a ToU tariff, which means that your power is more expensive at specific (peak) times and cheaper at other (off-peak) times. Batteries can be configured to “load shift”, charging up with half price power or free solar power during the day, and using that power during evening peak periods, thus largely avoiding the higher power prices. If a battery capacity is too small, it won’t fully offset the evening peak period when households generally use the most power.

Adequate Emergency Power Supply (EPS)

When the grid goes down, a battery kicks in to provide power to selected circuits in a house (normally a light and a power circuit, and sometimes a heat pump circuit). A larger capacity battery will last longer, depending on settings, daily solar levels and recent discharge rates. Powered appliances and lights will drain a battery quite quickly depending on their “electrical draw”, so a larger battery provides back-up flexibility. If a 2000W (2kW) fan heater is left on, and assuming a  battery has 10kWh available, then it will be depleted in 5 hours (5 x 2kW), for example.

Virtual Power Plant (VPP) / Energy Trading

Whilst Tassie doesn’t have a VPP currently available, these schemes allow a household to sell their solar-generated and battery-stored power to the grid at specific times for a handsome rate, typically at peak periods when the grid uses the most power. This allows network operators to respond quickly to sudden high demands for power, and provides a revenue stream for households. Yep – a bigger battery means you have the ability to sell more power.

Electric vehicle “fuel”

As EV adoption is accelerating (pun intended), your solar and battery system will become your new home-based fuel station. Your solar will be able to charge your vehicle during the day, or a larger home battery may be able to partially charge it at night in an emergency. New bidirectional charging technologies (search for “V2X”) integrate with the battery system promise to turn your vehicle into a home battery on wheels eventually, giving you greater energy independence.

Battery degradation over time

Just like a smartphone or laptop, home batteries degrade over time. Most batteries have a 10 year warranty (although there are power throughput limitation clauses), whereby many brands specify, say, 70% capacity after the warranty period. This means that a 10kWh battery will probably operate like a 7kWh battery in a decade. Installing a larger battery now will mitigate this to a large degree.

Minimum SOC (State of Charge)

Rather than depleting the battery down to 0%, most households specify a minimum SOC, say 20%, in case of an emergency outage. This is a valuable feature, but does often mean that a battery capacity is compromised as you can’t utilise all of your battery. A battery that has twice the capacity means that you can set the SOC to 10% and have the same amount of back-up capacity (e.g. 20% x 10kWh = 10% x 20kWh), for example.

Reallocate genset funds

People that wish to have Off Grid Mode (OGM) functionality are simply getting a bigger battery and solar combo instead of spending a few thousand dollars on a good diesel or petrol generator with an auto-start function. OGM is where, in the event of a multi-day electrical grid outage, your solar system can recharge a home battery day after day (assuming adequate sun!). OGM isn’t actually a standard feature when you retrofit a battery to dwelling with an existing solar system, incidentally, so beware cheap “deals”.

Solar Sharer Program providing free power during daytime periods

Starting in July 2026, the Solar Sharer Program will require Australian electricity retailers to offer at least three hours of free electricity daily, typically during peak solar generation hours around midday. This federal initiative aims to utilise the nation’s abundant solar surplus, lowering household bills and stabilising the grid by shifting demand away from expensive evening peaks.

For those considering a home battery, this program transforms your investment from a solar-only companion into a powerful grid-charging asset. A battery allows you to “soak up” this free grid power during the midday window and store it for use during high-cost evening periods, ensuring you maximise savings, even on cloudy days when your own panels might underperform. By pairing a battery with the Solar Sharer Program, you can dramatically shorten your system’s payback period.

I hope this is helpful with your battery deliberations. HEG™ have 8 residential energy consultants statewide (Launceston,  Hobart,  NW Coast), plus myself, that can assist with modelling your solar, battery storage and energy efficiency requirements. 

Respectfully, 

Adam “HEG-Master” Hirst
Founder, Home Efficiency Group