Battery Payback: Separate Storage Savings from Solar Savings

A battery's payback should use the extra savings created by storage. If you already have solar, the electricity your panels supply directly to the house is part of the starting position, not a new battery benefit.

For a combined purchase, compare solar alone with the same solar system plus storage. The difference in installed cost and ongoing bills is the battery decision. Keep the value of backup separate from the financial calculation.

Choose the right starting bill

Gather a full year of bills where possible, plus interval imports and exports. Keep the tariff, household usage and solar assumptions consistent between the two cases. Otherwise the comparison can credit the battery with unrelated changes.

For example, changing a gas appliance or buying an EV alters electricity use. Model that change in both cases if it is part of the household's plan.

Our electrification guide helps organise those stages.

Solar Victoria recommends considering when you use electricity and whether available generation can charge a proposed battery. Those two quantities need to meet in the savings calculation.

Solar Victoria battery guidance.

Follow one day's stored energy

Here is a deliberately simplified illustration, not a Melbourne tariff or product forecast. Assume 6 kWh of surplus solar charges a battery and 90% returns to household appliances: 5.4 kWh delivered.

At an assumed import rate of 30 cents per kWh, that avoids $1.62 of purchases. If the 6 kWh could have earned 5 cents per kWh when exported, the forgone credit is 30 cents. The illustrated net energy benefit is $1.32.

That example excludes fixed fees, finance, maintenance and changing capacity. It assumes all 5.4 kWh displaces purchases at the stated rate. Do not multiply it by 365 unless the annual data supports that repeated opportunity.

A flat import tariff can still support savings

Different peak and off-peak rates are not essential for solar self-consumption value. Even with one import rate all day, storing surplus solar can avoid a later purchase worth more than the forgone export credit and losses.

Time-of-use charging is a separate opportunity. Its value depends on the actual tariff spread and supported operation. Keep the two mechanisms visible rather than assuming every discharged kWh earns the most attractive rate on the bill.

Use your current plan documents and compare alternatives through Victorian Energy Compare. Check total annual charges, not only the advertised feed-in rate.

Turn annual benefit into a cautious estimate

Subtract additional recurring costs from the modelled annual benefit. Divide the extra installed battery cost by that annual net benefit for a simple payback estimate. If the benefit is zero or negative, there is no positive simple payback.

Simple payback does not capture every later cost or change. Run another case with less usable solar, lower avoided import costs or reduced delivered energy. Add finance separately if repayments apply.

Our battery cost guide can help check the installation amount. Ask a supplier to show its working before accepting an annual savings figure, particularly when solar and storage appear in one proposal.

The next decision may be smaller storage

A battery may be hard to justify on bill savings if daytime surplus or later consumption is low. Moving a suitable appliance into daylight can be worth comparing before buying storage for that same energy.

Backup can still be a reason to buy. Use the blackout planning guide to specify that purpose, then decide what it is worth to you without disguising it as an electricity-bill return.