Solar + battery. One clear quote.

How much battery storage do you actually need?

Start with electricity use after sunset and the amount of daytime solar available to charge a battery. A bill total alone cannot show either. Interval meter data, existing solar monitoring and your household routine help build a more useful picture of when storage could replace grid purchases.

Consider two separate objectives: reducing routine grid imports and keeping selected appliances running in an outage. Holding energy in reserve for backup leaves less available for everyday use. Your quote should explain the proposed reserve and how changing it affects the expected result.

Ask to compare a smaller and larger storage option using the same usage data. Include usable capacity, charge and discharge limits, expected losses and the assumptions about future consumption. Extra capacity only helps if there is a practical reason to charge and use it; a larger number on the specification sheet is not a savings forecast.

Adding a battery to existing rooftop solar

A retrofit assessment starts with the existing inverter model, panel capacity, system age and network connection arrangement. Provide installation documents or a photograph of the accessible equipment label if you have one. There is no need to open electrical equipment to gather these details.

Ask whether the proposed design keeps the current solar inverter, replaces it or adds a separate battery inverter. Each approach can change the equipment scope, monitoring and backup behaviour. The proposal should make clear which existing components stay in service and which warranties apply to the new work.

Future expansion also needs a specific answer. Confirm compatible modules, permitted capacity, any timing restrictions and whether adding storage later would require further installation or approval work. A description such as expandable is not enough to establish the eventual cost or available configurations.

What to compare across Tesla, Sigenergy and GoodWe

Use the same comparison headings for every battery brand: usable energy, continuous power, backup arrangement, installation location, monitoring, expansion and warranty conditions. This keeps the discussion focused on the Australian configuration you are actually being offered.

Check what is included alongside the battery. A gateway, controller, additional inverter, consumption meter or switchboard modification can make two apparently similar package prices very different. Ask for optional features to be priced separately so you can decide whether you need them.

Warranty length should be read with the operating conditions, retained-capacity terms and any throughput limits. Also ask about service support and whether the proposed location meets the manufacturer’s requirements. The best fit depends on your property and priorities, rather than a universal ranking of brands.

Backup, tariffs and VPP offers: separate decisions

For blackout protection, list the appliances you want to run and discuss their combined demand. Refrigeration, lighting and internet can present a different design problem from air conditioning or cooking. Confirm the backed-up circuits, phase coverage, switching arrangement and whether solar can recharge the battery during an outage.

Tariff modelling should use your actual electricity plan, including import periods, export rates and daily charges. Compare a battery scenario with the same household without storage. If a proposal assumes grid charging or a different plan, ask to see those assumptions clearly rather than treating them as guaranteed savings.

A virtual power plant offer may add payments or discounts in exchange for access to the battery. Review dispatch rights, reserve settings, fees and exit conditions. Compare the whole offer, including the electricity tariff, rather than choosing solely on a joining incentive.

Federal battery support also has product and installation conditions. Confirm eligibility, the installation date assumptions and the certificate discount in writing. For grid-connected systems, required VPP capability does not itself mean you must enrol in a VPP to receive the federal support.