Solar for granny flats and secondary dwellings in Perth

Perth's secondary dwelling (granny flat) boom means many households now have two dwellings on one lot. Solar for secondary dwellings raises specific questions about meters, export limits, and how to share generation between the main house and the flat.

First: how is the granny flat metered?

The metering arrangement determines everything about how solar interacts with both dwellings.

Single meter (most common for owner-built granny flats): Both the main house and the granny flat share one Synergy account and one electricity meter. The flat is wired from the main distribution board. In this arrangement, solar goes onto the main meter — and the generation naturally offsets electricity used anywhere on the property, including the flat.

Separate meter (separately metered granny flat or approved secondary dwelling): The flat has its own Synergy connection, its own meter, and its own account. This is common when the flat is set up as an independent rental. In this arrangement, the main house and the flat have separate electricity accounts — solar on the main house's meter doesn't offset flat electricity.

Check your situation: Look at the electrical switchboard. Are there two meters on the property (sometimes one near the street and one near the flat)? Or one meter that feeds both? This determines your solar options.

Single meter: standard solar applies

If both dwellings are on one meter, solar works exactly like a standard installation:

• Size the system to cover total consumption across both dwellings
• Solar generation offsets the combined household consumption
• DEBS export credits go to the single account

Sizing consideration: Add both dwellings' consumption together when sizing. A typical Perth home uses 15–25 kWh/day; a granny flat with one or two occupants might use 6–12 kWh/day. Combined: 21–37 kWh/day — suggesting a system in the range of 10–15kW if roof space allows.

Export limit: Western Power's export limit applies to the single connection point. Standard residential connections are typically limited to 5kW export. If you install a large system to cover both dwellings, confirm the export limit with your installer before sizing above 10kW.

Separate meters: independent solar considerations

If the flat has its own meter, each dwelling effectively needs its own solar decision.

Solar on the main house only: Main house gets the savings; flat continues paying its own electricity bill separately. Simple, but the flat doesn't benefit from solar.

Solar on both dwellings separately: Each dwelling gets its own solar system on its own meter. Both benefit. But two separate connections, two Western Power processes, two export limits, and two systems to maintain.

Complications:

• If the granny flat meter is under the tenant's name, the flat's solar and DEBS credits would go to the tenant, not the landlord — same dynamic as an investment property
• Adding solar to a separately-metered flat often requires a separate Western Power application and potentially a separate Western Power connection point (check with a licensed electrician)

Export limit: per connection point

Western Power's export limit applies per connection point, not per dwelling. If your main house and flat are on a single connection point (single meter), the 5kW export limit covers the entire property. This matters if you plan to install a large combined system.

If the flat has a separate meter and separate connection point, each gets its own export limit — but you've also got a more complex installation and two Western Power processes.

Battery and granny flats

If you have a battery, it can buffer generation from a larger system and reduce what needs to be exported. This is particularly useful on a single-meter property where combined consumption is high but export is limited to 5kW — the battery absorbs excess generation during the day and discharges during evening peak (particularly valuable on Midday Saver).

On a separate-meter property, the battery charges from the meter it's connected to. The flat can't access a battery on the main house meter, and vice versa.

Practical steps

1. Check your metering: call Synergy or look at your switchboard — is it one meter or two?
2. If single meter: size solar for combined consumption, confirm export limit with installer
3. If separate meters: decide whether to solar-enable just the main house or both; get a licensed electrician to advise on connection arrangements for the flat
4. Check planning rules: WA secondary dwelling planning permits may have conditions about external works — solar panels on a secondary dwelling typically don't require separate planning approval, but confirm with your local council if unsure
5. Talk to your installer about export limits: for larger combined systems (>10kW), a non-standard Western Power assessment may be required

Metering and connection arrangements vary by property. A licensed electrician can inspect your switchboard and advise on the specific configuration before you commit to a system.