Synergy tariffs and DEBS explained for WA solar

Most of Western Australia's population sits on the South West Interconnected System (the SWIS) — the grid that runs from Kalbarri down to Albany and east to Kalgoorlie. On that network, household electricity is not contestable: Synergy is the only retailer, so there is no plan-switching between providers the way there is on the east coast. Your choice is which Synergy tariff you sit on, not which company bills you.

That single fact reshapes the solar decision. Where an east-coast buyer might chase a retailer with a high feed-in tariff, a WA buyer can't — the buyback rate is fixed by the DEBS scheme (below), and it is deliberately modest. Value in WA comes from using and storing your own solar rather than exporting it, which is the opposite of the “export everything” logic a generic calculator assumes.

(One WA exception worth naming: gas retail is contestable — several providers compete — but that is a separate market from the electricity tariffs this guide covers.)

DEBS — the Distributed Energy Buyback Scheme — is the credit Synergy pays for the solar you send back to the grid. Unlike a single flat feed-in tariff, it is time-split, and the shape of the split is the point:

• •Peak export, 3pm–9pm: about 10c per kWh — paid when the grid actually needs the energy, as household demand climbs and solar drops off.
• •Off-peak export, the rest of the day: about 2c per kWh — the middle of the day, when every solar home is exporting at once and the grid is already flush with cheap power.

The peak window pays around 5× the daytime rate. There is also a daily export cap of 50 kWh — export beyond that in a day earns nothing — so a very large array pointed at midday export runs into diminishing returns fast.

The takeaway: the sunniest hours are precisely when exported solar is worth the least, and the hours it's worth most are the hours your panels have stopped producing. That mismatch is structural to WA, and it is what the next section turns into a sizing decision.

Put the two halves together and the WA logic falls out. Daytime solar you export earns the low off-peak buyback. The same energy, held in a battery and used at 3pm–9pm, offsets the peak usage rate you would otherwise pay — the most expensive power on a time-of-use plan. The value of a battery in WA is largely this arbitrage between a cheap daytime export and an expensive evening import, not backup alone.

Practical consequences worth carrying into a quote conversation:

• •Oversizing the array for export rarely pays. Past the point that covers daytime use plus battery charging, extra panels mostly feed the low off-peak buyback and hit the daily export cap.
• •A west-facing string can be worth more than a purely north one. Shifting some production later into the afternoon lines it up with the peak window — see the orientation guide.
• •Battery size follows your evening load, not your roof. Enough to cover the 3pm–9pm peak is usually the sweet spot — the battery sizing guide walks through it.
• •Rebates sit on top of this. A battery's payback also draws on the WA residential battery scheme and federal certificates — covered in the WA battery scheme guide and STCs and rebates.

None of this replaces a proper design for your roof and usage. WattMate isn't an installer — the point of understanding the tariffs first is that you can read an installer's quote critically, and tell a system sized for your bill from one sized for their catalogue. When you're ready, compare independent quotes through Get a quote.