WA's split electricity market - a quick recap
Western Australia runs two largely separate electricity networks. The South West Interconnected System (SWIS), retailed by Synergy, covers Perth metro and the south-west - roughly postcodes 6000–6385 plus 6800–6999. Outside of that, regional WA - the Pilbara, Kimberley, Mid West, Goldfields-Esperance and Gascoyne - is served by Horizon Power, which runs around 30 separate microgrids ranging from tiny single-town diesel grids to large mining-region systems.
This split matters because every aspect of battery economics - rebate, retail tariff, export rate, network constraint - works differently depending on which side of the line you're on.
The three big differences
1. The rebate is 50% bigger if you're on Horizon
The WA Residential Battery Rebate Scheme caps at $5,000 for Synergy customers and $7,500 for Horizon Power customers - both rebates apply at roughly the same per-kWh rate up to those caps. A 13.5 kWh battery hits the cap in both cases, so the absolute dollar difference is the full $2,500.
Why? Every battery installed in the Pilbara or Kimberley displaces expensive diesel generation. That's a much bigger saving for the state than reducing a marginal kilowatt-hour from a Collie coal plant on the SWIS. The state pays more because the policy benefit is bigger.
2. Export tariffs are completely different
Synergy SWIS customers fall under the Distributed Energy Buyback Scheme (DEBS): you're paid about 10c/kWh for solar exported during the 3pm–9pm peak window, and 2.5c/kWh outside that. The peak window is deliberately set when the grid needs the most power - which is exactly when batteries are designed to discharge.
Horizon Power's export tariffs vary by microgrid. Some Horizon towns have very low export caps (because the local grid can't absorb much rooftop solar). Some have flat-rate buybacks. A few have time-of-use buybacks similar to DEBS. If you're on Horizon, ask your installer to confirm your specific microgrid's export terms before sizing the system.
3. Retail electricity prices are higher on Horizon
Synergy SWIS Home Plan A1 customers pay around 32c/kWh for grid power. Horizon Power retail rates range from 33c/kWh in towns close to the grid to over 56c/kWh in remote diesel-only towns. The state subsidises Horizon tariffs significantly - but even with subsidies, regional WA generally pays more.
This matters because every kWh your battery offsets is a kWh you didn't have to buy. The higher the retail price, the bigger the saving per kWh - which means batteries pay back faster on Horizon.
A direct example - Perth vs Karratha
Two identical households, both installing a 13.5 kWh Tesla Powerwall 3 for $14,000 list price:
Perth (Synergy) household
- WA state rebate: $5,000
- Federal Cheaper Home Batteries rebate: ~$5,000
- Net cost: $4,000
- Annual bill savings: ~$1,400
- Payback: 2.9 years
Karratha (Horizon) household
- WA state rebate: $7,500
- Federal Cheaper Home Batteries rebate: ~$5,000
- Net cost: $1,500
- Annual bill savings: ~$2,300 (higher retail tariff, more aircon hours)
- Payback: 0.7 years
Yes - a Karratha household effectively pays back the battery inside a single year. That's because the rebate stack covers nearly the entire system cost, and bigger annual savings then mop up the small remainder.
The catch most installers won't mention
Horizon microgrids have export caps. Some are aggressive - a few towns won't let you export at all, others cap you at 1.5 kW. If you're on Horizon and your microgrid has a low export cap, the maths shifts: your battery becomes much more valuable for self-consumption (because you can't sell excess solar back), but you can't make money by exporting battery-stored energy during peak windows.
Ask your installer two specific questions before signing: (a) "What's my microgrid's export cap?" and (b) "Does that cap reset for battery-paired systems, or does it apply to total export?"
The DEBS strategy on Synergy
If you're on Synergy SWIS, a battery + solar combination unlocks a specific arbitrage: charge the battery from cheap midday solar, then discharge into the peak DEBS window (3pm–9pm) at 10c/kWh. For most homes the better use is self-consumption - but on days when you've over-generated, the battery effectively earns 4x the off-peak buyback rate.
Most modern batteries (Powerwall 3, Sungrow SBR) support this via "export during peak" or "DEBS optimisation" modes. Worth confirming the model you're quoted supports it.
So which is better?
If you have the choice (i.e. you're moving and considering location), Horizon Power customers come out further ahead on battery economics. But the choice rarely works that way - you live where you live. The real takeaway is that regardless of network, the rebate stack makes a battery one of the best returns available on home capital in WA right now.
If you're on Horizon, the upside is bigger but the export rules matter more. If you're on Synergy, the upside is smaller but the rules are simpler and DEBS lets the battery work harder.