Solar Sponge tariff in Perth: is it better than Midday Saver?

The term "Solar Sponge" refers to electricity tariffs or rates specifically designed to encourage consumption during periods of high solar generation on the grid — typically late morning and midday. By making electricity very cheap (or even free) during solar oversupply periods, these tariffs incentivise households to shift consumption and reduce curtailment of solar generation.

What a Solar Sponge tariff is

A Solar Sponge rate applies a very low or zero electricity price during the hours when the grid is saturated with solar generation. The idea originated in South Australia, where the state grid frequently experiences negative wholesale electricity prices at midday on high-solar days.

The problem it solves: When Perth's rooftop solar generates more electricity than the grid needs, excess generation must be curtailed (switched off) or the grid frequency rises to unsafe levels. Rather than curtailing solar, a Solar Sponge tariff encourages households to consume more during those hours — running dishwashers, washing machines, EV charging, hot water systems, and pool pumps during the oversupply window.

WA's Midday Saver is a Solar Sponge tariff

Synergy's Midday Saver (Smart Home) tariff is effectively WA's Solar Sponge product:

• Super off-peak: 8.85c/kWh (9am–3pm) — the solar generation window
• Peak: 55.33c/kWh (3pm–9pm)
• Off-peak: 24.34c/kWh (other hours)

The super off-peak window (9am–3pm) aligns directly with Perth's peak solar generation hours. At 8.85c/kWh, it's the cheapest residential electricity rate available in WA outside of free solar self-consumption.

This is the Solar Sponge in practice for Perth.

Is WA trialling a separate Solar Sponge rate?

The WA Government and the Economic Regulation Authority (ERA) have discussed further electricity tariff reforms as part of WA's Energy Transformation Strategy. This includes potential new tariff structures that could:

• Further reduce prices during midday solar oversupply periods
• Introduce variable prices that respond to real-time grid conditions (more like dynamic pricing)
• Create compensation mechanisms for households who actively help manage the grid

Current status (2026): Midday Saver remains the primary time-of-use tariff available to Perth residential solar households through Synergy. Additional tariff products may be introduced following ERA reviews, but Synergy is currently the only residential electricity retailer in the SWIS for standard customers.

Monitor announcements from Synergy, the WA Government's Energy Division, and the ERA for new tariff developments.

Midday Saver vs a hypothetical lower Solar Sponge rate

If WA were to introduce a 0c or 2c midday rate (closer to South Australia's Solar Sponge tariff), the key question is whether the lower midday rate compensates for the higher peak rate.

For Perth solar households: Most solar generation already occurs during 9am–3pm (the existing super off-peak window). The financial benefit of going from 8.85c to 0c/kWh in this window would be modest — because solar households are already largely self-consuming during that period, not importing from the grid.

The bigger savings driver on Midday Saver is avoiding the 55.33c/kWh peak rate (3–9pm) through battery storage or shifting consumption, not the 8.85c import rate.

Who benefits most from a Solar Sponge approach

Pool owners: Pool pumps timed to run 9am–3pm consume cheap midday electricity. A lower midday rate amplifies this benefit.

EV owners charging at home: EV charging during 9am–3pm at 8.85c/kWh (or lower) vs 55.33c/kWh in the evening is a dramatic difference. Solar Sponge tariffs directly benefit EV households who can schedule daytime charging.

Hot water heat pumps: Heat pump hot water systems timed to run 9am–2pm use cheap midday electricity (or solar) to heat water for the day's needs.

All appliance loads: Any household that can shift dishwashing, clothes washing, and similar loads to the 9am–3pm window benefits from Solar Sponge pricing.

What to do now

The practical action is to optimise against the current Midday Saver tariff rather than wait for a hypothetical new Solar Sponge product:

1. Switch to Midday Saver if you have a smart meter and solar (or high daytime consumption)
2. Time your appliances to run during 9am–3pm (timers on washing machines, dishwashers, pool pumps, hot water systems)
3. Add a battery to capture solar surplus for evening use (displaces 55.33c/kWh peak import)
4. Consider an EV with scheduled daytime charging for the biggest electricity cost reduction

These actions are valuable regardless of whether WA introduces a lower Solar Sponge rate in future — and if a lower midday rate does arrive, households already set up for daytime consumption optimisation will benefit immediately.

WA tariff products are governed by Synergy and the ERA. Check synergy.net.au for current tariff options and any new product announcements.