Midday Saver + battery Perth: how to use off-peak charging to cut your power bill

Synergy's Midday Saver tariff has a large spread between off-peak (9pm–9am) and peak (3–9pm) rates. Perth households with home batteries can exploit this spread by charging overnight and discharging during the expensive evening peak — an arbitrage strategy that doesn't rely on solar generation at all.

The Midday Saver rate structure (from 1 July 2026)

| Time period | Rate | |---|---| | Super off-peak (9am–3pm) | ~8.85 c/kWh | | Off-peak (9pm–9am) | ~24.34 c/kWh | | Peak (3pm–9pm) | ~55.33 c/kWh | | Supply charge | ~$1.33/day |

The key spread for battery arbitrage: charge at 24.34c overnight, discharge at 55.33c during peak = 31c/kWh spread.

Always confirm current Midday Saver rates at synergy.net.au — rates are subject to change.

How the battery arbitrage works

A Perth home on Midday Saver with a battery follows this daily cycle:

Night (9pm–9am): Grid charges battery at 24.34c/kWh. Battery fills to 90–100% state of charge by morning.

Day (9am–3pm): Solar panels generate at near-zero cost (panels already paid for). Household uses solar self-consumption during super off-peak hours — any grid import during this window is cheap (8.85c). Excess solar goes into the battery if not full.

Late afternoon and evening (3pm–9pm peak): Battery discharges to cover household loads. Grid purchases avoided at 55.33c.

Net saving per kWh discharged during peak: 55.33c - 24.34c = 31c/kWh (cost to charge overnight) - round-trip efficiency losses (~10%) = approximately 28c net saving per kWh cycled.

Annual battery savings calculation

For a 10kWh battery (usable capacity ~9kWh):

Assumption: Battery cycles once per day on average (some days partial, some days full cycles). 250 full cycles per year is a reasonable Perth estimate.

| Battery size | Usable capacity | Cycles/year | Gross saving | Efficiency adjustment (90%) | Net annual saving | |---|---|---|---|---|---| | 10kWh (e.g. Sungrow SBR100) | 9kWh | 250 | 9 × 250 × $0.31 = $697 | × 90% | ~$628/year | | 13.5kWh (e.g. Powerwall 2) | 13.5kWh | 200 | 13.5 × 200 × $0.31 = $837 | × 90% | ~$753/year |

Note: This is the grid arbitrage saving only — the difference between charging cost and discharge value. On top of this, the battery also captures solar generation during the day that would otherwise export at the DEBS export rate (2c/kWh), yielding additional self-consumption value at the peak rate.

Solar + battery + Midday Saver: the combined strategy

With solar panels AND a battery on Midday Saver:

1. Solar covers daytime loads at ~0c effective cost (sunlight is free once panels are paid off), displacing 8.85c off-peak imports.
2. Solar overproduction fills the battery during the day (9am–3pm super off-peak), so you may not need to use the overnight grid-charge.
3. Battery discharges during the 3–9pm peak at 55.33c value.
4. On cloudy days, battery charges overnight at 24.34c to cover the peak.

The super off-peak 8.85c rate is Synergy's cheapest import rate. If your solar is generating well during 9am–3pm, most of your consumption in that window can be covered by panels — meaning virtually no grid import at any time of day on good solar days.

Midday Saver vs A1 — which is better WITH a battery?

Without a battery, Midday Saver suits households that naturally consume less during the 3–9pm peak. With a battery, Midday Saver's large peak/off-peak spread becomes more favourable regardless of natural consumption patterns — because the battery handles peak coverage.

| Scenario | A1 battery saving | Midday Saver battery saving | |---|---|---| | 10kWh battery, 250 cycles | ~10kWh × 250 × 33.26c × 0.90 (avoided A1 rate) = ~$748/yr | ~$628/yr (arbitrage) + reduced peak import | | But on Midday Saver: peak is 55.33c vs 33.26c | Each peak kWh avoided is worth 22c more | On A1: 33.26c saved per kWh. On MS peak: 55.33c saved per kWh |

The more accurate comparison: On A1, battery avoids 33.26c/kWh of grid imports (offsetting flat rate). On Midday Saver with a battery, overnight charging at 24.34c and discharging at 55.33c yields a 31c spread AND the day solar generation is worth the avoided 55.33c peak rate (if used for evening needs) or 8.85c super off-peak rate (if used during the day).

Conclusion for battery owners: Midday Saver is almost always better than A1 when you have a battery. The 55.33c peak rate means every kWh the battery delivers during 3–9pm is worth significantly more than the 33.26c A1 rate.

Who benefits most

Highest benefit on Midday Saver + battery:

• Households with high evening consumption (aircon, cooking, TV, hot showers) in the 3–9pm peak
• Two-income households who are away during the day (low daytime consumption, high evening use)
• Households with EVs that can be programmed to charge during the 9pm–9am off-peak window (24.34c instead of 55.33c on Midday Saver peak)
• Any household where the battery can reliably cover 3–9pm loads from solar generation or overnight charge

Lower benefit on Midday Saver + battery:

• Households that already shift most consumption to midday naturally (few evening loads)
• Households where battery capacity is undersized relative to evening loads (battery depleted before 9pm, still buying at 55.33c)

Practical setup for Midday Saver battery users

Configure the battery schedule: Most battery management systems (Sungrow iSolarCloud, Fronius Solar.web, Tesla app) allow you to set:

• Charge window: 9pm–6am (using overnight off-peak at 24.34c)
• Discharge window: 3pm–9pm (peak window)
• Battery reserve for backup: 10–20% (in case of overnight grid disruption)

Monitor peak consumption: In the first month after switching, track your Synergy usage (via myaccount.synergy.net.au) to verify the battery is covering enough of the 3–9pm peak to justify the higher supply charge ($1.33/day vs $1.19/day on A1 — $51/year difference).

EV charging setup: If you have an EV, configure charging to the 9pm–9am window (24.34c on Midday Saver vs 55.33c if you charge at 6pm). An EV charging 15kWh per night at 24.34c = $3.65/charge. At the Midday Saver peak rate that would be $8.30/charge. Overnight scheduling saves $4.65/charge.

Midday Saver's 31c spread between off-peak (24.34c) and peak (55.33c) is the largest tariff arbitrage opportunity available to Perth battery owners. For households with batteries and evening loads, Midday Saver is likely to outperform A1. Always model your specific usage pattern — the break-even depends on how well the battery covers your natural 3–9pm peak consumption.