Why you still need Synergy at night with solar: understanding the grid relationship

One of the most common misunderstandings new solar owners have is that solar panels will cover their electricity needs entirely. In Perth, solar panels generate power for 8–10 hours a day (depending on season), and nothing at night. Here's a clear-eyed view of what solar actually covers, what doesn't change, and how a battery changes the picture.

Solar generation hours in Perth

Perth solar panels start generating roughly at sunrise and stop at sunset. Generation isn't constant — it follows a bell curve peaking at solar noon (around 12pm–1pm Perth time in summer, slightly later in winter due to standard time vs solar time).

Perth approximate solar generation hours:

• Summer (December): 5:30am – 7:30pm (~14 hours of daylight; useful generation ~8am–6pm)
• Autumn/spring (March/September): 6:30am – 6:30pm (~12 hours; useful generation ~8am–5pm)
• Winter (June): 7:30am – 5:30pm (~10 hours; useful generation ~9am–4pm)

The phrase "useful generation" refers to the period when panels are producing enough power to meaningfully offset consumption — the very early morning and late afternoon hours produce minimal power even in summer.

What happens at night with solar

From approximately sunset to sunrise, your solar panels produce zero power. Your home continues to consume electricity for:

• Lighting
• Refrigerator and freezer (always on)
• Television and entertainment
• Appliances used in the evening
• Air conditioning or heating overnight
• Overnight charging of phones, laptops, etc.

All of this comes from the Synergy grid — charged at your tariff rate (33.26c/kWh on A1, or the applicable rate on Midday Saver or HomePlan+).

Overnight consumption for a Perth home (approximate):

• Small household: 2–4 kWh per night
• Average household: 4–8 kWh per night
• Large household with overnight AC: 8–15+ kWh per night

How much of your bill solar eliminates vs what remains

A well-sized solar system (10kW) in Perth generates approximately 14,000 kWh/year. The same average household might use 18,000 kWh/year. Even with a perfectly sized system, solar cannot eliminate the bill:

• Daytime consumption covered by solar: ~6,000–9,000 kWh/year (varies by self-consumption rate)
• Evening/overnight consumption from grid: ~9,000–12,000 kWh/year
• Daytime surplus exported: ~3,000–6,000 kWh/year (earns DEBS credit)

The DEBS credit offsets some of the grid bill, but typically doesn't cover it entirely. Most Perth solar households see their annual bill reduced by 50–75%, not eliminated.

The fixed supply charge

Synergy charges a daily supply charge (also called service to property charge) regardless of how much electricity you consume or whether you generate solar power. On the A1 tariff, this is currently around $1.00–$1.20/day (approximately $365–$440/year).

This charge is not offset by solar generation or DEBS credits — it's a fixed cost for maintaining your connection to the network. Even Perth households who generate more solar than they consume still pay the supply charge.

How a battery changes the picture

A home battery (e.g., 10kWh BYD, Sungrow, Alpha ESS) stores surplus solar generation during the day and uses it overnight. This directly reduces nighttime grid draw:

With a 10kWh battery and 10kW solar:

• Daytime: Solar covers consumption + charges battery to full
• Evening/overnight: Battery powers 4–6 hours of average household consumption
• Late night/pre-dawn: Battery depleted, grid takes over (typically midnight–sunrise)

A 10kWh battery covers most but not all nighttime consumption for an average Perth household. Overnight consumption after the battery is depleted still comes from the grid.

Does a battery eliminate the Synergy bill? Rarely — for most households, a combination of solar + battery reduces grid consumption by 70–90%, with some residual grid draw in the pre-dawn hours and peak winter days when solar is limited.

Can Perth homes go off-grid?

True off-grid requires enough solar and battery storage to cover 100% of consumption, including the worst-case winter days (shortest days, lowest irradiance) and multi-day overcast periods (Perth averages 2–3 consecutive cloudy days in winter).

To cover a Perth household that uses 20kWh/day:

• Battery needed for 3 consecutive cloudy days: ~60kWh of battery storage
• Solar to recharge in winter: ~15–20kW of panels
• System cost: $80,000–$150,000+

This scale of off-grid system is genuinely not viable for most Perth suburban homes — the cost doesn't make economic sense when grid connection costs approximately $1,000–$2,000/year in supply charges and net grid consumption.

Grid-connected-as-backup is the right framing for Perth: solar provides most of the daytime power, a battery covers most evening loads, and the Synergy grid is the backup for overnight, peak winter, and extended overcast periods. The supply charge is the cost of maintaining that backup.

The evening peak problem

Perth's electricity use peaks between 3pm and 9pm — returning from work, cooking, cooling the house after a hot day. This is exactly when solar generation is winding down (4pm–7pm), creating a "solar cliff" where your system drops from generating 8kW to 0kW within a few hours.

Without a battery, this evening peak is covered entirely by the grid. With a battery charged during the solar peak (10am–3pm), the battery can cover 4–8 hours of evening consumption. This is the primary financial case for battery storage in Perth: avoiding the evening peak grid draw at A1 rates (33.26c/kWh) or Midday Saver peak rates (53.58c/kWh).

Solar with battery reduces most Perth households' Synergy bill by 70–90% — but eliminating it entirely requires the grid as a backup, especially for overnight pre-dawn consumption in winter. The supply charge remains regardless of solar output. The most cost-effective approach is right-sized solar + a 10kWh battery, keeping the grid connection as a reliable overnight backup.