Your Synergy bill goes negative after solar: what happens to the credit?

A solar household in Perth can generate more from DEBS export payments than they owe in energy and supply charges on their Synergy bill — particularly in summer when solar generation is highest. When your Synergy bill shows a credit balance, what happens to that money?

How a negative Synergy bill happens

Your Synergy bill charges you for:

1. Supply charge: A fixed daily charge (~$1.19/day on A1, ~$1.45/day on Midday Saver). Cannot be offset by solar.
2. Usage charge: Electricity consumed at your tariff rate, less any on-bill DEBS credits.

Your DEBS export payments reduce your bill. If DEBS credits exceed your usage charges, the net energy charge is zero or negative. But the supply charge remains.

Example — Perth summer month on A1:

• Supply charge: $1.19/day × 30 days = $35.70
• Usage charge (1,000 kWh @ 33.26c): $332.60
• Self-consumed solar: 600 kWh (avoided import)
• Exported solar: 400 kWh (60% in off-peak at 2c, 40% in DEBS peak at 10c)
• DEBS credit: (240 kWh × $0.02) + (160 kWh × $0.10) = $4.80 + $16.00 = $20.80
• Net bill: $35.70 + $332.60 − $332.60 (only 400 kWh imported from grid) − $20.80 DEBS credit

Wait — let me recalculate. If the household consumes 1,000 kWh and self-consumes 600 kWh from solar, they only import 400 kWh from the grid.

• Supply charge: $35.70
• Grid usage (400 kWh @ 33.26c): $133.04
• DEBS credit: $20.80
• Net bill: $35.70 + $133.04 − $20.80 = $147.94 — still positive in this example

For a bill to go negative, DEBS credits must exceed both the supply charge and the grid usage charge. This typically happens when:

• Solar generation significantly exceeds household consumption for the billing period (low usage + large system)
• A high proportion of exports fall in the DEBS peak window (3pm–9pm)

Most common scenario for negative bills: A household with a 10kW+ system, low occupancy, and summer peak exports — particularly if they're away during the day and export heavily.

What Synergy does with a credit balance

Synergy carries the credit forward: If your bill calculation results in a credit (e.g. −$45.20), Synergy records this as a credit balance on your account. The credit rolls forward to offset your next bill.

It accumulates across billing cycles: If you have multiple consecutive bills in credit (e.g. three summer months), the credits add up. Your credit balance appears on your bill as "Credit carried forward" or similar.

There is no automatic cash refund: Synergy does not proactively send you a cheque or bank transfer for credit balances. The credit offsets future usage charges (e.g. winter bills when solar exports are lower).

When does Synergy refund credit balances?

You can request a refund: If you have a substantial credit balance, you can contact Synergy and request a refund of the credit to your bank account. Synergy processes credit refunds — this isn't automatic, but it is available.

Practical threshold: most households don't bother requesting refunds for small credit balances (under $50–$100), as the credits will offset future winter bills anyway. Larger accumulated credits from a summer period are worth requesting back.

Account closure: If you close your Synergy account (moving house, etc.), any credit balance is refunded automatically.

Grandfathered REBS customers (40c FiT era)

Some Perth homeowners have contracts from the 2010–2013 era on 40c/kWh REBS rates. These contracts generated significant credit balances — sometimes hundreds of dollars per quarter — because the export rate was nearly double the import rate.

For these customers, Synergy's historical practice was to accumulate credits until customers requested a refund. If you're on a grandfathered high-FiT REBS contract and have an accumulated credit balance, contact Synergy to arrange a refund.

The supply charge cannot be offset

Regardless of how large your solar credit is, the daily supply charge (~$1.19/day on A1) cannot be eliminated by solar exports. This is a standing charge for connection to the grid.

For a household that goes 100% off-grid, the supply charge disappears — but so does the ability to use the grid as backup or to sell exports. For most Perth households, remaining grid-connected and paying the supply charge while using solar to reduce usage charges is the economical choice.

Strategies if your bills consistently run into credit

If DEBS credits consistently exceed your usage charges:

1. Your solar system may be oversized for your consumption. This is not inherently a problem — oversizing made more sense in the high FiT era, less so with DEBS at 2c off-peak. Future EV charging or battery storage can absorb excess solar productively.

2. Add battery storage. A battery shifts excess solar self-consumption from daytime (when you'd otherwise export at 2c) to evening (when you'd otherwise import at 33c). This dramatically improves the value of excess solar generation.

3. Shift more load to daytime. Scheduling washing machines, dishwashers, and pool pumps to run during solar generation hours increases self-consumption — converting 2c/kWh exports into 33c/kWh avoided imports.

4. Switch to a time-of-use tariff (Midday Saver) if your consumption is flexible. Midday Saver off-peak import rate (9am–3pm) is 8.85c/kWh — expensive solar is more valuable self-consumed than exported at 2c, but self-consumed during midday is also much cheaper than grid import.

What a credit balance looks like on your bill

Synergy bills display credit balances as either:

• A negative total (e.g. "Total amount due: -$32.45")
• A "Credit Carried Forward" line showing the accumulated balance
• Some bills display credits in brackets (e.g. $32.45 CR)

If your bill shows a credit and you're uncertain whether it will be carried forward or refunded, contact Synergy's residential team — 13 13 53 (residential customers).

A Synergy credit balance is real money — you can request it back at any time. But for most solar households, credits accumulated over summer naturally offset winter bills, making the accumulation a useful form of smoothing over the seasonal generation cycle.