Solar Savings Calculator

How it works

This calculator estimates how much a rooftop solar system could save on electricity bills each year, in four steps.

1. Generation. How many kilowatt-hours (kWh) the system produces over a year. Solar output depends heavily on location, roof orientation and tilt, and shading from trees, buildings or nearby structures — a precise figure only comes from a site assessment or installer quote against an actual address and roof. Because this calculator has no way to know your postcode or roof, and per-postcode generation data isn’t something we can verify or source here, it deliberately uses one rough, clearly-labelled Australia-wide average instead: 4.2 kWh generated per kW of installed system, per day. A 6.6kW system, for example, is estimated to generate 6.6 × 4.2 = 27.72 kWh a day, or roughly 10,118 kWh a year (× 365) — a starting estimate, not a location-specific prediction.

2. Self-consumption vs export. Not all of that generation is used the moment it’s produced. Some is used in the home as it’s generated (self-consumption) and the rest is sent back to the grid (export). This calculator assumes 40% self-consumption, a commonly-cited rough default for a typical household. The real split depends heavily on when people are home and when appliances like pool pumps, hot water systems or EV chargers run relative to daylight hours — a household mostly out during the day self-consumes less than one that’s home and drawing power throughout the day.

3. Bill savings. Self-consumed solar reduces how much electricity is bought from the grid, so it’s valued at the entered electricity rate (cents/kWh) — check a recent bill for the actual figure, since rates vary by retailer and state.

4. Export credits. Exported solar earns a feed-in tariff credit, usually applied to the bill, valued at whatever rate the retailer currently offers for exports. Feed-in tariffs vary a lot between retailers and states and change over time, so this is a required input here rather than an assumed figure — check your own plan for the current rate.

Adding bill savings and export credits together gives total estimated annual savings. If an installed system cost is entered, the calculator also works out an estimated payback period — system cost ÷ annual savings — the rough number of years before the savings add up to what the system cost to install. This ignores financing costs, electricity price changes over time and gradual panel degradation, so treat it as a starting estimate rather than a financial guarantee — a real installer quote and site assessment is the way to get a precise, address-specific figure.

Worked example

The Nguyen family in Hobart are considering rooftop solar and want a rough sense of the savings before requesting quotes. They plan to install a 6.6kW system — a common Australian residential size — and their current electricity bill averages $500 a quarter ($2,000 a year). For the rest of the inputs, they use this calculator’s default assumptions: a $0.30/kWh electricity rate and a $0.05/kWh feed-in tariff, both of which they’ll still need to confirm against their own bill and retailer plan before relying on them.

Step 1 — generation. Using the calculator’s Australia-wide average of 4.2 kWh per kW per day:

6.6 kW × 4.2 kWh/kW/day = 27.72 kWh a day 27.72 kWh/day × 365 = 10,117.8 kWh a year

This is a national average, not a Hobart-specific figure. Actual generation depends on the exact roof orientation, tilt and any shading from trees or nearby buildings, on top of broader regional differences in sunlight hours across Australia — a local installer’s site assessment is the only way to get an exact figure for a specific roof.

Step 2 — self-consumption and export. At the assumed 40% self-consumption rate:

Self-consumed: 10,117.8 × 0.4 = 4,047.12 kWh Exported: 10,117.8 × 0.6 = 6,070.68 kWh

Step 3 — savings.

Bill savings: 4,047.12 kWh × $0.30/kWh = $1,214.14 Export credits: 6,070.68 kWh × $0.05/kWh = $303.53 Total annual savings: $1,214.14 + $303.53 = $1,517.67

That’s roughly 76% of their $2,000 current annual bill.

Step 4 — payback. With an installed cost of $6,000:

$6,000 ÷ $1,517.67 ≈ 3.95 years, which the calculator rounds and displays as 4.0 years.

	Figure
System size	6.6 kW
Estimated annual generation	10,117.8 kWh
Self-consumed (40%)	4,047.12 kWh
Exported (60%)	6,070.68 kWh
Bill savings	$1,214.14
Export credits	$303.53
Total annual savings	$1,517.67
Payback period (on $6,000 system cost)	~4.0 years

These figures use the calculator’s Australia-wide average assumptions, not a Hobart-specific or address-specific number. An actual installer quote and site assessment is the only way to get a precise figure for a particular roof.