Solar Savings Calculator
Estimate annual and lifetime bill savings from a solar system.
Please note: Estimates for planning only. Actual solar output depends on your latitude, roof orientation, shading, weather and equipment. Get a site-specific assessment and quotes before committing.
What the Solar Savings Calculator does
Solar saves money two ways: energy you use as it is generated avoids buying it at the import rate, and surplus exported to the grid earns a lower export rate. Because import rates are usually three or four times export rates, how much you self-consume matters more than how much you generate.
Formula
Annual generation = System kW × Sun hours × (1 − Losses) × 365Self-consumed = min(Generation × Self-consumption share, Annual usage)Exported = Generation − Self-consumedSaving = Self-consumed × Import rate + Exported × Export rate
Inputs explained
| Input | Unit | Required | Notes |
|---|---|---|---|
| System size | kW | Yes | Accepts more than 0. |
| Peak sun hours per day | one of 7 options | Yes | Average daily equivalent hours of full-strength sunlight for your location. |
| System losses | % | Yes | Inverter, wiring, soiling, heat and mismatch losses combined. 20% is typical. |
| Monthly electricity use | kWh | Yes | Accepts more than 0. |
| Import rate per kWh | selected currency | Yes | Accepts more than 0. |
| Export rate per kWh | selected currency | Yes | What you are paid for surplus sent to the grid. Accepts 0 or more. |
| Self-consumption share | % | Yes | Share of generation you use directly rather than exporting. |
| Annual electricity price rise | % | Yes | — |
| Annual panel degradation | % | Yes | — |
| Years to project | number | Yes | Accepts 1 or more, up to 40. |
| Currency | one of 10 options | Optional | — |
How to use it
- Choose Peak sun hours per day and Currency.
- Enter System size, System losses, Monthly electricity use and Import rate per kWh and 5 more.
- Select Calculate.
Worked example
A 6 kW system at 4.5 sun hours, 900 kWh monthly use, 0.28 import, 0.08 export, 40% self-consumption.
- Size
- 6 kW
- Usage
- 900 kWh
- Import
- 0.28
- Export
- 0.08
- Self-use
- 40
Generates 7,884 kWh. Self-uses 3,154 kWh saving $883, exports 4,730 kWh earning $378 — $1,261 in year one.
Frequently asked questions
Why does self-consumption matter so much?
Because a kWh you use is worth the full import rate, while an exported kWh often earns a quarter of that. Raising self-consumption from 30% to 60% can lift savings by half.
How do I increase self-consumption?
Run appliances during daylight, charge an EV in the afternoon, or add a battery to store the midday surplus for evening use.