How Fishleg estimates work.
Fishleg Calculator is a deterministic, transparent model. No black boxes, no machine learning, no marketing math. Every number you see is derived from inputs you provide and assumptions you can audit.
The flow
- 1. Annual usage — derived from your quarterly bill ÷ retail rate.
- 2. Sun hours — peak sun hours by state (NSW 4.4, VIC 3.9, QLD 4.8, …).
- 3. System size — sized to your annual kWh, capped by roof space, adjusted for orientation and shading.
- 4. Self-consumption — base rate from time-of-use × occupancy; battery uplifts it by daily coverage.
- 5. Savings — self-consumed kWh × retail rate + exported kWh × feed-in tariff.
- 6. Payback — install cost ÷ annual savings, shown as a range.
Default assumptions
| Solar install cost | ~€1,100/kW + €2,000 fixed (indicative) |
| Battery cost | ~€1,000/kWh + €2,500 fixed (indicative) |
| VPP-ready premium | ~€800 for hybrid inverter and comms |
| Savings range | ±15% (solar), ±20% (battery), ±22% (VPP-ready) |
| Self-consumption cap | ~85% with battery (realistic ceiling) |
What this tool isn't
- Not a formal engineering or energy assessment.
- Not a binding quote — install cost depends on site survey.
- Not financial advice — payback depends on tariffs, usage, and degradation.
- Not a VPP earnings calculator — partner programs vary widely.
Want the real numbers for your home?
Run the calculator, then request a detailed quote.
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