Calculator inputs
Use the fields below to estimate solar energy offset, export value, and grid reliance.
Plotly graph
The chart compares estimated monthly solar generation against average monthly demand and remaining grid needs.
Example data table
| Scenario | System Size (kW) | Sun Hours | Annual Usage (kWh) | Self-Use Rate | Grid Tariff | Export Tariff |
|---|---|---|---|---|---|---|
| Compact home | 4.2 | 5.0 | 7,200 | 72% | 0.16 | 0.07 |
| Family home | 6.0 | 5.5 | 12,000 | 68% | 0.18 | 0.08 |
| Small business | 15.0 | 5.8 | 24,000 | 81% | 0.22 | 0.10 |
Formula used
1) Gross generation
Gross Generation = System Size × Sun Hours × Days Per Year
2) Net first-year generation
Net First-Year Generation = Gross Generation × Performance Ratio × (1 − Shade Loss) × (1 − Soiling Loss) × Inverter Efficiency
3) Degraded generation for selected year
Adjusted Generation = Net First-Year Generation × (1 − Degradation Rate)(Analysis Year − 1)
4) Energy split
Self-Consumed Solar = Adjusted Generation × Self-Consumption Rate
Exported Solar = Adjusted Generation − Self-Consumed Solar
5) Financial offset
Bill Offset = (Self-Consumed Solar × Grid Tariff) + (Exported Solar × Export Tariff)
6) Carbon reduction
CO2 Avoided = Adjusted Generation × Grid Carbon Factor
How to use this calculator
- Enter a direct system size, or enter panel wattage and panel count to derive it automatically.
- Add your location-driven average sun hours and confirm operating days.
- Set performance ratio, inverter efficiency, and expected shading or soiling losses.
- Choose an analysis year to include degradation over time.
- Enter annual electricity use, self-consumption rate, grid tariff, and export tariff.
- Add the grid carbon factor if you want emissions savings.
- Press Calculate Offset to show the results above the form.
- Use the CSV and PDF buttons to export the current result set.
FAQs
1. What does solar energy offset mean?
Solar energy offset shows how much of your electricity demand can be covered by solar production. It can be expressed as energy coverage, on-site self-use, or bill reduction depending on the metric you choose.
2. Why is self-consumption different from total generation?
A solar system may generate more electricity than you are using at certain times. The energy used instantly on-site is self-consumed, while the excess is exported or curtailed.
3. Why does the calculator include performance ratio?
Performance ratio compresses several real-world inefficiencies into one factor. It helps move the estimate closer to field performance instead of relying only on theoretical panel capacity.
4. What is a good self-consumption rate?
Homes without batteries often land around 30% to 60%. Homes with daytime loads, smart controls, or batteries can go much higher, improving bill offset even if total generation stays unchanged.
5. How does degradation affect long-term offset?
Solar panels usually produce slightly less energy each year. A degradation input lets you estimate future-year output instead of assuming year-one production lasts forever.
6. Should export tariff always be lower than grid tariff?
Not always, but it is often lower in many net billing programs. The calculator keeps both values separate so you can model your utility structure accurately.
7. Can this calculator estimate environmental impact?
Yes. By adding a grid carbon factor, the tool converts solar generation into avoided emissions. This helps compare financial and sustainability benefits together.
8. Is this result a replacement for a professional design?
No. It is a planning estimate. Final design should also consider roof geometry, local weather, inverter sizing, wiring losses, utility rules, and shading analysis.