How the Solar Savings Calculator Works
This site estimates solar PV value by separating generated electricity into two buckets: electricity you use at home and electricity you export. Everything else on the page flows from those two numbers.
Step 1: Estimate annual generation
Annual generation is the kWh your solar array is expected to produce in a year. The quick estimate button uses 900kWh per kW installed as a planning shortcut, but a roof-specific PVGIS or installer figure is better.
Step 2: Split generation into self-use and export
Self-consumption is the percentage of generated solar used in the home. The remainder is treated as exported. The calculator caps effective self-consumption at 95% to avoid implying perfect use of every unit.
Step 3: Value both buckets
| Bucket | Formula | Why it matters |
|---|---|---|
| Self-used solar | Self-used kWh x import unit rate | Represents bill savings from buying less electricity. |
| Exported solar | Exported kWh x export tariff | Represents SEG or export tariff income. |
Step 4: Calculate payback and net value
Annual benefit is bill savings plus export income. Simple payback is upfront cost divided by annual benefit. The calculator also shows 10-year and 20-year net figures so you can see beyond the break-even point.
How the battery toggle works
When you include a battery, the calculator adds battery cost to the upfront total and adds the selected uplift to self-consumption. This is a simple model. It is useful for comparison, but it doesn't simulate hourly battery charge, discharge, winter output or time-of-use arbitrage.
What the calculator doesn't include
- Finance interest or opportunity cost.
- Future energy price inflation or export tariff changes.
- Panel degradation, maintenance or inverter replacement.
- Roof repairs, planning constraints, DNO limits or structural survey outcomes.
Next: use the calculator · payback formula · payback factors