Compare solar investment, fixed tariffs, self-consumption and degradation using transparent annual cash flows.
Year 0 to year 25, left to right. Vertical range: -6,000 to 9,403 currency. Horizontal line marks zero.
Cumulative cash flowDiscounted cash flow
First payback crossing: 9.312 years
Edit cost or self-consumption to compare a fixed-tariff scenario. All amounts use the same currency.
Undiscounted cash-flow payback
9.312years
Use one currency consistently across costs and tariffs.
Check the values to see a result.
Fixed tariffs and annual operating cost. No financing, tax, grants or replacement costs. Payback is the first cumulative crossing, not a guarantee of positive lifetime value.
Annual net benefit = avoided import + export revenue − operating cost
The entered investment is first recovered after about 9.312 years under these assumptions.
Tip: Self-consumption fraction stays fixed as generation degrades. A detailed time-series tariff model is needed where prices or usage change.
Each unit consumed on site avoids the entered import unit price. Each exported unit receives the entered export payment. Fixed standing charges are not avoided by producing solar electricity. Enter an evidenced self-consumption fraction or compare clearly labelled scenarios. Prices in the form are illustrative, not regional tariff presets.
Each unit consumed on site avoids the entered import unit price. Each exported unit receives the entered export payment. Fixed standing charges are not avoided by producing solar electricity. Enter an evidenced self-consumption fraction or compare clearly labelled scenarios. Prices in the form are illustrative, not regional tariff presets.
Generation reduces by the entered annual degradation fraction after the first year. The same self-consumption fraction, tariffs and operating cost apply to every year. Net benefit is energy value less annual operating cost. Cumulative benefit starts at negative capital cost; the first crossing is interpolated within that year.
A short first payback does not guarantee a positive value over every later horizon, especially where operating cost continues while production falls. Net present value discounts each annual net benefit to year zero and subtracts capital cost. This simplified calculation excludes loans, tax, replacement equipment and changing tariffs; use a full project model for an investment decision.
Annual benefit is 200 currency units and payback is 5 years. At the end of 10 years, net benefit and NPV are both 1000 under the zero-discount, zero-degradation assumptions.
Undiscounted cash-flow payback 5 years Open in the calculator
Payback is Not reached. Energy value is 200 per year but operating cost is 300, so the project loses another 100 each year after the initial outlay. Ten-year net benefit is negative 2000.
Undiscounted cash-flow payback Not reached Open in the calculator
Any single consistent currency. Enter capital and operating costs in that currency and import/export prices per kWh in the same currency. The tool does not convert currencies.
No. It is transparent arithmetic for the assumptions you enter. It does not forecast electricity prices, tax treatment, financing or actual production.
The calculator assigns the import price only to electricity used directly on site. Exported electricity receives the separate export rate. Using the import rate for all generation would exaggerate savings wherever exports receive less. Enter the marginal unit prices actually affected by generation; fixed bill charges remain outside this calculation.