MundoKitSolar Payback Calculator
Enter a solar quote, annual generation and the value of self-used and exported electricity. Inspect annual savings and the cumulative balance over your chosen period.
Results
- First nonnegative year-end balance
- 13 years
- Net upfront cost
- 12,000.00 currency units
- First-year net savings
- 1,100.00 currency units
- Balance after model period
- 12,767.14 currency units
| Year | Generation kWh | Gross value | Net savings | Cumulative balance |
|---|---|---|---|---|
| 1 | 6,000 | 1,200.00 currency units | 1,100.00 currency units | -10,900.00 currency units |
| 2 | 5,970 | 1,194.00 currency units | 1,094.00 currency units | -9,806.00 currency units |
| 3 | 5,940.15 | 1,188.03 currency units | 1,088.03 currency units | -8,717.97 currency units |
| 4 | 5,910.45 | 1,182.09 currency units | 1,082.09 currency units | -7,635.88 currency units |
| 5 | 5,880.9 | 1,176.18 currency units | 1,076.18 currency units | -6,559.70 currency units |
| 6 | 5,851.49 | 1,170.30 currency units | 1,070.30 currency units | -5,489.40 currency units |
| 7 | 5,822.24 | 1,164.45 currency units | 1,064.45 currency units | -4,424.96 currency units |
| 8 | 5,793.12 | 1,158.62 currency units | 1,058.62 currency units | -3,366.33 currency units |
| 9 | 5,764.16 | 1,152.83 currency units | 1,052.83 currency units | -2,313.50 currency units |
| 10 | 5,735.34 | 1,147.07 currency units | 1,047.07 currency units | -1,266.43 currency units |
| 11 | 5,706.66 | 1,141.33 currency units | 1,041.33 currency units | -225.10 currency units |
| 12 | 5,678.13 | 1,135.63 currency units | 35.63 currency units | -189.47 currency units |
| 13 | 5,649.74 | 1,129.95 currency units | 1,029.95 currency units | 840.47 currency units |
| 14 | 5,621.49 | 1,124.30 currency units | 1,024.30 currency units | 1,864.77 currency units |
| 15 | 5,593.38 | 1,118.68 currency units | 1,018.68 currency units | 2,883.45 currency units |
| 16 | 5,565.41 | 1,113.08 currency units | 1,013.08 currency units | 3,896.53 currency units |
| 17 | 5,537.59 | 1,107.52 currency units | 1,007.52 currency units | 4,904.05 currency units |
| 18 | 5,509.9 | 1,101.98 currency units | 1,001.98 currency units | 5,906.03 currency units |
| 19 | 5,482.35 | 1,096.47 currency units | 996.47 currency units | 6,902.50 currency units |
| 20 | 5,454.94 | 1,090.99 currency units | 990.99 currency units | 7,893.48 currency units |
| 21 | 5,427.66 | 1,085.53 currency units | 985.53 currency units | 8,879.02 currency units |
| 22 | 5,400.52 | 1,080.10 currency units | 980.10 currency units | 9,859.12 currency units |
| 23 | 5,373.52 | 1,074.70 currency units | 974.70 currency units | 10,833.83 currency units |
| 24 | 5,346.65 | 1,069.33 currency units | 969.33 currency units | 11,803.16 currency units |
| 25 | 5,319.92 | 1,063.98 currency units | 963.98 currency units | 12,767.14 currency units |
- Payback is the first year-end crossing; a later replacement can make the balance negative again. No financing, discount rate, residual value or battery is included.
- Use generation after curtailment. Self-consumption share and annual costs stay constant; both energy rates escalate together. Fixed utility charges are not avoided. All monetary inputs use one currency.
This is a general estimate for information only, not tax, legal or financial advice. Real rules have more conditions than a calculator can show, so check the official source below or a qualified professional for your situation.
How it works
Value self-consumed generation at the avoided import rate and exports at their compensation rate, as described by the Australian Government. Enter generation after curtailment and use a realistic self-consumption share.
Year y value = first-year kWh × (1 − degradation)^(y−1) × [self share × import rate + export share × export rate] × (1 + escalation)^(y−1) Net savings = value − maintenance − replacement in its selected year
The cumulative balance starts at minus installed cost plus verified upfront incentives. Payback is the first nonnegative year-end balance, not a discounted investment return. Both rates escalate together; costs stay constant. Set escalation to zero for an unchanged-price scenario.
IRS guidance says section 25D is unavailable for expenditures after December 31, 2025. IRS FAQ 7 treats section 25D expenditures as made when original installation is completed, or when the taxpayer begins original use of a newly constructed or reconstructed structure. A 2025 prepayment for a 2026 installation does not qualify. No federal homeowner credit is applied automatically. Enter only incentives independently verified for your project.
Prices and loads are editable examples. The optional 30% self-use scenario is IPART’s typical NSW household assumption in its 2025–26 report, not a universal forecast. DOE describes about 0.5% annual module efficiency degradation; whole-system losses and outages may differ. Use monitoring or an installer’s simulation for project-specific assumptions. Use one currency throughout. Calculations keep full precision internally; a scale-aware floating-point tolerance recognizes exact zero-balance crossings without rounding cash flows; displayed energy and money are rounded, and year-end payback is shown in whole years where applicable.
Worked examples
Flat prices and no degradation
A 12,000 system generating 6,000 kWh, with 50% self-use at 0.30 and 50% export at 0.10, earns 1,200 per year. With maintenance of 100, no replacement and zero degradation or escalation, annual net savings are 1,100. First year-end payback is year 11 and the 25-year balance is 15,500.
Replacement shifts payback
For that same system, a 2,000 replacement at the end of year 10 delays first year-end payback to year 13. The 25-year balance becomes 13,500.
Frequently asked questions
Does this assume a federal tax credit?
How is export different from self-use?
Does it include financing or inflation?
Can payback reverse later?
What generation should I enter?
Sources
- Australian Government — solar savings and export value (checked 2026-11-14)
- US Department of Energy — solar savings and payback (checked 2026-11-14)
- IRS — termination of residential energy credits (checked 2026-11-14)
- IPART — 2025–26 solar feed-in report, executive summary footnote a (checked 2026-11-14)
- DOE — Understanding Solar PV Performance, module degradation (checked 2026-11-14)
Last reviewed 2026-11-14; next review due by 2027-01-15. The method is written out above so you can check our math.