Model your system costs, rebates, and tax credits. See cash flows across your chosen years. Understand rebate impact on payback, ROI, and NPV clearly.
Rebate is computed from installed cost using a percent or fixed amount, capped at installed cost.
Tax credit equals credit_basis × (credit_percent ÷ 100), where basis can be before or after the rebate.
Net out-of-pocket equals installed_cost − rebate − tax_credit.
Year t production equals year1_kWh × (1 − degradation)^(t−1).
Year t rate equals rate × (1 + escalation)^(t−1).
Net cash flow equals (production × rate + annual_credit) − O&M − replacement.
NPV equals Σ cashflow_t ÷ (1 + discount)^t, including year 0.
Simple payback is the first year where cumulative cash flow becomes non-negative.
| Item | Example value | Notes |
|---|---|---|
| System size | 8 kW | Residential rooftop |
| Installed cost | 12,000 | Turnkey price |
| Rebate | 15% | Local program |
| Tax credit | 30% | After rebate basis |
| Annual kWh per kW | 1,400 | Site estimate |
| Energy rate | 0.18 | Per kWh |
| Degradation | 0.6%/yr | Module aging |
| O&M | 150/yr | Basic service |
| Replacement | Year 12: 1,800 | Inverter event |
Solar rebates reduce the initial contract value and can immediately improve affordability. This calculator models a percentage or fixed rebate, capped at total installed cost, then recomputes the remaining project basis. By comparing scenarios side by side, you can quantify how incentives reshape the capital stack and reduce cash required at commissioning. Track the difference as an upfront reduction and as a change in project value.
Incentives often interact. Some programs calculate credits on the post-rebate basis, while others use the pre-rebate amount. Select the basis option to reflect your jurisdiction. The model then applies the credit percent to the chosen basis and subtracts the credit from net cost to estimate out-of-pocket exposure. Because credits may be claimed later, treat this as an estimate for planning rather than tax advice.
Annual savings are driven by first-year production, site yield per kilowatt, and the local energy rate. The calculator escalates the rate by your assumed annual percentage and degrades production by the selected factor to represent module aging. Optional annual net metering credits can be added to reflect bill credits or export compensation. If you use time-of-use rates, approximate with an average blended rate that matches your bills.
Operational costs matter in long-horizon evaluations. Enter annual operations and maintenance and apply escalation to reflect labor and service inflation. If you expect a major replacement, such as an inverter, specify the year and cost. The cash flow table automatically deducts that expense, revealing its effect on payback timing. Including these events prevents overstating returns and supports realistic reserve planning for facility owners.
For budgeting and procurement, the tool reports simple payback, discounted NPV, ROI, and an estimated IRR from yearly cash flows. NPV uses your discount rate to reflect capital cost and risk. Use these metrics to compare bids, set contingency, and document assumptions for stakeholder review and approvals. Pair results with engineering constraints, roof condition, and interconnection timelines to finalize a buildable scope.
1) What does “rebate impact” mean in this tool?
It is the difference between results with a rebate and results without a rebate, using the same assumptions for production, rates, costs, and time horizon.
2) Should I select credit basis before or after the rebate?
Use the basis required by your local incentive rules. If uncertain, run both settings and compare net cost and payback to understand the sensitivity.
3) Why can payback be “n/a”?
Payback becomes “n/a” when cumulative net cash flow never reaches zero within the analysis period, often due to low savings, high costs, or large replacements.
4) How is NPV calculated here?
NPV discounts each year’s cash flow using your discount rate, including the year‑0 net out-of-pocket cost. It helps compare options with different timing and risk.
5) Does the IRR include financing or taxes beyond the credit?
No. IRR is estimated from the modeled cash flows only. Loan payments, depreciation, and broader tax effects are not included unless you add them as costs or credits.
6) What inputs matter most for accuracy?
Installed cost, first-year production per kW, energy rate, escalation, and degradation usually drive results the most. Confirm these with quotes, shading analysis, and recent utility bills.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.