Plan solar spending with realistic production and pricing. See yearly savings, taxes, and maintenance quickly. Download cashflow reports and share results with investors easily.
These sample values illustrate a typical residential scenario. Use the “Load example inputs” button to populate the form.
| Parameter | Example value | Notes |
|---|---|---|
| System size | 5.0 kW | Context only |
| Installed cost | $3,500 | Before incentives |
| Annual production | 7,500 kWh | Year-1 output |
| Self-consumption | 70% | Rest exported |
| Grid rate | $0.18/kWh | Value of used energy |
| Export rate | $0.08/kWh | Value of sold energy |
Yearly energy: E_y = E_1 × (1 − d)^(y−1)
Tariff escalation: R_y = R_1 × (1 + g)^(y−1)
Gross benefit: B_y = (E_y×s)×R_y + (E_y×(1−s))×X_y
Net cashflow: CF_y = B_y − O\&M_y − Ins_y − Repl_y − Debt_y − Tax_y
NPV: NPV = Σ CF_t / (1 + r)^t
LCOE: LCOE = PV(Costs) / PV(Energy)
Annual kWh is the strongest driver of returns because it sets the value stream that tariffs and escalation apply to. Use a site-specific estimate based on orientation, shading, and inverter limits. The degradation input reduces output each year using a compounding curve, which better reflects long-term module aging than a flat annual subtraction. Validate using monthly production data and expected performance ratio.
The model separates self-consumed energy from exported energy. Self-consumption is valued at the grid rate because it offsets purchases, while exported energy is valued at the export rate. When rates escalate annually, both values rise over time, which can materially improve NPV for markets with high retail inflation and stable interconnection rules. If you have time-of-use pricing, adjust rates to reflect peak periods.
Returns are computed from net yearly cashflows: benefits minus O&M, insurance, taxes on savings, inverter replacement, and optional debt service. O&M and insurance can be escalated with inflation to keep future-year expenses realistic. A scheduled inverter replacement protects results from appearing overly optimistic during longer analysis periods. You can model reserves by increasing annual O&M for monitoring and minor replacements.
Simple ROI summarizes lifetime benefits relative to lifetime outflows, while payback highlights how quickly cumulative cashflow turns positive. NPV discounts future cashflows using your chosen rate to reflect opportunity cost. IRR is an approximate discount rate that makes NPV near zero, useful for comparing against alternative projects with different time profiles. Use LCOE to benchmark delivered energy cost against your utility price path. When comparing options, keep the analysis period consistent and review cumulative cashflow beyond payback.
If financing is enabled, debt payments reduce early cashflows and can shift payback even when total benefits stay similar. Review multiple scenarios by adjusting down payment, loan APR, and loan term. For sensitivity, vary self-consumption and the grid rate; these inputs often cause larger swings in NPV than modest changes in O&M. Because export policies can change, run conservative and best-case scenarios, then share the CSV or PDF.
It is the installed cost after applying an incentive percentage and any fixed rebate. It represents the project amount to be funded through cash or financing before ongoing operating costs.
Payback is the first time cumulative cashflow becomes positive. The calculator linearly interpolates within the payback year to estimate a fractional year value for smoother comparisons between scenarios.
IRR requires cashflows that cross from negative to positive in a way that creates a valid solution. If cashflows never produce an NPV sign change within the search range, the calculator reports N/A.
Grid rate values the energy you use on-site because it offsets purchases. Export rate values surplus energy sent to the grid under your utility compensation method, such as net billing or buyback.
Use a rate that reflects your alternative return, risk tolerance, and financing costs. A higher discount rate reduces the present value of future savings, making NPV more conservative.
The calculator provides optional inputs for incentive percent, fixed rebate, and a simplified tax on savings. For jurisdiction-specific rules, confirm details with your accountant and local program documentation.
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.