Solar Cost Recovery Calculator

• Total cost (size mode): Total = Size(kW) × 1000 × Cost per watt.
• Tax credit: Credit = max(0, Total − Rebate) × (Credit% / 100).
• Production with degradation: kWh_y = kWh₁ × (1 − d)^y−1.
• Tariff escalation: Rate_y = Rate₁ × (1 + e)^y−1.
• Effective rate: EffRate_y = Rate_y × (Self% + Export% × Credit%).
• Gross savings: Savings_y = kWh_y × EffRate_y.
• Net cash flow: Net_y = Savings − O&M − Replacement − Debt + Incentives.
• Loan payment: PMT = P·r·(1+r)ⁿ / ((1+r)ⁿ−1), with monthly r and n months.
• NPV: NPV = Σ Net_t / (1 + discount)^t, including Year 0.
• Payback: First year where cumulative cash flow becomes non‑negative.

1. Enter your system cost (or estimate it from size and cost per watt).
2. Add rebates, estimated tax credit percent, and any one‑time Year 1 incentive.
3. Provide Year 1 production, tariff, escalation, and net metering assumptions.
4. Set degradation, maintenance costs, replacement events, and a discount rate.
5. Select cash or loan financing, then submit to view payback and NPV.
6. Use the CSV and PDF buttons to download the year-by-year schedule.

Payback Timing Drivers

Payback is the first year when cumulative cash flow becomes non‑negative. It moves fastest when Year 1 production is strong, the retail rate is high, and incentives offset upfront cost. If your self-consumption is 70% and export credit is 80%, the model values each exported kilowatt-hour at 0.8× the retail tariff, which usually lengthens payback versus full retail credit.

Cash Flow Quality Beyond Payback

Net present value converts future savings into today’s money using the discount rate. A higher discount rate penalizes late benefits, so long lifetimes and high tariff escalation matter more when the discount rate is low. Internal rate of return summarizes annualized performance from the same cash-flow series, improving comparisons with deposits, bonds, or equipment upgrades. Discounted payback adds a timing lens when two options have similar simple payback.

Production and Tariff Sensitivity

Yearly production falls by the degradation rate, so 0.5% per year reduces output about 12% over 25 years. Tariff escalation compounds in the opposite direction, raising the value of each kilowatt-hour over time. Small changes in these rates can shift NPV materially, so use conservative assumptions when your tariff history is uncertain or your site has shading variability. If export credit drops from 80% to 50%, lifetime savings can decline sharply in export-heavy homes.

O&M and Replacement Risk

Maintenance is modeled as a Year 1 cost that escalates annually, covering cleaning, monitoring, and minor repairs. The inverter replacement line lets you stress-test midlife expenses; placing a replacement in year 10 to 15 is common for many string inverters. Adding a realistic replacement cost protects your forecast from surprise cash outflows and avoids overstating lifetime net benefit. When comparing bids, align O&M with warranty terms and local cleaning frequency.

Financing Scenario Comparison

Cash purchase concentrates cost in Year 0, then savings accumulate without debt. Loan mode separates a down payment from a monthly payment stream over the loan term, which can delay payback but preserve liquidity. Compare both modes using identical inputs, and confirm whether interest cost is justified by the cash you keep available. If you expect to claim a tax credit in Year 1, plan its timing against loan payments.

FAQs

Which inputs affect payback the most?

Installed cost, Year 1 production, your electricity rate, and incentives dominate payback. Self-consumption and export credit matter when exports are significant. Higher O&M, debt payments, or a replacement cost can delay break-even.

How can I estimate Year 1 production?

Use an installer proposal, utility interconnection study, or a reputable PV modeling tool. Start with expected annual kWh for your location, tilt, and shading, then enter that as Year 1 production.

What does export credit percent mean?

It’s the value of exported energy relative to the retail tariff. At 80%, each exported kWh earns 0.8 times the retail rate. Set it based on your net metering rules or buyback tariff.

Why is discounted payback often longer?

Discounting reduces the present value of future savings. When savings arrive later, they count less today, so cumulative discounted cash flow turns positive after the simple, non-discounted payback point.

What discount rate should I use?

Use your opportunity cost of capital: a conservative household rate might be 4–8%, while a business may use a higher hurdle rate. Consistency matters most when comparing scenarios.

Can I compare cash and loan results fairly?

Yes. Keep the production, tariff, and incentive assumptions the same, then switch purchase mode. The difference you see is driven by down payment and interest cost, not changes in energy performance.