Off-Grid Solar ROI Calculator 2026
- Payback period, NPV and 25-year net savings are the three key metrics for evaluating solar ROI.
- Most off-grid systems in moderate-sun areas show payback in 6–10 years and strongly positive NPV.
- Generator replacements and remote properties show the fastest payback — often under 3 years.
- The higher your electricity rate and the more sun you get, the better your ROI.
- DIY installation cuts payback period by 30–40% compared to professional installation.
Solar ROI Calculator
Understanding the metrics
Payback period
The year when cumulative savings equal total system cost (including replacements). Simple and intuitive — before this year you're in "debt" to the system; after it, every dollar of savings is pure return.
Net present value (NPV)
The most rigorous financial metric. Discounts all future cash flows to today's dollars using your cost of capital (discount rate). A positive NPV means the solar investment creates more value than leaving the money at your discount rate. Use your actual cost of capital: savings account rate if paying cash, loan interest rate if financing.
Total ROI
25-year net savings divided by system cost, expressed as a percentage. A 300% ROI means you made 3× your investment back over 25 years — roughly 12%/year compounded, which compares favourably to most financial instruments.
ROI benchmarks by scenario
| Scenario | Typical payback | 25-yr net savings |
|---|---|---|
| Remote cabin replacing generator ($400/mo) | 2–3 years | $60,000–$100,000 |
| Full-time RV ($600/mo campground fees) | 3–6 months | $100,000+ |
| Home in California ($250/mo bill) | 5–7 years | $60,000–$90,000 |
| Home in Texas ($150/mo bill) | 7–10 years | $35,000–$55,000 |
| Home in Louisiana ($100/mo bill) | 12–16 years | $15,000–$25,000 |
Frequently asked questions
What discount rate should I use?
If paying cash and your alternative is a savings account (4–5% in 2026): use 5%. If financing at 8%: use 8%. If you'd invest in equities (historical ~8–10%/year): use 8–10%. At 5% discount rate, most off-grid systems in moderate-sun areas show strongly positive NPV.
Why does the calculator show battery replacement at year 12?
LiFePO4 batteries at 1 cycle/day reach end of useful life at approximately 3,000–4,000 cycles — around 10–12 years. This is a real cost that affects your ROI and should be planned for. See our component lifespan guide.
How accurate is this calculator?
The model captures the main financial drivers: savings with electricity price inflation, system degradation (implicitly through the maintenance cost), mid-life replacements and discounting. It doesn't model: state incentives (add these by reducing your system cost), financing interest (use a higher discount rate to approximate), or variable sun by location (your savings input assumes a correctly-sized system).