Before investing in solar, you want to know the numbers: how much will you save, when will you break even, and what’s your return on investment? Understanding how to calculate solar ROI helps you make a confident, data-driven decision.
The Basic Solar ROI Formula
Solar ROI = (Lifetime savings – Net system cost) / Net system cost × 100
Net system cost is your total installation cost minus the federal tax credit and any state/local incentives. Lifetime savings include the total electricity bill savings over 25 years, including projected rate increases, plus any SREC income or performance payments.
Step-by-Step ROI Calculation
Step 1: Determine your system size and cost. A typical residential system is 6–10 kW costing $15,000–$25,000 before incentives.
Step 2: Subtract incentives. Apply the 30% federal tax credit and any state incentives. A $20,000 system becomes $14,000 after the federal credit.
Step 3: Calculate annual electricity savings. Multiply your system’s annual production (kWh) by your electricity rate ($/kWh). An 8 kW system in an average location produces about 11,000 kWh/year. At $0.16/kWh, that’s $1,760/year in savings.
Step 4: Account for electricity rate increases. With a conservative 2.5% annual increase, your savings grow each year as the electricity you’re avoiding gets more expensive.
Step 5: Factor in ongoing costs. Include inverter replacement ($1,500–$2,500 around year 12) and minimal maintenance ($100–$200/year).
Step 6: Calculate lifetime savings and ROI. Sum up 25 years of escalating savings minus ongoing costs. For our example: 25-year savings of approximately $58,000 minus $14,000 net cost = $44,000 net benefit. ROI = ($44,000 / $14,000) × 100 = 314%.
Payback Period
The payback period is when your cumulative savings equal your net investment. For most homeowners, this occurs at year 6–10. After that, every dollar of savings is pure profit.
Factors That Improve ROI
Higher electricity rates lead to bigger savings. Generous state incentives reduce your net cost. Strong net metering provides full credit for excess production. Increasing electricity rates amplify future savings. South-facing roofs with minimal shading maximize production.
Factors That Reduce ROI
Low electricity rates (under $0.10/kWh) extend payback periods. Significant shading reduces system output. Poor net metering policies reduce the value of excess production. Financing with high interest rates adds cost.
Free Tools to Calculate Your ROI
Google’s Project Sunroof estimates solar potential based on your address. EnergySage’s solar calculator factors in local incentives and rates. NREL’s PVWatts Calculator provides detailed production estimates. Your solar installer should also provide a detailed financial analysis specific to your home.
