How this calculator works
This calculator estimates how many years it takes a home solar system to pay for itself in electricity savings, simulated year by year rather than as a single average. Each year, the panels produce slightly less than the year before (a well-documented effect called panel degradation), while the electricity price they offset typically rises — so payback depends on how these two competing trends play out together, not just a static year-one number.
Every dollar figure that goes into this calculator (system cost, any incentive or rebate, electricity price, and price inflation) is something you enter yourself. This calculator does not assume any specific tax credit, utility rebate, or incentive program is available to you — check what actually applies in your location and enter it directly, since incentive programs vary by country, state or utility, and change over time.
Annual production per kW of installed solar capacity varies enormously by location, roof pitch and orientation, and shading from trees or nearby buildings — a system in a cloudy, high-latitude location can produce well under half as much per kW as the same system in a sunny, low-latitude one. The default value here is only a rough starting point; a solar installer's site-specific production estimate for your actual roof is the authoritative number to use.
How the simulation works
Net cost = system cost − incentive/rebate amountYear 1 production = system size (kW) × annual production per kWYear y production = Year 1 production × (1 − degradation rate)^(y−1)Year y electricity price = starting price × (1 + annual price increase)^(y−1)Year y savings = Year y production × Year y price; payback year is where cumulative savings first reach net costThis is a simple savings-based payback calculation, not a full financial model — it does not discount future savings to present value the way an NPV or IRR calculation would, and it assumes all saved electricity has the same value as the price you enter (true for offsetting your own usage, less true if excess production is sold back at a different rate).
Worked example: $20,000 system, no incentive, flat prices
- A 6 kW system producing 1,300 kWh per kW per year generates 6 × 1,300 = 7,800 kWh in year one.
- At $0.15/kWh, year-one savings are 7,800 × $0.15 = $1,170.
- With no price inflation and no panel degradation assumed, savings stay level every year, so payback is simply $20,000 ÷ $1,170 ≈ 17.1 years.
- Over 25 years at this flat rate, total savings are 25 × $1,170 = $29,250 — about $9,250 more than the system cost, even before accounting for any electricity price increases that would improve this further.
Frequently asked questions
Why doesn't this calculator include a specific tax credit or rebate?
Incentive programs differ by country, state, and even utility, and change frequently — asserting a specific percentage or dollar amount here could easily be wrong or outdated for your situation. Enter whatever incentive you have actually confirmed applies to you in the rebate field.
Why does production decline every year?
Solar panels lose a small amount of efficiency annually due to material degradation from sunlight and heat exposure — commonly cited manufacturer figures are in the range of 0.3% to 0.8% per year, which is why this calculator defaults to 0.5% but lets you adjust it.
How accurate is the default 1,300 kWh per kW production figure?
It's only a rough starting point. Actual annual production per kW of solar capacity can vary from under 900 to over 1,800 kWh depending on your latitude, local weather patterns, roof angle and orientation, and shading — a professional solar quote for your specific address and roof will always be more accurate than this default.
Does a shorter payback period always mean solar is a better investment?
It's one useful signal, but this calculator doesn't account for financing costs if the system is loan-funded, maintenance or inverter replacement costs, or the time value of money. It's a straightforward savings-based estimate, not a complete financial analysis.
What if my payback never happens within 25 years?
That usually means the system cost is high relative to the electricity it's expected to offset — worth revisiting the system size, a local price quote, and whether any incentives you qualify for were left out of the calculation.