Solar ROI Calculator
Estimate solar panel efficiency, electricity savings, and payback period
Estimates
Annual Savings
Annual Generation
System Size
20-Year Profit
What is Solar Calculator
Run the payback maths on a rooftop PV system: enter usable roof area, total installed cost, your electricity price, average daily sun hours and system efficiency — the tool estimates annual generation, annual savings, the payback period and a 20-year profit figure. Sign-in required.
How to use Solar Calculator
- Enter usable roof area, installed cost and your price per kWh
- Set daily sun hours and system efficiency
- Calculate and read generation, savings, payback and 20-year profit
Frequently asked questions
How much power fits on a roof?
The tooltips assume roughly 150–200 W per square metre — a 50 m² roof hosts about a 7.5–10 kW array. Shading, panel orientation and setbacks cut that in practice.
What efficiency should I enter?
75–80% covers inverter losses, wiring and gradual degradation for a typical system. Enter sun hours from local irradiance data — often 3.5–5 peak hours depending on region.
Is the 20-year figure guaranteed?
No — it assumes constant generation, price and no maintenance or replacement costs. Panels degrade ~0.5%/year and tariffs change, so treat it as a planning estimate, not a promise.
Is Solar Calculator free?
Solar Calculator is completely free — open the page and use every feature with no hidden charges.
Do I need to download or install Solar Calculator?
No download or installation is needed. It is an online tool that runs in the browser on your phone, tablet and computer.
Do I need an account to use Solar Calculator?
No. Use the tool right away — no account or sign-in required.
Does Solar Calculator work on mobile?
Yes. The page is fully responsive and works on phones, tablets and desktop browsers.