Solar ROI Calculator Widget
Add a solar payback calculator to an installer's quote page or an energy blog. Readers enter the system cost, any incentive, the yearly production and their electricity price, and see the payback year, the net savings over 25 years, the return on investment and a chart of cumulative savings.
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Under the widget on your page: Powered by A2Z Tools
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<iframe src="https://a2z.tools/embed/w/solar-roi-calculator" title="Solar ROI Calculator by A2Z Tools" width="100%" height="1180" style="border:0;width:100%" loading="lazy" allow="clipboard-write"></iframe>
A plain iframe. Works everywhere, including site builders that strip scripts. Adjust height if your content needs more room.
<div data-a2z-widget="solar-roi-calculator" data-height="1180"></div> <script async src="https://a2z.tools/embed.js"></script>
Adds a small script (what it does) that sizes the widget to fit its content, loads it lazily and keeps it isolated from your page's CSS.
Works with
How it works
The widget runs a year-by-year cash flow. In year t the system produces the first-year output reduced by panel degradation, P x (1 - d)^(t-1), and each kWh is valued at the electricity price grown by the yearly tariff rise, p x (1 + e)^(t-1); maintenance is subtracted. The default degradation of 0.5% a year is the median of almost 2,000 field measurements reviewed by NREL's Jordan and Kurtz. Cumulative savings start at minus the net cost (installed cost less the incentive) and climb each year; payback is the point the line crosses zero, interpolated within that year. ROI is the cumulative figure at the end of the analysis divided by the net cost - a simple, not annualised, return. A 6 kW system costing 18,000 that makes 8,400 kWh against 0.17 per kWh, with 2.5% tariff rises, pays back in 11.4 years and nets 27,666 over 25. Costs can be entered as a total or per watt, incentives as a percentage or an amount.
Calculation method
- Net cost = installed cost (or cost per W x kW x 1000) - incentive (percent of cost or fixed amount)
- Production_t = year-1 kWh x (1 - degradation)^(t - 1); price_t = price x (1 + escalation)^(t - 1)
- Saving_t = production_t x price_t - maintenance; cumulative_t = -net cost + sum of savings to year t
- Payback = (t - 1) + (-cumulative_(t-1) / saving_t) in the first year cumulative turns >= 0
- ROI = cumulative at year N / net cost x 100
Worked examples
US home system
Inputs: 6 kW; 18,000 installed; no incentive; 8,400 kWh a year; 0.17 per kWh; 2.5% tariff rise; 0.5% degradation; 25 years
Result: Payback 11.4 years; net savings 27,666; ROI 153.7%
Year-1 saving 8,400 x 0.17 = 1,428; savings over 25 years 45,666 minus 18,000.
Textbook check with rising tariffs
Inputs: 10,000 cost; 5,000 kWh; 0.20 per kWh; 3% rise; no degradation
Result: Payback 8.9 years; net savings 26,459; ROI 264.6%
Savings = 1,000 x (1.03^25 - 1) / 0.03 = 36,459; minus 10,000.
Flat case
Inputs: 10,000 cost; 1,000 a year saved; no rise, no degradation
Result: Payback 10 years; net 15,000; ROI 150%
10,000 / 1,000 = 10 years; 25 x 1,000 - 10,000.
An estimate for planning, not a quote or financial advice.
Limitations
- Assumes every kWh produced replaces a kWh bought at the retail price; export tariffs, net-billing rules and time-of-use rates can lower the value.
- No financing, discounting, inverter replacement, insurance or tax on savings is modelled.
- Production and price paths are smooth assumptions; real years vary with weather and tariff changes.
Where publishers use it
- Solar installers' proposal and landing pages next to the quote
- Energy-saving and personal-finance blogs weighing rooftop solar
- Utility and co-operative pages on net metering
- Housing-society and RWA newsletters planning a common-area system
- Sustainability reports for small businesses
Questions
What is a good payback period for solar?
It depends on the price you pay for grid power and the installed cost. At 3.00 per watt and 0.17 per kWh a 6 kW system pays back in about 11 years; at 60 per watt and 8 per kWh in India it is about 5 years. Many panel makers offer 25-year performance warranties, so a payback well inside that leaves years of savings.
Why include panel degradation?
Panels slowly lose output. NREL's review of nearly 2,000 measurements found a median loss of 0.5% a year. On 1,000 a year of savings with no tariff rise, 0.5% degradation trims the 25-year total from 25,000 to about 23,556.
What tariff rise should I assume?
Use your own utility's history; 2-3% a year is a common planning figure. With 3% a year, 1,000 of first-year savings grows to 36,459 over 25 years instead of 25,000 - the assumption matters, so try a low and a high value.
Should I enter the tax credit or subsidy?
Only an incentive you are sure to receive and can use. Credits and subsidies change by country, state and year, so check the current rules; enter it as a percentage of cost or a fixed amount.
Where does the production figure come from?
From your installer's proposal, or from a modelling tool such as NREL PVWatts (US) or the EU's PVGIS. The Solar Output Calculator widget estimates it from system size, peak sun hours and performance ratio.
Is the ROI annualised?
No. It is net savings over the whole period divided by the net cost, so 153.7% over 25 years is not 153.7% a year. Compare investments over the same horizon.
How does net metering affect payback?
Under full retail net metering every exported kWh earns the retail price and this widget's assumption holds. Under net billing or export tariffs, exported energy earns less, so payback lengthens unless most of the output is used on site during daylight - for example by shifting dishwasher, laundry or EV charging to midday.
Sources
- Photovoltaic Degradation Rates - An Analytical Review (Jordan & Kurtz, NREL/JA-5200-51664) - National Renewable Energy Laboratory (copy in the UNT Digital Library) . Nearly 2,000 degradation rates from the literature show a median value of 0.5% per year (mean 0.8%).
Cite or recommend this tool
If you reference this tool in an article, course or documentation, these formats are ready to copy. They are optional - nothing is added to your site unless you paste it.
A2Z Tools Solar ROI Calculator https://a2z.tools/embed/solar-roi-calculator
<a href="https://a2z.tools/embed/solar-roi-calculator">A2Z Tools Solar ROI Calculator</a>
[A2Z Tools Solar ROI Calculator](https://a2z.tools/embed/solar-roi-calculator)
Solar ROI Calculator by A2Z Tools - https://a2z.tools/embed/solar-roi-calculator
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