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Solar Payback Calculator for Sri Lanka: Rooftop Cost, Savings and Years to Repay

Enter the size of a rooftop system, what it costs installed, the peak sun hours on your roof and the export rate, and the tool shows the years to pay the cost back and a 20 year table of benefit.

Maintained by Hirantha Sandaruwan Lakshan. Rules checked 28 October 2026 against PUCSL, Annex 2: Summary of Approved Feed in Tariffs and 3 more sources.

About this tool

You can value the power two ways: Net Plus, where every unit is sold and the bill stays as it is, or use on site with the surplus sold. The default export rate, Rs. 23.11 a unit for new systems up to 10 kW, is the one the PUCSL set from 25 August 2026. Every rate is a box you can edit, so the answer is only as good as your inputs.

How it works

Yearly output is system kW times peak sun hours a day times 365 times the performance ratio. The performance ratio is the share of the panel rating that reaches the meter after heat, wiring and inverter losses. The defaults of 4.5 hours and 80% give 1,314 units a year for each kW, which is a cautious planning figure, not a measured one. The Ministry of Energy gives a wide range of sunshine across the island, so use your installer's estimate for your roof. Output then falls by the degradation rate each year, which you can set to zero.

In the Net Plus mode, every generated unit is paid at the export rate for the contract years, and your power bill is not reduced because generation and consumption are metered apart. After the contract the tool uses the rate you enter, which is zero by default because no later rate is known. In the use on site mode, units you use yourself save the tariff you type, up to your yearly use, and the rest earns the export rate. You can add a yearly tariff rise.

Simple payback is the cost divided by the year 1 benefit. The table payback adds each year's benefit, with degradation and the end of the contract, and finds the point where the running total passes the cost, counting part of a year. It reads Not within 20 years when that never happens in the table.

The tool leaves out inverter replacement, upkeep, loan interest, tax, batteries and any change to the export rate after 24 February 2027. Prices and rates are inputs, not live data, so confirm the scheme, rate and contract length with CEB or LECO and compare written quotations. Nothing you type leaves your browser.

Worked examples

5 kW system under Net Plus

5 kW x 4.5 hours x 365 x 80% = 6,570 units in year 1. At Rs. 23.11 that is 6,570 x 23.11 = Rs. 151,833. A cost of Rs. 1,500,000 gives a simple payback of 1,500,000 / 151,833 = 9.9 years. With 0.5% yearly degradation and the rate paid for 12 years, the table payback is 10.1 years and the 20 year net gain is Rs. 272,713.

Same system used on site

A home using 300 units a month uses 3,600 units a year. Using 60% of 6,570 would be 3,942 units, which is capped at 3,600. At a tariff of Rs. 44 that saves Rs. 158,400, and the 2,970 surplus units at Rs. 23.11 earn Rs. 68,637. Year 1 benefit is Rs. 227,037, so simple payback is 6.6 years.

Lower sun, higher cost

Change the sun hours to 4.0 and the cost to Rs. 1,800,000 in the Net Plus mode: 5 x 4.0 x 365 x 80% = 5,840 units, worth Rs. 134,962 at Rs. 23.11. Simple payback is 1,800,000 / 134,962 = 13.3 years, and with the rate paid for 12 years the table says it is not repaid within 20 years.

Export rates for new rooftop systems without storage, from 25 August 2026

System sizeRate (Rs. per unit)
Up to 10 kW23.11
Above 10 kW and up to 40 kW19.15
Above 40 kW and up to 250 kW17.11
Above 250 kW15.81

Frequently asked questions

What is the current price of solar energy per unit in Sri Lanka?

For new rooftop systems without storage, the PUCSL rates from 25 August 2026 are Rs. 23.11 a unit up to 10 kW, Rs. 19.15 above 10 kW to 40 kW, Rs. 17.11 above 40 kW to 250 kW and Rs. 15.81 above 250 kW. They are valid until 24 February 2027, so confirm the latest rate with CEB or LECO.

Is net metering still available for new solar systems in Sri Lanka?

pv magazine reports that systems connected after 5 March 2026 are no longer net metered and go on Net Plus instead. Existing agreements keep their terms. Confirm with CEB or LECO before you buy.

How does Net Plus work?

Two meters keep generation and consumption apart. You pay your normal tariff for everything you use, and you are paid for everything the system generates. That is why the Net Plus mode of this tool does not reduce your bill.

How many units does a 1 kW solar system make in Sri Lanka?

The tool's defaults of 4.5 sun hours and an 80% performance ratio give 1,314 units a year, which is near 110 units a month. That is an assumption, not a measured figure. Sunshine varies a lot across Sri Lanka, and shade, tilt, dirt and location change it, so use your installer's estimate if it differs.

How long is the solar payback period in Sri Lanka?

It depends on the cost, the rate and how you use the power. With the default numbers in the tool, a 5 kW system costing Rs. 1,500,000 repays in about 9.9 years under Net Plus and about 6.6 years when most output is used on site. Your own quotation and bill will give different answers.

How long does the export rate last?

A report on the 2026 change says new Net Plus agreements are limited to a maximum of 12 years, and the tool defaults to 12 years. Check the term in your own agreement, and change the box if it differs.

Does the calculator include loans, batteries or tax?

No. It leaves out loan interest, batteries, tax, inverter replacement and upkeep. Add them to the cost or compare them separately with a loan calculator.

Updated Oct 28, 2026