Everyday & Conversion · Solar & net metering
Solar Panel Payback Calculator
How long until the system pays for itself. Units you use yourself are worth your full tariff; units you export are worth the buyback rate — and that gap decides the answer.
Year by year
When you get your money back
| Year | Units generated | Saving | Cumulative | Position |
|---|
Only the first years up to payback are listed, plus a total line for the full system life.
Step by step
How the payback is worked out
Generation
System size × peak sun hours × efficiency after losses, every day of the year.
Split the units
What you consume on site, and what goes to the grid — they are worth different amounts.
Value each part
Self-used units at your tariff, exported units at the buyback rate.
Run it forward
Reduce output by the degradation rate each year and accumulate until the outlay is recovered.
Reading the result
Self-consumption is worth more than export
A unit you use while the sun is shining saves you the full retail tariff. A unit you export earns whatever the buyback arrangement pays, which under net billing is considerably less.
So two households with identical systems can have very different paybacks depending on when they use electricity. Running the washing machine, the pump and the iron during daylight is worth real money, and it costs nothing to change.
Degradation and derate are not pessimism
Panels produce slightly less each year, and a system never delivers its nameplate rating in practice — heat, dust, wiring losses and inverter efficiency all take a share. Dust matters more in Pakistan than most places; an unwashed array in a dry summer loses a noticeable percentage.
A payback calculated at nameplate output with no degradation will be optimistic by years.
The regime you are on changes the answer
A system installed under the older net metering terms and one installed under net billing do not have the same economics, because exported units are valued differently.
The net metering and net billing calculator shows that difference on a month's meter reading.
Where this stops
This models generation and savings from figures you enter. It does not price inverter replacement partway through the system's life, which is a real cost, nor battery storage if you add it.
FAQs
Solar payback FAQs
Why are the units I use myself worth more than the ones I export?
A unit you consume on site replaces a unit you would have bought at your tariff, so it is worth the full retail rate — including the slab you are sitting in. A unit you export is bought from you at the buyback rate under your net-metering agreement, which is normally well below retail. That gap is the single biggest driver of payback, which is why the split between self-consumption and export is an input here rather than an assumption.
What are peak sun hours?
Not daylight hours. It is the equivalent number of hours per day at full rated irradiance, and across most of Pakistan the annual average sits somewhere around four and a half to five and a half, better in the south and worse in a northern winter. Use a figure for your own location and remember it is an annual average, not a summer day.
What does the derate factor cover?
Everything between the panel rating and the meter: inverter losses, wiring, heat, dust and soiling, shading, and module mismatch. Dust alone is a serious factor in much of Pakistan and it is the one you can do something about. A system with no derate factor exists only in a brochure.
Is the payback figure conservative or optimistic?
It is exactly as conservative as your inputs. What the calculation does not include is the tariff rising over time — which shortens payback, often substantially — and it does not include inverter replacement partway through the system life, which lengthens it. It also assumes the buyback arrangement continues on the same terms, which is a policy question, not an engineering one.
Does it account for panels getting weaker?
Yes. Output is reduced each year by the degradation rate you enter, and both the payback point and the lifetime total are computed on the declining figure rather than on a flat first-year saving repeated. Most panel warranties describe a degradation curve — use the number from yours.
Should I include the cost of batteries?
Include whatever you are actually buying in the installed cost. Note that a battery mainly shifts when you use your own generation rather than creating new units, so on a grid-connected system with net metering it usually lengthens payback while improving your position during load shedding. Those are different objectives and worth being clear about before you buy.
Is net metering the same everywhere in Pakistan?
No — terms, buyback rates and approval processes differ by distribution company and have been revised more than once. The rate is an input here for that reason. Confirm the current terms with your DISCO before treating an export figure as fixed for the life of the system.
Related tools
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Build your bill from units, slabs, fuel adjustment and taxes to find your real per-unit rate.
Open Electricity Bill Calculator