How long does it take for solar panels to pay for themselves?

Add up what the system saves you each year, then divide what you paid for it by that number. The answer is driven by two figures: what you paid, and what a unit of electricity is worth where you are. Enter your own numbers rather than relying on any typical figure. A good system bought at a high price against cheap electricity can take a long time, and the same system in a different market can pay back in a few years.

I already have solar installed. How do I calculate what it has saved me?

Compare the units you bought from the grid a month before it went in with the units you buy now, and multiply the difference by your unit price. Because both figures are read off your own meter, that is a measurement rather than an estimate. This calculator is a planning tool rather than a meter reader, so it cannot do that comparison for you. It will tell you what the system should be saving, and comparing that with your own bills is how you spot shading, wear or a string that has failed.

How much extra solar capacity do I need to stop buying electricity from the grid?

Two different numbers, and they are not the same. To generate as much as you still buy, divide your remaining units by the units each kilowatt makes where you live. To bring the bill to zero you need more than that, because only the share of generation you actually consume displaces a purchase. The rest is exported at whatever your utility pays. Extra capacity can also be met with a battery, which moves midday power into the evening hours instead of making more, or with an export tariff on what you have not used. Enter your units a year on this page and it will tell you directly whether the size you have is already more than your household can absorb.

How do I work out how much my solar will save me each month?

Use a whole year of bills, not one month, because seasonal variation is large. Take the total you paid, subtract what an average year of solar would have avoided, and the remainder is your net saving. Be careful with any system that has never been metered separately: comparing a summer bill with a winter one produces numbers that look meaningful and are not. If your utility shows solar generation on a separate line, that figure and your unit price give you the answer directly.

Is it better to use my solar power myself or sell it to the grid?

Usually, yes, because a unit you use yourself saves you the full retail rate while the same unit sold to the grid is normally compensated at a lower one. It is a comparison of two prices, not a law: where a tariff pays a good export rate, or where your own consumption is small, the gap can close or reverse. The grid section on this page shows you both prices for your own system, what a spare unit earns you, and how much that shortens your payback.

Is it worth adding a battery to a solar system?

A battery does not make any extra electricity. It stores the power you could not use at midday and saves it for the evening, when electricity is at its most expensive. So it is only worth the money where what you pay per unit is well above what the grid pays you for spare power. If you want a battery for power cuts rather than for savings, size that separately.

What happens to my payback if electricity prices go up?

It gets shorter. Every unit you stop buying is worth more as the price rises, so a system that paid for itself in 10 years at today's tariff may pay for itself sooner over 25 years. We apply that rise to what you pay for electricity year by year. We do not apply it to what your utility pays for your surplus, because no utility is obliged to raise its buy-back price in step with what it charges. We assume a rise of zero so the headline does not depend on guessing, and you can set it in the advanced section to see how much of your return is riding on prices rising.

How accurate is this calculator?

Treat it as a planning estimate, not a quote. It uses a national average yield rather than a survey of your roof, a fixed rate of panel wear, a typical cleaning and repair cost and one inverter replacement, unless you enter your own measured output, which replaces the average entirely. The Yield Estimation tool works out a real figure for your roof, and typing that in replaces the average. Real output also depends on your roof angle, shading, dust and the panels you buy.

When Does Solar Pay For Itself? | Simple Solar Payback Calculator

When does solar pay for itself?

Four things about your own system and household, and we will show you when it pays for itself, how much it can earn over 25 years, what a battery changes, and what your spare power earns when you sell it to the grid. Every figure below traces back to a number you typed or an assumption we have labelled.

Your solar system

How much power the panels make. Your saving is this number multiplied by what a unit of power is worth to you, and your payback is what you paid divided by that saving.

Solar array size (kWp)

Units your system makes a year optional

Why these two are different questions

System size is how big the array is. Units your system makes a year is what that array will actually produce on your roof. They are usually close, but not always: the same 5 kW on an open roof in a cool climate produces far more than 5 kW on a hot, dusty, partly shaded city roof. Leave the second box empty and we multiply your kW by 1,440 units per kW a year, a national planning average.

Real output varies with location, orientation, tilt, shading, temperature, dust, equipment and system losses, so that average is a starting point rather than an answer. If you have a figure from your own bills, from your installer, or from the Yield Estimation tool, type it into the second box. It replaces the average completely, and every figure on the page then follows your number exactly.

Your electricity

How much your household uses, and what one unit is worth to you. The first decides how much of what the panels make you can use at all; the second is what every saving on this page is multiplied out by.

Units you use a year needed

Price you pay per unit needed

Why usage and price are asked separately

Units you use a year is what your household consumes, and it is required. Not because the arithmetic needs it in isolation, but because without it the page has to invent a figure, and everything downstream of that figure then describes a household that may not be yours. It decides what your bill looks like now, whether your system is bigger than your household can absorb, and it sizes a system for you if you have not entered one. If you do not know it, put an average monthly bill in the box under the field and press the button: monthly bill ÷ price per unit × 12.

Price you pay per unit is what a single unit costs you on the grid, taken from your bill rather than from a headline rate. If your tariff rises as you use more, use your top slab rate, and tick "My electricity is charged in slabs" further down to enter the whole ladder. This is the number the whole page turns on: change it from 50 to 25 and every saving on this page halves.

Cost and timing

The cost is the number your payback divides by, and it is the only input that changes the payback without changing your saving at all. When you use power decides how much of what the panels make you use directly, and how much room a battery would have.

What the system costs needed

No quote yet?

When do you use power? needed

How to fill these in

Enter what you were quoted for the installed system, or what you paid for it. If you have no quote yet, the button above fills in a rough number worked out from your system size, clearly marked as ours rather than yours. A real quote is always better: the saving does not depend on this figure, so a cheaper system shortens the payback in proportion.

Solar makes nothing after dark. If your power is mostly used while the sun is up, most of what the panels make is used directly and is worth your full price. If it is mostly used in the evening, more of it is left over and has to be sold at whatever your utility pays, which is normally much less. That single choice moves the export percentage in the grid section more than any other input on the page.

Answer the timing question with a number

…% of your power used while the sun is up

Use 0% if almost all of your electricity is used after dark, or 100% if it is all used while solar is producing. This overrides the dropdown above.

Tell us about your system

Your payback period, what happens to your bill, and what a battery or an export tariff would change all appear here.

Pays back in

--

Upfront cost after any rebate

Average monthly benefit year one, over 12 months

25-year net benefit after running costs

What this assumes

Everything above is arithmetic on those figures. Change any one of them and the payback moves.

Where every figure came from

Estimated energy bill

Now

With solar

Energy bill falls

Your numbers to compare with an installer

This is what you need the system to do, not what to buy. Take it to an installer and ask them to meet it.

The 25 years in detail

Keep paying the energy bill 25 years, no solar

With solar

You keep the difference

How to read this line

This line shows how far ahead or behind you are over time: money saved and earned, minus what the system cost. It starts below zero because you pay for the system before it starts generating savings. When it reaches zero, you have reached payback.

Year-by-year figures

Generation, annual saving and cumulative position at years 1, 5, 10 and 25
Year	Units made	Saved that year	Saved so far	Ahead / behind

What if I have this wrong?

Each card changes a single input and leaves everything else the same, so the difference between two cards is caused by that number and nothing else. Your answer as entered is the first card. They are scenarios, not predictions: they tell you which of your own numbers is worth checking before you sign anything.

Now try the other questions

Same system, one thing changed each time. Tap one to open it.

If you add a battery

What battery are you considering?

Two figures are enough. Size and price are what you know before you buy. Everything the calculation needs beyond those is either assumed and shown, or taken from the datasheet below.

Battery size (kWh)

Nameplate capacity. A sticker on the unit, or a figure on the quote.

Battery price

Installed price if you have one, otherwise the unit price you were quoted.

Use datasheet details for a more accurate result

These four are what a datasheet actually states. Leave them empty and we use the assumptions listed in the amber box, which are typical rather than measured.

% you can actually use

Depth of discharge. The rest is held back so the cells are not damaged.

Round-trip loss, %

Energy lost across a full charge and discharge, both directions together.

Good for about… years

Warranted calendar life. Under 25 years means it is bought again, and that is charged to the year it happens.

A replacement bank will cost

We fill this in at 80% of today's price, because battery prices have fallen. Change it if you expect a different future price.

Array cost panels and inverter

Battery costs

You pay up front array plus bank

Energy it can shift kWh a year

What the battery has to be able to do

This is the specification your system has to meet, not equipment to buy. Ask any installer to quote against it.

Usable storagekWh you can actually draw

Inverter ratingkW to refill it in 5 hours

NameplatekWh as delivered

The 25 years with a battery

How to read this chart

The upper line includes the battery's purchase and any replacement it needs inside 25 years. When it reaches zero, the solar plus battery system has recovered its total cost. The gap between the two lines is what the battery adds.

One unit of power, two ways

Sold to grid

Used yourself

Battery pays for itself in

Extra benefit, first yeara month, before any replacement

Equivalent cyclesfull cycles a year, expected

Sizing a battery for power cuts is a different question. Use the Battery Backup calculator to find the battery and inverter size needed for your loads and backup time.

If you sell spare power to the grid

Export settings

Two figures. What your utility pays for a unit you send back, and when you are paid for it. That price is set by your country and your utility, not by this page, so we ask rather than guess.

Price paid for spare power

What your utility pays for each unit you send back to the grid. Leave it empty and your spare power is assumed to earn nothing.

% of your output you use yourself

You will not use of what your panels make

The grid pays you for each unit you send back

You pay the grid

One unit used yourself is worth more than one unit sold to the grid

Grid income added to your saving

Sell one unit to the grid

Use one unit yourself

Your payback, with grid income selling spare power included

Without any grid income

What selling spare power is worth over 25 years

How to read this chart

The lower line is the same system with nothing earned from the grid. The gap between the two lines is the total value of selling spare solar, and the distance it pulls the upper line forward is what it does to your payback.

Not sure whether your system is the right size for how much you use? Use the System Size calculator.

Tell us more only if the simple answer isn't enough

My electricity price goes up as I use more Most tariffs bill in bands, so a unit of solar is worth your TOP band rate rather than your average one.

Subsidy or rebate

Panels lose % a year

Cleaning & repair, % a year

Electricity price rises, % a year

Zero keeps the headline honest.

Inverter replaced in year

Inverter costs, % of system

How we worked this out

Solar only produces energy while the sun is available. Your daytime-use answer tells us how much of that solar you can use directly, and how much becomes spare power.

Your solar savings come from two places: electricity you use yourself, which avoids buying power from the grid, and electricity you export, which earns the grid's export rate. Self-use is usually worth more when your purchase price is higher than your export rate.

If your tariff has usage tiers, the calculator values the solar against the part of your bill it actually replaces, rather than simply using the average tariff.

We model the year month by month rather than assuming the same solar output every month. Each month we estimate how much of your daytime electricity use solar can cover, then treat the remaining generation as spare. This matters because solar production and electricity use change through the year: extra solar in June cannot automatically cover a shortage in December. The result therefore depends on both how much your system generates and when you use electricity.

We subtract the operating and replacement costs you entered, or the stated assumptions. We also model 0.5% annual panel degradation, so generation gradually falls over time. The base case includes one inverter replacement in year 12. A subsidy or rebate is deducted from the price of the panels and inverter only: it is never applied to a battery.

What this model does not know

It is a monthly model, not an hourly one. Battery results are a monthly estimate of how much energy shifts from one part of the day to another. They are a planning figure, not a simulation of how your bank will actually operate.
The monthly shapes are generic. Generation and consumption follow a standard national seasonal profile. If you have a real monthly generation profile from the Yield Estimation tool, battery results become meaningfully more accurate.
No fixed charges. Everything here is units multiplied by a price. Standing charges, taxes and demand charges are not modelled, so treat the bill figures as your energy charge rather than your whole invoice.
No outages. A backup battery is judged here on what it saves, which is a different question from whether it keeps your lights on.

What can change your payback most

Lower system cost → shorter payback
More solar used yourself → more savings
Higher electricity prices → more savings
Higher export rates → more value from spare solar
Battery → only worthwhile when the extra savings justify its cost and losses

This is a planning estimate, not a quote. For a roof-specific result, use your site's generation estimate and your actual installation price. Confirm the final numbers with a written quote before committing.

Common questions

Where to go next

Take this to your installer

Everything on one card, so they know exactly what you are working from instead of guessing.

Planning estimate only. Your installer should confirm roof orientation, shading and panel choice before anyone signs anything.

This is a planning calculator, not a bankable financial model. It answers three practical questions: when solar pays back, what it can return over 25 years, and what changes if you add a battery or sell your spare power to the grid. It cannot see your roof, shading, equipment or final installation quote, so the result is an estimate. Use it to compare options, then confirm the numbers with a site-specific assessment and written quote before buying.