What is the Smart Export Guarantee?

The Smart Export Guarantee (SEG) is a UK obligation, in force since January 2020, requiring larger electricity suppliers to pay households for solar electricity they export to the grid. It replaced the Feed-in Tariff, which closed to new applicants in March 2019. Unlike the Feed-in Tariff, the SEG does not set the rate: each supplier decides what it pays, subject only to the rate being greater than zero.

How much do UK suppliers pay for exported solar electricity?

Export rates are set independently by each supplier and differ by more than an order of magnitude between the lowest and highest offers. Because the rate is a commercial decision rather than a regulated figure, it can change, and being on a competitive import tariff does not mean you are on a competitive export rate.

Is a home battery worth it in the UK?

It depends on how much electricity you use, when you use it, and what your export rate is. A battery earns its money by letting you consume electricity you would otherwise have exported at a low rate, so the saving is the gap between your import price and your export rate. For households with low consumption, an oversized battery, or a high installed cost per kWh, a battery often does not recover its cost within its warranty.

Why does Aperture Solar publish a range instead of one number?

Because a single figure implies a precision no yield model has. Weather varies year to year, tariffs move, and household consumption is never exactly what a profile says. We publish an expected figure alongside a lower bound the model stays above in nine out of ten simulated years, so the number you plan with is stated rather than hidden.

Do I have to give an email address to see my result?

No. The calculator shows your full result before asking for anything: the expected figure, the lower bound, the payback period and the verdict. The email field appears after the result and is optional.

/ Output, anywhere
/ What it is worth
/ When the answer is no

Most people with solar have never checked what it produces or what they are paid for it. Work out both from published yield data, in your own currency, and find out whether a battery is worth buying, including when it is not.

Every figure on this site is computed from a named source, or it is not published

What your solar
actually earns you.

Estimate what mine produce Read the guides

Showing: London

A 4 kWp roof here, facing the south, produces about

3,974kWh a year

Give or take 151 kWh from weather alone, which is 3.8% and is why we publish a range rather than a number.

Per kWp: 993.4 kWh
Source: PVGIS SARAH2
Averaged over: 2005–2020

Run it for your own roof

What you get back

The engine does not hand back a flattering number. It hands back a number with edges, and the reason for them.

See the number,
and its edges.

From a roof anywhere to a figure you can check line by line: what it produces, what that is worth in your money, and where the honest floor sits.

Estimate what mine produce Read the guides

01A range, not a single numberThe expected figure and the floor the model stays above in nine of ten simulated years.

02Your actual bill, rebuiltWe reconstruct a real energy bill line by line. If that is wrong, you have no reason to believe the rest.

03Including the answer “do not buy”When a battery will not earn its cost back inside its warranty, the page says so plainly.

What electricity costs

Electricity costs 64% more than it did in 2019.

That is the Ofgem cap, the regulated price most households pay. Here is what it has actually done, including the two quarters it fell, because a page that only showed you the rises would not be worth reading.

January 2019Cap launched16.00p

Jan–Mar 202627.69p

Apr–Jun 202624.67p

Jul–Sep 202626.11p

The cap resets every three months, and the last three moved down, down, then up. Anyone telling you what it does next is guessing, and that includes us.

And 57.19p a day is charged before a single unit is used, which no amount of solar removes.

That is the real case for generating your own: not a prediction that prices will climb, but the fact that nobody can tell you they will not. Electricity you generate and use yourself costs the same whichever way the cap moves. What it is worth depends on your roof, your usage and the rate you are paid for the rest, which is exactly what the calculator works out, and it will tell you when the answer is no.

Work out my figures

Unit rates for a direct-debit customer on the default tariff cap, published by Ofgem.

Quick estimate

What would a roof where you are produce?

Every step on screen, so you can check it on paper. Your own prices, your own currency, nothing converted.

Full calculation, Great Britain

Nearest locationPick the closest. Sunlight is the single biggest difference between one roof and another.Array sizeOn your installation paperwork. Roughly 0.4 kWp per modern panel.

kWp

Which way does the roof face?In the northern hemisphere a south-facing roof is the best one.Roof pitch

How much do you use at home? 35%The share of generation used in the house rather than exported. Nobody can know this without half-hourly data, so it is yours to set. Move it and watch the answer change.

CurrencyWe never convert. Enter your own prices in your own money.

You pay¢ per kWhYou are paid¢ per kWh

Both come off your own bill: what you pay for a unit, and what your supplier pays you for one you export. We do not fill these in for you, because the rate that matters is yours and it is not the national average.

Estimated annual generation

3,322 kWh

Glasgow, United Kingdom. Weather alone moves this by about 3.2% either way from one year to the next, before anything else is uncertain.

What that is worth, at 35% self-consumption

Enter what you pay for a unit of electricity, on the left, and this becomes a number. We will not guess it: electricity prices differ by more between two households in one country than between two countries.

The working

Every step, so you can check it on paper or redo it with different assumptions.

1
Start from published yield for your locationGlasgow, facing the south at 35°, from PVGIS PVGIS-SARAH2
830.6 kWh/kWp
2
Adjust for which way the roof facesFacing south (best) is 0%, measured at Manchester
× 1.000
3
Adjust for the pitch35° is 0% against 35°
× 1.000
4
Multiply by the array size831 kWh/kWp × 4 kWp
3,322 kWh
5
Split it into what you use and what you export3,322 kWh × 35% used, 65% exported
1,163 kWh / 2,160 kWh

What this estimate cannot do

It assumes nothing shades the roof. A chimney, a flue or a tree is not in these numbers, and object shading is the largest single reason a real array underperforms its model.
It uses the nearest city we hold, not your address, and orientation adjustments measured at Manchester for latitudes above 48°. For an exact figure, put your own coordinates into PVGIS.
It combines the orientation and pitch adjustments by multiplying them, which is an approximation. They are not strictly independent.
It says nothing about whether a battery is worth buying, because that depends on when you use electricity rather than how much.
It is not calibrated. There is no lower bound here, and you should not plan against the headline number.

Why real output is lower Where we model tariffs too

Yield from PVGIS 5.2 (European Commission Joint Research Centre), PVGIS-SARAH2, 2005–2020 average, 14% system loss, roof-mounted crystalline silicon. Retrieved 2026-09-12.

Limits

What these figures are, and what they are not

Modelled, not measured. Yields come from simulated weather rather than readings from your roof.

Our engine was built for the Dutch market, where the export rate is fixed by statute as a share of the import price. UK export rates are set independently by each supplier, so our UK tariffs are provisional and these figures are directional until the engine models them natively.

Our one physics validation against a real site did not meet the accuracy threshold we set. Until a field pilot says otherwise, treat these as well-reasoned estimates.

Tariffs change. Every figure on this site carries the date it was checked.

The lower bound is a modelled likelihood, not a guarantee, and no one is underwriting it.

Read the method

For installers

Your customers already distrust the number on your quote.

Give them a range with a floor you can defend, on your letterhead. Built from the same engine that produced the calculation they arrived holding.

Request a demo

What your solaractually earns you.

See the number,and its edges.