Money · 5 min read
Export payments, in plain English
How the Smart Export Guarantee works, what has to be in place before payments start, and why part of a solar saving is export income.
Read the guide
Your estimate
We collect data from the sky to inform designs back here on earth.
Give us a postcode and we read the roof from aerial imagery, size an array to fit it and price it with a battery and without one. Every assumption behind the numbers is on this page, and the survey then checks each figure.
- Visits before a price
- None
- Numbers on the estimate
- Ten
- Your bill and the battery
- Variables
Read from above
Measure, design, then price.
Aerial imagery gives us most of what a survey used to start with. We read it before anyone books a visit, so the visit checks our numbers instead of opening a sales conversation.
From roof to price
The metrics.
Each number rests on the one before it. Change an input and everything after it moves.
Size the array
The usable area, less what the array must clear, sets how many panels fit: 14 × 445 W on the example roof, a 6.2 kWp array.
Estimate what it makes
Pitch, orientation, shading and local sunshine set the yearly output: about 5,400 kWh from around 1,640 hours of sunshine on the example roof.
Turn your bill into units
We take your yearly bill, remove the standing charge and divide by the unit rate. A £1,500 bill at 30p a unit with a £210 standing charge is about 4,300 kWh.
Match use against output
We work through the year month by month, setting what the roof makes against when the home uses power. On the example estimate the home uses 28 per cent of what the roof makes as it’s made, or 48 per cent with a battery.
Price it both ways
The system is priced against the market: £7,200–£8,900 installed on the example estimate, or £11,700–£13,400 with a 10 kWh battery.
Work out saving and payback
Units you no longer buy plus units you export give the yearly saving. Set against the installed price, that gives payback: about seven years without a battery, about ten with one.
Example estimate · EX4
The numbers.
What we read from above tells us the array the roof can carry, what it should generate, what it costs installed and when it pays back. Part of the saving comes off your bill and part is paid to you for what you export, so we show the two apart. Add a battery and you’ll see which lines move. The survey checks the roof figures and the price; the saving depends on your tariff and how you use power.
£1,500a year
About 4,300 kWh a year, at 30p a unit on a £210 standing charge, with export paid at 16p. Tariffs and export rates vary by supplier.
System size6.2 kWp
Panels14 × 445 W
Roof area~28 m²
Energy output~5,400 kWh/yr
Sunshine~1,640 hrs/yr
Self-use of what the roof makes28%
Installed£7,200–£8,900
Payback~7 yrs
Saving~£1,080/yr£460off your bill£620exported
Batterynone
Example roof · EX4Every assumption
Payback
Year by year, the saving pays for the system.
What the example roof saves each year covers what it cost installed in about seven years without a battery, about ten with one, if tariffs and use stay as assumed. After that the saving keeps coming, less upkeep such as a replacement inverter.
Units you no longer buy
Power your roof makes while you’re using it, at the price you would have paid.
Units you’re paid for
What you don’t use goes to the grid, paid at your export rate.
What moves it
Paying for it How much of the roof’s power you use, and a battery. These figures assume 30p a unit and 16p for export; both vary by supplier.
The range
Why the price is a range, not a single figure.
An estimate is drawn from the air, and some of what sets the final price can only be seen up close. The rafters may need extra fixings. The consumer unit may need work before it can take the solar circuit. The covering may be harder to fix to than it looked. That is why the estimate gives a range.
The survey is where the range meets the house. The surveyor checks the rafters, the covering and the consumer unit, and explains anything that could move the price before they leave. Until then, we count payback against the middle of the range, so a price near the top pays back a little more slowly.
What the survey checks
Every assumption
Nothing on the estimate is a black box.
These are the numbers behind every figure above, for the example roof. Move the bill or add the battery and they stay the same; only the results change.
- The array
- 14 × 445 W = 6.2 kWp, pitch 35°, facing S–SW
- What it makes
- About 5,400 kWh a year; 11% of it between November and February
- Units you buy
- 30p each, on a £210 yearly standing charge
- Units you export
- 16p each. Export rates are set by each supplier and vary
- Your bill → your units
- (yearly bill − £210) ÷ 30p, to the nearest 50 kWh
- How use is spread
- Month by month, heavier in winter, each month split into five kinds of day from dull to bright
- Direct self-use
- About 5% of daytime use comes in short bursts, such as a kettle or a shower, bigger than the roof can supply at that moment
- The battery
- 10 kWh, 9.5 kWh usable, about 10% lost in charging and discharging; it covers about 82% of what you use after dark
- Installed price
- £7,200–£8,900 without a battery; £11,700–£13,400 with one (+£4,500)
- Payback
- Counted against the middle of each range (£8,050 and £12,550)
- Not included
- Panel ageing, price rises and finance costs
- What the survey checks
- The roof figures and the price. The saving depends on your tariff and how you use power
What the roof makes, month by month
Copies the ten figures above, as they stand now, to paste anywhere.
Your estimate · questions
Asked about the estimate.
01What are the ten numbers?
System size, panels, roof area, energy output, sunshine, self-use, the installed price, payback, the yearly saving and the battery. Each is drawn for your roof. The survey checks the roof figures and the price; the saving and payback depend on your tariff and how you use power.
02Why do you need my electricity bill?
Your bill tells us roughly how many units the house uses a year. That decides how much of the roof’s output you can use at home, which sets the saving and the payback.
03Can the estimate say solar isn’t worth it?
Yes. If the numbers don’t work for your roof, your estimate will say so.
04Does an estimate commit me to anything?
No. It is a set of numbers, not a contract. The next step is a survey, and nothing is signed on that day either.
From the guides
Read more before you decide.
Every guide explains one part of the job in plain English.
Your roof · 5 min read
What an aerial roof reading can and can’t tell you
The six things we read from above before anyone visits, how each one shapes the estimate, and what only a survey can see.
Read the guide
Battery · 5 min read
Battery or no battery: reading your own bill
Where your units go by the hour, how tariffs and export rates change the sums, and one roof priced with and without a battery.
Read the guideKeep reading
The rest of the service.
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Survey day
Roof, loft and meter, checked on site
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Battery storage
Priced both ways, side by side
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Paying for it
Savings, mortgage or a loan
Estimate or survey
Start with a postcode.
Our estimate is free. If you proceed to survey, our partner installer invoices you directly; we receive a referral fee from them, never from you, and it never affects which installer we introduce.
We use these details only to send your estimate and arrange a survey. Privacy Policy
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