Home/ Solar
Three parts, one system. Get the relationship between them right and the maths works.
Panels make the electricity. The inverter makes it usable. The battery decides how much of it you actually get to keep. Most disappointing solar installs come from someone specifying one of those three without thinking about the other two.
Where the money actually comes from
One number decides most of it
Every unit you generate and use yourself is worth about 26p. Every unit you export is worth about 6p. So the single biggest lever on your payback isn’t how many panels you fit – it’s what share of them you use rather than sell.
That’s why we ask whether anyone’s home during the day before we ask anything about your roof, and why we cap the system size we suggest against your actual consumption.
VALUE OF ONE UNIT OF ELECTRICITY
01 · Solar panels
Panels are the easy bit. Getting the system right is harder.
Almost every installer fits similar panels. What separates a system that pays for itself in nine years from one that takes fifteen is everything around them – the sizing, the inverter, the layout, and whether anyone bothered to look at how you actually use electricity.
What a panel actually does
Sunlight hits the panel, the panel makes direct current, the inverter turns it into the alternating current your house runs on. That’s it. There are no moving parts, which is why they last so long and need so little attention.
Panels work in daylight, not sunshine. A bright overcast day in Manchester still produces – just less. Which is exactly why our calculator uses regional yield figures rather than a national average.
No moving parts
25 year performance warranty
kWp
Kilowatt peak, or "system size"
The maximum your system could produce in perfect lab conditions. It’s a size label, not a promise. A 4.4 kWp system in the Midlands makes roughly 3,960 kWh a year, not 4.4.
440W
Panel wattage
The size of one panel. Ten 440W panels make a 4.4 kWp system. Higher wattage panels mean fewer of them for the same output, which matters if your roof is small or awkward.
kWh
Kilowatt hours, the thing you're billed for
Units of electricity. You currently pay about 26p for each one you buy, and get paid about 6p for each one you sell. That gap is the whole reason batteries exist.
Everything else is a rounding error by comparison. These are the exact numbers we apply in the calculator, published rather than hidden.
The three things that change your output
Direction, shade, and the weather where you live
ROOF DIRECTION
East-west is far better than people assume,
and often spreads generation more usefully
across the day.
SHADING
Shade on one panel can drag down a whole string. Optimisers or micro-inverters fix that, at a cost. If you've got a chimney or a big sycamore, mention it early.
WHERE YOU LIVE
A 20% spread top to bottom. Less than most people expect.
Sizing & degradation
More panels isn't automatically better
Filling every square metre of roof looks impressive on a quote. If you can’t use the extra generation, you’re selling it at 6p rather than saving 26p, and the panels that made it take fifteen years to pay for themselves instead of nine.
Panels also get about half a percent less efficient every year. A panel making 100 units today makes about 88 in year 25. Every reputable manufacturer publishes it and warranties against it, and every projection we show you includes it. If a savings estimate doesn’t mention degradation anywhere, it’s flattering itself by roughly 6% over the life of the system.
TYPICAL SIZING BY HOUSE
A starting point, adjusted for your roof and your bill. Not a menu.
OUTPUT OVER 25 YEARS
02 · Battery storage
Your panels are busiest at the exact moment your house is empty.
That’s the entire problem a battery solves. Not “energy independence”. Not “resilience”. Just the mismatch between when electricity gets made and when it gets used
A day in a typical home
With a battery, the surplus at lunchtime gets stored and spent at teatime. Self-consumption typically goes from around a third to around three quarters - and every unit you self-consume is worth 26p instead of 6p.
A battery doesn't always pay
If you’re retired, home most days and already using most of what you generate, a battery adds cost and saves less than the brochure suggests. If the house is empty from eight till six, it’s usually the single best thing you can add.
Our calculator shows you both versions side by side, with the payback year for each, so you can see the difference rather than take our word for it.
Sizing it properly
Most homes land on 5 to 10 kWh usable. Bigger isn’t better – a battery that never fills is money on a wall. Watch the difference between headline and usable capacity; they get quoted with the same number on the front.
Charging from cheap rates
On a time-of-use tariff you can fill the battery overnight at around 7p and use it through the peak. That works even in December, when your panels are doing very little.
Backup during a power cut
Possible, but it needs a specific setup and an extra circuit. It’s a nice-to-have, not a payback item. We’ll price it separately and tell you honestly how often you’d use it.
Lifespan
Typically 10 years or a stated throughput, whichever comes first. Batteries degrade too – usually to about 70% of original capacity by the end of warranty.
Out all day
Empty house between eight and six. Without storage you'd export most of your generation at 6p and buy it back at 26p a few hours later. This is the clearest case there is.
An EV on the drive
Charging at home in daylight is the best possible use of a surplus. A battery lets you keep charging after dark on electricity you made rather than bought.
On a time-of-use tariff
Fill the battery overnight at around 7p, run the house off it through the expensive early-evening peak. This works in January when the panels barely bother.
Probably not worth it if…
You're home most days, your bill is under about £90 a month, and you're already using most of what you generate. We'd rather say so than sell you one.
03 · The full system
The whole system, done properly
Why it matters
Three ways a mismatched system quietly costs you
None of these show up on the day. They show up in year three, when it’s expensive to fix.
01
An inverter that can't take a battery
Every unit your panels make and you use is a unit you don’t buy at 26p. This is where most of the saving comes from – not from selling it.
02
An array sized to the roof, not the bill
Filling every square metre looks impressive. If you can’t use it, you’re selling it at 6p and it takes fifteen years to pay back.
03
No thought given to what's coming
EV in two years? Heat pump in five? That changes the sizing today. It’s the cheapest thing in the world to plan for and the most expensive to retrofit.
Scaffolding
Up, used, and taken down. Not a line item that appears after you've signed. Typically £600 to £1,200 elsewhere.
DNO application
Your network operator has to agree to what you're connecting. We handle it.
Building control notification
Required, boring, and ours to sort out.
Bird protection
Mesh around the array. Cheap now, unpleasant to retrofit once pigeons have moved in.
Isolators and testing
Full commissioning and electrical certificates on handover.
Export tariff registration
MCS certificate issued and your SEG application submitted, so you actually get paid.
Included as standard
What's in the price, so it isn't added later
What to compare between two quotes
None of these show up on the day. They show up in year three, when it’s expensive to fix.
01
Panel wattage and brand tier
“10 panels” tells you nothing. 10 × 400W is 4.0 kWp; 10 × 460W is 4.6. That’s a 15% difference in output for the same roof.
04
Product vs performance warranty
Two separate things. One covers the panel breaking, the other covers it underperforming. Get both.
02
Inverter make and type
String, hybrid or micro. A hybrid means you can add a battery later without replacing it. Cheap quotes often assume you never will.
05
What's included
Scaffolding, DNO application, building control, bird protection, isolators. All of it should be in the price.
03
Usable battery capacity
Quoted capacity and usable capacity are different numbers. Ask for usable kWh, in writing.
06
MCS certification
No MCS certificate, no export tariff. That’s potentially a few hundred pounds a year you’d be giving away.
Four stages, realistic timings, and a clear point at which you can stop without owing anyone anything. No doorstep visits, no salesperson in your kitchen until half nine.
04 · The process
From postcode to switched on
Free roof check
We look at your roof on satellite and talk it through on a call. If it's not right for solar we'll say so.
20 minutes · no obligationYour design & fixed price
A proper system design for your roof, and a price that doesn't move afterwards.
Usually within a weekInstall
Scaffolding up, panels on, inverter and battery in, everything tested and certified.
One to two days on siteSwitched on
Monitoring set up, export tariff registered, and a handover that makes sense.
Same dayThe admin nobody mentions until afterwards
There is a surprising amount of it, and all of it is ours to do. If an installer is asking you to handle any of the below, that’s a flag.
Start to finish it’s usually four to six weeks, and most of that is the DNO application and scheduling scaffolding rather than anything we’re doing on your roof.
DNO application
Under 3.68kW it’s a notification. Above that it needs approval before installation, and that can take two to six weeks.
Building control notification
Solar installs are notifiable work. Ours goes through the competent person scheme, so no separate council application.
MCS certificate
Issued after commissioning. Without it you can’t register for an export tariff.
SEG registration
Your export tariff application, submitted with your MCS certificate and meter details.
Before any of this, get an estimate you can sanity-check. About 60 seconds, and no email needed for the first result.