A south-facing roof is the best orientation in the UK, and it beats south-east or south-west by about 4%. The bigger question is what you do with the midday spike, because a south array either uses it or sells it at 12p.
A south-facing roof at 30 to 40 degrees will generate more electricity per year than any other slope on your house. That part is settled. What almost nobody tells you is that the same feature making it the highest-yielding roof also makes it the hardest to spend the output on, and that gap is worth more money than the orientation itself.
- Expect 820 to 1,050 kWh per kWp per year. That is the full UK spread on a south-facing roof at 30 to 40 degrees pitch, north Scotland to the south coast. A 4.4 kWp array (10 panels at 440W) means about 3,600 kWh in central Scotland and about 4,500 kWh in Devon.
- Budget £5,800 to £7,800 fully installed for that array. London and the South East run £7,000 to £9,500 for the same specification. Prices checked August 2026. VAT is 0% on qualifying installs until 31 March 2027, then 5%.
- Payback lands at 8 to 10 years without a battery. Calculated on the October 2026 price cap of 26.32p/kWh and a 12p export rate. Both of those numbers moved this year, so treat any payback figure without a date attached as unreliable.
- South-facing is the worst orientation for self-consumption. Around 35% of generation gets used in the house without storage, against 45% to 50% for an east-west split. The rest is exported at roughly half the value.
- The thing that most often kills a south-roof install is planning, not shading. On terraces and post-war estates the south slope is frequently the front. In a conservation area, AONB or National Park that means a full application and a 12 to 18 week wait.
- What a south roof generates
- How much you lose off due south
- What it costs in 2026
- The payback arithmetic
- The midday spike problem
- Three ways to design the same roof
- The 3.68 kW ceiling
- Planning on a front elevation
- Choosing panels for a hot roof
- When south is the wrong slope
- Checking your own roof
- What a good quote looks like
- Frequently asked
What a south-facing roof actually generates
Between 820 and 1,050 kWh per kWp per year, depending on postcode. That is the whole UK range for a south-facing roof pitched at 30 to 40 degrees with no shading, and it is a narrower spread than most people expect from a country that runs from Penzance to Shetland.
The figure your installer should be using is the Kk value from MCS standard MIS 3002. MCS divides the UK into 21 postcode zones, each with a table of kWh per kWp for every combination of pitch and azimuth. The data comes from the European Commission’s PVGIS dataset with a performance ratio of 0.8 already applied, which is why the numbers look lower than the raw irradiance figures you find on solar forums. Shading is handled separately, through a sun-path assessment that produces a shade factor between 0 and 1.
If a quote gives you an annual generation figure without naming your postcode zone, it is a national average dressed up as a survey.
| Region | Kk (kWh/kWp) | 4.4 kWp array (kWh/yr) |
|---|---|---|
| Cornwall, Devon, south coast | 990 to 1,050 | 4,350 to 4,600 |
| London and South East | 950 to 1,010 | 4,180 to 4,450 |
| East Anglia | 940 to 1,000 | 4,140 to 4,400 |
| Midlands | 900 to 960 | 3,960 to 4,220 |
| Wales | 870 to 940 | 3,830 to 4,140 |
| North West and Yorkshire | 850 to 910 | 3,740 to 4,000 |
| Northern Ireland | 830 to 890 | 3,650 to 3,920 |
| Central Scotland | 810 to 870 | 3,560 to 3,830 |
| Northern Scotland | 780 to 840 | 3,430 to 3,700 |
Read the gap between top and bottom: about 27%, not the two-to-one difference the “we never see the sun up here” mood music implies. Put another way, a south-facing roof in Manchester at Kk 880 out-generates an east-facing roof in Brighton at an effective 840. Orientation moves the needle harder than latitude does within the UK.
Peak instantaneous output on a south-facing UK array usually happens in April or May, not July. Silicon loses roughly 0.3% of its output per degree of cell temperature above 25C, so the highest kW readings come on cold, clear spring days when the sun is already high but the panels are still cool. If your monitoring app shows your record output in April, nothing is wrong.
- Azimuth
- The compass direction your roof slope faces, measured as degrees away from due south. Due south is 0. South-west and south-east are both 45. East and west are both 90.
- Kk value
- The MCS figure for expected annual generation per kWp, corrected for your postcode zone, pitch and azimuth. Multiply by your system size in kWp to get the annual estimate.
- Self-consumption
- The share of what you generate that you use in the house rather than export. It matters because a self-consumed unit is worth the full import price, and an exported unit is worth the export rate.
- Clipping
- What happens when your panels can produce more DC power than the inverter can convert. The inverter holds output at its ceiling and the surplus is not generated. Often deliberate.
- G98 and G99
- Grid connection standards. G98 is a notification after the fact for inverters up to 3.68 kW on a single phase. G99 is an application in advance for anything larger.
- SEG
- Smart Export Guarantee, the scheme that replaced the Feed-in Tariff in January 2020. Suppliers set their own export rates, so the spread across the market is wide.
How much you lose by being off due south
Less than you would guess. A roof at 45 degrees off south, which covers every south-east and south-west slope in the country, gives up roughly 4% of annual yield. On a 4.4 kWp array in the Midlands that is about 165 kWh a year, worth around £35. It is not a reason to redesign anything.
The pattern to take from that chart: the penalty is flat across the first 45 degrees and then starts to bite. Anything from south-east round to south-west is effectively a south roof for financial purposes. Below 90 degrees off south the loss accelerates, and by the time you reach north-east it costs you more than a third of the yield.
Pitch matters much less than direction
On a due-south roof the optimum pitch in the UK is 35 to 40 degrees, and the curve around it is gentle. A 30 degree roof loses under 1%. A 25 degree roof loses about 2%. A 45 degree roof, which covers most Victorian terraces, loses about 2%. Even a completely flat roof with panels laid horizontal only gives up around 13%.
Most UK pitched roofs sit between 30 and 45 degrees, which is why installers rarely propose tilted frames on a pitched south slope. A frame costs £400 to £900, adds wind loading, needs deeper fixings and typically buys back 2% of yield. On a 4,100 kWh system that is 82 kWh a year, worth about £18. The maths does not work.
Use true south, not magnetic south, when you check your roof. Magnetic variation across most of the UK is under 2 degrees in 2026, so a phone compass is close enough for a first look, but the satellite view in Google Maps is easier and gives you true bearings without any correction.
What a south-facing install costs in 2026
£5,800 to £7,800 fully installed for a 4.4 kWp array on a straightforward south-facing pitched roof, as at August 2026. London and the South East run £7,000 to £9,500 for the same specification, mostly on labour and scaffolding rather than hardware. Add a battery and you are into a separate conversation covered further down.
A south-facing job is usually at the cheaper end of the range for one reason that has nothing to do with the sun: it is a single-elevation install. One scaffold, one roof slope, one set of flashings, one string of panels. An east-west split on the same house needs scaffold on two elevations and two MPPT inputs, and that typically adds £600 to £1,200 before a single extra panel goes on.
Two lines in that breakdown are where quotes diverge most. Scaffolding varies by £400 between a bungalow and a three-storey townhouse, and it is often the item an installer absorbs to win the job or inflates to pad it. Labour varies by region by more than the hardware does. The panels themselves, contrary to how most quotes are presented, are under a quarter of the total.
VAT on qualifying residential solar and battery installations is 0% until 31 March 2027, reverting to 5% on 1 April 2027. On a £6,150 install that final window is worth about £308. It is a reason to get the job booked, not a reason to sign with the first company that mentions it on the doorstep.
Adding a battery
A 5 kWh battery adds £3,000 to £4,500 installed. A 10 kWh battery adds £5,500 to £7,500. If it is fitted at the same time as the panels using a hybrid inverter you save roughly £600 to £900 against retrofitting later, because you avoid a second AC-coupled inverter and a second visit. Whether it pays back is a different question, answered in the next two sections.
The payback arithmetic, one number at a time
Nine years without a battery, on a Midlands south-facing roof, at August 2026 prices. Here is how that number is built, because the construction is where most quotes get misread.
Take the 4.4 kWp array above at £6,150 installed, generating 4,100 kWh a year in the Midlands. Without storage, a south-facing array delivers around 35% self-consumption for a typical household, because the output peaks between 11am and 2pm and most homes are empty then. That is 1,435 kWh used in the house. At the October 2026 cap rate of 26.32p, those units are worth £378. The remaining 2,665 kWh is exported. At 12p per kWh, the widely available rate after Octopus cut Outgoing Octopus from 15p on 1 March 2026, that export is worth £320. Year one total: £698. Divide £6,150 by £698 and you get 8.8 years.
Note which number each rate was applied to. The 26.32p only touched 35% of your generation. That single percentage is what a battery is really buying.
So run it again with a 10 kWh battery at £6,000. Self-consumption goes from 35% to around 80%, so 3,280 kWh is now used in the house at 26.32p, worth £863. Export falls to 820 kWh, worth £98. Year one total: £961. That is £263 a year more than the panels alone produced. Divide £6,000 of battery by £263 and the battery pays back in 22.8 years on solar storage alone, against a warranty that typically runs 10 to 12 years.
The battery case rests on tariff arbitrage. Overnight rates on smart tariffs sat in the 7p to 9p range through mid-2026. Charge 8 kWh overnight at 8p for 64p, use it during the day instead of buying at 26.32p for £2.11, and you have banked £1.47 in a single cycle. Run that 250 times a year and it is £368 on top of the solar figure. That is the number that makes a battery work, and it applies whether your roof faces south or not.
Year one value, 4.4 kWp south, Midlands. 35% self-consumed at 26.32p, 65% exported at 12p.
Same array, 80% self-consumed. Add tariff arbitrage and the combined figure reaches roughly £1,300.
Any payback figure quoted to you without a date on the export rate is close to meaningless. Outgoing Octopus dropped from 15p to 12p on 1 March 2026, its first change since September 2022. On a south-facing array exporting 2,665 kWh, that single change cut annual income by £80 and pushed payback out by roughly seven months. Ask which export rate the projection assumes and when it was last checked.
The midday spike is the south roof’s real problem
A south-facing array produces a narrow, tall generation curve centred on solar noon, and UK households consume electricity in the morning and the evening. That mismatch is the defining characteristic of a south roof, and it is the reason the highest-yielding orientation does not automatically produce the highest financial return.
The numbers behind it are consistent across UK and European monitoring. South-facing arrays without storage land around 35% to 40% self-consumption. An east-west split reaches 45% to 52%, because the curve is wider and flatter and the shoulders line up with breakfast and dinner. An east-west array generates 15% to 20% less in total and still keeps more of the money, because a self-consumed unit at 26.32p is worth more than twice an exported unit at 12p.
Add storage and the ranking flips back. With a battery, self-consumption on a south array climbs to 75% to 85%, and the tall midday peak fills the battery faster and more completely than an east-west curve does, particularly in the shorter days of March and October when a flat curve may never produce enough surplus to fill 10 kWh at all. A south roof is the better roof for anyone installing a battery. It is the worse roof for anyone who is not.
The two low scores are the ones worth acting on. Both have fixes: storage answers the self-consumption problem, and an early check of your local authority’s designation map answers the planning one.
Things a south roof lets you do that other roofs do not
- Run a heat pump’s daytime defrost and hot water cycles almost entirely on generation from March to October
- Charge an EV at home during the day at a marginal cost of zero rather than an overnight rate
- Heat a hot water cylinder with a solar diverter, worth roughly £120 to £200 a year against a gas boiler, more against immersion
- Fill a battery in a single midday window even on short shoulder-season days
- Run a home office, dehumidifier or workshop load during the exact hours the array is at full output
If any two of those apply to your household, the south-roof self-consumption penalty largely disappears without you buying anything extra.
Three ways to design the same south-facing house
Filling only the south slope is the default proposal, and it is not usually the best value per pound. Here are three designs for the same Midlands semi with a 22 m² south slope and a 22 m² north slope, plus a 12 m² west-facing garage roof.
- Array
- 4.4 kWp, 10 panels
- Annual yield
- 4,100 kWh
- Cost per annual kWh
- £1.50
- Grid application
- G98 notification
- Best for
- Tight budgets, simple jobs
- Array
- 6.6 kWp, 15 panels
- Annual yield
- 5,820 kWh
- Cost per annual kWh
- £1.36
- Grid application
- G99 or export limit
- Best for
- Evening-heavy households
- Array
- 5.0 kWp, 10 panels
- Annual yield
- 4,650 kWh
- Cost per annual kWh
- £1.59
- Grid application
- G99 or export limit
- Best for
- Small roofs, no second slope
The middle column wins on cost per annual kWh because the marginal panels are cheap: the scaffold, the inverter, the electrical works and the certification are all already paid for by the first ten. Five west-facing panels producing 1,720 kWh cost £1,750, which is £1.02 per annual kWh, well under the £1.50 the south array itself achieved. The right-hand column is the one to be careful with, because paying a premium per watt to squeeze more capacity onto the same slope has the worst ratio of the three unless roof space actually runs out.
The west panels also land their output between 3pm and 7pm, which is when households actually use electricity and when time-of-use export tariffs pay their peak rate. That is a second reason the middle column beats the first, and it does not show up in the annual kWh figure at all.
The 3.68 kW ceiling and why your south roof meets it first
If your inverter is rated above 3.68 kW on a single-phase supply, your installer needs G99 approval from the distribution network operator before the system goes in, and that takes up to 45 working days. At or below 3.68 kW it is a G98 notification submitted after commissioning, with no waiting. Around 95% of UK homes are single phase.
The threshold is set by inverter capacity, not panel capacity, which is why a 4.4 kWp or even 5 kWp array routinely sits behind a 3.68 kW inverter. The surplus DC capacity is deliberate. It lifts output through the long shoulders of the day and through cloudy conditions, where the array never approaches its rated power anyway.
A south-facing array is the one most likely to reach the ceiling, because its curve is tall and narrow rather than broad and flat. On a 4.4 kWp south array behind a 3.68 kW inverter, expect clipping losses of roughly 1% to 3% of annual generation, concentrated in perhaps 60 hours a year on clear days in April, May and June. On 4,100 kWh that is 40 to 120 kWh, worth £8 to £25 a year at a blended value. Set against a 45 working day delay and a G99 application, most households take the clipping.
Ask for a 5 kW hybrid inverter export-limited to 3.68 kW rather than a 3.68 kW unit, if the price difference is under about £250. You stay inside G98 today, and you have headroom to add a battery or a second array later without replacing the inverter or triggering a fresh application. Confirm in writing that the export limit is a configurable setting, not a hardware cap.
One thing that catches people out on retrofits: adding an AC-coupled battery with its own 5 kW inverter to an existing 3.68 kW solar system pushes the combined site capacity over the threshold and triggers a G99 application on a system that was previously fine. Plan the inverter capacity at the first install, not the second.
The south slope is often the front, and that is a planning problem
In a conservation area, AONB, National Park, the Broads or a World Heritage Site, panels on a roof slope that forms the principal elevation and fronts a highway need full planning permission. On rear slopes in the same areas, permitted development usually still applies. Which slope faces the road decides most of these cases on site.
This matters far more for the south-facing search than for any other orientation, because of how British housing is laid out. On a huge number of terraces, post-war estates and 1930s semis, the roof that faces south is the one facing the street. People search for “solar panels for south-facing roofs”, get told their roof is ideal, and only discover at survey that the ideal slope is the one the council will look at hardest.
Outside designated areas, roof-mounted solar in England is permitted development provided the panels project no more than 200mm from the roof plane and do not sit above the highest part of the roof, excluding the chimney. Most flush-mounted systems come in at 100mm to 160mm, so the limit is not usually the issue. Wales, Scotland and Northern Ireland run their own regimes with different limits.
Check for an Article 4 direction on your address before you take a single quote. Article 4 removes permitted development rights across defined streets, and several authorities apply them to solar in conservation areas. Where one is in force, even a rear slope can need a full application. Your local authority’s planning constraints map will show it, and the search takes about five minutes.
If you do need an application, budget 12 to 18 weeks from submission to decision on a conservation area case, and expect the officer to look at three things: whether the array is visible from the public realm, whether the panels are matte black rather than silver-framed, and whether an in-roof mounting system that sits flush with the tiles has been considered. In-roof adds roughly £700 to £1,400 to a 4.4 kWp install and converts a likely refusal on a prominent front slope into a viable application.
Check listed status, conservation area boundary and Article 4 on the council map before the first survey.
Ask installers to price both on-roof and in-roof if the south slope faces the highway.
Speak to the conservation officer before submitting. Most will tell you what they will accept.
Accept “solar doesn’t need planning permission” as a blanket answer. It is true in most cases and wrong in yours if you are in a designated area.
Pay a deposit before the planning position is confirmed in writing.
Assume a neighbour’s install sets a precedent. It may predate an Article 4, or have been done without consent.
Choosing panels for a roof that runs hot
Buy on efficiency and physical dimensions, not on temperature coefficient. The temperature argument gets made constantly in south-roof content and the money involved is trivial once you work it through.
Here is the arithmetic. A premium back-contact panel such as the LONGi Hi-MO X10 or REC Alpha Pure-RX has a temperature coefficient around -0.24% per degree C. A mainstream TOPCon panel such as a JA Solar DeepBlue sits closer to -0.30%. On a hot clear day a south-facing panel can reach 60C cell temperature, 35 degrees above standard test conditions. The premium panel loses 8.4% of rated output at that moment. The mainstream panel loses 10.5%. The difference is 2.1 percentage points, but only on the fraction of the year spent at high cell temperature, which in the UK is roughly 25% to 30% of annual generation. On a 4,100 kWh system that works out at about 25 kWh a year, worth around £5. Over 25 years, £125. Do not pay a £300 premium for it.
The reason to buy the premium panel is different and better: it fits more capacity on the same slope. A 24% efficient module puts roughly 480W to 500W in the same footprint where a 21.5% module puts 430W. On a 22 m² south slope that is the difference between 4.4 kWp and 5.0 kWp, which is 550 kWh a year, worth about £95. That is a real return, and it only exists when roof area is the binding constraint.
| Tier | Efficiency | Cost per panel | Buy it when |
|---|---|---|---|
| Mainstream TOPCon JA Solar, Jinko, Trina | 21% to 22.5% | £65 to £95 | The slope is big enough to fit what you need. This is the default and it is the right default. |
| High-efficiency back-contact Aiko Neostar, LONGi Hi-MO X10 | 23.5% to 24.5% | £110 to £150 | Roof area is the limit, or a chimney takes out two panel positions and you need the rest to work harder. |
| Premium long-warranty REC Alpha Pure-RX, Maxeon | 22.8% to 24% | £135 to £190 | Partial shading you cannot design out, or you want a 25 to 40 year product warranty rather than 12. |
Read that table as a decision about roof geometry rather than a decision about brand. If your south slope comfortably takes the array you want, the mainstream tier is the correct answer and the extra £600 across ten panels buys you almost nothing. If a chimney, a dormer or a soil vent pipe costs you two panel positions, the high-efficiency tier gets that capacity back for less than the yield is worth.
Optimisers are worth specifying only on the panels that are actually shaded. A chimney on a south slope typically shades two or three panels for part of the day. Fitting optimisers to those three costs around £180 and recovers most of the string loss. Fitting them to all ten costs £600 and recovers nothing extra.
When the south slope is the wrong place for the array
Four situations where an installer proposing the south roof is proposing the wrong thing. Any competent surveyor will raise these unprompted, and it is a useful test of the ones who do not.
- The slope is clear of chimneys, dormers and vent pipes
- You are fitting a battery now or within two years
- Someone is home during the day, or you run a heat pump or EV
- It is the rear elevation, or you are outside a designated area
- The slope is large enough for the capacity you need
- A chimney stack sits mid-slope and shades through 11am to 2pm
- The south slope is the front, in an Article 4 conservation area
- Your east-west pair together offer double the usable area
- The covering is due for renewal within ten years
- The house is empty 9 to 5 and no battery is planned
The shading case is the one that costs the most and gets missed the most. A chimney on the south slope of a semi shades panels during precisely the hours a south array earns its keep, and without optimisers a single shaded panel can drag a whole string down. An unshaded west slope at 82% of south’s potential will beat a south slope losing 25% to a stack, and it will beat it every single year.
The roof condition case is the cheapest to avoid and the most expensive to ignore. Removing and refitting a 4.4 kWp array so a roofer can strip and re-cover the slope costs £1,000 to £1,800, plus a second scaffold. If your south slope has 8 years of life left, do the roof first or put the array on the slope you re-covered five years ago.
Checking your own roof in ten minutes
You can settle most of this before you speak to anyone. Six steps, no equipment beyond a phone.
Open your address in Google Maps satellite view, which is oriented to true north. Read the angle of your ridge line. If the ridge runs east to west, one slope faces south. Anything within 45 degrees of due south counts as a south roof for planning purposes.
Stand side-on to the house and photograph the gable end. Most UK pitched roofs are 30 to 45 degrees, and anywhere in that band is within 2% of optimal for a south-facing array. Only a very shallow roof under 20 degrees changes the answer.
Note the chimney, aerial, satellite dish, soil vent, dormer and any tree or building to the south, south-east or south-west. Check the roof at 10am, 1pm and 4pm on a sunny day. Shadows between 10am and 3pm are the expensive ones.
A 440W panel is roughly 1.95m by 1.13m, so 2.2 m² each. Allow 300mm clear at eaves, ridge and verges. A 22 m² clear slope takes ten panels, which is 4.4 kWp. Measure from the satellite image if you cannot get a ladder to it safely.
Search your local authority’s planning constraints map for your address. You are looking for conservation area, Article 4 direction, listed status, AONB or National Park. If any apply and the south slope fronts a highway, budget for an application.
Look at your consumer unit and main fuse. Single phase with a 60A, 80A or 100A main fuse is standard and sets the 3.68 kW G98 threshold. Three phase raises it to 11.04 kW total and changes the whole design conversation.
What a good quote for a south-facing roof looks like
It names your MCS postcode zone and shows the Kk value used. If it does not, the generation estimate came from a national average and you cannot compare it against a rival quote that did the work properly.
- Your postcode zone and the Kk value applied. Plus the shade factor from the sun-path assessment, which should be a number between 0 and 1, not the word “minimal”.
- Panel make, model and wattage, plus the count. “10 x tier-1 440W” is not a specification. You want the model number so you can read the datasheet.
- Inverter make, model, rating and whether it is export limited. If export limited, at what value and whether the limit is a software setting.
- Whether the job is G98 or G99, stated explicitly. A G99 job has a lead time of up to 45 working days and the quote should say so.
- Scaffolding as a separate line, with the hire period. This is the single most commonly hidden cost and it varies by £400 between quotes for the same house.
- Two warranties, stated separately. Panel product warranty, inverter warranty and workmanship warranty are three different things with three different durations.
- The planning position in writing. Permitted development, or an application required, with who is submitting it and who pays the fee.
- Deposit no more than 25% of the total. Above that you are outside the usual consumer protection threshold on deposit insurance.
MCS certification is not optional if you want export income. Every SEG tariff above the supplier floor requires an MCS certificate and a smart meter. A non-MCS install is legal and cheaper, and it forfeits roughly £320 a year of export income on the 4.4 kWp array in this guide. Over 25 years that is a five-figure decision made to save a few hundred pounds.
Frequently asked
Do solar panels need a south-facing roof in the UK?
No. South-facing produces the most electricity per kWp, but south-east and south-west lose only about 4%, and east or west lose 15% to 20%. East and west arrays often return more money than the yield gap suggests, because their output lands when households are actually at home using it.
How much electricity does a south-facing 4 kW system produce a year?
Between about 3,300 and 4,200 kWh depending on your postcode zone, at a 30 to 40 degree pitch with no shading. A 4.4 kWp array of ten 440W panels produces roughly 3,600 kWh in central Scotland, 4,100 kWh in the Midlands and 4,500 kWh on the south coast.
What is the best angle for a south-facing roof in the UK?
35 to 40 degrees. The curve either side is shallow: 30 degrees costs under 1%, 45 degrees costs about 2%, and flat costs about 13%. Since most UK pitched roofs fall between 30 and 45 degrees, tilted frames on a pitched south slope rarely justify their cost.
How much does a south-facing solar installation cost in 2026?
£5,800 to £7,800 for a 4.4 kWp array fully installed by an MCS-certified contractor, as at August 2026. London and the South East run £7,000 to £9,500. Add £3,000 to £4,500 for a 5 kWh battery, or £5,500 to £7,500 for 10 kWh. VAT is 0% until 31 March 2027.
What is the payback period on a south-facing roof?
Roughly 8 to 10 years without a battery, on the October 2026 cap rate of 26.32p per kWh and a 12p export rate. Southern England lands at the shorter end, Scotland at the longer end. Adding a battery does not shorten it unless you also move to a smart tariff with cheap overnight rates.
Do I need planning permission for panels on a south-facing front roof?
Only if you are in a conservation area, AONB, National Park, the Broads or a World Heritage Site, or the building is listed. In those cases panels on the principal elevation fronting a highway need a full application, typically 12 to 18 weeks. An Article 4 direction can extend the restriction to other slopes. Everywhere else, flush-mounted panels projecting under 200mm are permitted development.
Should I fill the whole south roof or split across two slopes?
Split, if you have a second usable slope. Once the scaffold, inverter and certification are paid for by the first array, additional panels on a west or east slope cost around £1.00 per annual kWh against £1.50 for the south array itself. West panels also generate through the 4pm to 7pm window when time-of-use export rates peak.
Do south-facing panels overheat and lose output?
They run hotter than other orientations and lose roughly 0.24% to 0.30% of output per degree of cell temperature above 25C. In practice the difference between a premium low-coefficient panel and a mainstream one is worth about £5 a year on a 4 kWp UK array, so it is not a reason to pay a hardware premium.
Is a battery worth it on a south-facing roof?
More than on any other orientation, but not on solar storage alone. A battery lifts self-consumption from around 35% to 80% on a south array, worth roughly £260 a year, which does not repay £6,000 of hardware inside its warranty. It becomes worthwhile when you add overnight tariff arbitrage at 7p to 9p import rates, which can be worth a further £300 or more.
The orientation is the easy part
A south-facing roof at 30 to 40 degrees is the best slope on your house and will generate 820 to 1,050 kWh per kWp per year depending on where you live. Nothing in this guide changes that, and if you have one, use it.
What changes the return is everything downstream of the orientation. Whether a chimney sits mid-slope. Whether your south roof is the one facing the road in a conservation area. Whether the second slope gets five more panels at £1.00 per annual kWh while the scaffold is still up. Whether you have any way of spending a 3 kW midday peak, or are selling it at 12p.
The right question is not whether your roof faces south. It is what your specific slope generates after shading, what that costs to install this year, and how much of the output you can actually use rather than export. Get three MCS-certified quotes that each name your postcode zone and Kk value, and the comparison becomes straightforward.
METHODOLOGY: Generation figures use the MCS MIS 3002 Kk methodology (PVGIS-derived, performance ratio 0.8) for a south-facing array at 35 degrees with no shading. Installed pricing verified across MCS-certified contractor quotations and published UK market data in August 2026. Savings calculations use the Ofgem price cap electricity unit rate of 26.32p/kWh for 1 October to 31 December 2026 and a 12p/kWh export rate.
DISCLAIMER: All prices are indicative and will vary by region, roof access, scaffolding requirement and installer. We do not provide financial advice. The Smart Export Guarantee is administered by Ofgem and rates are set by individual suppliers, so confirm the live rate before applying. Planning rules differ in Wales, Scotland and Northern Ireland; always confirm the position with your local planning authority.
