South vs East-West Solar on Flat Roofs

A flat roof gives you something a pitched roof cannot: a choice over the direction and angle of your solar panels.

That freedom creates an important design decision. Should the panels be installed in separate south-facing rows, or arranged back-to-back with half facing east and half facing west?

South-facing panels normally generate more electricity per panel. An east–west layout can often fit more panels into the available roof area and spread generation across more of the day.

The best choice therefore depends on what you want to maximise:

Electricity from each panel
Total generation from the roof
Morning and afternoon production
Household self-consumption
Export income
Compatibility with a battery
Performance within an inverter or export limit

The correct layout must also leave room for drainage, maintenance and emergency access while remaining suitable for the roof structure and waterproof covering.

The key point

The best direction for an individual panel is not necessarily the best layout for the whole roof.

South-facing vs east–west: the quick answer

General tendencies, not guaranteed results. Panel angle, shading, location, roof geometry and the chosen mounting system can all change the outcome.
Consideration	South-facing rows	East–west rows
Generation per panel	Usually higher	Usually lower
Number of panels that fit	Often fewer	Often more
Peak generation	Stronger around midday	Lower and more distributed
Morning production	Moderate	Stronger from the east-facing panels
Afternoon production	Moderate	Stronger from the west-facing panels
Winter performance	Usually stronger	Usually weaker per panel
Row spacing	More clearance normally required	Rows can usually be packed more closely
Wind exposure	Can increase with panel tilt	Often a lower-profile arrangement
Best suited to	Maximising output per panel	Maximising installed capacity on a constrained roof

A good installer should be able to show you both options using the same roof dimensions and clearly explain why one is being recommended.

What does east–west mean on a flat roof?

An east–west flat-roof array normally consists of shallow, back-to-back rows. One side of each row faces east and the other faces west.

The result resembles a series of low ridges:

The roof itself does not need to face east or west. Unlike a pitched roof, the mounting frames determine the direction of the panels.

This is also different from placing panels on the two opposing slopes of a conventional pitched roof. Flat-roof systems are usually installed at a much shallower angle and can often be positioned more closely together.

Option one: south-facing rows

In a south-facing layout, the panels are arranged in parallel rows, with every panel facing broadly south.

This gives each panel favourable exposure to the UK’s southerly sun path and normally delivers the highest annual generation per panel.

Advantages of south-facing rows

Higher annual generation per installed kWp in most UK locations
Stronger output during the middle of the day
Better exposure to the low southern sun during winter
Simpler comparison with conventional pitched-roof systems
Potentially fewer panels, cables and mounting components for a given target capacity

Disadvantages of south-facing rows

Each raised row can shade the row behind it.
Greater row spacing may be required.
Fewer panels may fit on a constrained roof.
Higher panel angles can increase wind forces.
A strong midday peak may exceed household demand, inverter capacity or an export limit.

South-facing rows are often the stronger choice when the required system already fits comfortably on the roof and there is enough space to control inter-row shading.

Option two: east–west rows

An east–west layout places the panels back-to-back at a relatively shallow angle.

The east-facing panels produce more in the morning. The west-facing panels make a greater contribution later in the day. Because opposing panels support one another in a compact arrangement, the rows can normally be positioned more closely than separate south-facing rows.

Advantages of east–west rows

More panels may fit within the usable roof area.
Generation is distributed across a wider part of the day.
The array can have a lower combined peak for its installed capacity.
A shallow profile may help reduce wind exposure.
More panel capacity may be usable behind a constrained inverter or export limit.
It can suit homes with meaningful morning and afternoon electricity demand.

Disadvantages of east–west rows

Each panel normally generates less annually than an equivalent south-facing panel.
Winter performance can be noticeably weaker.
Both orientations must be handled correctly by the electrical design.
More panels mean more mounting equipment, cable and connections.
Increased panel count does not automatically produce a better financial return.

An east–west layout is not more efficient per panel. Its potential advantage comes from fitting more panel capacity onto the roof and changing when that capacity generates.

Could a hybrid layout be better?

The decision does not always have to be entirely south-facing or entirely east–west.

An irregular roof might support:

South-facing rows in the clearest area
East–west rows where space is more restricted
Panels aligned with the building rather than exactly south
Landscape panels around narrow sections
Separate groups positioned around rooflights, vents or plant

A hybrid design can make effective use of an awkward roof, but it may require more inverter inputs, separate strings or module-level electronics.

The additional panels must still justify their mounting, electrical and installation costs.

Compare the whole roof, not one panel

The fairest comparison uses two complete designs for the same roof.

Both designs should use:

The same roof dimensions
The same panel model
The same shading information
The same areas excluded for access
The same system-loss assumptions
The same household electricity profile
Appropriate inverter sizing for each option

The comparison should then show:

What to compare	Why it matters
Number of panels	Shows how each layout uses the roof
Installed capacity in kWp	Measures the rated size of the array
Annual generation in kWh	Estimates the electricity produced
Generation per installed kWp	Compares the productivity of the panels
Generation per square metre of roof	Compares roof utilisation
Monthly generation	Reveals seasonal differences
Half-hourly or hourly profile	Shows when the electricity is produced
Self-consumption	Estimates how much solar the home will use
Export	Shows how much may be sold to the grid
Inverter clipping	Estimates generation restricted by the inverter
Installed cost	Allows a financial comparison
Structural and ballast requirements	Confirms whether the design is practical

A south-facing design may win when measured in kWh per panel, while an east–west design wins when measured in total kWh from the roof.

Neither result tells you which system offers better value until consumption, export and installation costs are included.

How generation changes through the day

South-facing panels normally produce their strongest output around the middle of the day.

With an east–west array:

East-facing panels make a greater contribution during the morning.
Both orientations contribute around the middle of the day.
West-facing panels make a greater contribution during the afternoon and early evening.

This can create a broader generation profile, but it should not be described as a perfectly flat output curve. The difference also changes with the season.

During summer: Longer days give east-facing panels more morning sun and west-facing panels more late-afternoon and evening sun. This is when the broader east–west profile is most apparent.
During winter: The UK sun rises in the south-east, remains low across the southern sky and sets in the south-west. South-facing panels can therefore hold a much larger advantage during winter than the annual comparison suggests.

This matters for homes with heat pumps or high winter electricity consumption. A layout that produces plenty of additional summer electricity for export may still produce less during the months when the home needs electricity most.

Panel angle changes how many panels fit

Raising a solar panel improves its exposure to the sun up to a point, but also lengthens the shadow it casts behind it.

The relationship is straightforward:

Higher tilt → longer shadow → wider row spacing → fewer panels

Lower tilt → shorter shadow → closer rows → more panels

The correct spacing depends on:

Panel length and orientation
Mounting angle
UK location
Direction of the row
Height of the roof
Parapets and other obstructions
The time of year used for the shading calculation
The shading loss accepted by the designer

There is no universal one-metre spacing rule for flat-roof solar panels.

Designing out every minute of winter shading can require a very large gap because winter shadows are long. A competent design balances the value of avoiding shading against the generation available from fitting additional panels.

What reduces the usable roof area?

The external dimensions of a flat roof do not represent the area available for panels.

A layout may need to avoid or provide access to:

Parapets
Roof edges
Rooflights and skylights
Chimneys and flues
Soil and ventilation pipes
Smoke vents
Air-conditioning units
Aerials and other equipment
Gutters and drainage outlets
Existing areas of ponding water
Permanently shaded sections
Fire-escape routes
Maintenance walkways

Parapet shading can be particularly important. A parapet on the eastern side can reduce the expected morning benefit of east-facing panels, while a western parapet can affect afternoon production.

The effect becomes more pronounced in winter because the sun is lower and shadows are longer.

How are solar panels secured to a flat roof?

Flat-roof panels can be installed using ballasted, mechanically fixed or mechanically restrained mounting systems.

Ballasted mounting

A ballasted system uses calculated additional weight to resist movement without relying on fixings through the waterproof roof covering.

Its advantages include avoiding intentional penetrations and allowing the mounting system to sit above the existing covering.

However, ballast is not simply a matter of placing a standard number of concrete blocks behind every panel.

The amount and location of ballast depend on:

Building height and dimensions
Local wind conditions
Terrain and exposure
Position on the roof
Panel angle
Array layout
Mounting-system aerodynamics
Friction between the mounting system and roof covering

A compatible protection or slip layer is also required between the mounting system and waterproof covering.

Mechanically fixed mounting

A mechanically fixed system connects the mounting frame to the roof structure.

This can reduce the amount of ballast, but the fixing points and waterproofing details must be designed correctly. The condition and construction of the roof deck may need to be investigated, and pull-out tests may be required where the fixing strength cannot be reliably calculated.

Mechanically restrained ballast

Some systems combine ballast with an additional restraint such as a tether, kerb or suitably designed fixed point.

This can help control sliding without relying entirely on additional weight. It still requires a site-specific engineered design.

Structural loading and wind resistance

The roof must support more than the panels.

The structural assessment should consider:

Solar panels
Mounting frames
Ballast
Concentrated loads beneath supports
Wind uplift
Sliding
Overturning
Snow accumulation
Existing equipment
Ponding water

Wind pressure is not equal across a flat roof. Corners, edges and areas around upstands can experience greater forces than the central roof area.

This means the ballast may not be distributed evenly. Some positions may require more weight precisely where the roof structure has less spare capacity.

Moving the array farther inboard, changing the mounting system or strengthening the roof may be preferable to adding more ballast.

Important

For an MCS installation, the current MIS 3002 standard requires a qualified structural engineer to confirm that a flat roof can withstand the combined load of a ballasted PV system and its proposed ballast.

Ask for the structural assessment and the mounting manufacturer's site-specific wind and ballast calculation. A verbal assurance that the roof is “strong enough” is not the same thing.

Protecting the roof covering

A correctly installed solar array should not compromise the roof’s weather-tightness or structural integrity.

Before the layout is agreed, establish:

The type of roof covering
Its age and condition
Its remaining expected life
Whether it remains under warranty
Which protection layers are compatible
Whether the covering or insulation can carry concentrated loads
Who will accept responsibility for waterproofing details

Common flat-roof coverings include EPDM, other single-ply membranes, built-up felt, asphalt and GRP. Each has different compatibility and fixing considerations.

If the roof is likely to need replacement during the life of the solar system, renewing it first may be more economical than removing and reinstalling the array later.

Where the covering remains under warranty, consult the warranty provider before installation. Do not assume that a non-penetrating system automatically preserves the warranty.

Drainage must remain accessible

A flat roof is not normally completely level. It should have a slight fall that directs water towards outlets or gutters.

The solar layout must not:

Obstruct the roof’s drainage falls
Block outlets or gutters
Trap debris around mounting frames
Create or worsen ponding
Prevent future inspection and cleaning
Leave electrical connectors in standing water

Ballast and mounting supports can also compress insulation or create concentrated loads if they are not distributed correctly.

The drainage plan should therefore be visible on the proposed roof layout, not treated as a detail to solve during installation.

Maintenance and emergency access

Covering every available part of the roof with panels is rarely good design.

Space may be needed for:

Inspecting the panels
Replacing a failed module
Reaching cables and connectors
Clearing drainage outlets
Maintaining rooftop equipment
Inspecting the roof covering
Working safely around rooflights
Emergency-service access

Larger arrays may need to be divided into smaller blocks with access corridors between them. A clear route around part or all of the array may also be required.

The appropriate layout depends on the building, roof construction, fire strategy and applicable guidance. There is no single access-corridor dimension suitable for every roof.

Inverters, strings and east–west arrays

The electrical design must reflect the different panel orientations.

Panels are connected in groups called strings. A string inverter uses one or more maximum power point tracker inputs, usually shortened to MPPTs, to keep each connected group operating effectively.

Because east- and west-facing panels receive different levels of sunlight throughout the day, they will normally be assigned to separate MPPT inputs.

The designer must check:

Minimum and maximum string voltage
Maximum input current
Number of panels in each string
MPPT operating range
Module compatibility
Behaviour under partial shading
Maximum DC array capacity
Inverter AC output
Expected clipping

An east–west array can have a lower combined peak than the same panel capacity facing south. This may make a higher DC-to-AC ratio practical, allowing more panel capacity to be connected to a given inverter.

That does not mean the inverter can be selected without calculation. Manufacturer limits, electrical safety requirements and the grid-connection arrangement still apply.

Does an east–west layout help with an export limit?

A distribution network operator, or DNO, may approve the installation subject to a limit on how much electricity can be exported to the grid.

Because east- and west-facing panels reach their strongest outputs at different times, an east–west system may have a lower peak relative to its installed panel capacity.

That can mean:

Less generation reaches the export ceiling.
More panel capacity can sometimes be installed behind an export-limitation system.
A smaller share of annual generation may be restricted.
The inverter may spend less time clipping at its maximum AC output.

However, fitting more panels can raise the peak again. The installer must model the proposed system rather than assume an east–west layout will remain below the limit.

Does a battery change the best layout?

A battery can store surplus solar electricity for use later, but it does not automatically make one panel direction best.

A south-facing system may deliver a strong midday surplus that can be stored for the evening. An east–west system may reduce the size of that midday surplus while generating closer to the times the home uses electricity.

The result depends on:

Battery capacity
Maximum charging power
Minimum reserve setting
Household demand
Overnight tariff charging
Export tariff
Inverter rating
EV charging
Heat-pump consumption
Seasonal solar generation

The solar array, battery, inverter and household demand should be modelled as one system.

Which layout is likely to suit your home?

South-facing rows may be preferable when: The target system fits with adequate row spacing; roof area is not the main constraint; maximum generation per panel is the priority; winter performance is especially important; midday electricity can be used, stored or exported effectively; or the roof structure or budget limits the number of panels.
East–west rows may be preferable when: The usable roof area is constrained; the layout accommodates materially more panels; morning and afternoon generation is valuable; a lower peak helps with inverter or export constraints; the shallow arrangement works better with the roof geometry; or total generation from the roof matters more than output per panel.
A hybrid design may be worth considering when: Parapets or rooftop equipment divide the roof into separate areas; part of the roof has a particularly clear southern aspect; an irregular roof leaves narrow or awkward spaces; or multiple orientations can be handled correctly by the inverter.

Planning permission for flat-roof solar panels

England only

The following information applies to England. Scotland, Wales and Northern Ireland have separate planning systems.

Solar panels on a domestic flat roof can often be installed under permitted development rights, provided all the relevant limitations and conditions are met.

For a house or block of flats, the highest part of solar equipment on a flat roof must not be more than 600mm above the highest part of the roof, excluding the chimney.

Other restrictions include installations:

On listed buildings or buildings within their grounds
On scheduled-monument sites
Where permitted development rights have been removed
On designated land where prior approval may be required
On leasehold or shared buildings where third-party consent is needed

On Article 2(3) land, which includes conservation areas, National Parks, the Broads, National Landscapes and World Heritage Sites, installing solar equipment on a flat roof requires an application to the local planning authority to determine whether prior approval is needed.

Updated English permitted development rules took effect on 27 August 2026, with a 12-month transitional period ending on 27 August 2027. Check the current Planning Portal and your local planning authority before proceeding.

Planning permission and Building Regulations are separate. Even where planning permission is not required, the structural, electrical, fire-safety and weatherproofing requirements still apply.

What to request from your installer

Ask for a written comparison of the viable layouts rather than accepting a recommendation based solely on panel direction.

Your proposal should include:

A dimensioned roof plan
The usable and excluded roof areas
Panel make, model, size and rating
Panel count and installed capacity
Orientation and inclination
Row-spacing assumptions
Parapet and obstruction shading
Annual and monthly generation estimates
The expected daily generation profile
Household self-consumption assumptions
Expected annual export
Inverter make, model and rating
String and MPPT allocation
Expected inverter clipping
DNO application or export-limitation details
Mounting-system specification
Structural assessment
Wind and ballast calculation
Roof-covering compatibility
Roof-warranty confirmation
Drainage and maintenance access
Fire and emergency-access considerations
Itemised installed cost

Where both south-facing and east–west arrangements are practical, ask the installer to model both.

The final decision

Do not choose a flat-roof solar layout from a generic percentage or a picture of a similar property.

Use this sequence:

Establish the genuinely usable roof area
External dimensions are not the same as available area.
Identify shading, drainage and access restrictions
Parapets, rooflights, outlets and walkways.
Confirm the roof's condition and structural capacity
Covering, remaining life and load capability.
Produce viable south-facing and east–west layouts
Both for the same roof, using the same assumptions.
Model annual, seasonal and daily generation
Not just the annual total.
Match that generation to the home's electricity use
When the electricity arrives matters as much as how much.
Check the inverter, battery, DNO and export constraints
Including predicted clipping.
Compare installed cost and the financial value of the electricity
Self-consumed and exported, valued separately.

South-facing rows normally produce more from each panel. East–west rows can sometimes produce more from the whole roof.

The right design is the one that safely delivers the most useful, cost-effective electricity for your property.

Frequently asked questions

Is south-facing or east–west better on a flat roof?

South-facing normally produces more electricity per panel. East–west can often accommodate more panels and spread generation across more of the day. The better option depends on the roof area, shading, household consumption and system constraints.

Do east–west solar panels produce less electricity?

An individual east- or west-facing panel will normally generate less annually than an equivalent south-facing panel. However, an east–west layout may fit more panels, so the complete system can still produce more electricity from the available roof.

How much space is needed between solar-panel rows?

There is no universal distance. It depends on the panel dimensions, angle, orientation, location, nearby obstructions and the amount of shading the design permits.

What angle should panels use on a flat roof?

Flat-roof mounting systems commonly use relatively shallow angles to balance generation, row spacing, wind forces and roof capacity. The best angle cannot be selected independently of the complete layout.

Can solar panels be installed completely flat?

They can operate horizontally, but a completely flat installation may collect more dirt and water and can be harder to keep clean. Even a nominally flat roof normally has a drainage fall. The mounting system must be approved for the proposed inclination.

Do flat-roof panels need ballast?

Many flat-roof systems use ballast, but mechanically fixed and mechanically restrained systems are also available. The correct method depends on the roof structure, covering, warranty, exposure and mounting-system design.

How much weight does a ballasted solar system add?

There is no reliable universal figure. Required ballast varies with the building, location, panel angle, mounting system and position on the roof. A structural engineer must assess the proposed system and ballast load.

Can solar panels damage a flat-roof membrane?

A correctly designed system uses compatible protection layers and maintains drainage and weather-tightness. Damage remains possible if the materials are incompatible, loads are concentrated incorrectly, fixings are poorly sealed or access causes wear.

Does a battery make south-facing panels the better choice?

Not automatically. A battery can store a south-facing midday surplus, while an east–west layout may generate closer to the times electricity is consumed. The result depends on the battery, tariffs and household demand.

Do east- and west-facing panels need separate inverter inputs?

They will normally be connected to separate MPPT inputs because the two orientations experience different conditions. The precise arrangement depends on string lengths, inverter limits and manufacturer instructions.

Can optimisers solve inter-row shading?

Optimisers may reduce some electrical consequences of uneven shading, but they cannot recover sunlight that never reaches a panel. Good row positioning remains the first priority.

How close can solar panels be installed to the roof edge?

There is no single setback suitable for every roof. Wind calculations, planning, maintenance, fire access, drainage and safe working requirements all affect the usable perimeter area.

Do I need planning permission?

Many domestic flat-roof installations in England fall under permitted development, subject to limitations and conditions. Listed buildings, designated land, flats, leasehold properties and locations with restricted permitted development rights require additional checks.