East-west vs south module layout comparison

For commercial flat-roof PV systems, the choice between an East-West (symmetrical) and South (universal) module layout should be based on long-term return on investment (ROI) and levelized cost of energy (LCOE), not only on the initial price per Wp.

For installers and dealers, the optimal system layout often depends on roof constraints such as usable area, building height, and shading.
Below is a full comparison of both layouts for low-pitch flat-roof systems (10°–12° or 10°–15°).

1. Overall financial performance and profitability

Factor	East-West (Symmetrical)	South (Universal)	Key Insight
Profit & ROI	Often significantly more profitable. Example: 19.30% ROI vs. 17.20% for South.	Lower profit despite higher yield per Wp.	East-West energy is cheaper (€0.059/kWh vs €0.076/kWh).
Costs Per Wp	2.5%–5% cheaper per Wp. Cost advantage increases with system size.	Typically more expensive per Wp.	Efficient mounting and optimized inverter design reduce costs.
Fixed Costs	High roof density spreads fixed costs over more capacity.	Less efficient when fixed costs are high.	East-West helps absorb fixed costs more effectively.

2. Energy production and roof utilization

Yield per Watt-peak (Wp)

Winner: South layout

South-facing modules produce ~7.3% more energy per Wp compared to low-pitch East-West systems.
At larger tilts (e.g., 30°), South can exceed East-West by ~13%.
On commercial roofs (mostly low tilt), East-West compensates with higher density.

Yield per m² roof surface

Winner: East-West layout

East-West uses roof space more efficiently.
Up to 30% more Wp can be installed on the same roof.
Typically produces 20%–25% more total yield per m².
Example: 127 kWh/m² (E-W) vs. 100 kWh/m² (South).

If roof space is limited → choose East-West.

3. Yield distribution throughout the day

South Layout

Sharp production peak around noon.

East-West Layout

Smooth, extended production profile.
Better match to typical commercial consumption.
Lower peak power reduces inverter stress and allows higher DC:AC oversizing

4. Design and installation considerations

Factor	East-West	South	Design Implication
Shade	More shade-sensitive during morning/evening.	Better performance with morning/evening shade.	Extra attention needed for obstacles on East and West sides.
Mounting Costs	Up to 15% cheaper mounting. ~20% cheaper per Wp.	Requires more wind plates and material.	East-West uses back-to-back rows with minimal spacing.
Ballast & Weight	Requires less ballast; closed system, lower wind load.	Heavier with more ballast and wind deflectors.	Up to 30% lighter on roofs above 10 m height.

Conclusion for installers

While South-facing layouts generate higher yield per panel, East-West provides:

Higher total system yield per m²
Lower installation cost
Lower energy cost (LCOE)
Higher long-term profitability
Better use of limited roof space

Best analogy:

South layout = sprinter → highest peak performance.
East-West layout = marathon runner → more total output and better overall profitability.

For most commercial flat-roof projects, East-West is the optimal choice, especially when maximizing ROI, minimizing LCOE, and dealing with space constraints.