How Shading Affects Solar Panels — Impact, Solutions & Prevention

Why Shading Is Solar's Biggest Enemy

Shading is the single most damaging factor for solar panel performance. Unlike intuition might suggest, a shadow covering just 10% of a panel can reduce output by 30–50%. This is because solar cells in a string are connected in series — the weakest cell limits the entire string's current.

Types of Shading

• Hard shading: Direct shadows from chimneys, trees, buildings, or antennas. Can reduce affected panel output by 50–90%.
• Soft shading: Diffuse shadows from clouds, haze, or distant objects. Reduces output by 10–30%.
• Soiling: Dust, bird droppings, or leaves acting as partial shade. Reduces output by 5–25%.

How Bypass Diodes Help

Modern panels like LONGi Hi-MO include bypass diodes (typically 3 per panel) that allow current to flow around shaded cell groups. Without bypass diodes, a shaded cell becomes a resistive load, wasting energy as heat and potentially causing hot spots.

Half-Cut Cell Advantage

LONGi Hi-MO panels use half-cut cells with a split-circuit design. The top and bottom halves operate semi-independently, so shade on one half only affects that half while the other continues producing at full capacity. This makes half-cut panels significantly more shade-tolerant than full-cell designs.

Solutions for Shaded Installations

• Power optimisers (e.g., SolarEdge): Module-level MPPT allows each panel to operate independently. Best for partial shading.
• Microinverters (e.g., Enphase): Each panel has its own inverter, eliminating string effects entirely.
• String design: Place shaded and unshaded panels on separate strings/MPPT inputs.
• Site assessment: Use shade analysis tools before installation to identify and mitigate shadows.

Frequently Asked Questions

Can one shaded panel affect the whole system?

In a string inverter system, one heavily shaded panel reduces the current of its entire string. Bypass diodes and half-cut cells mitigate this but cannot eliminate it. Power optimisers are the best solution for significant shading.

Do LONGi panels handle shade better than others?

LONGi Hi-MO panels use half-cut cells with 3 bypass diodes, providing excellent shade tolerance compared to full-cell panels. However, all panels are affected by shade — proper system design is essential.

Should I avoid solar if my roof has partial shade?

No. With power optimisers or microinverters, even partially shaded roofs can be viable. The key is accurate shade analysis and appropriate system design.