Why Shadow Analysis is Critical Before Installing Solar

Updated: June 2026  |  ← Back to Blog

The String Effect — Why One Shadow Kills the Whole System

In a standard solar system, panels are wired in series forming a "string" to achieve the inverter's minimum DC voltage (200–600V). A series circuit is only as strong as its weakest link. If even one cell of one panel is shaded, the entire string's output drops to match that shaded cell — sometimes called the "Christmas tree light effect."

Real-world impact: A shadow covering just 10% of one panel in a 10-panel string can reduce total system output by 40–60% during that period.

Common Shading Sources on Indian Rooftops

• Overhead water tanks (OHT) — Most common. Fixed obstacle, hard to relocate.
• TV/DTH dish antennas — Easy to move before installation.
• Parapet walls — Low-angle winter sun hits panels placed near walls.
• Neighbouring buildings — In dense cities, adjacent buildings can shade your roof for hours daily.
• Trees — Grow over time. Shadow-free today may be shaded in 3 years.
• Lift rooms, staircase structures — Common in apartment buildings, casting east-west shadows.

How Professional Shadow Analysis Works

1. Site survey — Physical measurement of all obstacles: height, distance, position relative to proposed panel area
2. Sun path simulation — Using PVsyst, Helioscope, or SketchUp to simulate the sun's exact path for your latitude/longitude for every hour of every month
3. Shading loss calculation — Annual shading loss percentage. Ideally below 3%. Above 5% requires layout redesign.
4. Layout optimisation — Panels repositioned to avoid shade zones. Inter-row spacing validated for winter low-angle sun.

Inter-Row Spacing — The Formula

When panels are installed in multiple rows on a flat roof, rear rows can shade front rows in winter. Standard minimum spacing formula for India:

Row spacing = Panel height × cos(tilt) + Panel height × sin(tilt) ÷ tan(sun altitude at winter solstice)

For Indian latitudes (15°–30°N) with a 15° tilt, minimum inter-row spacing is approximately 2× the panel height. Ask your installer for their shading loss simulation — any credible installer can share a PVsyst or Helioscope report.

Solutions When Shading is Unavoidable

• Half-cut cell panels: Splits each cell in two — shadow on the bottom half doesn't affect the top half. Minimal extra cost. Now standard on most PERC and TOPCon panels.
• DC Power Optimisers (SolarEdge): Individual MPPT per panel. Adds ₹3,000–5,000 per panel.
• Microinverters (Enphase): One inverter per panel — complete isolation. Adds ₹4,000–7,000 per panel. Best for complex multi-directional rooftops.
• Reduce capacity: Install fewer panels in shadow-free zones rather than forcing panels into shaded areas.