About the Structure Deflection
A deflection check confirms that mounting-structure members (purlins, rafters) do not sag beyond safe limits under wind and dead load — excessive deflection stresses modules and clamps and can crack cells.
Formula
Allowable deflection = Span ÷ limit (e.g. L/180)
- Span
- Unsupported member length (mm)
- limit
- Code deflection ratio — L/180 typical, L/240 stricter
How to calculate it
- 1Compute the actual deflection of the member under the design load.
- 2Compare it against the allowable = span ÷ deflection ratio.
- 3If actual exceeds allowable, increase the section size or reduce the span.
What you can calculate
- δ = 5wL⁴/384EI
- L/200 limit
- IS 800:2007
- Utilization ratio
Standards & references
Frequently asked questions
What is the allowable deflection for a solar structure?
Purlins and rafters are commonly limited to span/180 under load; stricter designs use span/240. Staying within the limit protects the modules and mounting clamps from stress.
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