Solar & battery
Solar Panel Quantity Calculator
Panels to order for a system, with spares for breakage in transit and handling.
Result
Order a spare or two on anything sizeable. Glass breaks in transit and on roofs, and a single replacement panel ordered later often costs more in freight and delay than it does in equipment. Matching a discontinued model years later is worse again.
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About this calculator
Should panels all be the same model?
Within a string, yes. Mismatched panels drag the string down to the weakest one, and mixing models also complicates the voltage calculation.
How many spares?
One or two on a residential job. On commercial work a percentage is normal, both for breakage and so future repairs can use a matching module.
The formula
panels = system watts / panel watts, plus spares
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