Solar & battery
Solar Replacement Calculator
When replacing solar equipment pays, comparing degraded output against the cost of new.
Result
Panels rarely fail outright; they fade slowly and usually still work at 25 years. The case for replacing is normally about fitting more capacity on the same roof with better modules, or a roof that needs replacing anyway, rather than about degradation. Removing and refitting an array during roof work is a real cost that belongs in this comparison.
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About this calculator
Do panels just stop working?
Very seldom. They degrade slowly and most 25 year old arrays still produce 80% or more. Inverters are the component that actually fails.
When is repowering worth it?
Usually when the roof needs replacing anyway, or when modern panels would fit substantially more capacity into the same area. Both change the arithmetic far more than degradation does.
The formula
current output = new output x (1 - degradation)^age; payback = cost / (extra kWh x rate)
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