Solar Panel Efficiency and Degradation: What to Tell Your Customers

Customers compare panels on a single number — efficiency — and worry about a second — how fast they wear out. A good installer explains both honestly, because over-promising here destroys trust later.

What efficiency actually means

Panel efficiency is the share of sunlight a module converts to electricity. Higher efficiency means more power from the same roof area — which matters most when roof space is tight. On a large roof, a slightly lower-efficiency panel can be the smarter economic choice.

Degradation: panels age, slowly

Modern panels lose a small percentage of output in the first year, then degrade gradually each year after. Quality manufacturers warrant a guaranteed output (often around 80–90%) at 25 years. The honest message: production declines slowly and predictably, and is already factored into a good production estimate.

Temperature matters more than people think

Panels produce less as they get hotter. In hot climates, real-world output runs below lab ratings — which is exactly why production should be modelled from local irradiance and temperature data, not a flat assumption.

What to actually tell the customer

• Efficiency matters most when roof space is limited.
• Output declines slowly and is covered by a long performance warranty.
• Real production depends on heat, shading and orientation — not just the spec sheet.
• Trust a modelled estimate over a salesperson’s round number.

SolarStack’s assessment models real production across four independent data sources and accounts for shading and temperature — so the figure you quote is the figure that holds up.