Efficiency measures how effectively a panel converts sunlight into electricity.

• If 1,000 watts of sunlight hit a square meter of solar panel and it produces 200 watts of electricity, the panel’s efficiency is 20%.
• The rest is lost as heat, reflection, or electrical resistance.

Standard Test Conditions (STC) are used for ratings:

• Light intensity: 1,000 W/m²
• Cell temperature: 25°C (77°F)
• Air mass: 1.5

But real life is different. Weather, shade, panel angle, and system design all affect how much energy you actually get.

Efficiency vs Power Output: Why Size Matters

A common misconception is that higher-efficiency solar panels automatically generate more electricity. In fact:

• Two 400W panels (18% vs 23%) will both produce 400W.
• The difference is that the 23% panel needs less roof space.

If roof space is limited (urban homes, RVs, boats), high efficiency is critical.
If space is plentiful (farms, large roofs), lower-efficiency panels may deliver the same energy at a lower cost.