1.1.2 Why winter and summer production differ so much

A solar system can produce roughly half as much electricity in winter as in summer.

Some homeowners see their bill rise during winter and assume the system is broken. It usually isn't. There are four reasons for the gap:

1. Shorter daylight hours — 14+ hours of sun in summer, 9–10 in winter, roughly one-third less.
2. Lower sun angle — sunlight hits the roof at a steeper angle, so per-square-meter energy drops.
3. Weather — Southern California's rainy season starts in November; clouds, fog, and rain become more frequent.
4. Less overall light intensity — even though cooler panels are slightly more efficient, the longer atmospheric path in winter cuts the irradiance reaching your roof.

A lower winter output is a normal seasonal pattern, not a system failure.