1.1 A system has only three core components

Whatever a salesperson tells you, a residential solar + storage system has only three pieces at its core:

1. Solar Panels / PV Modules — convert sunlight into DC electricity.
2. Inverter — converts DC into the AC your home and the grid actually use, and orchestrates the energy flow.
3. Battery (Energy Storage System, ESS) — stores daytime surplus for evening, cloudy days, or outages.

Plus the necessary supporting hardware: racking & mounting, conduit & wiring.

And the optional add-ons: monitoring gateway / CT clamps, an ATS (Automatic Transfer Switch), a Critical Load (Backup) Panel, and a Production Meter.

1.1.1 What "panel wattage" actually means

You see panels marketed as 440W or 500W. Those are the instantaneous output under Standard Test Conditions (STC): 1000 W/m² irradiance, 25°C cell temperature, no dust, no shade, sunlight hitting the cell at a 90° angle. Under those exact conditions a 500W panel produces 500W; run that for two hours and you get one kilowatt-hour.

Real conditions almost never match STC, so real production is lower.

A useful Southern California benchmark: a 10kW system with a clean orientation and no shading produces about 700–800 kWh per month in winter and well above 1,400 kWh per month in summer.

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.