The Quick Formula

The number of solar panels you need depends on three things: how much electricity you use, how much sun your roof gets, and how efficient your panels are. Here's the quick formula:

Number of panels = Annual kWh usage ÷ (panel wattage × peak sun hours × 365) × 1,000

For most California homes, the answer falls between 15–25 panels, covering a 6–10 kW system. But let's dig into the details so you can get a more accurate estimate for your home.

Step 1: Find Your Annual Electricity Usage

Check your utility bill or online account for your annual kilowatt-hour (kWh) consumption. The average California home uses about 7,000–8,500 kWh per year, but this varies widely:

• Small home / low usage: 4,000–6,000 kWh/year → 10–15 panels
• Average home: 7,000–9,000 kWh/year → 16–22 panels
• Large home / high usage: 10,000–15,000 kWh/year → 23–35 panels
• Home with EV + pool: 15,000–25,000 kWh/year → 35–55 panels

Step 2: Account for California Sun Hours

Southern California gets approximately 5.5–6.0 peak sun hours per day, while Northern California averages 4.5–5.5 hours. More sun means fewer panels needed.

• Los Angeles area: 5.6 peak sun hours → excellent for solar
• San Diego: 5.7 peak sun hours → among the best in the state
• Inland Empire (Riverside/San Bernardino): 5.8–6.0 hours → ideal conditions
• Orange County: 5.5 peak sun hours → great for solar
• San Francisco Bay Area: 4.5–5.0 hours → still very productive

Step 3: Choose Your Panel Efficiency

Modern residential solar panels range from 370W to 440W per panel. Higher wattage means you need fewer panels for the same output. At Everysun, we use high-efficiency panels (up to 440W) that maximize production per square foot of roof space.

• Standard panels (370–390W): Good value, need more roof space
• High-efficiency panels (400–440W): Premium, fewer panels needed, better for limited roof space

System Size Examples for California Homes

Here are real-world examples based on typical California homes:

• 1,500 sq ft home, 2 people, low A/C: ~6 kW system = 14–16 panels
• 2,000 sq ft home, family of 4: ~8 kW system = 18–22 panels
• 2,500 sq ft home, family of 4, pool: ~10 kW system = 23–27 panels
• 3,000+ sq ft home, EV, pool, A/C: ~14 kW system = 32–38 panels

Roof Space Requirements

Each standard solar panel is about 17.5 sq ft (65" × 39"). Here's the roof space you'll need:

• 15 panels (6 kW): ~265 sq ft of usable roof space
• 20 panels (8 kW): ~350 sq ft
• 25 panels (10 kW): ~440 sq ft
• 35 panels (14 kW): ~615 sq ft

Not all roof space is usable — you need to account for setbacks from edges, vents, skylights, and shading. South-facing roof sections are ideal, but east and west-facing panels still produce 80–85% as much energy.

Should You Add Panels for an EV?

If you drive an electric vehicle (or plan to), you'll want to add panels to cover charging. The average EV adds about 3,000–5,000 kWh per year to your electricity usage:

• Moderate driving (10,000 miles/year): Add 3–4 panels
• Average driving (13,500 miles/year): Add 5–6 panels
• Heavy driving (20,000 miles/year): Add 7–9 panels

Battery Storage: Size It Right

Under NEM 3.0, adding battery storage maximizes your solar savings. A typical home battery stores 10–15 kWh, enough to power your home through peak evening hours. For larger homes or those seeking backup power, two batteries (20–30 kWh) provide extended coverage.

Get a Personalized System Design

Every home is different. The best way to know exactly how many panels you need is a professional site assessment that considers your roof orientation, shading, electricity usage patterns, and energy goals.

At Everysun, our team designs custom solar systems using satellite imagery and your actual utility data. Get a free consultation — we'll show you exactly what your system looks like and what it saves.