How Many Solar Panels Do I Need in California?
The honest answer: it depends on how much electricity you use, how much sun your roof gets, and how much of your bill you want to erase. Below is a real calculator that turns your monthly usage into an approximate system size, panel count, and roof area — plus the math behind it and two actual Cali Energy install sizes for reference.
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Estimate your system in about 30 seconds
Enter your usage, adjust the assumptions, and see an approximate size. This is an estimate — a rooftop site visit gives the real number.
Assumes California production of ~1,600 kWh per kW-year (typical range 1,500–1,700, per NREL PVWatts) and roughly 21 sq ft per panel before setbacks. Estimate only.
The math behind the number
Sizing solar is straightforward arithmetic once you have three inputs.
1. Annual energy you want to cover
Monthly kWh × 12 × your offset target. If you use 900 kWh/mo and want a 100% offset, that's 10,800 kWh/year.
2. How much each kW produces
In California, 1 kW of panels makes roughly 1,500–1,700 kWh per year depending on location, tilt, and shading, per NREL's PVWatts model. The calculator uses ~1,600 as a midpoint.
3. System size → panel count
System kW = annual kWh ÷ production per kW. Panels = system watts ÷ panel wattage. A 6.75 kW system of 400 W panels is about 17 panels.
Shading is applied as a production haircut: an open roof keeps the full ~1,600 kWh/kW, partial shading trims it by roughly 15%, and heavy shading by roughly 30%. Fewer productive hours means you need more panels to hit the same offset. These are planning approximations; a designer uses actual satellite/LIDAR shade analysis and your roof's true orientation to refine them.
How much California sun actually helps
Production per kW varies across the state. Approximate PVWatts-style figures for a well-oriented rooftop:
| Area | Climate | kWh per kW-year (approx.) |
|---|---|---|
| High desert / Inland Empire (e.g. Palmdale, Riverside) | Hot, very sunny | ~1,650–1,750 |
| LA basin / San Fernando Valley | Sunny, mild | ~1,550–1,650 |
| Coastal (e.g. Santa Monica, Long Beach) | Marine layer | ~1,450–1,550 |
Sources: NREL PVWatts Calculator. Figures are approximate and vary by roof pitch, azimuth, and shading.
What actually moves your panel count
Your usage
The single biggest driver. Pull 12 months of kWh from your bill — not a single summer or winter month. LADWP bills most homes every two months, so read the kWh, not just the dollars.
Panel wattage
Higher-wattage panels mean fewer panels for the same kW. A 6.4 kW system is 16 × 400 W panels or about 13 × 500 W panels — same output, less roof.
Shading & orientation
South-facing and unshaded is best. Trees, chimneys, and north slopes cut production, so you may need extra panels to reach the same offset.
Future loads
Adding an EV, heat pump, pool, or ADU raises usage. It's often cheaper to size for that now than to expand later. Tell your designer what's coming.
Two real Cali Energy install sizes
For a sense of scale, here are two systems our in-house crews actually built.
~2.3 kW · about 6 panels
A compact accessory dwelling unit with modest, steady usage. Roughly six 400 W panels covered most of its load — enough to offset lights, a mini-split, and everyday plug loads.
Small footprint; sized to a low-usage unit, not a full house.
~11.9 kW · about 30 panels
A larger single-family home with high consumption — likely AC, and room for an EV. Around thirty 400 W panels put it near a full offset under California conditions.
Bigger homes with electrification trend toward 10–14 kW; yours depends on your bill.
Two things to weigh before you finalize size
NEM 3.0 changes the "100% offset" logic. If you're on SCE, PG&E, or SDG&E and applied for interconnection on or after April 15, 2023, you're on the CPUC's Net Billing Tariff (NEM 3.0), where exported energy is credited at much lower rates than what you pay. That makes oversizing purely to bank credits far less valuable, and it's a big reason many Cali homeowners now pair solar with a battery to use their own production at night. Municipal utilities like LADWP, Burbank, and Glendale are not on NEM 3.0 and run their own net-metering rules — so the "right" size can differ by utility.
The 30% federal tax credit has ended for homeowner-owned systems. Per the IRS, the Residential Clean Energy Credit is not available for systems placed in service after December 31, 2025. If you were counting on it to justify a larger system, re-run your numbers without it (any credit from a 2025 install can still carry forward).
Don't forget roof space
Panel count only matters if the panels fit. A modern 400 W panel occupies roughly 21 square feet, but a real array needs fire-code setbacks, walkways, and clear paths around vents and skylights — so plan for meaningfully more roof than "panels × 21." A 20-panel array is a rough ballpark of ~420 sq ft of module area, but the usable roof plane needs to be larger. Complex or multi-plane roofs, and any north-facing sections, reduce how many panels realistically fit in good sun.
Frequently asked
How many solar panels does an average California home need?
Most California single-family homes land somewhere between 15 and 30 panels. A home using ~900 kWh/month typically needs roughly a 6–7 kW system (about 16–18 panels at 400 W) for a full offset, while high-usage homes with AC and an EV can reach 10–14 kW (25–35 panels). Your exact count depends on your actual usage, shading, and roof orientation.
How much roof space do I need per solar panel?
A modern 400 W panel takes up roughly 21 square feet. But a real installation needs fire-code setbacks and clear paths, so plan for noticeably more roof than just panels multiplied by 21. A 20-panel array is about 420 sq ft of module area, on a usable roof plane larger than that.
How much electricity does one solar panel produce in California?
In California, 1 kW of panels produces roughly 1,500–1,700 kWh per year according to NREL PVWatts. So a single 400 W panel makes about 600–680 kWh per year, varying with location, roof tilt, and shading.
Should I size my system for 100% of my bill under NEM 3.0?
Not necessarily. Under the CPUC's Net Billing Tariff (NEM 3.0) for SCE, PG&E, and SDG&E customers, exported energy earns low credits, so oversizing to bank credits is less valuable. Many homeowners now pair solar with a battery instead. LADWP and other municipal utilities are not on NEM 3.0 and follow their own rules.
Is the 30% federal solar tax credit still available in 2026?
No — for homeowner-owned systems, the IRS Residential Clean Energy Credit is not available for systems placed in service after December 31, 2025. Credit from a qualifying 2025 install can still carry forward. Re-run your numbers without the 30% credit before finalizing system size.
Does the calculator give me an exact panel count?
No, it's an estimate. It sizes the array to your usage using average California production. Your real number comes from a site visit that accounts for your 12-month usage, roof pitch and azimuth, shading, electrical panel capacity, and your utility and rate plan. Cali Energy provides an exact count before installation.
Related reading
Sources & methodology
Figures on this page come from the primary sources below and, where noted, from Cali Energy calculations using the stated assumptions. Rates, incentives, and program terms change; each was verified August 4, 2026.
Get your exact panel count
The calculator gets you close — a Cali Energy site visit gives you the real number for your roof, usage, and utility. In-house crews serving LADWP, SCE, Burbank, and Glendale. Call +1 (323) 844-7777.
Get a free estimatePrepared by Cali Energy, August 4, 2026. This article is for general educational purposes only and is not legal, tax, financial, engineering, or utility advice. Rates, incentives, codes, permit requirements, equipment specifications, prices, and program terms may change; figures and timelines are estimates, not guarantees. Confirm current requirements with the applicable utility, AHJ, program administrator, manufacturer, or a licensed professional. See our Content Disclaimer. Cali Energy · 19201 Parthenia St Unit E, Northridge, CA 91324 · CSLB #1032379 (B, C-10, C-39)