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How Many Solar Panels Do I Need? A Simple Sizing Guide
Quick Answer
Short answer: take your daily electricity use in kWh, divide by your area's peak sun hours, and divide again by your panel wattage. A home using 30 kWh a day in a 5-sun-hour location needs about a 7.5kW array — roughly nineteen 400W panels. Off-grid homes should size for winter sun, not summer, which usually means a bigger array than the grid-tied math suggests.
The Formula
- Step 1 — daily use: monthly kWh from your utility bill ÷ 30. (Off-grid? Add up your loads instead — our battery sizing guide shows how.)
- Step 2 — array size: daily kWh ÷ peak sun hours ÷ 0.85 (system losses) = array size in kW. Sun hours: roughly 4 in the cloudy north, 5 across most of the US, 6 in the desert southwest.
- Step 3 — panel count: array kW × 1,000 ÷ panel watts (400W is today's standard residential size).
Panel Count Table (400W Panels)
| Daily use | 4 sun hours | 5 sun hours | 6 sun hours |
|---|---|---|---|
| 10 kWh/day | ~3.0kW — 8 panels | ~2.4kW — 6 panels | ~2.0kW — 5 panels |
| 20 kWh/day | ~5.9kW — 15 panels | ~4.7kW — 12 panels | ~3.9kW — 10 panels |
| 30 kWh/day | ~8.8kW — 22 panels | ~7.1kW — 18 panels | ~5.9kW — 15 panels |
| 40 kWh/day | ~11.8kW — 30 panels | ~9.4kW — 24 panels | ~7.8kW — 20 panels |
Reality Checks
- Roof space: a 400W panel covers roughly 21 sq ft. Twenty panels need about 420 sq ft of usable, reasonably sunny roof (or a ground mount).
- Winter rules off-grid: December sun hours can be half of June's. Off-grid arrays are sized to the worst month you plan to live through, with a generator covering the tail.
- Panels are the cheap part now: in a battery system, storage and the inverter dominate cost (see our off-grid system cost guide). Oversizing the array modestly is inexpensive insurance for cloudy weeks.
- Match the inverter: your array must respect the inverter's max PV input and voltage — the EG4 12000XP accepts up to 24,000W, the 6000XP up to 10,000W.
The Bottom Line
Most grid-tied homes land between 15 and 25 panels; most serious off-grid homes land between 20 and 40. Browse the panels themselves in our solar panels collection or skip the arithmetic with a pre-engineered package from our solar kits.
Prices checked November 6, 2026 at Renewable Outdoors — an authorized dealer with a Lowest Price Guarantee and financing through Affirm at checkout. Shop solar panels and complete solar kits
Frequently Asked Questions
How many solar panels does an average house need?
A home using about 30 kWh per day needs roughly 15-22 panels of 400W, depending on local sun hours (about 18 panels at 5 peak sun hours). Smaller or efficient homes using 20 kWh a day need about 10-15.
How much power does one solar panel make per day?
A 400W panel makes roughly 1.6-2.4 kWh per day in most of the US (400W × 4-6 peak sun hours, before system losses). Winter production in northern states can be half the summer figure.
Do I need more panels if I have batteries?
Batteries do not change the energy math — your array still has to replace what you use — but off-grid battery systems are sized for the worst winter week rather than the average day, which usually means a somewhat larger array plus a generator for extremes.
Can I add panels later?
Usually yes, if your inverter has PV headroom and your roof or ground mount has space. It is cheaper to leave headroom in the inverter choice (max PV input and MPPT voltage) than to max out a small inverter on day one.
