How many solar panels to run a house?
Most homes require 15–25 solar panels to meet 100% energy needs, depending on household consumption (8,000–16,000 kWh/year), panel wattage (300–400W), and local sunlight hours. For example, a 400W panel generates ~1.6 kWh daily in 4 peak sun hours—20 panels yield 35kWh/day, covering a 10,000 kWh/year home. System losses (14%) and seasonal variations necessitate oversizing by 10–15%.
How is the number of solar panels calculated?
Calculate panels using annual kWh usage, panel wattage, and daily sunlight hours. Formula: (Yearly kWh ÷ 365) ÷ (Panel Watts × Sun Hours) ÷ 0.86 (inverter/line loss). A 10,000 kWh home with 400W panels in 5 sun hours needs (10,000 ÷ 365) ÷ (0.4kW × 5) ÷ 0.86 ≈ 16 panels.
Deep Dive: Start by auditing your last 12 utility bills for kWh/year. Next, divide by 365 for daily usage—27.4 kWh/day for 10,000 kWh. Factor in panel degradation (0.5%/year) and shading (10–25% loss). Pro Tip: Use NREL’s PVWatts tool for location-specific irradiance data. For example, a Phoenix home with 6.2 peak hours needs 30% fewer panels than a Seattle home with 3.8 hours. But what if your roof faces east-west? Expect 15–20% lower output versus south-facing.
| Scenario | Panels Needed | Notes |
|---|---|---|
| 10kW system | 25 x 400W | Ideal for 1,500+ sq.ft homes |
| Off-grid cabin | 8 x 350W | +20% for battery charging |
What factors affect solar panel count?
Key variables include panel efficiency (18–22%), roof space, battery storage, and energy habits. High-efficiency panels (e.g., SunPower 420W) need 23% less space than standard 320W models.
Deep Dive: Beyond panel specs, consider net metering policies—homes with 1:1 credits can undersize systems by 20%. Practically speaking, a 2,000 sq.ft roof fits 28–34 panels (15–18 kW system). Battery storage adds complexity: a 10kWh Powerwall requires 3–4 extra panels for charging. Why? Because charging losses and round-trip efficiency (90%) demand surplus solar. For example, Florida homes with pool pumps often add 5 panels to handle 3kW daytime loads.
| Panel Type | Efficiency | Panels Needed |
|---|---|---|
| Polycrystalline | 15–17% | 28 |
| Monocrystalline | 19–22% | 22 |
RackBattery Expert Insight
FAQs
Absolutely. Replacing HVAC (saves 30%) and LEDs (saves 15%) can cut panel needs by 8–12. Always audit usage first.
Do cloudy climates need more panels?
Yes—Seattle homes often add 35% more panels vs. Arizona. Microinverters help mitigate low-light underperformance.