Washington Solar Production & Irradiance Data
3.4 peak sun hours/day · 5,940 kWh/year from a 6kW system · below national average
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Washington receives an average of 3.4 peak sun hours per day, which translates to a Global Horizontal Irradiance (GHI) of 3.4 kWh/m²/day. When solar panels are tilted at the optimal angle for Washington's latitude, irradiance increases to 3.9 kWh/m²/day — a 15% boost over flat-mounted panels.
This puts Washington below the national average of 4.29 peak sun hours per day. While Washington receives less sunlight than sun-belt states, solar is still a sound investment — especially when electricity rates and local incentives are factored in. Germany, with similar sun hours, is one of the world's largest solar markets. These figures are derived from NREL solar resource maps and PVWatts reference calculations.
Expected Annual Output by System Size
| System Size | Annual Output | Avg Monthly | Annual Savings | 25-Year Savings |
|---|---|---|---|---|
| 4 kW (12-16 panels) | 3,960 kWh | 330 kWh | $519/yr | $12,975 |
| 6 kW (18-24 panels) | 5,940 kWh | 495 kWh | $779/yr | $19,475 |
| 8 kW (24-32 panels) | 7,920 kWh | 660 kWh | $1,038/yr | $25,950 |
| 10 kW (30-40 panels) | 9,900 kWh | 825 kWh | $1,298/yr | $32,450 |
Based on 3.9 kWh/m²/day tilt irradiance, 14% system losses, and 13.11¢/kWh electricity rate. Actual output varies by installation specifics.
Month-by-Month Solar Production in Washington
Estimated monthly output for a 6kW system:
Solar production in Washington peaks in July when a 6kW system generates approximately 772 kWh — about 13% of annual production in a single month. The lowest production month is December at approximately 208 kWh (3.5% of annual output). This 3.7:1 seasonal ratio is significant — battery storage or time-of-use rate plans can help smooth out this variation.
How Washington Compares Nationally
Tips for Maximizing Solar Production in Washington
While Washington's 3.4 peak sun hours is below the national average, solar is still viable and cost-effective. Maximizing panel tilt angle and ensuring zero shading are critical to getting the most from your system.
Cloud cover is common in Washington, but modern solar panels still produce 10-25% of their rated output on overcast days. Monocrystalline panels with higher efficiency ratings (20%+) perform better in diffuse light conditions and are a smart choice for Washington homeowners.
Consider adding battery storage to your Washington solar system. A 10-13 kWh home battery lets you store excess daytime production for evening use, maximizing your self-consumption and reducing grid dependence. This is especially valuable for backup power during outages.
Solar Irradiance Technical Data
Global Horizontal Irradiance (GHI): 3.4 kWh/m²/day. GHI measures the total solar radiation received on a horizontal surface, including direct sunlight and diffuse radiation from clouds and atmospheric scattering. This is the baseline measurement for solar resource assessment.
Tilt Irradiance: 3.9 kWh/m²/day. When panels are tilted at the optimal angle for Washington's latitude, they receive 15% more solar radiation than flat-mounted panels. This tilt optimization is one of the easiest ways to boost your system's output.
System Output Estimation: The annual production figures use the NREL PVWatts methodology: Tilt Irradiance × 365 days × System Size × (1 − System Losses) × Inverter Efficiency. We use 14% system losses (wiring, soiling, degradation, mismatch) and 96% inverter efficiency, matching PVWatts defaults.
Washington Solar Production FAQ
How many peak sun hours does Washington get?▼
Washington averages 3.4 peak sun hours per day, which is below the national average of 4.29 hours. Peak sun hours represent hours of full-intensity sunlight equivalent — a key factor in estimating solar panel output. This data is derived from NREL solar resource maps and PVWatts reference calculations.
How much electricity will a 6kW solar system produce in Washington?▼
A 6kW solar system in Washington produces approximately 5,940 kWh per year, or about 495 kWh per month on average. Production peaks in July (approximately 772 kWh) and is lowest in December (approximately 208 kWh). At Washington's average rate of 13.11¢/kWh, this saves you about $779/year.
What is the best month for solar production in Washington?▼
July is typically the best month for solar production in Washington, with a 6kW system producing approximately 772 kWh. The long daylight hours and high sun angle combine for maximum energy generation. The worst month is December, producing about 208 kWh — roughly 27% of the best month's output.
How does Washington's solar potential compare to other states?▼
Washington's average of 3.4 peak sun hours per day puts it below the national average of 4.29 hours. A 6kW system in Washington produces 5,940 kWh/year, compared to the national average of 7,562 kWh/year — that's -1,622 kWh/year (-21%). Even at Washington's 13.11¢/kWh rate, solar delivers solid returns.
What affects solar panel output in Washington?▼
Key factors affecting solar output in Washington include: roof orientation (south-facing is ideal), tilt angle (latitude tilt of 35° is optimal), shading from trees or buildings, panel efficiency rating, and local weather patterns. Washington's GHI (Global Horizontal Irradiance) is 3.4 kWh/m²/day, but panels tilted at the optimal angle receive 3.9 kWh/m²/day — a 15% improvement over flat-mounted panels.
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Washington Solar Data
- ☀️ Peak Sun Hours: 3.4 hrs/day
- 📊 GHI: 3.4 kWh/m²/day
- 📐 Tilt Irradiance: 3.9 kWh/m²/day
- ⚡ 6kW Output: 5,940 kWh/yr
- 📈 Best Month: July
- 📉 Worst Month: December
- 💡 Electricity Rate: 13.11¢/kWh
- 💰 Annual Savings (6kW): $779
- 📋 Data: NREL Reference Data