The Short Answer: Yes, But Less
Solar panels absolutely work on cloudy days. They produce electricity from light, not heat or direct sunlight specifically. On overcast days, they typically generate 10-25% of their rated capacity, depending on cloud thickness.
This is often a major concern for people in Seattle, Portland, the Northeast, or anywhere with significant cloud cover. The good news: solar works in all these places, and annual production—not daily weather—is what determines your savings.
How Much Power on Cloudy Days?
Solar panel output varies significantly based on cloud conditions. Here's what to expect:
| Weather Condition | Output vs Full Sun | 10 kW System Production |
|---|---|---|
| Clear, sunny day | 100% | 40-50 kWh/day |
| Partly cloudy | 50-70% | 20-35 kWh/day |
| Light overcast | 25-50% | 10-25 kWh/day |
| Heavy overcast | 10-25% | 4-12 kWh/day |
| Very dark/stormy | 5-10% | 2-5 kWh/day |
Edge of Cloud Effect
Interestingly, panels can briefly produce more than their rated capacity when the sun emerges at the edge of clouds. The combination of direct sunlight plus reflected light from nearby clouds can boost output by 10-30% for short periods.
Temperature Bonus
Cloudy days are often cooler, which actually helps solar panels. Panels lose efficiency at high temperatures (about 0.4% per degree C above 25C). So while cloudy days produce less light, the panels operate more efficiently on what light they receive.
Understanding Diffuse Light
Solar panels work with two types of light: direct and diffuse. Understanding this explains why they still produce on cloudy days.
Direct vs Diffuse Light
| Light Type | Description | Panel Response |
|---|---|---|
| Direct (beam) | Straight from sun, casts shadows | Maximum power output |
| Diffuse (scattered) | Scattered by atmosphere/clouds | Reduced but still significant |
| Reflected | Bounced from surfaces | Adds to total (minor) |
On a clear day, about 80% of solar energy is direct and 20% diffuse. On overcast days, it's nearly 100% diffuse. Panels convert both types to electricity, just more efficiently with direct light.
How Clouds Affect Light
- Thin clouds: Block some direct light, still allow significant diffuse
- Thick clouds: Block most direct, substantial diffuse remains
- Rain clouds: Block most light, some diffuse penetrates
- Fog: Similar to thin clouds, surprisingly productive
The Germany Example: Proof Solar Works in Cloudy Climates
Germany is the ultimate proof that solar works in cloudy climates. For years it was the world's #1 solar country, despite having weather similar to Seattle or Alaska.
Germany vs US Sunlight Comparison
| Location | Annual Sun Hours | Solar Viable? |
|---|---|---|
| Phoenix, AZ | 3,800+ | Excellent |
| Los Angeles, CA | 3,000 | Excellent |
| New York, NY | 2,500 | Very good |
| Seattle, WA | 2,200 | Good |
| Germany (average) | 1,600-1,800 | World leader |
Why Germany Succeeds
- Policy support: Strong feed-in tariffs and incentives
- High electricity rates: $0.35+/kWh makes solar very attractive
- System sizing: Systems sized for annual production, not peak
- Cultural adoption: Environmental priority drives adoption
- The lesson: Climate is NOT the determining factor—economics and policy are
Why Annual Production Matters More Than Daily Weather
Solar economics are based on annual production, not daily output. Net metering averages your production over time, so cloudy days are offset by sunny ones.
How Net Metering Handles Clouds
- Sunny day: Produce excess, export to grid, earn credits
- Cloudy day: Produce less, use credits from sunny days
- Monthly bill: Reflects net usage over entire period
- Annual true-up: Final reconciliation accounts for all seasons
Seasonal Variation Example
| Season | Solar Production | Usage Pattern | Net Result |
|---|---|---|---|
| Summer | High (long days) | AC increases use | Often net positive |
| Fall | Moderate | Low | Usually net positive |
| Winter | Low (short days) | Heating increases use | Often net negative |
| Spring | Moderate-high | Low | Usually net positive |
| Annual | Net zero to net positive (with proper sizing) | ||
Production Guarantees
Reputable solar installers provide production estimates based on:
- Historical weather data for your location
- Your specific roof orientation and tilt
- Shading analysis
- Equipment efficiency ratings
These estimates already account for typical cloud cover. Many installers even offer production guarantees—if your system underproduces, they compensate you.
Tips for Solar in Cloudy Climates
Optimize Your System Design
- Premium panels: High-efficiency panels capture more diffuse light
- Microinverters: Better performance in partial shading/clouds
- Size appropriately: Slightly oversize for annual offset
- West-facing option: More afternoon production when clouds often clear
Panel Technology Matters
| Panel Type | Cloudy Day Performance |
|---|---|
| Monocrystalline | Best (highest efficiency) |
| Polycrystalline | Good |
| Thin-film | Good-excellent (better diffuse capture) |
| Bifacial | Good (captures reflected light) |
Consider Battery Storage
In cloudy climates with time-of-use rates, batteries can help by storing surplus from sunny periods for use during cloudy days or peak rate hours. This maximizes the value of every kWh you produce.
The Bottom Line
Don't let cloudy weather deter you from solar. Panels work on overcast days, annual production matters more than daily weather, and net metering smooths out the variations. Germany proved that even very cloudy climates can be solar success stories. What matters most is your electricity rate, net metering policy, and roof suitability—not your weather forecast.
Concerned About Clouds in Your Area?
Tell us your location and we'll help you understand realistic solar production expectations and whether solar makes sense for your climate.
Get Climate-Specific Advice