Peak Sun Hours by City: US Solar Yield Reference for Apartment Balcony Panels

What Is a Peak Sun Hour?

Solar panels are rated at Standard Test Conditions (STC): 1,000 W/m² of irradiance, 25°C cell temperature, and standard spectrum. A 200W panel produces 200 watts under these exact conditions.

Real sunlight varies continuously. At dawn it's weak; at noon on a clear summer day it's near peak; clouds reduce it further. The "peak sun hour" concept converts all that variable real-world sunlight into a single daily number by calculating the equivalent number of hours at full STC intensity that would produce the same total energy.

A city with 5 PSH per day doesn't mean the sun is at full intensity for only 5 hours. It means the total daily solar energy received equals what you'd get from 5 hours of perfect STC sunlight. The actual sun might be above the horizon for 14 hours, but clouds, atmosphere, low-angle morning/evening sun, and seasonal variation reduce the effective total.

Annual Average vs Seasonal Variation

PSH data in this guide represents annual daily averages. Seasonal variation is significant:

• Summer (June–August): 20–40% higher than the annual average in most US cities
• Winter (December–February): 30–50% lower than the annual average
• Spring/Fall: Close to the annual average

For apartment balcony solar used as emergency backup, the annual average is the right figure for planning. If you're using solar to offset daily electricity costs, the seasonal variation matters more.

The Solar Yield Formula

For a conservative real-world estimate, use 0.75. For a well-optimized setup with ideal angle and no shading, use 0.85.

Example Calculations

Peak Sun Hours: 40+ US Cities

Data sourced from NREL PVWatts V8 (2023). Annual daily averages based on horizontal surface irradiance, adjusted for typical south-facing tilt. Actual values vary by specific location, microclimate, and panel orientation.

Daily Wh estimates assume 0.85 system efficiency. Actual production varies with panel tilt, shading, and panel degradation. PSH figures are annual averages from NREL horizontal plane irradiance data, adjusted for typical roof/balcony tilt.

What This Means for Charging Your Power Station

Assumes 200W panel at 0.85 system efficiency. Figures represent solar-only charging time from 0%. In practice, your power station is rarely empty when you start charging.

Balcony-Specific Factors That Affect Your Actual Yield

Tilt Angle

Solar panels produce maximum output when tilted at roughly your latitude angle facing south (in the northern hemisphere). A flat panel loses 10–20% of potential output compared to optimally tilted. Most balcony panels are placed leaning against a railing at roughly 60–80° from horizontal, steeper than optimal for most US cities but workable. The optimal tilt angle for each major US city is in our Balcony Solar Kit Guide.

Shading

Shading is the biggest yield killer for apartment solar. Even partial shading of a panel can reduce output by 50–80% because the shaded cells create resistance for the entire panel (unless it uses half-cut cells or microinverters). Check your balcony's sun exposure throughout the day before sizing your system. Buildings, awnings, and railings all cast shadows that move as the sun tracks across the sky.

Panel Orientation

South-facing is optimal. East or west-facing panels lose 15–25% of annual yield compared to south-facing at the same location. A panel mounted on a north-facing balcony loses 30–40% of potential yield (though it still produces significant power in summer when the sun is high).

Temperature

Solar panels produce less power as they heat up, roughly 0.3–0.5% efficiency loss per degree Celsius above 25°C. On a hot Phoenix day with the panel at 65°C, you'd lose about 12–16% of rated output. This is already partially accounted for in the 0.85 efficiency factor in our formula. Bifacial panels and panels with good rear ventilation tend to run cooler and lose less to temperature.

MPPT vs PWM Charge Controller

All portable power stations in our roundups use MPPT (Maximum Power Point Tracking) charge controllers, which capture roughly 10–30% more solar energy than older PWM (Pulse Width Modulation) controllers. This is already reflected in the 0.85 efficiency figure. If you're using a separate charge controller, make sure it's MPPT.

Related Guides

• Balcony Solar Kit Buyers Guide, Panel types, compatible power stations, and complete kit recommendations
• How Many Watt-Hours Do I Need?, Calculate what your solar system needs to sustain
• Are Balcony Solar Panels Legal?, State-by-state renter solar rights
• Best Portable Power Stations, Compatible power stations for your solar setup