Solar System Designer Tools
Peak Sun Hours Calculator by Location
Enter your city or address to get the average daily peak sun hours for your location — the most critical input for accurately sizing solar panels and predicting energy production.
What Are Peak Sun Hours?
A peak sun hour is one hour during which solar irradiance averages 1,000 watts per square meter (W/m²) — the standard testing condition used to rate solar panels. It is not the same as hours of daylight.
For example, a location that receives 5 peak sun hours per day means that the total daily solar energy is equivalent to 5 hours at 1,000 W/m², even though the sun might be up for 10–14 hours. Early morning and late afternoon contribute less energy than midday sun.
Why Peak Sun Hours Matter for Solar Sizing
- Panel sizing: Daily energy output = Panel Wattage × Peak Sun Hours
- Battery sizing: Your battery must store enough for the night plus cloudy days
- Charge time: More peak sun hours = faster battery recharge
- System ROI: Higher sun hours = faster payback period
Frequently Asked Questions
How do I use peak sun hours in my solar calculation?
Multiply your solar panel wattage by the peak sun hours to get daily energy production. Example: 2,000W array × 5 peak sun hours = 10,000 Wh (10 kWh) per day before losses. Apply a 20–25% derating for real-world efficiency to get ~7.5–8 kWh actual yield.
Does panel tilt and orientation affect peak sun hours?
Yes significantly. South-facing panels tilted at your latitude angle capture the most annual energy. East or west orientation reduces yield by 15–20%. Flat roofs lose 10–15% vs. optimal tilt. The lookup tool returns an estimate based on your location's horizontal irradiance — add tilt corrections for final system design.
What is the difference between peak sun hours and insolation?
They refer to the same thing. Solar insolation (measured in kWh/m²/day) at the 1,000 W/m² reference level equals peak sun hours numerically. A location with 5 kWh/m²/day insolation has 5 peak sun hours per day.
Should I design for average or worst-month peak sun hours?
For off-grid systems, always design for the worst month (typically December in the northern hemisphere). Grid-tied systems with net metering can be designed for annual average. An off-grid system sized for December will overproduce in summer, which is acceptable and often desirable for charging extra capacity.
How does shading affect my effective peak sun hours?
Even partial shading of one cell in a panel can reduce the entire panel's output by 50–80% unless the system uses module-level optimizers or microinverters. Trees, chimneys, or nearby structures that cast shadows between 9 AM and 3 PM will significantly reduce your effective peak sun hours.