Peak Sun Hours — The Number That Determines How Much Solar You Actually Get

You've seen the formula on solar quotations: kWp × Peak Sun Hours × Efficiency = Daily Output. But what exactly are peak sun hours — and why does the Philippines average 4.5?

What "Peak Sun Hours" Actually Means

Peak sun hours (PSH) is NOT the number of daylight hours. The Philippines gets roughly 12 hours of daylight — but most of those hours have low or moderate solar irradiance.

PSH is defined as the equivalent number of hours per day when solar irradiance averages 1,000 W/m² (full intensity). The sun might shine for 12 hours, but if the average intensity over those 12 hours is 375 W/m², that equals 4.5 peak sun hours (12 × 375/1000 = 4.5).

Peak Sun Hours Across the Philippines

The Monthly Variation — Why Summer Produces More

Using our 5.5 kWp system as an example, here's how monthly production varies across the year:

March–May is peak production season. July–August is the lowest due to the rainy season. But notice — even in the worst month, the system still produces 575 kWh and saves ₱6,325.

Why 85% System Efficiency?

No solar system converts 100% of the sun's energy. The 85% real-world efficiency factor accounts for:

• Inverter losses — DC to AC conversion (~3-5% loss)
• Heat derating — panels lose ~0.4% efficiency per °C above 25°C. In PH summers, panels reach 55-65°C, causing 12-16% heat loss
• Wiring losses — resistance in DC and AC cables (~1-2%)
• Dust and soiling — dirty panels lose 5-10% in dry season
• Shading and mismatch — even slight shading causes disproportionate losses in traditional string wiring

This is why installers should never quote you based on STC nameplate power alone — always ask for real-world yield calculations.

Our Solar Quotation Tool uses location-based peak sun hours and 85% real-world efficiency to give you accurate monthly production forecasts — not inflated marketing numbers.

Engr. Jason Morales — Founder, SolarEnergyPH