Explore More Physics Tools
Mastering Heat & Solar Energy
Whether you're designing a solar array, calculating insulation for a building, or studying thermodynamics, understanding Heat Flux is essential. It's simply the flow of energy through a surface. Our tool lets you convert units instantly and even estimate the power output of solar panels under different sky conditions.
Solar & Thermal Tools
Solar Power
Use the "Solar Calculator" tab to see how much energy a panel generates. Test Cloudy (100 W/m²) vs Clear Sky (1000 W/m²).
High Intensity
Working with lasers or CPUs? Convert to W/cm² to handle high-density heat flux measurements easily.
HVAC Design
Convert international SI units ($W/m^2$) to US Engineering units ($BTU/h\cdot ft^2$) for insulation and cooling load calcs.
What is Solar Irradiance?
The Power of the Sun
Solar Irradiance is just a fancy term for "Heat Flux from the Sun." In space, the sun blasts us with 1,361 Watts for every square meter.
By the time it travels through our atmosphere, we get about 1,000 W/m² on a clear day at noon. This figure (1 kW/m²) is the industry standard for rating solar panels.
Flux Levels
Did you know?
Solar Panel Ratings are optimistic.
A "400 Watt" solar panel produces 400W only when the heat flux is exactly 1000 W/m² and the temperature is 25°C. In real life, heat reduces efficiency! A hot roof can lower output by 10-20%, even on a sunny day.
Frequently Asked Questions
What is Heat Flux density?
Heat Flux Density (or simply Heat Flux) is the rate at which heat energy passes through a surface per unit area. Think of it like rain falling on a roof: Heat Flux is how much water (energy) hits each square meter every second.
What is standard Solar Irradiance?
Standard solar irradiance at Earth's surface on a clear day is approximately 1,000 W/m² (1 kW/m²). This value is often used to rate the peak power output of solar panels.
How do I convert W/m² to BTU/h·ft²?
Multiply your W/m² value by 0.317. For example, 100 W/m² ≈ 31.7 BTU/h·ft². This is useful for converting SI solar data into US HVAC standards.
How much power does a solar panel generate?
It depends on the Flux (Sunlight) and Efficiency. Formula: Power (W) = Irradiance (W/m²) × Area (m²) × Efficiency (%). Our 'Solar Calculator' tab does this math for you!
What is Critical Heat Flux?
Critical Heat Flux (CHF) is a limit in boiling heat transfer. If the heat flux exceeds this limit, bubbles form so fast they insulate the heater surface, causing temperature to spike dangerously (e.g., in nuclear reactors).
Why use W/cm²?
W/cm² is used for high-intensity heat sources where square meters are too big. For example, a CPU processor might emit 50 W of heat from a tiny 2 cm² chip, giving a massive flux of 25 W/cm².
What is the Solar Constant?
The Solar Constant is the flux density of solar radiation in space (outside Earth's atmosphere). It is approximately 1,361 W/m². Clouds and air absorb some of this, which is why we only get ~1,000 W/m² on the ground.
Does temperature affect Heat Flux?
Yes. Heat flux is driven by temperature difference (ΔT). The greater the temperature difference between two objects, the higher the heat flux flowing between them.
What is an R-Value?
R-Value measures resistance to heat flux. A high R-Value (like in good insulation) means low heat flux—it keeps heat from flowing through your walls.
Is 'Sunlight' heat flux?
Yes! Sunlight is electromagnetic radiation that carries energy. When it hits a surface (like your skin or a solar panel), that energy is absorbed as heat. This is why 1000 W/m² of sunlight feels hot!