Insolation

Insolation refers to the total amount of solar radiation received per unit area over a specific period of time. It represents how much sunlight (shortwave radiation) actually reaches a surface—typically measured in kWh/m²/day or kWh/m²/year. Insolation is one of the most important variables in solar system design because it directly determines how much energy a solar array can produce.

Across the solar industry, insolation data is used for PV modeling, system sizing, production forecasting, site comparison, tilt optimization, and shading analysis. Solar designers rely on accurate insolation maps and POA (Plane of Array) irradiance models to estimate real-world performance, especially when designing using tools like Solar Designing and shading assessment engines such as Shadow Analysis.

Key Takeaways

Insolation measures the total solar energy received over time—critical for PV performance modeling.
It varies by region, season, tilt, orientation, atmosphere, and shading.
POA insolation is the most accurate metric for real PV production.
High-insolation locations produce significantly more solar energy per installed kW.
Tools like SurgePV help designers model insolation accurately and optimize system performance.

What Is Insolation?

Insolation is the total solar energy received on a surface over a defined time period. Unlike irradiance, which measures solar power at a single moment, insolation measures the accumulated solar energy over hours, days, months, or years.

Solar professionals use insolation to:

Compare the energy potential of different project locations
Estimate daily and annual energy production
Optimize tilt and azimuth
Determine system sizing
Evaluate shading impacts over time

Foundational related terms include Solar Irradiance, Plane of Array Irradiance, and Shading Analysis.

How Insolation Works

The amount of insolation at a location depends on several environmental and geometric factors:

1. Sun Angle & Solar Geometry

Higher sun angles deliver more energy; lower angles deliver less.

Calculate using the Sun Angle Calculator.

2. Geographic Latitude

Regions closer to the equator receive higher annual insolation.

3. Tilt & Orientation

Optimizing the plane of the solar array increases total insolation exposure.

4. Atmospheric Conditions

Clouds, haze, humidity, and pollution reduce insolation.

5. Seasonal Variation

Summer months deliver higher insolation; winter yields significantly less.

6. Shading

Obstructions (trees, neighboring buildings, chimneys) reduce daily accumulated energy.

Evaluate shading using Shadow Analysis.

7. Albedo (Ground Reflectivity)

Higher-albedo surfaces (sand, concrete, snow) increase reflected irradiance:

See Albedo.

Types / Variants of Insolation

1. Global Horizontal Insolation (GHI)

Total sunlight received on a flat, horizontal surface.

Common metric used for regional solar resource maps.

2. Direct Normal Insolation (DNI)

Sunlight received when pointed directly at the sun.

Primarily used for concentrating solar systems.

3. Diffuse Horizontal Insolation (DHI)

Sunlight scattered through the atmosphere.

Important for cloudy regions.

4. Plane of Array Insolation (POA)

The most important insolation value for PV design.

Represents energy received by the actual solar panel tilt.

See POA Irradiance.

How Insolation Is Measured

Insolation is typically measured using:

kWh/m²/day or kWh/m²/year

The accumulated energy per square meter.

Pyranometers

Field instruments used in utility-scale monitoring.

Satellite Data & Solar Databases

Used in software-based modeling.

POA Modeling Engines

Used in design tools such as SurgePV to calculate real panel exposure.

Typical Values / Ranges

Solar designers use average annual insolation as a baseline for production forecasts.

Practical Guidance for Solar Designers & Installers

1. Always use POA insolation—not just GHI

POA reflects the actual array performance, incorporating tilt and orientation.

2. Use shading tools to adjust insolation values

Shading reduces daily insolation even if regional averages are high.

Run shade simulations using Shadow Analysis.

3. Optimize tilt for maximum insolation

Check tilt using the Roof Pitch Calculator.

4. Use insolation maps during site selection

Choose sites with higher insolation for utility-scale or C&I development.

5. Apply insolation to sizing tools

Use Solar Panel Sizer for residential/commercial systems.
Use Solar ROI Calculator to calculate payback based on insolation-driven production.

6. Review monthly insolation profiles

Seasonal variation affects inverter clipping, battery sizing, and system yield.

7. Validate insolation values in 3D modeling

Incorporate terrain, obstructions, and POA adjustments for large projects.

Real-World Examples

1. Residential Rooftop System

A home in California receives an average of 5.7 kWh/m²/day of insolation.

A 7 kW system generates approximately 10,500–12,000 kWh/year due to strong POA exposure.

2. Commercial Flat Roof

A warehouse in New Jersey receives 4.2 kWh/m²/day, requiring a slightly larger system compared to high-insolation regions to achieve the same output.

3. Utility-Scale Solar Farm

A desert site receives 7.8 kWh/m²/day, making it ideal for utility-scale PV.

Developers optimize tilt and row spacing to maximize annual insolation capture.