Shadow Analysis and Layout Optimization Using PVsyst for Rooftop Solar PV Systems

🔍 1. Why Shadow Analysis Matters

• Even partial shading of a single cell can lower the power output of the whole module or string.

• Shading creates mismatch losses, hot spots, and higher risk of long-term damage.

• A well-designed system must avoid shading especially during the solar window (9 AM – 3 PM).

📊 FACT: A single tree shadow on 10% of an array can reduce total energy output by up to 30%!

✅ 2. How PVsyst Helps

PVsyst is one of the most trusted PV design and simulation tools worldwide. It includes:

• 3D shading scenes to model your roof and surroundings.

• Sun path visualizations for any location.

• Hour-by-hour shading factors.

• Calculation of annual shading losses.

• Layout optimization tools for row spacing and module arrangement.

✅ 3. Key Technical Concepts

📏 3.1 Basic Shadow Length Equation

Where:

• $L$ = Shadow length (m)

• $H$ = Height of the obstacle above module plane (m)

• $\theta$ = Solar elevation angle (°)

Example:
A 2 m high obstruction located 2 m away, at 30° solar elevation:

📐 3.2 Inter-Row Spacing Formula

When designing multiple tilted rows:

Where:

• $D$ = Minimum row-to-row spacing

• $H$ = Height difference between rows

• $\theta_{min}$ = Lowest sun elevation for your worst-case season

✅ 4. PVsyst Workflow: Shadow Analysis & Layout Optimization

Below is a clear, practical, step-by-step process for a rooftop system.

⚙️ Step 1: Create Your Project

1. Open PVsyst → Project Design → Create New Project.

2. Enter Project Name, Site Location, and System Type (Grid-connected Rooftop).

⚙️ Step 2: Define Site & Climate Data

1. Click Geographical Site.

2. Search your city (e.g., Phoenix, AZ) or enter Latitude/Longitude manually.

3. Import or link weather data (e.g., Meteonorm, TMY, NSRDB).

⚙️ Step 3: Build 3D Shading Scene

1. In Near Shadings, click 3D Scene Construction.

2. Model your roof:

   • Draw roof dimensions (length, width, height).

   • Add parapets or tilt structure.

3. Add obstructions:

   • Use Insert Object to place trees, water tanks, HVAC units.

   • Set correct height and position.

4. Place modules:

   • Use the PV Table object.

   • Arrange modules as per planned rows and tilt.

   • Align with south-facing plane (in the northern hemisphere).

✅ Pro Tip: Check dimensions carefully to match the real roof layout.

⚙️ Step 4: Visualize Solar Path

1. Click Sun Path → Check different times/dates.

2. Use the Animation Tool to see how shadows move.

3. Identify critical times when shadows fall on modules.

⚙️ Step 5: Calculate Shading Losses

1. In Near Shadings, click Shading Calculation.

2. PVsyst calculates:

   • Linear shading factor (how much physical shadow area covers modules).

   • Electrical shading effect (accounting for string and bypass diodes).

Example:

• Obstruction shading in winter may create 3–5% annual loss.

• PVsyst outputs Monthly Loss Diagrams for easy visualization.

⚙️ Step 6: Optimize Layout

For Multiple Rows:

1. Click Tools → Optimize Tilt & Spacing.

2. Enter tilt angle and row dimensions.

3. PVsyst suggests minimum spacing to avoid inter-row shading at worst-case sun elevation.

Example:

• Tilt: 30°

• Module height difference: 0.7 m

• Min solar elevation: 20° (winter)

✅ Update your layout spacing in the 3D scene.

⚙️ Step 7: Run the Full Simulation

1. Go to Simulation → Run.

2. Review the Performance Ratio (PR) and check the breakdown:

   • Shading loss %

   • Soiling loss %

   • Mismatch loss %

3. Tweak your design if shading losses exceed your acceptable limit (typically < 3–5%).

✅ 5. Real Example – Phoenix Rooftop

• Location: Phoenix, AZ

• Roof: Flat concrete, 15 m × 10 m, parapet 1 m.

• Obstruction: 2 m high vent 3 m from modules.

• Solar elevation: 30° → Shadow length ≈ 3.5 m.

• Row tilt: 30°, row height diff: 0.7 m → Min row spacing ≈ 1.9 m.

After PVsyst simulation:

• Annual shading loss: ~2.5%

• PR: ~81%

• Annual yield: 1650 kWh/kWp

✅ 6. Best Practices

✔ Always build the 3D scene to scale — use site photos & drone data if possible.
✔ Run shading animations for critical dates (winter solstice).
✔ Keep your shading loss under 5% by repositioning modules.
✔ For unavoidable shade, use DC optimizers or microinverters.

✅ 7. FAQs

Q1: Is PVsyst’s shading analysis accurate?

Yes, if your 3D model matches real dimensions. Always cross-check on-site.

Q2: Can I import 3D models?

Yes! You can import SketchUp (.3DS) files into PVsyst for complex roofs.

Q3: Does PVsyst consider module bypass diodes?

Yes. It models electrical losses considering cell strings and diodes.

Q4: What if shading is seasonal?

You can define obstacles as seasonal or adjust height by month.

Q5: Should I still check shadows on-site?

Absolutely. On-site surveys validate the PVsyst model. Use a Solar Pathfinder or a drone for accuracy.

✅ Conclusion

Shadow analysis is non-negotiable for high-performance rooftop PV systems. PVsyst makes this easy with powerful 3D visualization, shading factor calculations, and layout optimization tools. Following this step-by-step process helps you achieve the highest yield, the best layout, and the lowest shading losses — every time.