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

Proper shadow analysis is essential for any rooftop solar PV design because shading dramatically reduces energy output. Using PVsyst, you can simulate real-world conditions, calculate shading losses accurately, and optimize the array layout for the best performance. This complete guide explains the technical concepts, equations, AND gives you a clear step-by-step workflow to use PVsyst — with examples — so you can do it confidently.

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🔍 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%!

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✅ 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.

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✅ 3. Key Technical Concepts

📏 3.1 Basic Shadow Length Equation

$$L = \frac{H}{\tan(\theta)}$$

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:

$$L = \frac{2}{\tan(30°)} \approx 3.46\;m$$

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📐 3.2 Inter-Row Spacing Formula

When designing multiple tilted rows:

$$D = \frac{H}{\tan(\theta_{min})}$$

Where:

• $D$ = Minimum row-to-row spacing

• $H$ = Height difference between rows

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

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✅ 4. PVsyst Workflow: Shadow Analysis & Layout Optimization

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

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⚙️ 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).

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⚙️ 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).

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⚙️ 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.

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⚙️ 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.

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⚙️ 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.

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⚙️ 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)

$$D = \frac{0.7}{\tan(20°)} ≈ 1.92\;m$$

✅ Update your layout spacing in the 3D scene.

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⚙️ 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%).

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✅ 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

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✅ 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.

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✅ 7. FAQs

Q1: Is PVsyst’s shading analysis accurate?

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

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Q2: Can I import 3D models?

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

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Q3: Does PVsyst consider module bypass diodes?

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

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Q4: What if shading is seasonal?

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

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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.

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✅ 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.

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