How to Size Solar PV Strings Correctly (550W Module Example

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🟦 Slide 1 – Hook Slide

Are You Sizing Solar Strings Correctly? ⚡

One wrong calculation →
Inverter damage.
System trips.
DISCOM rejection.

Let’s solve it step-by-step.

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🟦 Slide 2 – Why String Sizing Matters

PV string design must satisfy:

✅ Maximum inverter voltage (Cold condition)
✅ Minimum MPPT voltage (Hot condition)

Ignore temperature correction = Risky design.

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🟦 Slide 3 – Given Data (Real Case)

550W PV Module
Voc = 49.5V
Vmp = 41.2V

Inverter Range = 200V – 1000V

Site Temperature:
Min = –5°C
Max = 45°C

Temp Coefficient (Voc) = –0.28%/°C

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🟦 Slide 4 – Step 1: Correct Voc at Minimum Temperature ❄️

At low temperature → Voltage increases.

ΔT = 25 – (–5) = 30°C

Corrected Voc:

Voc = 49.5 + (0.0028 × 30 × 49.5)

Voc ≈ 53.66V

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🟦 Slide 5 – Step 2: Max Modules Per String

Max Modules
= 1000V ÷ 53.66V

= 18.63

We must round down.

✅ Maximum = 18 Modules per String

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🟦 Slide 6 – Step 3: Correct Vmp at High Temperature 🔥

At high temperature → Voltage decreases.

ΔT = 45 – 25 = 20°C

Vmp = 41.2 – (0.0028 × 20 × 41.2)

Vmp ≈ 38.9V

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🟦 Slide 7 – Step 4: MPPT Voltage Check

Total Vmp
= 38.9V × 18

≈ 700V

Check inverter minimum:

700V > 200V

✅ MPPT condition satisfied.

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🟦 Slide 8 – Final Design Summary

✔ Corrected Voc (–5°C) = 53.66V
✔ Max Modules = 18
✔ Corrected Vmp (45°C) = 38.9V
✔ Total String Vmp = ~700V

Design Status: SAFE ✅

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🟦 Slide 9 – Common Mistakes Indian EPCs Make

❌ Ignoring temperature correction
❌ Using STC voltage directly
❌ Not checking MPPT lower limit
❌ Oversizing beyond inverter max voltage

These mistakes cost lakhs in rework.

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🟦 Slide 10 – Engineering Insight

String sizing is not guesswork.
It’s temperature-based voltage engineering.

Correct design:

✔ Protects inverter
✔ Avoids winter overvoltage trips
✔ Ensures stable summer performance
✔ Improves long-term reliability

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🟦 Slide 11 – Call to Action

I build automated Solar String Sizing tools for EPC contractors.

If you want the Excel template used for this calculation:

Comment “STRING TOOL”
or DM me.

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📌 Caption for LinkedIn Post

Solar string sizing errors are one of the most common design mistakes in rooftop and ground-mounted projects.

In this post, I’ve broken down a real 550W module example with temperature correction.

If you're a solar contractor, EPC engineer, or electrical consultant — mastering this calculation is critical for safe and compliant system design.

Want the automated Excel string sizing tool?
Comment “STRING TOOL”.

#SolarEngineering #SolarPV #EPC #RenewableEnergy #ElectricalEngineering #SolarDesign #IndianSolar

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