Solar panels are the heart of solar power systems. They convert sunlight into electricity using semiconductors. Over the decades, these panels have evolved — becoming more efficient, more affordable, and more durable — shaping the green energy revolution we see today.
📆 The Journey of Solar Panel Technology
| Era | Technology | Characteristics |
|---|---|---|
| 1970s–90s | Crystalline Silicon (Mono & Poly) | Bulky, low efficiency (~10–14%) |
| 2000s | Thin-Film | Lightweight but less efficient |
| 2010s | Mono PERC | Higher efficiency (~18–21%), better low-light performance |
| 2020s | TOPCon & Bifacial | High efficiency (>23%), dual-side generation |
🌗 Monofacial vs. Bifacial Panels
🌞 Monofacial Panels
Absorb light only from the front side.
Work best when sunlight hits directly.
🌞🌞 Bifacial Panels
Generate electricity from both front and rear sides.
Rear side captures reflected light (e.g., from white roofs or ground).
Can boost power generation by 5–20% depending on installation.
🧪 What Is a Semiconductor and how It Powers the Solar Revolution?
Before we discuss on MonoPerc and Topcon Solar panels it is important to understand how the cells in the solar panel works and what is semiconductor of which the solar cells are made.
🔍 Definition:
A semiconductor is a material that conducts electricity under certain conditions, making it ideal for electronics and solar panels.
🔋 Simple Analogy to understand Semiconductors:
Think of a semiconductor like a gate in a dam:
When needed, it lets water (electrons) through in a controlled way.
It’s not always open (like conductors), and not always closed (like insulators).
They power all modern electronics—from solar panels to computers.The most commonly used is silicon.
⚙️ How It Functions
1. Atomic Structure
In a pure semiconductor (like pure silicon), each atom forms bonds with neighboring atoms. But at room temperature, some electrons gain energy and break free—leaving behind a “hole” (a place where an electron is missing).
Free electrons = negative charge carriers
Holes = positive charge carriers
These allow current to flow.
2. Doping: Enhancing Performance
By adding small amounts of impurities (called doping), we can control the behavior of the semiconductor:
- P-type (Positive): Creates more holes using elements like boron.
N-type (Negative): Extra electrons are added using elements like phosphorus.
3. P-N Junction: The Engine of Solar Panels
When P-type and N-type materials are joined, they form a P-N junction, which acts like a gate that only allows current to flow in one direction—key for creating diodes, transistors, and solar cells.
☀️ Role In Solar Panels:
Sunlight hits the P-N junction semiconductor.
Photons (light particles) energize electrons, causing them to move and create an electric current.
This creates direct current (DC) electricity, the P-N junction in the cell ensures that current flows in a usable direction.
🔍 What is Mono PERC?
Mono PERC (Monocrystalline Passivated Emitter and Rear Cell) uses a P-type base and a special rear-side passivation layer to reduce energy loss and enhance light absorption.
⚙️ Structure:
P-type silicon base
N-type emitter
Rear passivation
✅ Pros:
Affordable, mass-adopted
Improved over traditional monocrystalline
❌ Cons:
More prone to LID (Light Induced Degradation)
Lower temperature performance
Lower back-side light usage
🚀 What is TOPCon?
TOPCon (Tunnel Oxide Passivated Contact) uses an N-type silicon base with a tunnel oxide and passivated contact layer that dramatically reduces electron recombination.
⚙️ Structure:
N-type silicon base
P-type emitter
Tunnel oxide layer + rear passivated contact
✅ Pros:
Much higher efficiency (~23–24.5%)
Great low-light and high-temp performance
Excellent for bifacial setup
❌ Cons:
Slightly higher cost
⚔️ Comparison Between Mono PERC and TOPCon
⚖️ Mono PERC vs. TOPCon: Performance Comparison
| Feature | Mono PERC(P Type-Base) | TOPCon(N-Type Base) |
|---|---|---|
| Efficiency & Output | ~20–21% | ~23–24% ✅ |
| Bifacial Support | Limited | Excellent ✅ |
| Degradation Rate | 0.5–0.7%/year (More) | ~0.3%/year (Very Low) ✅ |
| Temperature Stability | Moderate | Better ✅ |
| Temp. Coefficient | ~-0.35%/°C | ~-0.29%/°C ✅ |
| Majority Carrier | Holes | Electrons ✅ |
| Light Sensitivity | Lower | Higher ✅ |
| Cost | Lower ✅ | Moderate |
🔍 Real-World Performance Comparison: Mono PERC vs. TOPCon
🌞 Scenario for comparison
| Feature | Mono PERC Panel | TOPCon Panel |
|---|---|---|
| Rated Power | 550W | 570W |
| Efficiency | 20.50% | 23.50% |
| Temp Coefficient | -0.35%/°C | -0.29%/°C |
| Degradation Rate | 0.6% per year | 0.3% per year |
| Ambient Temp | 45°C (avg day temp) | 45°C |
| Reference Temp | 25°C | 25°C |
| Sunlight | 6Peak Sun Hours/day | 6 Peak Sun Hours/day |
| Parameter | Mono PERC (550 W) | TOPCon (570 W) | Remarks |
|---|---|---|---|
| Initial Output (Ideal) | 550 W | 570 W | TOPCon has higher rated power and efficiency. |
| Temp. Loss @ 45 °C | (45-25) 20 °C × 0.35% = 7% → −38.5 W | (45-20) 20 °C × 0.29% = 5.8% → −33.1 W✅ | TOPCon performs better in high temperatures. |
| Net Output on Day 1 | 511.5 W | 536.9 W, ✅ | TOPCon gives ~25 W more per panel daily. |
| Year 1 Degradation | −3.3 W (0.6%) | −1.7 W (0.3%), ✅ | Slower degradation means TOPCon maintains output longer. |
| Year 1 Net Output | 508.2 W | 535.2 W, ✅ | Performance gap widens slightly over time. |
| Energy per Day (6 PSH) | 3.05 kWh/day | 3.21 kWh/day ✅ | TOPCon produces ~0.16 kWh more energy/day. |
| Annual Energy (1 panel) | ~1,113 kWh/year | ~1,171.5 kWh/year ✅ | ~58.5 kWh/year higher output → better ROI for commercial/residential use. |
| Extra Energy Gain | — | +5.3% over Mono PERC | More savings, especially valuable in high-load or high-cost areas. |
⚡ EXAMPLE 2: 10 kWp Solar Plant: Mono PERC vs. TOPCon – 1 Year & 25 Years Performance
Assumptions:
Plant size: 10 kWp
Sunlight: 6 Peak Sun Hours/day
Mono PERC Efficiency: ~20.5%, Degradation: 0.6%/year, Temp. Coeff: -0.35%/°C
TOPCon Efficiency: ~23.5%, Degradation: 0.3%/year, Temp. Coeff: -0.29%/°C
Location temperature: 45°C average
Reference temp: 25°C (standard test conditions)
📊 Table: Yearly and Lifetime Energy Generation – 10 kWp System
| Metric | Mono PERC (P-Type) | TOPCon (N-Type) | Remarks |
|---|---|---|---|
| Ideal Output (No temp loss) | 10 × 6 × 365 = 21,900 kWh | 10 × 6 × 365 = 21,900 kWh | Same design capacity |
| Temp Loss (20°C rise) | -7% → -1,533 kWh | -5.8% → -1,270 kWh | TOPCon performs better in heat |
| Year 1 Net Output | 21,900 − 1,533 = 20,367 kWh | 21,900 − 1,270 = 20,630 kWh | TOPCon generates ~263 kWh more |
| Degradation Over 25 Years | 0.6% per year | 0.3% per year | Slower decline with TOPCon |
| Cumulative Energy (25 years) | ~442,425 kWh | ~482,470 kWh | TOPCon gives ~40,045 kWh more over lifespan |
| % Gain with TOPCon | — | ~9% higher total yield | Better long-term ROI |
🧠 Key Takeaways
- Annual Gain: ~263 kWh/year more from 10 kWp TOPCon vs. Mono PERC
25-Year Gain: ~40,000+ kWh more, equal to ₹2–2.5 lakhs worth of power saved (₹5–6/unit)
Environmental Impact: Less panel waste due to slower degradation
Best Fit: Ideal for hot climates like much of India, where TOPCon’s thermal stability shines
🌗 Understanding The Impact of Bifacial Panels
Bifacial panels produce power from both front and rear sides by capturing reflected sunlight. This can boost energy output by 10–15% in well-designed setups, especially over reflective surfaces. They’re ideal for ground mounts and elevated rooftops, offering higher efficiency and better long-term returns.
Let’s take the above scenario of a 1o Kwp solar plant to understand the impact.
📌 Assumptions for the 10 kWp Solar Plant Comparison:
The solar system size is 10 kilowatts (kWp).
The location receives about 6 Peak Sun Hours per day.
There are 365 days in a year.
The average ambient temperature is around 45°C.
The standard test condition temperature is 25°C.
The degradation rate (performance drop per year) is:
0.6% per year for Mono PERC panels
0.3% per year for TOPCon panels
Bifacial panels (like TOPCon bifacial) can capture about 10% extra energy from the rear side, assuming good ground reflection (white/bright surface or open area).
All panels are mounted in a way that allows decent airflow and exposure, typical of rooftop or ground-mount systems in India.
📊 Table: 10 kWp Plant – Year 1 and 25-Year Generation Comparison
| Type | Year 1 Output (kWh) | 25-Year Total (kWh) | Remarks |
|---|---|---|---|
| Mono PERC (Monofacial) | ~20,367 | ~442,425 | Lower efficiency + higher degradation |
| TOPCon (Monofacial) | ~20,630 | ~482,470 | Better temp performance + lower degradation |
| TOPCon Bifacial | ~20,630 + 10% = 22,693 | ~530,700 | Rear-side gain adds ~2,000+ kWh/year extra |
🔍 Explanation:
TOPCon monofacial already gives ~263 kWh/year more than Mono PERC.
TOPCon bifacial gives another ~2,063 kWh/year gain due to rear-side reflection (ground, white surfaces, etc.).
Over 25 years, bifacial TOPCon can produce ~88,000 kWh more than Mono PERC!
This could equal ₹4–5 lakhs in extra savings (₹5–6/unit) depending on usage or net metering.
🌞 Bifacial Panel Advantage & Limitations:
✅ What Bifacial Panels Add:
Bifacial panels capture sunlight from both front and rear sides, using reflected light from the ground or surroundings.
In ideal conditions (white surface, elevated mounting), they can give up to 10–15% more energy compared to monofacial panels.
Perfect for open ground mounts, elevated rooftops, or solar carports with good rear-side exposure.
⚠️ Limitations of Bifacial Panels:
Limited rear-side gain if mounted flat on rooftops or without ground clearance.
Surface type matters – dark or shaded ground gives minimal reflection.
Soiling on rear (dust, bird droppings) also reduces effectiveness.
Slightly higher upfront cost and design complexity.
Incompatibility with some rooftop racking or small-scale setups.
🧾 Conclusion
- As solar technology evolves, TOPCon and bifacial panels are setting new benchmarks in performance, durability, and energy yield.
- Compared to traditional Mono PERC, TOPCon offers higher efficiency, better temperature tolerance, and lower degradation.
- When combined with bifacial design, it delivers even greater energy gains—especially in suitable environments.
- While initial costs may be slightly higher, the long-term benefits in terms of output, reliability, and savings make TOPCon bifacial panels the smarter choice for future-ready solar installations.
- For those aiming to maximize return and sustainability, the shift beyond Mono PERC is not just a trend—it’s the next standard.
