Why this topic is important for ECET?
Solar energy is one of the most important renewable energy sources, frequently asked in ECET exams because of its role in power generation, sustainability, and government initiatives in India. Understanding solar radiation, collectors, photovoltaic principles, and efficiency helps you solve both theoretical and numerical questions in ECET 2026 Mechanical.
📘 Concept Notes
🔹 What is Solar Energy?
Solar energy is the energy received from the sun in the form of electromagnetic radiation (light and heat). It is free, clean, and renewable.
- The Earth receives about 1.73 × 10¹¹ MW of solar energy continuously.
- This energy can be converted into:
- Thermal energy (using solar collectors, solar heaters).
- Electrical energy (using solar photovoltaic (PV) cells).
🔹 Key Terms
- Solar Constant (Gsc):
- The rate of solar radiation received on a unit area outside Earth’s atmosphere on a surface normal to sun rays.
- Value ≈ 1367 W/m².
- Solar Radiation at Earth Surface:
- Reduced due to absorption and scattering by atmosphere.
- Average clear sky value: 1000 W/m² (1 kW/m²).
- Solar Collector Types:
- Flat Plate Collectors (FPC): Low temperature (up to 100°C).
- Concentrating Collectors: Medium to high temperature (above 100°C, up to 2000°C).
- Solar Photovoltaic (PV) Cell:
- Directly converts solar radiation into DC electricity using semiconductors (silicon).
- Efficiency ≈ 15–20%.
- Applications of Solar Energy:
- Domestic: Solar water heater, solar cooker.
- Industrial: Solar power plants, desalination, drying.
- Rural: Street lighting, irrigation pumps.
🔹 Advantages of Solar Energy
- Renewable and eco-friendly.
- Reduces dependency on fossil fuels.
- Suitable for decentralized power.
🔹 Limitations
- Intermittent (depends on weather/daytime).
- Requires large land area.
- Initial installation cost is high.
⚙️ Formulas
- Solar Constant:
Solar Radiation on Earth (clear sky):
Solar Energy Collected by Area A:
where
- QQQ = Useful solar energy output (W)
- GGG = Solar insolation (W/m²)
- AAA = Collector area (m²)
- η\etaη = Collector efficiency
- Efficiency of PV Cell:
🔟 10 MCQs
Q1. The value of solar constant is approximately:
a) 1000 W/m²
b) 1367 W/m²
c) 1500 W/m²
d) 2000 W/m²
Q2. The average solar radiation available on Earth’s surface under clear sky is about:
a) 200 W/m²
b) 500 W/m²
c) 1000 W/m²
d) 2000 W/m²
Q3. A solar collector of area 5 m² receives insolation of 800 W/m² with efficiency of 50%. The useful heat gain is:
a) 1000 W
b) 1500 W
c) 2000 W
d) 2500 W
Q4. In a solar PV cell, the main semiconductor used is:
a) Copper
b) Silicon
c) Aluminum
d) Graphite
Q5. Flat plate collectors are generally used for:
a) High temperature applications (>1000°C)
b) Medium temperature applications (~200–500°C)
c) Low temperature applications (<100°C)
d) Nuclear energy conversion
Q6. Efficiency of commercial solar PV cells is generally in the range of:
a) 5–10%
b) 10–20%
c) 20–30%
d) 30–40%
Q7. The main limitation of solar energy is:
a) Abundant supply
b) Seasonal and weather dependency
c) Zero maintenance cost
d) High power density
Q8. A solar PV panel of 2 m² exposed to 1000 W/m² insolation gives output of 300 W. Its efficiency is:
a) 10%
b) 15%
c) 20%
d) 30%
Q9. The concentrating type solar collectors are mainly used for:
a) Cooking only
b) Low temperature heating
c) Medium and high temperature applications
d) Storage purpose
Q10. The unit of solar radiation (insolation) is:
a) Joule
b) W/m²
c) Newton
d) kWh
✅ Answer Key
| Q | Ans |
|---|---|
| 1 | b |
| 2 | c |
| 3 | c |
| 4 | b |
| 5 | c |
| 6 | b |
| 7 | b |
| 8 | b |
| 9 | c |
| 10 | b |
🧠 Explanations
- Q1: Solar constant = 1367 W/m² → (b).
- Q2: At Earth’s surface under clear sky = ~1000 W/m² → (c).
- Q3: Q=800×5×0.5=2000WQ = 800 × 5 × 0.5 = 2000 WQ=800×5×0.5=2000W → (c).
- Q4: PV cells mainly use silicon semiconductor → (b).
- Q5: Flat plate collectors work at low temp (<100°C) → (c).
- Q6: PV efficiency is 10–20% → (b).
- Q7: Main drawback = dependency on sunlight/weather → (b).
- Q8: η=300(1000×2)×100=15\eta = \frac{300}{(1000×2)} × 100 = 15%η=(1000×2)300×100=15 → (b).
- Q9: Concentrators are used for high-temperature apps → (c).
- Q10: Insolation is measured in W/m² → (b).
🎯 Motivation / Why Practice Matters
In ECET 2026, Energy Sources (especially Solar Energy) is a scoring area. Questions are usually direct, formula-based, and application-oriented. Practicing them builds speed and accuracy.
👉 Remember, a 2-mark solar question can be solved in 20 seconds if you’re clear with constants and formulas. That’s how you build a competitive edge over others!
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