UPSC Prelims 2014 Q7: Science & Technology – Energy & Environment
With reference to technologies for solar power production, consider the following
statements:
1. 'Photovoltaics' is a technology that generates electricity by direct conversion of light into
electricity, while 'Solar Thermal' is a technology that utilizes the Sun's rays to generate heat
which is further used in electricity generation process.
2. Photovoltaics generates Alternating Current (AC), while Solar Thermal generates Direct
Current (DC).
3. India has manufacturing base for Solar Thermal technology, but not for Photovoltaics.
Which of the statements given above is/are correct?
- (a) 1 only
- (b) 2 and 3 only
- (c) 1, 2 and 3
- (d) None
Answer: (a) 1 only
Explanation
Technologies for solar power
| Statement | Verdict | Fact |
|---|---|---|
| 1. Photovoltaics converts light directly into electricity, while Solar Thermal uses the Sun's rays to generate heat which is then used to generate electricity | Correct | This is the basic difference |
| 2. Photovoltaics generates Alternating Current (AC), while Solar Thermal generates Direct Current (DC) | Incorrect | It is the reverse: PV cells give DC; solar thermal plants drive a turbine and give AC |
| 3. India has manufacturing base for Solar Thermal technology, but not for Photovoltaics | Incorrect | India manufactures photovoltaic cells and modules |
The two technologies compared:
| Feature | Photovoltaics | Solar Thermal (CSP) |
|---|---|---|
| Works by | Photovoltaic effect in silicon cells | Mirrors focus heat to make steam |
| Output | DC (an inverter makes it AC) | AC from a turbine |
| Storage | Batteries | Molten salt stores heat |
Answer: (a) 1 only.
Why each option is right or wrong
- (a) CORRECT. Only statement 1 describes Photovoltaics and Solar Thermal correctly.
- (b) Incorrect. Statements 2 and 3 are both false.
- (c) Incorrect. Statement 2 swaps AC and DC, and statement 3 is false.
- (d) Incorrect. Statement 1 is true, so 'None' is wrong.
Key point
Photovoltaics: light to electricity directly, DC output. Solar thermal: heat to steam to turbine, AC output. India makes PV cells and modules.
Remember
PV = DC from light; solar thermal = AC from heat.
Common mistakes
- Swapping which technology gives AC and which gives DC.
- Thinking India has no photovoltaic manufacturing.
- Confusing solar thermal power with solar water heaters.
Exam tip
Cells give DC; turbines give AC. A solar cell has no moving parts, so it cannot make AC.
Sources
- Ministry of New and Renewable Energy — Solar energy: photovoltaic and solar thermal programmes
- NCERT Class XII — Physics Part II (Semiconductor Electronics: solar cell)