Question
Classify the following as renewable or non-renewable energy sources: solar, coal, wind, natural gas, biomass, nuclear. What are the advantages and limitations of solar energy?
(CBSE Class 10 — Sources of Energy)
Energy Source Classification
flowchart TD
A["Energy Sources"] --> B["Renewable"]
A --> C["Non-Renewable"]
B --> B1["Solar Energy"]
B --> B2["Wind Energy"]
B --> B3["Hydroelectric"]
B --> B4["Biomass / Biogas"]
B --> B5["Geothermal"]
B --> B6["Tidal / Wave"]
C --> C1["Coal"]
C --> C2["Petroleum"]
C --> C3["Natural Gas"]
C --> C4["Nuclear (Uranium)"]
B --> D["Replenished naturally, won't run out"]
C --> E["Finite reserves, will exhaust"]Solution — Step by Step
| Source | Type | Reason |
|---|---|---|
| Solar | Renewable | Sun’s energy is practically infinite |
| Coal | Non-renewable | Takes millions of years to form from dead organisms |
| Wind | Renewable | Wind is driven by solar heating, constantly available |
| Natural gas | Non-renewable | Fossil fuel, limited reserves |
| Biomass | Renewable | Plants can be regrown; cattle dung is continuously produced |
| Nuclear | Non-renewable | Uranium reserves are finite (though last longer than fossil fuels) |
- Abundant — India receives about 5,000 trillion kWh of solar energy per year
- Clean — No pollution, no greenhouse gases during operation
- Free fuel — Sunlight costs nothing (only the equipment has a cost)
- Versatile — Can generate electricity (solar cells), heat water (solar heaters), cook food (solar cookers)
- Decentralised — Can be installed on rooftops in remote areas without grid connection
- Intermittent — Not available at night or on cloudy days
- Low efficiency — Current solar cells convert only 15-22% of sunlight to electricity
- High initial cost — Solar panels and batteries are expensive to install
- Large area needed — To generate significant power, large surface area is required
- Storage challenge — Storing solar energy in batteries adds cost and environmental concerns
Why This Works
Energy sources are classified based on their replenishment rate compared to consumption. Renewable sources are replenished by natural processes within a human lifetime. Non-renewable sources took millions of years to form (fossil fuels from ancient organisms, uranium from stellar processes) and are being consumed far faster than they form.
The distinction matters because over-reliance on non-renewable sources leads to depletion, price spikes, and environmental damage (CO2 emissions, climate change).
Alternative Method — Energy Conversion Chain
Every energy source involves conversions:
- Solar cell: Light → Electrical
- Wind turbine: Kinetic → Electrical
- Thermal plant (coal): Chemical → Heat → Mechanical → Electrical
- Hydroelectric: Potential → Kinetic → Electrical
- Nuclear: Nuclear → Heat → Mechanical → Electrical
More conversion steps generally mean lower overall efficiency.
CBSE often asks: “Why are we looking for alternative sources of energy?” The answer covers three points: (1) fossil fuels are finite and will run out, (2) burning fossil fuels causes air pollution and climate change, (3) fossil fuel prices are rising. Always mention all three for full marks.
Common Mistake
Students sometimes classify nuclear energy as renewable because “it produces no CO2.” While nuclear power is cleaner than fossil fuels, uranium is a finite resource mined from the earth — it will eventually run out. Some classify it separately as “non-conventional non-renewable.” For CBSE, treat it as non-renewable unless the question specifically discusses nuclear fusion (which uses hydrogen — practically unlimited, but not yet commercially viable).