Energy: renewable and non-renewable sources; conserving energy
Coal, petroleum and natural gas are non-renewable and pollute. Solar, wind, water and biomass energy are renewable and cleaner. Saving energy helps both.
Sources of energy
| Source | Type | Indian example | Merit or problem |
|---|---|---|---|
| Coal and lignite | Non-renewable | Neyveli and Mettur thermal power stations | Cheap, but gives smoke, CO₂ and fly ash |
| Petroleum and natural gas | Non-renewable | Vehicles, LPG; Cauvery basin wells | Limited stock; air pollution |
| Nuclear (uranium) | Non-renewable | Kudankulam (Tirunelveli district), Kalpakkam | Little CO₂, but radioactive waste |
| Solar | Renewable | Kamuthi solar park (Ramanathapuram district); rooftop panels | Clean, but needs sunny days |
| Wind | Renewable | Muppandal and Aralvaimozhi (Kanyakumari district) | Clean, but works only in windy places |
| Hydro (water) | Renewable | Mettur dam; Pykara (Nilgiris) | Clean, but dams flood forests and villages |
| Tidal and wave | Renewable | Possible sites on the Gujarat coast | Clean, but few suitable places |
| Geothermal | Renewable | Puga valley (Ladakh), Manikaran (Himachal Pradesh) | Heat from inside the Earth; few sites |
| Biomass and biogas | Renewable | Gobar gas plants in villages | Uses waste; the slurry is good manure |
Biogas
Biogas forms when cow dung, kitchen waste and plant waste rot without air in a closed tank called a digester. Bacteria break the waste down and give a gas that is mainly methane (up to 75%), with some carbon dioxide. It burns with a blue flame and no smoke, so it is good for cooking and lighting. The leftover slurry is a rich manure for fields.
Non-renewable vs renewable energy
Conserving energy
- Switch off lights, fans and the TV when not in use.
- Use LED bulbs instead of filament bulbs.
- Buy appliances with more BEE stars (more stars mean less electricity used).
- Use public transport, cycle or walk, and share rides.
- Use solar water heaters and solar cookers.
- Cook in pressure cookers and cover vessels to save LPG.
- Keep vehicles serviced, and switch off the engine at red signals.
Worked example: saving with LED bulbs
A family replaces 5 filament bulbs of 60 W with 5 LED bulbs of 9 W. Each bulb is used 5 hours a day. How many units are saved in 30 days, and how much money at an example rate of ₹ 7 per unit?
- Power saved per bulb = 60 W − 9 W = 51 W
- Power saved for 5 bulbs = 5 × 51 W = 255 W
- Energy saved per day = 255 W × 5 h = 1275 Wh = 1.275 kWh
- Energy saved in 30 days = 1.275 kWh × 30 = 38.25 kWh = 38.25 units (1 unit = 1 kWh)
- Money saved = 38.25 × ₹ 7 = ₹ 267.75
38.25 units are saved, worth ₹ 267.75 (about ₹ 268) a month at the example rate of ₹ 7 per unit.
Tamil Nadu has some of India's biggest wind farms at Muppandal and a huge solar park at Kamuthi. At home, cooking dal in a pressure cooker saves LPG.
2 marks: “What is biogas? Write its uses.” A gas, mainly methane, made when dung and waste rot without air in a digester. Used for smokeless cooking and lighting; the slurry is manure.
4 marks: “Distinguish between renewable and non-renewable sources of energy, with examples.” Renewable: never run out, little pollution, supply varies (solar, wind, biogas). Non-renewable: limited, pollute, steady supply (coal, petroleum, natural gas).
7 marks: “Explain any three renewable sources of energy and the ways to conserve energy.” Solar (Kamuthi), wind (Muppandal), biogas (methane, slurry); merits; conserving: switch off, LED, BEE stars, public transport, pressure cooker, solar heaters.
Some Wise Homes Try Green Bulbs: Solar, Wind, Hydro, Tidal, Geothermal, Biomass.