5. Towards Green Energy
You will learn Use of various energy sources • Generation of electrical energy • How power generation impacts the environment • Clean (green) alternatives like hydro, wind & solar.
Can you recall?
- What is Energy and its forms (mechanical, chemical, sound, light, heat)?
- Where do you use electricity daily and how is it produced?
Energy & Use of Energy
Modern life runs on energy—cooking, lighting, mobility, communication, industry. Energy can be converted from one form to another (e.g., chemical → thermal → mechanical → electrical).
Make a quick table (examples)
| Form Needed | Device / Example | Source feeding it |
|---|---|---|
| Light | LED Lamp | Electric grid (often from thermal/hydro/renewable) |
| Heat | Geyser / Solar water heater | Electricity / Solar radiation |
| Motion | Fan / Metro train | Electric motors (electrical → mechanical) |
| Chemical | Battery charging | Electricity stored chemically |
Generation of Electrical Energy — Faraday’s Principle
Most power plants use electromagnetic induction (Michael Faraday). When magnetic flux through a conductor changes, an emf is induced:
Faraday’s Law \( \quad \mathcal{E} \;=\; -\,\dfrac{d\Phi_B}{dt} \)
Flux changes if (i) a magnet rotates near a stationary coil, or (ii) a coil moves in a steady magnetic field. An electric generator exploits this. A turbine spins the generator’s rotor.
Thermal Energy–Based Power Station (Coal)
How it works
- Coal burns in a boiler → water becomes high-pressure, high-temperature steam.
- Steam spins the turbine → turbine spins the generator.
- Steam is condensed back to water in a condenser (via cooling tower) and recirculated.
Energy transformations: Chemical (coal) → Thermal (steam) → Kinetic (turbine) → Electrical.
Key parts
- Boiler • Steam turbine • Generator
- Condenser & Cooling tower
- Stack (exhaust gases)
Problems
- Air pollution (CO₂, SOₓ, NOₓ) and soot; respiratory issues.
- Finite coal reserves.
Examples (Capacity)
| Plant | State | Capacity (MW) |
|---|---|---|
| Vindhyanagar | Madhya Pradesh | 4760 |
| Mundra | Gujarat | 4620 / 4000 |
| Tamnar | Chhattisgarh | 3340 |
| Chandrapur | Maharashtra | 3340 |
Nuclear Energy–Based Power Station
Core idea
Controlled fission of Uranium-235 or Plutonium releases heat → generates steam → spins turbine → generator → electricity.
Typical fission: \( \mathrm{^{235}U + n \rightarrow ^{236}U \rightarrow ^{Ba} + ^{Kr} + 3n + \sim200\,MeV} \)
The chain reaction is controlled using control rods.
Energy steps
Nuclear → Thermal → Kinetic (steam) → Kinetic (turbine) → Electrical.
Issues
- Nuclear waste disposal (radioactive).
- Severe risk in case of accidents (radiation release).
Power Plant Using Energy of Natural Gas
Sections
- Compressor → pressurised air.
- Combustion chamber → natural gas burns with air.
- Gas turbine → hot, high-pressure gas spins turbine → generator.
Often higher efficiency than coal; natural gas contains negligible sulphur → less SOₓ.
Examples (Capacity)
| Plant | State | MW |
|---|---|---|
| Samaralkota | Andhra Pradesh | 2620 |
| Anjanwel | Maharashtra | 2220 |
| Bawana | Delhi | 1500 |
| Kondapalli | Andhra Pradesh | 1466 |
Process of Generation of Electricity & Environment
- Fossil fuels → air pollution (CO, CO₂ → global warming; NO₂ → acid rain; soot → respiratory issues).
- Finite reserves: coal, oil, gas formed over millions of years → depletion risk.
- Nuclear → waste management, accident risk.
Conclusion Fossil & nuclear pathways are not wholly environment friendly. We need green energy.
Hydroelectric Energy
How it works
Water stored in a dam has potential energy. Via penstock, the fast-flowing water (kinetic energy) spins the water turbine → generator → electricity.
Transformations: Potential → Kinetic (water) → Kinetic (turbine) → Electrical.
Advantages
- No fuel combustion → no stack pollution.
- Dispatchable if reservoir has enough water.
Concerns
- Submergence of forests/fertile land; rehabilitation of displaced people.
- River ecosystem disruption (aquatic life).
Examples
- Tehri (Uttarakhand) — 2400 MW
- Koyna (Maharashtra) — 1960 MW
- Srisailam (Andhra Pradesh) — 1670 MW
- Nathpa Jhakri (Himachal Pradesh) — 1500 MW
Electricity Generation Using Wind Energy
Concept
Wind’s kinetic energy turns the rotor blades. Through a gearbox, the shaft spins the generator.
Transformations: Wind kinetic → Turbine kinetic → Electrical.
Notes
- Clean energy; best near sea coasts & high-wind corridors.
- Commercial turbines: ~2 kW (home) to ~7 MW (offshore).
- Limitation: adequate wind speed not available everywhere.
Solar Energy — Photovoltaic (PV)
PV Basics
Solar cell (semiconductor, e.g., silicon) converts sunlight directly to DC electricity (photovoltaic effect).
- ~1 cm² silicon cell: ~30 mA, ~0.5 V.
- Area ↑ → current ↑ (voltage ~same per cell).
- Series adds voltages; Parallel adds currents.
- Typical module efficiency ~15% (good cell).
From Cell to Grid
- Cells → Panel/Module → String → Array.
- DC → Inverter → AC; transformer to grid voltage; feed to grid.
- Daytime generation; batteries needed for night DC loads.
Solar Thermal Power Plant
Solar radiation is concentrated (mirrors/reflectors) onto an absorber → converts to heat → produces steam → turbine → generator → electricity.
Transformations: Solar → Thermal → Kinetic (steam) → Kinetic (turbine) → Electrical.
Energy Sources for Electricity — World vs India (Illustrative)
| Source | World (%) | India (%) |
|---|---|---|
| Coal | 41 | 60 |
| Natural Gas | 22 | 08 |
| Hydroelectric | 16 | 11 |
| Nuclear | 11 | 04 |
| Renewables (wind, solar etc.) | 06 | — |
| Total | 100 | 100 |
Towards Environment-Friendly “Green” Energy
- Hydro — no combustion; site-specific social & ecological considerations.
- Wind — clean; depends on wind resource.
- Solar PV & Thermal — zero fuel, clean; daytime-only PV, storage/integration needed.
Think Green Use energy efficiently and shift to renewables to reduce pollution and conserve finite fuels.
Quick Think & Apply
- Why is \(\mathrm{CO_2}\) rise linked to global warming? What are your actions to cut it?
- For a home, which loads can run on DC from solar directly? Which need an inverter?
- In a PV panel: 36 cells in series each ~0.5 V → about \(36\times0.5=18\text{ V}\).
5. Towards Green Energy — Exercise (Perfect Solutions)
1) Remake the table by matching Column I – II – III correctly.
Correct Table
| I (Source / Fuel) | II (Energy Form) | III (Power Plant) |
|---|---|---|
| Coal | Thermal Energy | Thermal Power Plant |
| Uranium | Nuclear Energy | Nuclear Power Plant |
| Water (Reservoir) | Potential Energy | Hydroelectric Plant |
| Wind | Kinetic Energy | Wind Electricity Plant |
2) Which fuel is used in thermal power plant? What problems are associated?
Fuel: Coal.
Problems:
- Air pollution (CO₂ → global warming; SOₓ/NOₓ → acid rain; soot → respiratory issues).
- Finite reserves → coal will deplete with continued high use.
- Fly-ash handling, high water use & thermal pollution from cooling systems.
3) Other than coal-based thermal plant, which plants use thermal energy? How is the heat obtained?
- Nuclear Power Plant — heat from controlled nuclear fission (U-235 / Pu-239).
- Natural Gas Power Plant — heat from combustion of natural gas in a combustor (gas turbine).
- Solar Thermal Power Plant — heat from concentrated sunlight (mirrors/heliostats focus radiation on an absorber).
4) Which type involves maximum/minimum steps of energy conversion?
Maximum (~4 steps): Coal Thermal, Natural Gas, Nuclear, Solar Thermal
Source → Thermal → Kinetic (steam/gas) → Kinetic (turbine) → Electricity
Minimum (1 step): Solar Photovoltaic (Sunlight → Electricity directly).
Intermediate: Hydroelectric (3 steps), Wind (2 steps).
5) Crossword clues — Fill the words
- (a) Maximum energy generation in India is done using coal energy.
- (b) Wind energy is a renewable source of energy. (Solar/Hydro are also renewable.)
- (c) Solar energy can be called green energy.
- (d) Kinetic energy of wind is used in wind mills.
- (e) Potential energy of water in dams is used for generation of electricity.
6) Explain the difference
a) Conventional vs Non-conventional Sources
| Conventional | Non-conventional |
|---|---|
| Coal, Oil, Natural Gas, Large Hydro | Solar (PV/Thermal), Wind, Small Hydro, Biomass* |
| Finite (except hydro) | Perpetual / Renewable |
| Higher pollution & GHG | Low/No local emissions |
| Mature, baseload capable | Site/weather dependent; storage often needed |
*Biomass is renewable if sourced sustainably.
b) Thermal (Coal) vs Solar Thermal Electricity
| Thermal (Coal) | Solar Thermal |
|---|---|
| Heat from coal combustion | Heat from concentrated sunlight |
| Continuous fuel supply needed | Daytime resource; storage possible (molten salt) |
| Air pollutants & CO₂ | No combustion emissions at site |
| Fuel logistics & ash disposal | Large land; clear skies preferred |
7) What is meant by green energy? Which sources are green and why? Examples.
Green energy = energy from sources that are renewable/perpetual and have minimal environmental impact during operation.
Green sources: Solar (PV/Thermal), Wind, Hydroelectric (site-dependent), and sustainable Biofuels.
Why: Little/no air pollution, very low lifecycle GHG, abundant resource.
Examples: Rooftop solar PV, Wind farms, Run-of-river hydro.
8) Explain
a) Fossil-fuel energy is not green because burning coal/oil/gas emits CO₂ (warming), SOₓ/NOₓ (acid rain), and particulates (health hazards). Reserves are finite.
b) Saving energy reduces fuel consumption, pollution, and cost; it also delays depletion and eases grid load. Efficiency = the first fuel.
9) Answers
a) Getting required output from solar panels: Connect in series to raise voltage; connect in parallel to raise current. Mix both to meet a specific V–A (power) target.
b) Solar energy pros/cons:
- Advantages: Clean, silent, modular, low operating cost, scalable from mW to MW.
- Limitations: Daytime/intermittent, needs area; storage/inverter adds cost; output depends on weather.
10) Step-by-step energy conversion (with diagrams)
a) Thermal Power Plant (Coal)
b) Nuclear Power Plant
c) Solar Thermal Power Plant
d) Hydroelectric Power Plant
11) Give scientific reasons
a) Maximum energy generation in India is coal-based because India has large coal capacity and coal plants provide dispatchable baseload.
b) Wind energy is renewable; the wind resource is naturally replenished by solar heating & Earth’s rotation.
c) Solar energy is called green energy: no fuel burning, negligible operational emissions.
d) Windmills use the kinetic energy of wind to turn blades and generators.
e) Hydropower uses the potential energy of stored water, converted to kinetic at the turbine.
f) Turbines differ by plant type (steam, gas, or water) because fluid properties (temperature, pressure, density, flow rate) and nozzle/runner design must match the working medium.
g) Nuclear fission must be controlled (control rods, moderators) to keep the chain reaction steady; unchecked reactions can overheat and be dangerous.
h) Hydro, solar and wind are called renewable because their primary resources (water cycle, sunlight, wind) are naturally replenished.
i) Solar PV can scale from mW (calculators) to MW (solar farms) by combining cells → modules → strings → arrays.
12) Draw a schematic of solar thermal electric generation
13) Are hydroelectric plants environment-friendly?
Balanced opinion: During operation, hydro emits no stack pollutants and provides flexible, renewable electricity. However, large reservoirs can submerge forests/farmland, require rehabilitation of displaced people, and can alter river ecosystems. Conclusion: Conditionally green—site selection, ecological flows, fish passages, and fair rehabilitation make projects more environment-friendly.
14) Neat labelled diagrams
a) Energy transformation — Solar Thermal
b) Solar array to get 72 V and 9 A from panels of 18 V, 3 A
Plan: 4 panels in series → \(18\times4=72\) V (still 3 A). Then make 3 such strings in parallel → current \(3\times3=9\) A. Total panels = 4 × 3 = 12.
15) Short note: Electrical energy & the environment
Electricity underpins modern life, but its generation pathway determines environmental impact. Fossil-based routes emit greenhouse gases and pollutants; nuclear avoids air pollution but requires safe waste handling; renewables (hydro, wind, solar) offer clean operation yet need careful siting, storage, and grid integration. A sustainable electrical environment blends efficiency (demand-side savings), clean supply (renewables), smart grids, and equitable planning to minimize ecological and social footprints.