Towards Green EnergyClass 10 Science Part 2 Chapter 5 Notes – Maharashtra Board

Summary: Towards Green Energy

Energy is essential for human activities but conventional energy sources (coal, oil, natural gas) are non-renewable and emit greenhouse gases causing climate change. Renewable energy sources—solar, wind, hydroelectric, geothermal, biomass—are sustainable and clean. Solar energy uses photovoltaic cells or solar thermal collectors to convert sunlight into electricity or heat. Wind turbines convert wind energy into electricity. Hydroelectric plants use falling water. Geothermal energy taps Earth's internal heat. Biomass uses plant/animal waste as fuel.

Solar energy is abundant: Earth receives ~170,000 TW of solar power; even 0.1% could supply humanity's energy needs. Photovoltaic (PV) panels convert sunlight directly to electricity via the photoelectric effect. Solar thermal systems heat water or air. Advantages: renewable, clean, no emissions, scalable. Disadvantages: weather-dependent, requires energy storage, manufacturing has environmental costs.

Wind and hydroelectric energy are also major renewable sources. Wind turbines are efficient in coastal and elevated areas. Hydroelectric dams provide reliable baseload power but affect ecosystems. Geothermal energy is reliable and available continuously in tectonically active regions. Biomass from agricultural waste is renewable and carbon-neutral if sustainably harvested. A diverse mix of renewable sources, energy efficiency improvements, and storage technologies (batteries, pumped hydro) can transition society to clean energy.

Key points to remember

• Fossil fuels: coal, oil, natural gas. Non-renewable, emit CO₂ (greenhouse gas), cause climate change, air pollution, and other environmental damage.
• Renewable energy: solar, wind, hydroelectric, geothermal, biomass. Sustainable, clean, low emissions, increasingly cost-competitive.
• Energy crisis: growing demand (development, population growth), finite fossil fuel reserves, need to reduce emissions.
• Solar constant: ~1,361 W/m² at Earth's orbit; at surface ~1,000 W/m² on clear day (atmospheric absorption).
• Photovoltaic effect: photons excite electrons in semiconductor, creating current. Photovoltaic cell: p-n junction separates electrons and holes into current.
• Solar panel efficiency: typically 15-20%; laboratory prototypes exceed 40% with multi-junction cells.
• Wind energy: kinetic energy of moving air converted by turbines. Capacity factor: typical ~25-35% (depends on wind speed variability).
• Wind power density: P = ½ρAv³ (density, area, velocity). Power increases with cube of velocity; doubling wind speed increases power ~8×.
• Hydroelectric: gravitational potential energy of elevated water. Capacity factor: typically 40-50%; very reliable and dispatchable.
• Geothermal: Earth's internal heat from radioactive decay. Available continuously; reliable baseload power.
• Biomass: solar energy stored in plant/animal matter. Carbon-neutral if sustainably harvested (replanted/regrown).
• Energy storage: batteries (lithium-ion), pumped hydro, compressed air, thermal storage. Essential for managing intermittency of solar/wind.
• Smart grid: bidirectional energy and information flow; integrates distributed renewable sources and storage.
• Energy efficiency: reducing energy consumption through better technology and behavior. Often cheaper than new generation.

Towards Green Energy – Notes

1. Solar energy conversion

• Solar radiation: electromagnetic waves from Sun; Earth receives ~170,000 TW (compared to global consumption ~18 TW).
• Photoelectric effect: photons with sufficient energy knock electrons from atoms, creating electric current.
• Semiconductor: material with intermediate conductivity (silicon, gallium arsenide). Doped with impurities: n-type (extra electrons), p-type (missing electrons/holes).
• Photovoltaic cell: p-n junction creates electric field; photons create electron-hole pairs; field separates them into current.
• Module: multiple cells connected; array: multiple modules connected for increased power output.
• Inverter: converts DC output from panels to AC for use in homes/grid.
• Solar thermal: concentrates sunlight to heat fluid (water, molten salt) for hot water or steam generation.
• Advantages: renewable, scalable, no emissions, modular, minimal maintenance. Disadvantages: intermittent, weather-dependent, requires land, panel production energy-intensive.

2. Wind and water energy

• Wind formation: differential solar heating creates pressure differences, driving wind.
• Wind turbine: blades catch wind, drive generator. Capacity depends on wind speed (cubic relationship), blade area, generator efficiency.
• Wind resource assessment: measure wind speed/direction over time; identify high-potential sites.
• Offshore wind: stronger, more consistent wind; higher capacity factor (~40-50%) than onshore (~25-35%).
• Hydroelectric: water elevation creates gravitational potential energy (PE = mgh). Falling water spins turbine connected to generator.
• Types: run-of-river (minimal storage), reservoir (dam, large storage), pumped hydro (pump water uphill for storage).
• Advantages: reliable, dispatchable (can turn on/off), long lifespan. Disadvantages: geographic limitations, ecosystem impacts, sedimentation.

3. Geothermal, biomass, and other renewables

• Geothermal heat: Earth's interior temperature increases ~25°C per km of depth. Heat from radioactive decay and primordial heat.
• In tectonically active regions (Iceland, New Zealand), hot water and steam near surface drive turbines.
• Advantages: continuous, reliable, high capacity factor (~70-90%). Disadvantages: location-specific, induced earthquakes possible.
• Biomass: wood, agricultural waste, food waste, algae. Can be burned for heat, fermented for ethanol, processed into biogas.
• Carbon-neutral: if sustainably harvested, CO₂ released during combustion equals CO₂ absorbed during growth.
• Biogas (methane): produced by anaerobic decomposition of organic matter. Can fuel generators, vehicles, or replace natural gas.
• Advantages: uses waste, renewable. Disadvantages: competition with food production, land use, not carbon-neutral if not sustainably harvested.

4. Energy storage and grid integration

• Storage problem: solar and wind are intermittent; storage allows energy use when production is low.
• Battery storage: lithium-ion (Tesla Powerwall, EV batteries) dominates. Store electrical energy electrochemically; quick response.
• Pumped hydro: pump water uphill during low-demand periods; release during peak demand. High capacity, long duration.
• Compressed air: compress air during low-demand, release through turbine during peak demand.
• Thermal storage: molten salt or water stores heat from solar concentration; releases during night for continuous generation.
• Smart grid: two-way communication and power flow. Integrates distributed solar/wind, storage, load control, demand response.
• Demand response: adjust consumption based on available generation (e.g., charge EV batteries during windy night).

5. Transition to renewable energy

• Energy transition: shift from fossil fuels to renewables to mitigate climate change.
• Challenges: intermittency (solar, wind); geographic constraints (hydro, geothermal); energy density (biomass vs. oil); infrastructure investment.
• Solutions: diverse renewable portfolio (reduces intermittency), storage, smart grid, efficiency improvements, transmission upgrades.
• Grid stability: maintain balance between supply and demand. Renewables reduce frequency stability; fast storage/demand response help.
• Cost trends: solar and wind are cheapest electricity sources in many regions; battery costs dropping rapidly.
• Policy drivers: renewable energy mandates, carbon pricing, subsidies/tax credits, grid-friendly regulations.

Formulas at a glance

Key terms

Towards Green Energy – Flashcards

Read the question, answer it in your head, then tap the card to check. 20 cards.

Towards Green Energy – MCQ Quiz

15 questions. Tap an option — you will see at once if it is right and why.

How to study Towards Green Energy

⏱ About 4 hours over 3 days

1. Day 1 — Renewable energy types
   Study solar, wind, hydro, geothermal, biomass. Understand how each converts energy.
2. Day 2 — Advantages and challenges
   Compare renewables with fossil fuels. Learn environmental benefits and intermittency issues.
3. Day 3 — Solutions and transition
   Study energy efficiency, storage, smart grids, and policies for renewable transition.

✍️ Diagrams to practise

• Renewable vs nonrenewable energy sources
• Solar panel photovoltaic conversion
• Wind turbine energy conversion
• Hydroelectric water-turbine-generator system
• Greenhouse gas emissions by energy source