Renewable Power Generation (EX-503 (C)) - Unit 2 Short Notes

Unit 2: Renewable Power Generation – Exam-Focused Short Notes

I. Introduction to Renewable Energy

Renewable Energy Scenario

• Global context: Renewables (solar, wind, biomass, etc.) are fastest-growing energy sources, driven by climate policies and falling costs.

• Indian scenario:

  • National targets: 500 GW non-fossil capacity by 2030.

  • State-specific (Tamil Nadu): Leader in wind power (~10 GW), significant solar potential; strong policy support (Tamil Nadu Energy Development Agency).

  • Future prospects: Focus on hybrid systems, green hydrogen, offshore wind.

• Achievements & applications: Rural electrification (solar home systems), grid-scale plants, water pumping, industrial process heat.

Advantages and Limitations

Energy Resources Reserve Assessment

• Definition: Estimation of technically recoverable energy from a source over time.

• Key factors: Geographical potential, technological conversion efficiency, economic viability, environmental constraints.

• India’s reserves:

  • Solar: ~5,000 trillion kWh/year (high insolation zones).

  • Wind: ~300 GW at 80m hub height (onshore), plus offshore.

  • Biomass: ~500 GW thermal (agricultural residues, municipal waste).

  • Geothermal: ~10 GW (Himalayan geothermal belt, Andaman-Nicobar).

  • Tidal: ~8 GW (Gulf of Kutch, Sundarbans).

• [!TIP] Exam often asks for state-specific potentials (e.g., Tamil Nadu wind, Gujarat solar).

II. Solar Energy

A. Solar Radiation and Geometry

• Terms for locating a point:

  • Latitude (φ): Angular distance from equator.

  • Longitude (λ): Angular distance from Prime Meridian.

  • Declination (δ): Angle between solar rays and equatorial plane; varies ±23.45° annually.

  • Hour angle (ω): Angular displacement of sun from local solar noon; ω = 15° × (hours from noon).

  • Solar altitude (α): Angle between sun’s rays and horizontal plane.

  • Solar azimuth (γ): Angle between sun’s projection on horizontal plane and true south (N. Hemisphere).

• Key formulas:

$$ \sin \alpha = \sin \phi \sin \delta + \cos \phi \cos \delta \cos \omega $$

$$ \cos \gamma = \frac{\sin \phi \cos \alpha - \sin \delta}{\cos \phi \sin \alpha} $$

• [!TIP] For 9 AM solar time, ω = –45°; use correct sign convention.

B. Solar Thermal Systems

Classification of Solar Energy Collectors

1. Low-temperature (<100°C): Flat plate, evacuated tube (water heating, space heating).

2. Medium-temperature (100–250°C): Concentrating parabolic trough (industrial process heat).

3. High-temperature (>250°C): Solar tower, parabolic dish (power generation).

Flat Plate Collectors

• Components & functions:

  | Component | Function | |---------------------|------------------------------------------------------------------------------| | Glazing | Transparent cover (glass/plastic) reduces convection/radiation losses. | | Absorber plate | Black-coated surface absorbs solar radiation, transfers heat to fluid. | | Insulation | Minimizes bottom/side heat loss (e.g., mineral wool, polyurethane). | | Casing/Housing | Protects internal components, provides structural support. | | Tubes/Channels | Circulate heat transfer fluid (water, glycol mixture). |

• Performance factors:

  • Insolation (incident solar radiation).

  • Tilt & orientation (optimal tilt = latitude ± 15°).

  • Ambient temperature & wind speed (increase losses).

  • Transmittance-absorptance product (τα).

• Efficiency equation:

$$ \eta = \frac{Q_u}{A_c I_t} = F_R \left[ (\tau \alpha) - \frac{U_L (T_i - T_a)}{I_t} \right] $$

where $$\displaystyle Q_u $$ = useful heat, $$\displaystyle A_c $$ = collector area, $$\displaystyle I_t $$ = total radiation, $$\displaystyle F_R $$ = heat removal factor, $$\displaystyle U_L $$ = loss coefficient, $$\displaystyle T_i $$ = inlet temp, $$\displaystyle T_a $$ = ambient temp.

Solar Thermal Power Generation

• Concentrating technologies:

  • Parabolic trough: Linear focus, heat transfer fluid (oil, molten salt), steam turbine.

    Diagramparabolic trough with receiver tube, tracking mirrors

  • Solar power tower: Central receiver on tower, heliostat field, molten salt storage.

    Diagramtower with receiver, heliostats

  • Parabolic dish: Point focus, Stirling engine or micro-turbine.

    Diagramdish with receiver and engine

• [!TIP] Distinguish between trough (line focus) vs. tower/dish (point focus).

C. Solar Photovoltaic (PV) Systems

• Principle: Photoelectric effect – photons excite electrons in semiconductor (e.g., silicon), creating DC current.

• Key elements:

  • PV cells → modules → arrays.

  • Inverter (DC-AC conversion).

  • Mounting structure, wiring, charge controller, battery storage (off-grid), grid interface.

• PV Cell Characteristics:

  • I-V curve: Shows current (I) vs. voltage (V) at constant irradiance/temperature.

    • Short-circuit current ($$\displaystyle I_{sc} $$): Current at V=0.

    • Open-circuit voltage ($$\displaystyle V_{oc} $$): Voltage at I=0.

    • Maximum power point (MPP): Point ($$\displaystyle V_m $$, $$\displaystyle I_m $$) where $$\displaystyle P = V \times I $$ is max.

  • Fill factor (FF):

$$ \boxed{FF = \frac{V_m I_m}{V_{oc} I_{sc}}} $$

(Typical 0.7–0.8 for silicon cells).

• Maximum power:

$$ P_{max} = V_m \times I_m $$

• Cell efficiency ($\eta$):

$$ \boxed{\eta = \frac{P_{max}}{P_{in}} \times 100\% = \frac{V_m I_m}{A \cdot G} \times 100\%} $$

where $A$ = cell area, $G$ = irradiance (W/m²).

• Example (Dec 2024):

  Given: $$\displaystyle V_{oc}=0.24 $$ V, $$\displaystyle I_{sc}=10 $$ mA, $$\displaystyle V_m=0.14 $$ V, $$\displaystyle I_m=6.5 $$ mA, Intensity=24 W/m², Area=4 cm² = 0.0004 m².

  • $$\displaystyle P_{max} = 0.14 \times 6.5 \times 10^{-3} = 0.91 \times 10^{-3} $$ W = 0.91 mW.

  • $$\displaystyle P_{in} = 24 \times 0.0004 = 0.0096 $$ W.

  • $$\displaystyle \eta = (0.91 / 0.0096) \times 100\% = 9.48\% $$.

  • $$\displaystyle FF = (0.14 \times 6.5) / (0.24 \times 10) = 0.91 / 2.4 = 0.379 $$.

• Applications: Rooftop solar, solar farms, solar pumps, off-grid systems, space satellites.

III. Wind Energy

A. Fundamentals

• Principle: Wind kinetic energy → mechanical rotation (blades) → electrical energy (generator).

• Wind characteristics:

  • Speed (v): Varies with height, terrain; power ∝ $$\displaystyle v^3 $$.

  • Density (ρ): ρ = P/(R T) (P = pressure, T = temp, R = gas constant). Standard ρ ≈ 1.225 kg/m³ at 15°C, 1013.25 hPa.

  • Distribution: Often modeled by Weibull distribution; important for energy estimation.

B. Wind Turbine Technology

Classification of Wind Energy Systems

• By axis: Horizontal Axis Wind Turbines (HAWT), Vertical Axis Wind Turbines (VAWT).

• By location: Onshore, offshore.

• By power rating: Small (<100 kW), medium (100 kW–1 MW), large (>1 MW).

Horizontal Shaft Windmill Components

• Rotor blades: Capture wind energy; aerofoil shape creates lift.

• Nacelle: Housing containing gearbox and generator.

• Gearbox: Increases rotational speed (low-speed shaft from blades → high-speed shaft to generator).

• Generator: Converts mechanical rotation to electricity (usually induction or synchronous).

• Tower: Supports rotor/nacelle; height affects wind speed.

• Yaw system: Rotates nacelle to face wind (motor-driven, passive).

• Foundation: Anchors turbine (gravity, piled).

• Anemometer & wind vane: Measure wind speed/direction for control.

Performance and Limitations

• Betz limit: Maximum theoretical efficiency = 59.3% (capturable kinetic energy).

• Actual efficiency: 35–45% (aerodynamic, mechanical, electrical losses).

• Limitations:

  • Intermittent, variable wind.

  • Noise (aerodynamic, mechanical).

  • Visual impact, bird/bat mortality.

  • Requires suitable wind sites (>4–5 m/s average).

  • Grid integration challenges (voltage fluctuations).

C. Site Selection and Environmental Aspects

• Site criteria:

  • Mean annual wind speed ≥ 5–6 m/s at hub height.

  • Low turbulence intensity.

  • Consistent wind direction.

  • Away from obstacles (trees, buildings).

  • Proximity to grid (reduces transmission cost).

  • Environmental sensitivity (avoid migratory paths, protected areas).

• Safety & environmental:

  • Safety: Blade failure (rare), fire (lightning, electrical), ice throw.

  • Environmental: Noise (dB limits), shadow flicker, habitat fragmentation, visual impact.

  • Mitigation: Siting studies, noise barriers, shutdown during high winds/ice.

D. Control and Performance

• Control schemes:

  • Pitch control: Adjust blade angle to regulate power at high winds.

  • Stall control: Fixed-pitch blades; aerodynamic stall limits power.

  • Yaw control: Align rotor with wind direction.

  • Power electronics: Convert variable frequency to grid frequency; maximum power point tracking (MPPT).

• Performance calculations:

  • Wind power (theoretical):

$$ \boxed{P_{wind} = \frac{1}{2} \rho A v^3} $$

where $$\displaystyle A = \pi R^2 $$ (R = blade length), ρ = air density, v = wind speed.

• Actual power output:

$$ P_{out} = P_{wind} \times C_p \times \eta_g \times \eta_m $$

$$\displaystyle C_p $$ = power coefficient (≤0.593), $$\displaystyle \eta_g $$ = generator efficiency, $$\displaystyle \eta_m $$ = mechanical efficiency.

• Energy output (May 2024 example):

  Given: blade length r = 10 m, efficiency η = 40% (overall), v = 15 kph = 4.167 m/s, P = 1013.25 hPa, T = 15°C = 288.15 K.

  • ρ = P/(R T) = 101325/(287 × 288.15) ≈ 1.225 kg/m³.

  • A = π × 10² = 314.16 m².

  • $$\displaystyle P_{wind} = 0.5 × 1.225 × 314.16 × (4.167)^3 ≈ 0.5 × 1.225 × 314.16 × 72.34 ≈ 13,900 $$ W.

  • $$\displaystyle P_{out} = 13,900 × 0.4 = 5,560 $$ W = 5.56 kW.

  • Energy over 3 h: E = 5.56 × 3 = 16.68 kWh.

• [!TIP] Always convert units: kph → m/s, cm² → m², pressure to Pa, temperature to K for ρ.

IV. Biomass and Biogas

A. Biomass Resources and Conversion

• Agriculture/organic waste problems:

  • Open burning → air pollution (PM, CO, VOCs).

  • Landfill methane emissions (GHG).

  • Water contamination (leachate).

  • Vector breeding (mosquitoes, rodents).

• Electricity generation advantages:

  • Renewable, carbon-neutral (closed cycle).

  • Waste reduction, landfill diversion.

  • Rural employment (collection, processing).

  • Baseload capability (with storage).

• Biomass applications:

  • Cogeneration (CHP): Simultaneous heat & power; high efficiency (70–90%).

  • Pyrolysis: Thermal decomposition (400–600°C, no oxygen) → bio-oil, biochar, syngas.

  • Gasification: Partial oxidation → producer gas (CO, H₂) for engines/turbines.

  • Anaerobic digestion: Biogas (CH₄, CO₂) from organic waste.

  • Direct combustion: Steam generation for turbines.

B. Biogas Technology

Working Principle of Biogas Plants

• Anaerobic digestion stages:

  1. Hydrolysis: Complex polymers (carbohydrates, proteins) → soluble sugars, amino acids.

  2. Acidogenesis: Soluble compounds → volatile fatty acids, alcohols, CO₂, H₂ (acidogenic bacteria).

  3. Acetogenesis: Acids/alcohols → acetic acid, H₂, CO₂ (acetogens).

  4. Methanogenesis: Acetic acid/H₂/CO₂ → CH₄ + CO₂ (methanogens).

• Optimal conditions: 35–40°C (mesophilic), pH 6.5–7.5, C/N ratio 20–30:1, retention time 20–60 days.

Types of Biogas Plants

• Deen Bandhu biogas plant:

  • Design: Fixed dome (cylindrical), underground; inlet/outlet chambers.

  • Operation: Feed slurry from inlet, biogas collects in dome, slurry exits via outlet. Simple, low-cost, but requires manual mixing.

• Pragati design biogas plant:

  • Improvement over Deen Bandhu: Separate inlet/outlet chambers with slanting walls; better mixing, reduced scum formation; higher gas yield.

• Community biogas plants:

  • Large-scale (50–100 m³/day), common feedstock (cattle dung, vegetable waste).

  • Operational problems:

    • Scum formation (floating layer) → reduces gas volume.

    • Temperature fluctuation → slows digestion.

    • Inadequate mixing → poor contact between bacteria and substrate.

    • High solid content → clogging.

Materials Used for Biogas Generation

• Primary substrates: Cattle dung, poultry litter, pig manure.

• Crop residues: Straw, stover, bagasse (pre-treated).

• Organic waste: Kitchen waste, food processing waste, municipal solid waste (organic fraction).

• Energy crops: Napier grass, sugarcane tops.

• Co-digestion: Mixing substrates (e.g., dung + crop residue) to balance C/N ratio.

C. Advanced Biomass Conversion

• Pyrolysis (small-scale unit):

  DiagramSmall pyrolysis unit: feed hopper → reactor (heated) → condenser (liquid bio-oil) → char collector → gas outlet

  • Process: Feedstock dried → heated in absence of oxygen (400–600°C) → vapors → condensed to bio-oil; char (solid) and non-condensable gases (syngas) collected.

  • Applications: Bio-oil for boilers, upgraded to transportation fuels; char as soil amendment.

• Landfill gas power generation:

  DiagramLandfill gas system: gas collection wells → pipes → blower → gas treatment (H₂S, moisture removal) → generator

  • Advantages:

    • Captures methane (potent GHG, 25× CO₂ global warming potential).

    • Reduces odor, explosion risk.

    • Renewable energy source (10–20 year landfill life).

    • Low operating cost after installation.

V. Geothermal Energy

Advantages and Potential (India)

• Advantages:

  • Baseload power (24/7, weather-independent).

  • Low emissions (CO₂, NOₓ).

  • Small footprint.

  • Direct use (heating, spas, agriculture).

• India’s potential:

  • Geothermal provinces: Himalayas (Manikaran, Parvati Valley), Andaman-Nicobar (volcanic), Cambay basin, Son-Narmada-Tapi line.

  • Estimated potential: ~10 GW (medium-to-high enthalpy resources).

  • Current status: Exploratory drilling, pilot projects (e.g., Puga Valley, Ladakh).

Geothermal Power Plants

Binary Fluid Power Plant

• Working:

  1. Geothermal fluid (hot water/steam, <200°C) passes through heat exchanger.

  2. Secondary fluid (low boiling point, e.g., isobutane, ammonia) vaporizes.

  3. Vapor drives turbine → generator.

  4. Vapor condenses (cooling water) → pumped back to heat exchanger.

  5. Geothermal fluid reinjected.

• Why flashing not always possible?

  • Flashing requires high-temperature fluid (>150°C) to produce steam directly.

  • If geothermal fluid has:

    • Low temperature (<150°C): Insufficient pressure drop for flashing.

    • High non-condensable gases (CO₂, H₂S): Corrosive, reduce steam quality.

    • High salinity/mineral content: Scaling, corrosion in flash chambers.

  • Binary cycle avoids these issues; works with lower temperatures (85°C+).

Hybrid Geothermal-Fossil Systems

• Types & working:

  | Type | Working | |------------------------------|-----------------------------------------------------------------------------| | Binary-fossil backup | Geothermal binary plant + fossil fuel boiler; fossil fires when geothermal output drops. | | Flash-fossil supplement | Geothermal flash plant + fossil fuel superheater; increases steam temperature/power. | | Cogeneration | Geothermal for electricity + fossil for process heat; optimized overall efficiency. |

• Benefits: Improved reliability, higher capacity factor, better economics.

VI. Ocean Energy

A. Tidal Energy

• Site selection for tidal power plants:

  • High tidal range (>4 m) for barrage systems (e.g., Gulf of Kutch, Sundarbans).

  • Narrow inlet/bay → reduces civil works cost.

  • Strong tidal currents (>2 m/s) for tidal stream turbines.

  • Favorable geology (bedrock for foundations).

  • Minimal sediment transport (to avoid siltation).

  • Environmental sensitivity: Avoid mangroves, fisheries, migratory routes.

  • Proximity to grid/load centers.

• Mode of electricity generation:

  • Tidal range (barrage): Dam across estuary; gates open at high tide, close at low tide; water drives turbines as it flows out/in.

  • Tidal stream: Underwater turbines (like wind turbines) in fast currents; no barrage.

• Schematic layout of tidal power house:

  DiagramTidal barrage: dam with gates, turbine housings, ship lock, embankments, upstream/downstream basins

  • Components: Barrage/dam, gates (sluice), turbine-generator units (in tunnels), ship lock, embankments, control room.

  • Operation: Flood tide → gates open → fill upstream basin; Ebb tide → gates close, open turbines → water exits through turbines.

B. Ocean Thermal Energy Conversion (OTEC)

Closed OTEC System Principle and Diagram

• Working:

  1. Warm surface water (25–30°C) evaporates secondary fluid (e.g., ammonia, R-134a) in evaporator.

  2. Vapor expands through turbine → generates power.

  3. Cold deep water (5–10°C, from 1000 m depth) condenses vapor in condenser.

  4. Liquid secondary fluid pumped back to evaporator (closed loop).

• Challenges: Low temperature difference (ΔT ~20°C) → low Carnot efficiency (~3–4%).

• Applications: Electricity + desalination + aquaculture (cold water for fish farms).

VII. Hydrogen and Fuel Cells

A. Hydrogen Energy

• Advantages:

  • Zero emissions at point of use (water only).

  • High energy density (120 MJ/kg, ~3× gasoline).

  • Can be produced from various sources (renewables, natural gas with CCS).

  • Storage and transport possible (gas, liquid, carriers).

• Disadvantages:

  • Production cost high (electrolysis ~$4–6/kg; SMR cheaper but emits CO₂).

  • Low volumetric energy density (requires high pressure/liquefaction).

  • Safety concerns (flammable, wide explosive range).

  • Infrastructure lacking (production, distribution, refueling).

Hydrogen Storage Methods

B. Fuel Cells

• Classification by electrolyte:

  | Type | Electrolyte | Operating Temp | Applications | |---------------|-------------------|--------------------|--------------------------------------| | PEMFC | Polymer membrane | 60–80°C | Vehicles, backup power. | | SOFC | Ceramic (oxide) | 800–1000°C | Stationary power, CHP. | | MCFC | Molten carbonate | 600–700°C | Utility-scale power. | | AFC | Alkaline (KOH) | 60–90°C | Spacecraft, military. | | PAFC | Phosphoric acid | 200°C | CHP, hospital backup. |

• Working principle:

  • Anode: H₂ → 2H⁺ + 2e⁻ (oxidation).

  • Cathode: ½O₂ + 2H⁺ + 2e⁻ → H₂O (reduction).

  • Overall: H₂ + ½O₂ → H₂O + electricity + heat.

  • Functions: Convert chemical energy directly to electricity (no combustion); high efficiency (40–60%, up to 85% with CHP).

VIII. Hybrid Renewable Energy Systems

• Concept: Integration of two or more renewable sources (and/or storage/fossil) to overcome intermittency and improve reliability.

• Types and configurations:

  • Solar-wind: Complementary generation (wind at night/winter, solar day/summer); reduces storage need.

  • Wind-hydro: Wind power with pumped hydro storage; hydro provides backup/regulation.

  • Renewable-diesel: Diesel generator backup for renewables; common in off-grid.

  • Renewable-battery: Battery storage smooths output.

  • Renewable-fossil hybrid: Geothermal-solar thermal, biomass-coal co-firing.

• Integration benefits:

  • Improved power quality and reliability.

  • Reduced energy storage capacity/cost.

  • Better utilization of infrastructure.

  • Enhanced security of supply.

• [!TIP] Exam may ask for specific examples (e.g., solar-wind hybrid in Rajasthan).

IX. Cross-Cutting Topics

A. Site Selection Criteria (General)

B. Environmental and Safety Aspects

• General environmental impacts:

  • Solar: Land use (large farms), manufacturing emissions (silicon production), end-of-life panel waste.

  • Wind: Bird/bat mortality, noise, visual impact, shadow flicker.

  • Biomass: Air pollution (combustion), ash disposal, deforestation risk (if unsustainable).

  • Geothermal: Induced seismicity (EGS), brine disposal, gas emissions (H₂S, CO₂).

  • Tidal/OTEC: Marine ecosystem disruption, navigation hazards, thermal pollution (OTEC).

• Safety considerations:

  • Wind turbine: Blade throw, fire, lightning, ice accumulation → siting setbacks, lightning protection, regular inspection.

  • Biogas: Methane leaks (explosive), H₂S poisoning → gas detectors, ventilation, safety valves.

  • Hydrogen: Flammability, embrittlement → leak detection, ventilation, material selection.

  • Geothermal: High-pressure/temperature wells, scaling/corrosion → well integrity, monitoring.

C. Performance Metrics and Calculations

• Solar collector performance:

  • Efficiency η = (useful heat gain)/(solar radiation × area).

  • Factors: τα (transmittance-absorptance), $$\displaystyle U_L $$ (overall loss coefficient), $$\displaystyle F_R $$ (heat removal factor).

• Wind energy calculations:

  • Power: $$\displaystyle P = \frac{1}{2} \rho A v^3 C_p \eta $$.

  • Capacity factor = (Actual energy output)/(Rated power × 8760 h).

• PV cell efficiency metrics:

  • Efficiency η = ($$\displaystyle V_m I_m $$)/($A \cdot G$).

  • Fill factor FF = ($$\displaystyle V_m I_m $$)/($$\displaystyle V_{oc} I_{sc} $$).

  • Performance ratio (PR) = (Actual energy output)/(Energy output at STC).

• [!TIP] Always check units: v in m/s, A in m², ρ in kg/m³, G in W/m².

Final Note: This summary aligns strictly with RGPV EX-503(C) past papers (Jun 2025, Dec 2024, May 2024). Focus on diagram descriptions, formulas in boxes, and numerical problem patterns (e.g., solar angles, PV efficiency, wind power). Prioritize topics with repeated questions: solar PV characteristics, wind turbine components, biogas plants (Deen Bandhu/Pragati), OTEC, geothermal binary, tidal site selection, hydrogen storage.