Wind & Solar Energy (EX-503 (B)) - Unit 2 Short Notes

UNIT 2: RENEWABLE ENERGY TECHNOLOGIES (WIND & SOLAR FOCUS)

1. Introduction to Renewable Energy

Definition & Classification: Renewable energy sources (RES) are naturally replenishing but flow-limited. Major types:

• Solar: Direct (PV) and indirect (thermal) from the sun.

• Wind: Kinetic energy from atmospheric circulation.

• Biomass: Organic matter from plants/animals.

• Geothermal: Heat from Earth's interior.

• Ocean: Tidal, wave, and Ocean Thermal Energy Conversion (OTEC).

• Hydrogen: Energy carrier, not a primary source.

Need for RES:

• Depletion of fossil fuels (finite reserves).

• Environmental pollution (GHG emissions, local pollutants).

• Energy security (reduce import dependence).

• Sustainable development (meeting present needs without compromising future).

Global Scenario: Rapid growth in installed capacity, led by China, USA, EU. Solar PV and wind are dominant.

Indian Scenario:

• Policies: National Solar Mission (target 100 GW solar by 2022, now part of 500 GW non-fossil by 2030), National Wind-Solar Hybrid Policy.

• Capacity: India is a global leader in renewable capacity addition.

• State Potential: Tamil Nadu & Gujarat (wind), Rajasthan & Gujarat (solar).

• Achievements: Lowest cost of solar/wind power globally.

• Challenges: Grid integration, storage, land acquisition, financial health of discoms.

Future Strategies:

• Massive capacity targets (500 GW non-fossil by 2030).

• Grid integration with smart grids and flexibility.

• Large-scale energy storage (batteries, pumped hydro).

• Hybrid renewable systems (solar-wind-storage).

• Green hydrogen production.

Merits & Demerits vs. Conventional:

Energy Reserves:

• Classification: Proven (P90), Probable (P50), Possible (P10).

• Fossil Fuels: Finite, depleting (coal, oil, gas reserves for decades).

• Renewables: Not "reserves" in same sense; potential is vast but harnessable fraction depends on technology, land, and economics.

[!TIP] Exam Focus: Be ready to compare RES with conventional sources (thermal, hydro, nuclear) on cost, reliability, and environmental impact. Indian state-wise potential is frequently asked.

2. Solar Energy

2.1 Solar Radiation and Geometry

Solar Radiation Types:

• Extraterrestrial: Outside atmosphere, constant ~1367 W/m² (Solar Constant).

• Terrestrial: After atmospheric attenuation.

  • Direct (Beam): Unscattered sunlight.

  • Diffuse: Scattered by atmosphere.

  • Reflected: From ground/objects.

Solar Geometry Key Angles:

• Latitude (φ): Angular distance from equator.

• Declination (δ): Angle between sun-Earth line and equatorial plane. Varies ±23.45° annually.

$$\delta = 23.45^\circ \sin\left(\frac{360}{365}(284 + n)\right)$$

where $n$ = day number.

• Hour Angle (ω): Angular displacement of sun from local meridian. $$\displaystyle \omega = 15^\circ \times \text{hours from solar noon} $$.

• Sun's Position:

  • Altitude (α): $$\displaystyle \sin \alpha = \sin \phi \sin \delta + \cos \phi \cos \delta \cos \omega $$

  • Azimuth (γ): Angle from south (N. Hemisphere). $$\displaystyle \cos \gamma = \frac{\sin \delta \cos \phi - \cos \delta \sin \phi \cos \omega}{\cos \alpha} $$

Radiation on Tilted Surface: Optimal tilt angle ≈ latitude for annual max, or latitude ± 15° for seasonal max. Orientation: True South (N. Hemisphere).

Measurement:

• Pyranometer: Measures global (direct+diffuse) horizontal radiation.

• Pyrheliometer: Measures direct normal irradiance (DNI).

• Sunshine Recorder: Records bright sunshine hours.

Data Sources: Typical Meteorological Year (TMY) data, solar radiation maps (e.g., from NASA, IMD).

[!TIP] Common Pitfall: Confusing solar azimuth angle reference (usually from South in N. Hemisphere). Practice numerical problems for α and γ.

2.2 Solar Thermal Systems

Principle: Absorption of solar radiation by a dark surface (absorber) converts it to heat, transferred to a fluid.

Collector Classification:

1. By Temperature:

   • Low-Temp (<100°C): Flat plate, for water heating.

   • Medium-Temp (100-300°C): Concentrating, for process heat.

   • High-Temp (>300°C): Concentrating, for power generation.

2. By Concentration:

   • Non-concentrating: Acceptance angle ~180°, no tracking (flat plate).

   • Concentrating: Acceptance angle <~10°, requires tracking (parabolic trough, dish, tower).

Flat Plate Collector Components & Function:

1. Absorber Plate: Blackened metal (copper/aluminum) to absorb radiation.

2. Glazing: Transparent (glass/plastic) to reduce convective/radiative losses (greenhouse effect).

3. Insulation: Behind/edges to minimize conductive losses.

4. Casing: Weatherproof enclosure.

5. Tubes/Channels: Carry heat transfer fluid (water, glycol) through/on absorber. Performance Parameters:

• Efficiency (η): $$\displaystyle \eta = \frac{\dot{m} c_p (T_{out} - T_{in})}{A_c I_t} $$

• Heat Loss: Characterized by overall heat loss coefficient ($$\displaystyle U_L $$).

• Useful Energy Gain: $$\displaystyle Q_u = A_c F_R [I_t (\tau \alpha) - U_L (T_i - T_a)] $$

  where $$\displaystyle F_R $$ = heat removal factor, $\tau \alpha$ = transmittance-absorptance product.

Concentrating Collectors:

• Parabolic Trough: Line focus, tracks sun in one axis, heat transfer fluid (oil, molten salt) in receiver tube. Concentration Ratio (CR) = Aperture area / Receiver area.

• Parabolic Dish: Point focus, high CR, Stirling engine or PV at focus.

• Solar Tower: Central receiver on tower, field of heliostats (flat mirrors) tracks sun.

Solar Thermal Power Plant Layout:

1. Solar Field: Collectors (troughs/dishes/tower).

2. Heat Exchanger / Steam Generator: Transfer heat to working fluid (water/steam or secondary fluid).

3. Turbine: Expands steam to produce mechanical work.

4. Generator: Converts rotation to electricity.

5. Condenser & Cooling System: Condenses exhaust steam (wet cooling tower or dry cooling).

6. Power Block: Conventional Rankine cycle components.

Applications: Domestic hot water, industrial process heat, utility-scale power (e.g., SEGS, USA; PS10, Spain).

Performance Factors: Insolation level, ambient temperature, wind speed (increases losses), flow rate, tilt/orientation, dust on glazing.

[!TIP] Exam Focus: Know the difference between flat plate and concentrating collectors. Be able to write the useful energy gain equation for a flat plate collector. Sketch of solar thermal power plant layout is important.

2.3 Solar Photovoltaic (PV) Systems

Principle - Photovoltaic Effect:

• Absorption of photons in p-n junction creates electron-hole pairs.

• Built-in electric field separates charges, generating DC voltage/current.

PV Cell Construction:

• Material: Silicon (most common).

  • Monocrystalline: High efficiency (~22%), uniform dark blue, round cells.

  • Polycrystalline: Lower efficiency (~18%), blue speckled, square cells.

  • Thin-Film: CdTe, CIGS, a-Si. Lower efficiency but flexible, lower cost.

• Layers: Anti-reflective coating, n-type layer, p-type layer (or vice-versa), back contact, front grid.

I-V Characteristics & Parameters:

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

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

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

• Fill Factor (FF): Measure of "squareness" of curve.

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

• Efficiency (η):

$$\boxed{\eta = \frac{V_{oc} I_{sc} FF}{P_{in}}} = \frac{P_{max}}{P_{in}}$$

where $$\displaystyle P_{in} $$ = incident solar power (W/m² × cell area).

PV System Components:

1. Modules/Arrays: Series/parallel connection of cells.

2. Inverters: DC-AC conversion.

   • Central: For large arrays.

   • String: For medium systems.

   • Micro: Attached to each module (module-level optimization).

3. Charge Controller: Regulates battery charging (in off-grid).

4. Battery Bank: Energy storage (lead-acid, Li-ion).

5. Mounting Structure: Fixed or tracking.

6. Wiring & Protection: DC disconnects, fuses, grounding.

7. MPPT (Maximum Power Point Tracker): Algorithm in inverter/controller to operate at MPP under varying irradiance/temperature.

System Design Steps:

1. Load assessment (daily Wh requirement).

2. Sizing PV array: $$\displaystyle P_{pv} = \frac{E_{load}}{H_{sun} \times \eta_{sys}} $$ where $$\displaystyle H_{sun} $$ = peak sun hours, $$\displaystyle \eta_{sys} $$ = system efficiency.

3. Sizing battery: $$\displaystyle C_{bat} = \frac{E_{load} \times \text{days of autonomy}}{DOD \times \eta_{inv} \times \eta_{bat}} $$

4. Sizing inverter: ≥ peak load.

Applications:

• Standalone: Rural electrification, solar home systems, water pumping, street lights.

• Grid-Connected: Rooftop (residential/commercial), utility-scale farms.

• Solar Vehicles, BIPV.

Advantages/Limitations:

• Adv: Noiseless, low maintenance, modular, no fuel cost.

• Lim: Intermittent (no sun at night), low efficiency (~15-22%), high storage cost, area-intensive.

Recent Advances: Perovskite cells (high efficiency potential), bifacial modules (capture albedo), BIPV (integrated into building envelope).

[!TIP] Exam Focus: Numerical problems on FF, efficiency, and system sizing are common. Know the basic I-V curve and MPP concept. Differentiate between module, panel, array.

3. Wind Energy

3.1 Wind Resource Assessment

Wind Characteristics:

• Speed Distribution: Often modeled by Weibull Distribution:

$$f(v) = \frac{k}{c} \left(\frac{v}{c}\right)^{k-1} e^{-(v/c)^k}$$

where $k$ = shape factor, $c$ = scale factor (m/s). Rayleigh is special case (k=2).

• Direction: Rose diagram shows frequency from each direction.

• Turbulence Intensity (TI): $$\displaystyle \frac{\sigma_v}{\bar{v}} $$, measure of variability.

• Wind Shear: Increase in wind speed with height (logarithmic/power law).

• Tower Shadow Effect: Periodic drop in wind speed when blades pass behind tower.

Measurement:

• Cup Anemometer: Measures speed (rotating cups).

• Wind Vane: Measures direction.

• Sonic Anemometer: Ultrasonic, no moving parts, measures 3D wind.

• Data Duration: Minimum 1 year for reliable statistics (to capture seasonal variation).

Assessment Methods:

1. Wind Atlas Method: Uses regional wind atlas and adjusts for local topography.

2. WAsP Software: Wind Atlas Analysis and Application Program; uses meteorological data and terrain model.

3. Computational Fluid Dynamics (CFD): Detailed numerical simulation of flow over complex terrain.

4. Measurement Campaign: On-site mast with sensors (most accurate).

Site Selection Criteria:

• Resource: Avg. wind speed > 6 m/s at hub height (typically 80-120m).

• Topography: Flat, hills (acceleration), mountain passes.

• Accessibility: Road access for transport of large components.

• Grid Proximity: Near transmission lines to reduce connection cost.

• Environmental: Avoid bird migration paths, protected areas, minimize noise impact on settlements.

• Land Use: Compatible with agriculture/ grazing; minimal obstacles.

Potential:

• Global: North Sea (Europe), Great Plains (USA), coastal China.

• India: Tamil Nadu (largest), Gujarat, Maharashtra, Karnataka; offshore potential in Gulf of Khambhat, Bay of Bengal.

• Offshore: Higher, more consistent winds; less visual/noise impact; higher installation/maintenance cost.

[!TIP] Exam Focus: Know Weibull distribution parameters. Site selection factors are frequently asked. Distinguish between onshore and offshore challenges.

3.2 Wind Energy Conversion Systems (WECS)

Working Principle: Kinetic energy → Rotor mechanical energy → Generator electrical energy.

Betz Limit: Theoretical max power coefficient $$\displaystyle C_{p,max} = 0.593 $$ (59.3%). No turbine can extract more than 59.3% of kinetic energy in wind.

Wind Power Equation:

$$\boxed{P = \frac{1}{2} \rho A V^3 C_p}$$

where:

• $P$ = power (W)

• $\rho$ = air density (~1.225 kg/m³ at sea level, 15°C)

• $$\displaystyle A = \pi R^2 $$ = swept area (m²), R = blade length (radius)

• $V$ = wind speed (m/s)

• $$\displaystyle C_p $$ = power coefficient (≤ 0.593)

Types of Wind Turbines:

HAWT Components:

1. Rotor Blades: Aerofoil shape, materials: fiberglass, carbon fiber. Pitch mechanism (variable pitch) or stall (fixed pitch).

2. Hub: Connects blades to main shaft.

3. Nacelle: Housing on top of tower.

   • Gearbox: Increases rotational speed (low-speed shaft → high-speed shaft). Some are direct-drive (no gearbox).

   • Generator: Converts rotation to electricity (see 3.3).

   • Control Systems: Pitch, yaw, braking, monitoring.

4. Tower: Tubular or lattice. Height increases wind speed (shear).

5. Yaw System: Rotates nacelle to face wind (motor-driven).

6. Foundation: Concrete base.

Performance Parameters:

• Capacity Factor (CF): $$\displaystyle \frac{\text{Actual Energy Output (kWh/yr)}}{\text{Rated Capacity (kW)} \times 8760 \text{ h}} $$. Typically 25-45% for onshore.

• Availability: % time turbine is operational to generate.

• Power Curve: Graph of power output vs. wind speed. Key speeds: cut-in (~3-4 m/s), rated (~12-15 m/s), cut-out (~25 m/s).

• Annual Energy Production (AEP): Integral of power curve over site's wind speed frequency distribution (Weibull).

Control Schemes:

• Stall Control: Fixed pitch; blades designed to stall (lose lift) at high wind, limiting power.

• Pitch Control: Blades rotate to reduce angle of attack, regulating power smoothly.

• Yaw Control: Aligns rotor to wind direction.

• Braking: Aerodynamic (pitch to feather), mechanical (disk brake), electrical (generator torque).

Limitations: Intermittency, noise (aerodynamic + mechanical), visual impact, avian/bat mortality, transportation/logistics for large components.

[!TIP] Exam Focus: Derive/recall wind power equation. Know Betz limit. Compare HAWT vs. VAWT. Understand power curve and capacity factor calculation.

3.3 Wind Turbine Generators

Generator Types:

1. Induction Generators (IG):

   • Squirrel Cage (SCIG): Fixed speed. Simple, rugged. Requires capacitor banks for power factor correction. Draws reactive power from grid.

   • Doubly-Fed Induction Generator (DFIG): Most common for variable speed. Rotor connected to grid via back-to-back converters (partial-scale, ~30% of rated power). Allows wide speed range (±30% around synchronous speed), independent control of active/reactive power. Requires slip rings.

2. Synchronous Generators (SG):

   • Wound Rotor: Requires slip rings for excitation current.

   • Permanent Magnet Synchronous Generator (PMSG): No slip rings, no external excitation. High efficiency, low maintenance. Often used in direct-drive turbines (no gearbox). Full-scale power converter needed.

3. Power Electronics:

   • Converters: AC-DC-AC (for DFIG, PMSG) to enable variable speed operation and grid interface.

   • Functions: MPPT-like control (maximize $$\displaystyle C_p $$), power factor control, fault ride-through (FRT).

Grid Integration Requirements (Grid Codes):

• Fault Ride-Through (FRT): Stay connected during voltage sags, provide reactive current support.

• Power Factor Control: Operate at specified PF (often leading 0.9-1.0).

• Frequency Support: Provide inertial response or synthetic inertia.

• Voltage Control: Reactive power capability.

Offshore Wind Farms:

• Advantages: Higher & more consistent wind speeds, less noise/visual impact, larger scale possible.

• Challenges: Harsh marine environment, installation (special vessels), maintenance (access), cabling (long export cables), corrosion.

[!TIP] Exam Focus: Know the difference between SCIG, DFIG, and PMSG. Why DFIG is popular? Understand need for power electronics in variable speed turbines. Grid code requirements are key.

3.4 Environmental and Safety Aspects

Environmental Impacts:

• Noise: Aerodynamic (blade passing) and mechanical (gearbox, generator). Increases with tip speed.

• Visual Impact: "Landscape scarring," especially in scenic areas.

• Shadow Flicker: Stroboscopic effect when blades cast moving shadows on dwellings.

• Avian/Bat Mortality: Collision and barotrauma (pressure change). Higher risk in migration corridors.

• Land Use: Physical footprint small (<1% of area), but spacing requires large land area (can coexist with agriculture).

• Electromagnetic Interference: Possible with TV/radio signals.

Safety Considerations:

• Blade Failure: Catastrophic; requires exclusion zone.

• Nacelle Fire: Hydraulic oil, electrical components; fire suppression systems.

• Lightning Protection: Direct strikes to blades/tower; grounding.

• Emergency Shutdown: Braking systems (aerodynamic, mechanical).

• Access: Safe procedures for maintenance at height (60-150m).

Mitigation Measures:

• Siting away from migration paths, using radar-triggered shutdowns.

• Low-noise blade designs, operational curtailment at night.

• Proper grounding and lightning protection systems.

• Avian monitoring and post-construction studies.

[!TIP] Exam Focus: List specific environmental impacts and mitigation for wind. Safety systems (braking, lightning) are important.

4. Biomass Energy

4.1 Biomass Resources and Conversion Technologies

Biomass Types:

• Agricultural Residues: Crop straw, husks (rice, wheat), bagasse (sugarcane).

• Forest Residues: Logging waste, branches.

• Energy Crops: Jatropha, sugarcane (for ethanol), short-rotation trees (poplar, eucalyptus).

• Animal Waste: Dung (for biogas).

• Municipal Solid Waste (MSW): Organic fraction.

• Industrial Waste: Pulp, food processing waste.

Conversion Routes:

Advantages/Limitations:

• Adv: Renewable, carbon neutral (if sustainably managed), waste management solution.

• Lim: Low energy density (bulky), seasonal availability, collection/transport cost, emissions if combustion inefficient (particulates, CO).

[!TIP] Exam Focus: Match biomass type to conversion technology (e.g., dung → anaerobic digestion, wood → gasification). Know main products of each route.

4.2 Biogas Plants

Anaerobic Digestion Process (4 Stages):

1. Hydrolysis: Complex polymers (carbohydrates, proteins, fats) → simple sugars, amino acids, fatty acids.

2. Acidogenesis: Sugars → volatile fatty acids, alcohols, CO₂, H₂, etc.

3. Acetogenesis: Fatty acids → acetic acid, H₂, CO₂.

4. Methanogenesis: Acetic acid & H₂/CO₂ → Methane (CH₄) + CO₂ + H₂O (by methanogens).

Biogas Composition: 50-70% CH₄, 30-50% CO₂, traces H₂S, H₂O vapor.

Biogas Plant Types:

1. Floating Drum (KVIC): Movable steel gas holder floats on slurry. Constant gas pressure. More expensive, maintenance of moving parts.

2. Fixed Dome (Deen Bandhu): Brick masonry, fixed gas holder (dome shape). Cheaper, but gas leakage issues, requires perfect masonry.

3. Pragati Design: Improved fixed dome with better gas tightness (using cement plaster, polythene lining).

4. Community Biogas Plants: Larger scale, common feedstock collection. Problems: Inconsistent feedstock supply, poor management, inefficient gas utilization, scum removal difficulty.

Components:

• Digester: Inlet (feedstock entry), outlet (slurry exit), gas space.

• Gas Holder: Stores biogas (in floating/fixed types).

• Piping & Burner/Engine: Gas delivery and utilization.

Operation Parameters:

• C/N Ratio: Optimal 20-30:1 (Carbon to Nitrogen). Too high → slow digestion; too low → ammonia inhibition.

• Moisture Content: 60-80% (slurry consistency).

• Retention Time: 20-50 days (depends on temperature).

• Temperature:

  • Mesophilic: 30-38°C (common, stable).

  • Thermophilic: 50-55°C (faster, less pathogen survival, less stable).

Materials for Biogas: Any biodegradable organic matter with suitable C/N ratio. Avoid: toxic substances (pesticides), high lignin (hard to hydrolyze), excessive sand/soil.

[!TIP] Exam Focus: Sketch and explain KVIC and Deen Bandhu plants. List problems in community plants. Know the 4 stages of anaerobic digestion and optimal C/N ratio.

4.3 Other Biomass Conversion

Pyrolysis:

• Thermal decomposition in absence of oxygen.

• Slow Pyrolysis: Maximizes char production.

• Fast Pyrolysis: High heating rate, short residence → maximizes bio-oil (liquid fuel). Small-scale units can produce bio-oil for engines/boilers after upgrading.

Gasification:

• Partial oxidation at high temperature (700-900°C) with air/oxygen/steam.

• Gasifier Types:

  • Updraft: Air from bottom, ash removal easy, tar high.

  • Downdraft: Air introduced mid-way, gas passes through hot char → lower tar, common for engines.

  • Crossdraft: Air and gas flow perpendicular.

• Syngas Cleaning: Remove tars, particulates, alkali metals before use in engines/turbines.

Landfill Gas:

• Generated from anaerobic decomposition of MSW in landfills.

• Collection: Wells and pipes drilled into landfill, vacuum applied.

• Utilization: Gas engines or turbines for power generation. Advantages: Waste disposal + energy recovery, reduces GHG emissions (CH₄ is potent GHG).

Biomass Applications:

• Direct Combustion: For heat/steam (cogeneration/CHP most efficient).

• Biofuels: Bioethanol (sugarcane juice/molasses), Biodiesel (jatropha, palm oil).

• Biogas: For cooking (stoves), electricity generation (dual-fuel engines), piped as CNG (after purification).

5. Geothermal Energy

5.1 Geothermal Resources

Types:

1. Hydrothermal: Hot water/steam reservoirs (most common). Subtypes: Vapor-dominated (steam), Liquid-dominated (hot water).

2. Geopressured: Hot water under high pressure (often with methane).

3. Hot Dry Rock (HDR): Impermeable hot rock; requires artificial fracture network (EGS - Enhanced Geothermal Systems).

4. Magma: Molten rock (very high temp, extremely challenging).

Resource Assessment:

• Temperature gradient drilling.

• Geophysical surveys (seismic, resistivity, gravity).

• Chemical tracers in springs/wells.

• Geological mapping of faults/volcanic activity.

Indian Potential:

• Locations: Puga Valley (Ladakh), Manikaran (Himachal), Chhattisgarh (Tatapani), Tamil Nadu (Boranahalli), Cambay basin.

• Status: Exploratory drilling, resource confirmation. Estimated potential ~10,000 MW (conservative).

• Challenges: Deep drilling costs, technical risks in frontier areas.

[!TIP] Exam Focus: Differentiate between hydrothermal, HDR, and magma resources. Know key Indian geothermal sites.

5.2 Geothermal Power Plant Technologies

1. Dry Steam Plant:

   • Steam from reservoir directly drives turbine.

   • Simplest, but requires natural steam reservoir (rare).

   • Steam condensed and reinjected.

2. Flash Steam Plant:

   • High-pressure hot water from reservoir is flashed (pressure drop) to steam in a separator.

   • Single Flash: One separation.

   • Double/Multiple Flash: Steam from first flash is flashed again for more extraction. Increases efficiency.

   • Most common type.

3. Binary Cycle Plant:

   • Geothermal fluid (hot water) passes through heat exchanger.

   • Secondary fluid (butane, pentane, ammonia) with low boiling point vaporizes and drives turbine.

   • Geothermal fluid never contacts turbine; reinjected.

   • Suitable for low-temperature resources (85-170°C).

   • Efficiency lower, but resource utilization better.

4. Hybrid Geothermal-Fossil Systems:

   • Topping: Geothermal steam first, then fossil fuel superheats.

   • Bottoming: Fossil fuel heat first, then geothermal.

   • Parallel: Separate cycles, combined output.

   • Purpose: Boost output, use waste heat, or when geothermal temp alone insufficient.

5.3 Advantages and Limitations

Advantages:

• Baseload Power: High capacity factor (>90%), runs 24/7.

• Low Emissions: Very low CO₂, NOₓ, SOₓ compared to fossil.

• Small Land Footprint: Minimal surface area per MW.

• High Efficiency for Direct Use: >50% for heating (no Carnot loss of power cycle).

Limitations:

• Site-Specific: Only in tectonically active regions (volcanic belts, rift zones).

• High Exploration/Drilling Cost: Deep wells, high risk of dry holes.

• Scaling & Corrosion: Dissolved minerals (silica, carbonates) precipitate; H₂S causes corrosion.

• Induced Seismicity: Fluid injection can trigger small earthquakes (EGS).

• Water Consumption: Some plants consume water (cooling, reinjection losses).

[!TIP] Exam Focus: Compare dry steam, flash, and binary cycles. Why binary is used for low-temp resources? List advantages (baseload) and key limitations (site-specific, cost).

6. Ocean Energy

6.1 Tidal Energy

Principle: Harness kinetic energy of tidal currents or potential energy of tidal range (height difference).

Site Selection:

• Tidal Range (Barrage): > 4-5 m average range. Suitable basin geometry (estuary), minimal environmental impact, navigation lock needed.

• Tidal Current (Stream): Current speed > 2-3 m/s. Suitable bathymetry (channeling), away from shipping lanes, anchorages.

Tidal Power Plant Types:

1. Tidal Barrage: Dam across estuary.

   • Single Basin: One-way generation on ebb/flood tide (2-4 generations/day).

   • Double Basin: Two basins at different phases; can generate continuously.

   • Schematic Layout:

     DiagramSEARCH: "tidal barrage power plant schematic layout"
     Includes: barrage, sluice gates, turbine-generator units, ship lock, powerhouse.

2. Tidal Stream Turbines: Underwater "wind turbines" on seabed/mounted. No dam. Lower environmental impact, but less mature.

Advantages: Highly predictable (astronomical), high energy density (water ~800x air). Disadvantages: Very high capital cost, significant environmental impact on estuary ecology/sediment, limited suitable sites (few global examples: La Rance, France; Sihwa, Korea).

6.2 Wave Energy

Conversion Principle: Oscillatory motion of water particles in waves.

Wave Energy Converters (WECs):

1. Oscillating Water Column (OWC): Partially submerged chamber; wave rises/falls, compresses/rarefies air → drives Wells turbine (unidirectional).

2. Point Absorber: Floating buoy heaving with waves; drives hydraulic pump or linear generator.

3. Attenuator: Long, multi-segment floating structure (like Pelamis); flexes with wave; hydraulic rams at joints drive motors.

4. Overtopping Device: Wave runs up ramp, fills reservoir; water drains through turbine.

Challenges: Harsh marine environment (storms, corrosion), low conversion efficiency, maintenance difficulty, grid connection from sea.

6.3 Ocean Thermal Energy Conversion (OTEC)

Principle: Utilize temperature difference ($\Delta T$) between warm surface water (25-30°C) and cold deep water (5-10°C). Requires $$\displaystyle \Delta T > 20^\circ C $$ (tropical oceans).

Types:

1. Open Cycle:

   • Warm seawater enters evaporator at low pressure (vacuum) → flashes to steam.

   • Steam drives low-pressure turbine.

   • Steam condensed by cold seawater in condenser → produces fresh water as byproduct.

2. Closed Cycle:

   • Secondary fluid (ammonia, Freon) with low boiling point (~0°C) circulates in closed loop.

   • Warm seawater evaporates fluid in evaporator.

   • Vapor drives turbine.

   • Cold seawater condenses vapor in condenser.

   • Fluid pumped back to evaporator.

   • Schematic:

     DiagramSEARCH: "closed cycle OTEC system diagram"
     Shows: evaporator, turbine, condenser, pump, working fluid cycle.

3. Hybrid: Combines open and closed cycles.

Advantages: Renewable, baseload potential in tropics, produces desalinated water (open cycle). Limitations: Very low thermodynamic efficiency (3-4% due to small $\Delta T$), high capital cost (large seawater pipes), cold water pipe challenges, biofouling.

[!TIP] Exam Focus: Distinguish between tidal barrage vs. stream. Explain closed OTEC cycle with diagram. Why is OTEC efficiency low?

7. Hydrogen and Fuel Cells

7.1 Hydrogen Energy

Hydrogen as Energy Carrier: Not primary; must be produced from other sources (water, hydrocarbons, biomass).

Production Methods:

• Electrolysis: $$\displaystyle 2H_2O \xrightarrow{electricity} 2H_2 + O_2 $$. "Green H₂" if electricity from RES.

• Steam Methane Reforming (SMR): $$\displaystyle CH_4 + H_2O \rightarrow CO + 3H_2 $$ (then water-gas shift). "Grey H₂" (with CO₂ emissions); "Blue H₂" with CCS.

• Biomass Gasification: Biomass → syngas (CO+H₂) → shift reaction → H₂.

• Advanced: Photobiological (algae), Photoelectrochemical (solar-to-H₂).

Storage Methods:

Applications: Fuel cells (main), combustion in modified engines, industrial feedstock (ammonia, refining).

Advantages: High energy density by weight, clean combustion (only water), versatile. Disadvantages: Very low density by volume (at ambient), storage/transport challenges, production cost (esp. green H₂), flammability (wide explosive range 4-75% in air).

[!TIP] Exam Focus: Compare storage methods. List production routes with their "color" (green, blue, grey). Safety aspects of H₂ (flame invisible, wide flammability).

7.2 Fuel Cells

Principle: Electrochemical device; fuel (H₂) and oxidant (O₂) supplied continuously; electricity + heat + water produced.

General Reactions:

• Anode: $$\displaystyle H_2 \rightarrow 2H^+ + 2e^- $$

• Cathode: $$\displaystyle \frac{1}{2}O_2 + 2H^+ + 2e^- \rightarrow H_2O $$

• Overall: $$\displaystyle H_2 + \frac{1}{2}O_2 \rightarrow H_2O $$

Classification by Electrolyte:

Components: Anode (catalyst), Cathode (catalyst), Electrolyte (ion conductor), Bipolar plates (gas flow, current collection).

Applications: Transportation (FCEVs), stationary (backup, remote, CHP), portable (laptops, military).

Advantages: High efficiency (40-60% electrical, >80% with CHP), low emissions (water, heat), modular, quiet. Challenges: High cost (catalyst, materials), durability (degradation), hydrogen infrastructure, fuel purity (for PEMFC).

[!TIP] Exam Focus: Compare PEMFC vs. SOFC (temp, fuel, app). Write anode/cathode reactions. Why is PEMFC suitable for vehicles? Why SOFC for stationary?

8. Other Emerging Technologies

8.1 Magneto-Hydro Dynamic (MHD) Generation

Principle: Direct conversion of thermal energy to electrical energy without moving parts. Ionized hot gas (plasma) passes perpendicularly through magnetic field → EMF induced (Faraday's law).

Types:

• Faraday Generator: Electrodes perpendicular to both magnetic field and gas flow. Current flows through load.

• Hall Effect Generator: Electrodes at an angle to magnetic field; higher voltage output.

Components & Working:

1. Combustor: Air + fuel (coal-derived gas, natural gas) burned with seed (potassium/cesium) to lower ionization temperature (~2500K).

2. Nozzle: Accelerates plasma to high velocity (~1000 m/s).

3. Electrode Array: In channel, collects current.

4. Magnet: Powerful (superconducting for high field).

5. Seed Recovery: Essential to remove and recycle seed from exhaust.

Advantages: Theoretically high efficiency (50-60% with bottoming cycle), no moving parts (reliability), fast response. Challenges: Extreme temperatures (2000-3000K) cause material degradation, slag deposition, seed recovery cost, high capital cost, plasma stability. Commercial deployment limited.

8.2 Cogeneration (Combined Heat and Power, CHP)

Definition: Simultaneous generation of electricity and useful thermal energy (heat/steam) from same fuel source.

Types:

• Topping Cycle: Generate electricity first → use waste heat (exhaust, cooling) for process/space heating. (Most common).

• Bottoming Cycle: Generate heat first for industrial process → use waste heat (from hot exhaust/effluent) for power generation (e.g., steam bottoming cycle in combined cycle gas turbine).

Applications: Biomass power plants (use steam for drying), geothermal plants (use brine heat), refineries, chemical plants, hospitals, campuses.

Advantages: Overall efficiency 70-90% (vs. 30-40% for condensing power plants), fuel savings, reduced emissions, cost-effective if heat demand exists. Challenges: Heat demand must be constant/coincident with power generation; thermal storage may be needed; system design complex.

[!TIP] Exam Focus: Differentiate topping vs. bottoming cycle. Why is CHP efficient? Give examples.

9. Hybrid Renewable Energy Systems

9.1 Concept and Need

Definition: Integration of two or more renewable energy sources (and/or storage, conventional backup) into a single system.

Need: Overcome intermittency of single sources (solar only day, wind variable), improve reliability, reduce storage requirement, better resource utilization.

Advantages:

• Reduced energy storage capacity/cost.

• Complementary generation profiles (e.g., solar day, wind night/seasonal).

• Increased overall capacity factor and reliability.

• Improved power quality and grid stability (if connected).

Challenges:

• Increased complexity in control, management, and protection.

• Higher initial capital cost.

• Requires more space/area.

• Need for sophisticated energy management system (EMS).

9.2 Configurations

1. Solar-Wind Hybrid: Most common. PV arrays + wind turbines share inverters, battery storage, grid connection. Generation profiles complementary.

2. Solar-Biomass Hybrid: Solar PV + biomass power plant (base load). Biomass provides stable output, solar peaks during day.

3. Wind-Biomass Hybrid: Similar.

4. Solar-Wind-Hydro Hybrid: Include small hydro or pumped storage for large-scale storage and grid balancing.

5. Hybrid with Conventional Backup: Diesel generator for reliability in standalone systems.

6. Integration with Storage: Batteries (Li-ion), pumped hydro, flywheels, supercapacitors.

9.3 Design and Control

• Sizing: Based on resource assessment (solar irradiation, wind speed), load profile, desired reliability (Loss of Load Probability - LOLP).

• Energy Management Strategies (EMS):

  • Priority-Based: e.g., use solar/wind first, then battery, then diesel.

  • Predictive: Use weather forecasts to schedule sources/storage.

  • Optimal: Mathematical optimization (linear programming) to minimize cost or maximize renewable fraction.

• Case Studies: Remote villages, islands, microgrids, telecom towers.

[!TIP] Exam Focus: Explain why hybrid systems are needed. Give examples of configurations. What is role of EMS?

10. Economic and Planning Aspects of Renewable Energy

10.1 Power Plant Economics

Cost Components:

• Fixed Capital Cost (FCC): Land, equipment, installation, grid connection, development. One-time.

• Operating & Maintenance Cost (O&M): Routine maintenance, repairs, insurance, staff. Annual.

• Fuel Cost: Significant for thermal, biomass; negligible for solar/wind (but cleaning for solar).

• Decommissioning Cost: End-of-life dismantling (often included in FCC via sinking fund).

Levelized Cost of Energy (LCOE):

$$\boxed{LCOE = \frac{\sum_{t=1}^{n} \frac{I_t + O_t + F_t}{(1+r)^t}}{\sum_{t=1}^{n} \frac{E_t}{(1+r)^t}}$$

where:

• $$\displaystyle I_t $$ = Investment expenditure in year t

• $$\displaystyle O_t $$ = O&M expenditure

• $$\displaystyle F_t $$ = Fuel cost

• $$\displaystyle E_t $$ = Energy generated (kWh)

• $r$ = Discount rate

• $n$ = Plant life LCOE is average cost per kWh over lifetime. Used to compare technologies.

Tariff Types:

• Flat Rate: Fixed charge per unit (kWh), regardless of consumption/time.

• Block Rate: Increasing blocks (higher rate for higher consumption).

• Time-of-Day (TOD) Tariff: Different rates for peak, normal, off-peak hours.

• Two-Part Tariff: Fixed charge (demand/capacity) + Variable charge (energy).

• Power Factor-Based: Incentive/disincentive based on PF (important for industrial consumers).

Peak Load Pricing: Higher tariffs during system peak demand hours (e.g., 6-10 PM). Encourages load shifting. Relevant for renewables with storage (sell stored energy during peak).

10.2 Load Analysis

Load Curve: Graph of load (kW) vs. time (hourly/daily/monthly/annual). Shows variation.

Load Duration Curve (LDC): Load values sorted in descending order vs. time percentage. Shows how often a certain load level is exceeded. More useful for capacity planning.

Key Factors (Always < 1):

1. Load Factor (LF): $$\displaystyle \boxed{LF = \frac{\text{Average Load}}{\text{Maximum Demand}} = \frac{\text{Energy (kWh)}}{\text{Max Demand (kW)} \times \text{Time (h)}}} $$

   • Measures how "flat" the load curve is. Higher LF → better asset utilization → lower cost per unit.

2. Demand Factor (DF): $$\displaystyle \boxed{DF = \frac{\text{Maximum Demand}}{\text{Connected Load}}} $$

   • Connected load = sum of nameplate ratings of all equipment. Not all equipment runs at max simultaneously.

3. Capacity Factor (CF): $$\displaystyle \boxed{CF = \frac{\text{Actual Energy Output}}{\text{Rated Capacity} \times \text{Time}}} $$

   • For power plant. Accounts for outages, maintenance, intermittency (for RES). CF ≤ LF.

4. Utilization Factor (UF): Similar to CF; sometimes defined as energy produced / energy that would be produced if operated at full capacity all the time. Essentially same as CF.

Relationship: Energy = Max Demand × Time × LF = Rated Capacity × Time × CF.

Effect on Cost: Higher LF/CF spreads fixed costs over more units → lower LCOE.

10.3 Load Forecasting

Need: Generation scheduling, maintenance planning, grid stability, economic dispatch, unit commitment.

Types:

• Short-Term: Hourly/daily (up to 1 week). For dispatch.

• Medium-Term: Weekly/monthly (up to 1 year). For maintenance, fuel scheduling.

• Long-Term: Yearly/decadal. For capacity expansion planning.

Methods:

• Statistical: Regression, Time Series (ARIMA, exponential smoothing).

• Machine Learning: Artificial Neural Networks (ANN), Fuzzy Logic, Support Vector Machines (SVM).

• Hybrid Models: Combine statistical and ML.

• For RES: Weather-based forecasting (solar irradiance, wind speed) using Numerical Weather Prediction (NWP) models.

10.4 Economic Dispatch and Scheduling

Problem: Minimize total fuel cost $$\displaystyle C_{total} = \sum C_i(P_i) $$ while meeting load demand $$\displaystyle \sum P_i = P_D + P_L $$ and generator limits $$\displaystyle P_{i,min} \leq P_i \leq P_{i,max} $$.

Incremental Cost Theory: Optimal dispatch when incremental fuel costs of all online units are equal ($\lambda$), considering transmission losses.

$$\frac{dC_1}{dP_1} = \frac{dC_2}{dP_2} = ... = \lambda$$

where $\lambda$ = incremental cost of received power ($/MWh$).

Transmission Losses: $$\displaystyle P_L = \sum_{i} \sum_{j} B_{ij} P_i P_j $$ (B-coefficients). Penalty Factor (PF) for plant i: $$\displaystyle \boxed{PF_i = \frac{1}{1 - \frac{\partial P_L}{\partial P_i}}} $$. Plant's incremental cost adjusted: $$\displaystyle \frac{dC_i}{dP_i} \times PF_i = \lambda $$.

Lambda-Iteration Method:

1. Guess $\lambda$.

2. For each unit, solve $$\displaystyle \frac{dC_i}{dP_i} = \lambda $$ for $$\displaystyle P_i $$, respecting limits.

3. Calculate total power generated $$\displaystyle \sum P_i $$ and losses $$\displaystyle P_L $$.

4. Check if $$\displaystyle \sum P_i = P_D + P_L $$. If not, adjust $\lambda$ and repeat.

Sample Problem (From Jun 2025):

Given:

$$\frac{dC_1}{dP_1}=0.15 P_1+150$$

$$\frac{dC_2}{dP_2}=0.25 P_2+175$$

$$\displaystyle P_1 = P_2 = 400 $$ MW, $$\displaystyle \frac{\partial P_L}{\partial P_2} = 0.2 $$.

Find penalty factor of plant 1.

Solution:

At economic dispatch: $$\displaystyle \frac{dC_1}{dP_1} \times PF_1 = \frac{dC_2}{dP_2} \times PF_2 $$ $$\displaystyle PF_2 = \frac{1}{1 - 0.2} = \frac{1}{0.8} = 1.25 $$

Calculate ICs at given power: $$\displaystyle \frac{dC_1}{dP_1} = 0.15(400) + 150 = 60 + 150 = 210 $$ Rs/MWh $$\displaystyle \frac{dC_2}{dP_2} = 0.25(400) + 175 = 100 + 175 = 275 $$ Rs/MWh

Now, $$\displaystyle 210 \times PF_1 = 275 \times 1.25 = 343.75 $$ $$\displaystyle \boxed{PF_1 = \frac{343.75}{210} \approx 1.6375} $$

10.5 Reserve Capacity and Reliability

Types of Reserves:

• Spinning Reserve: Online generators synchronized, can increase output within minutes.

• Non-Spinning (Hot) Reserve: Offline but can start quickly (gas turbines, hydro).

• Cold Reserve: Offline, longer start-up time (coal, nuclear).

Reliability Indices:

• Loss of Load Probability (LOLP): Probability that load exceeds available capacity over a period.

• Expected Energy Not Served (EENS): Expected energy (MWh) that cannot be supplied due to capacity shortage.

Reserve Requirement: Determined by:

• Forced Outage Rates (FOR) of generators.

• Load forecast uncertainty.

• Variability of intermittent RES (wind/solar).

[!TIP] Exam Focus: LCOE formula, tariff types, LF/CF/DF definitions (always <1), economic dispatch with equal incremental costs, penalty factor concept. Numerical problems on LF/CF from given data are very common.

11. Environmental, Safety, and Site Selection Aspects (Cross-Cutting)

11.1 Environmental Impacts of Renewable Energy

General Impacts:

• Land Use: Large area for solar/wind farms (but can coexist with agriculture).

• Water Use: Cleaning (solar PV), cooling (solar thermal, geothermal, biomass).

• Material Extraction: Mining for silicon (PV), rare earths (wind generators, batteries).

• End-of-Life Waste: PV module recycling, wind blade disposal (composite material).

Source-Specific:

• Solar PV: Land disturbance, hazardous materials (Cd in CdTe, Pb in solder), water for cleaning, module disposal/recycling challenge.

• Wind: Noise, visual, shadow flicker, bird/bat mortality, electromagnetic interference.

• Biomass: Air emissions (PM, CO, VOCs) if combustion inefficient, ash disposal, indirect land use change (if energy crops compete with food).

• Geothermal: Emissions of H₂S (rotten egg smell), CO₂, water consumption, induced seismicity (EGS), scaling/corrosion.

• Tidal/Ocean: Marine ecosystem disruption, sediment transport changes, noise, collision with marine life.

• Hydrogen: Production emissions if from fossil fuels (SMR), safety.

Life Cycle Assessment (LCA): Cradle-to-grave analysis of environmental impacts (energy payback time, carbon footprint). RES generally have much lower LCA emissions than fossil fuels.

11.2 Safety Considerations

• General: Electrical hazards (DC in PV, AC in all), fire hazards, working at height (wind), confined spaces (biogas digesters).

• Wind Turbine: Blade throw (exclusion zone), tower collapse, nacelle fire, lightning, emergency descent procedures.

• Solar PV: High DC voltages (series strings), arc flash, roof mounting fall protection.

• Biogas Plant: Explosion risk (CH₄ 5-15% in air), asphyxiation (CH₄, CO₂), gas leakage detection, ventilation.

• Hydrogen: Flammability (4-75% in air), invisible flame, leakage detection, ventilation, explosion-proof equipment.

11.3 Site Selection Criteria Summary

12. Small Hydro and Pumped Storage

12.1 Small Hydro Power (SHP)

Definition: Typically < 25 MW (or < 10 MW in some countries). Run-of-river with/without small pondage.

Components:

1. Weir/Dam: Small barrage to raise water level.

2. Intake: Screens to debris, water enters penstock.

3. Penstock: Pressure pipe carrying water to turbine.

4. Turbine: Pelton (high head > 300m), Francis (medium head 30-300m), Kaplan (low head < 30m, propeller-type).

5. Generator: Coupled to turbine.

6. Tailrace: Returns water to river.

Hydrograph & Flow Duration Curve (FDC):

• Hydrograph: Discharge (m³/s) vs. time (daily/monthly). Shows seasonal variation.

• Flow Duration Curve: Discharge values sorted in descending order vs. percentage of time exceeded. Crucial for SHP design: indicates dependable flow (e.g., flow exceeded 90% of time, Q₉₀).

Advantages/Limitations:

• Adv: Low environmental impact vs. large hydro, renewable, long life.

• Lim: Site-specific, seasonal flow variation, sedimentation, initial cost.

12.2 Pumped Storage Hydro (PSH)

Principle: Reversible pump-turbine. During off-peak (low electricity price), use excess grid power to pump water from lower to upper reservoir. During peak demand, release water from upper to lower through turbine to generate.

Plant Layout:

• Upper Reservoir: At higher elevation.

• Lower Reservoir: River/lake or separate lower reservoir.

• Penstocks: Connect reservoirs to powerhouse.

• Powerhouse: Contains pump-turbines, generators/motors, transformers.

• Tailrace: From turbine to lower reservoir.

Operation Cycles:

• Pumping Cycle: Off-peak hours. Motor drives pump-turbine as pump.

• Generation Cycle: Peak hours. Water drives turbine as generator.

Merits:

• Excellent peaking capability and fast response (minutes).

• Large-scale energy storage (hours to days).

• Provides grid services: frequency regulation, spinning reserve, black start.

• Long life (50-100 years).

Demerits:

• Very high capital cost and long construction time.

• Significant environmental impact (land inundation, water loss by evaporation/seepage, aquatic ecology).

• Geographical constraints (need two reservoirs at different elevations).

Role in Renewable Integration: Critical for balancing intermittent solar/wind. Stores excess renewable generation (off-peak/daytime) for use during evening peak or low-wind periods.

[!TIP] Exam Focus: Sketch of SHP and PSH. Explain working of PSH cycle. Compare turbine types for SHP based on head. Why PSH is important for grid stability with high RES penetration?