Renewable Energy Technology (ME-604 (C)) - Unit 5 Short Notes

I. Introduction to Renewable Energy

Definition & Classification:

• Renewable Energy (RE): Energy derived from natural sources that replenish faster than consumption. Unlike fossil fuels, they are inexhaustible on a human timescale.

• Classification:

  • Solar: Direct (PV) and indirect (thermal, biomass).

  • Wind: Onshore, offshore.

  • Hydropower: Large, small, micro.

  • Biomass & Biofuels: Organic matter.

  • Geothermal: Earth's internal heat.

  • Ocean: Tidal, wave, OTEC.

  • Hydrogen & Fuel Cells: Energy carriers.

Need for Renewable Energy:

• Energy Security: Reduces dependence on imported fossil fuels.

• Sustainability: Meets present needs without compromising future generations.

• Environmental Protection: Mitigates climate change, reduces air/water pollution.

• Economic Development: Creates jobs, rural electrification.

Environmental Impacts of Fossil Fuels:

• Climate Change & Global Warming: Caused by increased Greenhouse Gas (GHG) emissions (CO₂, CH₄, N₂O).

• Greenhouse Effect: Natural process where GHGs trap infrared radiation, warming the Earth. Enhanced by human activities.

  \[ \text{Incoming Solar Radiation} = \text{Reflected} + \text{Absorbed by Earth} \]

  \[ \text{Outgoing IR Radiation} \xrightarrow{\text{Trapped by GHGs}} \text{Re-radiated to surface} \]

Sensible vs. Latent Heat:

• Sensible Heat: Heat exchanged that causes a temperature change (e.g., heating water from 20°C to 80°C). \( Q = m c_p \Delta T \)

• Latent Heat: Heat exchanged during a phase change at constant temperature (e.g., evaporation, condensation). \( Q = m h_{fg} \)

II. Solar Energy

A. Solar Radiation Fundamentals

Sun-Earth Relationship:

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

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

(n = day number)

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

• Solar Time: Based on sun's position. \( \text{Local Solar Time} = \text{Clock Time} + \text{Equation of Time} + 4(\text{Standard Meridian} - \text{Longitude}) \).

Solar Geometry:

• Altitude Angle (α): Angle between sun's rays and horizontal plane.

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

(φ = latitude)

• Solar Azimuth (γₛ): Angle of sun's projection on horizontal plane from south.

• Incidence Angle (θ): Angle between sun's rays and normal to surface.

$$ \cos \theta = \sin \phi \sin \delta \cos \beta - \sin \phi \cos \delta \sin \beta \cos \gamma + \cos \phi \cos \delta \cos \omega \cos \beta + \cos \phi \sin \delta \sin \beta \cos \gamma \cos \omega + \cos \delta \sin \omega \sin \beta \sin \gamma $$

(β = tilt angle, γ = surface azimuth from south).

Solar Radiation on Tilted Surface:

• Total Radiation (Iₜ): \( I_t = I_b \cos \theta + I_d + I_r \)

  (I_b = beam, I_d = diffuse, I_r = ground-reflected).

• Optimum Tilt (β): For max annual insolation, \( \beta \approx \phi \). For seasonal adjustment, \( \beta = \phi \pm 15^\circ \) (winter/summer).

Measurement:

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

• Pyrheliometer: Measures direct beam radiation (sun-facing).

• Sun-tracking required for pyrheliometer.

B. Solar Thermal Systems

Solar Collectors Classification:

Flat Plate Collector (FPC) Construction & Working:

• Components:

  1. Absorber Plate: Black-coated metal (copper/aluminum) to absorb radiation.

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

  3. Insulation: Mineral wool/foam at back/sides to minimize conductive loss.

  4. Casing: Protective enclosure.

  5. Tubes/Channels: Carry heat transfer fluid (water/glycol mix).

• Working: Solar radiation passes through glazing, absorbed by plate → heats fluid in tubes → hot fluid outlet.

Solar Water Heating Systems:

• Thermosyphon (Natural Circulation):

  • No pump. Density difference drives circulation (hot fluid rises from collector to tank).

  • Tank must be above collector.

  • Simple, reliable, low cost.

• Forced Circulation:

  • Pump circulates fluid between collector and storage tank.

  • Tank can be placed anywhere.

  • Requires controller & pump (electricity).

Applications:

• Domestic/commercial water heating.

• Space heating (radiators/underfloor).

• Industrial process heat (<200°C).

• Solar drying (agricultural products).

• Solar distillation.

C. Solar Photovoltaic (PV) Systems

Principle of Photovoltaic Conversion:

• Photoelectric Effect: Photons with energy > bandgap (E_g) strike semiconductor → electron-hole pair generation.

• p-n Junction: Built-in electric field separates charges → creates voltage (V_oc) and current (I_sc) under illumination.

  \[ E_{\text{photon}} = h\nu \geq E_g \]

Solar Cell Types & Materials:

PV System Components:

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

2. Charge Controller: Regulates battery charging (prevents overcharge).

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

4. Inverter: DC → AC conversion (for AC loads/grid).

5. Mounting Structure & Tracking.

6. Maximum Power Point Tracker (MPPT): Operates PV at max power point (V_mpp, I_mpp).

Maximum Power Point Tracking (MPPT) - Perturb & Observe (P&O):

1. Measure initial V, I → calculate P.

2. Perturb (increase/decrease) duty cycle (D) of DC-DC converter → changes V.

3. Measure new P.

4. Compare ΔP:

   • If ΔP > 0 → continue perturbation in same direction.

   • If ΔP < 0 → reverse perturbation direction.

5. Repeat periodically. Simple but can oscillate around MPP.

Applications:

• Standalone: Remote homes, street lights, water pumping (with battery).

• Grid-Connected: Rooftop, solar farms (no battery, feed-in).

• PV Generation Systems: Large-scale solar parks.

Limitations of SPV Systems:

• Intermittency & Variability: No sun at night, weather-dependent.

• Low Efficiency: 15-22% (module), 10-15% (system).

• High Initial Cost: Though LCOE decreasing.

• Storage Requirement: For nighttime/cloudy periods (adds cost).

• Land Area: Large utility-scale farms require significant space.

• Temperature Sensitivity: Efficiency decreases with rising temperature (~0.5%/°C).

P-V Characteristics:

• Curve shows Short-Circuit Current (I_sc), Open-Circuit Voltage (V_oc), Maximum Power Point (MPP).

• Fill Factor (FF): \( \text{FF} = \frac{V_{mpp} I_{mpp}}{V_{oc} I_{sc}} \) (indicates curve "squareness").

III. Wind Energy

A. Wind Fundamentals

Aerofoil:

• Definition: Shaped cross-section (like airplane wing) that generates lift when air flows over it.

• Types:

  • Symmetrical: Zero camber, used in vertical-axis turbines (Darrieus).

  • Cambered: Curved upper/lower surfaces, higher lift-to-drag ratio, used in HAWT blades.

• Lift & Drag: Lift (perpendicular to flow) is desired for rotation. Drag (parallel) is resistance. High L/D ratio is efficient.

Wind Energy Estimation:

• Wind Speed Distribution: Often follows Weibull Distribution:

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

(k = shape parameter, c = scale parameter).

• Wind Power Density (WPD): Power per unit swept area.

$$ \text{WPD} = \frac{1}{2} \rho \overline{v^3} $$

(\( \overline{v^3} \) = mean cube wind speed, ρ = air density ~1.225 kg/m³).

Power in Wind & Betz Limit:

1. Kinetic Energy of Air: \( KE = \frac{1}{2} m v^2 \)

2. Mass Flow Rate: \( \dot{m} = \rho A v \) (A = swept area)

3. Available Power: \( P_{\text{available}} = \frac{1}{2} \dot{m} v^2 = \frac{1}{2} \rho A v^3 \)

4. Extracted Power: \( P_{\text{extracted}} = \frac{1}{2} \rho A v (v_1^2 - v_2^2) \) (v₁ = upstream, v₂ = downstream).

5. Betz's Law: Maximum possible fraction of power extracted = 16/27 ≈ 0.593 (Betz limit).

   \boxed{P_{\text{max}} = \frac{16}{27} \cdot \frac{1}{2} \rho A v^3 = \frac{8}{27} \rho A v^3}

   Actual turbines achieve \( C_p \approx 0.35-0.45 \).

Power Curve of Wind Turbine:

• Cut-in Speed (v_ci): ~3-4 m/s. Turbine starts generating.

• Rated Speed (v_r): Speed at which turbine reaches rated power (P_r).

• Cut-out Speed (v_co): ~25 m/s. Turbine shuts down for safety.

• Power Coefficient (C_p): \( C_p = \frac{P_{\text{actual}}}{P_{\text{available}}} \). Varies with Tip-Speed Ratio (λ = ωR/v).

B. Wind Energy Conversion Systems (WECS)

Main Components:

1. Rotor Blades: Capture wind energy (aerofoil shape).

2. Nacelle: Housing on top of tower.

3. Gearbox: Increases rotor speed (low) to generator speed (high) (not in direct-drive).

4. Generator: Converts mechanical to electrical (async/sync).

5. Tower: Supports rotor/nacelle (height ↑ wind speed).

6. Yaw System: Rotates nacelle to face wind (wind direction sensor + motor).

7. Control System: Pitch control (blade angle), brakes.

Types of WECS:

Selection for Wind Farms:

• Site Wind Regime: Mean speed, Weibull k & c, turbulence intensity.

• Rotor Diameter vs. Hub Height: Match turbine to local wind profile.

• Grid Connectivity: Proximity to transmission lines.

• Environmental Constraints: Bird migration, noise, visual impact.

• Logistics: Access for transport/installation.

C. Challenges & Hybrid Systems

Limitations/Barriers to Large-Scale Wind:

• Intermittency & Variability: Not dispatchable; requires backup/storage/grid flexibility.

• Grid Integration: Voltage/frequency stability issues with high penetration. Need for HVDC, smart grids.

• Environmental: Noise, avian/bat mortality, visual impact.

• Economic: High capital cost, long payback, transmission cost for remote sites.

• Social: Public acceptance ("Not In My Backyard" - NIMBY).

Wind-Diesel Hybrid System:

• Configuration: Wind turbines + diesel gensets + (often) battery bank + control system.

• Operation:

  • Wind → primary source when available.

  • Diesel genset → fills gap, provides base load, stabilizes frequency.

  • Battery → smooths short-term fluctuations, provides backup.

• Advantages:

  • Reduces diesel fuel consumption & cost (up to 50-80%).

  • Lowers emissions (CO₂, particulates).

  • Increases energy security for remote communities/islands.

  • Can operate in isolated "island mode".

IV. Biomass Energy

A. Biomass Resources & Production

Definition & Usefulness:

• Biomass: Organic material from plants/animals (wood, crops, residues, manure, algae).

• Usefulness:

  • Energy: Combustion, biogas, biofuels.

  • Chemicals: Platform for biochemicals.

  • Soil Amendment: Biochar, compost.

Biomass Production - C3 vs C4 Plants:

B. Biomass Conversion Technologies

1. Biochemical Conversion:

• Anaerobic Digestion (AD): Microbial breakdown of organic matter without oxygen in stages:

  1. Hydrolysis: Complex polymers → sugars, amino acids.

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

  3. Acetogenesis: Acids → acetic acid, H₂, CO₂.

  4. Methanogenesis: Acetic acid/H₂/CO₂ → Biogas (CH₄ ~60%, CO₂ ~40%).

• Digesters Types:

  DiagramCANVAS: Schematic of fixed-dome (concrete dome, slurry inlet/outlet), floating-drum (movable gas holder), bag-type (flexible bag), plug-flow (horizontal tank).

  | Type | Construction | Operation | Pros/Cons | |-------------------|--------------------------------------|----------------------------------------|----------------------------------------------------| | Fixed Dome | Concrete/brick dome, gas space above slurry | Gas pressure pushes slurry out. | Low cost, no moving parts. Gas leakage risk. | | Floating Drum | Steel drum floats on slurry in tank | Drum weight provides constant pressure. | Good gas sealing. Moving parts, maintenance. | | Bag-Type | Flexible gas bag (nylon/rubber) | Bag inflates with gas. | Cheap, portable. Durability, weather sensitivity. | | Plug Flow | Long, narrow, inclined tank | Plug of digesting mass moves slowly. | Good for cattle dung. Mixing issues. |

• Biogas Plant Design Considerations:

  • Feedstock type/availability.

  • Retention time (15-30 days).

  • Temperature (mesophilic ~35°C, thermophilic ~55°C).

  • C/N ratio (20-30:1).

  • pH (6.8-7.5).

  • Loading rate.

2. Thermochemical Conversion:

• Biomass Gasification: Partial combustion at 700-900°C with limited air/oxygen → Producer Gas (CO, H₂, CH₄, N₂).

  | Type | Air/Gas Flow | Gas Temp | Tar Content | Efficiency | |----------------|------------------------|--------------|-----------------|----------------| | Updraft | Bottom → Top | Low (~200°C) | High | Lower | | Downdraft | Top → Bottom | High (~700°C)| Low | Higher | | Crossdraft | Side → Opposite side | High | Moderate | Moderate | | Fluidized Bed| Air suspends particles | Uniform | Very Low | Very High |

• Combustion: Direct burning with excess air → heat/steam.

• Pyrolysis: Thermal decomposition without oxygen → bio-oil, char, gas.

Other Biomass Energy Production:

• Direct Combustion: For heat/power (steam cycle).

• Biofuels: Ethanol (fermentation), Biodiesel (transesterification).

• Bio-oil: From fast pyrolysis (liquid fuel).

C. Sustainability & Applications

• Feedstock Availability: Must be sustainable (no deforestation, food vs fuel conflict). Use residues, energy crops on marginal land.

• End Uses:

  • Biogas: Cooking, lighting, electricity (dual-fuel engine), vehicle fuel (after upgrading to biomethane).

  • Bio-oil: Boiler fuel, upgraded to transportation fuels.

V. Hydro Energy

A. Hydropower Systems

Classification (based on capacity):

Main Components of Small Hydro System:

1. Intake: Diverts water from river, screens debris.

2. Penstock: Pressurized pipe (headrace) carries water to turbine.

3. Turbine: Converts water's kinetic/potential energy to mechanical.

4. Generator: Converts mechanical to electrical.

5. Tailrace: Returns water to river.

Site Selection Criteria:

• Head (H): Vertical drop (m). Higher head → smaller turbine, less civil work.

• Flow (Q): Water discharge (m³/s). Higher flow → larger turbine.

• Environmental Impact: Fish migration, sediment flow, flooding.

• Geology & Access: Stable foundation, road access.

• Distance to Grid: Transmission cost.

B. Turbines

Classification:

Construction & Working - Pelton Wheel (Impulse):

• High-head, low-flow sites.

• Nozzle: Converts pressure to high-velocity jet.

• Buckets (Cups): Double-cup shape splits jet, reverses direction → maximum impulse transfer (change in momentum).

• Runner: Buckets mounted on wheel.

• Casing: Directs used water to tailrace, prevents splashing.

• Working: Water jet strikes bucket → force on bucket → torque on shaft → generator.

Turbine Selection (based on Head & Flow):

\boxed{\text{High Head (}>100\text{ m) + Low Flow} \rightarrow \text{Pelton (Impulse)}}

\boxed{\text{Medium Head (30-100\text{ m)} \rightarrow \text{Francis (Reaction)}}

\boxed{\text{Low Head (}<30\text{ m) + High Flow} \rightarrow \text{Kaplan/Bulb (Reaction)}}

Speed & Voltage Regulation:

• Speed Regulation (Governor): Maintains constant rotational speed (frequency) despite load changes. Uses flyball or electronic governor to adjust wicket gate (guide vane) opening → changes water flow.

• Voltage Regulation (Excitation System): Controls generator's field current to maintain terminal voltage. Uses AVR (Automatic Voltage Regulator).

VI. Geothermal Energy

A. Geothermal Resources

Types of Geothermal Deposits:

Site Selection for Geothermal Power Plant:

• Geological: High heat flow, recent volcanism, fractures/permeability.

• Hydrological: Adequate recharge, reservoir size/depth.

• Economic: Proximity to grid/load center, drilling cost, resource temperature (>150°C for electricity).

• Environmental: Minimal seismic risk, subsidence potential, gas emissions.

B. Power Generation

Thermodynamic Principles:

• Based on Rankine Cycle (steam) or Binary Cycle (organic fluid).

• Working Fluid: Water/steam (high-temp), low-boiling-point organic (isobutane, pentane) for binary.

Generation Processes:

1. Dry Steam Plants:

   • Use natural steam directly from vapor-dominated reservoir.

   • Steam → turbine → condenser → reinjection.

   • Simplest, oldest (The Geysers, USA).

2. Flash Steam Plants:

   • Hot water (180-350°C) from reservoir → throttled (flashed) to lower pressure →部分蒸发成蒸汽。

   • Steam separated → turbine → condenser.

   • Remaining water + condensate → reinjected.

   • Most common type.

3. Binary Cycle Plants:

   • Moderate-temp (100-180°C) geothermal fluid heats secondary working fluid (organic) in heat exchanger (evaporator).

   • Organic vapor → turbine → condenser → reinjected.

   • Geothermal fluid never contacts turbine → no scaling/corrosion issues.

   • Allows use of lower-temperature resources.

C. Environmental & Economic Aspects

Environmental Benefits:

• Very low GHG emissions (mostly CO₂, H₂S - can be captured).

• Small land footprint per MW.

• Minimal water consumption (binary/closed-loop).

Potential Impacts:

• Subsidence: Reservoir pressure drop if reinjection insufficient.

• Emissions: Non-condensable gases (CO₂, H₂S, CH₄) - need abatement.

• Water Use: High in flash plants (cooling). Binary uses air-cooled condensers.

• Induced Seismicity: (Enhanced Geothermal Systems - EGS).

• Chemical Discharge: Brine with minerals (boron, arsenic) - reinjection needed.

VII. Ocean Energy

A. Tidal Energy

Principle:

• Converts potential energy of tide (water level difference) into kinetic energy (turbine rotation).

• Tidal Range (H): Vertical difference between high & low tide.

• Tidal Basin: Enclosed area (A) by dam/barrage.

Tidal Power Plant Types:

1. Single Basin (One-way): Simple barrage. Generation only during flood (incoming) or ebb (outgoing) tide. Intermittent (4-6 hrs generation, 4-6 hrs standby).

2. Double Basin: Two basins at different levels. While one fills (generation), other empties. Can generate continuously.

3. Dual Operation (Pumping): Can pump water back during low electricity price to generate during peak.

Tidal Energy Calculation (Single Basin, Ebb Generation):

• Potential Energy per cycle (E):

$$ E = \frac{1}{2} \rho g A H^2 \eta_t $$

Where:

ρ = seawater density (1025 kg/m³)

g = gravity (9.81 m/s²)

A = basin area (m²)

H = **effective head** (tidal range minus minimum operating head, h_min)

η_t = overall turbine-generator efficiency

• Given: A = 30×10⁶ m², H_tidal = 12 m, h_min = 3 m → Effective H = 12 - 3 = 9 m.

• Energy (kWh): Calculate E in Joules → convert (1 kWh = 3.6×10⁶ J).

B. Ocean Thermal Energy Conversion (OTEC)

Principle:

• Uses temperature gradient between warm surface water (25-30°C) and cold deep water (5-10°C) → heat engine.

• Requires ΔT ≥ 20°C (tropical oceans).

• Carnot Efficiency: Very low (~3-4%).

Types of OTEC Systems:

1. Open Cycle (Flash Evaporation):

   • Warm surface water → low-pressure chamber → flashes to low-pressure steam.

   • Steam → low-pressure turbine → condenser (cooled by cold deep water) → condensed fresh water (byproduct).

   • Working fluid = seawater.

2. Closed Cycle:

   • Warm surface water heats volatile working fluid (e.g., ammonia, R-134a) in evaporator → vapor → turbine → condenser (cooled by cold water) → liquid → pump → repeat.

   • Working fluid = ammonia (low boiling point).

   • More common, higher efficiency.

Working of Closed-Cycle OTEC:

C. Wave Energy

Characteristics of Sea Waves:

• Significant Wave Height (Hₛ or H₁/₃): Average height of highest one-third of waves in a record. Standard measure of wave energy potential.

• Wave Period (T): Time between successive wave crests.

• Wave Energy Flux (P): \( P = \frac{\rho g^2}{64\pi} H_s^2 T \) (kW/m of wave crest).

Wave Energy Conversion Technologies:

VIII. Fuel Cells

A. Fundamentals & Classification

Working Principle:

• Electrochemical device converts chemical energy of fuel (H₂) and oxidant (O₂) directly into electricity.

• Anode: Fuel oxidation: \( H_2 \rightarrow 2H^+ + 2e^- \)

• Cathode: Oxidant reduction: \( \frac{1}{2}O_2 + 2H^+ + 2e^- \rightarrow H_2O \)

• Electrolyte: Conducts ions (H⁺, O²⁻, CO₃²⁻) but blocks electrons.

• Overall: \( H_2 + \frac{1}{2}O_2 \rightarrow H_2O + \text{ Electricity} + \text{Heat} \)

• Efficiency: 40-60% (electrical), up to 85% (with CHP).

Classification (by Electrolyte):

Construction & Working - PEMFC (Example):

1. Membrane Electrode Assembly (MEA): Catalyst-coated membrane.

2. Bipolar Plates: Conduct current, distribute gases, remove water/heat (graphite/composite).

3. Gas Diffusion Layer (GDL): Porous carbon paper/cloth → distributes gases, conducts electrons, removes water.

4. Process:

   • H₂ enters anode → diffuses through GDL → Pt catalyst splits into H⁺ + e⁻.

   • H⁺ migrates through solid polymer electrolyte to cathode.

   • e⁻ flows through external circuit (load) → cathode.

   • O₂ enters cathode → combines with H⁺ + e⁻ → H₂O (and heat).

B. Fuel Cell Systems

Components of Fuel Cell System:

1. Fuel Processor/Reformer: Converts hydrocarbon fuel (CH₄, methanol) → H₂-rich gas (for non-PEMFC types). (PEMFC needs pure H₂).

2. Fuel Cell Stack: Series-connected cells → higher voltage/current.

3. Power Conditioner: DC-DC converter, inverter → AC output.

4. Heat Management: Cooling system (radiator, pump).

5. Air Management: Compressor, humidifier (for PEMFC).

6. Control System: Monitors temperature, pressure, flow.

Advantages:

• High Efficiency: 40-60% (electrical), 85%+ (CHP).

• Low Emissions: Only H₂O (if H₂ fuel). Near-zero NOₓ, SOₓ, PM.

• Modular & Scalable: From watts (portable) to MW (stationary).

• Quiet, Vibration-free.

• Fast Refueling (for H₂ fuel cells).

Applications:

• Stationary: Backup power, CHP for buildings, remote power.

• Portable: Laptops, military, camping.

• Transportation: Fuel cell electric vehicles (FCEV), buses, trains.

IX. Integration, Economics, and Policy

A. Hybrid Renewable Energy Systems

Concept & Configuration:

• Combine two or more RE sources + storage + (often) conventional backup (diesel) → reliable, cost-effective power.

• Common Configurations:

  • Solar-Wind-Battery: PV + wind turbine + battery bank. Complementary generation profiles (wind at night, solar day).

  • Wind-Diesel: Wind + diesel genset + battery. Reduces diesel consumption.

  • Solar-Biomass: PV + biomass gasifier/CHP. Biomass provides baseload, PV peak.

• Control Strategy: Maximize RE use, minimize diesel/battery cycling, manage power balance.

Benefits:

• Improved Reliability & Power Quality: Reduced intermittency.

• Reduced Storage Size/Cost: Sources complement → smaller battery.

• Lower Overall Cost: Optimal sizing, reduced diesel fuel.

• Higher Renewable Fraction.

B. Energy Storage & Management

Need for Storage:

• Match supply (intermittent RE) with demand (time-varying).

• Provide backup, grid stability (frequency/voltage), arbitrage (buy low/sell high).

Storage Technologies:

Energy Storage Management Principles:

• State of Charge (SOC) Control: Keep battery within safe limits (e.g., 20-80%).

• Charge/Discharge Strategy: Based on load profile, RE forecast, electricity tariff.

• Prioritization: Use RE first → then storage → then diesel/grid.

• Peak Shaving & Load Leveling: Reduce peak demand charges.

C. Electricity Tariffs & Policy

Types of Tariffs:

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

• Tiered (Increasing Block): First X kWh at lower rate, next Y at higher, etc. (lifeline tariff).

• Time-of-Use (TOU): Different rates for peak, off-peak, shoulder periods. Encourages shifting load.

• Feed-in Tariff (FiT): Fixed, above-market rate paid to RE producers for electricity fed into grid. Key policy driver for early RE adoption.

• Net Metering: Consumer's meter runs backward when generation > consumption → credits at retail rate.

Policy Drivers for RE Adoption:

• Renewable Purchase Obligations (RPO)/Quotas: Mandate utilities to source X% from RE.

• Subsidies & Tax Incentives: Capital subsidies, investment tax credits, accelerated depreciation.

• Carbon Pricing: Tax/credit on GHG emissions → makes RE competitive.

• Research & Development (R&D) Support.

• Grid Access & Priority Dispatch: RE must be given grid connection and priority over fossil fuels.

X. Cross-Cutting Topics (Frequently Recurring)

Environmental Benefits (Universal):

• Reduced GHG Emissions: Mitigates climate change.

• Improved Air/Water Quality: No SOₓ, NOₓ, PM, ash, mercury.

• Sustainable Resource Use: Inexhaustible sources.

• Reduced Water Use (compared to thermal/nuclear).

Common Limitations/Barriers:

Design Calculations (High-Frequency):

1. Wind Power Derivation: See Section III.A. (Betz limit derivation often asked).

2. Solar Geometry (Incidence Angle): Use formula in II.A. (Given date, time, location, tilt, azimuth).

3. Tidal Energy: \( E = \frac{1}{2} \rho g A H_{\text{eff}}^2 \eta_t \) (Convert to kWh). Key: \( H_{\text{eff}} = \text{Tidal Range} - h_{\text{min}} \).

4. Biogas Production: \( \text{Biogas yield} \approx 0.3-0.5 \ \text{m³/kg VS added} \). VS = Volatile Solids.

System Components (Definitions & Working):

• Turbines: Impulse (Pelton) vs Reaction (Francis, Kaplan). Selection based on Head & Flow.

• Collectors: Flat plate (low temp) vs Concentrating (high temp).

• Digesters: Fixed dome, floating drum, etc. (See IV.B table).

• Fuel Cells: PEMFC (low temp, transport), SOFC (high temp, stationary). Working via electrochemical reaction.

Hybrid Systems:

• Wind-Diesel: Configuration (wind turbines + diesel genset + battery). Advantage: Diesel savings, reliability.

• Solar-Wind-Battery: Complementary generation profiles → reduced storage needs. Control: maximize RE, minimize diesel.

[!TIP] Exam Focus:

• Derivations: Wind power (Betz), tidal energy formula.

• Diagrams: Flat plate collector, Pelton wheel, PEMFC, tidal single-basin, anaerobic digester (any one).

• Comparisons: Turbine types, fuel cells, biomass digesters, hydro classifications.

• Calculations: Solar incidence angle, tidal energy, wind power density.

• Definitions: Aerofoil, C3/C4 plants, sensible/latent heat, significant wave height, MPPT.

• Applications & Limitations: For each technology.