UNIT 3: Renewable Energy Sources - Short Notes

(Based on RGPV CE-504(C) Syllabus & Past Papers)

I. Introduction to Renewable Energy

Prospects of Non-Conventional Energy Sources in India

• Abundant Resources: High solar insolation (4–7 kWh/m²/day), extensive coastline (7500 km) for wind/wave, large biomass potential from agricultural residues.

• Energy Security: Reduces dependence on imported fossil fuels (India imports ~80% of its oil).

• Environmental Benefits: Low GHG emissions, aligns with Paris Agreement commitments (NDC targets).

• Economic Growth: Job creation in manufacturing, installation, and maintenance; rural electrification.

• Government Initiatives:

  • National Solar Mission (target 100 GW solar by 2022, expanded to 500 GW non-fossil by 2030).

  • Offshore wind policy, biomass cogeneration incentives.

• Challenges: Intermittency, grid integration, initial capital costs, land acquisition.

Role and Potential of Renewable Energy (Global & National)

• Global Context: Renewables accounted for ~30% of global electricity (2023); solar/wind are cheapest new-build sources in most countries.

• India’s Potential:

  • Solar: ~500 GW (utilizing 1% of land area).

  • Wind: ~300 GW (onshore + offshore).

  • Small hydro: ~20 GW.

  • Biomass: ~25 GW (from surplus agricultural waste).

• National Targets:

  • 50% cumulative electric power installed capacity from non-foss fuels by 2030.

  • 30% of energy consumption from renewable sources by 2030 (updated NDC).

• Grid Integration: Need for storage (batteries, pumped hydro), smart grids, and flexible generation.

[!TIP]

Exam Focus: Always link prospects to India’s specific resources (e.g., Thar Desert for solar, Western Ghats for wind). Mention government schemes like KUSUM for solar pumps.

II. Solar Energy

A. Solar Thermal Energy – Principle of Conversion

• Principle: Solar radiation absorbed by a collector (flat plate or concentrating) heats a fluid (water, oil, air). The thermal energy is used directly (water heating) or for power generation via steam turbine.

• Key Components:

  1. Collector: Absorbs radiation (black-coated surface).

  2. Heat Transfer Fluid (HTF): Carries heat (water, glycol, molten salt).

  3. Storage Tank: Stores heated fluid for later use.

  4. Heat Exchanger/Steam Generator: Transfers heat to produce steam.

• Types:

  • Low-temperature: Flat plate collectors (domestic hot water).

  • Medium-temperature: Evacuated tube collectors (industrial process heat).

  • High-temperature: Concentrating collectors (parabolic troughs, power towers) for electricity.

• Efficiency: η = (useful heat output)/(solar radiation input). Typically 30–60% for thermal systems.

[!DIAGRAM]

DiagramSEARCH: solar thermal flat plate collector diagram

DiagramSEARCH: parabolic trough solar thermal power plant

B. Solar Photovoltaic Systems

1. Solar Cell Materials

2. Maximum Power Point Tracking (MPPT) for PV Systems

• Need: PV I-V curve shifts with irradiance/temperature; MPPT ensures operation at Maximum Power Point (MPP) where \( P = V \times I \) is maximized.

• Key Condition: At MPP, \( \frac{dP}{dV} = 0 \) or \( \frac{dI}{dV} = -\frac{I}{V} \).

• Common Algorithms:

  • Perturb and Observe (P&O): Perturb voltage, observe power change; simple but oscillates.

  • Incremental Conductance (IC): Uses \( \frac{dI}{dV} = -\frac{I}{V} \); faster, less oscillation.

  • Constant Voltage: Maintains \( V \approx k \times V_{oc} \); easy but less accurate.

• Implementation: DC-DC converter (buck/boost) with controller (microcontroller/PLC).

[!TIP]

Exam Focus: Derive MPP condition from \( P = V \times I(V) \). Compare P&O vs. IC: IC is more precise under rapid irradiance changes.

C. Solar Radiation Fundamentals

Extraterrestrial vs. Terrestrial Solar Radiation

• Extraterrestrial Radiation (\( H_0 \)):

$$ H_0 = \frac{24 \times 3600}{\pi} G_{sc} \left(1 + 0.033 \cos\frac{360n}{365}\right) \left[ \cos\phi \cos\delta \sin\omega_s + \frac{\pi \omega_s}{180} \sin\phi \sin\delta \right] $$

Where:

\( G_{sc} \) = solar constant (1367 W/m²),

\( n \) = day number,

\( \phi \) = latitude,

\( \delta \) = solar declination,

\( \omega_s \) = sunset hour angle.

• Terrestrial Radiation (\( H \)): \( H_0 \) reduced by atmospheric effects (absorption, scattering). Measured by pyranometer.

Factors Causing Variation at Earth’s Surface

1. Atmospheric Composition:

   • Absorption: O₃ (UV), H₂O/CO₂ (IR).

   • Scattering: Rayleigh (molecules), Mie (aerosols) → diffuse radiation.

2. Cloud Cover: Reflects/scatters radiation; reduces direct component.

3. Air Mass (AM): Path length through atmosphere; AM 1.5 is standard for PV testing.

4. Latitude & Season: Solar zenith angle variation.

5. Time of Day: Sun’s position changes.

6. Surface Albedo: Reflection from ground (snow ↑, water ↓).

7. Pollution/Dust: Attenuates radiation, especially in arid regions.

[!DIAGRAM]

DiagramSEARCH: solar radiation atmospheric attenuation diagram

DiagramSEARCH: spectral distribution of extraterrestrial vs terrestrial solar radiation

III. Wind Energy – Wind Power Generation Specifications

• Rated Capacity: Maximum power output at rated wind speed (typically 12–15 m/s).

• Cut-in Speed: Minimum wind speed to start generation (3–4 m/s).

• Rated Speed: Wind speed at which rated power is achieved.

• Cut-out Speed: Maximum safe operating speed (25–30 m/s); turbine shuts down to prevent damage.

• Hub Height: Height of turbine rotor center; higher → higher wind speed (wind shear exponent α ≈ 1/7).

• Rotor Diameter: Determines swept area \( A = \pi (D/2)^2 \); power ∝ \( D^2 \).

• Power Coefficient (\( C_p \)): Fraction of wind power converted to mechanical; Betz limit \( C_{p,\max} = 16/27 \approx 0.593 \).

• Capacity Factor: Actual energy output / (rated capacity × 8760 h); typically 20–40% for onshore.

• Other Specs: Tip-speed ratio (λ), generator type (async/sync), gearbox presence.

[!TIP]

Exam Focus: Relate cut-in/cut-out to turbine safety and economics. Use \( P = \frac{1}{2} \rho A v^3 C_p \) to explain why small increase in v greatly increases power.

IV. Biomass Energy – Biomass Conversion Processes

[!TIP]

Exam Focus: Differentiate gasification (limited O₂) vs. combustion (excess O₂). Link transesterification to biodiesel production steps.

V. Ocean Energy

A. Wave Energy Conversion – Advantages & Limitations

• Advantages:

  • High energy density (∼30× wind, ∼50× solar per m²).

  • Predictable (weather patterns days in advance).

  • Abundant resource (∼2 TW global potential).

• Limitations:

  • Device survivability in storms, corrosion, biofouling.

  • Maintenance challenges (offshore, harsh environment).

  • Intermittency and variability.

  • Grid connection costs.

  • Environmental concerns (noise, habitat disruption).

• Common Technologies:

  • Oscillating Water Column (OWC).

  • Point Absorber (buoy).

  • Attenuator (snake-like).

B. Ocean Thermal Energy Conversion (OTEC)

Closed Cycle OTEC System – Working Principle

1. Warm surface water (∼25–30°C) evaporates low-boiling-point fluid (e.g., ammonia) in evaporator.

2. Vapor drives turbine connected to generator.

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

4. Fluid recycled via pump.

• Efficiency: Low (3–4%) due to small temperature difference (ΔT ∼ 20°C).

• Key Equation: Net power = turbine power – pump power.

Advantages of Closed Cycle over Open Cycle

[!DIAGRAM]

DiagramSEARCH: closed cycle OTEC system diagram

DiagramSEARCH: open vs closed cycle OTEC comparison

VI. Geothermal Energy – Classification of Geothermal Sources

1. Hydrothermal:

   • Hot Water: High-temperature water aquifers (150–250°C).

   • Dry Steam: Natural steam (e.g., Larderello, Italy).

   • Flash Steam: High-pressure hot water flashed to steam.

2. Geo-pressured: Hot water (150–250°C) under high pressure with dissolved methane; can produce both heat and gas.

3. Hot Dry Rock (HDR): Impermeable hot rock (150–300°C); requires hydraulic fracturing to create reservoir.

4. Magma: Molten rock (>600°C); highest potential but technically challenging.

5. Low-Temperature: <150°C; used for direct heating (greenhouses, spas).

[!TIP]

Exam Focus: Hydrothermal is most commercial (e.g., Geysers in USA). HDR is Enhanced Geothermal Systems (EGS).

VII. Hydro Energy – Small Head (Low-Head) Hydro Power Development

• Definition: Head < 30 m; capacity typically < 10 MW (but up to 25 MW in India).

• Types:

  • Weir/Barrage: Low dam across river; water flows through turbines.

  • Run-of-River (ROR): Minimal storage; diverts part of flow via canal/tunnel.

  • Pumped Storage: For energy storage (but usually high-head).

• Potential:

  • India: Estimated 20,000 MW (mostly in Himalayan states, Western Ghats).

  • Suitable for remote areas, mini/micro grids.

• Challenges:

  • Seasonal flow variations (monsoon-dependent).

  • Sedimentation in reservoirs.

  • Environmental flow requirements (maintain river ecology).

  • High cost per MW compared to large hydro.

  • Land acquisition and social issues.

• Turbines Used: Kaplan (propeller), Francis (medium head), Turgo (high head but low flow).

[!TIP]

Exam Focus: Distinguish small hydro from large: small hydro has lower environmental impact, no large reservoirs.

VIII. Energy Efficiency and Management

A. Energy Management Strategies

1. Policy & Planning: Set targets, energy codes, standards.

2. Monitoring & Targeting (M&T): Install meters, establish baseline, track consumption.

3. Awareness & Training: Employee engagement, behavioral changes.

4. Technology Upgradation: Replace inefficient equipment (motors, lighting, HVAC).

5. Energy Audit: Identify savings opportunities (see below).

6. Renewable Integration: On-site solar/wind to offset grid consumption.

7. Life Cycle Cost Analysis: Consider total cost (not just upfront) for investments.

B. Energy Audit

• Concept: Systematic examination of energy use to identify savings opportunities without compromising output.

• Types:

  1. Preliminary Audit (Walk-through): Quick visual inspection, low-cost measures (lighting, HVAC tuning).

  2. Detailed Audit (Comprehensive): Data logging, measurements, detailed analysis, investment-grade proposals.

  3. Targeted Audit: Focus on specific equipment/process.

• Steps:

  • Data collection (energy bills, process parameters).

  • Identify energy-intensive areas.

  • Quantify savings (techno-economic analysis).

  • Recommend measures and ROI.

C. Energy Efficient Motors

• Factors Affecting Performance:

  1. Design:

     • Core material (thin laminations reduce eddy currents).

     • Slot design (reduces stray losses).

     • Windings (copper vs. aluminum; higher copper fill).

  2. Losses:

     • Stator loss (∼30%), rotor loss (∼20%), core loss (∼20%), friction/windage (∼10%), stray load (∼20%).

  3. Efficiency Standards:

     • IE1 (Standard), IE2 (High), IE3 (Premium), IE4 (Super Premium), IE5 (Ultra Premium).

     • Premium efficiency (IE3) motors have 2–5% higher efficiency than IE1.

  4. Operating Conditions:

     • Load factor (motors most efficient at 75–100% load).

     • Power quality (voltage imbalance increases losses).

• Benefits: Lower energy costs, reduced cooling needs, longer lifespan.

[!TIP]

Exam Focus: Energy audit types differ in depth; preliminary is quick, detailed involves measurements. For motors, IE3 is now minimum standard in many applications.

IX. Power Electronics and Control in Renewable Energy Systems

A. Electronic Load Controllers (ELC)

• Purpose: For wind/hydro systems with fixed-speed turbines; maintain constant power/voltage by diverting excess energy to a dump load (resistive heater).

• Working:

  • Sensors monitor voltage/frequency.

  • Controller (microprocessor) triggers thyristor/IGBT switch to connect dump load when output exceeds limit.

  • Prevents turbine overspeed and generator damage.

• Applications: Small wind turbines, micro-hydro (without grid).

B. Thyristor Applications in Renewable Systems

• Thyristor (SCR): 4-layer PNPN device; acts as switch when gate-triggered.

• Applications:

  1. Inverters: Convert DC (PV/battery) to AC; used in line-commutated inverters (grid-tied).

  2. Phase Angle Control: Regulate AC power (e.g., for dump load in ELC).

  3. AC/DC Converters: For battery charging from AC source.

  4. Voltage Regulation: In wind turbine generators (e.g., DFIG rotor side converter).

• Advantages: High voltage/current handling, robust.

• Limitations: Cannot turn off by gate; requires current zero-crossing (for AC).

C. Magneto-Hydrodynamic (MHD) Generation

• Principle:

  1. Ionized gas (plasma) from combustion (fossil fuel or nuclear) flows through magnetic field.

  2. Lorentz force: \( \vec{F} = q(\vec{v} \times \vec{B}) \) → electrons deflect, creating voltage across electrodes.

  3. Direct conversion of thermal + kinetic energy to electricity, bypassing mechanical rotation.

• Efficiency: Theoretical ∼50–60% (higher than Rankine cycle ∼35%).

• Applications:

  • Topping cycle for coal/nuclear plants (increase overall efficiency).

  • Space power generation (nuclear MHD).

• Challenges: High-temperature materials (electrodes, channel), plasma stability, seed material (e.g., potassium) for ionization.

[!DIAGRAM]

DiagramSEARCH: MHD generator schematic diagram

DiagramSEARCH: electronic load controller block diagram for wind turbine

Final Note: These notes consolidate key concepts frequently asked in RGPV exams. Practice derivations (e.g., MPPT condition, solar radiation formulas) and diagram labeling. Relate technologies to Indian context (e.g., solar in Rajasthan, wind in Tamil Nadu).