Robotics (ME-604 (A)) - Unit 1 Short Notes

UNIT 1: RENEWABLE ENERGY FUNDAMENTALS & SOLAR ENERGY

I. INTRODUCTION TO RENEWABLE ENERGY

Definition & Need

Renewable Energy (RE) is energy derived from natural sources that replenish faster than consumption.
Need: Depleting fossil fuels, environmental pollution, energy security, sustainable development.

Classification of Renewable Energy Sources

• Solar (Thermal & Photovoltaic)

• Wind (Onshore/Offshore)

• Biomass (Agricultural residues, energy crops)

• Hydro (Large, Small, Mini, Micro)

• Geothermal (Hydrothermal, Enhanced)

• Ocean (Tidal, Wave, OTEC)

• Hydrogen/Fuel Cells

Environmental Impact of Fossil Fuels

• Climate Change & Global Warming: Caused by greenhouse gas (CO₂, CH₄) emissions.

• Greenhouse Effect: Trapping of infrared radiation by atmospheric gases; natural effect enhanced by human activities.

Basic Thermal Concepts

• Sensible Heat: Heat causing temperature change ($$\displaystyle Q = m c_p \Delta T $$).

• Latent Heat: Heat during phase change without temperature change (e.g., vaporization).

Energy Storage Management

Techniques to balance supply-demand:

• Battery Storage (electrochemical)

• Thermal Storage (sensible/latent heat)

• Pumped Hydro, Flywheels, Hydrogen

Electricity Tariffs

• Flat Rate: Fixed charge per unit.

• Tiered/Block Rate: Increasing cost with consumption.

• Time-of-Use (TOU): Varies by peak/off-peak hours.

Exam Tip: Tariffs influence RE adoption by affecting economic viability of storage and self-consumption.

II. SOLAR RADIATION AND GEOMETRY

Sun-Earth Relationship

• Rotation (daily) & Revolution (annual) cause seasonal/diurnal variations.

• Solar Declination ($\delta$): Angle between Sun-Earth line and equatorial plane.

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

where $n$ = day number.

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

Solar Angles

• Altitude Angle ($\alpha$): Angle between Sun and horizontal plane.

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

• Azimuth Angle ($$\displaystyle \gamma_s $$): Sun's projection on horizontal plane from south (N Hemisphere).

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

• Angle of Incidence ($\theta$) on Tilted Surface (tilt $\beta$, azimuth $\gamma$):

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

For south-facing ($$\displaystyle \gamma=0 $$):

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

Measurement of Solar Radiation

• Pyranometer: Measures global (diffuse + direct) solar irradiance (W/m²).

• Pyrheliometer: Measures direct normal irradiance (DNI).

• Units: W/m² (instantaneous), kWh/m²/day (insolation).

Solar Radiation on Tilted Surfaces

• Isotropic Model (diffuse uniformly from sky):

$$H_T = H_b R_b + H_d R_d + H_\rho R_\rho$$

where $$\displaystyle R_b = \frac{\cos\theta}{\cos\theta_z} $$ (incidence/zenith), $$\displaystyle R_d = \frac{1+\cos\beta}{2} $$, $$\displaystyle R_\rho = \frac{1-\cos\beta}{2} $$.

• Anisotropic Models (e.g., HDKR) account for circumsolar diffuse.

Solar Geometry Calculations

Exam Tip: Always convert local time to solar time: $$\displaystyle ST = LT + \frac{4(L_{st} - L_{loc})}{60} + E $$ (E = equation of time).

III. SOLAR THERMAL ENERGY SYSTEMS

Solar Collectors

Flat Plate Collector (FPC)

• Construction: Blackened metal absorber (copper/aluminum), tempered glass glazing, insulation at back/sides, casing.

• Working: Solar radiation passes through glazing, absorbed by plate, heats fluid (water/air) in tubes.

• Efficiency:

$$\eta = \frac{S}{G_T} - \frac{U_L (T_i - T_a)}{G_T}$$

where $S$ = useful energy gain, $$\displaystyle G_T $$ = incident radiation, $$\displaystyle U_L $$ = overall loss coefficient, $$\displaystyle T_i $$ = inlet temp, $$\displaystyle T_a $$ = ambient.

Solar Water Heating Systems

• Thermosyphon (Natural Circulation):

  • No pump; density-driven flow from cold water tank to collector to hot water tank.

  • Simple, reliable, used in residences.

• Forced Circulation:

  • Pump circulates fluid; controlled by differential thermostat.

  • Allows storage tank placement above/below collector.

Applications of Solar Thermal

1. Domestic Water Heating (most common).

2. Space Heating (air collectors, radiant floors).

3. Industrial Process Heat (drying, preheating).

4. Solar Driers: Box-type, cabinet-type, tunnel-type (agricultural products).

Solar Collector Performance

• Losses: Conduction (insulation), convection (wind), radiation (emission from absorber).

• Testing: Standard test method (ASHRAE 93) gives $I-V$ curve, efficiency at given $$\displaystyle G_T $$, $$\displaystyle T_a $$, $$\displaystyle T_i $$.

IV. SOLAR PHOTOVOLTAIC (PV) SYSTEMS

Principle of Photovoltaic Conversion

• Photoelectric Effect: Photons with energy $$\displaystyle E = h\nu $$ excite electrons from valence to conduction band if $$\displaystyle E \geq E_g $$ (band gap).

• P-N Junction: Built-in electric field separates electron-hole pairs, generating DC current.

$$V_{oc} \propto \frac{E_g}{q}, \quad I_{sc} \propto \text{light intensity}$$

Solar Cells & Modules

• Fabrication: Wafering → Texturing → Doping (P-N) → Anti-reflective coating → Metallization → Encapsulation (EVA, glass).

• Cell Parameters (from I-V curve):

  • $$\displaystyle I_{sc} $$: Short-circuit current.

  • $$\displaystyle V_{oc} $$: Open-circuit voltage.

  • $$\displaystyle P_{max} = V_{mp} I_{mp} $$: Maximum power.

  • Fill Factor (FF):

$$FF = \frac{V_{mp} I_{mp}}{V_{oc} I_{sc}}$$

• Efficiency ($\eta$):

$$\eta = \frac{P_{max}}{P_{in}} = \frac{V_{mp} I_{mp}}{G \cdot A_{cell}}$$

PV System Components

1. PV Array: Series/parallel connected modules.

2. Inverter:

   • Standalone: Converts DC to AC for loads; often with battery.

   • Grid-Tied: Synchronizes with grid; no battery (net metering).

3. Charge Controller:

   • PWM: Simple, but inefficient.

   • MPPT: Tracks maximum power point (see below).

4. Energy Storage: Batteries (lead-acid, Li-ion) for autonomy.

Standalone vs Grid-Connected Systems

Limitations of SPV Systems

• Intermittency: No generation at night/cloudy days.

• Efficiency: 15–22% (commercial Si).

• Cost: High initial investment (though decreasing).

• Storage: Batteries add cost & maintenance.

• Space: Large area needed for utility-scale.

Maximum Power Point Tracking (MPPT)

• Need: PV I-V curve varies with irradiance/temperature; MPP changes. MPPT ensures operation at $$\displaystyle P_{max} $$.

• Perturb & Observe (P&O) Algorithm:

  1. Measure initial $$\displaystyle P(k) = V(k)I(k) $$.

  2. Perturb voltage by $\Delta V$ (increase or decrease).

  3. Measure new $P(k+1)$.

  4. If $$\displaystyle P(k+1) > P(k) $$, continue perturbing in same direction.

  5. If $$\displaystyle P(k+1) < P(k) $$, reverse perturbation direction.

  6. Repeat periodically.

  Exam Tip: P&O oscillates around MPP under rapid irradiance changes; "hill-climbing" method.

Applications of PV Systems

• Rooftop Systems (residential/commercial).

• Solar Farms (MW-scale ground-mounted).

• Off-Grid: Lighting, water pumping, remote telecom.

• Building Integrated PV (BIPV): PV as building material (facades, windows).

V. SOLAR ENERGY CALCULATIONS & DESIGN

Energy Estimation

• Daily/Monthly/Annual energy from solar radiation data:

$$E_{day} = H_{avg} \times A_{array} \times \eta_{system}$$

where $$\displaystyle H_{avg} $$ = average daily insolation (kWh/m²/day), $$\displaystyle \eta_{system} $$ = overall efficiency (module × inverter × losses).

Sizing of PV Systems

1. PV Array:

$$A_{array} = \frac{E_{load}}{H_{avg} \times \eta_{system}}$$

or $$\displaystyle P_{array} = \frac{E_{load}}{H_{avg} \times \eta_{system}} $$ (if $$\displaystyle H_{avg} $$ in kWh/m²/day, $$\displaystyle P_{array} $$ in kWp).

2. Inverter:

$$P_{inv} \geq \frac{P_{peak\ load}}{\text{efficiency}} \times \text{safety factor (1.25)}$$

3. Battery (for standalone):

$$C_{bat} = \frac{E_{load} \times \text{days of autonomy}}{V_{sys} \times \text{DoD} \times \eta_{inv}}$$

where DoD = depth of discharge (e.g., 0.5 for lead-acid).

Performance Metrics

• Capacity Factor:

$$CF = \frac{\text{Actual annual energy (kWh)}}{P_{rated} \times 8760 \ \text{hours}}$$

• Yield:

$$Y = \frac{\text{Annual energy (kWh)}}{P_{rated} \ (kW)} \ \text{(kWh/kWp)}$$

Economic Aspects

• Cost per Watt: $$\displaystyle \text{Cost} = \frac{\text{Total system cost}}{P_{rated} \ (W)} $$.

• Payback Period:

$$\text{PBP} = \frac{\text{Total investment}}{\text{Annual savings}}$$

Annual savings = energy produced × tariff + incentives.

VI. INTEGRATED SOLAR SYSTEMS & HYBRIDS

Solar-Wind Hybrid Systems

• Advantage: Complementary generation (wind at night/winter, solar day/summer).

• Configuration: PV + wind turbines + battery/grid; reduces storage size and improves reliability.

Solar-Biomass Hybrids

• Biomass provides baseload power; solar reduces biomass fuel consumption during daytime.

• Used in rural electrification, industrial cogeneration.

Solar with Energy Storage

• Battery Storage: Short-term (hours), for daily cycling.

• Thermal Storage: Molten salt, phase-change materials; for CSP plants (hours to days).

Exam Tip: Hybrid systems improve capacity factor and reduce LCOE (levelized cost of energy) compared to standalone RE sources.