Renewable Energy Source Overview: Solar Photovoltaic, Solar Thermal, Wind Energy, and Batteries/Fuel Cells

Solar Photovoltaic (PV)

• On-Grid System:
  • Components: Solar panel, grid-connected inverter, electricity meter, AC isolator, fuse box.
  • Optional components: Battery, charge controller, DC isolator.
  • Diagram illustrates electron and "hole" flow within a solar cell.
  • PV system includes cabling, junction, mounting, and tracking system.
  • Assembly: Solar cell → Solar module → Solar panel → Solar array.

Solar Energy

• How it Works:
  • Solar power plants: Steam production to turn turbines.
  • Solar heating: Active and passive systems.
  • Photovoltaic cells: "Solar batteries" use special semiconductors.
• Advantages:
  • Renewable and free.
  • High energy yield.
  • Clean source: No air/water pollution during operation.
  • Low operating costs; pays for itself over time.
• Disadvantages:
  • Intermittent source; energy storage issues.
  • Low energy density; requires significant land area.

Solar Energy Conversion

• Forms of Energy Conversion:
  • Light energy to electrical energy (solar cells).
  • Light energy to thermal energy (passive solar heating).
  • Light energy to chemical energy (photosynthesis, solar water-splitting).

Solar to Chemical Energy

• Photosynthesis:
  • $CO<em>2 + H</em>2O \rightarrow Sugar + O_2$
• Photocatalytic Water Splitting:
  • $2H<em>2O \rightarrow 2H</em>2 + O_2$
• Process Overview:
  • Light harvester absorbs light.
  • Excited state (LUMO/CB) facilitates electron transfer (reduction).
  • Water oxidation catalyst (or sacrificial electron donor, D) generates holes.
  • Catalyst or enzyme facilitates fuel formation.
• Components:
  • Light harvester.
  • Water oxidation catalyst.
  • Reduction catalyst.

Solar Thermal

• Concentrated Solar Power (CSP):
  • Heat liquid at focal point to produce steam, which turns a turbine.

Concentrating Solar Power Plant

• Components:
  • Heliostats: Reflect sunlight.
  • Receiver: Absorbs concentrated sunlight.
  • Steam drum, reheater, feedwater.
  • Turbine and generator produce electricity.
  • Steam condenser.

Conventional Parabolic Trough System

• Process Flow:
  • Hot oil (~390°C) heated by solar field.
  • Heat exchanger transfers heat to generate steam.
  • Steam turbine generates electricity.
  • Condenser cools steam back to liquid.
• Molten-Salt Parabolic Trough System:
  • Uses molten salt instead of oil (higher temperature ~550°C).
• Advantages of Molten Salt System:
  • Higher turbine efficiency.
  • Less volume of storage required.
  • Oil-MS heat exchanger not required.

Molten Salt System

• Process:
  1. Sunlight concentrated by heliostat field onto a receiver tower.
  2. Molten salt heated to 566°C (1050°F) in receiver.
  3. Heated salt stored in hot salt tank.
  4. Molten salt pumped through steam generator to create steam.
  5. Steam drives turbine, generating electricity.
  • Cold salt at 288°C (525°F) flows back to cold salt tank.

PS10 Solar Power Plant (Spain)

• Operation:
  • 624 heliostats concentrate sunlight onto a central solar power tower.
  • Generates 11 MW.

Concentrated Sunlight Conversion

• Process:
  1. Software-controlled heliostat field concentrates heat on a boiler mounted on a central tower.
  2. Concentrated sunlight converts water in boiler to steam.
  3. Steam powers a generator and produces electricity.
  4. Electricity is transmitted to the grid.

Solar Thermal Storage

• Advances in storage may reduce costs and enable 24-hour on-demand power.

Solar Thermal (Direct Heating)

• Components:
  • Collector, sensor, controller.
  • Hot water storage tank.
  • Auxiliary heat (electric or gas).
  • Expansion tank, check valve, drain.
  • Air vent.
• Variations:
  • System with secondary heat exchanger.

Solar Thermal System

• Components:
  • Glazing, flat-plate collector assembly, absorber plate.
  • Shutoff valve, circulator, controller.
  • Vent, expansion tank, foam insulation, sensor, check valve.
  • Insulated hot-water tank, tempering valve, backup heating element, heat-exchange coil.

Solar Thermal Power Plant

• Process:
  • Solar pond heats water.
  • Evaporator boils working fluid.
  • Turbine generates electricity.
  • Condenser and cooling tower.

Photovoltaics Overview

• Production:
  • Large plants and centralized production.
  • Decentralized units per household.

Floating Solar and Hybrids

• Example: Floating solar hybrid in Alqueva, Portugal.

Utility-Scale Solar Power Plants in California

• Types: PV power plants (gold), solar thermal power plants (red).
• Size: Proportional to total installed capacity.

California Solar PV Capacity

• Capacity: 46,874 MW installed by the end of 2023.
• Power Output: Enough to power 13.9 million homes.

Wind Power Overview

• Wind Resource Areas in California: Identified wind speed at 90 m.
• Offshore Wind:
  • Data interpolated to 90 m and extrapolated to 50 nautical miles by NREL.
  • Contours indicate water depth and distance from shore.

Wind Turbine Types

• Horizontal-Axis Turbines:
  • Up-stream power station.
• Vertical-Axis Turbines:
  • Darrieus, Savonius, H rotor.

Wind Energy

• How it works:
  • Wind turbines directly generate electricity.
  • Efficient, function of wind speed and blade area.
• Challenges:
  • Location: Not near population centers.
  • Visual appearance, noise, and intermittent supply.

Wind Installations (Global)

• Total Installed Capacity (2023): 1,051,078 MW.
• Annual Growth Rate (2013-2023): +19.1%.
• Leading Countries:
  • China: 441,895 MW (+11.6% growth)
  • US: 148,020 MW (+9.4% growth)
  • Germany: 69,459 MW (+7.6% growth)

Batteries

• Chemical Basis:
  • Based on reduction-oxidation (redox) reactions, where electron transfer occurs.
• Process:
  • Oxidation half-reaction at the anode.
  • Electrons flow from anode to cathode through an external circuit.
  • Reduction half-reaction at the cathode.
• Rechargeable Batteries:
  • Regenerate redox reactants through electrolysis using an external electricity source.

Battery Example

• Components:
  • Graphite rod (cathode).
  • MnO2 paste, KOH paste (electrolyte).
  • Zinc can (anode).
• Reactions:
  • Anode (oxidation): $Zn + 2OH^- \rightarrow Zn(OH)_2 + 2e^-$
  • Cathode (reduction): $2MnO<em>2 + H</em>2O + 2e^- \rightarrow Mn<em>2O</em>3 + 2OH^-$

Battery Example 2

• Components:
  • Negative plates (lead grids filled with spongy lead).
  • Positive plates (lead grids filled with $PbO_2$).
  • $H<em>2SO</em>4$ electrolyte.

Battery Types and Growth

• Ragone Plot:
  • Graphs volumetric energy density (Wh/L) vs. gravimetric energy density (Wh/kg).
• Battery Categories:
  • Pb-acid, Ni-MH, Li-Ion, Li-Polymer, Metal-air.
• Trends:
  • Research stage: Organic radical, Lithium-air.
  • Partially commercialized: Li-Thin Film.
  • Fully commercialized: Pb-acid, Ni-MH, Li-Ion.

U.S. Battery Market

• Market Size (2030 Projection): Significant growth from 2020.
• Dominant Types Lithium Ion, Lead Acid, Nickel Metal Hydride.
• Challenges:
  • Environmental: Land, water, radioactive, and air pollution; greenhouse-gas emissions.
  • Social: Health and safety, child labor, fair working conditions, discrimination, indigenous rights.
  • Governance: Transparency, customer health, information management, tax evasion, corruption.

Li-ion Battery Demand

• Expected Growth: 27% annually, reaching ~4,700 GWh by 2030.
• Regional Demand: China, Europe, United States, Rest of the world.
• Sector Demand: Mobility, stationary storage, consumer electronics.

Batteries Future

• Cathode Materials:
  • NMC (nickel manganese cobalt) is dominant in EV batteries.
  • Alternative: Lithium iron phosphate (LFP) - low-cost, growing market share.
  • Tesla, Ford, and Volkswagen are adopting LFP batteries.

Fuel Cells

• Basic Principle:
  • Similar to a battery, but reactants are continually supplied, and products are continually removed.
• Types:
  • Most common: Hydrogen fuel cells.
• Scalability:
  • Scalable; can power homes/neighborhoods or small appliances.
• Distributed Generation:
  • Decentralized power system with hydrogen generators and fuel cells.

Fuel Cells Operation

• Components Anode, cathode, catalyst, proton exchange membrane (PEM).
• Process:
  • Hydrogen (H2) flows through channels to anode.
  • Oxygen (O2) flows through channels to cathode.
  • H+ ions move through PEM.
  • Water (H2O) is produced.

Hydrogen Fuel Cells: Scalable Hydrogen Economy

• Concept:
  • Large-scale system where hydrogen is the primary form of energy storage.
  • Fuel cells convert hydrogen to electrical energy.
• Advantages:
  • Clean and potentially more reliable (distributed generation).
• Challenges:
  • Efficient hydrogen production, storage, and transport.

Fuel Cell Reactions

• Process:
  • Hydrogen supplied to anode.
  • Proton exchange membrane facilitates ion transport.
  • Oxygen supplied to cathode.
  • Water produced as a byproduct.

Fuel Cell Basic Operation

• Process:
  • Anode: $2H_2 \rightarrow 4H^+ + 4e^-$
  • Cathode: $O<em>2 + 4H^+ + 4e^- \rightarrow 2H</em>2O$
  • Overall: $2H<em>2 + O</em>2 \rightarrow 2H_2O$

Alkaline Fuel Cell (AFC)

• Components:
  • Anode, cathode, electrolyte (hydroxyl ions).
• Reactions
  • Anode: $2H<em>2 + 4OH^- \rightarrow 4H</em>2O + 4e^-$
  • Cathode: $O<em>2 + 2H</em>2O + 4e^- \rightarrow 4OH^-$
  • Overall: $2H<em>2 + O</em>2 \rightarrow 2H_2O$