April 25 - Open Seminar

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RENEWABLE ENERGY

RESOURCES

Attendees: 10 Students

Recording

Renewable Energy Resources:

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Wind, Solar, Biofuels & Emerging Applications

Mariela Cueto

Mechanical Engineering

San Diego Mesa College

DER Connect Outreach

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Technical Talk

4/25/2025

Why Renewables?

Climate Change

• Earth's temperature stays stable when incoming solar radiation equals outgoing infrared radiation
• Greenhouse gases absorb and reemit infrared radiation, trapping heat and warming the lower atmosphere and surface
• Estimated that coal is responsible for 72.5% of the global CO₂-eq emissions, despite it only contributes 31.8% of the global power supply

Increasing Energy Demand

• Total world consumption of marketed energy expands from 549 quadrillion Btu (2012) to 629 quadrillion Btu (2020) and to 815 quadrillion Btu in 2040

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Alternatives

• Nuclear energy (a stable supply source) carries high externalities

Overview

Solar Power (PV)

Wind Energy (Turbines)

Bioenergy (Biofuel)

Renewables in Aviation

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Future of Renewables

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Recap

What is Solar Energy?

• Solar radiation is light that is emitted by the sun and solar technologies capture this radiation and convert it into usable energy
• Each location on Earth varies in how much light it receives

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Solar Power (PV): Intro

• Irradiance: the power per unit area of electromagnetic radiation incident on a surface
• Irradiation: Energy received over time (kWh/m² per day/month/year)
• Solar Constant: ~1361.5 W/m² — max potential solar power at Earth’s orbit
• Direct radiation reaching the earth surface (or a device) never exceeds 83% of the original extraterrestrial energy flux
• Beam vs. Diffuse Radiation:
• Beam: Direct sunlight, can be concentrated
• Diffuse: Scattered light, not easily concentrated

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Solar Power (PV): Key Terminology

Irradiance

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Solar Power (PV): Key Terminology

Irradiation

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Main Components:

• Concentrator: uses optics to focus sunlight onto smaller areas of a solar cell

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Solar Power (PV): How Solar Panels Work

*This equation is adequate only when the radiation flux is uniform over the aperture

• Electrons in silicon need energy to become mobile
• A P-N junction (p-type + n-type semiconductors) directs electron flow
• The junction creates an electric field that separates electrons and hole
• This generates a potential difference across the junction
• When a load is connected, electrons flow, creating DC current

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• Receiver (PV Cell): concentrated sunlight is absorbed and causes photovoltaic effect in the material of the solar cell, which generates electric current

Purpose: Maximize solar irradiance by keeping panels aligned with the sun

Cosine Effect: G vector is broken into components and G|| is the non-useful component, so G⊥ is maximized by reducing the angle

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Solar Power (PV): Sun Tracking Systems

Dual Axis

• Movement: Follows the sun in two directions
• Goal: Keeps the panel perpendicular to the sun all day, all year.
• Energy gain: 30–40% more than fixed panels

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Single Axis

• Movement: Follows the sun along one direction, typically east to west
• Goal: Tracks the sun’s daily motion, but not its seasonal height in the sky
• Energy gain: 15–25% more than fixed panels

Solar Azimuth: the direction of the sun measured clockwise from north, ranges from 0 to 360 degrees

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Solar Altitude: refers to the angle between the sun and the horizon, ranges from 0 to 90 degrees

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Solar Power (PV): Solar Azimuth & Altitude

Solar Altitude and Azimuth for:

📍 Location: San Diego Mesa College (32.8049° N, 117.1676° W)

📅 Date: April 25 (day 𝑛=115)

⏰ Time: 1:00 PM local standard time

Latitude 32.8049° N → this is 𝜙

1. Solar Declination Angle

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δ: angle between the rays of the sun and the equator

(changes throughout the year.)

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2. Hour Angle H

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H: how far the sun is from solar noon

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Solar Power (PV): Solar Position 4/25

3. Solar Altitude h

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h: height of the sun above the horizon.

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4. Solar Azimuth Az

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Final Result — April 25 @ 1:00 PM PST

Solar Altitude: ~65.8°

Solar Azimuth: ~218.7° (Southwest)

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Coordinates:32.8049° N, 117.1676° W

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X-axis: Solar Azimuth (0° = North, 180° = South, etc.)

Y-axis: Solar Altitude (0° = Horizon, 90° = Directly overhead)

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🔵 Blue Curves (Sun Path for Different Dates):

Each blue curve shows how the sun moves across the sky over the course of a specific day

🔴 Red Curves (Hourly Sun Positions):

These curves connect all the sun positions that occur at the same local standard time on different days.

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Solar Power (PV): San Diego Mesa College

• Shockley-Queisser Limit- The maximum theoretical efficiency for a single p-n junction solar cell illuminated with non concentrated light is 31%
• To estimate the efficiency of solar energy conversion, you would need:
• Solar irradiance data
• Performance data
• Improving Output:
• Concentration of Light (focus more sunlight)
• Sun Tracking (maintain optimal orientation)
• System Scale-Up (increasing the size of the module by adding more cells to the system, increasing cell area, or multiplying modules (scale-up) would increase the total active area of conversion (A))

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Solar Power (PV): Efficiency & Power Output

How do wind turbines generate energy?

• A wind turbine turns wind energy into electricity using the aerodynamic force from the rotor blades
• Converts kinetic energy → mechanical energy → electrical energy
• Speed of wind increases with height and becomes less turbulent
• Can be Upwind or Downwind:
• Up efficiency is usually higher (30-50%)
• Down efficiency (25-40%)

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Wind Energy (Turbines): Intro

• Material: Made of reinforced glass fiber
• Aerofoil shape → maximizes lift force and minimize drag, causing the rotor to spin
• As wind flows across the blade, the air pressure on one side of the blade decreases.
• The difference in air pressure across the two sides of the blade creates both lift and drag.
• Betz’s Limit =the most efficient wind turbine possible can only extract 59.3% of the wind’s kinetic energy
• Increasing angle of attack maximizes lift, but at a certain point causes streams to become turbulent and less effective

Wind Energy: Blades

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Bernoulli’s Principle + Incompressible Fluids

↓P when ↑V

P₁+½ ρV₁²+ ρgh₁= P₂+½ ρV₂²+ ρgh₂

P₂-P₁=½ρ(V₁²-V₂²)

• Anemometer:
• Measures wind speed
• Adjusts blade angle (controls the pitch motor inside of the hub allowing adjustment)
• Cut-In Speed: Minimum wind speed to start generating power
• Cut-Out Speed: Blades are feathered to stop generation for protection
• Wind Vane:
• Detects wind direction
• Sends signal to release Yaw Brakes and activate Yaw Motors
• Aligns nacelle with wind direction, then re-applies brakes

Wind Energy: External Nacelle Components

• Drive Train Process:
• Blades → Hub → Main Shaft (low speed, high torque)
• Shaft → Gearbox (increases RPM)
• Gearbox → Generator Rotor (produces voltage)
• Output sent to Transformer (at tower base) → Electric Grid
• Speed Conversion Example:
• Input speed: 18 RPM
• Gearbox ratio: ×100
• Output speed: 1,800 RPM (suitable for electricity generation)

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Wind Energy: Internal Nacelle Components

What is bioenergy?

• A form of renewable energy that is derived from recently living organic materials known as biomass, which can be used to produce transportation fuels, heat, electricity, and products

What is biomass?

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Biomass → Energy

• Direct combustion
• Biological
• Chemical conversion
• Thermochemical conversion

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Bioenergy: Intro

Direct Combustion

• The most common method for converting biomass to useful energy
• Combustion: Biomass is burned in a furnace or boiler, creating hot gases
• Turbine Power: The steam drives a turbine, which in turn rotates a generator to produce electricity
• Applications:heating buildings, industrial processes, and electricity generation

Bioenergy: Direct Combustion, Biological, & Chemical

Biological

• Process that uses microorganisms and biochemical processes to convert biomass into usable forms of energy

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Chemical

• Alcoholysis (or Transesterification) is the chemical reaction where an alcohol reacts with an ester to produce a new set of alcohols and ester

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Bioenergy: T.C. Pyrolysis

Pyrolysis:

Involves heating organic materials to between 800° F and 900° F in the nearly complete absence of free oxygen

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Hydrotreatment:

A process used to improve the quality of bio-oil produced from pyrolysis

Requires hydrogen and a catalyst

• Reduces the oxygen content in bio-oil
• Removes oxygen-containing functional groups
• Saturates double bonds

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PRODUCT

RESULT

• Involves heating organic materials to between 1,400° F and 1,700° F in a vessel and injecting controlled amounts of free oxygen or steam into the vessel to produce a carbon monoxide and hydrogen-rich gas called synthesis gas or syngas.
• Syngas can be used as a fuel for diesel engines, for heating, and for generating electricity in gas turbines
• When the hydrogen is separated from the syngas, the syngas and the hydrogen can be burned or used in fuel cells
• The syngas can be further processed to produce liquid fuels using the Fischer–Tropsch process…

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Bioenergy: T.C. Gasification

• In 2023, biomass accounted for about 5% of U.S. energy consumption, or about 4,978 trillion British thermal units (TBtu). The types, amounts, and the percentage shares of total biomass energy consumption in 2023 were:
• Biofuels—2,662 TBtu—53%
• Wood and wood waste—1,918 TBtu—39%
• Municipal solid waste, animal manure, and sewage—398 TBtu—8%

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Bioenergy: U.S. Bioenergy Consumption

Wet and dry biomass could generate approximately 1,079 trillion British thermal units (Btu) of energy.

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Bioenergy: Potential in the U.S.

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Wet Waste Potential (2017 BETO Report):

(Organic material with high moisture content)

• The U.S. could utilize 77 million dry tons of wet waste annually
• Some of these materials can't always be dried effectively

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Dry Biomass Potential (2016 Billion-Ton Report sponsored by DOE)

• 702 million dry tons of biomass annually, without negatively affecting food production, the environment, or land use

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Why?

• Air transport is essential to global business and connectivity, but it also contributes significantly to greenhouse gas emissions
• It is expected that by 2030, the carbon emission from the transport sector and

the energy requirement will increase up to 80%

• According to the report from the U.S. Energy Information Administration (IEA), for the next thirty years, the jet fuel cost will increase gradually and

the average price in the year of 2013 was ($2.82/gal)

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Renewables in Aviation

• 77th IATA Annual General Meeting in Boston, USA, (4 October 2021) a resolution was passed by IATA member airlines committing them to achieving net-zero carbon emissions from their operations by 2050
• This pledge brings air transport in line with supporting efforts of the Paris Agreement's temperature goal
• To substantially reduce global greenhouse gas emissions to hold global temperature increase to well below 2°C above pre-industrial levels and pursue efforts to limit it to 1.5°C above pre-industrial levels

Net Zero Pledge:

• Unless air traffic demand is cut dramatically, this emissions gap can only be closed by transforming the aviation sector’s energy base from fossil to renewable.
• Despite promising biofuel technologies under development, large-scale utilization of biogenic materials for fuel production generally poses risks
• An example of a renewable non-biogenic technology is power-to-liquids (PtL)

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Strategy:

*IATA strategy towards net zero CO2 emissions

What is PtL?

• PtL is a synthetically produced liquid hydrocarbon used to create synthetic fuels that can be used in aviation and other sectors
• 3 Main Constituents:
• Electricity
• Water
• Carbon Dioxide (CO₂)
• 3 Main Steps:
• First, hydrogen is produced in an

electrolyzer

• Then, hydrogen and CO₂/CO are

synthesized to hydrocarbons

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Power-to-Liquids (PtL)

• Positive side (anode) contains the KOH electrolyte
• Positive electrode attracts negatively charged OH⁻ ions
• Electrons flow through the external circuit toward the cathode
• The electrons then react with the water in in the alkaline solution
• The final product is a combination of Oxygen and Hydrogen gas
• Only 71% of the input electricity is effectively converted into hydrogen energy

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PtL: Alkaline Electrolysis

NaOH

KOH

Anode RXN

Cathode RXN

Net RXN

• FT Synthesis was developed in 1920s Germany by Franz Fischer and Hans Tropsch to produce liquid hydrocarbon fuels

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PtL: Fischer-Tropsch Pathway

• Syngas (CO and H₂) is put under specific conditions:
• Catalyst: Iron or Cobalt
• Temperature:Co catalysts are only used in the low-temperature range
• Pressure: 2 to 5 MPa
• With respect to aviation, FT-based synthetic jet fuel has been approved for use in commercial aviation in blends of up to 50 % with conventional jet fuel

*FT Reactor

Recap

Future of Renewables

Policy

• Climate Paris Agreement and Goals: substantially reduce global greenhouse gas emissions to hold global temperature increase to well below 2°C above pre-industrial levels
• The Executive Order on Paris Agreement withdrawal, signed by President Trump on January 20, 2025

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Technology

• Energy Storage: Renewables like solar and wind are intermittent
• Large-scale, efficient, and cost-effective energy storage systems (Ex. BESS)
• Enhancing conversion technologies
• High initial costs

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Case Study: Biofuel in Aviation

• Cooking oil used as airplane fuel (bio-kerosine) in Spain

Final Thoughts and Questions

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