TAE020 - Sustainable Energy: Comprehensive

Energy Problem

• High carbon emissions

• Oil

• Expanding global demand (1-2% increase per year)

Factors

• Slow progress for fossil fuel alternatives

• Changing limitations

  • Policy

• Late response (yesterday was to act, act now)

Global Energy Use/Development

Consumption increased 2.5 times from 1970 to 2015 about 2% per year until 2013, and around 1.0 % from 2014-2016.

• Most growth occurred up to 2000 in the developed countries and after 2000 in the developing countries.

Non-OECD (82% population) consumes energy at a rate of:

52 MBtu per capita

(compared to whopping 184 MBtu in OECD countries)

Energy per capita increased by __% in non-OECD countries, while it dropped by __% in the US and 8% in all other OECD countries

58, 15

Core indicators of human welfare/standards of living/education/income are reflected in the use of:

high-quality energy

Energy Use in the USA

The energy intensity of the economy improved by 27%, and per capita consumption dropped by 15%.

• Electricity consumption increased significantly from 2000-2007

• Petroleum consumption has decreased since 2006, and

  reliance significantly (25-60%) on imports.

Agri-food sector currently consumes __ percent of the total energy demand globally,

30

Around _-_% of total final energy consumption is used directly in the agriculture sector, about _._% of total US primary energy consumption.

3-5, 1.9

Greenhouse Effect

1. Specific molecules transmit short-wavelength solar radiation but block irradiated long-wavelength

2. Equilibrium surface temperature increases

3. All energy establishing equilibrium is from the sun

4. Geothermal only accounts 0.1% of earth’s total heat

Equilibrium w/o atmosphere is __^oC

-19

Solar power absorbed by the planet: Formula

Solar power radiated from the planet: Formula

Global energy balance from the above two sources & sinks:

The earth's surface temperature will be higher (+__°C) than predicted by the simple model, which excludes the atmosphere (-__°C).

11, 19

The atmosphere traps heat, causing the greenhouse effect and increasing the earth's average temperature by more than __°C

30 (degrees)

Climate Change (Carbon Emissions)

Combustion of fossil fuels produces CO₂

This CO₂ adds to GHG → equilibrium raised

Evidence of Global Warming

Reduction in Arctic sea ice: The area has decreased by about 9 % in the past decade, and the thickness has decreased by 15 – 40 % over the past 30 years.

• I.e. migration routes, geographic ranges

• Increased sea levels

Predicted Temperature Changes for the Next Century

Global temperature increases of 2 to 8 C ° above the preindustrial level can be expected by 2100

Carbon Sequestration

Capturing and storing atmospheric carbon dioxide. It is one method of reducing the amount of carbon dioxide in the atmosphere with the goal of reducing global climate change.

Climate Change Scientific Consensus/Initiatives

• Reduce energy consumption to mitigate enviro. effects

• Major industrialized countries: binding 6-8% reduction in greenhouse gas emissions relative to 1990

• IPCC

• Paris Agreement/Accord

• Kyoto Protocol

• UNFCCC

100% Solution: Hypothetical Roadmap

Transition energy infrastructures to clean, renewable (Wind, Water, and Solar) (WWS) using existing technologies for 80% of all electricity, transportation, heating/cooling, industry, and agriculture/forestry/fishing by 2030 and 100% by 2050.

Energy

The ability/capacity to work

Work (W)

The product of force (F) and the distance (d) over which it acts

Force

Newton’s Law

• F = ma

Work done against a gravitational field to lift an object to a height (h) is:

W = mgh

Power

The rate at which the work is done

Energy

The product of power (P) times time over utilization (t)

Kinetic Energy

Associated with the movement of an object

Two Types of Kinetic Energy

Translational motion (E = 1/2(m)(v)²)

Rotational motion (E = 1/2(l)(w)²)

Potential Energy

Most commonly associated with the energy of an object in a gravitational field given by:

E = mgh

Thermal Energy

Kinetic energy associated with the microscopic movement of molecules

E = 3/2(nRT)

A quantity of energy supplied Q supplied to material of mass and specific heat will increase the temperature by delta T.

Delta T = Q/mC

Chemical Energy

• Energy associated with chemical bonds between atoms

• Exothermic and endothermic reactions

• Energy released in combustion reactions →

Nuclear Energy

Energy associated with bonds between neutrons and protons in the nucleus

• Much greater than chemical energy

• Energy release during an exothermic nuclear reaction → changes in total mass of system

Electrical Energy

Energy associated with flow of electreons in a conductor

• Current (I) in conductor will experience voltage drop

  • Ohm’s law

• V = IR

• Energy of the electric and magnetic fields associated with electromagnetic waves (such as light).

• Waves have a wavelength (λ) related to the frequency (f) and the velocity (c, speed of light).

Laws of Thermodynamics

0: Two systems both in thermodynamic equilibrium with a third system are in equilibrium

1: Energy is conserved

2: A closed system will move towards equilibrium

3: It is impossible to attain absolute zero temperature

Zeroth Law Thermodynamics

Implies that the thermodynamic state of system can be defined by a single parameter, the temperature

• PV = nRT

• Ideal Gas Law: linear relationship between temp and pressure

First Law Thermodynamics

When energy is applied through heat:

1. Internal energy of the gas increases if piston of tube is fixed

2. Energy is used to lift piston if piston moves

Second Law Thermodynamics

Heat naturally flows from hot to cold

• Analogous to gravitational potential energy: object in a gravitational field only works if it moves from point of high potential to low

Total Energy in a system is calculated simply as:

= useful energy delivered + wasted energy

Energy efficiency (Ƞ) =

Useful energy delivered/energy input

Overall efficiency of a system =

product of all individual efficiencies

Efficiency

reducing the amount of energy input needed to meet our energy output needs

Conservation

reducing energy output needs or waste, e.g., through behavior/lifestyle changes

Types of Efficiency

• Conversion efficiency

• Functional/system efficiency

• Heating your home

Specific Heat

Energy to raise a unit of mass by one degree

Heat Capacity

Ability of a substance to store heat

Solar Constant

Power density of the sun’s radiation at a distance from the Earth’s orbit

The solar constant is defined as the total power radiated by the Sun per unit _______ ____ of a _______ at Earth's orbit.

surface area, sphere

1367 W/m²

A blackbody radiation curve appoximates the solar radiation at ____K outside Earth’s atmosphere.

6000

The Earth’s atmosphere reflects and absorbs solar radiation. Certain _________ _______ in the atmosphere absorb at specific wavelengths.

molecular species

Total radiation on the Earth: _____ _________ times the _____-________ area of the Earth's disk.

Solar constant, cross-sectional

About ____ of radiation is absorbed or reflected by the Earth’s atmosphere.

half

Average (horizontal) insolation is the ________ ___________ arriving at the Earth’s surface divided by the _____ ____ of the earth.

Horizontal insolation, surface area

Distribution of Insolation

Solar insolation depends on:

1. Time of day

2. Day of year

3. Latitude

Overcast Day: Insolation/Solar Intensity

10-25% of that on a clear day, represents a 75-90% drop

Distribution of Insolation

1. Azimuth

2. Altitude angle

3. Zenith angle

   1. Angle of incidence

Azimuth

Angle between the projection of sun rays and line due north/south

Altitude Angle

Angle between the horizontal and the line to the sun

Zenith Angle

Angle between the sun ray and the vertical directly overhead

Angle of Incidence

Angle between a sun ray and the perpendicular line to a surface at the point of contact

Electromagnetic Spectrum: Trends

Shorter wavelengths: higher energy intensity

Longer wavelengths: lower energy intensity

99.9% of solar energy is between UV and Infrared wavelengths

Electromagnetic Spectrum: Composition

UV 2%

Visible 47%

Infrared 51%

Electromagnetic Spectrum/PAR

Photosynthetically active radiation (400-700nm)

Photometric Sensor

• Measures light as seen by the human eye in lux or lumens or foot-candles.

• A good relative indication of the intensity and uniformity of lighting for human perspective.

Radiometric Sensor (Pyranometer)

• Measurement of electromagnetic radiation (or radiant energy) emitted by the source, often defined in terms of power, W/m2.

• Provide a relative indication of solar intensity for the whole spectrum.

PAR Sensor

• Units of measurement: μmol m^-2 s^-1.

• Compare PAR values at various points in the plant canopy and check PAR uniformity and intensity

Heat Transfer

Conduction, convection, radiation

Conduction

Heat transfer by conduction through a piece of material:

• Temperature difference across the material (Th - Tc)

• Cross sectional are of the material (A)

• Thickness of the material (l)

• The thermal conductivity of the material (k)

Thermal Conductivity

Refers to the ability of a given material to conduct/transfer heat.

Convection

Transport of thermal energy by fluid (gases or liquids) movement.

Free convection

Air or water moves away from the heated body as the warm air or water rises and is replaced by cooler air or water.

Forced convection

Air or water is forcibly moved across the body surface (such as in wind or wind-generated water currents) and efficiently removes heat from the body

Radiation

All objects radiate energy according to Stefan Boltzmann

Perfect Black Body

Not Perfect Black Body

Most common materials have emissivities of around eta = 0._

0.9

Emissivity

Measures a material's efficiency in emitting thermal radiation compared to a perfect blackbody.

Earth Emissivity

Most natural Earth surfaces is a unitless quantity and ranges between approximately 0.6 and 1.0

Emissivity: Less than 0.85

restricted to deserts and semi-arid areas

High emissivities above 0.95 in thermal infrared wavelength

Vegetation, water, ice

Solar Energy Conversion

• Conversion to electricity (photovoltaic effect);

• Conversion to usable heat (for example, via thermal collectors);

• Conversion to matter / fuel (for example, production of biomass through photosynthesis)

Solar Electric Generation

1. Use of photoelectric device

2. Conversion of solar radiation into heat → run a heat engine to drive a generator

Suitable temperature for operating a heat engine:

90 to 105ºC

Three most notable solar devices

1. Parabolic troughs

2. Dishes

3. Central receivers (solar towers)

PV cells are composed of ____________ material.

Semiconductor

Function of a semiconductor

Exposed to light; it absorb the light's energy and transfer it to negatively charged particles in the material called electrons. Extra energy allows the electrons to flow through the material as an electrical current.

PV Efficiency is regarded simply as:

the amount of electrical power coming out of the cell compared to the energy from the light shining on it.

______ efficiency is lower than individual cell efficiency.

Module

Solar cell efficiencies vary from _% for amorphous silicon-based solar cells to __._% with multiple junction production cells, and __._% with multiple dies assembled into hybrid packages.

6, 44.0, 44.4

Solar cell energy conversion efficiencies for commercially available Si PV are around __-__%.

14-22

_______ is, by far, the most common semiconductor material used in solar cells, representing approximately 95% of the modules sold

silicon

About 95% of solar panels on the market today use either _______________ silicon or _______________ silicon

monocrystalline, polycrystalline

Monocrystalline silicon

Comprise of one crystal structure

• Efficiency higher → electrons move freely

• Expensive

Polycrystalline silicon

Made up of many different crystals

• Less expensive manufacturing

Thin Film Solar Cells

deposited layers of PV material on supporting material → glass, plastic, metal

• amorphous silicon, cadmium telluride, and copper indium gallium selenide.

• light, flexibility

• Efficiencies 7-18%

• Curved surfaces: greenhouses

Photo-selective Solar Cells: Opaque

Non-selective Solar Cells

UV/NIR-selective Solar Cells

Factors of PV Performance

• Transparent glazing (top surface)

• Encapsulant: thin sheets of ethyl vinyl acetate holding top surface, solar cell, rear surface

• Rear layer: substrate

• Frame: typically aluminum

• Electrical connection