Renewable Energy Resources Flashcards
How do photothermal systems work?
pump water into cells and run it through thin pipes to increase surface area
water heats up
What is the water from photothermal systems used for?
bathing, washing, space heating
Examples of passive solar architecture
windows on south facing walls
elongate buildings - largest wall = south facing
light stone = reflects light, dark stone = absorbs light
How do solar assisted heat pumps work?
heat pump contains liquid with very low BP, so gas at low temperatures
liquid raises its temp in the panel
gas is compressed to liquid, releasing energy in the form of heat
heat exchanger used to heat water
Photovoltaic system: N-type side
doped with phosphorus
adds electrons
Photovoltaic system: P-type side
doped with boron
electron deficient
How do photovoltaic systems work?
excess electrons on N-type side gain energy from the Sun
electrons move to P-type side
continuous movement of electrons creates a current
What is sandwiched in a photovoltaic cell?
silicon
Advantages of solar power
renewable
reduces electricity bills
low operating costs
versatile applications
predictable
Disadvantages of solar power
high initial costs
intermittent
habitat loss due to space requirements
energy storage costs
limited energy production
made of finite materials recovered by mining
low energy density
Solar power case study: Australia
highest solar energy use per capita
10% of electricity in 20-21
more than 30% of households have rooftop photovoltaics
What is a heliostat?
device with mirrors that reflect sunlight towards a specific point to generate electricity
mirrors move for optimum angle
What is a parabolic reflector?
curved mirror that focuses rays of light onto a single point
New technology: concentrating solar power (CSP) with thermal storage
large scale
thousands of mirrors reflecting to central point, often on top of tower
salt heated to over 100 degrees, molten salt retains heat longer/ after Sun’s gone
New technology: anti-reflective surfaces
bumpy/ grooved solar panel surfaces = higher surface area
mimic structure of moth corneas
New technology: multi-junction photovoltaic cells
more layers than traditional photovoltaic cells
each layer absorbs different wavelengths of light, more light absorbed, more energy produced
New technology: photovoltaic/thermal hybrid systems (PVT)
reduces energy lost during conversion
New technology: transparent PV cells
used as windows
increases amount of cells that can be put on buildings
New technology: self cleaning panels
hydrophobic outer layer
rain runs off and removes dirtt
What features of the environment allow for the development of a HEP scheme?
large catchment
high and regular rainfall
steep sided valley with impermeable rock
no seismic activity
low turbidity
close to grid system/end user
HEP schemes: high head
use natural downward flow of river to utilise kinetic energy
significant drop in elevation (100m+)
HEP schemes: low head
less than 15m drop
utilises existing weirs
HEP schemes: run of the river
harvest the energy from flowing water
Advantages of HEP
renewable
low emissions
reliable
energy storage
flood control
Disadvantages of HEP
habitat loss
displacement of communities
high initial costs
risk of dam failure
sedimentation
high embodied energy
affects migration
lack of nutrients downstream
How is wind generated?
differences in temp and pressure
air moves to reach equilibrium
What locational factors impact the placement of wind farms?
high winds for significant amount of time
prevailing wind direction
land use conflicts
public opposition
local planning constraints
interference with telecommunications
Horizontal Axis wind turbine
centre of turbine is attached perpendicular to the post
most common
Advantages of Horizontal Axis wind turbines
renewable
low emissions
increases energy independence
scalability
higher energy outputs (installed at greater heights)
lower maintenance costs as more common
Disadvantages of Horizontal Axis wind turbines
noise pollution
ruins aesthetics
bird and bat strikes
high installation costs
high embodies energy
public opposition
reduces soil biota
Advantages of Vertical Axis wind turbine
smaller footprint than HA
rotate in any wind direction
rotate in lower wind velocities
Disadvantages of Vertical Axis wind turbine
same as HAWTs
produce less energy
Case study: offshore wind farm
dogger bank
18-60m depth = shallow
fixed seabed turbines
5% of UK’s demand
1 rotation = power home for 2 days
Case study: onshore wind farm
hyndburn wind farm
12 turbines
generate enough electricity to power over half the homes in hyndburn each year
community benefit fund established
Developments in wind energy production: blade tip fins
curved edges reduces air resistance
increased efficiency
Developments in wind energy production: nacelle brushes
reduce air escaping from the base of the blades and the nacelle
more kinetic energy absorbed by the blades
Developments in wind energy production: direct drive turbines
no gearbox so, quieter, cheaper, able to generate electricity at lower wind speeds
electricity produced in DC, so inverter needed
Developments in wind energy production: helical VAWT blades
concave blades
reduces wind resistance
increases efficiency
rotates smoother and at lower wind speeds
Developments in wind energy production: wind assisted ships
uses wind assisted propulsion
decreases fuel consumption
What type of energy is harnessed from waves?
KE
vertical movement
What factor produces large waves?
strong winds
What are the best sites to harness wave power?
far out at sea
areas of large fetch
open water
Wave energy technologies: point absorber
rises and falls as waves pass
attached to a base on the seabed
movement of floating part turns generator
Wave energy technologies: overtopping device
waves force water into an above sea level storage reservoir
water flows back to the sea through a turbine, generating electricity
Wave energy technologies: oscillating wave surge converter
waves move water cyclically
pushes a paddles which moves pistons that pump fluid over a turbine to generate electricity
Wave energy technologies: surface attenuator
hinged floating device
moving sections push and pull pistons which force water over a turbine, generating electricity
Wave energy technologies: oscillating water column
rise and fall of water forces water up and down in a submerged chamber
air that is forced in and out flows over turbines, generating electricity
Advantages of wave power
high energy density compared to wind and solar
predictable
minimal land use
useful in isolated communities
Disadvantages of wave power
high initial costs
disrupts marine ecosystems
limited locations
maintenance challenges
conflicts with fishing and shipping industries
What crops are deliberately grown for their energy value as biofuels?
wood, elephant grass, corn, barley, rapeseed, palm
How are biofuels best described?
carbon neutral
Examples of waste materials used as biofuels
domestic and commercial = burned in an incinerator
anaerobic decomposition of DOM = produces methane
Advantages of biofuels
reduced GHG emissions
increased energy security
waste reduction
compatible with existing infrastructure
easy to store and transport
abundant
predictable
high energy density
Disadvantages of biofuels
land use competition
resource intensive
CO2 emissions when burned
impact on biodiversity due to monocultures
public opposition
Where does geothermal energy come from?
radioactive decay of isotopes of thorium, uranium and potassium in the Earth’s mantle
residual heat from the formation of the solar systems
heat rises from within the earth and is transferred to the crust
Geothermal low temperature schemes: geothermal springs
groundwater heated by hot rocks may come to the surface in hot springs
Geothermal low temperature schemes: geothermal aquifers
hot groundwater pumped to the surface from aquifers
Geothermal high temperature schemes: geothermal steam systems
hot groundwater brought to the surface using a borehole, producing steam = used to generate electricity by turning a turbine
Geothermal high temperature schemes: hot dry rock systems
water is pumped down an injection borehole and steam is recovered using a second borehole
underground rocks are fractured to increase permeability and surface area for heat absorption
What factors are needed to harness geothermal energy?
high temp schemes require tectonic activity
low temp schemes require large magma intrusions
Advantages of geothermal power
low intermittency
predictable
low cost per unit of energy
easily converted to electricity
low technological advancements
Disadvantages of geothermal power
local constraints (requires 150 degrees)
emits CO2 and hydrogen sulfide
waste water contains salts and heavy metals
difficult to transport
dangerous due to tectonic acitivty
Geothermal: binary cycle power plant
hot groundwater passed through heat exchanger
heats secondary fluid and vaporises due to low BP
steam turns turbine, generating electricity
vapor is cooled and condensed
condensed fluid is pumped back into the heat exchanger to be heated again
What causes the tides?
gravitational attraction between moon and earth creates tides
How often are the tides?
2 high and 2 low every 25 hours
What factors make harnessing tidal power viable?
harnessed at the coast
seabed topography
large intertidal range
What can be done to increase the velocity of water?
direct water to a narrower channel
Ways to harness tidal power: tidal barrages
dam across estuary or bay
water flows over/through it at high tide
opens at low tide and water flows through a turbine, generating electricity
Ways to harness tidal power: tidal lagoons
surrounds a selected part of an estuary or bay
fills at high tide
water released at low tide, flowing over turbines
Ways to harness tidal power: in-stream turbines
fixed to seabed
absorbs kinetic energy at high and low tide
Advantages of tidal power
renewable
predictable
no GHG emissions
long lifespan
energy storage potential
Disadvantages of tidal power
blocks shipping routes
migration barriers
expensive to build
intermittent
maintenance challenges
New tidal technology: tidal reefs
not as tall as a tidal barrage
water flows over the reef to allow marine wildlife to move over it
tidal flow turns turbines to produce electricity
What is a primary fuel?
natural resource that can be used directly for energy production
Examples of primary fuels
coal, oil, gas, nuclear, biomass
What is a secondary fuel?
an energy source that is derived from the processing or conversion of primary fuels
How does a coal fired power station work?
pulverise coal
combust pulverised coal
heat produced used to convert water to steam
steam turns turbines connected to generator
steam is cooled and condensed, then pumped back into the system
scrubbers remove sulphur dioxide and electrostatic precipitators capture particulates
What is a fuel cell?
a chemical battery
uses chemical energy to produce electricity
What is the most common type of fuel cell?
hydrogen
How does a fuel cell work?
hydrogen oxidised to H+
H+ move through partially permeable membrane, electrons forced to find alternative pathway, creating an electric current
H+ meet O2- to produce H2O
only waste = water
What is peak shaving?
storing energy at a time of excess production for a later time of high demand
How is electricity transported?
electricity generated
step-up transformer=increases voltage
electricity travels faster
travels through cables and pylons
step-down transformer
end user
Advantages of using electricity
applicable to many uses
clean energy when generated by renewables
easily transported
allows for technological advancements
rapid energy delivery
scalability
reliable
no pollutants released upon use
How is hydrogen produced by the electrolysis of water?
place electrodes in water
current splits water into H2 + O2
collect gases using an inverted container over the system
H2 is purified
How can hydrogen be stored?
pressurised container
liquid hydrogen
metal hydrides
chemical storage
adsorption
What problems are associated with the storage of hydrogen?
explosive
high cost
public opposition
large tanks due to low energy density
hydrogen causes materials to become brittle
Ways of releasing chemical energy from hydrogen: combustion
used similarly to natural gas
pumped into an existing network
Ways of releasing chemical energy from hydrogen: fuel cells
feed cell with hydrogen and oxygen
hydrogen loses electrons, becomes H+
H+ move through partially permeable membrane and combine with O2- to form water
electrons forced through alternative pathways, generating a current
Why do we need to store energy?
balance supply and demand
save excess energy generated during peak production
Causes in fluctuations in energy supply
variability of renewable energy sources
equipment failures
changes in demand
Causes in fluctuations in energy demand
seasonal changes
daily patterns
holidays
population growth
increased energy efficiency
How can we store energy?
batteries
pumped hydro storage
compressed air energy storage
flywheels
thermal energy storage
fuel cells
Pumped storage: HEP
excess electricity used to pump water from the lower reservoir to the upper reservoir at times of low demand
stores energy at GPE
when demand increases, stored water is released back down to the lower reservoir, drives turbines that generate electricity
Advantage of pumped storage
quickly responds to changes in demand
Compressed gas storage
air is compressed using excess electricity and stored in high pressure tanks or underground caverns
released when demand increased, compressed air expands and drives turbines to generate electricity
effective for large scale energy storage
Small scale rechargeable batteries
smartphones
laptops
electric vehicles
portable electronics
power tools
Large scale rechargeable batteries
grid energy storage
frequency regulation
backup power
microgrids
Disadvantages of the use of rechargeable batteries
limited lifespan
high cost
environmental impact
charging time
temperature sensitivity
performance degradation
Types of storage systems: V2G systems
energy transfer between grid and vehicle batteries
all vehicles plugged into the grid when parked for an extended period of time
avoids cost and environmental impacts of power stations
Types of storage systems: P2G systems
uses surplus electricity to produce gaseous fuel
water electrolysed to produce hydrogen
hydrogen used to produce methane, which is fed into the natural gas pipe network
Types of storage systems: Heat energy
short-term storage of thermal energy
uses high thermal mass materials
Types of storage systems: High volume storage
low SA:VOL, reduces heat loss
used for inter-season energy storage
Types of storage systems: molten salt
stores heat from concentrated solar power photothermal systems
heat can be used later to boil water in a steam turbine power station
Types of storage systems: high thermal mass buildings
constructed or material with a high thermal mass
reduces overheating during hot weather
reduces need for space heating in winter
Types of storage systems: kinetic energy
temporary store of KE
used to drive machinery
generates electricity
e.g. flywheels
Types of storage systems: electricity super capacitors
uses an electrochemical process
future applications of large scale electricity storage
creates a difference in charge, stop electrons flowing, electricity released when needed
