Energy Resources - Secondary Fuels and Energy Storage Flashcards
What are the main forms of secondary fuels?
- Electricity
- Hydrogen
What is a primary fuel?
An energy resource found in nature which can be directly used
What is a secondary fuel?
An energy resource produced by the conversion of a primary fuel
What types of energy can be converted to electricity?
- Kinetic (generators)
- Chemical (electrochemical cells)
- Light (PV cells)
Why are secondary fuels more useful than primary fuels?
- Easier to use
- More applicable
How is chemical energy converted to electricity?
- Electrochemical cells
- Rechargeable batteries
- Fuel cells
What is the main disadvantage of electricity?
Difficult to store
How does a coal-fired power station work?
- Coal is pulverised to coal dust
- Furnace used to produce steam
- Steam turns a turbine and drives a generator
- Condensing tower recycles steam
How do coal-fired power stations reduce environmental impacts?
- Cooling towers remove heat from water
- Limestone slurry removes sulfur from leftover coal deposits to prevent acid rain
- Electrostatic precipitators remove particulates from the smoke
How is hydrogen produced?
Electrolysis of water using electricity from surplus primary energy resources
What is peak shaving?
Storing energy during periods of excess generation to be used in periods of high demand
How can chemical energy from hydrogen be released?
- Combustion to produce heat (similar to natural gas)
- Fuel cells
What is a fuel cell?
A chemical battery which produces energy through a chemical reaction
How does a hydrogen fuel cell work?
- H2 and O2 is fed in
- H2 loses electrons and become H+ ions
- H+ ions move through a membrane to produce H2O with O2- ions
- Electrons cannot pass through the membrane and take another route (produces a current)
Which waste product do fuel cells produce?
Water
How is electricity transported?
- Generation
- SU transformer (increases V and reduces R - travels faster)
- Cables and pylons at 400,000V
- SD transformer (reduces V and increases R)
How can hydrogen be produced by electrolysis?
- Anode and cathode placed in water
- H2O is split
- O2- ions attracted to the anode (+)
- H+ ions attracted to the cathode (-)
How can hydrogen be stored?
- Compressed gas in pressurised storage tanks
- Liquid hydrogen (high pressure, low temp)
- Material-based storage (as ammonia - NH3)
How can hydrogen solve the issue of intermittency with renewables?
Excess electricity can be used to produce hydrogen and be used in a fuel cell during periods of high demand
What are the problems with hydrogen storage?
- Low volumetric energy density
- Easily lost to the atmosphere
- Liquid hydrogen must be cryogenically stored
- Requires pressurised containers
How is hydrogen used for combustion?
Used like natural gas in existing networks
What is the hydrogen economy?
The vision of using hydrogen alongside renewables to provide net zero energy security without intermittency
What can cause surplus electricity to be available?
- Wind farms at night
- Solar farms on bright days
- Increased energy efficiency
Why might energy supply fluctuate?
- Weather conditions (e.g. wind speed, sunlight hours)
- Bulk delivery of non-renewable resources
Why might energy demand fluctuate?
- Periods of peak demand
- Public events (TV ‘pickup’)
- Climate and weather
How does pumped storage HEP work?
- Excess electricity is used to pump water from a low to a high level reservoir
- Energy is stored as GPE
- Gates opened at periods of high demand and water flows over turbines
How does compressed gas work?
- Excess electricity used to pump compressed gas into depleted gas reservoirs
- Compressed gas is allowed to escape through pressure turbines during periods of high demand
How rechargeable batteries be used?
- Small scale batteries for phones and domestic use
- Large scale batteries for grid energy storage
What are the disadvantages of rechargeable batteries?
- Limited lifespan
- High environmental impact when not recycled correctly
- Long charging time
What are V2G systems?
Vehicle to grid - energy is transferred from EVs parked for long periods to the grid
What are P2G systems?
Power to gas - surplus electricity is used to produce gaseous fuel (e.g. H2 produced, converted to CH4)
What are heat energy storage systems?
Short term storage of heat using materials with a high SHC
What is high volume storage?
Very large heat stores which can be used for inter-season storage (reduces the rate of heat loss)
What is molten salt?
Can be used in CSP - potassium nitrate can be heated up to 550C and used at night to produce steam
What are thermal mass buildings?
Using construction materials with a high SHC reduce the need for heating as the building warms and cools slowly
How can kinetic energy be used for energy storage?
Rotating flywheels can temporarily store Ek for later use (4 hours on average)
What are electricity super capacitors?
Could be used for large-scale energy storage using an electrochemical process
What is specific heat capacity?
The heat energy required for a 1C rise in temperature
