1. What is happening here and how is it linked to what we’ve been studying?
Click picture for guardian link

2. Secondary Fuel & Energy Storage
Key Questions:
What is secondary fuel?
2.What are the different types of Secondary Fuel?
3. How can energy be stored?

3. What is a Secondary fuel?
‘Fuels that are made from other fuels’
Example 1:electricity is a clean, easily transportable form of energy created using many primary sources
Uses generator:
to generate electricity
Fossil fuels (chemical energy in coal, oil, gas)
heat water to produce steam
turns turbines (KE)
turns turbines (KE)
Nuclear fuel (uranium, plutonium)
heat water to produce steam
generate electricity
PV cell
Light energy
electricity
Tidal flow
(kinetic energy)
turns turbines (KE)
generate electricity
Disadvantages
Low efficiency of generation
Difficult to store

4. Example 2: hydrogen produced by electrolysis of water
Hydrogen fuel cell
Hydrogen flows to the anode and splits into protons and electrons
Oxygen flows to the cathode
The protons flow through the membrane to the cathode
The electrons are forced through an external circuit, creating an electric current
The oxygen then reacts with the protons and electrons and is reduced to water – the only waste product _ + -e
Hydrogen (H2) in
Oxygen (O2) in
Flow Field
Membrane
FUEL CELL
Water (H2O) out
Fuel cells can power vehicles and space craft and provide electricity in remote locations

5. Secondary fuels
Advantages
Can be generated using surplus or intermittent primary energy sources e.g. wind which can’t be stored
Combustion product is water
Hydrogen stores could be used to top up primary supplies when needed
The “hydrogen economy” may supply a major proportion of consumer’s energy requirements
The high energy density store of hydrogen can be released in two ways:
Combustion to produce heat for space heating, heating objects or to heat water to produce steam for electricity generation
Electrochemically, in a fuel cell where the hydrogen reacts with oxygen to form water

6. Hydrogen production
Hydrogen production and use from 4 primary energy sources
Energy available from coal (780 units)
Coal fired power station
Energy available from nuclear fuel
(800 units)
Energy available from wind (850 units)
Energy available from sunlight (1500 units)
Nuclear power station
Wind generator
PV Cell
Energy available from electricity 300 units
Electrolysis splitting of water
Energy available from hydrogen (200 units)
Fuel cell
Energy available to power car (100 units)
The flow diagram shows four different ways of generating 300 units of electricity. Which of the four is the most efficient?

7. Hydrogen power Will cars powered by hydrogen be pollution-free?
Possibly, if renewables are used to generate electricity to produce hydrogen. No if we burn fossil fuels to generate electricity to produce hydrogen
But manufacture of equipment/car produces pollution
The biggest problem is storing enough hydrogen safely in a form that can easily be used by the fuel cells.
Compressed gas – the hydrogen is kept at 200 atmospheres pressure.
Liquefied gas – the hydrogen is kept liquid by combined refrigeration and compression but very low temperatures are required.

8. Solar photo-voltaic cells (PV)
Hydrogen power
In the future we may use renewable methods of producing hydrogen
Wind
Hydroelectricity
Solar photo-voltaic cells (PV)

9. Hydrogen power
The ultimate goal is to produce HYDROGEN directly from water using ordinary light, without any other ingredients.
Current research indicates this may be possible in the future using :
Biological catalysts in certain bacteria OR
Clever catalysts based on titanium dioxide (TiO2)
2 molecules of water molecules of hydrogen / one of oxygen

10. Energy storage
Demand for energy fluctuates over a number of timescales
Daily – peaks at meal times
Weekly – less demand at weekend because less industrial activity
Seasonal – greater in winter because it’s colder
Yearly – as the nature or amount of industrial activity changes as and as a country develops
Supply also varies – fossil fuel power stations may be shut down for repairs, supplies from wind/solar will fluctuate with weather conditions
Energy storage
can:
Help match supply to demand by “topping up” when other supplies are reduced
Maintain constant supplies for essential industrial applications
Help maintain sufficient quantities to be transported

11. Energy storage Type of fuel Use as energy store Fossil fuels
Surplus electricity is used to pump water up to the top reservoir. This stores the potential energy of the raised water. When electricity is needed, the water is allowed to flow downhill (kinetic energy) to turn turbines
Nuclear fuel
Surplus electricity can be used to produce hydrogen by electrolysing water. The electricity can then be stored as hydrogen which can then be turned back into electricity in a fuel cell
Pumped HEP
High energy density (coal>oil>gas) but also high activation energy – the energy needed (heat) to break chemical bonds to begin the combustion reaction
Storage involves keeping them cool to avoid accidental combustion
Rechargeable batteries
Extremely high energy density
Storage involves prevention of a chain reaction – store less than the critical mass of fissile fuel in one place and away from a moderator
Hydrogen
Store chemical energy that can be released as electricity

12. Energy storage - Answers
Type of fuel
Use as energy store
Fossil fuels
High energy density (coal>oil>gas) but also high activation energy – the energy needed (heat) to break chemical bonds to begin the combustion reaction
Storage involves keeping them cool to avoid accidental combustion
Nuclear fuel
Extremely high energy density
Storage involves prevention of a chain reaction – store less than the critical mass of fissile fuel in one place and away from a moderator
Pumped HEP
Surplus electricity is used to pump water up to the top reservoir. This stores the potential energy of the raised water. When electricity is needed, the water is allowed to flow downhill (kinetic energy) to turn turbines
Rechargeable batteries
Store chemical energy that can be released as electricity
Hydrogen
Surplus electricity can be used to produce hydrogen by electrolysing water. The electricity can then be stored as hydrogen which can then be turned back into electricity in a fuel cell

13. Types of Energy storage
Type of fuel
Use as energy store
Fossil fuels
Nuclear fuel
Pumped HEP
Rechargeable batteries
Hydrogen