What is happening here and how is it linked to what we’ve been

studying?

Secondary Fuel & Energy Storage

Key Questions:

1.What is secondary fuel?

2.What are the different types of Secondary Fuel?

3. How can energy be stored?

What is a Secondary fuel?

Example 1:electricity is a clean, easily transportable form of energy created using many primary sources

‘Fuels that are made from other fuels’

Fossil fuels (chemical energy in coal, oil, gas)

heat water to produce steam

turns turbines (KE)

Uses generato

r:

to generate electricityNuclear fuel

(uranium, plutonium)

heat water to produce steam

turns turbines (KE)

generate electricity

Light energy electricityPV cell

Tidal flow (kinetic energy)

turns turbines (KE)

generate electricity

Disadvantages• Low efficiency of generation• Difficult to store

Disadvantages• Low efficiency of generation• Difficult to store

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

Fuel cells can power vehicles and space craft and provide electricity in remote locations

Fuel cells can power vehicles and space craft and provide electricity in remote locations

_ +

-e -e

Hydrogen (H2) in

Oxygen (O2) in

Flow Field Flow FieldMembraneFUEL CELL

Water (H2O) out

Example 2: hydrogen produced by electrolysis of water

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

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

• 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

Hydrogen productionHydrogen production and use from 4 primary energy sources

The flow diagram shows four different ways of generating 300 units of electricity. Which of the four is the most efficient?

Energy available from coal (780 units)Energy available from coal (780 units)

Coal fired power stationCoal fired power station

Energy available from nuclear fuel (800 units)

Energy available from nuclear fuel (800 units)

Energy available from wind (850 units)Energy available from wind (850 units)

Energy available from sunlight (1500 units)Energy available from sunlight (1500 units)

Nuclear power station

Nuclear power station

Wind generatorWind generator

PV CellPV Cell

Energy available from electricity 300 units

Energy available from electricity 300 units

Electrolysis splitting of water

Electrolysis splitting of water

Energy available from hydrogen (200 units)

Energy available from hydrogen (200 units)

Fuel cellFuel cell

Energy available to power car (100 units)

Energy available to power car (100 units)

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. 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.

Liquefied gas – the hydrogen is kept liquid by combined refrigeration and compression but very low temperatures are required.

Hydrogen power

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

Will cars powered by hydrogen be pollution-free?

In the future we may use renewable methods of producing hydrogen

Wind Hydroelectricity

Solar photo-voltaic cells (PV)

Hydrogen power

1. Biological catalysts in certain bacteria OR

2. Clever catalysts based on titanium dioxide (TiO2)

2 molecules of water 2 molecules of hydrogen / one of oxygen

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 :

Energy storageDemand 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

Energy storageType of fuel Use as energy storeFossil 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 reactionStorage involves keeping them cool to avoid accidental combustion

Rechargeable batteries

Extremely high energy densityStorage 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

Energy storage - AnswersType of fuel Use as energy storeFossil fuels High energy density (coal>oil>gas) but also high activation

energy – the energy needed (heat) to break chemical bonds to begin the combustion reactionStorage involves keeping them cool to avoid accidental combustion

Nuclear fuel Extremely high energy densityStorage 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

Types of Energy storageType of fuel Use as energy store

Fossil fuels

Nuclear fuel

Pumped HEP

Rechargeable batteries

Hydrogen