Energy storage

Question 1

What are the four types of storage technologies?

Answer 1

Electromechanical
- Batteries
- Flow batteries
- Hydrogen
Electromagnetic
- Super capacitors
- Magnetic (SMES)
Thermodynamic
- Compressed Air Energy Storage
Mechanical
- Flywheel

Question 2

Name and describe a mechanical energy storage device?

Answer 2

Flywheel
- Energy from an intermittent source drives a motor to spin a flywheel
- Clutch is disengaged, electric motor stops, flywheel spins freely
- Clutch is engaged, electrical machine now functions as a generator

Question 3

Name and describe a Thermodynamic energy storage device?

Answer 3

Compressed Air Energy Storage
- Intermittent energy source supplies an electric motor to drive an air compressor (waste heat can be used in a domestic context)
- Stored energy is recovered as electricity using an air turbine to drive a generator
Issues:
- Noise
- Pressure vessel integrity

Question 4

Name and describe an electromechanical energy storage method?

Answer 4

Batteries
- Reversible conversion of DC electricity to chemical energy (rectifier converts AC to DC and then inverter DC to AC)
Lithium Ion batteries:
+ high energy density
+ low rate of self discharge
+ low maintenance
~ relatively fast degradation

Question 5

Name and describe electromagnetic energy storage method?

Answer 5

Super Magnetic Energy Storage (SMES)
- stores energy within the magnetic field of a coil of superconducting wire with near zero loss of energy
- can store and discharge large quantities of energy almost instantaneously
+ enables short bursts power to maintain grid reliability (helps balance intermittent renewables)
~ Expensive in terms of cost per kWh

Question 6

Talk about hydrogen

Answer 6

• Electrolysis process has efficiency of around 70%
• however issue is that it needs to be compressed or liquified to have acceptable energy density which requires significant energy input
  => this means overall process isnt very efficient
• Hydrogen also has low ignition energy, long term storage and transportation is problematic and costly

Question 7

Talk about aqueous flow batteries

Answer 7

• Electrolyte tanks separated by a membrane across which electrons and protons can transfer, reversibly store and generate electricity
  + highly scalable
  + rapid charging/discharging
  + low charge loss
  ~ low power density
  ~ relatively large and complex

Question 8

What are some short and long term thermal storage solutions?

Answer 8

Short:
- Chilled/hot water tank
- Phase change materials
- Storage heaters
- Molten salts (large scale)

Long:
- Ground storage with heat pump
Aquifers (large scale)

Question 9

What was the NINES project?

Answer 9

• Shetland has high carbon setup, setup to increase use of RE, reduce reliance on diesel/gas, reduce consumption without impacting comfort
• Active Network Management employed (AMN), use of forecasts of next day demand and supply
• Domestic demand side management trialled using a schedule
  + Peak loads reduced by 0.5MW
  + Load shifting displaced 385 MWh of fossil fuel each year
  ~ Communication issues meant that only 50-60% of system available for load shifting at any one time
  ~ System cost more to run than what it saved