Topic 9: Energy Storage

Question 1

What problems does energy storage solve?

Answer 1

Larger quantity of fuel can be accumulated, more economic transportation
Constant energy production rates
Energy from intermittent sources can be stored

Question 2

How does energy storage improve the use of intermittent sources?

Answer 2

Means whats available can be stored for when its needed
Storing surplus means future shortages can be met- known as peak shaving

Question 3

Give 5 reasons for fluctuations in energy demand

Answer 3

Short-term weather-related fluctuations
Seasonal fluctuations
Weekday/weekend fluctuations in industrial use
24 hr day/night fluctuations
Short term behaviour-related fluctuations; meal times, TV ‘pick up’

Question 4

Although there is no large scale electricity storage, what can result in the production of surplus electricity?

Answer 4

Base-load power stations generate electricity 24 hrs a day even though less is used at night- uneconomic to switch them off
If the demand for electricity drops, it will do so more rapidly than the output of owner station can be reduced

Question 5

How is unused electricity lost?

Answer 5

As heat from cables

Question 6

What are the 5 developments in energy storage technology?

Answer 6

Peak shaving using pumped-storage HEP
Chemical energy
Rechargeable batteries
Compressed gas
Types of storage system

Question 7

How has peak shaving using pumped-storage HEP been used to improve energy storage?

Answer 7

Surplus electricity is used to pump water uphill storing is as gravitational potential
Potential can be converted to kinetic when the water moves into lower reservoir,turning turbines and generating electricity at peak times
The pumped-storage HEP can be more responsive to energy demand than other power stations
Can go from standby to full power in 15 seconds

Question 8

How is chemical energy being used as a way of improving energy storage?

Answer 8

Fósil fuels, biofuels,hydrogen,batteries and fuel cells use chemical energy as a store
Hydrogen is being developed as a form of storage which will use chemical energy

Question 9

What form of energy do rechargeable batteries use as storage?

Answer 9

Chemical energy
They use the electricity to reform the original chemicals so the batteries can be reused

Question 10

What factors affect the viability of rechargeable batteries?

Answer 10

The efficiency of storage cycle
The number of charge-discharge cycles
Energy density
Cost per unit of energy stored
Recharging speed
Self discharge in periods of non-use
Safety issues: toxicity, fire risk

Question 11

Since when has compressed gas been used as a form of energy storage ?

Answer 11

On a small scale since 1870

Question 12

How is compressed gas currently being developed as a form of energy storage?

Answer 12

Current research focuses on large scale systems that produce power from compressed air stored in underground caves
A compressed air system with heat storage can recover over 90% of original energy

Question 13

What types of energy storage systems are being developed to improve energy storage?

Answer 13

V2G systems, P2G systems, heat energy, high volume storage, molten salt, high thermal mass building materials, kinetic energy, electricity supercapacitors

Question 14

V2G systems

Answer 14

Vehicle to grid systems

Question 15

Explain the proposal of V2G systems

Answer 15

Systems where energy can be transferred between the national electricity grid and vehicle batteries
The proposal is all vehicles are plugged into the grid when parked for long periods
Peak in demand can use energy from vehicles
If there is surplus energy in the grid it can be used to recharge vehicle batteries

Question 16

How do P2G systems work?

Answer 16

They use electricity to produce gaseous fuel that can be stored
Water is electrolysed to produce hydrogen
This can be used to produce methane and added to the natural gas pipe network

Question 17

What is high volume storage and how does it improve energy storage?

Answer 17

As the volume of a heat store increases, the SA:Vol ratio goes down so the rate of heat loss declines
Can be used for inter-season storage e.g. that from surplus solar energy from summer for heating buildings in winter q

Question 18

How does molten salt work as an improved way of storing energy?

Answer 18

Advantages over water for the storage of thermal energy- potassium nitrate has a higher boiling point
The heat can later be used to boil water for steam, to turn turbines, to generate electricity
A hot water storage system would need high pressures to maintain the temperatures, adding to the cost

Question 19

How is high thermal mass building materials an improved form of energy storage?

Answer 19

Materials with a high thermal heat capacity like concrete, warm up and cool down slowly which reduces overheating in hot weather, so reduces need for air con
Reduces need for heating at start of cold weather

Question 20

How can kinetic energy be stored?

Answer 20

Flywheels can be used as a temporary store
Rotating flywheel can be used to drive machinery/generate electricity when needed

Question 21

What are electricity supercapacitors and how do they store energy?

Answer 21

Store energy as electrical charge on flat plates of conducting materials, separated by an insulator
Newer ones use electrochemical processes and have a much higher energy density
Might be used for large scale storage in the future