Properties Of Renewables And The Issues Of Intermittency

Question 1

What is intermittency?

Answer 1

When a resource isn’t available all of the time so is unable to be the only energy source

Question 2

What are some examples of intermittent energy sources?

Answer 2

Solar- weather unpredictable don’t know when the sun will shine
Wind- don’t know how strong the wind will be and for how long

Question 3

How are fluctuations in energy usage affected by intermittency of renewables ?

Answer 3

We use more energy at certain times of the day and at different times of the year (more energy in winter) we can’t ask the wind to blow more so we might not be able to provide energy

Question 4

Why is energy usage highest Monday to Friday in developed countries?

Answer 4

This is the typical working week for companies and factories
Sunday is the lowest as most workplaces are closed then

Question 5

When is there always a peak of energy on Monday morning?

Answer 5

Everybody gets up for work
Factories that have been turned off over the weekend will now power up machinery

Question 6

How does the USA and UK energy usage look different in summer months?

Answer 6

Uk relatively low as not warm enough for air conditioning this is the opposite in USA

Question 7

What can cause fluctuations in energy supply?

Answer 7

If it comes from an intermittent source (wind,solar) there will be leaks and deficits
Raw material has to be transported
Oil is shipped
Gas is piped in
Coal is shipped in
Biofuels need to be grown and processed and may need shipping in

Question 8

How can excess energy lead to waste?

Answer 8

If too much is produced then they have to turn off the source to stop the grid ‘exploding’ 2014 wind farm paid £8 million to turn off turbines

Question 9

What would the benefits of energy storage be?

Answer 9

More energy could be transported making energy more economical and cheaper for the consumer
We would be able to make the same amount of energy all the time making production cheaper
When intermittent energy sources produce a surplus the surplus could be stored for later

Question 10

What is peak shaving?

Answer 10

When a surplus of energy is created so it is stored and kept for when its needed

Question 11

How can HEP make peak shaving?

Answer 11

When there is a surplus of energy the HEP dam will use the extra energy to pump water back uphill putting it back in the reservoir

Question 12

How long does a HEP dam take to go from standby to full power?

Answer 12

15 seconds

Question 13

What are traditional methods of rechargeable batteries?

Answer 13

Having a solar panel and a battery as separate units connected by wires

Question 14

What is the problem with the traditional method of rechargeable batteries?

Answer 14

Expensive, bulky, inflexible require more space and packaging requirements an underground energy loss through external wires

Question 15

What are the most common type of battery?

Answer 15

Lithium ions

Question 16

What is the problem with lithium ion batteries?

Answer 16

The bigger it gets the less useful it becomes

Question 17

What is the problem with trying to store wind and solar energy?

Answer 17

Would require warehouses full of massive batteries
Cycling stability
Thermal runoff

Question 18

What is cycling stability?

Answer 18

The number charging and discharging until its capacity is reduced (50-80% reduced)

Question 19

What is the cycling stability of lithium ion batteries?

Answer 19

1000 cycles reducing the feasibility of long term investments

Question 20

What is thermal runaway?

Answer 20

When a battery gets hot during charging
The bigger the battery the higher the temperature making this likely in it battery storage areas increasing the risk of a fire

Question 21

What is compressed gas energy storage?

Answer 21

Involves converting electrical energy into high-pressure compressed air that can be released at a later time to drive a turbine generator to produce electricity

Question 22

What is are the positives of compressed gas energy?

Answer 22

Can work along other energy production like wind to provide and store energy 24/7 especially when surplus
Could produce 200Mw if compressed in old salt mines
90% efficient

Question 23

What is vehicle to grid? (V2G)

Answer 23

Energy stored in car batteries of electric vehicles could be used to ‘top up’ the national grid at times when needed
And surplus energy from the grid would be used to power up car batteries

Question 24

What is a requirement of V2G?

Answer 24

All cars to be plugged into the grid when parked up for a period of time

Question 25

What is the positive of V2G?

Answer 25

Better for the environment as there would be less need for rapid response power stations

Question 26

What company is already doing something similar to V2G?

Answer 26

Google with their cars

Question 27

What is power to gas? (P2G)

Answer 27

When during an during a period with excess energy the surplus is made to gaseous fuels

Question 28

What is the first step in P2G? (Surplus energy)

Answer 28

Use the surplus electrical energy to produce hydrogen (oxygen as by product)

Question 29

What do you do with the hydrogen created in the first stage of P2G?

Answer 29

The hydrogen produced by electrolysis can be used directly in many applications

Question 30

What additional processing step can take place in P2G?

Answer 30

The hydrogen can be reacted with a carbon source (CO or CO2) to produce methane which can be fed into the gas network

Question 31

What is thermal storage?

Answer 31

Short term storage of heat (efficient)
Heat store with a high heat capacity so you can store as much as possible
Small heat stores are most effect as there is small surface area for heat loss

Question 32

How is molten salt being used as an energy store?

Answer 32

Used for storing solar energy at a high temperature
Commercially used tech to store heat form concentrated solar power
Heat can be converted into superheated steam to power conventional turbines to generate power at night or in bad weather

Question 33

What is high thermal mass buildings?

Answer 33

Thermal mass can store thermal energy during the day and re-radiate it at night
Correct use can delay heat flow through buildings by as much as 10-12 hours making a house warmer in night and winter and a cooler one in summer

Question 34

What high density material are used to have a high thermal mass building?

Answer 34

Concrete bricks and tiles

Question 35

What are the benefits of hydrogen?

Answer 35

Its a reactive gas that can be made form electrolysis from surplus energy meaning intermittent source will be able to store energy

Question 36

How is hydrogen being researched?

Answer 36

Hydrogen vehicles

Question 37

What are the advantages of hydrogen vehicles?

Answer 37

Rapidly refuelled in a couple of minutes and have a range of hundreds of kilometres

Question 38

What is the hydrogen economy?

Answer 38

Transforming our existing hydrocarbon-based infrastructure to run on hydrogen in order to cut carbon and carbon dioxide emissions

Question 39

How can hydrogen be stored as compressed gas?

Answer 39

Compressor pumps 700 times the normal volume into storage tanks

Question 40

What is the disadvantage of storing hydrogen as compressed gas?

Answer 40

Energy is required to run the compressor

Question 41

What is the process of storing hydrogen as a liquid?

Answer 41

Liquefied under high pressure at a very low temperature

Question 42

What is the disadvantage of turing hydrogen into a liquid?

Answer 42

Energy is required for refrigeration and to run the compressor

Question 43

What is the process of turning hydrogen into metal hydride systems?

Answer 43

Hydrogen is absorbed on to the surface of a metal matrix enabling low pressure hydrogen storage

Question 44

What is the disadvantage of turning hydrogen into metal hydride system?

Answer 44

The storage tanks are larger and heavier than a petrol tank that stores the same amount of energy

Question 45

What is the process of turning hydrogen into ammonia?

Answer 45

Surplus primary energy is used to produce ammonia

Question 46

What is the disadvantage of turning hydrogen into ammonia?

Answer 46

Some energy required but much less then alternatives as the process doesn’t require high pressure of low temperatures