Properties Of Renewables And The Issues Of Intermittency Flashcards
What is intermittency?
When a resource isn’t available all of the time so is unable to be the only energy source
What are some examples of intermittent energy sources?
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
How are fluctuations in energy usage affected by intermittency of renewables ?
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
Why is energy usage highest Monday to Friday in developed countries?
This is the typical working week for companies and factories
Sunday is the lowest as most workplaces are closed then
When is there always a peak of energy on Monday morning?
Everybody gets up for work
Factories that have been turned off over the weekend will now power up machinery
How does the USA and UK energy usage look different in summer months?
Uk relatively low as not warm enough for air conditioning this is the opposite in USA
What can cause fluctuations in energy supply?
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
How can excess energy lead to waste?
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
What would the benefits of energy storage be?
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
What is peak shaving?
When a surplus of energy is created so it is stored and kept for when its needed
How can HEP make peak shaving?
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
How long does a HEP dam take to go from standby to full power?
15 seconds
What are traditional methods of rechargeable batteries?
Having a solar panel and a battery as separate units connected by wires
What is the problem with the traditional method of rechargeable batteries?
Expensive, bulky, inflexible require more space and packaging requirements an underground energy loss through external wires
What are the most common type of battery?
Lithium ions
What is the problem with lithium ion batteries?
The bigger it gets the less useful it becomes
What is the problem with trying to store wind and solar energy?
Would require warehouses full of massive batteries
Cycling stability
Thermal runoff
What is cycling stability?
The number charging and discharging until its capacity is reduced (50-80% reduced)
What is the cycling stability of lithium ion batteries?
1000 cycles reducing the feasibility of long term investments
What is thermal runaway?
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
What is compressed gas energy storage?
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
What is are the positives of compressed gas energy?
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
What is vehicle to grid? (V2G)
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
What is a requirement of V2G?
All cars to be plugged into the grid when parked up for a period of time
What is the positive of V2G?
Better for the environment as there would be less need for rapid response power stations
What company is already doing something similar to V2G?
Google with their cars
What is power to gas? (P2G)
When during an during a period with excess energy the surplus is made to gaseous fuels
What is the first step in P2G? (Surplus energy)
Use the surplus electrical energy to produce hydrogen (oxygen as by product)
What do you do with the hydrogen created in the first stage of P2G?
The hydrogen produced by electrolysis can be used directly in many applications
What additional processing step can take place in P2G?
The hydrogen can be reacted with a carbon source (CO or CO2) to produce methane which can be fed into the gas network
What is thermal storage?
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
How is molten salt being used as an energy store?
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
What is high thermal mass buildings?
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
What high density material are used to have a high thermal mass building?
Concrete bricks and tiles
What are the benefits of hydrogen?
Its a reactive gas that can be made form electrolysis from surplus energy meaning intermittent source will be able to store energy
How is hydrogen being researched?
Hydrogen vehicles
What are the advantages of hydrogen vehicles?
Rapidly refuelled in a couple of minutes and have a range of hundreds of kilometres
What is the hydrogen economy?
Transforming our existing hydrocarbon-based infrastructure to run on hydrogen in order to cut carbon and carbon dioxide emissions
How can hydrogen be stored as compressed gas?
Compressor pumps 700 times the normal volume into storage tanks
What is the disadvantage of storing hydrogen as compressed gas?
Energy is required to run the compressor
What is the process of storing hydrogen as a liquid?
Liquefied under high pressure at a very low temperature
What is the disadvantage of turing hydrogen into a liquid?
Energy is required for refrigeration and to run the compressor
What is the process of turning hydrogen into metal hydride systems?
Hydrogen is absorbed on to the surface of a metal matrix enabling low pressure hydrogen storage
What is the disadvantage of turning hydrogen into metal hydride system?
The storage tanks are larger and heavier than a petrol tank that stores the same amount of energy
What is the process of turning hydrogen into ammonia?
Surplus primary energy is used to produce ammonia
What is the disadvantage of turning hydrogen into ammonia?
Some energy required but much less then alternatives as the process doesn’t require high pressure of low temperatures
