3 Technical Concepts and Overview Flashcards
When is an object said to have done work?
When it has been displaced against physical resistance
What it the formula to find work in terms of integrals?
W = β« F*dl
What is a Joule?
Work done moving 1 meter against a force of 1 newton
What is energy?
Capacity to perform work
What are the 3 forms of energy?
- Kinetic
- Potential
- Chemical
What is power?
Power is the rate of doing work
What is a Watt defined as?
Watt, defined as 1 Joule per second
What two quantities does ohms low relate?
Ohms law relates the voltage difference and the electrical current flowing through the resistance
How does heating a wire affect the current?
Heating in wire increases with the square of the current
Whats the maximum solar power at the Earths surface?
1ππ/π^2
Whats the rating of an open cycle gas turbine?
300 ππ
How much is 1 barrel of oil equivalent?
6GJ
How much is 1 cubic meter of gas?
40 MJ
What is the fossil fuel equivalent conversion?
- Is approximate and depends on the reference fuel
- Depends on where the fossil fuel equivalent has come from
Which laws of thermodynamics need to applied?
- The First Law of Thermodynamics
- The Second Law of Thermodynamics
What is the first law of thermodynamics?
Energy is neither created nor destroyed but converted from one from to another
How is energy in a frictionless environment?
π = π + ππππ
What is the second law of thermodynamics?
A device operating continuously cannot export only work from an isolated source of heat
What is a device doing work paired with?
Energy from a higher temperature
What are energy flows associated with in society?
- Static engines
- Chemical process plant
- Keeping warm and cool
- Transport of people and goods
What is an example or the second law of thermodynamics?
Heat engine that extracts mechanical work from a heat source
What does the 2nd law state in terms of q?
q β 0
What happens as energy flows through a process?
Grade deteriorates
What is the theoretical maximum extractable work called?
Exergy
What is a heat source exergy like and what does it depend on?
<100%
- Hot source temperature
- ambient temperature
What happens if heat source tends to infinity?
The source tends to pure exergy and is said to be very high grade
What happens if heat source is close to ambient?
There is little content left and the heat source is very low grade
How do you calculate efficiency?
π = Output/input
What is first law efficiency?
Uses energy arriving at the process ignoring grade or upstream energy system losses
What is primary energy efficiency?
Replaces the delivered energy* input by the primary energy* required to produce it
What is exergy efficiency?
Compares the actual consumption against that required by a thermodynamically ideal process
How do you calculate exergy efficiency?
π = required exergy/total exergy input
What is an energy system?
Accepts one or more energy flows and transforms them to produce one or more energy flows of different grade
Where is there a large amount of exergy lost in a conventional power station?
Between the combustion flame and the steam entering the turbine
What a Combined Cycle Power Plant?
Use a gas turbine to take exergy from the gas flame and pass the cooled down gases (if 500C is cool!) to a steam
plant driving a steam turbine.
What is an ideal heat engine called?
Carnot Engine
What two energy systems are exergetically more efficient?
- Heat Pump
- Combined Heat and Power
How does heat pump work?
Energy is taken from a cool (low grade source) and power is supplied (100% exergy) to raise its grade to discharge as heat at a higher temperature
How does the Carnot engine work?
Takes energy at a rate πΜ from a heat source at π_h and discharges waste heat at a rate πΜ to a heat sink at π_c. while producing power πΜ , without loss of exergy in the process
What does a refrigerator do in a heat pump system?
Extracts energy from a cold volume and discharges it at above kitchen temp at the back of the fridge.
what is the function of an air
conditioning mit?
Removes heat from a room and discharges at a higher temp in a βcondenserβ usually located on the roof
How is power supplied in refrigerant circuit?
Compressor
How does an air-to-air heat pump work?
Takes heat from ambient and ups its grade by adding exergy of its shaft power to the flow of energy into building
How much work supplied to heat pump?
13% of the heat requirement
What is the temp of the heat flow of an air-to-air heat pump?
30 - 40ΛC
What is the equation for COP?
πΜ = 3 β 4 πΜ
How can performance of a2a improve?
Geothermal heat source rather
than air
Why is condensing at 35ΛC in a steam turbine not good?
Too low for use in central heating, and therefore it is genuinely waste heat
What is CHP?
Use of a heat engine or power station to generate electricity and useful heat
What is raw fuel entering the economy termed as?
Primary energy
What are the examples of secondary energy?
- Refined oil
- Town gas
- Electrical power
What is useful energy?
Energy may need to be converted on site to provide the final service
Why must energy supply match demand approximately?
To ensure stability of the energy grid and constant supply, despite the variability in consumption
How is electricity stored in the UK, and what is its significance?
Limited to short durations, typically 1-2 minutes using batteries with around 1GW capacity
What are the challenges in electricity supply and demand matching in the UK?
- complex real-time system operations
- spatially-distributed and time-varying demand
- need for a variety of generators
What mechanisms are used in the UK to ensure electricity supply meets demand?
regulated electricity market
What happens if sufficient capacity is not provided in markets like housing and transport?
- Housing price goes up
- Impacts on time and GDP in the transport market
How is the electricity market different from other markets when capacity is insufficient?
Insufficient capacity can lead to system failure
What does the βday ahead marketβ in the electricity sector signify?
The day ahead market represents the wholesale price of electricity for the next day, reflecting anticipated demand and available supply.
Whyβs is capacity not always utilised?
- Variability in renewable energy sources (like wind and solar)
- Market demands
- Maintenance cycles
- System efficiency
What is the capacity factor?
Ratio of average generation rate to installed capacity
What is the LCoE?
Lowest price that consumers need to pay for the electricity generated to break even at the end of the project lifetime
How do you calculate LCoE?
(OPEX + CAPEX)/E
What is the learning rate?
Characteristic parameter that defines the cost reduction [%] for each doubling of cumulative capacity.
What cost reductions due to?
Mainly due to technology innovation and to a reduction in perceived risk.
