Lec. 02: Energy Balances Flashcards
Define primary, secondary, final and useful energy as well as energy services.
These definitions of energy are oriented towards conventional energy sources like coal, oil and gas.
Primary energy
- Is energy found in nature before it undergoes any conversion performed by humans
- Specific: crude oil, untreated coal, untreated natural gas, untreated uranium, untreated biomass, wind, solar radiation
Secondary energy
- Is energy after the initial conversion processes, either chemical or physical
- E.g. refined fuels like gasoline or diesel, electricity from a coal power plant, hydrogen from electrolyzer
Final energy
- Is the energy as it is sold to end users
- E.g. electricity from power outlet in household, gasoline from gas station
Useful energy
- Is the energy after conversion by the consumer, available to be used
- E.g. heat in a home, light from lightbulb, mechanical work done by washing machine
Energy services
- Is what the consumers actually want
- E.g. a warm home, transportation from A to B, manufactured goods
Provide the classification of energy sources.
Non renewables
- Primary: nuclear; coals, crude oil, NGLs, natural gas, oil shale
- Secondary: petroleum products, manufactured solid fuels and gases; heat and electricity
(Wastes)
Renewables
- Primary: Heat and non-thermal electricity; biofuels
- Secondary: Any fuels derived from renewables; heat and electricity
Compare slide 7
What is the caloric value?
What is the tonne of oil equivalent?
(The calorific value of oil is 41,88 MJ/kg)
Caloric value [J/kg] or [J/m^3]
- Energy content of specific fuel
- Measures the heat from combustion
Tonne of oil equivalent [toe]
- Is the energy generated by burning one metric ton of oil
- Since the calorific value of oil is 41,88 MJ/kg –> 1 toe = 41,88 GJ/t
What is missing?
Unit prefixes
k = “…”
M = “…”
G = “…”
T = “…”
P = “…”
E = “…”
Unit prefixes
k = kilo = 1e3
M = Mega = 1e6
G = Giga = 1e9
T = Tera=1e12
P = Peta = 1e15
E = Exa = 1e18
What is the lower (LHV) and the higher heating value (HHV)?
Lower Heating Value (LHV)
- Is the maximum amount of usable heat from combustion excluding the condensation enthalpy of water vapor contained in the exhaust gas
- It is always lower than the HHV
- Is most commonly used in European statistics
Higher Heating Value (HHV)
- Is the maximum amount of usable heat from combustion including the condensation enthalpy of water vapor contained in the exhaust gas
- It is always higher than the LHV
- Relevant in e. g. condensing combined heat and power plants (CHP) where vapor is condensed
Units
What is power?
Power [W] = [J/s]
- Is the rate of energy consumption (e.g. home appliance, electrolyzer) or energy generation (e.g. power plants).
Units
What is energy?
Energy [J]
- In the electricity sector energy is usually measured in [Wh]
- 1 kWh = power consumption/generation of 1 kW for one hour
- It is easy to convert this back to the SI unit for energy: 1 kWh = (1000 W) * (1 h) = (1000 J/s)*(3600 s) = 3.6 MJ
What is the capacity factor of a given power plant?
capacity factor = average generation [W] or [J] / capacity [W] or [J]
Germany consumes around 600 TWh per year, written 600 TWh/a.
What is the average power consumption in GW?
600 TWh/a = (600 TW) ∗ (1 h) (365 ∗ 24 h)
= 600 TW 8760
= 68.5 GW
What is efficiency?
Efficiency n = useful energy output / energy input
How is primary energy of renewables measured?
How to value primary energy of carriers which do not have a calorific value, e.g. wind, solar PV, hydroelectricity?
Measuring primary energy of renewables
Fictive efficiency principle/Direct equivalent method
- Assume there is a 1-to-1 correspondence between primary energy and electricity for wind, solar, hydro (i.e. 100% conversion efficiency)
- Most common method
Substitution principle
- Assume the conversion efficiency from primary energy to electricity is the same as in a thermal (fossil or nuclear) power plant (e.g. 35-45%)
Efficiency Principle
- Actual efficiency of respective technology
- E.g. hydro 80-90% gravitational potential energy of water to electricity, wind 30-55% kinetic energy of air to electricity, solar 10-25% radiation to electricity
Compare slide 20
Illustrate the fictive efficiency vs. the substitution principle for electricity generation.
Compare slide 20
Suppose 50% of electricity is provided by wind and solar, the rest by fossil plants with 33% efficiency.
What is the fraction of renewables in primary energy for electricity:
1) Using the fictive efficiency principle
2) Using the substitution principle
Compare to notes
1) Using the fictive efficiency principle
25 %
2) Using the substitution principle
50 %
How does the primary and final energy will change with the expansion of the renewables and a growing electrification?
Assumption: fictive efficiency principle
Primary energy
- Will decrease due to the higher efficiency of renewables between primary and secondary energy (1-to-1 efficiency)
- The thermal losses occurring when burning fossil fuels in e.g. thermal power plants will decrease
Final energy
- Will decrease due to the higher efficiencies of electricity applications between final and useful energy
- E.g. heat pumps and electric motor require less final energy than gas heating and combustion engines for the same amount of useful energy due to the higher efficiencies
True or false?
With the growing electrification one can assume that electricity will become the dominant final energy and the metric primary energy becomes less relevant.
Other metrics such as the fraction of electricity from non-emitting sources or efficiency of electricity meeting energy services will become more important.
True!
