Exam Q/A (old papers)

Question 1

1. When discussing the need for making a global energy transition to minimize damages from climate change, often a term called climate sensitivity is used.

a). Explain what is meant by climate sensitivity (exact physical definition not required), and what
unit is most commonly used to measure it. (3p)

Answer 1

a. According to the IPCC (Forth Asessment), “Climate sensitivity is a metric used to characterise the response of the global climate system to a given forcing. It is broadly defined as the equilibrium global mean surface temperature change (°C) following a doubling of atmospheric CO2 concentration.

Uncertainties in future emission scenarios and various feedback such as rates of oceanic heat uptake, clouds, changes in water vapor, ice and snow cover, and the “lapse rate” all
contribute to the uncertainty about the future rate of temperature change.

Question 2

1. When discussing the need for making a global energy transition to minimize damages from
   climate change, often a term called climate sensitivity is used.

b). Approximately what is the best current estimate of this parameter, and roughly what is the
uncertainty range? (3p)

Answer 2

b. The “likely” (> 66% probability) range of climate sensitivity is between 1.5 –4.5 °C, according to IPCC AR5. Most mainstream scientists put their “best guess” for climate sensitivity somewhere in the middle of the range, between 2.5 and 3.5 C.

Question 3

1. When discussing the need for making a global energy transition to minimize damages from climate change, often a term called climate sensitivity is used.
   c) . What are the implications of this uncertainty for the global energy system? (4p)

Answer 3

c. There are many implications for this uncertainty for the global energy system. For
example, stabilizing global temperature change to be below the 2 °C target will require very fast reductions of global emissions and the rate of reduction will depend on the climate sensitivity. If climate sensitivity is high (4.5 °C per doubling of CO2conc.), even reducing emissions to zero will not be enough. Global net emissions must be reduced below zero using negative emission technologies (e.g. BECCS). However, if climate
sensitivity is low (e.g. 1.5 °C per doubling of CO2), we have plenty of time to solve the problem (50-100 years).

Question 4

What is emission factor?

Answer 4

Measure of the average amount of a specific pollutant or material discharged into the atmosphere by a specific process, fuel, equipment, or source. It is expressed as number of pounds (or kilograms) of particulate per ton (or metric ton) of the material or fuel.

Question 5

What is Capacity Factor?

Answer 5

The net capacity factor is the unitless ratio of an actual electrical energy output over a given period of time to the maximum possible electrical energy output over the same amount of time.[1] The capacity factor is defined for any electricity producing installation, i.e. a fuel consuming power plant or one using renewable energy, such as wind or the sun. The average capacity factor can also be defined for any class of such installations, and can be used to compare different types of electricity production.

Question 6

3. a). Name the three general categories of CO2 capture processes from power production. (3p)

Answer 6

a. (1) flue gas separation, (2) oxyfuel combustion in power plants, and (3) precombustion separation.

Question 7

3b). Once CO2 are captured, what are the options to store CO2? Name at least three options. (3p)

Answer 7

b. Captured carbon can be stored in geologic sinks and the deep ocean. Geologic storage options include deep saline formations (subterranean and sub-seabed), depleted oil and
2 gas reservoirs, formations for enhanced oil recovery operations, and unminable coal seams. Deep ocean storage approaches include direct injection of liquid carbon dioxide into the water column at intermediate depths (1000–3000 m), or at depths greater than 3000 m, where liquid CO2 becomes heavier than seawater, so CO2 would drop to the ocean bottom and form a ‘‘CO2 lake.’’ Other storage approaches are proposed, such as enhanced uptake of CO2 by terrestrial and oceanic biota (mineral carbonation). Finally, captured CO2 can be used as a raw material by the chemical industry.

Question 8

what is load factor?

Answer 8

In electrical engineering the load factor is defined as the average load divided by the peak load in a specified time period.[1] It is a measure of variability of consumption or generation; a low load factor indicates that load is highly variable, whereas consumers or generators with steady consumption or supply will have a high load factor.

F load=Average load/Mx. load in given time period

An example, using a large commercial electrical bill:
peak demand = 436 kW
use = 57200 kWh
number of days in billing cycle = 30 d
Hence:
load factor = { 57200 kWh / (30 d × 24 hours per day × 436 kW) } × 100% = 18.22%

Question 9

…4d). Briefly discuss (qualitatively) the effect of price elasticity of demand on CO2 avoidance cost.
What happens to the mitigation cost when the demand is more vs. less elastic? (3p)

Answer 9

d. When demand is responsive to prices, less emissions will occur as a result. The more
elastic the demand is, the lower the mitigation cost.

Question 10

…4d) Mention three possible factors that could prolong the era of fission energy. (3p)

Answer 10

d) Discovery of new resources and reserves becoming economical due to increased
price of Uranium, better technology etc.
Reprocessing the spent fuel and using the fissionable materials in it.
Breeder reactors that can convers U238 and other fertile isotopes into fuel.

Question 11

7. Explain how a fuel cell functions and name a relevant application for such a technology. (3p)

Answer 11

7. A fuel cell uses the chemical energy of hydrogen or another fuel to produce electricity. If
   hydrogen is the fuel, electricity, water, and heat are the only products. The basic chemical
   reaction is H2 + ½ O2 -> H2O. Fuel cell applications include:
   • small scale: chargers, laptop
   • medium scale: cars and heavy trucks, solar energy systems
   • large scale: back-up power, stationary power.

Alternative answer:
A fuel cell is an electrochemical cell that converts the chemical energy from a fuel into electricity through an electrochemical reaction of hydrogen-containing fuel with oxygen or another oxidizing agent.[1] Fuel cells are different from batteries in requiring a continuous source of fuel and oxygen (usually from air) to sustain the chemical reaction, whereas in a battery the chemical energy comes from chemicals already present in the battery. Fuel cells can produce electricity continuously for as long as fuel and oxygen are supplied.

Question 12

1. Give brief answers to the following questions on basic concepts.
   • What is the energy efficiency gap?
   Point out 4 factors that contribute to, or can explain why the energy efficiency gap exist? (4 pt)

Answer 12

Energy efficiency gap refers to the improvement potential of energy efficiency or the difference between the cost-minimizing level of energy efficiency and the level of energy efficiency actually realized. It has attracted considerable attention among energy policy analysts, because its existence suggests that society has forgone cost-effective investments in energy efficiency, even though they could significantly reduce energy consumption at low cost.

• “Transaction costs”: costs of searching and processing information
o Transaction costs are not absolute, they differ between actors
o Imperfect information. Households and small companies often lack energy
knowledge causing high transaction costs
o High in relation to energy which is often a small part of expenditures
o Bounded rationality: cognitive limitations to rational choices
• ”Split incentives”:
o E.g. Tenant- landlord problems:
§ The landlord chooses major appliances, the tenant pays the electricity
• Consumers have high discount rates
• Consumers maybe risk adverse.
• Consumers have

Question 13

1. Give brief answers to the following questions on basic concepts.
   - Define price elasticity and write down the formulae for ε. (4 pt)

Answer 13

Price elasticity:
• Price elasticity of demand (ε) is the change in demand for a good due to a change in price. The formula is:
• ε = (dQ/Q) / (dP/P)
• i.e., the percent change in quantity (Q) divided by the percent change in price (P)

Question 14

Name and describe four variation management (sometimes also called load management, load shifting or load smoothing) techniques for the electricity system. (4 pt)

Answer 14

Variation management:
• Active – thermal plants, wind curtailment, demand side management, storage, cogeneration and fuel production (hydrogen), Transmission and trade – both passive and
active.
• Thermal generation: Start-up /shut down, Part load
• Wind power curtailment
• Transmission and trade (Wind variations are reduced as geographical scope increases;
Trade with hydropower rich regions can reduce impact of variations
• Storage
• Demand side management
• Co-generation and fuel production (such as hydrogen production)

Question 15

2. A. Explain why is it that it is NOT necessarily the technology with the lowest levelised cost of electricity that is the most profitable to invest and that private actors on a market will invest in.
   (4 pt)

Answer 15

A. If you have a technology A and a technology B to produce identical cars, and the cost of
producing a car using technology A is lower than when using technology B, then it is most
profitable to use technology A. This is not necessarily true for electricity because the price of
electricity varies over time1! Take two different technologies, for instance solar PV and coal.
They produce electricity at different points in time. This means that they will also generate
different revenues of income per kWh. For instance, if the price of electricity is higher during
the middle of the day when the sun shines, solar PV would get higher average revenues per kWh of electricity produced than coal, because coal also generates a lot of electricity night time when electricity prices are lower. This, in turn, means that the profitability of solar PV can be higher than that of coal even if the levelised cost of electricity from solar PV is higher than that of coal based electricity. Thus, the key here is to make a distinction between the profitability and the levelised cost of a given technology. Profitability is basically revenues minus costs. The problem with the levelised cost concept is that it does not consider variations in revenues (the price of the product sold).

Question 16

what is levelized cost of electricity?

Answer 16

In electrical power generation, the distinct ways of generating electricity incur significantly different costs. Calculations of these costs at the point of connection to a load or to the electricity grid can be made. The cost is typically given per kilowatt-hour or megawatt-hour. It includes the initial capital, discount rate, as well as the costs of continuous operation, fuel, and maintenance. This type of calculation assists policy makers, researchers and others to guide discussions and decision making.
The levelized cost of electricity (LCOE) is a measure of a power source which attempts to compare different methods of electricity generation on a consistent basis. It is an economic assessment of the average total cost to build and operate a power-generating asset over its lifetime divided by the total energy output of the asset over that lifetime. The LCOE can also be regarded as the average minimum cost at which electricity must be sold in order to break-even over the lifetime of the project.

Question 17

Previous:2. A. Explain why is it that it is NOT necessarily the technology with the lowest levelised cost of
electricity that is the most profitable to invest and that private actors on a market will invest in.

Actual question: If there are certain problems associated with this method and how it is being interpreted,
why do you have to learn about a concept such as the levelised cost of electricity? (4 pt)

Answer 17

B. The concept of levelized cost was primarily developed to compare the cost of technologies that generate baseload electricity and operate most of the time. Then the variation in the price of electricity over the day or the year does not really matter since all power plants meet the same price variation. In such circumstances, the technology with the lowest levelised cost of electricity will also be the most profitable to invest in. It is still useful to understand this concept since in public debates and in media, when people compare the cost of different technologies they (most often, if not almost always) use the levelised cost of technology as their method, and then it is good to know how it works and which conclusions you may draw and also, as pointed out here, the problems that exist with it.

Question 18

What is baseload electricity?

Answer 18

Base load is the minimum level of electricity demand required over a period of 24 hours. It is needed to provide power to components that keep running at all times (also referred as continuous loa

What is Baseload Power?
The argument basically goes like this. When the wind isn’t blowing and the sun isn’t shining, renewables like solar and wind aren’t producing electricity. What happens during that time when we need energy? We need something more reliable — something that produces electricity all the time and that we can rely on. That’s baseload power, provided by reliable sources such as nuclear and coal fire power plants.

Question 19

What is peak load?

Answer 19

Peak load is the time of high demand. These peaking demands are often for only shorter durations. In mathematical terms, peak demand could be understood as the difference between the base demand and the highest demand.

Question 20

What is load (e.g. base load and peak load)?

Answer 20

Load, in electrical engineering, is the amount of current being drawn by all the components (appliances, motors, machines, etc.).

Load is further categorised as base load and peak load depending upon the nature of the electrical components connected. As you may be familiar, all electrical appliances at your home do not run at all times.

A toaster or microwave oven may be used for a few minutes,
A television or computer may be used for a few hours
Lighting in the house is only required during the evening and so on.
There are several appliances which keep running at all the times, no matter what. The refrigerator, for example, has to be plugged in at all the times. Another such example are the heating, ventilation and cooling systems in the house (HVAC system).

Question 21

What is GWe?

Answer 21

Gigawatt electrical, abbreviated GWe

Question 22

4. a. Define Kaya identity (equation).

3 pt

Answer 22

The Kaya equation is an equation relating factors that determine the level of human
impact on the environment or climate, in the form of emissions such as the greenhouse gas carbon dioxide. In the case of climate impact, it decomposes GHG emissions into the
product of four drivers: population, GDP per capita, activity level per capita, and
emission factors (gCO2 per unit activity).
GHG = ( GHG/E) x (E/GDP) x (GDP/POP) x POP = POP x GDP x El x Cl

Alternative answer from lecture notes:
• Kaya identity is a form of decomposition
• Breaks GHG emissions into the product of several important (nonindependent)
drivers
• Simple yet important and useful framework for understanding the drivers of
changes in emissions

Equation: GHG= (Polulation) (GDP/Capita)(Energy/GDP)(GHG/Energy)

• Acvity is represented by economic ac@vity per capita
• Energy Intensity is represented by energy per unit of economic acvity
• Carbon Intensity is represented as the CO2/GHG emissions per unit of energy

Question 23

Kaya identity.

c. What are the pros and cons of using historical trends to make this type of projections? (3 pt)

Answer 23

• Strengths

• Uses empirical / historical trends
• Good for business-as-usual forecasts and short-term forecasting
• Econometric approach is a more detailed form

• Weaknesses
o Cannot predict discontinuous events
o May miss structural changes
o May discourage determining underlying drivers
o Trends can be misleading (e.g. between 2005-2010 the global economy was
significantly affected by the economic crisis. It may not happen again between
2010 and 2020).
o Overlooks physical limits that prevent trends from continuing

Question 24

what is the meaning of the saying “you cannot derive an ought from an is”

Answer 24

The role of science
• Science can make descriptive statements …
̶ ”If we burn all coal resources, global warming will exceed x°C.”
• …but not norma@ve, prescrip@ve, value-based statements.
̶ “Therefore, we should leave most of the coal in the ground.”
̶ This is the realm of politics, not science!
• David Hume (Sco€sh philosopher, 1711-1766):
“you cannot derive an ought from an is”.

Question 25

what is Climate Sensitivity?

Answer 25

a. According to the IPCC (Forth Asessment), “Climate sensitivity is a metric used to
characterise the response of the global climate system to a given forcing. It is broadly
defined as the equilibrium global mean surface temperature change (°C) following a
doubling of atmospheric CO2 concentration.
Uncertainties in future emission scenarios and various feedback such as rates of oceanic
heat uptake, clouds, changes in water vapor, ice and snow cover, and the “lapse rate” all
contribute to the uncertainty about the future rate of temperature change.

Question 26

What does BECCS imply?

Answer 26

Negative emissions with BECCS
(BioEnergy with Carbon Capture & Storage)

So basically it means having CO2 captured after the industrial process, then it will go to the atmo, then to biomass, then to industry again where the rest of CO2 (not all) processed again to be put in the geological storage.

The net effect of BECCS is “scrubbing”
the atmosphere of CO2!

Question 27

What is base load power?

Answer 27

Base load power: plants with high capital cost and low running costs, often runs on constant (max) load. Examples:
coal and nuclear.

Question 28

What is peak load power?

Answer 28

Peak load power: plants with low capital cost but high running costs. Cost-effective for (thin but high) demand peaks. Typically single cycle gas turbines fueled by oil.

Question 29

what is capacity factor?

Answer 29

The net capacity factor is the unitless ratio of an actual electrical energy output over a given period of time to the maximum possible electrical energy output over the same amount of time.[1] The capacity factor is defined for any electricity producing installation, i.e. a fuel consuming power plant or one using renewable energy, such as wind or the sun. The average capacity factor can also be defined for any class of such installations, and can be used to compare different types of electricity production.

Question 30

what is load curve?

Answer 30

In a power system, a load curve or load profile is a chart illustrating the variation in demand/electrical load over a specific time. Generation companies use this information to plan how much power they will need to generate at any given time. A load duration curve is similar to a load curve. The information is the same but is presented in a different form. These curves are useful in the selection of generator units for supplying electricity.

Question 31

what is load duration curve?

Answer 31

A load duration curve (LDC) is used in electric power generation to illustrate the relationship between generating capacity requirements and capacity utilization.
A LDC is similar to a load curve but the demand data is ordered in descending order of magnitude, rather than chronologically. The LDC curve shows the capacity utilization requirements for each increment of load. The height of each slice is a measure of capacity, and the width of each slice is a measure of the utilization rate or capacity factor. The product of the two is a measure of electrical energy (e.g. kilowatthours).
A price duration curve shows the proportion of time for which the price exceeded a certain value.
Together, the price duration curve and load duration curve enable the analyst to understand the behaviour of the electricity market, for example, the likelihood of peaking power plant being required for service, and the impact that this might have on price.

Question 32

what is rebound effect? What is direct and indirect?

Answer 32

the rebound effect (or take-back effect, RE) is the reduction in expected gains from new technologies that increase the efficiency of resource use, because of behavioral or other systemic responses. These responses usually tend to offset the beneficial effects of the new technology or other measures taken.
The rebound effect has two components. The first is direct rebound. This is the percentage of energy savings from efficiency that are offset by increased use. Efficiency makes an energy-consuming technology less expensive to use, so people use it more often.

Direct rebound is acknowledged by a wide range of energy economists. It is generally small in developed countries, so a 10% improvement in efficiency might provide “only” a 9% reduction in energy use.

The other component is indirect rebound. This results from how you spend the money you save.

Let’s assume your new car cuts fuel consumption by 50% and you drive 6% more. You buy 53% as much gasoline as before. You spend some of those savings on other goods and services, which require energy to produce.

But if you save $100 on gasoline costs, whatever else you buy with that $100 is not 100% energy; that expenditure also covers labor, materials, and capital. The energy share of your re-spending is typically on the order of 10%.

We can save money through cutting waste and use that money to meet other needs or desires? What’s not to like?

I’ll reiterate two points from before: 1) indirect rebound from energy efficiency is responsible for much or most of the economic growth over the past 200 years, and 2) we can use some of the economic gains to invest in clean energy resources.

Question 33

what is levelized cost of electricity?

Answer 33

The levelized cost of electricity (LCOE) is a measure of a power source which attempts to compare different methods of electricity generation on a consistent basis. It is an economic assessment of the average total cost to build and operate a power-generating asset over its lifetime divided by the total energy output of the asset over that lifetime. The LCOE can also be regarded as the average minimum cost at which electricity must be sold in order to break-even over the lifetime of the project.

ADD FORMULA

Question 34

7. Most nuclear reactors in the world today are light water reactors. However, some countries have chosen to operate heavy water reactors based on the Canadian CANDU reactor design, which uses
deuterium oxide (heavy water) as a moderator. The main advantage of heavy water reactors is that natural uranium can be used as a fuel instead of enriched uranium.

a. Why is it not possible to run light water reactors directly on natural uranium? (1p)

Answer 34

7a. Light water absorbs too many neutrons, so with natural uranium the chain reaction cannot occur. Enriching uranium makes it more likely for neutrons to find an U-235 atom and cause a fission.

Question 35

Give brief answers to the following questions on basic concepts.
a. Explain the difference between a 2°C climate sensitivity and a 2°C climate target! (1p)

Answer 35

1a. A 2°C climate sensitivity means that average surface temperature increases with 2°C for a doubling of
the concentration of CO2 in the atmosphere. A 2°C climate target is a target of not increasing surface
temperature with more than 2°C compared to pre-industrial temperature.

Question 36

1. Give brief answers to the following questions on basic concepts.
   b. In the future we may need to achieve negative emissions to reach low climate targets. Give at least two examples of how CO2 can be removed from the atmosphere! (1p)

Answer 36

1b. Examples:
 Bioenergy with Carbon capture and storage (BECCS)
 Biochar (charcoal from biomass to increase soil carbon)
 Reforestation/afforestation (only a net sink while forests grow, then CO2 neutral)
 Direct air capture (chemically scrubbing CO2 from the air)
 Enhanced weathering (powdered minerals that absorb CO2)
 Iron fertilization (to stimulate ocean plankton growth)
 Ocean liming (dump lime in oceans to neutralize acidity)

Question 37

1. Give brief answers to the following questions on basic concepts.
   c. What are feed-in tariffs and how do they work? (1p)

Answer 37

1c. Feed-in tariffs provide a long-term contract for the electricity price when renewable power is sold to the grid. It is a technology-specific support, so every renewable energy source has its own tariff. The cost of the scheme is distributed among all electricity consumers.

Question 38

1. Give brief answers to the following questions on basic concepts.
   d. What is meant by “carbon leakage”? Within the EU Emissions Trading System emission permits are allocated for free to companies sensitive to carbon leakage while the power sector has to buy auctioned emission permits. Explain why! (2p)

Answer 38

1d. Carbon leakage is the situation that may occur if, for reasons of costs related to climate policies, business were to transfer production to other countries which have laxer constraints on greenhouse gas emissions. Within the EU ETS, emission permits are allocated for free to companies sensitive to carbon leakage in order to reduce global emissions and to benefit European industry. The power sector has to buy auctioned emission permits since they normally need to be located closer to the consumer and therefore have less
opportunity to transfer production to other countries. It is also easier for the power sector to transmit the cost of emission rights to the consumer without a large drop in demand.

Question 39

2. Marginal electricity is a useful concept for determining the environmental impact of a change in the electricity system. In the course we have discussed instantaneous, annual and structural (or strategic, or long-term) marginal electricity production.
   a. Give examples (along with a brief motivation) of what technologies are typically “on the
   margin” for all three main types of marginal electricity, for a system which has access to large
   amounts of hydro power. (1.5p)
   b. Answer the same question for a thermal electricity system (i.e. a system that has large
   amounts of coal and/or gas power, but very little hydro power). (1.5p)
   c. What principle determines what is on the instantaneous margin in a thermal system? (1p)

Answer 39

2a. System with large amounts of hydro power
Instantaneous margin – hydro because it can react fast and is cheap.
Annual margin – since hydro is cheap, it is used up on annual bases and the increase will come from something that is higher in the merit order, most likely coal
Structural margin – can be anything depending on available resources and policies

2b. Thermal system with very little hydro power
Instantaneous margin – hydro will likely not be available, so depending on demand level it will be either coal or gas.
Annual margin – sum of the instantaneous margins so a mix of coal and gas.
Structural margin – can be anything depending on available resources and policies.

2c. Merit order curve + demand + flexibility of the source.

Question 40

4. The Montreal Protocol from 1987 regulating ozone depleting substances is widely regarded as an
   environmental “success story”. Atmospheric concentrations of most CFCs and related gases have
   peaked or even declined significantly, and the ozone layer is expected to recover around 2050-
5. Discuss why the climate change problem is expected to be much more difficult! (3p)

Answer 40

3a. Base load technologies have high investment costs and low variable costs, so that they are operated very early in the merit order. They therefore tend to have high capacity factors. Historically they have been
operated constantly at near maximum capacity for most of the year, but this is expected to change in the
future as intermittent sources grow. Some base load technologies like nuclear are relatively inflexible and
cannot change output levels quickly and cheaply, but this does not matter when they operate at constant
capacity.
Peak load technologies have very low investment costs but usually high running costs. Their purpose is to
provide cheap capacity when electricity demand is very high (not many hours per year), so the high variable
costs are not important. These are the technologies that are operated last in the merit order.
Solar PV (and wind power) have the same economic characteristics as traditional base load technologies.
Near-zero variable costs mean that they are used first in the merit order, even before other base load such
as nuclear or cheap coal power. The intermittency of the solar/wind resources means that they cannot run at
near maximum capacity like traditional baseload, but this is of secondary importance compared to the
economic properties.
In the chart, solar and wind appear above the other technologies. This does not mean that they are peak load
technologies! This is just for graphical reasons – it is easier to read a stacked chart if the elements with the
most variation are at the top.
However, solar PV does have one property that resembles peak load. The maximum output of solar is at
midday and correlates very well with the typical daily variations of electricity demand. This means that solar
PV can reduce the need for traditional peak load, but nevertheless it is itself more like a base load
technology.