EE6623 Sustainable Energy Systems
The Complete Exam Bible · Semester A, 2026/27EE6623 Overview
- City University of Hong Kong
- Semester A, 2026/27
- 3 credit units
- Postgraduate
- Two-hour examination
What this course connects
Sustainable energy is treated as a complete system rather than as a list of technologies. The first two units establish how wind and sunlight become electrical power, including the environmental variables and operating limits that make output move.
- Assessment Two quizzes, one assignment and a sixty per cent examination.
- Pass rule Meet the separate continuous-assessment and examination minimums.
- Core method Label the physical boundary before selecting a formula.
- Revision focus Practise original calculations across resource, conversion, storage and grid stages.
How EE6623 is assessed
| Component | Weight | Format |
|---|---|---|
| Quiz 1 | 15% | Continuous assessment; current date shown as 8 October 2026 and marked to be confirmed |
| Quiz 2 | 15% | Continuous assessment; current date shown as 19 November 2026 and marked to be confirmed |
| Assignment | 10% | Continuous assessment task; current details are controlled on Canvas |
| Examination | 60% | Two-hour examination |
The current course-information document gives quizzes at 30%, split equally between Quiz 1 and Quiz 2, assignment at 10%, and examination at 60%. The official catalogue confirms continuous assessment at 40%, examination at 60%, a two-hour duration, and separate 30% minimum requirements in coursework and the examination. Quiz dates printed in the course information are marked to be confirmed, so use the live Canvas settings for operational details.
Assessment structure
Segment widths reproduce the published weights and total 100%.
Current EE6623 dates
| Date | Item | Control |
|---|---|---|
| 8 October 2026 | Quiz 1 | Printed in the current course information and marked to be confirmed. |
| 19 November 2026 | Quiz 2 | Printed in the current course information and marked to be confirmed. |
Dates are as published in the captured course-information document for the Semester A, 2026/27 offering. Confirm exact deadlines and submission settings in the live LMS.
What EE6623 covers
Ten chapters follow the five published units from wind and photovoltaics through storage and smart grids to carbon policy and Hong Kong's transition.
Wind Resource and Available Power
air density, swept area, the cube law, hub-height correction and energy conversionStart with the air stream
Available wind power is a resource calculation before it is a turbine calculation. Air crossing the rotor plane has mass because density multiplies the swept volume, and it has kinetic energy because that mass moves.
- Mass flow through swept area
- The wind-speed cube law
- Air density, temperature and pressure
- Hub-height power-law correction
- Available, captured and electrical power
- Energy from power and time
Wind Turbines and Generator Control
power-curve regions, tip-speed ratio, generator topologies, slip and reactive powerControl changes across the power curve
A wind turbine faces different objectives at different speeds. Below cut-in, useful generation is unavailable.
- Betz efficiency and practical coefficients
- Tip-speed ratio and rotor speed
- Cut-in, rated and cut-out regions
- Pitch and power limiting
- Synchronous and induction machines
- Doubly-fed slip power
Solar Geometry and Irradiance
sun paths, altitude, azimuth, collector incidence, beam, diffuse and reflected radiationGeometry comes before output
Solar irradiance on a collector depends on where the sun is and how the surface is oriented. Latitude fixes the site, declination moves seasonally, and hour angle follows the sun around solar noon.
- Solar spectrum and radiation basis
- Latitude, declination and hour angle
- Altitude, azimuth and zenith
- Sun-path diagrams
- Collector tilt and incidence
- Beam projection
PV Cells, Modules and MPPT
semiconductor conversion, equivalent circuits, series-parallel arrays, shading and maximum powerRead the operating curve
A photovoltaic device converts absorbed photons into mobile charge carriers that the junction separates.
- Photon energy and band gap
- Photovoltaic junction operation
- The single-diode equivalent circuit
- Series and parallel resistance
- I-V and P-V curves
- Module and array wiring
Renewable Variability and Storage Options
solar ramps, wind variability, storage duration, conversion paths and technology choiceStart from the service
Solar and wind variability appear on different timescales. A clear solar day can produce a smooth rise and fall, while cloud edges cause fast ramps. Wind can vary from minute to minute and also show daily or seasonal patterns.
- Solar ramps and daily profiles
- Wind variability and seasonality
- Power versus energy requirements
- Pumped hydro and compressed air
- Electrochemical storage
- Flywheels and supercapacitors
Battery Management and System Sizing
cell balancing, state of charge, state of health, equivalent models and cumulative energyIntegrate a signed power balance
Battery sizing begins with power at each interval. Choose a sign convention, calculate generation minus load or the reverse, and keep the sign consistent.
- Signed battery power
- Interval energy and cumulative balance
- Peak-to-peak sizing
- Initial state of energy
- Passive and active balancing
- Battery-management functions
Renewable Grid Integration
frequency, voltage, power quality, congestion, demand response and reactive supportDiagnose the constrained variable
Renewable integration is a group of problems rather than one problem. Variable active power can disturb supply-demand balance and frequency.
- Variability and active-power balance
- Inertia and frequency response
- Voltage and reactive power
- Power quality and distortion
- Transmission capacity and congestion
- Forecasting and reserves
Smart Grid Monitoring and Power Control
phasor measurements, SCADA, feedback latency, FACTS, HVDC, automation and ICTClose the information and power loop
A smart grid monitors, protects and optimises interconnected assets through a feedback chain.
- Smart-grid aims and motivation
- PMU and synchronised measurement
- SCADA supervision
- State estimation and latency
- Fault detection and restoration
- FACTS and STATCOM
Paris Agreement and Carbon Markets
national contributions, allowances, credits, mitigation transfers and double-counting controlKeep target, market and accounting distinct
The Paris Agreement combines a shared temperature direction with nationally determined contributions.
- Paris temperature and adaptation aims
- Nationally determined contributions
- Transparency and reporting
- Caps and allowances
- Project credits and baselines
- International mitigation transfers
Hong Kong Energy Transition
coal phase-out, renewable and zero-carbon shares, buildings, transport, waste and hydrogenRead milestones as a connected system
Hong Kong's Climate Action Plan 2050 sets carbon neutrality as the destination and organises action across electricity, buildings, transport and waste.
- Carbon neutrality by 2050
- Coal phase-out for daily generation
- Renewable energy share bands
- Zero-carbon energy imports
- Energy saving and green buildings
- Green transport and charging
The storage unit then asks how variable supply can be reshaped across time. Grid integration and smart-grid material ask whether the power can be balanced, transmitted, monitored and controlled. The final unit places those engineering choices inside international carbon policy, trading rules and Hong Kong's transition plan.
What makes the calculations difficult
Most errors begin at a boundary.
Wind power may refer to energy in the air stream, power captured by the rotor, shaft power, generator output or grid delivery. Solar data may be measured normal to the beam, on a horizontal surface or on a tilted collector. Battery power is a rate while battery energy is an accumulated balance.
A converter can exchange active and reactive power inside one rating, and a carbon unit can represent a physical outcome or the right to claim it. The guide keeps those nouns beside every result.
How the examination preparation works
The official catalogue publishes a two-hour examination and the course information gives it sixty per cent of the final grade.
It also states separate minimum passing requirements for continuous assessment and the examination. This guide therefore trains a repeatable method instead of guessing a paper layout: sketch the system, label the requested boundary, state the relationship, substitute with units, calculate, and finish with a direction or operating-limit check.
The integrated practice uses original questions shaped by the calculation types in the units and tutorials.
The course sequence
Wind chapters cover the cube law, density, swept area, power-curve regions, tip-speed ratio and generator control. Solar chapters move through sun position, collector irradiance, cell behaviour, series-parallel arrays and maximum-power-point tracking.
Storage chapters distinguish power from energy, compare conversion paths, build a cumulative-energy ledger and separate state of charge from state of health. Grid chapters diagnose frequency, voltage, congestion, reactive support, monitoring, latency and actuation. Policy chapters reconcile allowance and credit ledgers, prevent double counting and connect official transition milestones to infrastructure.
Worked example · free
Size a battery from a signed power schedule
- 2Take the largest power magnitude for the converter rating.
- 4Multiply by three hours and build the cumulative energy trace.
- 4Use the peak-to-peak swing and shift the minimum to zero.
Key terms
- Available Wind Power
- The kinetic power crossing a rotor's swept area before aerodynamic or electrical conversion losses.
- Tip-speed Ratio
- Blade-tip speed divided by wind speed, used to locate an efficient rotor operating condition.
- Solar Altitude
- The angular height of the sun above the horizon at a stated place and time.
- Maximum Power Point
- The voltage-current operating pair at which a photovoltaic device produces its greatest power under the current conditions.
- State of Charge
- Present stored charge or energy expressed relative to the battery's current usable capacity.
- State of Health
- Current battery capability expressed relative to a defined reference capability, often the initial condition.
- Demand Response
- A controlled change in electricity consumption that helps match demand to system conditions or variable supply.
- Reactive Power
- The alternating-power component used to support electric and magnetic fields and influence voltage.
- Phasor Measurement Unit
- A device that supplies time-synchronised electrical measurements for comparing conditions across the grid.
- Nationally Determined Contribution
- A country's stated climate action plan under the Paris Agreement, updated within the international framework.
- Carbon Allowance
- A unit authorising a defined amount of emissions inside a capped trading system.
- Double Counting
- The error in which one physical mitigation outcome supports more than one emissions or target claim.
EE6623 FAQ
How is the course assessed?
The current course information assigns fifteen per cent to each of two quizzes, ten per cent to an assignment and sixty per cent to the examination. The official catalogue confirms the forty-sixty split between continuous assessment and examination. Read the current Canvas entries for submission and quiz settings because the printed quiz dates are marked to be confirmed.
What must I achieve to pass?
The published materials set separate minimum requirements of thirty per cent in continuous assessment and thirty per cent in the examination. Treat them as independent constraints. A strong result in one domain does not erase the minimum in the other, so protect both coursework completion and examination preparation.
How long is the examination?
The official catalogue publishes a duration of two hours. Use the live course page for current instructions about the paper structure, question directions and permitted materials. This guide trains the calculation and systems methods supported by the course units without inventing an examination format.
What is the most important habit in wind and solar calculations?
Label the physical boundary before choosing an equation. For wind, distinguish air-stream, shaft and electrical power. For solar, identify whether irradiance is normal, horizontal or on the collector plane, then keep cell, module, string, array and AC output levels separate.
How should I size an energy-storage system?
Calculate signed battery power at each interval, take the largest magnitude for converter power, integrate interval energy in time, and use the peak-to-peak cumulative swing for ideal energy capacity. Apply efficiency, operating-window, reserve and ageing assumptions afterwards, each at its proper boundary.
What makes renewable grid integration difficult?
Variability can create active-power imbalance, voltage movement, power-quality concerns or congestion depending on location and timescale. Diagnose the measured variable and constrained element first. Forecasts, storage, reactive support, demand response and transmission each reach different parts of that problem.
How do carbon markets avoid counting one reduction twice?
A registry records issuance, ownership, transfer and use, while authorised international transfers require corresponding treatment in the participating accounts. The host cannot retain a national claim over the same transferred outcome used by the buyer. Baseline quality and additionality remain separate integrity tests.
Which Hong Kong transition targets appear in the course?
The course material presents carbon neutrality by 2050, renewable energy at 7.5 to 10 per cent of the fuel mix by 2035 and 15 per cent thereafter, and zero-carbon energy at 60 to 70 per cent by 2035. It also covers coal phase-out, efficiency, transport, waste and hydrogen trials.
Questions students ask in each EE6623 chapter
- Why is wind speed cubed in the power equation?
- Mass crossing the rotor each second already grows linearly with wind speed, while kinetic energy per unit mass grows with speed squared. Multiplying those effects produces a cube. That is why a modest speed change can dominate a larger linear change in density. Chapter 01 · Wind Resource and Available Power
- Why does turbine output stop following the cube law?
- The cube law describes available power in the undisturbed wind. Once equipment reaches rated output, control deliberately reduces aerodynamic capture to protect the generator and converter. At still higher wind speed, shutdown protection can drive output to zero even while the resource keeps rising. Chapter 02 · Wind Turbines and Generator Control
- Why can clock noon differ from solar noon?
- Solar noon is the moment the sun crosses the local meridian and hour angle is zero. Clock time also reflects the time-zone reference longitude and other corrections. Use the time basis supplied by the problem rather than assuming twelve o'clock is exact solar noon. Chapter 03 · Solar Geometry and Irradiance
- How does irradiance move the photovoltaic curve?
- Higher irradiance mainly raises current, so short-circuit current and maximum power increase strongly while open-circuit voltage changes more modestly. Temperature has a different effect and commonly reduces voltage as the cell becomes hotter, so keep the two influences separate. Chapter 04 · PV Cells, Modules and MPPT
- Why are megawatts and megawatt-hours both needed?
- Megawatts state how quickly a device can charge or discharge, while megawatt-hours state how long it can sustain that exchange. A short cloud ramp can need high power and little energy, whereas evening shifting can need moderate power and substantial energy. Chapter 05 · Renewable Variability and Storage Options
- Why is daily net energy not enough for sizing?
- Net energy can be zero while the battery still needs a large operating window. The cumulative path depends on interval order: an early deficit requires initial stored energy, while a later surplus needs charge headroom. Peak-to-peak cumulative energy captures that path. Chapter 06 · Battery Management and System Sizing
- How are frequency and voltage problems different?
- Frequency is closely tied to active-power balance across an interconnected system, while voltage is strongly influenced by local network conditions and reactive power. The same converter may assist both, but the control command, location and available rating differ. Chapter 07 · Renewable Grid Integration
- What makes an electricity network a smart grid?
- The defining feature is a closed operational loop linking measurement, communication, estimation, decision and physical action. A collection of digital meters without controllable assets or verified response adds visibility but does not by itself optimise or restore the network. Chapter 08 · Smart Grid Monitoring and Power Control
- How does cap and trade reduce compliance cost?
- A fixed cap creates scarce allowances, while trading lets firms compare internal marginal abatement cost with the allowance price. Firms with cheaper reductions can reduce more and sell surplus, while higher-cost firms buy. Monitoring and surrender still have to keep total emissions inside the cap. Chapter 09 · Paris Agreement and Carbon Markets
- What 2035 electricity targets are taught?
- The course material states renewable energy at 7.5 to 10 per cent of the fuel mix by 2035 and 15 per cent thereafter. It also states zero-carbon energy at sixty to seventy per cent by 2035, supported by stronger cooperation and imported electricity. Chapter 10 · Hong Kong Energy Transition
How to study for the exam
Begin with one systems sheet divided into resource, converter, storage, grid and policy columns. After each lecture, add only the equations and distinctions that cross a boundary, with units and one limiting condition. Work the tutorial type once with notes and once without them. For wind and solar, redraw the curve or geometry before calculating.
For battery problems, build the signed interval ledger even when the arithmetic looks simple. For grid questions, place every device relative to the constrained line or bus. For carbon questions, draw the ownership ledger separately from the physical reduction. In the final revision week, alternate one numerical problem with one explanation problem so the symbols remain attached to meaning.
Check every final number by direction, order of magnitude and unit. Use the published two-hour duration for a timed rehearsal only after the live course instructions provide the current paper structure. Protect both assessment domains because the course publishes separate minimum requirements for continuous assessment and the examination.
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