Change in supply side: Moving towards low/zero carbon energy supply.

Change in demand side: Reducing demand for high-carbon energy.

Removing or offsetting remaining emissions.

Energy Security

Energy Equity

Energy Sustainability

z₀ for cities and forests? 0.7m

z₀ for suburbs and wooded countryside? 0.3m

Roughness length in villages and countryside with trees and hedges?

What about flat grassy plains?

0.1m

0.01m

Roughness length in open farmland?

What about flat deserts or rough seas?

0.03m

0.001m

1) Flow is steady-state

2) Flow is incompressible

3) Friction can be neglected

Can't be assumed:

4) Energy is balanced - no energy is being injected or extracted from the fluid

- Stall has no moving parts, pitch regulation requires a control system and actuators to rotate the blades which are mounted on the hub with bearings.

- Gives smooth power control, whilst pitch can result in large power transients due to dynamic behaviour of wind flow.

- Cheaper

- Gives maximum power extraction, whilst stall can be difficult to predict along the blade.

- Additional braking techniques are required in stall regulation, whist pitch alterations can be used for pitch regulation.

- At high speeds, high wind speeds induce large thrust forces on the rotor in stall regulation. In pitch regulation, pitching can reduce the forces.

- Needs to convert rotational mechanical power to electrical power

- Connect to the national grid

Not essential but beneficial:

- Control turbine speed to enable maximum power point tracking

- Allow control of power factor/reactive power

- Ride through a fault on the electricity network

- Provide services (e.g. frequency response) to the electricitynetwork

1) DC Machine

2) Induction (Asynchronous) Machine

3) Synchronous Machine

DC Machine - Proportional to voltage

Induction (Asynchronous) Machine - Proportional to frequency with slip

Synchronous Machine - Proportional to frequency

- Induction machines are mechanically simple, robust and widely used.

- They generally have no connection to the "squirrel cage" rotor.

- As the name would suggest, they are inductive – they consume reactive power (lagging power factor).

What happens in induction machines if slip is negative? What about positive?

• Rotor has its own excitation

• Rotor follows stator magnetic field

• Rotor and stator must be going at the

same speed (dictated by the grid)

- A magnetic field is generated by the stator

- The rotor has its own magnetic field, which wants to align with the stator field

- The AC current across the causes the stator field to rotate.

- The alignment causes the rotor to rotate at the same speed

- Load angle

- Load angle is the angular displacement between the rotor's magnetic field and the stator's induced magnetic field

- Doubly-fed induction generator is a more complex design with power electronics. 

- This design allows for some reactive power control. 

- Unlike a standard IG, DFIG allows speed variability (about 30%).

- Standard IG only used in early turbines, DFIG are now widely used in onshore turbines.

What are the advantages of using a synchronous machine with a fully rated converter?

Where are they used?

- Full control of reactive power and speed

- No gearbox needed (direct drive).

- Design is simple (although large power electronics requirements).

- Used widely in large offshore wind turbines.

- Rotational speed of the rotor in synchronous machines is equal to the synchronous speed of the rotational magnetic field.

- In asynchronous machines, the two are different (defined by slip).

- Shape of the coastline and seabed (greater when closer to the shore).

- Gravitational and centrifugal force of the moon (lunar tides).

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- Solar tides (added in spring, subtracted for neap tides).

- Lunar tide is 1 per unit.

- Solar effect is 0.464 per unit, therefore spring tide is 1.464 per unit and neap is 0.536.

- High/low tides occur every 12 hours and 25 minutes (as in switches every 6 hours approx).

Extraction of gravitational potential energy from the water. Lagoons and barrages create a height difference between high and low tides. 

There is some storage, but if the energy is generated too far from low tide, some energy will be

wasted

Where is wave energy most abundant?

What is a challenge for wave energy conversion?

Far from shore.

Waves vary in height, length, and frequency, which makes technology design challenging.

Large - greater than 10MW

Small - 10MW or less

Mini - 100kW to 1MW

Micro - 10kW to 100kW

World's largest Hydroelectric Dam?

Capacity?

Three Gorges Dam, Hubei.

22.5GW

632km² of land flooded.

Triggering landslides

May have been tied to major earthquakes

 Affecting biodiversity and fragmentation of habitats.

Decrease in freshwater flow downstream.

- Head 'H' (the difference in height between where the water enters and leaves).

- Flow 'Q' (the volume of water crossing the turbine).

- Crossflow

- Turgo

- Pelton Wheel

-Water potential energy converted to kinetic energy at a nozzle or spout.

- Uses velocity of water to move the turbine runner.

- Discharges to atmospheric pressure.

- Water stream hits each bucket on the runner

- Suitable for high head, low flow

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- Francis Turbine

- Kaplan Turbine

- Archimedes Screw

- Water potential energy converted to pressure energy

- Uses the pressure drop across the turbine/runner.

- Suitable for wide range of head and flow conditions.

Deciding suitable hydroelectric turbine to use.

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What is N_S in this equation?

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- Storability

- Uncertainty

- Land use

- End of life management

When cells are interconnected, a shaded cell will act as a resistor, and limit the output voltage of the string.

Bypass diodes can reduce the shading effect.

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By changing the value of the resistor, the operating point changes. The power changes for the same irradiation.

The same can be achieved through the power converter used to interface the PV with the grid.

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As the output power can be variable, grid interface should be able not only to serve as a suitable conversion stage but also extract maximum power. This increases efficiency and thus profits.

DC/AC power converter needed.

1) Capture max. power from the PV

2) Increase the voltage levels (voltage boosting).

3) Synchronise with the grid delivering the power (active/reactive power control).

Investment planning - planning horizon is more than 1 year

Maintenance planning - planning horizon less than 1 year

Operational planning - planning horizon less than 1 week

- Generation technologies

- Transmission technologies

- Distribution technologies

Power flow limitations - for all planning horizons:

- Kirchoff's circuit law

- Kirchoff's voltage law

Capacity of units and lines - all planning horizons.

Operational limits of thermal units - usually short-term:

- Ramp-up and ramp-down

Time Limits:

- Construction time

-Maintenance time

- Minimum up-time and down-time of thermal units

Reliability, resiliency, and flexibility limits – super critical

Financial constraints

Continuous variables:

- Active/reactive power of units

- Active/reactive flow of lines

- Voltage/current

Discrete variables:

 - Investment status of components: 0 (not-built) or 1 (built)

- Maintenance status of components: 0 (unavailable) or 1 (available)

- Operation status of components: 0 (off) or 1 (on)

275kV or 400kV.

132kV

- Two-way real-time connection (as opposed to none/one-way, not real-time)

- Active customer interaction (rather than passive).

- Digital metering allows for real-time pricing and metering.

- Generation can be both centralised and decentralised

- Power flow control is fully automated (rather than partially)

- Rather than radial (one-way) power flow, it is meshed (bi-directional).

National Grid Energy Transmission

They are responsible for:

- Maintaining network assets

- Upgrading existing assets

- Providing new connections

- Developing interconnectors

National Energy System Operator

Often summarised as 'keeping the lights on'.

Need to balance supply and demand.

The entity responsible for managing and planning the UK's electricity and gas networks.

Owned and operated by 'DNOs'. Distribution Network Operators.

Ones with most customers:
UK Power Networks (8.3 million)

Western Power Networks (7.9 million)

Energy Recommendation P2/7

DNOs are obligated to design networks based on it.

It defines:

- The time allowed to restore customers after a fault depending on the capacity of customers connected (group demand)

- Options for redundancy and reconfiguration

- Buy energy from the wholesale market and arrange for it to be delivered to the end consumer. 

Offered by all suppliers, however consumer needs a smart meter or dedicated Economy 7 meter to get them.

Consumer is charged different rates for peak (higher price) and off-peak (lower price) electricity use.

Active: W, kW, MW

Reactive: VAr, kVAr, MVAr

Apparent: VA, kVA, MVA

- Low-Voltage connections 230V+10/-6%

- Medium-Voltage connections (11kV) ±6%

- High-Voltage connections (33kV) ±10%

- It can lead to a rise in voltage.

- In the winter this generally isn't an issue, but in summer it can lead to voltage outside of the tolerance band.

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On-Load (OLTC)

De-energised (DETC)

The turns-ratio is altered

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All assets that power travels through must be rated to carry the continuous current and withstand fault current for a short duration.

Equipment ratings must be observed and seasonal ratings are often applied. Environmental conditions will have an impact. Thermal timescales are relatively long (short term overload is permissible).

What is a direct impact on energy frequency in the grid?

It is a physical outcome of the difference between supply and demand.

If demand is greater than generation, frequency decreases. If generation is greater than demand, frequency increases.

What is the main source of system inertia for the power grid?

Impact of system inertia?

Steam generators.

The system inertia dictates sensitivity to imbalances in supply and demand.

Statuatory: 49.5-50.5 Hz

Operational: 49.8-50.2 Hz

Primary Response: Within 10s, hold for 20s.

Secondary Response: Within 30s, hold for 30mins.

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Difference between de-rated generation and underlying demand. De-rated margin of 4.8GW (8.3%). This accounts for the likelihood of availability when needed.

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- The CM provides revenue in the form of capacity payments to potential capacity providers. 

- In return, participants must commit to delivering electricity at times of system stress and face penalties if they fail to do so.

- Capacity payments are determined via competitive Auctions, held four years (T-4 Auction) and one year (T-1 Auction) before each delivery period.

Based on the needs at system peak, but demands need to be met at ALL times.

Considerations:

- Maintenance cycles

- Variability in resources

-Contingencies (such as if a generation plant is lost).

A strategy to ensure a reliable and consistent supply of electricity from intermittent renewable sources like wind and solar. This is achieved by integrating other energy resources, such as storage or dispatchable generators, to balance the variability of renewables and meet consistent demand. 

Domestic units: 5kW, 10kWh

Secondary distribution: 50kW, 100kWh

Primary Distribution: 6MW, 10MWh

Transmission: 1.8GW, 10GWh

- Monitoring of all assets (real-time)

- Ensuring all technical limitations of the network cost-effectively

- Reacting to any changes in production/consumption and the network

Adjusting the consumption (or production), 'behind-the-meter', to change the net electricity demand seen by the distribution network.

Consumers provide DSR in response to a specific incentive (reduction in costs).

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- It is less expensive to control load than to upgrade infrastructure.

- No reduction in initial energy use

- Final energy use might increase

- Process quality might decrease

- New peak might be created

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- Demand-Side Response Offered

- Reductions in fraud and theft

- Reductions in meter reading costs

- Reductions in peak demands (lower costs)

- Reduction in energy demands

• A manual response – simplest approach

• A response to a measured quantity

• A response to a direct control signal

• A response to a specific algorithm

- Identifying critical assets and their interdependencies

- Amending security in response to previous incidents

 - Backing up data and maintaining reserve systems

- Communicating risks to external stakeholders

- Preparing and testing incident response plans 

NOP - Unfilled Circle

NCP - Filled Circle

- Reductions of power losses

- Planned outages (MV or HV) 

- Unplanned outages (MV or HV)

- Excessive power flow on the MV or upstream HV feeder

- Excessive voltage drop/rise on the MV or upstream HV feeder

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What would be the effect if the NOP was shifted one to the right?

Increase in losses on the left, decrease in losses on the right. 

Unclear what the impact on overall losses would be.

Manual carried out by operators at substations, semi-auto requries a SCADA or similar system.

Manual more common in poorer countries:
- Less safe and slower

- Safety implications for people close to switches

Manual can take several hours and several people if many locations.

- Increased operation of assets may have adverse impacts on the lifetime of the asset.

- Frequent switching (especially on-load) will increase wear on components.

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Static ratings:

Rating is fixed during a season

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Dynamic ratings:

Rating is calculated in real time, based on the conditions of the conductor.

- Controllable consumption with DSR + Storage

- Controllable production with storage

- Network reconfiguration

- Real-time thermal rating

- Back-to-back converters

Enables two AC networks to pass power between them despite differences of frequency, number of phases or phase shift (circulating currents).

Can be both scaled down and scaled up.

- Smaller scale power generators can be integrated with more flexibility. 

- Can integrate at secondary distribution or even low voltage level.