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1)Write brief notes on ways to de-carbonise the electricity system of Great Britain
- Energy demand reduction and more efficient use of electrical energy is an essential element of any strategy to de-carbonise the GB electricity system.
- It is hoped that Smart Meters will assist in this by giving customers better information about their electricity use.
- The only ways we have to generate electrical energy without emitting CO2 are through:
- Fossil generation with CCS
List the main options that are available for decarbonisation and comment on their advantages and disadvantages
- Advantages: Very high power units available (e.g. 1600 MW)
- Disadvantages: Disposal of waste remains unresolved
- Advantages: Now well established, particularly onshore and offshore wind energy
- Disadvantages: Output is intermittent and difficult to predict
- Fossil generation with CCS
- Advantages: Can be used with either gas or coal as the fuel
- Disadvantages: Has yet to be demonstrated at commercial scale.
Why are large wind turbines operated at variable speed?
- Large wind turbines are operated at variable speed to:
- Relieve mechanical loads by allowing the rotor to change speed in turbulent winds
- Maintain operation at the peak of the Cp/λ curve over a wide range of wind speeds
Adv and disadv of offshore wind turbines
The advantages of locating very large wind turbines offshore are:
- Reduced visual impact
- Higher mean wind speeds
- Lower turbulence
- The disadvantages are
- Increased cost of construction and O&M
- Cost of transmission to shore
Impulse turbines operate by extracting the kinetic energy from a jet of water. The jet is atatmospheric pressure. Types include: Pelton, Turgo and Cross flow. Generally impulseturbines are used for high heads or small units
Reaction turbines operate by chaging the direction of the water flow. The water arrivingat the runner is still under pressure and the pressure drop across the turbine accounts for asignificant part of the energy extracted. Types include: Francis and propeller types(Kaplan)
The Environmental impacts of coal fired power stations
The Environmental impacts of coal fired power stations can be split into 3.
Local effects are due to particulate emissions
These are controlled using filters and electrostatic precipitators to remove the particles from the stack gases. The particles are then either placed into land fill or used for building material. In the US there isalso concern over the increase in water temperatures from once through cooling.
The key regional effects are due to SOx and NOx. SO2 causes acid rain that has led to considerable environmental damage while the production of NOx has significant health consequences. SO2 emissions are reduced by burning low sulphur coal or byfitting Flue Gas Desulpurisation equipment. The EU Large Conbustion Plant Directive effectively bans the use of coal other than in plants with FGD.
The Global effect is the creation of Green House Gases (particularly CO2) that lead to global warming. Burning of any fossil fuel leads to the emissions of CO2 but particularly coal because of its high Carbon content.
Environmental impact of coal fired generators
- Coal fired generators produce a range of environmental impacts including:
- CO2 emissions leading to Climate Change (approx 1000 tonnes/GWh)
- SOx and NOx emissions leading to Acid Rain (approx 3 tonnes/GWh)
- Particulate emissions causing damage to human health
Main environmental impacts of wind farms
- The main environmental impacts of wind farms are:
- Visual intrusion
- Shadow flicker
- Impact on flora and fauna (particularly birds)
Main environmental impacts of the Severn Barrage
- The main environmental impacts of the Severn Barrage are likely to be:
- Impact on sediment transport
- Impact on wading birds
- Positive impact on yachting/recreation
Smart Meters for both electricity and gas (26 million each) are being introduced in GB from 2014 with completion of the roll out by 2020. They will provide regular and accurate measurement of energy consumption (granularity of measurements at least every30 minutes). The readings will be made available to the energy suppliers at least every 30 days.The electricity meters will have a remote read-out, e.g. for location in the kitchen, to show real-time energy consumption.The main benefit anticipated is a reduction in electrical energy demand and peakelectrical power use of around 5%. However care is necessary to recognise the likely reduction in these benefits over time (Rebound effect) and the need for constant intervention by the energy suppliers.It is also anticipated that there would be a reduction in meter management costs. At present there is no anticipation of integrating Smart Meters into power system operational though this has obvious potential.
P-V equivalent circuit
The simple equivalent circuit is a current source proportional to irradiance in parallel witha forward biased diode representing the p-n junction
Technologies the UK might use to “decarbonise the electric power sector by 2030” as proposed by the Climate Change Committee.
The technologies that are proposed for the de-carbonised energy system are:
- • Renewables
- Up to 2020, the dominant technology is likely to be wind energy, both onshore and offshore. After 2020 tidal stream and wave power will begin to make significant contribution.
- • Nuclear
- The present intention is to replace the AGR (Advanced gas-cooled reactor) fleet that is coming to the end of its life but, depending on how the electrical load grows as we move to a decarbonised energy system there will be a requirement for further nuclear plants. The technology is likely to be PWR.
- • Fossil with CCS.
- CCS may either be pre or post combustion. Post-combustion involves extracting the CO2 from the flue gases (likely for coal-fired steam plants).Pre-combustion involves creating hydrogen from the fuel and extracting andstoring the CO2 (more likely for gas turbines.
It is also important to recognise the importance of the Demand Side. Integration of Electricity Demand into the operation of the power system is likely to be necessary to operate a power system consisting of intermittent renewables and constant output generation.
Smart Metering and how it can contribute to reducing Green House Gas emissions
Smart Metering consists of electronic metering (both electricity and gas) with bidirectional communications to the Energy Supplier (in GB).Metering informationis passed to the Supplier (AMR) while control information (and tariffs) iscommunicated to the meter.Smart Metering can contribute to GHG emission reductions by:• Improving the efficiency with which the energy system is operated (Gasand Electricity). Smart Metering will bring much greater visibility to the lowvoltage system (at present there are very few measurements made there.
- • Stimulating customer behaviour modification and hence energy demand reduction. It is thought that providing better information to customers willencourage them to reduce their energy demand. Evidence from trials suggests an energy reduction of up to 10% are possible but with a“rebound” effect.
- • Increasing flexibility of the power system and enabling integration of renewables and constant output generating plant (Nuclear and CCS). It is necessary to balance supply and demand on a second-by-second basis and this can only be done in a de-carbonised power system by involving the demand side.
- Nuclear and CCS generation will be operated at a constant output and renewable energy will fluctuate.