Issue 3. Should we use more renewable energy as electricity source. in Hong Kong?

Transcription

1 Issue 3 Should we use more renewable energy as electricity source in Hong Kong? Objectives 1. To know the source of electricity in Hong Kong 2. To briefly understand how electricity is generated 3. To understand renewable energy and the world trend of using renewable energy for electricity generation 4. To understand how 4 types of renewable energies are used to generate electricity Outline 1. Status of Hong Kong electric companies 1.1 The Hongkong Electric Co., Ltd. (HEC) 1.2 CLP Power Hong Kong Limited (CLP Power) 2. Principle of electricity generation 3. Renewable energy and the world trend employing multiple fuels for generating electricity 4. Four types of renewable energy 4.1 Hydropower 4.2 Wind power 25

2 4.3 Solar energy 4.4 Biomass power (Biofuel) Lesson Plan Lesson Concepts/knowledge to be learnt Contents and activity Time (min) 1 Principle of electricity generation Hong Kong electricity supply World Trend in Uses of 1. Status of Hong Kong electric companies Worksheet 1:Renewable energy in Hong Kong and the World 2. Principle of electricity generation 3. World Trend in Uses of fuels for generating Power fuels for generating Power 2 Fossil fuels: advantages & disadvantages What is renewable energy? 3. World Trend in Uses of fuels for generating Power (Cont d) 3.1 Fossil fuels Worksheet 2: Collect information about renewable energy 3 Renewable energy: Types, principles, advantages and disadvantages 4 Renewable energy (Cont d) Should we use more renewable energy as Worksheet 2: Presentation on renewable energy (Cont d) 4. Four types of renewable energy 4. Four types of renewable energy (Cont d) Worksheet 3: Forum or group discussion: Should we use more renewable energy as energy source to generate electricity in Hong Kong? electricity source in Hong Kong? 26

3 Introduction There is a world trend on the use of renewable energy to supplement the fossil fuel for generating electricity. As Hong Kong is an international city, shall we adopt similarly the use of renewable energy in generating electricity? What are the advantages and disadvantages of using renewable energy? Question: What is the current status of the local electricity supply? 1. Status of Hong Kong electricity supply At present, there are two electrical companies supplying electricity to different parts of Hong Kong. 1.1 The Hongkong Electric Co., Ltd. (HEC) The HEC supplies electricity to 556,000 customers living in Hong Kong Island and Lamma Island. (HEC, 2005). All of the electricity generation was carried out at Lamma Power Station. The existing capacity of the Station is 3,420 MW (megawatt), including eight coal-fired units, five gas turbines and one combined cycle unit. Over 99% of the fuel used is coal. Oil firing is only used for start-up, shutdown or flame stabilization at low loads. In 2004, coal consumption was around 4.24 million metric tones. A 300 MW class combined cycle gas-fired unit is put into operation in 2006 and the first commercial-scale wind turbine system in Hong Kong is now being constructed at Tai Ling on Lamma Island with capacity of 800 kw (kilowatt) (HEC, 2006). 1.2 CLP Power Hong Kong Limited (CLP Power) CLP Power Hong Kong Limited (CLP Power) supplied 2.2 million families, representing 80% of Hong Kong's population, in an area including Kowloon, the New 27

4 Territories and most outlying islands (CLP Power, 2006a). The company runs Castle Peak Power Station which uses coal, Black Point Power Station which uses natural gas and Penny's Bay Power Station which uses diesel as backup system. It also obtains power from the Guangdong Nuclear Power Station in Shenzhen ( 深 圳 ) and Guangzhou ( 廣 州 ) Pumped Storage Power Station in Conghua ( 從 化 ). About 6,908 MW of electricity were supplied to Hong Kong customers in 2005 and 6,595.5 MW of electricity were generated in the 3 stations in Hong Kong (CLP Power 2005). CLP has also been planning to have a commercial scale wind turbine built on either Kau Sai Chau or Hei Ling Chau. This will be a 80 m tall wind turbine with the electricity generating capacity of at least 800 kw to be commissioned by 2007 (CLP Power, 2006b). Questions: How much electricity in Hong Kong is generated from renewable energy? Suggested activity: Renewable energy in Hong Kong and the world (Worksheet 1). Let students learn the data deduction skill in analyzing the contribution of renewable energy towards electricity generation in Hong Kong and the world. Question: How is electricity generated? 2. Principle of electricity generation In a closed chamber, when liquid water is heated up, vapour is formed and with the kinetic energy, the gas phase expands in size. The expanded vapour will leak 28

5 whenever an opening is present. So when the chamber is connected with a steam turbine, the steam turbine will be forced by vapour to rotate. This rotation force is carried to a motor, and electricity is generated. To heat up the water, various kinds of energy are used, e.g. fossil fuel, heat released from nuclear fission, geothermal energy, flammable solid, liquid or gas. At present, most of the electricity generated was from motors or motor-like facilities driven by steam turbine, water turbine or wind turbine. In solar cells, when certain matter, e.g. a silicon plate is exposed to light, voltage difference appears on its two ends, and thus electricity is generated (Hong Kong PolyU Industrial Center, 2006). Questions: What is renewable energy? What is the difference between renewable and non-renewable energy? As fossil fuels are non-renewable, do we face an energy crisis? If so, what can we do? Could multiple fuels be used to generate electricity? What are the advantages and disadvantages? 3. Renewable energy and the world trend employing multiple fuels for generating electricity Renewable energy refers to the fuel sources which can be regenerated with a natural process which has larger regeneration rate than the rate of consumption. These fuels are directly or indirectly from sun, or from deeper part of earth. In contrast, non-renewable energy utilizes energy sources that cannot be regenerated or have very low regeneration rate with natural processes when compared to usage rate. The most widely used non-renewable energy is fossil fuel in terms of oil, natural gas and coal contributing about 77% of the world electricity. 29

6 For fossil fuels like oil or coal, they have limited storage on earth; They will not be available after certain years. Also, a fossil fuel needs to be mined or drilled and then processed before the fuel can be used. This contributes to local pollution and thus has devastating effect to local species and habitat. Further, as a fossil fuel is used in the form of combustion, carbon dioxide and various kinds of toxic organic and inorganic compounds are formed during combustion. With an increased level of carbon dioxide, the greenhouse effect will be more intense and global temperature will rise. Global warming leads to extinction of certain species and rising sea level will destroy coastal cities. Various kinds of toxic organic and inorganic compounds will have different levels of damage to many species and have harmful effect to human. With the uneven distribution of the fossil fuels and the fluctuating oil price, economic development, especially of the developing countries, is highly affected. Exploitation of renewable energy is a way to secure fuel supply. In 2004, the total power generation capacity in the world was 3,800 GW (gigawatts) whereas the total renewable power capacity was 160 GW worldwide (excluding large hydropower), occupying roughly about 4% of global power capacity (Table 1) (REN21, 2005). Large scale hydropower accounts for 720 GW, 16% of the world s electricity. The other major types are: small hydro-power, wind power and biomass power. Developing countries including China as a group have 70 GW (44%) of the 160 GW total, primarily biomass and small hydro power (Figure 1). The European Union (25 countries) has 57 GW (36%), a majority of which is wind power. The top five individual countries are China (37 GW), Germany (20 GW), the United States (20 GW), Spain (10 GW), and Japan (6 GW) (REN21, 2005). 30

7 Table 1. The power capacities of renewable energy (REN21, 2005). Power capacity in 2004 (GW) Contribution to the world power capacity (%)* Large scale hydropower Small scale hydropower Wind turbines Biomass power Geothermal power Solar Photovoltaic (PV), off-grid Solar PV, grid-connected Solar thermal power Ocean (tidal) power Total renewable power capacity *, World electric power capacity at the end of 2004: 3,800 GW. 160 Power Capacity (GW) Small hydropower Wind Biomass Geothermal Solar Photovoltaic (grid) 40 0 World Developing countries European Union (25 countries) China Germany U.S.A. Spain Japan Figure 1. Renewable power capacities of European Union (25 countries), top 5 countries and developing countries in 2004 (REN21, 2005). 31

8 Table 2. The cost for generating electricity from fossil fuels, nuclear power and renewable energy (ICCEPT, 2002). Technology Projected future costs beyond Current cost (U.S as the technology matures cents/kwh) (U.S. cents/kwh) Biomass Energy - Electricity Heat Wind electricity - Onshore Offshore Solar Thermal electricity (insulation of 2500kWh/m 2 per year) Hydro-electricity - large scale small scale Geothermal energy - Electricity Heat Marine Energy - Tidal barrage (e.g. the proposed Severn Barrage) Tidal stream Wave Grid Connected Photovoltaics, according to incident solar energy (insulation) kWh/m 2 per year (e.g. UK) kWh/m 2 per year (e.g. Southern Europe) kWh/m 2 per year (e.g. most developing countries) Stand alone system (incl. batteries), 2500kWh/m 2 per year Nuclear energy Electricity grid supplies from fossil fuel (incl. T&D) Rural electrification Capital cost will come down with scientific advances, but many technologies are mature, and Cost of central grid supplies, excluding transmission and price may be offset by rising fuel distribution: cost which may be due to - Natural Gas 2-4 political reasons and/or - Coal 3-5 commercial consideration 32

9 The popularity in employing renewable energy depends on availability and cost-effectiveness. Table 2 shows the investment cost (ICCEPT, 2002). At present, solar energy is still expensive. In terms of the cost, large scale hydro-electricity and on-shore wind electricity are comparable with the fossil fuel-generated electricity. This may explain for the popularity of the two renewable energy types. With technology advancement, it is expected to further lower the investment cost for most renewable energy. Questions: As renewable energy is popular throughout the world, could you name some types of renewable energy? What are they? Suggested activity: Presentation on renewable fuel (Worksheet 2) Let students collect information about various kinds of renewable energy and explain to classmates. 4. Four types of renewable energy 4.1 Hydropower When water is at a higher place, it has higher potential energy. When it flows to a lower place, the potential energy is converted to kinetic energy. Through blocking water with a dam and installation of a water turbine at the water exit, some kinetic energy will be converted to electricity (Figure 2). 33

10 Figure 2. The dam-style hydroelectric power generation. To use hydropower, a stream or river is needed. A dam must be built to block and store water. Also, a control gate is needed to control the water flow rate and thus the electricity generation rate. A filter should be present to block objects from entering and damaging the turbine. One way to use hydropower is to use the dam to collect water and release the water in a controlled rate. Another way of using hydropower is to use it as energy storage; when the electricity usage is low at a certain period of time, excess electricity was used to pump the water up and store at the dam. When electricity usage is high, water is released from dam to generate electricity. This is how Guangzhou Pumped Storage Power Station operates. The advantages of using hydropower include: - it does not have any direct pollution to the environment, 34

11 - The electricity generation rate can be controlled and predicted, and thus it can provide stable electricity supply. The disadvantages of using hydropower are: - A dam will adversely affect immediate local land and water habitats and thus have damaging effect to certain local species, e.g. terrestrial species which lives near water or depends on multiple habitats in different parts of river in its life cycle, e.g. salmon. - The local residents need to abandon their houses and are moved to other places. 4.2 Wind power When wind passes through a wind turbine, the wind turbine rotates and generates electricity (Figure 3). To generate electricity from wind, a place with constant wind from one direction is preferable. A wind turbine is built high above ground to catch the movement of air with less hindrance. Also ancillary equipment may be added to orientate the wind turbine, control the electricity generation and ensure the wind turbine to operate within designed parameters so that it will operate safely. Figure 3. The wind turbines. There are two types of wind turbines; One type is land based and the other type 35

12 is marine based. Arrangement of land based wind turbines is determined by the availability of land. Marine based wind turbines are located either near the shore at shallow water region or built on artificial islands. The advantages of using wind power include: - no direct pollution; - relative low impact to local habitat. The disadvantages of using wind power are: - The electricity generated is affected by the availability and speed of wind. Additional equipments are installed to store the energy to provide and control the electricity output. - It requires land for the construction and installation of wind turbines. - Birds may be killed by an operating wind turbine. 4.3 Solar energy When a dark plate is exposed to light, the plate increases in temperature. This can be used as heat source for electricity generation (Solarthermal). The capture of solar energy can be improved by a high heat capacity fluid to store the heat energy or coating to collect the wider range of electrical magnetic wavelength of sunlight. As a solarthermal system needs a much larger area for reception of sunlight, photovoltaic device (solar cells, Solar Photovoltaic (PV)) is more commonly used as it can be installed in small scale in most places instead of a single large area (Figure 4). For solarthermal system, light is concentrated with mirrors to fluid (commonly water) storage to heat up for electricity generation. For PV, solar cells are made of matters like silicon which generate electricity when it is exposed to light, and the silicon plate must be protected by glass which is at high purity so that the maximum 36

13 amount of light can pass through it. Tracking system is needed to orientate the solar cells to receive the maximum amount of sunlight. Also, the electricity generated is direct current (DC), which must be converted to alternative current (AC) for normal usage. Figure 4. The rooftop solar panels. The advantages of using solar energy as electricity source are: - no direct or indirect pollution; - low impact to local habitat; - the period of energy generation is similar to the period of peak electricity usage at daytime. - For PV, it can be installed in most places, e.g. rooftop. The disadvantages of using solar energy to generate electricity include: - the energy supply is affected by day length and sunshine intensity. Additional equipments are installed to regulate and stabilize electricity generation; - the cost of using solar energy, especially PV, is relatively higher than other renewable fuels. 37

14 4.4 Biomass Power (Biofuel) With light, plants grow. Herbivorous animals feed on plants, and microorganisms feed on dead or living organisms. Through the food chain/web relationship, the energy flow between organisms is originated from photosynthesis which converts solar energy to chemical energy or chemical compounds (carbohydrates) in plants. The more this conversion happens, more biomass builds up. If masses of dead biomass go through a very long period of high temperature and pressure, it becomes coal, oil and natural gas, the fossil fuel. Fossil fuel is not regarded as renewable as it will take very long period of time to generate. Biomass comes from various sources. There are 2 major types, first, certain plants with high sugar or oil content were planted and harvested. After further processing, they become fuel, e.g. biodiesel which are esters of fatty acids converted from plant oil; bioethanol which is converted by sugar fermentation. Another type is wastes from various sources, e.g. animal manure, domestic and industrial organic wastes, agriculture wastes. This waste to biofuel includes biogas generation. Beside these liquid and gas fuels, solid biofuels are also generated. Firstly, some plants can be grown in large scale as fuelwood for direct combustion to generate electricity as charcoal. Other organic waste can also be directly combusted for electricity. However, as there are many impurities with solid biofuels, toxic compounds are more likely to be generated and released in air. For direct combustion, as there are more impurities, the combustion chamber and emission channel have to be specially designed to reduce or remove the particulate matter (carbon soot) and other pollutants (sulphur (S)- and nitrogen (N)-containing airborne pollutants). Secondly, pyrolysis or gastrification is used. The biomass or waste was heated at high temperature (~ C) with very little or no oxygen, hydrocarbon rich gas mixture, liquid oil which can be used as fuel and solid charcoal like compounds are 38

15 formed. The gas and oil products can be used for electricity generation while the solid matter is regarded as low-quality fuel. For pyrolysis or gastrification, an extra step of high temperature heating is needed, and extra energy is needed. Thirdly, anaerobic digestion can take place on wet substrates, e.g. animal manure, waste water. When organic matter is available to some microorganisms in anaerobic condition, methane, hydrogen and carbon dioxide are formed. Methane and hydrogen can be used for combustion to generate electricity. Methane is called biogas commonly collected in a landfill site or through composting (Figure 5). For anaerobic digestion, first, the microorganism must be mixed with the physically broken down organic matter. Then a digestion chamber with a monitoring system and environmental control is needed so that the gas generation is at an optimal speed. Figure 5. Biogas generation systems in a landfill site (left image) and a farm composting yard (left image). Fourthly, fermentation takes place on organic matter rich in sugar, e.g. starch, and cellulose. Sugar and cellulose are broken down by brewery yeast (a unicellular fungus) under anaerobic condition to form ethanol, which can be used for combustion. Distillation is carried out so that the 10-15% ethanol in the fermentation mixture is extracted with 95% purity (EMSD HK, 2006). The advantage of using biofuel is: 39

16 - waste that is to be disposed can be minimized and energy is generated. The disadvantages of using biofuel include: - as there are more impurities generated in direct combustion, pyrolysis and gastrification, more severe pollution may result than using fossil fuel if not treated properly. i.e. a renewable energy is not necessary a clean fuel. - for production of biofuel from biomass, usually a large growing area is needed to produce the raw materials. - the electricity generation efficiency may not be high compared to other renewable fuels and fossil fuels (Table 2). Using renewable energy is a world trend but there is no standardized guideline for the use of renewable energy as the source of electricity. Suggested activity: Should we use more renewable fuel to generate electricity in Hong Kong? (Worksheet 3) Let students form different groups and discuss the pros and cons of developing renewable energy for generating electricity in Hong Kong. Reflective Questions: Could we totally depend on the renewable energy for generating electricity? If not, what is the favourable percentage of electricity from renewable energy for Hong Kong? What types of renewable energy are suitable for Hong Kong? 40

17 References 1. HEC, 2006, Over 110 Years of Energy, 2. HEC, 2005, Annual report, Company at a glance, f101_col_e.pdf 3. CLP Power, 2006a, Our business, 4. CLP Power, 2005, Business Overview, 5. CLP Power, 2006b, Commercial scalewind turbine pilotdemonstration, 6. Hong Kong PolyU Industrial Center, 2006, 3.1 太 陽 能 及 其 光 電 效 應, 7. REN 21 (Renewable Energy Policy Network for the 21 st Century), 2005, Global Status Report, Global Market Overview, The WorldWatch Institute EMSD HK, 2006, New and Renewable Energy, 41