Look around your home and different places in Hong Kong. Are you amazed by the variety of energy sources we depend on day and night? We use electricity to turn on a desk light, work at a computer, make a phone call, or travel by an MTR train. Petrol and diesel are important fuels for vehicles which take us to school and work every day. The supplies of town gas and liquefied petroleum gas (LPG) allow us to cook and enjoy hot baths.
Our lifestyle and technology require huge and continuous supplies of energy. While enjoying all the conveniences of city life made possible by these abundant supplies of energy, have you ever wondered where all the energy comes from? Do you know what people consider when choosing between different energy sources? Have you thought about trends in energy usage in Hong Kong?
In Hong Kong, the most common energy sources are electricity, town gas, liquefied petroleum gas (LPG), diesel and petrol. Town gas and LPG are commonly used for cooking and heating water at home. Petrol is the most common fuel for passenger cars. Ships and heavy vehicles burn diesel as fuel. Town gas, LPG, petrol and diesel all come from petroleum, which is a kind of fossil fuel. Electricity is generated by nuclear power or by burning fossil fuels like coal and natural gas in power stations. So apart from the electricity generated by nuclear power, almost all energy currently consumed in Hong Kong comes directly or indirectly from fossil fuels. But where do fossil fuels come from?
Coal, petroleum and natural gas are fossil fuels. Fossil fuels were formed from living organisms that lived hundreds of millions of years ago. Coal was formed from the remains of plants buried deep under layers of mud and sand. Natural gas and petroleum were both formed from the remains of small sea animals and plants covered by mud and sand at the bottom of seas. Therefore, they are often found together. For millions of years, the motion of Earth's crust and layers of rocks has exerted enormous pressure and heat on these materials, changing them slowly into the fossil fuels that we use today.
Click on following animation to see how coal, petroleum and natural gas were formed.
Coal and natural gas are the most common fuels used in power stations to generate electricity. When the fuel is burnt, energy is released to turn a turbine. The turbine in turn drives a generator to generate electricity (for details, please see the module Electricity Generation and Transmission in Hong Kong). As a result, when we use electricity, we are indirectly using coal and natural gas. Nuclear energy provides an alternative way to generate electricity, and may become a solution to the energy crisis in the future.
Petrol and diesel come from petroleum (crude oil). Petroleum is a complex mixture of hydrocarbons, appearing as a dark-coloured, flammable liquid in the upper layers of some areas of Earth's crust. Petroleum has to be separated into different useful parts by fractional distillation. The different parts are called fractions. Petrol and diesel are two of the fractions that can be burnt as fuels to provide power for vehicles. Both are mixtures of hydrocarbons. Diesel is denser, more oily and less volatile than petrol. Diesel also requires less refining to produce than petrol, and is consequently cheaper.
Town gas is not directly obtained by the fractional distillation of petroleum, but by the refining of one of the fractions called naphtha. Naphtha is treated by Catalytic Rich Gas (CRG) process at gas production plants in Hong Kong.
During the CRG process, naphtha is first converted into a methane-rich gas at low temperature and high pressure. Then the methane-rich gas is divided into two parts. One part further reacts with high temperature steam in a tubular reformer, and is then mixed with the other part at a controlled proportion to produce a reformed product of suitable caloric value. The reformed product is then allowed to pass through a high temperature converter, where most of its carbon monoxide is removed by reaction with steam to produce carbon dioxide and hydrogen. Other processes further reduce the amount of carbon dioxide content and add smell to the product. Finally, town gas is obtained. It consists mainly of hydrogen (49%), methane (28.5%), carbon dioxide (19.5%), and a small amount of carbon monoxide (3%) .
Natural gas is often found together with petroleum. Its main component is the lightest hydrocarbon, methane. In some countries, natural gas is used for cooking and heating water at home. In Hong Kong, natural gas is not available for domestic use, but is used in power stations to produce electricity. Natural gas is imported to Hong Kong in a gaseous state from the Yacheng Gas Field near Hainan Island through a gas pipe under the sea. In countries like Japan, natural gas is imported in a liquid state called Liquefied Natural Gas (LNG). LNG is formed when natural gas is chilled to -162 oC and then condenses to a liquid state. LNG is transported over long distances by special insulated LNG ships . As LNG is only about one six hundredth of its original volume in gaseous state, transporting it over long distances is more economical than transporting natural gas through pipes.
When natural gas is drawn from a gas well, 90% is methane, the remaining gas is LPG. LPG consists mainly of the hydrocarbons propane and butane. It is also produced as one of the byproducts when petroleum is refined. LPG is a gas at room temperature and pressure. When it is stored in a pressurized tank, it is liquefied.
Why are certain fuels used for particular applications but not others? The following examples of transportation and cooking will help you answer this question.
Petrol and diesel has become the most important fuels for vehicles because of their abundance, high energy content, suitable ignition temperature and volatility, and convenience of storage and refueling. Diesel is cheaper and has a higher energy content than petrol. It can also be used in engines with higher compression ratios to achieve higher fuel efficiency. However, petrol engines are less expensive, and produce less particulate air pollution and noise during operation. That is why petrol engines are so popular in passenger cars. Diesel engines, on the other hand, are the most common choice for large or commercial vehicles, for which high fuel efficiency and low fuel cost are more important. Recently, there is a trend of replacing diesel vehicles like taxi and light buses with LPG vehicles in Hong Kong. LPG is very clean to burn, and has a high fuel efficiency. This will help improve the air condition in Hong Kong where air pollution has become a serious problem. Nowadays, all taxis in Hong Kong are LPG taxis.
Nowadays, transportation in large cities like Hong Kong has become more electrified: Mass transportation systems like the MTR and KCR are fast, are not affected by traffic congestion, produce no pollution in the places they travel, and have high energy efficiency in view of the large number of people they are able to carry.
What about small vehicles? Electric cars were invented long ago. The fuel cost of electric cars is much less than that of petrol cars. According to the U.S. Environmental Protection Agency Fuel Economy Guide , the electric car Toyota RAV4 EV, 2003 model, consumes electrical energy equivalent to 2.1 litres of petrol every 100 km while the petrol version Toyota RAV4 2WD, 2003 model, consumes 9.0 litres of petrol every 100 km. This means the electric version consumes less than one quarter the energy of the petrol version, and a corresponding reduction in energy cost. So why are electric cars so rare on the streets? The main drawback of electric cars lies in the rechargeable batteries which is bulky, low in capacity, short-lived, rather expensive, and slow to recharge. These factors make using electric cars costly and inconvenient. However, recent technological breakthroughs like fuel cells and hybrid engines have partially solved the battery problems. These breakthroughs may bring about fundamental changes to the transportation of our future.
Town gas and LPG are the most common fuels for cooking in Hong Kong. Traditional Chinese cooking was developed long ago, relying on flame cooking using charcoal. Using town gas and LPG to cook seems to be natural extension of this custom in modern times. Chefs make use of high power gas stoves to prepare delicious Chinese cuisine in many restaurants. LPG is often used for cooking at home. Small tanks of LPG are a convenient fuel source for cooking hot pots and outdoor cooking.
Recently, electricity has become popular for cooking. The introduction of induction cooking equipment has made cooking cleaner, faster, safer, and more energy efficient than before. Induction cooking makes use of an electromagnetic field to transmit energy. Heat loss to the surroundings is much reduced. Induction cooking equipment can therefore cook food up to 30% faster than most gas cookers, and with an exceptionally high thermal efficiency of about 90% . The heat distribution is also more even. However, up to now, many Hong Kong people still prefer to use gas stoves. Some chefs in traditional Chinese restaurants may lack the confidence to cooking with induction wok ranges. Some say that no-flame cooking will make the food lack "zest" and taste bland. Do you think these comments have scientific bases?
People in Hong Kong can often choose from various energy sources for the same applications. Some use electricity to cook or heat water while others use town gas or LPG. Statistics of energy use in Hong Kong can be found in "Hong Kong Energy End-use Data"  published by the Electrical and Mechanical Services Department (EMSD). From the data, we can see that from 1992 to 2002, the use of electricity, town gas and LPG had been increasing while the use of other petroleum (e.g. diesel) and coal products have dropped, especially in 2001 and 2002.
Let us take a closer look at the energy use in 2002. The total amount of energy used by end-users in Hong Kong was about 283 922 Terajoules. The breakdown of how this amount of energy was consumed in each sector is shown in the figure below.
It is important for the government to estimate the needs of energy in different sectors so that strategic planning can be done. In the following activity, you will look at some statistical data about energy end-use, and try to interpret this data based on your knowledge of the social and economical changes taking place in Hong Kong.
In formulating policy on the use of energy sources based on statistical data and future trends, the government needs to ensure the energy sources used are in a continuous and steady supply. There are also concerns over environmental impact.
With a projected world population of 9.1 billion by the year 2050 (2004 Revision of the official United Nations population estimates and projections), the increasing global energy demand will bring about more rapid depletion of the world's fossil fuel reserves. In view of this, any wastage of energy resources should be avoided. We should all help saving energy as much as we can.
Whatever energy source we use, there is always some energy loss to the surroundings. For example, cooking makes the kitchen hot because energy loss from the cooking appliance heats the surrounding air. We can save energy by minimizing this energy loss. Other than following various energy saving tips and using energy efficient products, we can also minimize the energy loss by choosing the right fuel for a certain purpose. For example, we can choose to use induction cookers to conserve energy during cooking. Using petrol of a suitable octane or choosing a more efficient engine helps reduce the fuel consumption of vehicles. On a larger scale, people are becoming more aware of the importance of energy efficiency in industry and power generation. Using natural gas in combined cycle operation has greatly increased the efficiency of electricity generation in power plants.
Other than saving energy, we also need to reduce the adverse effects brought about by using various energy sources on our environment. As mentioned above, the majority of the energy produced in Hong Kong comes from the burning of fossil fuels. This generates air pollutants such as carbon dioxide, sulphur dioxide, nitrogen oxides and respiratory suspended particulates. Carbon dioxide is a greenhouse gas which may be related to global warming. Sulphur dioxide, nitrogen oxides and suspended particulates can cause respiratory problems.
To address these problems, the electricity and gas companies in Hong Kong have taken various measures to help reduce the pollution problems caused by burning fossil fuels.
Environmental protection measures currently undertaken by electricity companies 
Environmental protection measures currently in place by gas companies 
Besides conserving fossil fuels, many countries are exploring the use of alternative energy sources, especially those that are renewable, i.e. exist perpetually and in an abundant quantity in the environment. Most of these alternative energy sources are environmentally friendly. In Hong Kong, solar power and wind power are the most commonly mentioned alternatives to burning fossil fuels.
To use solar power, solar photovoltaic technology can be used. Photovoltaic cells made from semi-conducting materials such as silicon can produce electricity when they are exposed to sunlight. This technology is currently being applied in Hong Kong to provide power to weather monitoring equipment, as well as lighting and heating systems in many government facilities. Building Integrated Photovoltaic (BIPV) cells, where photovoltaic cells are included as part of the building structures e.g. in windows and skylights, are also used in Hong Kong under programmes like the "Building Integrated Photovoltaic School Design for Hong Kong" .
Wind is the movement of air. A wind turbine is a device which captures the kinetic energy of wind to turn a generator for producing electricity. The Hongkong Electric Co. Ltd. installed Hong Kong's first commercial scale wind turbine at Tai Ling on Lamma Island in February 2006  .
CLP is also planning to build a 600 kW, 80 metre tall, commercial scale wind turbine, possibly in Kau Sai Chau (Sai Kung) or Hei Ling Chau. This is expected to be commissioned in 2007 .
Other than the use of solar power and wind power, examples of using landfill gas as an energy source can also be found in Hong Kong.
Landfill gas is produced in landfills. Under anaerobic conditions (lacking oxygen), cellulose (a major component of city solid waste found in wood, paper and plant material) reacts with water and bacteria. This reaction produces carbon dioxide and methane (together with various trace components). Methane gas is useful for energy generation.
At present, most landfill sites in Hong Kong use landfill gas as an energy source in the landfill's leachate treatment plant or as a fuel to produce electricity for on-site consumption. The landfill gas from Shuen Wan Landfill is currently being utilized as the energy source to produce town gas .