Offshore Wind Energy

One possibility being developed with wind energy is placing the wind turbines out in the ocean shore, where they are not invasive to property and the wind speeds are greater. The wind speeds around Hong Kong's shores are about 6 m/s at 60 m height. Turbine power is related to the cube of the wind speed, so to account for the greater power from higher occasional velocites we use an effective velocity of 7.5 m/s. The wind turbines are usually placed at 100 m height, and the increased height will cause the turbine to see an even higher velocity. To find this velocity we use the equation V=7.5*(100/60)^(1/7). This yields a velocity of 8.1 m/s seen by the turbine. The power produced by the turbine is Pi/400*(density)*(V)^3. Using the calculated velocity and standard density of air, we get a turbine producing 4.82 W/m2. If we then assume that they can be placed up to 10 km offshore over a third of the coastline, and using a coastline distance of 7330 km, we get a total turbine power of 41 kWh per day per person for Hong Kong.

Offshore wind turbines have two different structures, which are separated by whether they are shallow offshore or deep offshore. It is useful to separate these because the difficulty of maintaing deep offshore turbines. Approximately 1/3 of the area described above is shallow water, so for shallow offshore power we get 13.7 kWh per day per person, and 27.3 kWh per day per person for deep offshore power.

Solar Energy Possibility

A commonly talked about renewable energy source is solar energy, or the energy released from the sun. Above Hong Kong, the solar radiation is approximately 200 W/m^2. There are 3 main ways that this energy can be used: direct heating, PV cells, and creating PV cell farms. We will assume each person is allowed 10 square meters for the different approaches.

For thermal heating, we assume that the heaters are 50% efficient at making hot water. So 50%*10 m2*200 W/m2*24/1000 kWh/W yields 24 kWh per day per person for heating.

For electrical power, we will give everybody a 15% efficient PV converter. More expensive ones could get up to 20% efficient, and cheaper ones can be as low as 10%, so we are taking the median of those for mass production. We then get 15%*10 m2*200 W/m2*.024 kWh/W yielding 7.5 kWh per day per person.

The PV cells could theoretically be put into farms as well. If we assume that 10% of the land area (11.04 km2) can be made into a PV farm, then each person would get about 16 m2. We also assume that because these will be mass produced that the cheapest panels will be used which are 10% efficient. So we take 16 m2*10%*200*.024 kWh/W yields about 8 kWh per day per person produced. This is much lower than other countries due to the fact that so much of Hong Kong is city.

Energy Consumption: Food

People obtain the energy they have through the consumption of food. However, how much energy does it take to produce the food we are consuming?

Milk/dairy:
A typical dairy cow produces 16 litres of milk per day. If we assume that the average person drinks one pint of milk and uses 50g of cheese (equivilent to 450g of milk) for cooking, than each person needs 1/16 of a cow every day. Assuming a cow weighs 450 kg and has similar energy requirements as a person, it consumes about 21 kWh/day. So 1/16 of that means each person consumes about 1.5 kWh per day for dairy (McKay).

Eggs:
We will assume that a person eats an average of 2 eggs per day for breakfast. An egg-producing chicken eats about 110 g per day, which translates to 0.4 kWh per day if we assume the same ratio of energy to kg as people. If an average egg-laying chicken lays about 290 eggs per year, then eating the 2 eggs in the morning is equivilant to 1 kWh per day (McKay).

Meat:
In Hong Kong, the average person eats 365.2 kg of meat per day. Assuming that this meat is of equal amounts of chicken, pork, and beef, then each person is using about 13 lbs of chicken, 107 lbs of pork, and 268 lbs of beef. This is a total of about 280 kg of animal meat. If we multiply by our conversion of 3 kWh/day per 65 kg, this gives us a total of 12.8 kWh per day.

Farming and Fertilizer usage are negligible in Hong Kong, because less than 8% of the land area is used for farming. Hong Kong is essentially an entire city. So when we total the usage of all the food and farming kWh's, we get a total of about 16 kWh per day per person.

Energy Consumption: Cars

To determine the average kWh a person in Hong Kong uses each day by car transportation, the amount of motor gasoline used per person is found as 325,000 tons. The population of Hong Kong is about 6.9 million people. By dividing and using the conversion of 31.75 gallons per ton and 3.79 liters per gallon we obtain liters of gas used per person. We can then use the same assumption as McKay of 10 kWh per liter.

After the above calculations, we get an average of 57 kWh per person.

Source: http://www.nationmaster.com/graph/ene_mot_gas_con_in_roa_tra-motor-gasoline-consumption-road-transport

Energy Consumption: Airplanes

To find the kWh used flying in Hong Kong per person per day, first the amount of passengers from Hong Kong airports per years was found to be 20,010,000 passengers/year. Then the average flight time was assumed to be 3 hours, using flights going out of Hong Kong. Like McKay, we assumed all flights were a 747 which cruises at 565 miles/hour, has a fuel economy of 0.138 miles/gallon and carries 416 passengers when full. Also using McKay's assumption of 10 kWh per litre which translates to 37.9 kWh per gallon.

Therefore:

This amount of energy usage may seem high, however there are a few reasons that could contribute to such a high number. First, the amount of airline passengers per capita (1) is 2.9 passengers per capita, this is the 13th highest around the world. Also, many of the passengers going to and from Hong Kong would be business related, therefore while still using Hong Kong's resources, they are not included in the per capita count.

(1) http://www.nationmaster.com/graph/tra_air_tra_pas_car_percap-transport-passengers-carried-per-capita

Heating and Cooling Homes In Hong Kong

Heating and cooling are amongst the biggest energy consumption sources throughout the world. The reason is simple; air conditioning and heating have no longer become a luxury in many cities throughout the world, but a necessity. Hong Kong holds true to this instance. September 29^th, 2010 Hong Kong attempted to have their first “No Air Conditioning Night.” 50,000 households did their best, while the other 2,285,000 homes didn’t have the dedication to turn a/c units off. Air conditioning has become so large that during the summer months, air conditioning contributes to 60% of the total energy  consumption.

The average home size in Hong Kong is only 600 ft² and generally houses 2.9 people per household. With an average ceiling height of 8’, each person in Hong Kong contributes to 1600 ft³ of heating  and cooling their homes. The average temperature during the 6 colder months is 66° F, and 81.8° F in the warmer 6 months. Through a simple calculation, the total energy consumed for cooling can be found. Air has a density of 0.08lb/ft³, and has a specific heat of 0.241 BTU/Lb*F.  Applying the formula Q=m*Cp*∆T, a rough estimate for the energy consumed by a Hong Kong resident for warming/cooling their homes can be calculated. Assuming an air conditioner is circulating the air throughout the house in 0.5 hours, 6144 lbs. of air needs to be cooled per day per person. Applying these values to our formula and assuming households are set to remain at 70°F we get:

Qcool=6144*0.214*(81.8-70)=15514.8 BTU.

15514.8 BTU = 4.54694 kWh/day for cooling.

For heating the house up to 70°F,

Qheat=6144*0.214*(70-66)=5259 BTU.

5259 BTU = 1.54 kWh/day for heating.


Additional heating and cooling arises from other applications such as hot water for baths, showers, cleaning, etc., refridgeration purposes, and for cooking. The kW/day per person for these applications were found using the number of Terajoules used in each of these sections as provided in the "Hong Kong Energy End-use Data 2010" published by EMSD (Electrical and Mechanical Services Department).  Refridgeration came out to 2.51 kW/day per person, 4.26 kW/day per person for hot water, and 7.26 kW/day per person for cooking.


Taking all calculations into consideration, the total energy used for heating and cooling in Hong Kong comes out to about 20.1 kW/day per person.

Red Stack Vs. Green Stack

When analyzing the energy consumption of a country and determining how much each item contributes, it is helpful to utilize the Red Stack Vs. Green Stack technique. The red stack represents the summation of energy consumption. This stack is generally split up into energy consumption used for transportation, heating and cooling, lighting, information systems, food, and manufacturing. The green stack is a breakdown of sustainable energy production such as wind, solar, hydroelectric, etc. The purpose of putting these stacks next to each other is to answer the question, “Can we live on sustainable energy sources?” An example of how this completed breakdown will look is displayed below. Here David JC MacKay broke down energy consumption and sustainable energy for the UK. We will be going through and doing the same breakdown for Hong Kong, to see what the chances are of Hong Kong being able to run purely on sustainable energy sources.

Steam engines and other sources of greenhouse gases

The steam engine is considered to be one of the most important influences in the industrial revolution. This steam engine revolutionized not only industry but transportation as well. Before this engine, the emissions from human production were almost at practically nothing. However, after the new steam engine was created there is a visible jump in CO2 concentration in the atmosphere.  Steam engines are generally are generally heated by coal, which produces about 2.86 tons of CO2 per ton burned (1).  With the steam engine fueling the Industrial Revolution, human emissions have been steadily growing due to a better ability to produce and an insatiable appetite for more. The different amounts of greenhouse gas that transportation, industry, residential and commercial give off in Hong Kong can be seen on the piechart breakdown below. 

Is Energy Important?

Energy is necessary for our everyday lives. Energy is used for everything from heating water to running our cars. A large portion of this energy is powered by fossil fuels. Different economies use different amounts of energy, and in different areas. These fluctuations can be due to geographical differences, differing cultures, and varying technologies amongst other things. The energy use breakdown for Hong Kong can be seen in the figure below, as discovered by the Electrical and Mechanical Services Department (EMSD).

A more detailed breakdown by the different areas that use this consumption and what it is being used for can be seen below. Figures such as these prove to be important because it shows which areas are consuming the most energy, thus revealing which are areas that need to be focused on for reducing energy consumption.

The Greenhouse Effect For Dummies

One of the most problematic side effects of fossil fuels is the lasting effect it has on our planets ecosystem, commonly referred to as the greenhouse effect. This is a natural effect that arises from the planets absorption of thermal radiation given off by the sun. The sun emits solar radiation that passes through the earth’s atmosphere. Naturally some of this radiation is absorbed into the Earth, giving a warming effect, while other is reflected off. Greenhouse gasses play a significant role throughout this process because they also absorb some of the sun’s radiation, and then emit the radiation back into the Earth’s atmosphere.  The Image below provides a visual representation of this effect.

The highest contributor to this greenhouse effect is Carbon Dioxide which is given off from the use of fossil fuels. Currently, with the burning of such large quantities of fossil fuels, more and more of these greenhouse gases are building up in the atmosphere. This results in additional radiation being re-emitted back to the Earth, providing a warming effect. Hence, the Greenhouse effect. In Hong Kong specifically, CO2 is the overwhelming Green House Gas that is being emmited, as can be seen in the figure below.

The effects on the environment without changing the current energy profile

The current energy consumption profile is shown on the figure below. 80.3% of the energy produced in the World is fossil fuel. Fossil fuels are non-renewable and will eventually run out. Also, since fossil fuels are carbon based, when burned CO2 is released into the atmosphere.  The technology available today should be used to create more efficient ways of obtaining renewable energy, rather than better methods of fossil fuel extraction.  Increasing renewable energy usage will cut down on CO2 in the atmosphere, thereby reducing the greenhouse effect. Without changing the current energy usage profile, CO2 will continue to be pumped into the atmosphere at an unsustainable rate, thus increasing the temperature of the planet. This affect, although it sounds relatively harmless, can wipeout coastal cities and have devastasting effects on marine life.

Figure :  http://www.personal.psu.edu/kdh5039/Assignment6/Assignment6.html

The Three Components of Sustainability

                            

The ability to meet the needs of the present generation, while not compromising the ability to meet future generations’ needs.  Social, Ecological, and Economic were deemed “The Three Pillars” of sustainability at the 2005 World Summit.  In order to be sustainable, all three requirements must be met. If something is using very little resources and is socially acceptable but not affordable, clearly it can not be considered sustainable. The figure above shows the different ways resources can be used and what is considered sustainable.

What else affects the Earth's climate?

Because there are so many other factors that affect the climate other than human actions, it can be beneficial to group them based on whether they help warm or cool the Earth. These factors are also known as "forcings." If a forcing helps warm the Earth, it is a positive forcing. This includes things such as solar flares and sun spots, volcanic activity, and the release of greenhouse gases into the atmosphere such as the burning of fossil fuels. A negative forcing then helps cool the Earth. One of the major negative forcings is the polar ice caps, which reflect a lot of solar radiation back towards space. As the Earth continues to warm, the ice caps are beginning to melt and break apart, increasing how quickly the Earth warms. Other negative forcings include actions that decrease the concentration of Greenhouse gases in the atmosphere, such as reforestation. The new plants take CO2 out of the atmosphere and return oxygen. A major factor is the Earth's albedo, or how well it reflects solar emissions. With the melting of the ice caps, the Earth's overall albedo is decreasing, allowing the Earth to warm at an increasing rate.

What proof is there that humans are the cause?

Some skeptics may ask for scientific proof that human activities are causing the increase in global average temperatures, and not natural effects. As shown in figures 1 and 2, the global average temperature and CO2 emissions begin to take off around 1900-1910. When compared to levels from the past obtained by ice sampling, tree-ring analysis, and other methods, it can be seen in figure 2 that in the past 100 years, changes have occurred that normally would take hundreds of thousands of years, and corresponds to when the the industrial revolution took place. The concentration of CO2 in the atmosphere is nearly 30% higher than has ever been  seen in history. This evidence leads to the conclusion that natural causes cannot have caused these kinds of changes so rapidly.

Figure 1

(http://data.giss.nasa.gov/gistemp/graphs/)

Figure 2

(http://www.fs.fed.us/ccrc/primers/climate-change-primer.shtml)

Figure 3

(http://climatechangedownunder.wordpress.com/page/2/)

Figure 3 shows the temperature variation with the CO2 variation from the past 800 thousand years obtained by ice core sampling. The data shows that a change of 100 parts per million (0.01%) of carbon dioxide concentration corresponds with a change of 10 degrees Celsius in average global temperature. Today's high concentration of carbon dioxide (highest ever recorded in over 800 thousand years) will undoubtedly cause drastic changes unless something changes. They also show that human activity causing increases in the carbon dioxide levels, such as the burning of fossil fuels, is causing irreversible changes to the Earth's climate.

Why is the Earth's temperature increasing?

The Earth's temperatures have been slowly increasing due to the Greenhouse effect. When solar radiation reaches the Earth, it is able to pass through the atmosphere because of it is high frequency radiation. Some of this radiation is then reflected back towards space at a lower frequency. Greenhouse gases, such as carbon dioxide and methane, in the atmosphere trap the low frequency emissions, and release them in random directions. As more Greenhouse gases are put into the atmosphere, less of the reflected heat from the sun is able to get to space, so the Earth gets warmer and warmer.
The ability of a greenhouse gas to trap heat over a certain amount of time is measured as it is compared to carbon dioxide. This is known as the Global Warming Potential of the gas. For example, methane has a 20 year GWP of 72. This means that if equal weights of carbon dioxide and methane were put into the atmosphere, over 20 years the methane would trap 72 times the amount of heat as carbon dioxide. Although carbon dioxide does not warm the earth as much, it is the largest percentage of the atmosphere. Carbon dioxide also is the gas with the most emissions from human activities such as the burning of fossil fuels. This is why when talking about global warming carbon dioxide is the gas most talked about.