The following case study demonstrates the application of the strategic analysis of complex systems (SACS) method described in Chapter 13. This case study was the final project of an honors course on sustainable energy in which the following students participated: Nathaniel Amack, Anna Balzer, Michael Belazis, Jesse Fife, Nicholas Haase, Carl Husmann, Gideon Irving, Scott Pawlowski, and Charles Tse. The assignment asked the students to determine the steady-state carrying capacity of the island of Oahu based on food, energy, water, transportation, and population. As a first step, the students were asked to make back-of-the-envelope estimates to ascertain which of the above would be the limiting factor that determines the population that the island could support sustainably.
Sustainable Oahu
by
Nathaniel Amack
Anna Balzer
Michael Belazis
Jesse Fife
Nicholas Haase
Carl Husmann
Gideon Irving
Scott Pawlowski
Charles Tse
1. Introduction
Within the next few years the world will change dramatically. Some weeks ago the United Nations proclaimed that the human population has passed 7 billion and predicted that it will reach 9 billion by the year 2048. This is a huge number of people which may exceed the carrying capacity of the global ecosystem.
The Earth is a closed system and except for an occasional asteroid its only energy exchange with the universe is by radiation; it is irradiated by the sun and radiates heat into space. Thus for a sustainable future, this energy exchange must come into balance. Although the amount of solar radiation reaching the earth is enormous, the usable energy to sustain an industrial society is limited by the laws of thermodynamics. The global energy balance was changed a few hundred years ago when humans discovered fossil fuels and began to use them at an ever increasing rate. This has led to a more complex social structure that has become increasingly vulnerable to collapse as the supply and quality of fossil fuels diminishes. There is global concern about an energy crisis, particularly about a decline in oil production, often called “peak oil”. But there are other factors, such as food and water, which may soon limit the population in some parts of the world.
The concept of an “ecological footprint was proposed in 1990 by William Rees and Mathis Wackernagel. Calculators are now available to measure humanity’s demand on nature. The measure indicates how much land and water a given human population requires to produce the resource it consumes using current technology. “Carrying capacity” is a concept often applied at a global scale. It expresses the biophysical limits of the environment as a way to estimate the maximum population that can be supported indefinitely by a particular geographical environment. This paper reports the work of an interdisciplinary senior level course offered in the Department of Mechanical Engineering at the University of Colorado at Boulder. The class wanted to explore the questions of ecological footprint and carrying capacity from an engineering perspective. The engineer’s job is to apply science and facts about the physical world in order to design and build systems that work to achieve specified requirements. The case study of the Hawaiian island of Oahu was used, and new methods of Transition Engineering were applied. The method was to first assess the ability of Oahu to support the current population of one million, and then to examine the limiting environmental and natural resource availabilities to determine the population carrying capacity. Finally, strategic analysis of the possible supply and demand options was carried out to identify opportunities for sustainable development.
1.1 Case Study on Oahu
Captain James Cook arrived in 1778 it is estimated that there were about 300,000 native Kanaka Maoli islanders on the 7 Hawaiian Islands. Today, there are between 225,000 and 250,000 people of Hawaiian descent living on the islands. But the arrival of Europeans brought many diseases to which the natives had no immunity and the population shrank to 154,000 by the year 1900 according to the U.S. Census Bureau. By 1950 the population grew to half a million and today it is estimated that 1.2 million people live on all the islands with about 1 million on Oahu.
Hawaii’s gross state product is about $44 billion with financial services, tourism, government, and trade (including transportation), contributing about $10 billion each. Manufacturing contributes only about $1 billion. The islands import virtually all their food and fuel (mostly oil). The need to import oil also for electricity generation is responsible for its exorbitant cost of 26 cents per kWh, the highest in all the USA. This state of affairs is obviously unsustainable and for the future of the state, it is important to estimate its carrying capacity, especially of Oahu, where more that 80 % of its population lives. Shown below is a schematic of the island.
1.2 Carrying Capacity Analysis
The looming energy crisis on Oahu due to declining world oil supply is only one facet of sustainability. Sustainability is multidimensional and interconnected, requiring consideration of a wide range of elements. For this case study of sustainability we selected the small island of Oahu, which is rich in renewable resources, but lacks any fossil fuels. Thus, it provides an excellent example for such a case study.
We focused in our study on five key elements generally considered necessary for a sustainable society:
1. Food
2. Energy
3. Water
4. Transportation
5. Shelter
Initially we did not know whether any one the 5 would be the most important or if a combination of them would be the limiting factor on island population. Since each of them involved social and technical aspects of the question, each of the five elements was addressed by an interdisciplinary team of two students, one from within the engineering program and one from outside engineering. An analytic approach developed by Krumdieck and Hamm[1] was used for the work. The approach entails developing a matrix of possibilities for each of the elements of sustainability. These matrices correlate possible resource supply and demand options and identify which combinations of supply and demand could be sustainable. These combinations are further evaluated for their energy impacts, costs, and risks.
Each student team developed a possibility matrix for its focus area. These matrices were then compared to identify interactions and limiting resources. The information from this collaboration was used to refine the possibility matrices and develop conclusions. Each team reported on their focus area for the conclusion of an honors course in Global Sustainability. This article represents an abstract of that work.
2. FOOD and AGRICULTURE
Agriculture is one of the key issues when determining if a society is sustainable. Currently little agriculture exists on the island of Oahu because of the high land prices. All crops planted on the island are sold for profit, such as coffee beans. This section of the sustainability analysis will look at the arable land available on the island and develop a rough estimate of the population that can be sustained on the island with various types of diet.
ASSUMPTIONS
The following lists the assumptions made for this section:
· The amount of arable land is estimated at 125,000 acres.
· Electric tractors and other vehicles used in harvesting and transport of foods will be available.
· The current diet and calorie intake of the population of Oahu was assumed to be the same diet and calorie intake as consumed by the people on the mainland.
· The diet of the entire population of Oahu is assumed to be uniform and identical.
SYSTEM ANALYSIS
Using data of the average yields per acre, calculations were done to find out if the current population of one million can be sustained on Oahu given several diet-calorie-intake combinations. It was found that Oahu did not have sufficient arable land to sustain a population of one million.
To estimate the sustainable population the following table was constructed to see what population can be sustained based on the amount of land required per person per year. This number is dependent on the diet of the population. The acreage per person per year is listed in the table. The vegetarian diet was estimated to require 0.6 acre per person per year because the diet requires more land than the vegan diet to raise dairy cows. The pescatarian diet was assumed to require 0.4 acre per person per year because the diet allows fish to replace high protein vegetables, yet doesn’t require arable land. With these figures, the total sustainable population of Oahu ranged from about 200,000 to 300,000 people. For the purpose of this study, the higher figure was used because there are additional opportunities to grow food on rooftops and backyards.
This population, along with the food energy multiplier and the calorie intake, can be used to calculate the energy required in the agricultural sector. The food energy multiplier is a measure of the behind-the-gate farm inputs, processing, packaging, storage and preparation energy in the food system. The food energy multiplier decreases as the calorie intake decreases because it was assumed that a lower calorie diet contains a higher percentage of nutritious food. Higher calorie diets were assumed to contain more processing, packaging, transporting and storage processes, which is why the energy multiplier is higher. The current food energy multiplier for mainland American diets is 10-12 times the actual food energy content.
The chart uses the following color code to represent the possibility of implementing the diet-calorie-intake combination into Oahu’s society:
· Red indicates that the combination cannot sustain a population of 200,000 to 300,000.
· Orange means that the combination can sustain a population of 200,000, but requires a dramatic change in lifestyle.
· Yellow means that the combination can sustain a population of 200,000 with some changes in lifestyle and little exports.
· Green means that the combination can sustain a population of 300,000 with some changes in lifestyle and significant export of fruits and fish.
Table 1: Agricultural Sustainability Chart.
DEMANDSUPPLY / 2700 / 2500 / 2300 / 2100 / 2000 / Calorie intake (kCal/person-day)
Acres/ person-yr. required / Total sustainable population / 14 / 10 / 7 / 5 / 2 / Food Energy Multiplier
3209 / 2122 / 1367 / 891 / 340 / Energy Demand (GWh/year)
Current Diet / 1.2 / 104167
Pescatarian / 0.4 / 312500
Vegetarian / 0.6 / 208333
Vegan / 0.5 / 250000
Pre-Industrial / 2.6 / 48077
Arable Land (acres) / 125000
Total sustainable population / 300000
With a sustainable population of 300,000 people, a rough estimate about the total water required to produce the food for each diet can be found. For the vegetarian, vegan, and pescatarian diets, the required amount of water ranges from 26 billion gallons to 39 billion gallons. The latter amount of water is available as shown in Section 4.
DISCUSSION
The red boxes in the matrix show that the current U.S. diet and the pre-industrial diets which cannot sustain a population of 300,000 because it would require too much arable land.
The orange boxes in the matrix show the diets that can sustain a population of about 300,000 people. This combination would require dramatic changes to the lifestyles of the inhabitants due to the reduction in energy use. Implementing this plan would eliminate refrigeration and storage, as well as processing and packaging of foods. The energy used would only be for cooking and minimal storage. Families would have to visit the outdoors market for fresh produce and fresh milk frequently. Daily fishing would also need to be done and food could not be exported.
The yellow boxes in the matrix show the diets that can sustain a population of 300,000, and there would not be dramatic changes to the lifestyles of the inhabitants. This plan would allow enough energy for storage, some processing and packaging, and cooking. However, little to no fruits and vegetables will be available for export. The fish caught could all be available for export, except for the pescatarian diet.
The green boxes in the matrix show the diets that can sustain a population from 250,000 to 300,000 people with some fruit, vegetables, and fish exports. This plan would only require a few changes in lifestyles. There would be enough energy to process, package, cook and store food. There would also be enough energy to freeze fish or coffee for export. The only change to the lifestyle of the inhabitants would be a change in diet.
3. Energy
In order for the island of Oahu to be a sustainable system it will need to provide all of its energy needs from indigenous renewable sources. For the purposes of this project, solar and wind sources on Oahu will be assumed to be the sole providers of energy through wind turbines and solar photovoltaic (PV) electricity.
ASSUMPTIONS
· No storage for electricity production (although pumped storage sites are available).
· Flexible consumption to match the produced renewable electricity.
· An adequate electric transmission system.
PV / Amount / Wind / AmountMaximum land available for PV production / 90,000 acres / Maximum land available for wind production / 75,000 acres
Total rated capacity of PV on 90,000 acres / 14,000,000 kW / Turbine rated capacity / 2 MW
PV capacity factor / Roughly 20% / Wind capacity factor / 30%
PV annual maximum production / 2.6E+10 kWh / Wind annual maximum production / 1.5 E+10 kWh
SYSTEM ANALYSIS
Using these assumptions, the chart below shows the feasibility of different annual production levels of electricity for Oahu (the x-axis) when produced by varying levels of wind and solar (the y-axis). Red squares indicate impossible or impractical scenarios (technologically and/or economically), orange indicates plausible but high risk and high cost scenarios, yellow indicates probable scenarios with some risk and cost concerns, and green indicates the most feasible scenarios in terms of supply source and production level.
Table 2: Energy Sustainability Chart
Current Total Energy Usage / Twice Current Production Capacity / Current Electricity Production Capacity / Current Electricity Usage / Half Current Electricity Usage6.0E+10 kWh/year / 3.0E+10 kWh/year / 1.5E+10 kWh/year / 8.0E+9 kWh/year / 4.0E+9 kWh/year
All Wind / 2.00E+05 / 1.00E+05 / 5.00E+04 / 2.66E+04 / 1.33E+04
75/25 Wind/PV / 2.00E+05 / 1.00E+05 / 5.00E+04 / 2.66E+04 / 1.33E+04
50/50 Wind/PV / 2.00E+05 / 1.00E+05 / 5.00E+04 / 2.66E+04 / 1.33E+04
25/75 Wind/PV / 2.00E+05 / 1.00E+05 / 5.00E+04 / 2.66E+04 / 1.33E+04
All PV / 2.00E+05 / 1.00E+05 / 5.00E+04 / 2.66E+04 / 1.33E+04
Values in table are kWh/person/year based on theoretical maximum sustainable population of 300,000
Current consumption kWh/person/year – 6.00E+4
DISCUSSION