DFE2008 Residential Micro Cogeneration

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Brief Background

Micro Cogeneration (CHP for combined heat and power) is a process whereby two forms of energy such as electricity and heat are provided by a single source in a highly efficient manner to a consumer rated at 15kWel or less[1]. Our scope for this report has been taken as a single household with an electricity requirement of 4200kWh (approx 1.2kW). Several technologies are presently available that meet this criteria and we examined three of these in this report namely hydrogen fuel cells, Stirling Engine Systems and power off the grid which utilizes natural gas plants, fossil fuel burning plants, nuclear plants and hydroelectric power plants.

Summary

In order to make educated comparisons, we considered both economic and environmental aspects of the systems. The baseline (power from the grid) and the two alternatives were first examined to establish that they each were able to meet the requirements of a household. Each technology then underwent a cost analysis, a streamlined lifecycle assessment (SLCA) and an environment input output lifecycle assessment (EIOLCA).

Three comparative studies were performed on the results based on performance, environmental impacts and economics. The performance of the system was judged on three subcategories. They were efficiency, portability and durability. On grounds of efficiency and durability, two clear winners were evident, Stirling engine systems and power plants respectively. The criteria for portability was inconclusive as both Stirling Engine systems and fuel cells proved to be equally competitive.

Environmental impacts were considered very seriously in this report. The baseline and alternatives were analysed using an EIOLCA and by closely examining the total releases and global warming potentials of the three options we concluded that the fuel cells were the most environmentally friendly power source.

The last comparison drawn between the options was economics. Even though the most environmentally friendly power source was evident, it may not be highly feasible and indeed this was the case. The two alternatives were compared to the baseline in order to realize relative benefits. Both the alternatives showed almost equal annual savings on energy costs however due to the extremely high initial investment required to install fuel cells they had a very high payback period (21 – 42 years) as compared to Stirling Engine systems (4.85 – 9.87 years).

Each power generation system analysed in this report could hold its own in one way or another. In order to attempt a conclusive comparison, a comparison matrix was formed listing the three systems against the subcategories. On giving appropriate scores between one and four, we see the Stirling Engine system comes out as having the highest potential. It should be noted however that each subcategory was weighed equally in this comparison matrix.

There is still immense room for improvement in both fuel cell and Stirling Engine technologies. If fuel cell manufacture could use fewer precious metals and Stirling Engine systems could decrease their CO2 equivalent releases, a clearer decision would be made possible.

Project Information[edit]

Study title: Residential Miro-Cogeneration

Course: MIE315

Section: 2

Group: 1B

Institution: University of Toronto

Team members:

  • Team leader: Ahmed Al-Nimer (ID: "ahmed.alnimer").
  • Baseline: Oliver Ibrahim (ID: "ibrahi40").
  • Stirling engines: Baber Nasir (ID: "Bbr").
  • Fuel cells: Dan Amariei Voicelescu (ID: "DanAV25").

Highlights and Recommendations[edit]

This section hopes to recommend the best technology for providing micro CHP to residential houses. In this section, several comparisons will be made on performance requirements, environmental impacts, and costs of the baseline (power from the grid) and the two proposed micro CHP alternatives; fuel cell systems and Stirling engines, respectively.

System Performance[edit]

The performance of a micro CHP system has a considerable impact on how much it appeals to society. Factors that affect the performance of a CHP system include the efficiency of the system in achieving the desired function, the portability of the system, and the durability of the system. To begin, the electrical efficiencies of hydro power plants, fossil fuel power plants, and nuclear power plants are listed in table below[2].

The electrical efficiency of power supplied by the Ontario’s power grid is approximately 57%. This was determined by finding the efficiencies of all power plants used by Ontario and then multiplying each of those values by the corresponding plant’s percentage usage by the city. It is clear from the data that a nuclear or fossil fuel power plant is not as efficient as a hydro power plant.

By contrast to the efficiency of power from the grid, the electrical efficiency of a fuel cell can reach up to 45%[3]. Also, the electrical efficiency of a Stirling engine can reach about 88%[4]. It is clear that a Stirling engine is the better choice when it comes to electrical efficiency. The efficiency of heat generation of all systems also shows that a Stirling engine is a clear winner[5]. Therefore, a first conclusion about performance is that a Stirling engine can easily outperform fuel cells and power plants when it comes to efficiency.

The next performance characteristic of interest is the portability of the system. By definition, one of the main goals of a micro CHP system is to reduce or eliminate the reliance on power provided from the grid by producing condensed power generation systems for each building separately[1]. By this definition, power plants are instantly eliminated as portable systems. Typical residential fuel cells, however, weight approximately 150kg, and have a volume of up to 90 × 75 ×30 cm3[6]. This is very comparable to the weight and size of a residential Stirling engine, which could also reach approximately 150-200kg in weight[6]. Hence, a Stirling engine and a fuel cell both prove to be equal in this category of comparison, while power plants fail.

The final performance characteristic has to do with maintainability and durability of the system. To a residential home owner, a power plant is a rather invisible infinite source of power that never depletes. Certainly, power from the grid proved to be very durable with hardly any blackouts. Fuel cells and Stirling engines, on the other hand, are chemical and mechanical technologies, respectively, meaning that they have several components in them that could fail eventually[5][7]. Replacement parts for fuel cells have a high chance of containing precious metals such as platinum and nafion, which are expensive metals with prices that could reach $2000/ounce[8][9]. This suggests that a Stirling engine can be placed second to power plants in terms of durability and maintenance as far as a house owner is concerned. The performance comparisons outlined above will be summarized in the conclusion section of this study.

Environmental Impacts[edit]

Streamlined LCA[edit]

Judging by the streamlined LCA scores (40 for the baseline, 65 for fuel cells, and 67 for Stirling engines), the Stirling engine is the most environmentally friendly micro CHP system, while power plants are the least environmentally friendly. Closer examinations of the results reveal that the scores for fuel cells and Stirling engines are very close. Since the scores of a few individual cells of the streamlined LCA were chosen based on a best guess due to lack of information, a winner cannot chosen yet.

EIOLCA[edit]

Results from the EIOLCA greatly help in deciding a winner. The results obtained from such an analysis are more subjective, as they take into account numerous factors that have an impact on the environment, ranging from transportation of materials to waste management. The EIOLCA of capital costs for the baseline and the two alternatives were presented in chapters 1-3, and are listed, for convenience, in appendices 1-9, 2-3, and 3-1. For simplicity, a stacked column plot showing the total toxic releases resulting from capital, operational, and end of life stages is shown in chart 4-1 below. Also shown is a stacked column plot showing the global warming potential of the baseline, the fuel cell, and the Stirling engine; respectively.

Based on the charts, it is clear most toxic releases are generated by the power plants from the baseline (approximately 40kg per household). This is due to the large amounts of natural gas and fossil fuels going into the operational costs of these power plants[10][11][12][13][14]. The total releases for fuel cells are the lowest at about 5kg per household. By a similar hypothesis, the GWP for fuel cells is the lowest at about 0.1 MTCO2E per household. The GWP is the highest, however, for Stirling engines, at about 16 MTCO2E. From these results, a fuel cell can be deemed the most environmentally friendly technology out of the three.

Economics[edit]

In this section, only the relative benefit of the two alternatives (fuel cells and Stirling engines) to the baseline will be considered. Table 4-3 below summarizes the payback periods and total savings of the alternatives.

From the table, it is quite clear that the Stirling engine is the winner in this comparison. Both fuel cells and Stirling engines return almost the same amount of money due to annual savings on energy costs. However, the high initial investment required to pay for a fuel cell (prices that could exceed $25,000[5]) results in an unrealistic payback period that could exceed 20 years. The use of precious metals in fuel cells has a major impact on its economics. Until less expensive alternatives to precious metals are found, fuel cells are going to remain to expensive to realize a return on investment in a realistic amount of time.

Conclusion[edit]

Perhaps the easiest way to compare and make a final choice on a micro CHP system with potential would be via a comparison matrix:

A Stirling engine is therefore the micro CHP system with high potential. Note that the comparison assumes that all categories of performance, environmental concerns and economics are of equal weight. If environmental concerns were to have a higher weight compared to the rest of the categories, the fuel cell would prove to be the best choice. Regardless, room for improvement exists for both fuel cells and Stirling engines. Fuel cells could benefit from non precious materials in the economics category, while Stirling engines could be improved for less CO2 equivalent releases. In the end, this study helped only prove that a winner cannot be decided just yet.

Power and heat from Ontario's power grid[edit]

Functional analysis[edit]

Power Generation

In Ontario, power is generated from 64 hydroelectric, 5 fossil, and 3 nuclear stations, which produce a total of more than 22, 000 megawatts of electricity[15]. The breakdown is OPG’s Generating Mix can be seen in Figure 1-1.

File:Figure 1-1 Breakdown of Ontario's Electricity Production -1-1-.JPG
Figure 1-1 Breakdown of Ontario's Electricity Production[15]

Nuclear Power

Nuclear power alone in Ontario could fulfill 50% of its electricity needs, and has a combined capacity of 6,600 megawatts[15].
Advantages[15]:

  • Low operation costs
  • Virtually no emissions which lead to smog, acid rain, or global warming

Disadvantages[15]:

  • High initial cost
  • Decommissioning of plant is extremely expensive
  • Highly radioactive waste


Fossil-Fuel Power

OPG operates five stations which run off fossil fuel, with a combined capacity of 8,600 megawatts[15]. One of these stations is fueled by oil and natural gas, while the other four are fueled by coal. Their production of electricity is determined by demand, price and the availability of nuclear and hydroelectric power.
Advantages[15]:

  • Well established
  • Easier to create and decommission than nuclear power plants.

Disadvantages[15]:

  • Significant releases of green house and other harmful gases


Hydroelectric Power

Hydroelectric power is a renewable and clean energy source harnessing the energy of water as it travels from a higher elevation to lower elevation. It is Ontario’s lowest-cost power source with a combined capacity of 6800 megawatts, supplying 32% of Ontario’s energy[15].
Advantages[15]:

  • Low operational costs
  • Reliable
  • Flexibility to meet base as well as peak demands
  • Reliance on water – an indigenous, renewable resource

Disadvantages[15]:

  • Limited by natural locations where hydroelectric energy stations can be made good use of.


Natural Gas

The baseline option being analyzed uses natural gas heating which is produced at a Natural Gas Processing Plant. It is used for both space and water heating in a large percentage of the residences in Ontario[16].
Advantages[16]:

  • Well Established
  • Convenient

Disadvantages[16]:

  • Large emissions of harmful gases from life cycle


Ontario Electricity Rates:

As of May 1, 2007, electricity prices for consumers who use less than 250,000 kilowatt hours per year, which is where a typical homeowner would lie under, will be 5.3 cents per kilowatt hour (kWh) for the first 600 kWh they use each month, and 6.2 cents per kWh for electricity used per month over this amount[17]. However a typical 4.0 cents/kWh + GST reflects an Electricity Cost of around 10 cents/kWh[17].


Ontario Natural Gas:

In Ontario deregulated natural gas rates vary around 36 cents/m3, and regulated natural gas rates are approximately 27 cents/m3 based on 3100 m3/year with a delivery charge of 14 cents/m3. The average cost of natural gas for a residence is typically around 37 cents/m3[18].

File:Table 1-1 Average Annual Heating and Electricity Cost -1-5-.JPG
Table 1-1 Average Annual Heating and Electricity Cost[19]



  • See Table 1-1 for Average Annual Heating and Electricity Cost




Streamlined Life Cycle Assessment[edit]

Using a streamlined LCA, a Natural Gas processing plant as well as the three types of electricity generation plants, Nuclear, Fossil Fuel, and Hydroelectric were compared (Table 1-2). Immediately one can notice that hydroelectric power scored approximately twice as high as the other three processes in this LCA, implying it is the most environmentally friendly process. The reasoning behind these scores will be discussed in the following paragraphs.

File:Table 1-2 Process Streamlined LCA for Natural Gas Processing Plants and Hydroelectric, Fossil, and Nuclear Power Plants.JPG
Table 1-2 Process Streamlined LCA for Natural Gas Processing Plants and Hydroelectric, Fossil, and Nuclear Power Plants

Natural Gas Processing and Fossil Fuel Power Plants received the lowest scores in the streamlined LCA for many of the same reasons, and will be discussed together. The major areas in which these two processes did very poorly were the primary and complementary process operation. This is because Coal plants as well as Natural Gas plants have very high gas residue emissions which contribute significantly to global warming. The materials of choice, gas and coal, with which these plants operate, are also a non renewable resource and result in significant population.


Hydroelectric power got the highest score in this analysis for many reasons, however the most important reason was that it had significantly better scores in the primary and complimentary process implementation. This is because a hydroelectric station has almost no emissions, and residues from its operation due to its usage of water as its “fuel”.


Nuclear power scored the second highest even though its choice of fuel is uranium which he highly toxic and radioactive. This is mainly a result of operation residues being extremely low due to its clean operation. The reasons for which it didn’t score higher however are due to the material choice for fuel being not only harmful during its use, but also harmful after its end of life in which case a vast amount of energy must be put into decommissioning the radioactive waste coming from a nuclear power plant.


Financial analysis[edit]

Electricity:


A summary of the capital and operational costs of the three types of power generation plants used by OPG can be found in Table 1-4.

Sample Calculation:

Coal Cost = $50/ton[10]

Coal Cost Per GWh = 450 ton/GWh * 50 $/ton ≈ 22,500 $/GWh[11]

Annual Coal Cost = 22,500 $/GWh * 25,000 GWh/yr = 562,500,000 $/yr[11]

Percentage of Ontario’s Population in GTA = 46.4%[12]

Percentage of Power in Ontario Used for Housing = 16%[13]

Number of Households in GTA = 1,965,935[14]

Annual Cost Cost Per house = 562,500,000 $/yr * 0.464 * 0.16 / 1,965,935 = 21.24 $/yr


Plants are not expected to run at max capacity for an entire year. The difference between the annual max capacity and the actual amount of electricity produced is converted into a reduced number of hours of operation at maximum capacity.

File:Table 1-3 Regulated Annual Hours of Operaion -1,1-.JPG
Table 1-3 Regulated Annual Hours of Operaion[15]



  • See Table 1-3 for Regulated Annual Hours of Operation



Sample Calculation:

Annual MAX Power Output (Hydro) = 6,800MW * 8,760hr/yr = 59,568,000MWh/yr

Actual Production (Hydro) = 33,3000,000MWh/yr

Regulated Annual Hours of Operation Per Year:


Natural Gas:


A summary of the capital and operational costs of a Natural Gas Processing plant, used to supply the required amount of heating to homes in the GTA, can be found in Table 1-5.

Calculations:


Average Annual Cost for heating a household = $1150[19]

Average Total Cost for natural gas to household = $0.37/m3[18]

Number of Households in GTA = 1,965,935[14]


Required Production to Support GTA:

Average usage per day for one household =
$1150 * (1m3/$0.41) * (35.3147ft3/1m3) * (1year/365days) = 271.3ft3/day


Average usage per day for households in the GTA =

271.3(ft3/day) * 1,965,935 = 533,513,969ft3/day = 533.51MMscfd


Note: MMscfd stands for Million Standard Cubic Feet per Day of gas

The capital cost of a Natural Gas Processing plant which has a capacity for 533.51MMscfd is $75,000,000[27].

The Annual operating costs of a Natural Gas Processing plant which has a capacity for 533.51MMscfd is $253,150,495[26].


  • See Table 1-6 for Baseline Total Capital and Operational Costs
  • See Table 1-7 for Baseline Total End of Life Costs
File:Table 1-6 Baseline Total Capital and Operational Costs.JPG
Table 1-6 Baseline Total Capital and Operational Costs














End of Life Cost of a Nuclear Power Plant:

EOL Cost = 15% of capital Cost[29]

= $ 9,900,000,000 * 0.15 = $1,485,000,000

Cost of Decommissioning Nuclear Waste = 5 $/MWh[28]


End of Life Cost of Fossil Fuel Plant:

= ($1,485,000,000 – 5$/MWh * 1,000,000MWh/TWh * 46.9TWh) * (10,750M$/9,900M$) = $1,357,866,162


End of Life Cost of Natural Gas Processing Plant:

= $1,357,866,162 * (75M$/10,750M$) = $9,473,484.848


End of Life Cost of Hydroelectric Plant:

EOL cost = 17 million $ per 22 MW capacity[30]

= 6,800MW/22MW * 17M$ = $5,254,545,455


Sample Total End of Life Costs per House in GTA : (Waste Removal)

= (3000.00 + 212.25 + 654.19 + 4.16)M$ * 0.464 * 0.16 / 1,965,935 * 1,000,000 = $146.7


The capital and end of life cost of hydroelectric, nuclear, fossil fuel and natural gas plants however can’t be all lumped into one payment as they are expected to last approximately 40 years[31]. Annual portion of average capital cost is equal to:



Total Average Annual Cost per house in GTA = $40.94 + $216.40 = $257. 34


By observing this data one can notice a lot of things about how the economics for electricity generation in Ontario break down. The capital costs involved in creating all three types of power plants are very high, which is due to the shear scale of these plants, making them a long term investment. Since the capital and end of life costs of the plants are spread over a long time period, it can be seen that the largest component of the annual cost per household is composed of the operational costs needed to run them. Nuclear and Fossil fuel plants have very high operating costs due to the cost and quantity of fuel required to run them, where as hydroelectric plants utilize water at no expense. Even though the fuel in nuclear power plants is approximately half as cheap as that used in fossil fuels[28], when you factor in the high price for decommissioning the nuclear fuel they are more evenly matched. One should also notice that as an annual expense, heating ones home with natural gas has a greater cost compared to electricity usage.

Economic Input Output Life Cycle Assessment[edit]

In order to make the total process easier to visualize, the individual Capital, Operating, and End of Life Costs for Hydroelectric, Nuclear, Fossil Fuel, and Natural Gas plants were summed together and converted into 1997 dollars on which the model is based. The Capital, Operating, and End of Life Costs were all broken down into sub-sections, which were assigned an appropriate fraction of the total cost of the four processes combined. It is with these costs, which are allocated to EIOLCA sectors that are used in the model to determine the complete environmental impact. The data used in this model was designed to analyze the cost for an individual household in the GTA. As a result, total costs were divided based on the appropriate fractions which would be allocated to one household based on its percentage use of the total production. Due to the fact that Capital and End of Life Costs are in real life distributed over the entire life of the various plants, a direct comparison with the operating costs would not be reasonable when looking at a one year time frame. To facilitate for this, the EIOLCA was done on the complete life, which was taken as 40 years[31]. The scope of this analysis was focused on Global Warming Potential (GWP) and Total Mass Releases of the four plants. Finally a sensitivity analysis was performed by varying values plus and minus ten percent in order to observe how the EIOLCA will react. The central results of the EIOLCA can be seen in Tables 1-14, 1-15, 1-16. By analyzing the data in these tables the impact over a 40 year life of using the Baseline option in a household can be determined. Below is a summary of the results found using the EIOLCA model (Chart 1-1, 1-2).

File:Chart 1-1 GWP ratings for power and heat generation from the grid.JPG
Chart 1-1 GWP ratings for power and heat generation from the grid +- 10%
File:Chart 1-2 Total releases for power and heat generation from the grid.JPG
Chart 1-2 Total releases for power and heat generation from the grid +- 10%
















These plots clearly show that the Operational period for the four processes being analyzed is the largest contributor to both the GWP and Total releases. Due to the fact that the Capital Costs and End of Lift Costs of a plant only make up approximately 8% of the total environmental impact, it can be seen to be much less of a stress on the environment than the operational costs, when looking at the full life. Conclusions that can be made from this data show that in order to significantly reduce the impact that Power Generation and Natural Gas Processing have on the environment, considerable research and development must be put into making the Operational Phase of these plants more environmentally friendly. Finally, the results of the sensitivity analysis performed on the data showed a linear trend in the reductions or increases of costs to the corresponding GWP and Total Release outputs.


Summary of EIOLCA Data

  • EIOLCA Capital Cost break down can be found in Table 1-8
  • EIOLCA Capital Cost Sensitivity Analysis Data can be found in Table 1-9
  • EIOLCA Operational Cost break down can be found in Table 1-10
  • EIOLCA Operational Cost Sensitivity Analysis Data can be found in Table 1-11
  • EIOLCA End of Life break down can be found in Table 1-12
  • EIOLCA End of Life Sensitivity Analysis Data can be found in Table 1-13
  • EIOLCA Model Output for Capital, Operational and End of Life Costs can be found in Tables 1-14, 1-15, 1-16
File:Table 1-8 EIOLCA Capital Cost Break Down.JPG
Table 1-8 EIOLCA Capital Cost Break Down
File:Table 1-9 EIOLCA Capital Cost Sensitivity Analysis.JPG
Table 1-9 EIOLCA Capital Cost Sensitivity Analysis
File:Table 1-10 EIOLCA Operational Cost break down.JPG
Table 1-10 EIOLCA Operational Cost break down
File:Table 1-11 EIOLCA Operational Cost Sensitivity Analysis.JPG
Table 1-11 EIOLCA Operational Cost Sensitivity Analysis
File:Table 1-12 EIOLCA End of Life Cost Break down.JPG
Table 1-12 EIOLCA End of Life Cost Break down
File:Table 1-13 EIOLCA End of Life Cost Sensitivity Analysis.JPG
Table 1-13 EIOLCA End of Life Cost Sensitivity Analysis
File:Table 1-14 EIOLCA Model End of Life Cost - GWP ordered.JPG
Table 1-14 EIOLCA Model End of Life Cost - GWP ordered
File:Table 1-14 EIOLCA Model Output for Capital Cost - GWP ordered.JPG
Table 1-15 EIOLCA Model Output for Capital Cost - GWP ordered
File:Table 1-15 EIOLCA Model Output for Operational Cost - GWP ordered.JPG
Table 1-16 EIOLCA Model Output for Operational Cost - GWP ordered







































Alternative 1 - Stirling engines[edit]

Functional analysis[edit]

A Stirling engine is very different from the internal combustion engines seen in cars. There is no gaseous exchange with the environment and there are no explosions within the engine. This makes the Stirling Engine very quiet. The engine requires an external heat source to function but this does not need be via combustion of a fuel but may be heat generated by solar cells or even decaying plants[32]. The gas used in the Stirling engine is of a fixed volume and is sealed within the engine (Usually Hydrogen). The principle used in a Stirling Engine is the understanding that if you raise the temperature of a fixed amount of gas in a fixed volume of space, you will increase its pressure and compressing a fixed amount of gas will raise the temperature of the gas. With these concepts in mind, we can examine the design of a basic Stirling Engine System.

A simplified Stirling Engine would consist of two cylinders. One cylinder is heated by an external heat source (such as fire), and the other is cooled by an external cooling source (such as ice). The gas chambers of the two cylinders are connected, and the pistons are connected to each other mechanically by a linkage that determines how they will move in relation to one another. In order to utilize Stirling Engines in a household, the Stirling Engines needs to be coupled with at least three other parts. The mechanical output of the Stirling Engine is connected to a multi-pole generator which converts the mechanical energy into electric energy and a heat exchanger with a supply of cold water is used as a cooler. Heat energy in the Stirling Engine is transferred to the water which is then distributed throughout the house. A furnace is also needed to maintain a high temperature at one of the pistons[33].

Efficiencies in a Stirling Engine are very high. In fact, theoretically, a Stirling Engine can achieve the Carnot Efficiency[7]. This is not the case in practice due to non-ideal properties of the gas and engine parts (e.g. Thermal conductivity, creep, friction etc.). The high efficiency of Stirling engines is mainly due to heat conservation. In practice, the electrical efficiency of Stirling engines is very low and they are used in households as substitutes for old boilers. Electricity is taken as a by product. Over the last 5 years, cogeneration for detached housing has been a great source of interest for development and today there are efficient systems available for use. An assessment was recently carried out by the Canadian Center for Housing Technology in late 2004 where they compared two households, one of which had a Stirling Engine based system installed. The CHP unit efficiency was 88% at total capacity[4]

The average household uses approximately 4200 kWh of electricity[34] and 20,000 kWh or thermal energy annually[35]. The study referenced above (Canadian Center for Housing Technology) used a target of 20kWh of electricity consumption daily using an engine capable of producing up to 40kWe[4]. This shows that the system is capable of meeting household requirements. Stirling engine systems available right now range from the Honda MCHP system which provides 3kW of thermal and 1kW of electrical power[36] to the Disenco HomePowerPlant (HPP) which can deliver 15kW of thermal and 3kW or electrical power[37].

A Stirling Engine system is expensive when compared to taking energy straight off the grid. It would cost approx. £2500 for installation (approx. $CAD 5000). However, this cost may come down to as much as £1500 ($CAD 3000) for multiple installations[38].

Streamlined Life Cycle Assessment[edit]

The streamlined life cycle assessment for a Stirling Engine led to a score of 65. The actual table is below followed by a stage by stage analysis of that score to further understand the assessment.

Table 2-1 Streamlined Life Cycle Assessment

Material Use

Energy Use

Solid Residue

Liquid Residue

Gaseous Residue

Sum

Pre-manufacture

2

2

2

2

2

10

Manufacture

2

2

3

3

1

11

Product Delivery

3

2

2

4

2

13

Product Use

3

3

4

4

3

17

Disposal/Recycle

3

2

2

4

3

14

Total

65


We now justify the scores for each of the five life stages of the product (Note: each score is out of 20)

Cells (1,1) – (1,5) The first life stage is pre-manufacture and a score of 10 was given. The Stirling Engine is made mainly of steel but also has brass and possibly graphite parts. Virgin materials are used but the use of recycled material is very possible.

Cells (2,1) – (2,5) Stage two of the cycle is product manufacture. This stage was given a total score of 11. The lowest scoring stressor in this stage was gaseous residues. The making of the engine would require casting of metal parts. Large amounts of fuel would be consumed to achieve high temperatures and therefore would release large amounts of harmful gases into the air. This same reason is responsible for low scores for materials choice and energy use.

Cells (3,1) – (3,5) The next stage for the life cycle is the product delivery and packaging and it got a score of 13. The lowest scoring stressors were gaseous residues, solid residues and energy use. The main reason for this is transport. Deliveries would require the combustion of fuel which would release toxic gases. Solid residues scored low because plastics may be involved in the packaging that may not be recyclable.

Cells (4,1) – (4,5) This brings us to product use which had the highest cumulative score of 17 out of 20. The only negative factor in this stage is natural gas combustion required to maintain a temperature gradient for the Stirling engine. It scores a perfect on solid and liquid residues as there are either none or minor amounts.

Cells (5,1) – (5,5) The last stage of the cycle is disposal/recycling. The Stirling Engine got a score of 14 for this stage. The Stirling Engine is a closed system. It contains a pressurised gas within and is therefore sealed tight. As it is made mainly of steel, it is recyclable though separating it into different components may be a difficult task and therefore it scores slightly on the lower end.

Financial analysis[edit]

Even though the environmental impacts of a given system may be considerably lower than its competitors, it is also important to analyse the economic aspects of the given system.

Table 2-2 Cost Analysis
Description Cost ($)
Capital Costs
Catalytic Heat Exchanger[39]

970.00

Multi-pole Generator[40]

1000.00

Furnace[41] 1000.00
Stirling Engine[42]

1000.00

Plastics[43]

100.00

Metal Casing[44]

300.00

Total

4370.00

Operational Costs
Gas Consumption

7857.91

Maintenance

250.00

Labor

250.00

Total

8357.91

Disposal (Worst Case Scenario: Landfill)
Transport and dismantling costs (5% of Capital cost)

218.50

Total

218.50

Disposal (Best Scenario: Recycling)
Transport and dismantling (5% of Capital cost)

218.50

Return from sale of scrap (2% of Capital cost)

-87.40

Total

131.10

Table 2-2 is a Cost analysis of the life cycle of a single Stirling Engine system. A number of approximations were made in order to calculate the values used in the table. First of all, we assumed that the Stirling engine employed in the system has an output of 6kW thermal energy. This allowed us to calculate the given cost of $1000[42]. The plastics were the second approximation made to account for sealants used to hermetically seal the Stirling engine. The cost of Hydrogen was excluded as it was negligible. We will now calculate the cost attributed to Gas consumption. The Freewatt MCHP system uses approximately 750 Therms of gas[45]. If each Therm is equal to 100 cubic feet of natural gas[46] we get a grand total of 2123.76 m^3 of gas. If we the take the cost of gas as 37 cents/m^3[47] we get (for a 10 year life span):

Cost of gas consumed = (0.37* 2123.76)*10 = $7857.91

Payback period

The costs of heating your household for ten years (20,000 kWh annually = 5.5kW[35]) and supplying it with all its electrical needs (4200 kWh annually = 1.16kW[34]) would be as follows (Note: 0.08 $/kWh of electricity[48] and 0.16kW of electricity needs to be purchased as the MCHP only provides 1kW and 1.16 kW[34] is needed every year)

Total Cost with MCHP = Cost of gas consumed + Cost of electricity needed from grid = 7857.91 + (0.16*3600*0.08)*10[A] = $ 8318.71

Total Cost without MCHP = Cost of gas consumed + Cost of electricity needed from grid = (4134.25*.37)*10[B] + (1.16*3600*0.08)*10[A]= 15289.325 + 3340.80 = $ 18630.125

Total savings = 18630.125 – 8318.71 = $ 10311.415[C]

Annual savings = 10311.415/10 = $ 1031.1415

Sale Price = 4370*108/100[D] = $4719.60

Payback period = 4719.60 / 1031.1415 = 4.57 years.

Notes:

[A] (Power required * Conversion factor for energy * Dollars per kWh) * Lifetime

[B] (Volume of natural gas in m^3[49] * Dollars per m^3) * Lifetime The volume of natural gas used is a very rough estimate. The value referenced is from a survey done in 1997. The overall gas used by a household can be modelled as constant.

[C] (Total Cost without MCHP – Total Cost with MCHP)

[D] (Capital Cost * Mark up)

We assume a conservative yet common mark up of 8%. The payback period is reasonable and will fall as the price of Stirling Engine systems falls and the systems become capable of producing more power with greater efficiencies.

Economic Input Output Life Cycle Assessment[edit]

Over the life of the Stirling Engine System many processes lead to negative effects to the environment. It is important to be able to quantify these effects in a manner that can be easily communicated to others. This is done by performing an Environmental Input Output Lifecycle Assessment on the Stirling Engine System. The product is first broken down into smaller parts and each part is associated with a particular sector. The sectors are then given a dollar value and the environmental effects due to that particular sector are found (The tool used to generate this information can be found at [1]. Also note that dollar values must be in 1997 dollars i.e. the amounts must be adjusted to 1997 dollars using the CPI[50])

Sensitivity Analysis

In order to allow for variances in the future, it is prudent to couple the EIOLCA with a sensitivity analysis. The sensitivity analysis is merely taking into account the worst and best possible scenarios in terms of costs incurred. We will do this by adding or subtracting 5% to 20% to/from the values we got from our Cost Analysis (Table 2-2) as is appropriate e.g. the costs of manufacturing a Furnace will not vary as much as a Stirling engine and the price of gas is more likely to rise than to fall. Table 2-3 (below) is an excerpt from an EIOLCA. Two such EIOLCAs were conducted (Best and worst case) and these can be used to generate charts. These charts can illustrate for example the GWP emissions or the total land releases over the lifetime of the Stirling Engine (Operational costs could be modelled as the Natural gas distribution sector). On such charts it is clearly visible that the total GWP emissions and releases over a ten year life are the highest during the use phase however, it only accounts for 0.1% of total releases (which are mainly generated in the Manufacturing phase).

Table 2-3 Environmental Input Output Life Cycle Assessment

Sector

Total Economic (mill $)

SO2 (mt)

CO (mt)

NOx (mt)

GWP (MTCO2E)

Total (TJ)

Total Releases (kg)

Total for all sectors

0.007

0.006

0.023

0.005

2.36

0.028

6.37

221100

Power Generation and supply

0

0.004

0

0.002

0.688

0.008

0.141

331111

Iron and Steel mills

0

0

0.004

0

0.419

0.005

0.268

332410

Power Boiler and Heat exchanger manufacture

0.002

0

0

0

0.151

0.003

0.167

484000

Truck Transportation

0

0

0.09

0

0.132

0.01

0

562000

Waste management and remediation services

0

0

0.001

0

0.109

0

0.049

331312

Primary aluminum production

0

0

0.002

0

0.097

0

0.04

212100

Coal mining

0

0

0

0

0.057

0

0.006

327410

Lime manufacture

0

0

0

0

0.045

0

0.001

211000

Oil and gas extraction

0

0

0

0

0.038

0

0.003

481000

Air transportation

0

0

0

0

0.032

0

0

Alternative 2 - Fuel cells[edit]

Functional analysis[edit]

The first fuel cell was invented by Sir William Grove in 1839[51]. A fuel cell system is an electrochemical energy device that produces electricity from a chemical fuel source and a system of chemical reactions. Typically in a fuel cell hydrogen gas is introduced at the anode on one side of the fuel cell while oxygen from the air in the atmosphere is introduced to the cathode located on the opposite side of the fuel cell[52]. A platinum catalyst is used at the anode to split the hydrogen fuel into positive hydrogen atoms and electrons. The electrolyte membrane only allows the positively charged atoms to flow through the fuel cell, forcing the electrons to flow through an external wire system to the cathode, consequently creating an electrical current.


The final step in this system occurs at the cathode where the positively charged hydrogen atoms and electrons combine with the oxygen to form water, which is one of the byproducts of the fuel cell system in addition to heat generated by the chemical reaction and electricity[52]. A illustration of the fuel cell system can be seen below[52].


There are many fuel cell types that can be considered for use in micro co-generation. These include: metal hydride, Electro-galvanic, Direct formic Acid, polymer/proton exchange membrane or hydrogen, solid oxide, alkaline, molten-carbonate, phosphoric-acid, direct-methanol, zinc-air, reversible, direct carbon and planar solid oxide[51][53]. In typical micro cogeneration applications polymer/proton exchange membrane or solid oxide fuel cells are used[54]. It is important to note that one of the key flaws in using fuel cell as a micro cogeneration system is heat extraction, as it is evenly distributed throughout the system and can not be extracted at a well defined point in the system, leading to increased fuel cell system cost[55].


Fuel cell systems have been used in space and defense systems applications since the 1950’s and have proven to be an efficient and reliable power generation system.[3]. Thus they are a safe and reliable system to implement inside residential homes.


A fuel cell systems consists of almost zero emissions, negligible nitrogen oxide and sulphur oxide emissions, and is a very quiet system where the only noise comes from the exhaust fan[56]. The electrical efficiency of the system can reach 40-45% and whit heat the combined efficiency can reach 90%[56]. The system life time is expected to reach 40000 hours or 10 years in the near future.


The fuel cell system is thus an effective micro co-generation system that can achieve high overall efficiency and is very environmentally friendly. Unfortunately it will be seen that is also the most expensive option available on the market today at prices ranging from $3250 to $4800 per kilowatt[56].

Streamlined Life Cycle Assessment[edit]

1,1: Some virgin material like platinum and catalysts need to be used while others like metal for product casing and structure can come from mostly recycled material.

2,1: Mainly good material choices, some lead solder waste and some catalysts need to be carefully handled during manufacturing to prevent contamination.

2,2: Energy use during the manufacturing is very high.

2,5: Small amounts of volatile hydrocarbons emitted along with other gaseous residues from the metal smelting and manufacturing processes.

3,3: Packaging during shipping is almost at the optimal amount due to the usually rectangular shapes of the products.

3,4: Negligible amount of liquids are generated by packaging and during shipping assuming there are no major unforeseen events like oil spill of transport ship.

4,2: The product is very energy efficient and natural gas delivery system is currently available to almost every household.

4,4: Fluid systems sometimes leak and cause fuel cell to saturate.

5,4: Liquid residues of saturated fuel cells difficult to recycle.

5,5: Recycling involves the open burning of residues for some product components.

Financial analysis[edit]

The cost analysis of a hydrogen fuel system is done in two stages. The first stage is the part cost and is outlined by Table 3-1. The second part of the cost analysis is capital cost, operation cost and disposal cost approach and this one can be found in Table 3-2. Finally the third method of cost analysis that will be conducted will be seen in Table 3-3 as a list of major materials used and their prices on today’s markets. After the presentation of the three data sets a comparison will be made on return to scale based on initial investment.


Table 3-1 Analysis of a Reformate Based System Fuel Cell.


The typical natural gas system or direct hydrogen gas system would have almost no fuel processor costs and reduce the cost of all other components including the fuel cell stack. The price of the fuel cell micro-cogeneration 10kw system is estimated to be 24000 dollars based on the fact that a 50kw system is estimated to be 30000 dollars for cars and that stationary fuel systems should cost on average 10 times more then a mobile one[61][62].

File:Table 3-2.jpg
[64][65]Cite error: Closing </ref> missing for <ref> tag [66][67][68][69]

Table 3-2 displays the average cost of about $ 38339.47 for a fuel cell system. Table 3-3 displays the cost of some of the most important materials used in the system. The above data coupled with the payback analysis below clearly shows that fuel cells are not currently economically viable and this is true as advances are constantly being made like research into replacing platinum with palladium which is worth a quarter of the value of platinum[73]. This shows that the cost analysis conducted is very volatile to technologies being introduced.


An analysis can be done to see if a fuel cell is a good investment and economically viable. Typically the costs of heating a household for ten years apply to 30,000 kWh annually = 8.33kW[74] and the cost of supplying it with all its electrical needs apply to .4200 kWh annually = 1.16kW[75]).


A typical fuel cell system produces about 40% electricity and 50% heat[56] the energy needed will be met while some heat still need to be bought from the current baseline alternative. A profit can be made by selling the excess electricity of (4kw-1.16kw)*8760 hours/year* $0.045/kwh*10 years[76]= $11195.28. A further fuel cell cost due to the need to purchase the heat energy still need to complete the home is ((8.33kw-5kw)/11.01kwh/m^3)* 8760hours/year * $0.37/kwh*10years = $9803.08.


Thus a total of

in energy profits is realized with the fuel cells over their lifecycle. To this value the cost of the gas used by the system is subtracted, bringing overall savings to $139.22/year -($1215.57/ 10 years) = $17.66/year. Finally to this value the cost of using the base line alternatives is added. $17.66/year + ((30000kwh/year)/(11.11kwh/m^3))*$0.37/kwh+(3650kwh/year* $0.045/kwh) =$1181.01/year in savings. It can clearly be seen that there is no payback period for this system as savings per year on the magnitude of $4000+ would be needed. Thus severe manufacturing and technological changes still need to occur for fuel cell micro-cogeneration systems to be economically viable.


It is however important to note that while a fuel cell currently does not provide a payback of the investment the environmental economical results of using fuel cells on a large scale can create a favourable return on investment due to the decrease of pollution cause by using the fuel cells alternative over the current baseline.

Economic Input Output Life Cycle Assessment[edit]

The EIOLCA (economic input/output life cycle analysis) for a fuel cell based microcogeneration system was conducted using the model found at www.eiolca.net. This model is based in the year 1997, thus the dollar amounts of each sector used in the EIOLCA were adjusted based on the consumer price index[76]. A conversion factor from 2008 to 1997 was used, taking into account that this is an approximate conversion due to the fact that some of the data that was used in the analysis of this alternative dates back to before 2008. Table 3-5 represents the breakdown topics used in conducting The EIOLCA. These topics are based on the fuel cell component breakdown that can be seen in tables 3-2a, 3-2b. The total EIOLCA input cost was $16178.35 which is near the expected value of almost equal of 24000$ considering most of the major components of a fuel cell system (over 60% of product cost).


The sensitivity cost analysis conducted in Table 3-6 in the fuel cell appendix displays that a pessimistic outlook of fuel cell manufacturing will cause the value of the economics input in the analysis to rise about 10% due to reasons like continuation of no mass production and the rise of commodity prices like platinum and nafion. In contrast a positive outlook for the alternative would only see an economic input value drop of about 10% due to the low volume manufacturing and the time taken to introduce to market evolving fuel cell micro-cogeneration systems. Charts 3-1 and 3-2 on the next couple of pages show the GWP (global warming potential) and total toxic releases plotted for one residence in terms of capital costs, operational costs and end of life costs. Note that end of life costs contribute the least while capital and operational costs contribute almost equally for toxic releases. For GWP however, operational costs contribute the most due to the continuous use of natural gas. These charts were constructed for a ten year life of the fuel cell.


The EIOLCA Results comparison is done in appendix 3-1, where all of the major components of an EIOLCA analysis are displayed. These include the global warming potential, total releases, total energy used, metric tons of carbon monoxide, sulphur dioxide and nitrogen oxides economic supply chain purchases required to produce one fuel cell micro-cogeneration systems.

Appendices and details[edit]

Appendix 1: Baseline[edit]

Appendix 3: Fuel cells[edit]

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