Design for the Environment/Residential Micro-cogeneration

This page is part of the Design for the Environment course As the demand for energy grows and the reduction of greenhouse gas emissions becomes more important, cogeneration (combined heat and power) solutions emerge as an immediate solution. Considering that the residential sector accounts for 17% of Canada’s energy utilization, reducing the electrical demand could alleviate the need to use non-renewable energy sources and develop new power generation facilities. Residential micro-cogeneration systems act as an alternative or supplement to provide electricity and heat to a home by burning fossil fuels with net efficiencies of up to 90%. The energy obtained from these methods, will have lower greenhouse gas emissions than that from typical fossil fuel electricity generating stations running at an average of 30 – 35% efficiency.

This article focuses on the investigating the practicality of implementing cogeneration units into a new residential subdivision in Brampton, Ontario. The baseline alternative is to purchase grid electricity from Hydro One Brampton and natural gas from Direct Energy to be used in a conventional furnace and water boiler. The two cogeneration alternatives being investigated are the Stirling Engine and the Proton Exchange Membrane Fuel Cell (PEMFC). The three alternatives are compared based on their ability to produce 1.96kW electrical power and 7.86kW thermal power to a single home. The recommendation to the developer of the residential subdivision is based on functional, environmental, economical and social factors.



Project Information

 * MIE315 Section 1 Group 1
 * Andrew Lui (Andrewlui)
 * Kun Liang (liangkun)
 * Damon Quan (DamonQuan)
 * Alain Liu (liualain)

Highlights and Recommendations
Functional The capability of each alternative to meet the required energy demand is undoubtedly the most important aspect of this analysis. The baseline alternative is not limited with respect to the obtainable quantities and can therefore meet the functional requirement of 1.96kW electrical and 7.86kW thermal power. Both of the cogeneration alternatives can not meet the electrical power requirement and must therefore supplement grid power. In addition, the Ebara-Ballard PEMFC can not meet the thermal demands and must supplement extra thermal power. The two cogeneration alternatives run on natural gas and therefore would not require little change to the typical household infrastructure to be implemented. While all the alternatives are capable of meeting the functional requirement, the reliance of the cogeneration systems on the baseline without any advantages (except for backup power during blackouts) makes the simplest solution the superior one. Based on functional requirements, the baseline provides the simplest and most reliable solution.



EIO-LCA The EIOLCA results of the three alternatives show similarities with respect to the stages which pose the greatest environmental concern. The resource provisioning stage which includes the production and distribution of electricity and natural gas, accounts for between 40-70% of ongoing GHG emissions. Observing the relationship between the GWP due to electricity generation and natural gas distribution, the environmental contribution of lowering the electrical demand seems to be generally negated by the increase in demand of natural gas. The process implementation phase is representative of the environmental effects of the capital cost of each system. While there are effects of implementing the furnace and water boiler, they are neglected because the cogeneration alternatives require them as supplements. The manufacturing of the fuel cell not only has less of an environmental impact than the Stirling engine, but it also has twice the operational lifespan. The main concern in the process operation phase is the GWP due to the burning of natural gas. Since the Stirling engine generates both electricity and heat from natural gas, it burns about 50% more gas and results in about 50% more CO2 emissions when compared to the baseline. Even though the emissions of the fuel cell itself is low, the emissions from the steam reforming to extract hydrogen and supplementary thermal power generation end up resulting in a higher GWP than that of the baseline. In addition to the baseline having the lowest GWP in this phase, it also has the lowest on-going (resource provisioning + process operation) GWP and NOx emissions while having only slightly higher SO2 emissions. From the environmental aspect, using grid electricity and natural gas heating alone is the most favourable on-going solution. Not only does it result in the lowest net GWP and toxic relaeses, but the implementation of the baseline has the least complexity. It can be safely concluded that the baseline is the currently the most environmentally friendly of the available options for this situation.

SLCA The results from the streamlined life cycle assessments of the three alternatives yield similar findings. The resource provisioning stages are consistently scored low in all fields because of the impacts involved in obtaining the natural gas required to power all of the alternatives. The process implementation phase is scored in a similar way due to the need to use mostly metal in the manufacturing of the alternatives. In the case of the PEMFC, in which platinum is needed, the material choice is the main problem. The operation phases are generally scored high because the principal concern is the gaseous residues from burning natural gas. The fuel cell appears to be the most environmentally friendly based on its total sLCA score primarily due to the fact that the operation has very low emissions.

Economics The capital cost of the baseline has not been considered since all the alternatives need to have it. As an additional cost to this however, the WhisperGen Stirling engine requires about $6100 CAD and the Ebara-Ballard PEMFC requires $11600 CAD. Whilst the PEMFC seems impractical at such a high cost, it has twice the lifetime of the WhisperGen, making the WhisperGen the most expensive alternative (assuming continuous replacement) in terms of capital costs. As shown in Figure 1, the annual savings obtained from using less electricity is outweighed by the cost of extra natural gas and maintenance of the cogeneration devices. This is largely due to the low cost of electricity in Ontario created by government subsidies. The summarized data shows that the baseline not only has a lower capital cost but also has a lower annual operating cost. The baseline is therefore the most economically viable alternative to use.

Societal While the two cogeneration alternatives provide a sense of preparation for an upcoming blackout, they come with many hassles not seen by the baseline alternative. Both the WhisperGen and the Ebara-Ballard PEMFC give off background noise. While the noise levels are stated to be relatively low, the baseline alternative has no noise, which is preferable. The lifespan and maintenance of the alternatives varies significantly. The WhisperGen requires maintenance every 1000 working hours and has a short lifespan of 2.3 years (running all the time). The Ebara-Ballard PEMFC has twice the lifetime of the WhisperGen (running all the time), making its apparent value higher. The baseline has the least maintenance that has to be done by the consumer, and the lifetime of the furnace and boiler range from 10 – 25 years.

Final Recommendation Based on the obtained data and the results summarized above, the baseline is the most promising alternative from the environmental, economical and societal aspect. From the functional perspective, none of the options seem to have a specific advantage. The Ebara-Ballard PEMFC would be ranked second and the WhisperGen Stirling engine would be the least practical option.

Baseline: Grid electricity & Natural Gas water heater, furnace
The base line, which is grid electricity and natural gas heating, is to be analyzed and compared with the alternatives. Grid utilities has been in service for many decades and is capable of reliably providing continuous electrical energy flow of 1.96KW and 7.86KW thermo energy flow as required. The main advantage of grid utilities are their wide coverage. In addition, the energy lost during transmission is very small .For grid electricity, the energy lost is only 7.2% during transmission. The main concern of the baseline is the pollution and GWP resulting from electricity generation and natural gas extraction and combustion. In fact, power generation plants release large amount of pollutants and “OPG (Ontario Power Generation) [is] Canada’s largest individual air pollution source in its coal fired generating stations.”. Furthermore, since the grid lines are interconnected, when the energy sources have problems, many consumers will be affected due to cascading failure.

Alternative 1: Stirling Engine


The WhisperGen on-grid Stirling engine is capable of providing up to 1000W of electrical power and 7.5-12kW of thermal power. While the thermal output meets the functional requirement but the electrical component does not, therefore additional electricity must be supplied via the grid. It is assumed that the Stirling engine is to run 24 hours a day. The Stirling engine is a closed system engine and operates between a temperature differential. The difference in temperature drives a piston inside the engine that is confined with a working fluid which in this case is compressed nitrogen. Also most types of Stirling engines have the bearing and seals on the cool side of the engine thus reducing lubricant usage and reducing maintenance. Furthermore, the Stirling engine does not produce a lot of noise and runs quietly without any air supply. On the other hand, the Stirling engine requires heat exchangers that operate under high temperature differences resulting in specific material choice. Large radiators are also required to increase thermal efficiency.

Alternative 2: PEM Fuel Cell
The Proton Exchange Membrane Fuel Cell (PEMFC) is a technology in its early commercial stages before cost effective production. The Ebara-Ballard Mark1030 v3 unit is currently one of the fuel cell units in field testing in Japan, with subsidies provided by Japan’s Ministry of Economy, Trade and Industry (METI). While providing at rated, 1kW of electric and 1.52kW thermal power (overall efficiency is 74.5%), it can not meet the electrical or thermal requirements alone, therefore additional electric and thermal power must be supplemented via the baseline. The principle behind the PEMFC’s operation is reverse electrolysis of hydrogen gas. Natural gas (primarily composed of methane) is reformed under heat and a catalyst (platinum or its alloy), and is converted to hydrogen gas and carbon dioxide. The hydrogen is then separated from the electron by the water filled polymer membrane (Nafion), again in the presence of the catalyst, platinum. The electron is used to generate DC power which is converted into AC for home use. The amount of water within the membrane is critical in producing maximum power, which is electronically controlled and supplied by the reverse electrolysis process and the house’s water supply. The most delicate component of the fuel cell is the Membrane Electrode Assembly (MEA), which houses the platinum catalyst and Nafion membrane. Platinum is easily susceptible to CO contamination and the membrane’s efficiency is affected by dehydration, or other molecules puncturing the membrane. Thus it is only rated for a service life or 40,000 hours.

Economic Input Output Life Cycle Analysis
Economic Input Output Life Cycle Analysis (EIOLCA) is an excellent tool to analyze the environmental impacts of a sector. However, during the primary and secondary process phase, it was impossible to EIOLCA thus a hybrid approach was used. Each alternative was assumed to run for 24 hours a day for a span of one year.

Baseline: Grid electricity & Natural Gas water heater, furnace
The baseline EIOLCA is split into two different sections, gridline electricity and natural gas. Also, the resource provisioning stages in both sections are accounted for when calculating the distribution of natural gas and grid electricity.

Grid electricity:

Process Implementation: The implementation process of a power plant is neglected because it is not in the scope of a house hold. In addition, the environmental impact for installation of circuit breaker and ground wire for a house is considered insignificant. Furthermore, since both alternatives use the grid electricity, for the purpose of comparison, the environmental impact of manufacturing electrical components is neglected.

Primary and Secondary process: The environmental impacts are due to the delivery and power generation of 17.2MWh of grid electricity annually.

End of Life: The disposal of electrical components at end of their service life will not produce significant environmental impacts therefore negligible. In addition, the electrical components can be recycled through Region of Peel, a waste management company in Brampton, which contributes to reduction of virgin material use.

Natural gas:

Process Implementation: Similar to grid electricity, natural gas distribution facilities are shared among many homes, the environmental impact due to a single home is negligible. In addition, the environmental impact of installing natural gas water heater and space heating furnace are very small and is also negligible. The environmental impacts caused by manufacturing of water heater and space heating furnace can be obtained from EIOLCA.

Primary and Secondary process: This phase consist mainly extraction, distribution and combustion of natural gas. The environmental impacts of natural gas extraction and distribution can be modeled using EIOLCA but the environmental impact of burning natural gas is obtained from.

End of Life: The disposal of natural gas station and natural gas distribution system is not residential level. Also, the environmental impact due to disposal of natural gas water heater and furnace are not significant. Thus, the pollution from end of life is negligible.

Results: The GWP from primary process is significantly greater then resource provisioning and process implementation where 35% is from power generation and 65% from combustion of natural gas. Furthermore, during process implementation, toxic releases are greater than GWP but still insignificant compared to the GWP in the primary process.

Alternative 1: Stirling Engine
EIOLCA accounts for mining minerals and transportation when analyzing the manufacturing process. Thus the analysis of resource provisioning and process implementation phase was grouped together.

Resource Provisioning and Process Implementation: The WhisperGen Stirling engine is to run on natural gas and the distribution and extraction of natural gas was taken into account. Also the WhisperGen Stirling engine is composed of a burner module, stirling engine, generator module and microprocess controller. It was assumed the cost of a WhisperGen Stirling engine is divided into 60% for the engine, 20% for the burner module, 15% for the generator and 5% for the microprocessor.

Primary and Secondary Process: The use phase consists mainly of burning natural gas and supplementing the difference in electrical output with gridline electricity.

End of Life: The WhisperGen Stirling Engine is composed of mainly steel and aluminum, it is assumed that at the end of life it is going to be recycled. With this assumption, the environmental impacts are mainly transportation from the product to the recycling centre. The energy input to disassemble the engine and melt the metals to recycle and reuse. These emissions are assumed to be insignificant compared to natural gas distribution and primary process of the WhisperGen.

Results: As shown, GWP during the primary process stage with 30% from power generation and 70% from combustion of natural gas. Also, GWP from resource provisioning is approximately 31.5% of GWP during primary process. Process implementation does not produce as much GWP but significantly larger amounts of pollutants and toxic releases as the other two stages.

Alternative 2: PEM Fuel Cell
Resource Provisioning: Using the suggested electric and thermal demands for each Toronto household, the excess electric and thermal power demands for a Brampton household using an Ebara-Ballard unit at the average load, is estimated to be: electricity from the grid: 8.42 MWhr/yr and total natural gas is: 54.34 MWhr/yr.

Process Implementation: The target price for 2008 has been ¥1.2 million ($11 400 USD) [29, 30]. The component cost distribution is broken down as follows: Fuel Cell Stack (65%), Reformer (25%), Heat exchanger/Water System (5%), and Control Electronics (5%).

Primary and Secondary process: The operation of the fuel cell requires inputs of water, oxygen gas and natural gas. The unit would be with water initially and any additional water would be taken in from the utilities. Although it automatically regulates the amount of water needed for the fuel cell, its assumed that the cost would be insignificant compared to the total water usage of the household.

End of Life: With information quoted from Ballard, most parts of the fuel cell are reusable or recyclable. Also, there have been developments in recycling the Nafion membrane at the end of the unit’s life cycle. Regardless, if there are any laws to enforce recycling of decommissioned units, there is great incentive to recycle the unit, especially the MEA subassembly, which would reduce costs and environmental impacts dramatically. A rough estimate was done to simulate the effects of recycling platinum and Nafion, two of the most expensive and highly recyclable materials.

Results: Toxic releases from PEM are higher than the baseline method and WhisperGen Stirling engine with a total of 15.43kg of toxic releases mainly from process implementation and primary process. This is because the mining sector has a large influence on land release due to the fact that there is a growing demand for platinum and technologies for loading the catalyst is still being optimized.

Streamlined Life Cycle Analysis
SLCA was performed on the different options for home energy usage. The guidelines for assessing each life cycle stage and environment stressor can be found in ‘Streamlined Life Cycle Analysis’ by T. Graedel. The Resource Provisioning stage represents the acquisition of resources to generate energy to meet consumer demand. Process Implementation would involve the transmission and the manufacturing of equipment involved in generating energy (Power plant, transmission lines, WhisperGen, Ebara-Ballard Mark1030 v3). Primary Process Implementation involves the actual generation of energy, such as the use of Uranium or the combustion of natural gas, while Secondary Process Implementation involves the operation of sub-assemblies indirectly involved in the production of electricity or heat. Lastly, the End of Life stage represents the disposal phase of such equipment or infrastructures.

Baseline: Grid electricity & Natural Gas water heater, furnace
The SLCA for generating electricity and natural gas for home use are treated as two different environmentally responsible processes. The final combined score is calculated using weights given by the percentage of their annual energy consumption (20% for electricity and 80% for thermal). It is shown through the subtotal that the Resource Provisioning stage has the most environmental impact for both the electricity and natural gas generation. Both utilize non-renewable resources such as uranium for nuclear power, and natural gas is extracted with equipment running on fossil fuel. Also, there are significant amounts of residues released during both processes . Also, during the process operation stage, coal is used for electricity production in coal power plants, which emits a lot of pollutants such as SOx. In EIOLCA, similar results are obtained. For natural gas, it can be seen that resource provisioning (natural gas extraction from mining), process implementation (construction of infrastructures, water heater, and furnace), as well as natural gas combustion produce significant amounts of pollution. The disposal of infrastructures for natural gas distribution and electricity generation uses large amount of energy and release significant amounts of solid and liquid residues similar to the implementation process . Overall, the natural gas process scored slightly higher in all categories, except for the primary phase when some emissions are given off when natural gas is burned. The use phase for electricity is not significant as it produces no direct emissions from the usage of electricity. The adjusted total score of these two process is 51.6.

Alternative 1: Stirling Engine
Life stages that could potentially present itself as environmental liabilities are Resource Provisioning and Process Implementation stages. Mining metal ores and producing steel creates a lot of residues such as slag and bauxite residue and also, producing metal alloys in factories creates a lot of gaseous residues, as well as red mud and sludge.

Comparing these results to the EIOLCA, it was predicted that the process implementation stage would have a lot of emissions and high residues, but in fact the manufacturing phase of a WhisperGen does not emit as much GHG compared to other stages such as resource provisioning and primary process. Additionally, SLCA is less accurate than EIOLCA due to lack of quantifiable information and the use of personal opinions. The total score for the life cycle of a Stirling engine is 51.

Alternative 2: PEM Fuel Cell
Although natural gas and hydrogen fuel cells have been publicly viewed as a “clean” fuel, the burden of the environmental impacts and pollution are in the other life cycle stages. Both SLCA and EIOLCA clearly show that there are emissions related to the processing of natural gas, similar to the results in the other alternatives. The scores for the use phase of the PEMFC are relatively high, since the process of converting natural gas to hydrogen is fairly clean and the usage of hydrogen in the fuel cell is very direct. But it is still a non-renewable resource and would still have CO2 emissions from reforming. In the process implementation and disposal stage of the PEMFC, there comes great concern of how much virgin material, specifically platinum and Nafion, are used for each unit of PEMFC. With demands and prices for platinum rising, it is vital that platinum and Nafion be recycled within a closed loop, due to the impacts of mining and chemical processing . The total score for the life cycle of a PEMFC is 59.

Direct Cost
The direct cost is cost paid by the consumers and it is one of the main factors that can influence the consumer’s decisions. The direct cost analysis is conducted based on the average energy consumption of a house in Brampton, Ontario. As mentioned previously, the annual electricity consumption is 17.2MWh and the natural gas consumption is 68.8MWh. All costs are converted to Canadian Dollars.

Baseline (Grid electricity and natural gas water heater, furnace) The long product life and maintenance-free equipments provide economic advantages.
 * The life expectancy of the water heater and furnace is approximately 15 years.

Alternative 1(Stirling engine): The short product life is an economic disadvantage.
 * The life expectancy of the Stirling engine is 2.28 years.

Alternative 2: (PEM Fuel cell)
 * The life expectancy of the PEM fuel cell is 4.6 years . One of the major costs associated with PEMFC is the expensive initial cost, which is an economic disadvantage.

According to the cost graphs above, clearly, it can be seen that the baseline has lowest capital cost per product life year compared to the alternatives. In addition, the baseline has lower annual operating cost compared to the alternatives. Thus, economic wise, the baseline is the recommended option for the consumers.

Indirect Cost
The indirect costs include environmental protection and health care costs from the pollution paid by the government. These costs are directly proportional to the pollutant emission. Based on the EIOLCA and SLCA, it can be concluded that the baseline, which is conventional grid electricity and water heater, furnace, option produces slightly higher pollutant emission than the Stirling engine option, while the PEM Fuel Cell option produces a lot less pollutant emission. Therefore, the PEM Fuel Cell option is expected to have lower indirect cost compared to the conventional grid electricity and natural gas water heater, furnace and Stirling engine. However, this result will not have significant influence on consumer’s decision making because indirect costs are not paid by the consumers

Operating Environment
The size of a WhisperGen is 0.48m x 0.56m x 0.84m (w x d x h), this is about the size of an average dish washer. Furthermore, during operation it produces a noise level of 63dB which is about the average noise level of conversational speech or business office. Depending on the lifestyle of the consumer, the noise level might deter consumers. Sound from running the PEMFC would not pose a problem as it does not contain any moving mechanical parts; only the fan or compressor can be heard. The PEMFC unit is less than a meter tall and can be placed indoors or outdoors with the hot water tank.



Consumer Motivation
In Canada, the nominal price of the grid electricity is increasing, the real price shows a decreasing trend, so the cost of grid electricity and natural gas are affordable by most consumers. The WhisperGen unit has a life span of 2.28 years (20000 hrs) and is sold for £3000 ($6,005 USD). The Ebara-Ballard unit has a predicted lifespan of 4.6 years (40,000 hrs) and costs ¥1.2 million ($11,400 USD) . The question of “is it worth it?” might come up due to the low life span of the both cogeneration units and whether or not it offers significant cost savings over the traditional system.

Government Intervention
Currently in Ontario, nuclear power has been subsidized by the federal government for a long time. The result of these actions artificially made the price of electricity cheaper than what it actually costs. However, the usage of cogeneration options for residential use should rise in the foreseeable future. With heavy marketing campaigns to promote the “clean” side of using natural gas, against higher electricity prices, micro CHP would be a very attractive option, as currently it is done in Japan. Also, subsidies from the government would greatly promote and increase awareness. Currently, Japan’s Ministry of Economy, Trade and Industry (METI) is leading a program to subsidize fuel cells in Japan for the average consumer before it reaches a mass production stage. A good example is the heavy involvement from METI to support PEMFC companies to meet demands from the Kyoto Protocol. From 2004 to 2008, the price of the Ebara-Ballard unit has decreased approximately nine times ($95,000 to $11,400 USD) .