Fuel Cell Report

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FEASIBILITY STUDY FOR FUEL CELL RURAL

ELECTRIFICATION IN SCATTERED AND CLUSTEREDCOMMUNITIES

Final Report for Energy Systems IIProfessor: Dr. Barriga

Submitted by: Stephen WeltyUniversity of Calgary


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Table of Contents

Table of Contents................................................................................................................ 2

List of Figures .................................................................................................................... 2

Introduction........................................................................................................................ 3

Fuel Cells............................................................................................................................ 3

Fuel cell operation ......................................................................................................... 3

Efficiencies ..................................................................................................................... 5

Applications ................................................................................................................... 6

Fuels and Methods ............................................................................................................. 7

Natural Gas.................................................................................................................... 7

Other hydrocarbons ...................................................................................................... 8

Hydrogen........................................................................................................................ 8

Life cycle analysis considerations...................................................................................... 8

Economic Analysis ........................................................................................................... 10

Establishing the demand cases ................................................................................... 10

Stand alone power generation.................................................................................... 10Clustered Community ............................................................................................... 10

Local production of fuels for fuel cells ...................................................................... 15

Waste Heat and Exhaust Recovery.................................................................................. 18Conclusions ...................................................................................................................... 19

Bibliography ..................................................................................................................... 21

List of Figures

Figure 1: Schematic for the operation of PEM and Phosphoric Acid fuel cells................ 4

Figure 2: Comparison of efficiencies for ideal heat engines and Fuel Cells with a Carnotlow temperature of 30C....................................................................................................... 6Figure 3: Greenhouse Gas emissions of energy options. ................................................... 9Figure 4: The effect on UCE for different values of installed costs for the SOFC system15 Figure 5: Waste heat and water exhaust for different energy generation levels. ............ 18


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Stephen Welty Page 3 5/26/2002

Introduction

Currently, there are roughly 2 billion inhabitants of this planet that do not have access toelectricity. In the mind of modern western man, electricity is a basic need and the lackthereof implies a significantly lower quality of life. To accommodate those of the

roughly 2 billion people without electricity that would like to gain access to the westernway of life, a number of rural electrification schemes have been devised both from theprivate sector and the government. The most common way to provide inhabitants withelectricity is with the electricity grid. However, this is not always possible oreconomically feasible and other distributed energy generation methods have beenemployed. This paper is aimed at evaluating a relatively new technology for thisapplication.

This study has as its main goal to evaluate different fuel cell technologies that would besuitable for electricity generation in small off-grid communities. The study will considerboth scattered settlements and clustered settlements where two different power generation

schemes will have to be considered to be economically feasible. Fuel cells can useavailable hydrocarbons ranging from methane to diesel but different methods will have tobe used for different fuel supply scenarios and these will be discussed.

Additionally, fuel cells can be combined with renewable energy that provides irregularsupply of energy. In this case energy would be stored in hydrogen through electrolysisand that hydrogen would be supplied to the fuel cell to meet electricity demand.Essentially, the proposition is that fuel cells could replace batteries in renewable energysystems if it is economically viable.

An important possible advantage of fuel cells is supplying clean drinking water for the

community. A number of fuel cells have wastewater exiting the system as steam, whichcould be condensed and used as relatively pure drinking water. This possibility willdepend on the fuel cell technology used and the purity of the fuel supply.

In this study a simple economic analysis tool was applied to give a first order view of theeconomics of the fuel cell generating system compared with other available generatingsystems. A brief view of the life cycle analysis of fuel cells will be discussed todetermine its real environmental impacts compared with other technologies as well as todetermine its economic feasibility in terms of reliability, durability and replacementcosts.

Fuel Cells

Fuel cell operation

A fuel cell is an electrochemical device, which produces DC electricity directly from thechemical energy of a substance (usually hydrogen). It is very similar to a battery with themain difference being that it is an open system with the fuel constantly supplied to the


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device. Fuel cells are comprised of two electrodes, an electrolyte and an external circuit.The electrolyte provides for ion migration from one electrode to the other. One of theelectrodes is a positive anode and the other is a negative cathode. The reactants,hydrogen in most cases, lose electrons at the negative electrode through an oxidationreaction and the electrons travel through an external circuit to the positive electrode. The

positively charged hydrogen ions from the oxidation reaction travel through the ionicconductor or electrolyte to the positive electrode. At the positive electrode a reductionreaction takes place where the electrons combine with the positively charged hydrogenions and oxygen to form exhaust water. In the process, heat is also released which insome applications can be captured for useful thermal energy. This process is typical ofProton Exchange Membrane and Phosphoric Acid fuel cells but there are other processesusing different fuels and in some cases the oxygen picks up electrons at the cathode andthen migrates to the anode to react with the positive hydrogen ions.

Figure 1: Schematic for the operation of PEM and Phosphoric Acid fuel cells

1

.

There are a number of different methods to produce the effects described above leadingto a number of different technologies within the fuel cell technology general field. Table1 is a list of the different fuel cell types and some of their characteristics. The list is notcomprehensive and there are a number of differences between manufacturers materialsand methods for manufacturing fuel cells that in many cases are proprietary andconfidential. The types of fuel cells can be broken down into two different categories:low temperature fuel cells and high temperature fuel cells. The low temperature fuelcells include AFC, PEM and PAFC and the high temperature technologies are MCFC andSOFC. The newest technologies are the DMFC and URFC, which are furthest from

commercialization. PAFC is the most commercially developed fuel cell type and hasbeen used most in stationary power supply. The PEM or SPFC technology is the mostpromising technology for transport applications since it has a high power density and aquick response time to load but it is also suitable for stationary power applications andwhen it is commercialized, it is expected to be the lowest cost fuel cell technology. AFCtechnology was the first developed fuel cell technology and was used in space

1 Taken from americanhistory.si.edu website.


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applications in the 1960s but the costs of this technology have been considered to be toohigh for commercialization. Therefore, it has received little attention from manufacturersand has received little funding for development. SOFC span the largest application rangeand are considered slated for commercialization before 2004. They also could have thehighest efficiencies of the fuel cell technologies when combined with gas turbine energy

generation (up to 70%).

A single cell (a combination of two electrodes and an electrolyte) produces only about0.7 volts under load. In order to achieve a practical voltage, the cells are put together intoa stack. To do this, an interconnect is put between the anode of one cell and thecathode of the next cell.

Fuel Cell Type Acronym OperatingTemp [C]

AchievedEfficiencies

Electrolyte Electrodes Fuels

Alkaline AFC 150-200 40% KOH in H2O Platinumcatalysts

H2 and O2Compressed

ProtonExchange

Membrane

PEM orSPFC

80-100 35 to 40% Solid Polymer Platinumcatalysts

Purified H2

PhosphoricAcid

PAFC 150-200 35 to 40% PhosphoricAcid

Platinumcatalysts

Gasoline, H2,Natural Gas

MoltenCarbonate

MCFC 650 50 to 55% Na, K or MgCarbonates

Ni catalysts H2

Solid Oxide SOFC 1000 45 to 50% Ca or Zioxides

La-Mncathode and

Ni-Zr anode

H2 No Reformer

DirectMethanol

DMFC 80-100 35 to 40% Solid Polymer Pt and Ru Methanol

Regenerative URFC 80-100 35 to 40% Solid Polymer Varies Purified H2

Table 1: Fuel cell types and their characteristics. Efficiencies based on electricity out/Lower heating

value of fuel in.

Efficiencies

The efficiencies of the fuel cells listed in table 1 range from 35% to 55%. To get a betterunderstanding of the efficiencies it is useful to compare these efficiencies to themaximum possible efficiencies from internal and external combustion machines. Fuelcells are not subject to the thermodynamic efficiencies associated with the second law ofthermodynamics and the Carnot efficiency limitation. The Carnot efficiency is definedfor a heat engine whose temperature extremes are known as follows:

H

LH

T

TTCarnot

=

where TH is the high temperature reservoir and TL is the low temperature reservoir. Thetheoretical maximum efficiency of an electrochemical device such as the fuel cell isdefined not by its temperature extremes but by the ratio of the Gibbs free energy value(G) over the enthalpy value (H) or total heat energy of the fuel at a giventemperature. Figure 2 is a graph comparing the two theoretical efficiencies assuming a30C low temperature for the heat engines. The discontinuity in the graph of the fuel cellefficiency at 100C is due to the change in phase of the exhaust water from liquid to gas.


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This change in phase affects both the enthalpy of the water and the entropy, whichdirectly affects the Gibbs free energy value.

An important aspect of fuel cells is their low pollution. For the low temperature types, itis critical to have a relatively pure supply of hydrogen and this results in pure exhaust

water with no pollutants such as NOx or SOx or CO2. However, in some cases the methodof extracting hydrogen from a hydrocarbon may release some pollutants but on a muchsmaller scale than combustion of those fuels. With the high temperature fuel cells theemissions are also very low though some SOx are produced and in the case of SOFC withan operating temperature of 1000C, there is the possibility of forming NOx. If hydrogenis obtained from electrolysis of water using renewable energies, then there are nopollutants released because of the pure hydrogen. Additionally, there would be no carbondioxide emissions.

0.00%

10.00%

20.00%

30.00%

40.00%

50.00%

60.00%

70.00%

80.00%

90.00%

100.00%

0 200 400 600 800 1000 1200

Temperature [C]

Efficiency%

Discontinuity due to change fro m liquid to gas

phase of exhaust water (Delt a Enthalpy =

41kJ/mol@100C)

Figure 2: Comparison of efficiencies for ideal heat engines and Fuel Cells with a Carnot low

temperature of 30C

Applications

The applications for fuel cells are quite broad and rather specific to fuel cell type. Theapplications range from replacement of batteries in consumer electronics to large-scaleelectricity generating plants. Table 2 gives an idea of the applications and reasonable

power ranges for a module of the different fuel cell types. The applications of interest forthis study are domestic power and small-scale power.

It can be seen from the table that all of the fuel cell types would be applicable to the caseof a small clustered community requiring small-scale power and most of the technologieswould be applicable for domestic power. MCFC technology would not be applicable todomestic power because the minimum module size is reported to be 250kW, which is

Fuel Cell

Carnot Heat En ine


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much more than an individual household would need. The only technologies availablefor a 1kW domestic power fuel cell are AFC, SPFC and SOFC.

Fuel celltype

Module sizerange [kW]

Waste heatoutput [C]

Waste wateroutput

Domesticpower

Small-scalepower

Large-scalecogeneration

Transport

BatteryReplacement

AFC


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temperature steam and broken down into hydrogen, carbon monoxide and carbondioxide. The second step consists of exposing the carbon monoxide from the first step tohigh temperature steam and producing more hydrogen and carbon dioxide. This processcan reach efficiencies of 70 to 90%. The hydrogen and carbon dioxide are thensequestered and stored in tanks. The hydrogen can then be used directly as a reactant for

the fuel cell. In high temperature fuel cells there is a possibility of internal reforming ofthe natural gas in the fuel cell, which would not require an extra reformer. The issues forinternal reforming are the same as the external reforming case.

Other hydrocarbons

Hydrocarbons such as gasoline, coal, LPG and methanol can also be used as fuels in fuelcells. These other hydrocarbons still require a reforming process that will release evenmore carbon dioxide than the reforming of methane and reduce the overall efficiency ofthe system. The only advantage to using other hydrocarbons in fuel cells is the fuelavailability. The most desired hydrocarbons for hydrogen production are those fuels that

have the highest hydrogen to carbon ratio and the least amount of other components.Natural gas is the best hydrocarbon for the production of hydrogen.

Hydrogen

Since hydrogen is the reactant used in most fuel cells it would be ideal to get the fuelsupplied directly as hydrogen. If pure hydrogen is supplied to the fuel cell the onlyproducts will be water and heat. This would lead to a zero-emissions technology forgenerating electricity, which would be very attractive in light of current environmentalconcerns. The difficulty with supplying pure hydrogen to the fuel cell is its availabilityand difficulties in storage. It could be obtained by electrolysis of water to obtain oxygenand hydrogen but this process requires energy. Some advocates of this method suggest

using renewable energies to provide the energy for the electrolysis process. This wouldreduce the problems associated with the intermittent nature of the availability ofrenewable energy technologies such as photovoltaics, wind energy and micro hydro. Inthis context, the hydrogen becomes an energy storage and transport method rather than afuel as such. There are other methods of obtaining hydrogen such as thermal watersplitting, thermochemical cycles which use high temperature heat to split water,photoelectrolysis (sunlight directly splits water into hydrogen and oxygen), photobiology(using sunlight and microorganisms), and radiolysis. Although these methods may havefuture potential, they are currently a long way from commercialization.

Life cycle analysis considerations

Life cycle analysis is important in determining the economics, environmental impacts andgeneral feasibility of a technology. Life cycle analysis is also known as cradle to graveassessment of a technology. In the case of fuel cells this includes the energy to fabricatethe device, the energy to produce hydrogen fuel, the carbon dioxide and other emissionsin the process of removing hydrogen from hydrocarbons, and the energy required torecycle or dispose of the device at the end of its useful life. This life cycle analysis is


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used to determine the environmental impact of a technology but some of these issues canbe translated into dollar costs for an economic analysis.

Figure 4: Greenhouse Gas emissions of energy options4.

Figure 4 shows the greenhouse gas emissions from given technologies per TWh ofenergy produced. The lowest emitting technologies are hydro, wind, solar and nuclear.The emissions of fuel cell technology is calculated based on a natural gas supply and are

similar to the emissions of a natural gas power plant. However, as discussed in theprevious section, other sources of hydrogen could be used which would reduce theemissions of fuel cells to a level similar to wind and solar.

An important aspect in the life cycle analysis of a technology is the life of a device. Forinstance, if an electrification program were to last 20 years and the device had a projectedlife of 5 years, the devices would have to be replaced 4 times in the duration of theproject which would add to the cost of the project and to the environmental impact. ForPAFCs, the most commercialized fuel cell technology, the life is projected to be about40,000 hours or five years. The short life of PAFC technology seems to be characteristicof technologies using liquid electrolytes. The MCFC technology also uses liquid

electrolytes and has a similar life expectancy. However, SOFCs, which use a solidceramic as their electrolyte, are expected to have lifetimes of 10 to 20 years. PEM fuelcells also use a solid electrolyte, which would yield longer lifetimes but they arepoisoned by gases from impure fuel. It is necessary to have extensive fuel processing

4Taken from Comparing power generation options by Hydro Quebec.


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facilities before the fuel can be used in the fuel cell, which both increases price andreduces efficiency down to about 42%.

At this time there is not enough information on manufacturing, disposal or recycling costsfor fuel cell technologies to do an in depth life cycle analysis. It is sufficient to say that

the operational emissions and energy consumption is much less than diesel generatorsand coupled with renewable energies could offer near zero operational emissions.

Economic Analysis

Establishing the demand cases

For the purposes of doing a preliminary economic analysis of fuel cells, an arbitrarycommunity has been devised. For the case of the clustered and scattered communitiesthere are 800 households each consuming 800Wh/day leading to a total energy demandof roughly 640 kWh/D. For the clustered community it was determined to be moreeconomical to get a central generation station and transmit the electricity to the different

households via transmission wires. It is assumed that the transmission lines are alreadyin place due to a previous generation station that now needs replaced. For the scatteredcommunity, there are no transmission lines and it is considered more economical togenerate power at each individual household.

Item Quantity Load [W] Use [h/d] Energy [Wh/d]

Lights 4 13 5 260

Radio 1 20 3 60

TV 1 30 3 90

Refrigerator 1 16 24 384

Per family Peak 55.3 Daily 794

Community Peak 28756 Daily 635200

Table 3: Distribution of Consumption for a typical household. Refrigerator consumption based on

an efficient single temperature refrigerator.

Table 3 shows the consumption of a typical household. The per family peak demand iscalculated assuming only 70% of the items will be on at the same time during the peakhours of demand for the community. The community peak demand is calculatedassuming a 0.65 simultaneity factor. The peak demand that the generation system mustbe designed for is about 29kW.

Stand alone power generation

Clustered CommunityThe first case to be studied will be the clustered community where the generation systemwill be put in a fixed location and transmission wires will supply the community withelectricity at the point of use. As mentioned earlier this case will be studied assumingthat there was a diesel generator at the location previously and that the transmission linesare already in place. This assumption gives an advantage to the central generationscheme since putting in transmission wires could be a significant cost depending on thelayout of the community. However, the object of this study is not to compare central


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generation to distributed-generation but to compare different technologies within a givenscheme of electrification. Table 4 gives the values for the costs associated with putting inanother diesel generator.

Total Energy Demand per day 640kWh/D Required capacity of gen-set 37.7kW

Peak demand for the community 29kW Price for this gen-set $15,080Heating Value of Diesel 42000kJ/kg Life of the gen-set 170,000hours

Gen-Set with efficiency of: 15.00% Maintenance/year is assumed 3% of I.C. $452$/year

Gen-set $/kW system cost: $400$/kW Labor per year with one person 1/4 time: $2,080$/year

Safety factor for peak demand: 1.3 Other unforeseen costs: $1,000$/year

Interest rate for capital 12.00% Project Duration 20years

Conversion kg/gal of diesel 3.30kg/gal Diesel $1.20USD/gal

Regular overhaul every 5 years $3,000

Year Present Value of overhaul Fuel Consumption/year (345 days) Total Initial Cost $18,296USD

5 $1,702.28 2304000kJ/D Annui ty $2,449USD/year

10 $965.92 365.71kg/D Yearly fuel cost $45,881USD/year

15 $548.09 126171.43kg/year Total yearly cost $51,862USD/yearUCE $0.23USD/kWh

Table 4: Unified Cost of Electricity for a Gen-Set in a clustered community with existing

transmission lines.

The yearly fuel cost for this generation scheme is about 88% of the total yearly cost,therefore, any fluctuation in diesel price during the duration of this project could have asignificant impact on the UCE.

Another case for electrification of this community is shown in Table 5. A PhosphoricAcid fuel cell was selected for this case because it is the only commercially available fuelcell to date. The PC25 is a PAFC manufactured by United Technologies Company and

has a capacity of 200kW. The fuel cell needed in this case is only a 29kW fuel cell.Although that model is not currently available, the analysis was done assuming that whensuch a model is available, it would cost roughly the same in $/kW as the PC25.However, as these fuel cells are manufactured in larger volumes, the prices will certainlycome down and different technologies will fit into different size categories. It may be thecase that a 30kW PAFC is never available but it is very likely that a SOFC or PEMFCwill be available in the near future to accommodate this size range. It is also important tonote that the expected lifetime of a PAFC is only about 40,000 hours and will requirereplacement in about the same intervals as batteries in a photovoltaic system. SOFC andPEMFC using solid electrolytes have the potential to last much longer. The calculationsshown in table 5 include the cost of replacement every 5 years and even with this, a

PAFC at 3,500$/kW has a similar unified cost of electricity as a diesel generator.

It is also important to note that the methane cost was taken at $250/thousand cubic meters($0.35/kg), which was the cost of natural gas in the United States in 2000. In Ecuador,for example the cost of LPG, which could also be reformed to extract the hydrogen foruse in fuel cells, is 0.10$/kg. The yearly cost of fuel in the calculations in table 5 is only23% of the total yearly cost making this system much less susceptible to the volatility offossil fuel prices. Additionally, methane can be produced through thermal gasification of


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biomass or in biogas digesters, which make it possible for fuel cells to be a renewableenergy and assure the security of supply for remote regions.

Total Energy Demand per day 640 kWh/D Required capacity of fuel cell 37.7kW

Peak demand for the community 29 kW Price for this fuel cell $131,950

Heating Value of Methane 54000 kJ/kg Life of the fuel cell 40,000hours

PAFC with efficiency of: 40.00% Maintenance/year is assumed 3% of I.C. $3,959$/year

PAFC $/kW system cost: $3,500 $/kW Labor per year with one person 1/4 time: $2,080$/year

Safety factor for peak demand: 1.3 Other unforeseen costs: $1,000$/year

Interest rate for capital 12.00% Project Duration 20years

Density of Methane 0.72 kg/m^3 Methane costs $0.25USD/m^3

Inverter $5,000.00USD

Year PV of Replacement Fuel Consumption/year (345 days) Total Initial Cost $278,413USD

5 $74,871.97 2304000 kJ/D Annuity $37,274USD/year

10 $42,484.37 106.67 kg/D Yearly fuel cost $12,778USD/year

15 $24,106.77 36800 kg/year Total yearly cost $57,090USD/year

UCE $0.26USD/kWh

Table 5: Generation scheme using a PAFC at current market value using existing transmission lines.

The case shown in table 6 is a little more future-based than the previous two cases sincethere are no commercially available SOFC to date. The reason for doing this case was toinvestigate the effect on the UCE if instead of being replaced every 5 years, as the PAFC

Total Energy Demand per day 640kW h/D Required capacity of fuel cell 37.7 kW

Peak demand for the community 29kW Price for this fuel cell $75,400

Heating Value of Methane 54000kJ/kg Life of the fuel cell 170,000 hours

SOFC with efficiency of: 50.00% Maintenance/year is assumed 3% of I.C. $2,262 $/year

SOFC $/kW system cost: $2,000$/kW Labor per year with one person 1/4 time: $2,080 $/year

Safety factor for peak demand: 1.3 Other unforeseen costs: $1,000 $/year

Interest rate for capital 12.00% Project Duration 20 years

Density of Methane 0.72kg/m^3 Methane costs $0.25 USD/m^3

Regular overhaul every 5 years $5,000 Inverter $5,000.00 USD

Year Present Value of overhaul Fuel Consumption/year (345 days) Total Initial Cost $85,760 USD

5 $2,837.13 2304000kJ/D Annui ty $11,482 USD/year

10 $1,609.87 85.33kg/D Yearly fuel cost $10,222 USD/year

15 $913.48 29440kg/year Total yearly cost $27,046 USD/year

UCE $0.12 USD/kWh

Table 6: Unified Cost of Electricity for the case of a SOFC in the clustered community

would have to be, there was just an overhaul cost every five years. The overhaul cost istaken as 6% of the initial cost of the equipment every five years. It is uncertain how

accurate this value is since there is no field experience available other than some fieldtrials, which were not available to the author for inclusion in this paper. It is reasonableto assume, however, that the overhaul and maintenance cost of fuel cells will be muchlower than diesel generators since there are no moving parts in a fuel cell. SOFCs alsohave the potential to be from 50% to 55% efficient, reducing the fuel consumption of thesystem. The UCE for this case is 0.12$/kWh which is getting competitive with large-scale power plants supplying the grid. And this is based on a price of $2000/kW, which


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is predicted by some companies to drop to $800/kW in volume production. The only wayof verifying the veracity of these statements is to wait until the technology is available.

The last case investigated for the clustered community was the use of a traditionalphotovoltaic system using batteries. Table 7 shows the values used in the calculations for

this case and the results.

Total Energy Demand per day 640kWh/D Autonomy of batteries 3.00days

Peak demand for the community 29kW Depth of Discharge 60.00%

Daily Solar Energy 4.2kWh/m^2 Battery Safety Factor 1.3

D.S.E. Factor 0.65 Required capacity of batteries 4160kWh

PV system efficiency 10% Battery price/kwh $165$/kWh

Safety factor for peak demand: 1.3 Price for batteries $686,400USD

Peak Wattage 234432W(p) Life of the batteries 40,000hours

PV system cost: $6$/W Maintenance/year is assumed 5% of initial cost $8$/year

Cost of PV panels $1,406,400USD Labor per year with one person 1/30 time: $277$/year

Required Area 2344.32m^2 Other unforeseen costs: $20$/year

Project Duration 20years Interest rate for capital 12.00%Inverter $5,000.00USD

Year Present Value of battery replacement Total Initial Cost $2,833,687USD

5 $389,481.79 Annuity $379,371USD/year

10 $221,002.43 Total yearly cost $379,676USD/year

15 $125,402.71 UCE $1.72 USD/kWh

Table 7: Photovoltaics with batteries for the clustered community with existing transmission lines.

It is clear from the results of this case that solar electricity is the least attractivetechnology economically unless fuel supply is tremendously difficult. The UCE is morethan five times higher than the most expensive alternative analyzed. The mainadvantages of solar power have traditionally been that no fossil fuel is required, and that

it is an environmentally friendly technology. These studies suggest that in the case ofsmall-scale centralized electricity generation, fuel cells may fill the niche thatphotovoltaics began to fill and may in many cases displace diesel generators.

Scattered Community

The case of the scattered community requires onsite power generation at each household.Traditionally this has been done with the use of photovoltaic panels and possibly windturbines. The difficulty with using diesel generators for on-site generation is the noise,pollution and the access to fuel since many times these dwellings are in difficult to reachareas.

Table 8 shows the case for a photovoltaic system for each household. In the centralgeneration schemes analyzed for the clustered community it is necessary to have asignificant amount of labor but since the worker is working to generate much more powerthan the cases of the scattered community, the fraction of labor in the overall cost will bemuch lower. In all of the cases analyzed for the scattered community, labor wasincluded, but it can be argued that with sufficient training the system can be maintainedby the homeowner with a small amount of his time. This would yield the labor costs


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irrelevant. With labor costs in table 8 the UCE is $2.86/kWh and without labor costs itwould be $1.85/kWh.

Per family Energy Demand per day. 0.8kWh/D Autonomy of batteries 3.00 days

Peak demand of the household 0.055kW Depth of Discharge 60.00%

Daily Solar Energy 4.2kW h/m^2 Battery Safety Factor 1.3

D.S.E. Factor 0.65 Required capacity of batteries 5.2 kWh

PV system efficiency 10% Battery price/kwh $165 $/kWh

Safety factor for peak demand: 1.3 Price for batteries $858 USD

Peak Wattage 293W(p) Life of the batteries 40,000 hours

PV system cost: $6$/W Maintenance/year is assumed 5% of I.C. $8 $/year

Cost of PV panels $1,800USD Labor per year with one person 1/30 time: $277 $/year

Required Area 2.93m^2 Other unforeseen costs: $20 $/year

Project Duration 20years Interest rate for capital 12.00%

Inverter $30.00 USD

Year Present Value of battery replacement Total Initial Cost $3,608 USD

5 $486.85 Annuity $483 USD/year

10 $276.25 Total yearly cost $789 USD/year

15 $156.75 UCE $2.86 USD/kWh

Table 8: Unified Cost of electricity for one household in a scattered community using a conventional

PV system.

Table 9 shows the case for a small-scale fuel cell in the scattered community. This casealso includes labor costs but the same argument could apply to this system as to thephotovoltaic system. With labor the UCE is $1.34/kWh whereas without the labor coststhe UCE would be $0.33/kWh.

Per family Energy Demand per day. 0.8kW h/D Required capacity of fuel cell 0.0715 kW

Peak demand of the household 0.055kW Price for this fuel cell $143

Heating Value of Methane 54000kJ/kg Life of the fuel cell 170,000 hours

SOFC fuel cell with efficiency of: 50% Maintenance/year is assumed 5% of I.C. $7 $/year

Take SOFC to have $/kW cost of: $2,000$/kW Labor per year with one person 1/30 time: $277 $/year

Safety factor for peak demand: 1.3 Other unforeseen costs: $20 $/year

Interest rate for capital 12.00% Project Duration 20 years

Density of Methane 0.72kg/m^3 Methane costs $0.25 USD/m^3

Regular overhaul every 5 years $200 Inverter $30.00 USD

Year Present Value of overhaul Fuel Consumption/year (345 days) Total Initial Cost $387 USD

5 $113.49 2880 kJ/D Annuity $52 USD/year

10 $64.39 0.11 kg/D Yearly fuel cost $13 USD/year

15 $36.54 36.8 kg/year Total yearly cost $369 USD/year

UCE $1.34 USD/kWh

Table 9: Unified cost of electricity for one household in a scattered community using a SOFC.

This case was done using a SOFC cost of $2000/kW and assuming that the lifetimewould be 170,000 hours and the system only requires an overhaul every five years.

Since the SOFC cost is not known and there are many claims about the potential ofreducing the costs in volume production, it is instructive to investigate the effects on theunified cost of electricity for different price ranges. Figure 5 shows the effect on the


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UCE for changing values of the installed cost of the SOFC system without labor costs.The graph shows that even for relatively expensive SOFC systems, the UCE is muchlower than that of the photovoltaic system without labor ($1.85/kWh).

$0.00

$0.10

$0.20

$0.30

$0.40

$0.50

$0.60

$0 $1,000 $2,000 $3,000 $4,000 $5,000 $6,000Installed Cost $/kW

UCE$/kWh

Figure 5: The effect on UCE for different values of installed costs for the SOFC system

Even in the on-site generation scheme investigated here, the fuel cell technology has aclear economic advantage over photovoltaics. There are some assumptions made in theanalysis that should be emphasized again. It is assumed that fuel cell technology will beavailable in these size ranges in the near future and that the lifetimes will be 170,000hours or more so that frequent replacement is not necessary.

Local production of fuels for fuel cellsOne possible disadvantage to using fuel cells in remote communities is the need for aconstant supply of fuel as in the case of the diesel generator even though the fuel requiredis much less for fuel cells. However, a number of local hydrogen or methane generationmethods are possible for fuel cells. Among them are biogas from digesters, producer gasfrom thermal gasification of biomass and electrolysis of water using renewable energies.

For the biogas digesters, approximately 0.5-0.6 m3 of biogas can be produced perkilogram of volatile solids added to the digester. Biogas is composed mainly of methane(60%) and carbon dioxide (40%) with small amounts of other gases. While it is not theaim of this paper to do an in depth analysis of the biogas potential, it is important to note

that it is technically and economically feasible. A 3 m3

digester will produce roughly 1m3 of biogas per day under optimal conditions. Since the digester can be constructed oflocal materials and local labor, it becomes an economically feasible endeavor.Additionally, the added social and health benefits must be considered. A properlydesigned and maintained digester will eliminate over 90% of the disease causing agentsfrom animal and human wastes. In areas where using human waste directly as fertilizer isa common practice there wouldnt be much of a cultural barrier to using human waste inthe digester and it would considerably increase the quality of their foods. In areas where


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human waste is not traditionally used as fertilizer, there may be some resistance to usingthis technique.

For the case of the SOFC in table 6, approximately 120 m3 of methane is required whichtranslates to about 200 m3 of biogas at 60% methane content. This biogas supply could

be met by a community bio-digester of 600 m

3

and an input of 400 kg of volatile solidsper day. For the on-site generation SOFC in table 8, a biogas supply of 0.26 m3 isrequired which could be supplied by a 0.8 m3 household bio-digester with a volatilesolids input of 0.5kg per day. However, the technological complexity of a biogasdigester is rather high when one considers all of the conditions that must be met foroptimal biogas production.

Table 10 shows an analysis of using hydrogen produced from photovoltaics to run theSOFC. An electrolysis efficiency of 80% is used along with an electrolysis device cost of600$/kW. This case is the same as the case in table 7 for the clustered community withthe difference of using hydrogen to store the energy and fuel cells to recuperate it when

needed. The unit cost of electricity for the conventional PV system using batteries intable 7 is 1.72$/kWh whereas with the system in table 10 the UCE is $2.25/kWh.

Total Energy Demand per day 640kW h/D Fuel Cell Safety Factor 1.3

Peak demand for the community 29kW Fuel Cell Capacity 37.7 kW

Daily Solar Energy 4.2kWh/m^2 Fuel Cell Price $/kWh $3,000 $/kW

D.S.E. Factor 0.65 Price for fuel cell $113,100 USD

PV panel efficiency 13% Life of the fuel cell 170,000 hours

Safety factor for peak demand: 1.3 Maintenance/year is assumed 3% of I.C. $3,393 $/year

Peak Wattage 586081W(p) Labor per year with one person 1/4 time: $2,080 $/year

PV system cost: $6$/W Other unforeseen costs: $1,000 $/year

Cost of PV panels $3,516,600USD System Overhaul every 5 years $5,000 $/year

Required Area 4508.31m^2 Inverter $5,000 USD


Electrolysis Efficiency 80.00% Electrolysis Device $16,000.00 USD

Fuel Cell Efficiency 50.00% Hydrogen Storage Tank $12,000.00 USD

Year Present Value of battery replacement Total Initial Cost $3,668,060 USD

5 $2,837.13 Annuity $491,075 USD/year

10 $1,609.87 Total yearly cost $497,548 USD/year

15 $913.48 UCE $2.25 USD/kWh

Table 10: PV/fuel cell system using hydrogen as energy storage for the clustered community.The main disadvantage of the PV/fuel cell system is that the efficiency of performingelectrolysis coupled with the fuel cell efficiency makes the photovoltaic panels neededmuch greater. This fact is the greatest contributor to the higher electricity cost of the

system. It is likely that a system with wind turbines or micro-hydro to performelectrolysis would be much more economically feasible than a system with photovoltaics.

The case for the scattered community is shown in table 11. Once again the maineconomic disadvantage is the requirement of more PV panels. When compared to thecase in table 8 of a conventional PV system with the same demand case, it can be seenthat using fuel cells in this context yields no economic advantage increasing the UCEfrom $2.86/kWh to $3.79/kWh.


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Per family Energy Demand per day. 0.8kW h/D Fuel Cell Safety Factor 1.3

Peak demand of the household 0.055kW Required capacity of fuel Cell 0.0715kW

Daily Solar Energy 4.2kW h/m^2 Fuel cell price/kw $2,000$/kW

D.S.E. Factor 0.65 Price for fuel cell $143USD

PV panel efficiency 13% Life of the fuel cell 170,000hours

Safety factor for peak demand: 1.3 Maintenance/year is assumed 5% of I.C. $100$/year

Peak Wattage 733W (p) Labor per year with one person 1/30 time: $277$/year

PV panel cost: $6$/W Other unforeseen costs: $20$/year

Cost of PV panels $4,200USD Regular overhaul every 5 years $200$/year

Required Area 5.64m^2 Inverter $30.00USD


Hydrogen Storage Tank $200.00USD Electrolysis Device $50.00USD

Fuel Cell Efficiency 50.00% Electrolysis Efficiency 80.00%

Year Present Value of 5 year overhaul Total Initial Cost $4,837USD

5 $113.49 Annuity $648USD/year

10 $64.39 Total yearly cost $1,045 USD/year

15 $36.54 UCE $3.79USD/kWh

Table 11: Scattered community PV/fuel cell system with hydrogen as energy storage.

The case for thermal gasification of biomass has more potential for being economicallyfeasible than the photovoltaics system of generating hydrogen. In order for producer gastechnology to be sustainable, the biomass used in the production must be harvestedsustainably. Typically, 60-70% of the energy content of the biomass is recovered in theproducer gas. Using an average energy content for the biomass as 17 MJ/kg and a dailyenergy consumption of 2,300 MJ as in the case of the SOFC in table 6, the annualconsumption of biomass is 49,400 kg. But considering that only 60% of the energycontent is recovered in the producer gas the actual consumption is 82,300kg/year.

With a demand of 82,300 kg/year the area required for sustainable production can becalculated once a few assumptions are made. The solar insolation of the area will beassumed to be 4.2 kWh/m2 per day and the main plants grown are C3 plants with a 10year growing cycle. C3 plants are roughly 1.5% efficient in capturing the solar radiationso the incoming solar radiation converted to plant matter can be calculated to be 23kWh/m2 over an entire year. Assuming these plants have a heating value of 17,000 kJ/kg, thearea per kilogram required for plant production is 4.9 kg/m2-year. For the case of theSOFC in table 6, the required area for a 10 year plant harvested sustainably is 168,000 m2or 16.8 hectares.

For an economic analysis of this method of fuel production, the value of the land used for

other purposes as well as labor costs should be analyzed. In many cases, this systemcould prove to be both economically viable and socially acceptable within thecommunity.


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Waste Heat and Exhaust Recovery

The products of the reaction within the fuel cell to generate electricity are water and heat.In many cases the heat can be used for water heating or space heating. This application

would be especially useful and practical in the on-site generation schemes discussedabove where the heat does not have to be transported very far to get to its end users.Additionally, if the exhaust water is free of contaminants it can also be used for cleandrinking water eliminating the need to boil water, which would in turn save a good dealof primary energy. In the case of Alkaline Fuel Cells, the exhaust water has been usedfor drinking water for astronauts during space missions. Depending on the technologyused and the purity of the hydrogen supply, this may not be a feasible option.

0

200

400

600

800

1000

1200

1400

0 500 1000 1500 2000

Energy [kWh/day]

WaterExhaust[L/day]

0

10

20

30

40

50

60

RecoverableHeat[kJ/s]

Water L/day Waste Heat

Figure 6: Waste heat and water exhaust for different energy generation levels.

Figure 6 is a graph of the amount of exhaust water and recoverable waste heat fordifferent levels of daily energy generation. For the case shown in table 9 for the SOFCthe amount of water generated is only about liter and the waste heat rate is 17 J/sassuming an 800 C temperature difference. Half of a liter is not enough drinking water

for a family per day but at that heating rate 18L of water could be heated from 25C to45C for bathing which could be sufficient for a family of two or three.

In the case of the clustered community using a SOFC (table 6), the water generated ismuch more substantial. At the energy consumption rate of 640kWh/day, the amount ofwater generated from the fuel cell is about 367 liters. This amount of water would not beenough to supply the entire of community of 800 households with potable water butcould be used to reduce the amount of water that must be boiled. In this case, the waste


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heat could be recovered but it would be more difficult to transport it to the location offinal use. There may be some other industrial demand in the community where theexcess heat could be used. But as the electricity demand in the community grows, a gasturbine could be used in a combined cycle system to generate more electricity. Thiscombination of a high temperature SOFC and a gas turbine has the highest potential for

fuel to electricity efficiency of any electricity generation scheme currently available orprojected to be available in the near future. However, this application is limited by thesizing of the gas turbines and is probably not available at such low steam generationlevels as studied here.

It is generally the case that once a community has a highly reliable and high qualityelectricity supply the electricity usage readily increases. As the electricity demandincreases, so will the amount of water produced from the fuel cell per person, whichwould make recovery of the exhaust water a more practical proposition in the on-sitegeneration case.

ConclusionsRural electrification has become a priority among a number of different governments andnon-governmental organizations. As projects are identified it is important to note thetime frame of the project as well as the potential sources of energy. If the time frame islong, it may be worth looking into cutting-edge technologies that may be available withinthe time frame of the project. With the increasing concern about environmental impactsand future possibilities of converting avoided carbon dioxide emissions into USD,renewable energies or more clean technologies could have a marked advantageeconomically as well.

The most promising technologies for domestic electricity generation are SOFC and PEM.Both of these fuel cell technologies use solid electrolytes and are less susceptible tocorrosion than their counterparts, which makes them more rugged and gives them longerlifetimes. The only commercially available fuel cell to date is a PAFC in the 200kWrange. The main disadvantage of this technology is its 40,000 hour expected life. For a20 year project the fuel cell would have to be replaced three times.

SOFC technology has an advantage over PEM fuel cells in that it can tolerate a lesserpurity of hydrogen and its high temperatures can be used to steam reform the methaneinto hydrogen. This translates into a lower cost and a higher efficiency for the SOFCtechnology since less energy is required to reform and purify the fuel. The higher

temperatures of the SOFC also make waste heat recovery more of a possibility.However, PEM fuel cells have a higher energy density and a much more rapid responsetime, making them a favorite in the transportation sector. As PEM fuel cells areintroduced into the transportation market, it will lead to a much higher volume ofproduction than the SOFC, which in turn will reduce its cost.

Fuel cells, although not yet readily available in the size ranges discussed in this paper,have had a great deal of development funding over the years. It is possible that within the


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next few years these devices could be available in the size ranges discussed. If theybecome available and they meet the projected costs and lifetimes, they would have a clearadvantage in a number of applications.

Technology Clustered Community Scattered Community Table #

Diesel Genset 0.23$/kWh UCE N/A Table 4PAFC 0.26$/kWh UCE N/A Table 5

SOFC 0.12$/kWh UCE 1.34$/kWh UCE Table 6, 9

PV/battery system 1.72$/kWh UCE 2.86$/kWh UCE Table 7, 8

PV/fuel cell system 2.25$/kWh UCE 2.79$/kWh UCE Table 10, 11

Table 12: Summary of electrification cases.

Table 12 is a summary of the cases investigated and shows that the SOFC would be thecheapest electricity alternative in the clustered community. In the case of on-sitegeneration for the scattered community, the diesel generator was not analyzed because ofnoise and pollution problems. Instead, SOFC technology was compared to conventionalPV technology and it was found that there is a clear economic advantage for the SOFC.

Since the actual installed cost of the SOFC is unknown right now, an analysis of theeffect of the installed cost on the UCE was carried out. It was found that even forinstalled costs of $5,500/kW, the UCE of the SOFC was below $0.50/kWh for thescattered community if yearly labor costs were not included (an assumption based on thefact that the owner could be trained to service the equipment).

An additional advantage of fuel cells is their ability to be used as renewable energyconversion machines. If biogas or producer gas is used, the net carbon dioxide emissionsfrom operation could be near zero. In the case of generating hydrogen from renewableenergies, the case studied here of a photovoltaic system producing the gas proved to beuneconomical. However, using renewable energies to produce hydrogen should not beruled out as it may prove to be a viable option if wind resources or hydro resources areavailable.

Waste heat recovery and exhaust recovery in fuel cell systems provide for someinteresting possibilities for enhancing energy efficiency in cogeneration and potablewater that should not be overlooked. The possibilities for retrieving drinking water fromthe fuel cell exhaust will depend on the purity of the fuel input and the fuel celltechnology used. Waste heat recovery for domestic use is more practical for the on-sitegeneration schemes studied as the heat is close to the location of end use. However, evenwith the central generation station, the waste heat could be used in industry where theheat does not need to be transported very far.


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Bibliography

Brandon, Nigel and David Hart.An Introduction to fuel cell technology and economics.Imperial College of Science and Technology. Center for Energy Policy andTechnology. July 1999. UK.

Barra, Luciano.Hydrogen technology: status and perspectives. Class Handout.

EG&G Services, Parson Inc., Science Applications International Corporation. Fuel CellHandbook: Fifth Edition. US DOE. October 2000, Morgantown WV.

Gagnon, Luc. Comparing Power Generation Options. Hydro-Quebec, direction-Environment. April 2000.

Websites:

Smithsonian: National Museum of American History Behring Center.http://americanhistory.si.edu

Brennstoffzellen in Jlich http://www.fuel-cell.deDOE Fossil Energy website. http://www.fe.doe.govUnited Technologies Company http://www.utcfuelcells.com

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