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An electric grid for transportation in Los Angeles
Vol. 17, No. 8, pp. 761-767, 1992 Printed in Great Britain. All rights reserved
Energy
0360-5442/92 $5.00 + 0.00 Copyright @ 1992 Pergamon Press Ltd
AN ELECTRIC GRID FOR TRANSPORTATION IN LOS ANGELES WILLIAM tSuite
48, 4158
J. CARMODY~$
and
JOHN HARADEN~~
Decor0 Street, San Diego, CA 92122 and 9149 Eleventh Del Mar, CA 92014,
Street,
U.S.A.
(Received 29 July 1991)
Abstract-Electric vehicles will be introduced into the Los Angeles area to reduce air pollution. Currently proposed battery-powered electric vehicles are expensive to operate and have limited range and power. A grid system of overhead wires to power electric vehicles while on the main roads offers savings in battery-depreciation costs, together with greater vehicle range and power. We estimate the annual cost of the grid-battery system and compare it to the battery-only system. Air-pollution impacts of the two systems are also compared. With a sufficiently large number of electric vehicles, the grid system yields significant cost reductions and provides better service to vehicle users while offering air-pollution reduction advantages.
INTRODUCTION
To improve air-quality standards, the California Air Resources Board has mandated the introduction of electrically-powered vehicles into Los Angeles by 1997. The proposed vehicles are battery powered, costly to operate, and have limited range and acceleration. A grid system of overhead wires strung along the principal roads and used with auxiliary batteries may provide a cheaper and cleaner electric system and may provide better service to the vehicle user. With the grid system, the vehicles are battery powered on secondary roads. On the principal roads, a pantograph or light mechanical linkage on the vehicle collects electric current from the overhead wires and delivers it to the electric motor. Since the vehicles draw electricity from the overhead wires, they have more range and acceleration than vehicles that are powered by batteries.
DESIGN
AND COST OF THE GRID
SYSTEM
Description of the grid system
At the present time, the Los Angeles Air Basin contains approximately 13 million people and 9 million internal-combustion vehicles.’ Our proposed grid is a rough triangle that includes most of the population of the basin. One leg of the triangle stretches along the southern edge of the San Gabriel mountains and past the city of San Bernadino. Another leg runs southwest from San Bernadino and includes the cities of Riverside, Corona, Tustin, Irvine, and Newport Beach. The Pacific Ocean forms the third side of the triangle. The land area of the triangular grid is about 1600 square miles. Within the grid, all of the main streets and freeways are electrified. The total length of these electrified roads is about 3000 miles. If these roads were laid out in a square array, the grid spacing would be about 1.1 miles. The electrical system for the grid is a modified version of those used in electric railroads and
light rail passenger systems. In these systems, one rail serves as a ground and an overhead wire serves as a hot conductor. In the grid system for electric vehicles, both the ground and hot wires are overhead. Supported by poles about 200 feet apart, there are two catenary wires __--*To whom
all correspondence
should
be addressed. 761
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WILLIAM J. CARMODY and JOHN HARADEN
whose heights vary according to a catenary law. Each catenary wire supports a level contact wire. One is the hot wire and the other is the ground wire. These level lines then contact the pantograph on the vehicle and supply power to the engine. The system is 600 V d.c., which is a standard for urban transport systems with overhead wires. One thousand 1500 kW, substations are placed at intervals along the grid. These convert a.c. current from public utility lines to d.c. current and supply it to the overhead wires. For the initial grid, only the extreme right-hand lane of each major road is wired. With the specified pattern of substations and wire sizes, the grid could power about 1.5 million electric vehicles. This number is about 15% of the total number of internal-combustion vehicles that are currently operating in the Los Angeles Air Basin. The initial grid may be viewed as a modified rail system in terms of environmental impacts and costs. For more electric vehicles, additional overhead wires and substations are needed to supply the additional required power. Capital cost of the grid system
We base the capital cost for the grid system on the costs for two electric railroad designs and a design study for the Dallas Area Rapid Transit system (DART). The railroads are single catenary systems. Adjusted for inflation, the line and pole costs for the railroads are $180,000 and $147,000 per mile in 1990 dollars.2,3 After examining cost breakdowns, it seems reasonable to increase the total cost by 20% to cover the additional cost of an overhead ground wire. The corresponding costs for the DART system, a dual catenary system, are $400,000 per mile.4 Since there is sufficient wire in the DART system for both conductors, there is no reason to adjust the cost for an additional overhead wire. Aesthetic concerns over the appearance of the system play a significant role in the higher cost of the DART system. Depending on factors at the particular location and concerns over visual impact, we expect the lane cost to be between $176,000 and $400,000 per mile. For a reasonable system, we use a lane cost of $300,000 per mile and, therefore, a grid cost of $600,000 per mile of electrified road. With a substation cost of $400,000 each, the total capital cost of the grid is 3000($600,000) + 1000($400,000) or $2.2 billion.5 Annual cost
The annual life-cycle costs are largely fixed and independent of the use level of the system. These include 0 & M costs and the amortization fee for the capital cost of the grid. Since poles and non-contact wires usually have lives of 40-50 yr6 and since the anticipated substation life is 30 yr, we use a 2.5% annual depreciation rate for these components. Using information on electric railroad catenary maintenance,6 we expect a 1.5% rate for maintaining the overhead wires, poles, and substations. With a 6% real rate of return on capital as the capital cost, we obtain a 10% annual cost for the entire system. Therefore, the annual fixed cost of the grid is 0.10 ($2.2 billion) = $220 million. Under heavy use, contact-wire wear may be significant. Using a contact-wire wear rate of 0.5 mi1/10,000 pantograph passages, a 30% allowable wire wear, and a $75OO/mile wire replacement cost, we estimate a wear cost of $6OOO/mile for every million pantograph passes.’ This value may be an overestimate of the wear cost since the estimate is derived from operating experience on railroads. Railroads have higher currents than are proposed for the grid system, and the principal cause of the wear is probably current loading.
BATTERY
COST
Reliable battery costs exist only for a few classes of electric vehicles such as British milk floats, mining vehicles and golf carts. Since these vehicles move slowly and stop frequently, their performances and battery costs are probably not indicative of those of battery-powered
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in L.A.
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vehicles on major roads. Vehicles suitable for use on major roads are not generally available on a commercial basis and their estimated battery costs are based on data for experimental vehicles under test conditions. Actual road conditions may differ substantially from test conditions and may entail vastly different costs. Some electric vehicles are also used for testing new battery types such as nickel-iron and sodium-sulfur batteries. Since these batteries are not manufactured on a commercial scale, even their production costs are speculative. Reliable manufacturing costs exist only for lead-acid batteries. We therefore restrict all of our battery-cost analysis to lead-acid batteries. The battery-powered vehicles to be introduced under the mandates of the Air Resources Board may be similar to the vehicle that is being developed by Asea Brown-Boveri, which carries four passengers, weighs 3300 lbs, and is powered by a 32 kWh sodium-sulfur battery. This vehicle has a 96 mile range at a constant speed of 54 mph (0.33 kWh/mile), a 60 mile range at a constant speed of 72 mph (0.53 kWh/mile), and a 120 mile range in the European driving cycle (0.27 kWh/mile).’ For a typical battery-powered vehicle, we choose a version of the Asea Brown-Boveri vehicle powered by lead-acid batteries. This vehicle would weigh approximately 4000 lbs and consume more battery energy than the original version powered by a sodium-sulfur battery. We estimate 0.33 kWh/mile as the d.c. energy consumed by this vehicle and use this value as the energy consumption for a typical electric car powered by batteries. Hamilton estimates $O.l4/mile (1990 dollars) as the battery-depreciation cost for electric vehicles in low-mileage, low-speed delivery service.” Moore cites $0.25/mile as the batterydepreciation cost for the field-tested General Motors G-Van. “’ This vehicle has a d.c. energy consumption of approximately 0.55 kWh/mile. Since our standard vehicle has a d.c. energy we estimate that this value represents a consumption of approximately 0.33kWh/mile, battery-depreciation cost of $O.l5/mile for our standard vehicle. Using a computer program, Marr and Walsh have calculated a user cost of $0.60/mile (1990 dollars) for passenger cars with optimized lead-acid batteries. 1” Without field tests of an actual vehicle with specified tasks and therefore power requirements, it is difficult to make accurate cost estimates. Taking all of the available data into consideration, we estimate $O.l5/mile as the battery-depreciation cost for our average electric vehicle.
a.c.
ELECTRICITY
USE
AND
COSTS
Q.C.electricity we In order to compare electricity costs between the systems, we must estimate the difference in electricity use. Energy losses in the battery system and differences in vehicle weights account for the variation in electricity consumption. Weights of electric vehicles used with a grid should be significantty lighter than without a grid. A quantitative estimate of the weight difference requires a detailed analysis to which we now turn. The proposed pure battery electric vehicles carry approximately 40% of their weight as batteries. The batteries are sized to meet the specified range and power requirements. We expect that an electric vehicle optimized with the grid in place would require only half as large a battery. For most applications, the range would be much greater than that of an electric vehicle with full-sized batteries operated without a grid. We also expect that the minimum power requirements could be met with only half the total battery complement. As lead-acid batteries are discharged, the power output falls. The decline is rapid when maximum discharge is reached. Electric vehicles operated on a grid would only rarely discharge the battery more than 50% of total storage capacity. By avoiding the steep decline in power output near full discharge, vehicle-power requirements can still be met with only half the battery complement. The reduction in battery weight leads to a 25% vehicle-weight decrease, 20% for the battery
764
WILLIAM J. CARMODY and JOHN HARADEN
and 5% for the supporting structures. Since in urban use, approximately two-thirds of the final vehicle energy consumption is weight-related, we obtain a resulting 17% reduction in d.c. energy consumption. With the grid in place, losses in the battery charger and in the battery itself are reduced. Battery chargers are only about 90% efficient in converting a.c. energy into d.c. energy.” Existing lead-acid batteries for vehicle applications are only 70% efficient in transforming d.c. energy supplied to the battery into d.c. energy withdrawn from the battery.i3 Taking the weight-related differences and battery system losses into account, we find that electric vehicles operated on the grid require 48% less a.c. energy than pure battery electric vehicles. a. c. electricity costs
The costs of the a.c. energy used in these systems depend on the price as well as the quantity consumed. We make the simplifying assumptions that all electricity supplied to the grid arrives during the day at high day-time prices and that the batteries are recharged only overnight at low night-time prices. A 1982 survey of United States electricity prices showed that the average daytime charge was $0.08 per kWh while the average night-time charge was $0.045 per kWh.14 The lower ac. electricity use compensates for the higher day-time electricity price and results in a slightly lower a.c. electricity cost with the grid.
AIR-POLLUTION
CONTROL
IMPACTS
The State Air Resources Board is planning to require the introduction of electric vehicles into California in order to reduce air-polluting emissions associated with internal-combustion engines. If half of these mandated vehicles are operated in the Los Angeles Air Basin, this translates to the addition of 20,000 electric vehicles in 1998 and rising to 100,000 in 2003. An interim goal of a total of 200,000 electric vehicles in the Los Angeles Air Basin by 2000 has been established.r5 By the year 2010, the authorities want at least 30-40% of all of the vehicles to be electric. Systemcost comparison
Since the grid is very extensive and most points are less than half a mile from the grid, we assume that 80% of all vehicle miles will involve utilization of the grid. Using 12,000 miles/year as the average vehicle mileage and $O.lS/mile as the battery-depreciation expense, we find an $1440 annual additional battery cost in the pure battery system.16 Taking the fixed and variable costs of the grid into account for 160,000 vehicles, the extra cost of the grid is balanced by the saving in battery depreciation cost. This is 1.6% of the number of vehicles we project to be in the Los Angeles Air Basin in 1997. At the 2000 goal of 200,000 electric vehicles, the grid system is significantly lower in cost than the pure battery system. If 10% of the total number of vehicles are electric, the payback period for the grid is about 20 months and the annual saving is 1.2 billion dollars. Air pollution from electricity generation
We expect that with the grid in place, air pollution from electricity generation will be significantly reduced since the grid reduces the a.c. electricity consumption by approximately 40%. This change is due to the 48% reduction in a.c. electricity use while vehicles utilize the grid, combined with approximately 80% of vehicle mileage taking place with use of the grid. However, since the pure battery system uses night-time electricity and the grid uses day-time electricity, we must know the actual electricity sources, type and location of generation to make a quantitative comparison. We expect the amount of air pollution generated as the result of day or night electricity production to be similar. Consequently, the reduction in air pollution from electricity production should be approximately 40%.
An electric
grid for transportation
in L.A.
765
Vehicle utilization
Without the grid, electric vehicles have only a limited range. The General Motors G-Van, is currently being field tested, has a range of only 50-60 miles for low average-speed applications. The electric vehicles, that will be introduced into the LOS Angeles Air Basin will of necessity be utilized in limited mileage applications. With the grid in place, these electric vehicles could be shifted to high-mileage applications, thereby yielding larger air-pollution reductions. which
Heavy trucks and buses
Large electric trucks and buses have a very limited range when they are powered by batteries. In most applications, their use would be impractical. With the unlimited range and large amounts of power offered by the grid system, many of these vehicles could be shifted from internal-combustion engines to electric motors. With this transformation. a significant air-pollution reduction could be achieved. User incentives
Air-pollution control authorities are mandating the introduction of electric vehicles. Besides the high user cost due to rapid battery depreciation, the vehicles have limited ranges and acceleration. These features produce a disincentive to use the vehicle after it has been acquired. With the grid in place, marginal operational costs are low, perhaps less than those for internal-combustion engines. Vehicle range, acceleration, and top speed should be substantially equivalent to those of internal-combustion-powered vehicles. These characteristics give the electric vehicle vwner an incentive to use the electric vehicle and not continue with the use of internal-combustion-powered vehicles.
ISSUES
FOR
FURTHER
STUDY
We have demonstrated that an overhead wire supply system can effect significant cost and air-pollution reductions if a large number of electric savings, service improvements, vehicles are operated. However, before construction of such a system, many important issues warrant careful study. System capacity
System capacity estimates are based on hourly traffic variations from 1970 San Diego County data.” These are similar to Los Angeles patterns. Vehicle miles traveled during the peak hour were found to be 2.52 times greater than the hourly average over the entire day. Using the 12,000 annual miles per vehicle and the 0.27 kWh/mile electricity consumption for the typical vehicle while on the grid, we calculate the average peak-power demanded by each vehicle to be 0.75 kW = [(12000 mi/yr)(0.80)(0.27 kWh/mi)(2.52)]/(8760 h/yr). With 1,500,OOO electric vehicles in use, the expected peak power demand is 1,125,OOOkW. This is 75% of the 1,500,000 kW system design capacity. Since the substations can provide signiticant overload capacity for 20-30 min periods, we expect this to be sufficient capacity to handle the peak load. But very careful studies of traffic patterns would be necessary to determine whether this capacity could meet all temporal and spatial fluctuations in demand. Vandalism
Vandalism may be a problem, especially in svme urban areas. Cost estimates for vandalism based on railroad experience may not be suitable for overhead lines placed in urban areas. We EGY 17:8-C
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WILLIAM J. CARMODY and JOHN HARADEN
don’t expect a large increase in maintenance cost due to this problem, but it is impossible to accurately forecast. Segregating the overhead lines into electrically isolated sections and building parallel feeders that automatically bypass any shorted-out sections would provide a simple technical solution in any location with such a problem. The batteries on board the vehicles provide sufficient range for passage through any temporarily disabled sections. Power outages All electrically based systems are vulnerable to power outages. Nuclear attacks or major earthquakes, for example, may destroy generating plants and long distance transmission lines that provide electrical power to the Los Angeles area. Power failures, local or general, may occur for any number of other reasons. We anticipate that vehicles in the battery-only system would have twice the electric storage capacity as vehicles optimized with the grid in place. The extra capacity would be advantageous in the event of a power failure. Of course, users that would be seriously affected by a power failure can carry extra batteries even if the grid is in place. In case of prolonged failure of significant parts of the electric power system, the grid may confer advantages. If only limited electric power were available, this could be used to power the grid and restore some level of electric transportation service. In the battery-only system, the recharging would be totally decentralized. The entire electric power distribution system would have to be repowered to restore electric transportation service. Aesthetic concerns
Aesthetic considerations play a large role in the design of contemporary electric railroads and light rail urban transport systems. A serious effort to design an aesthetically satisfactory pole and wire system should be made before the construction of such a vast 3000 mile system. In fact, some individuals may prefer the battery-only system over the grid because of the negative visual impact of the poles and wires of the grid system. The authors of this paper judge that, at the 10% electric vehicle penetration level, the approximate billion dollar annual savings provided by the grid along with increased quality of service to users and lower air pollution from electricity generation fully offset any negative visual impact of the grid. However, this is ultimately a fundamental public choice issue that can only be decided by the citizens living in the Los Angeles Air Basin. As part of any preliminary work on the electric grid, examples of the poles and wires should be constructed in public places in order that the citizens may be fully informed about the aesthetic impacts of the grid before any decision on its possible construction.
CONCLUSIONS
This study has demonstrated that a battery plus grid electric-vehicle system is approximately equal in cost to that of pure battery vehicles when the electric-vehicle share is about 1.6% in the Los Angeles Air Basin. At higher electric-vehicle shares, the grid system offers markedly lower costs than the pure battery system; a 1.2 billion dollar annual saving is realized at a 10% market penetration. The grid system offers a much higher quality of service, greater range and power, and a possible 40% reduction in air-pollution emissions from electricity generation in comparison with the pure battery system. The significant cost reductions offered by the grid system may also permit much more rapid introduction of electric vehicles into the Los Angeles Air Basin with concomitant reduction in air-polluting emissions. It is very important that such a grid system receives a careful examination by air-pollution control authorities at the present time. Standards must be established for voltages and wire configurations well before grid construction because of the significant lead-time required to construct vehicles to given specifications.
An electric grid for transportation in L.A.
767
REFERENCES 1. L. B. Lave, W. E. Walker, W. S. Reis, and D. A. Ross, Environ. Sci. Technol. 24, 1128 (August 1990). 2. L. E. Carlson and G. E. Griggs, “Hard Alloy Aluminum in Contact Wire-An Engineering Feasibility Study,” 1981 Joint ASMEIIEEE Railroad Conf., pp. 45-52, IEEE, New York, NY (1981). 3. H. I. Hayes and T. B. Tolentino, “Special Designs Incorporated into the Electrification of the Deseret Western Railroad,” 1985 Joint ASMEfiEEE Railroad Conf., pp. 42-47, IEEE, New York, NY (1985). 4. T. A. Kneschke, “Design Considerations for the DART Traction Electrification System,” 1987 IEEEIASME Joint Railroad Conf., pp. 1-11, IEEE, New York, NY (1987). 5. S. R. Lee, “Substations-Standard or Prefabricated-It’s Your Choice,” Proc. of the 1988 Joint ASMEIIEEE Rail Conf., pp. 175-179, American Society of Mechanical Engineers, New York, NY (1988). 6. H. W. Barber, “The Economic Case for the Continued Development of the Diesel Electric Locomotive,” Conf. on Rail Engineering-The Way Ahead, pp. 63-65, Mechanical Engineering Publications, London, England (1975). 7. C. M. S. Maguire, “The Suburban Aspects of British Rail Electrification,” Conf. on Performance of Electrified Railroads, pp. 163-208, Institution of Electrical Engineers, London, England (1968). 8. C. H. Dustmann and J. Angelis, ABB Review, pp. 9-14, Asea Brown-Boveri, Zurich, Switzerland (March/April 1988). 9. W. Hamilton, “Costs of Electric Vehicles in Local Fleet Service,” 19th Intersociety Energy Conversion Engineering Conf., Vol. 2, pp. 736-742, American Nuclear Society, New York, NY (1984). 10. T. Moore, EPRIJ, pp. 4-15 (April/May 1991). 11. W. W. Marr and W. J. Walsh, “A Computerized System for Establishing Electric Vehicle Battery Requirements,” l%h Inter-society Energy Conversion Engineering Conf., Vol. 2, pp. 786-792. American Nuclear Society, New York, NY (1984). 12. W. Hamilton, “Electric and Hybrid Vehicles” in Handbook of Energy Technology and Economics, R. A. Meyers ed., pp. 1032-1052, Wiley-Interscience, New York, NY (1983). 13. W. H. DeLuca, A. F. Tummillo, J. E. Kulaga, C. E. Webster, K. R. Gillie, and R. L. Hogrefe, “Performance Evaluation of Advanced Battery Technologies for Electric Vehicle Applications,” Proc. of the 25th intersociety Energy Conversion Engineering Conf., Vol. 3, pp. 314-319. American Institute of Chemical Engineers, New York, NY (1990). 14. M. M. Collins and G. H. Mader, “The Timing of EV Charging and its Effect on Utilities,” IEEE Trans. on Vehicular Technology, Vol. 32, pp. 90-97, IEEE, New York, NY (February 1983). 15. J. Pasternak, “AQMD Approves Changes to Region’s Clean Air Plan,” Los Angeles Times, p. 1. Los Angeles, CA (13 July 1991). 16. R. E. Faries, Highway Statistics 1987, U.S. Government Printing Office, Washington, DC (1988). “San Diego Clean Air Project, Vol. 4,” Rand 17. J. H. Bigelow, B. F. Goeller, and K. L. Petrushell, Corporation Report, Rand Corporation, Santa Monica, CA (December 1973).
Energy
0360-5442/92 $5.00 + 0.00 Copyright @ 1992 Pergamon Press Ltd
AN ELECTRIC GRID FOR TRANSPORTATION IN LOS ANGELES WILLIAM tSuite
48, 4158
J. CARMODY~$
and
JOHN HARADEN~~
Decor0 Street, San Diego, CA 92122 and 9149 Eleventh Del Mar, CA 92014,
Street,
U.S.A.
(Received 29 July 1991)
Abstract-Electric vehicles will be introduced into the Los Angeles area to reduce air pollution. Currently proposed battery-powered electric vehicles are expensive to operate and have limited range and power. A grid system of overhead wires to power electric vehicles while on the main roads offers savings in battery-depreciation costs, together with greater vehicle range and power. We estimate the annual cost of the grid-battery system and compare it to the battery-only system. Air-pollution impacts of the two systems are also compared. With a sufficiently large number of electric vehicles, the grid system yields significant cost reductions and provides better service to vehicle users while offering air-pollution reduction advantages.
INTRODUCTION
To improve air-quality standards, the California Air Resources Board has mandated the introduction of electrically-powered vehicles into Los Angeles by 1997. The proposed vehicles are battery powered, costly to operate, and have limited range and acceleration. A grid system of overhead wires strung along the principal roads and used with auxiliary batteries may provide a cheaper and cleaner electric system and may provide better service to the vehicle user. With the grid system, the vehicles are battery powered on secondary roads. On the principal roads, a pantograph or light mechanical linkage on the vehicle collects electric current from the overhead wires and delivers it to the electric motor. Since the vehicles draw electricity from the overhead wires, they have more range and acceleration than vehicles that are powered by batteries.
DESIGN
AND COST OF THE GRID
SYSTEM
Description of the grid system
At the present time, the Los Angeles Air Basin contains approximately 13 million people and 9 million internal-combustion vehicles.’ Our proposed grid is a rough triangle that includes most of the population of the basin. One leg of the triangle stretches along the southern edge of the San Gabriel mountains and past the city of San Bernadino. Another leg runs southwest from San Bernadino and includes the cities of Riverside, Corona, Tustin, Irvine, and Newport Beach. The Pacific Ocean forms the third side of the triangle. The land area of the triangular grid is about 1600 square miles. Within the grid, all of the main streets and freeways are electrified. The total length of these electrified roads is about 3000 miles. If these roads were laid out in a square array, the grid spacing would be about 1.1 miles. The electrical system for the grid is a modified version of those used in electric railroads and
light rail passenger systems. In these systems, one rail serves as a ground and an overhead wire serves as a hot conductor. In the grid system for electric vehicles, both the ground and hot wires are overhead. Supported by poles about 200 feet apart, there are two catenary wires __--*To whom
all correspondence
should
be addressed. 761
762
WILLIAM J. CARMODY and JOHN HARADEN
whose heights vary according to a catenary law. Each catenary wire supports a level contact wire. One is the hot wire and the other is the ground wire. These level lines then contact the pantograph on the vehicle and supply power to the engine. The system is 600 V d.c., which is a standard for urban transport systems with overhead wires. One thousand 1500 kW, substations are placed at intervals along the grid. These convert a.c. current from public utility lines to d.c. current and supply it to the overhead wires. For the initial grid, only the extreme right-hand lane of each major road is wired. With the specified pattern of substations and wire sizes, the grid could power about 1.5 million electric vehicles. This number is about 15% of the total number of internal-combustion vehicles that are currently operating in the Los Angeles Air Basin. The initial grid may be viewed as a modified rail system in terms of environmental impacts and costs. For more electric vehicles, additional overhead wires and substations are needed to supply the additional required power. Capital cost of the grid system
We base the capital cost for the grid system on the costs for two electric railroad designs and a design study for the Dallas Area Rapid Transit system (DART). The railroads are single catenary systems. Adjusted for inflation, the line and pole costs for the railroads are $180,000 and $147,000 per mile in 1990 dollars.2,3 After examining cost breakdowns, it seems reasonable to increase the total cost by 20% to cover the additional cost of an overhead ground wire. The corresponding costs for the DART system, a dual catenary system, are $400,000 per mile.4 Since there is sufficient wire in the DART system for both conductors, there is no reason to adjust the cost for an additional overhead wire. Aesthetic concerns over the appearance of the system play a significant role in the higher cost of the DART system. Depending on factors at the particular location and concerns over visual impact, we expect the lane cost to be between $176,000 and $400,000 per mile. For a reasonable system, we use a lane cost of $300,000 per mile and, therefore, a grid cost of $600,000 per mile of electrified road. With a substation cost of $400,000 each, the total capital cost of the grid is 3000($600,000) + 1000($400,000) or $2.2 billion.5 Annual cost
The annual life-cycle costs are largely fixed and independent of the use level of the system. These include 0 & M costs and the amortization fee for the capital cost of the grid. Since poles and non-contact wires usually have lives of 40-50 yr6 and since the anticipated substation life is 30 yr, we use a 2.5% annual depreciation rate for these components. Using information on electric railroad catenary maintenance,6 we expect a 1.5% rate for maintaining the overhead wires, poles, and substations. With a 6% real rate of return on capital as the capital cost, we obtain a 10% annual cost for the entire system. Therefore, the annual fixed cost of the grid is 0.10 ($2.2 billion) = $220 million. Under heavy use, contact-wire wear may be significant. Using a contact-wire wear rate of 0.5 mi1/10,000 pantograph passages, a 30% allowable wire wear, and a $75OO/mile wire replacement cost, we estimate a wear cost of $6OOO/mile for every million pantograph passes.’ This value may be an overestimate of the wear cost since the estimate is derived from operating experience on railroads. Railroads have higher currents than are proposed for the grid system, and the principal cause of the wear is probably current loading.
BATTERY
COST
Reliable battery costs exist only for a few classes of electric vehicles such as British milk floats, mining vehicles and golf carts. Since these vehicles move slowly and stop frequently, their performances and battery costs are probably not indicative of those of battery-powered
An electric grid for transportation
in L.A.
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vehicles on major roads. Vehicles suitable for use on major roads are not generally available on a commercial basis and their estimated battery costs are based on data for experimental vehicles under test conditions. Actual road conditions may differ substantially from test conditions and may entail vastly different costs. Some electric vehicles are also used for testing new battery types such as nickel-iron and sodium-sulfur batteries. Since these batteries are not manufactured on a commercial scale, even their production costs are speculative. Reliable manufacturing costs exist only for lead-acid batteries. We therefore restrict all of our battery-cost analysis to lead-acid batteries. The battery-powered vehicles to be introduced under the mandates of the Air Resources Board may be similar to the vehicle that is being developed by Asea Brown-Boveri, which carries four passengers, weighs 3300 lbs, and is powered by a 32 kWh sodium-sulfur battery. This vehicle has a 96 mile range at a constant speed of 54 mph (0.33 kWh/mile), a 60 mile range at a constant speed of 72 mph (0.53 kWh/mile), and a 120 mile range in the European driving cycle (0.27 kWh/mile).’ For a typical battery-powered vehicle, we choose a version of the Asea Brown-Boveri vehicle powered by lead-acid batteries. This vehicle would weigh approximately 4000 lbs and consume more battery energy than the original version powered by a sodium-sulfur battery. We estimate 0.33 kWh/mile as the d.c. energy consumed by this vehicle and use this value as the energy consumption for a typical electric car powered by batteries. Hamilton estimates $O.l4/mile (1990 dollars) as the battery-depreciation cost for electric vehicles in low-mileage, low-speed delivery service.” Moore cites $0.25/mile as the batterydepreciation cost for the field-tested General Motors G-Van. “’ This vehicle has a d.c. energy consumption of approximately 0.55 kWh/mile. Since our standard vehicle has a d.c. energy we estimate that this value represents a consumption of approximately 0.33kWh/mile, battery-depreciation cost of $O.l5/mile for our standard vehicle. Using a computer program, Marr and Walsh have calculated a user cost of $0.60/mile (1990 dollars) for passenger cars with optimized lead-acid batteries. 1” Without field tests of an actual vehicle with specified tasks and therefore power requirements, it is difficult to make accurate cost estimates. Taking all of the available data into consideration, we estimate $O.l5/mile as the battery-depreciation cost for our average electric vehicle.
a.c.
ELECTRICITY
USE
AND
COSTS
Q.C.electricity we In order to compare electricity costs between the systems, we must estimate the difference in electricity use. Energy losses in the battery system and differences in vehicle weights account for the variation in electricity consumption. Weights of electric vehicles used with a grid should be significantty lighter than without a grid. A quantitative estimate of the weight difference requires a detailed analysis to which we now turn. The proposed pure battery electric vehicles carry approximately 40% of their weight as batteries. The batteries are sized to meet the specified range and power requirements. We expect that an electric vehicle optimized with the grid in place would require only half as large a battery. For most applications, the range would be much greater than that of an electric vehicle with full-sized batteries operated without a grid. We also expect that the minimum power requirements could be met with only half the total battery complement. As lead-acid batteries are discharged, the power output falls. The decline is rapid when maximum discharge is reached. Electric vehicles operated on a grid would only rarely discharge the battery more than 50% of total storage capacity. By avoiding the steep decline in power output near full discharge, vehicle-power requirements can still be met with only half the battery complement. The reduction in battery weight leads to a 25% vehicle-weight decrease, 20% for the battery
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and 5% for the supporting structures. Since in urban use, approximately two-thirds of the final vehicle energy consumption is weight-related, we obtain a resulting 17% reduction in d.c. energy consumption. With the grid in place, losses in the battery charger and in the battery itself are reduced. Battery chargers are only about 90% efficient in converting a.c. energy into d.c. energy.” Existing lead-acid batteries for vehicle applications are only 70% efficient in transforming d.c. energy supplied to the battery into d.c. energy withdrawn from the battery.i3 Taking the weight-related differences and battery system losses into account, we find that electric vehicles operated on the grid require 48% less a.c. energy than pure battery electric vehicles. a. c. electricity costs
The costs of the a.c. energy used in these systems depend on the price as well as the quantity consumed. We make the simplifying assumptions that all electricity supplied to the grid arrives during the day at high day-time prices and that the batteries are recharged only overnight at low night-time prices. A 1982 survey of United States electricity prices showed that the average daytime charge was $0.08 per kWh while the average night-time charge was $0.045 per kWh.14 The lower ac. electricity use compensates for the higher day-time electricity price and results in a slightly lower a.c. electricity cost with the grid.
AIR-POLLUTION
CONTROL
IMPACTS
The State Air Resources Board is planning to require the introduction of electric vehicles into California in order to reduce air-polluting emissions associated with internal-combustion engines. If half of these mandated vehicles are operated in the Los Angeles Air Basin, this translates to the addition of 20,000 electric vehicles in 1998 and rising to 100,000 in 2003. An interim goal of a total of 200,000 electric vehicles in the Los Angeles Air Basin by 2000 has been established.r5 By the year 2010, the authorities want at least 30-40% of all of the vehicles to be electric. Systemcost comparison
Since the grid is very extensive and most points are less than half a mile from the grid, we assume that 80% of all vehicle miles will involve utilization of the grid. Using 12,000 miles/year as the average vehicle mileage and $O.lS/mile as the battery-depreciation expense, we find an $1440 annual additional battery cost in the pure battery system.16 Taking the fixed and variable costs of the grid into account for 160,000 vehicles, the extra cost of the grid is balanced by the saving in battery depreciation cost. This is 1.6% of the number of vehicles we project to be in the Los Angeles Air Basin in 1997. At the 2000 goal of 200,000 electric vehicles, the grid system is significantly lower in cost than the pure battery system. If 10% of the total number of vehicles are electric, the payback period for the grid is about 20 months and the annual saving is 1.2 billion dollars. Air pollution from electricity generation
We expect that with the grid in place, air pollution from electricity generation will be significantly reduced since the grid reduces the a.c. electricity consumption by approximately 40%. This change is due to the 48% reduction in a.c. electricity use while vehicles utilize the grid, combined with approximately 80% of vehicle mileage taking place with use of the grid. However, since the pure battery system uses night-time electricity and the grid uses day-time electricity, we must know the actual electricity sources, type and location of generation to make a quantitative comparison. We expect the amount of air pollution generated as the result of day or night electricity production to be similar. Consequently, the reduction in air pollution from electricity production should be approximately 40%.
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Vehicle utilization
Without the grid, electric vehicles have only a limited range. The General Motors G-Van, is currently being field tested, has a range of only 50-60 miles for low average-speed applications. The electric vehicles, that will be introduced into the LOS Angeles Air Basin will of necessity be utilized in limited mileage applications. With the grid in place, these electric vehicles could be shifted to high-mileage applications, thereby yielding larger air-pollution reductions. which
Heavy trucks and buses
Large electric trucks and buses have a very limited range when they are powered by batteries. In most applications, their use would be impractical. With the unlimited range and large amounts of power offered by the grid system, many of these vehicles could be shifted from internal-combustion engines to electric motors. With this transformation. a significant air-pollution reduction could be achieved. User incentives
Air-pollution control authorities are mandating the introduction of electric vehicles. Besides the high user cost due to rapid battery depreciation, the vehicles have limited ranges and acceleration. These features produce a disincentive to use the vehicle after it has been acquired. With the grid in place, marginal operational costs are low, perhaps less than those for internal-combustion engines. Vehicle range, acceleration, and top speed should be substantially equivalent to those of internal-combustion-powered vehicles. These characteristics give the electric vehicle vwner an incentive to use the electric vehicle and not continue with the use of internal-combustion-powered vehicles.
ISSUES
FOR
FURTHER
STUDY
We have demonstrated that an overhead wire supply system can effect significant cost and air-pollution reductions if a large number of electric savings, service improvements, vehicles are operated. However, before construction of such a system, many important issues warrant careful study. System capacity
System capacity estimates are based on hourly traffic variations from 1970 San Diego County data.” These are similar to Los Angeles patterns. Vehicle miles traveled during the peak hour were found to be 2.52 times greater than the hourly average over the entire day. Using the 12,000 annual miles per vehicle and the 0.27 kWh/mile electricity consumption for the typical vehicle while on the grid, we calculate the average peak-power demanded by each vehicle to be 0.75 kW = [(12000 mi/yr)(0.80)(0.27 kWh/mi)(2.52)]/(8760 h/yr). With 1,500,OOO electric vehicles in use, the expected peak power demand is 1,125,OOOkW. This is 75% of the 1,500,000 kW system design capacity. Since the substations can provide signiticant overload capacity for 20-30 min periods, we expect this to be sufficient capacity to handle the peak load. But very careful studies of traffic patterns would be necessary to determine whether this capacity could meet all temporal and spatial fluctuations in demand. Vandalism
Vandalism may be a problem, especially in svme urban areas. Cost estimates for vandalism based on railroad experience may not be suitable for overhead lines placed in urban areas. We EGY 17:8-C
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don’t expect a large increase in maintenance cost due to this problem, but it is impossible to accurately forecast. Segregating the overhead lines into electrically isolated sections and building parallel feeders that automatically bypass any shorted-out sections would provide a simple technical solution in any location with such a problem. The batteries on board the vehicles provide sufficient range for passage through any temporarily disabled sections. Power outages All electrically based systems are vulnerable to power outages. Nuclear attacks or major earthquakes, for example, may destroy generating plants and long distance transmission lines that provide electrical power to the Los Angeles area. Power failures, local or general, may occur for any number of other reasons. We anticipate that vehicles in the battery-only system would have twice the electric storage capacity as vehicles optimized with the grid in place. The extra capacity would be advantageous in the event of a power failure. Of course, users that would be seriously affected by a power failure can carry extra batteries even if the grid is in place. In case of prolonged failure of significant parts of the electric power system, the grid may confer advantages. If only limited electric power were available, this could be used to power the grid and restore some level of electric transportation service. In the battery-only system, the recharging would be totally decentralized. The entire electric power distribution system would have to be repowered to restore electric transportation service. Aesthetic concerns
Aesthetic considerations play a large role in the design of contemporary electric railroads and light rail urban transport systems. A serious effort to design an aesthetically satisfactory pole and wire system should be made before the construction of such a vast 3000 mile system. In fact, some individuals may prefer the battery-only system over the grid because of the negative visual impact of the poles and wires of the grid system. The authors of this paper judge that, at the 10% electric vehicle penetration level, the approximate billion dollar annual savings provided by the grid along with increased quality of service to users and lower air pollution from electricity generation fully offset any negative visual impact of the grid. However, this is ultimately a fundamental public choice issue that can only be decided by the citizens living in the Los Angeles Air Basin. As part of any preliminary work on the electric grid, examples of the poles and wires should be constructed in public places in order that the citizens may be fully informed about the aesthetic impacts of the grid before any decision on its possible construction.
CONCLUSIONS
This study has demonstrated that a battery plus grid electric-vehicle system is approximately equal in cost to that of pure battery vehicles when the electric-vehicle share is about 1.6% in the Los Angeles Air Basin. At higher electric-vehicle shares, the grid system offers markedly lower costs than the pure battery system; a 1.2 billion dollar annual saving is realized at a 10% market penetration. The grid system offers a much higher quality of service, greater range and power, and a possible 40% reduction in air-pollution emissions from electricity generation in comparison with the pure battery system. The significant cost reductions offered by the grid system may also permit much more rapid introduction of electric vehicles into the Los Angeles Air Basin with concomitant reduction in air-polluting emissions. It is very important that such a grid system receives a careful examination by air-pollution control authorities at the present time. Standards must be established for voltages and wire configurations well before grid construction because of the significant lead-time required to construct vehicles to given specifications.
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