Nissan LEAF EV

            The Nissan LEAF (Leading, Environmentally Friendly, Affordable, Family Car) is an all electric, zero-emission passenger vehicle. The BEV has a max speed of 87mph, 80 kW (110HP) / 280 N-m (210 ft-lb) front mounted motor, front wheel drive train, a 24kWH lithium-ion (Lithium-Manganese) battery pack, and a 100 mile range for city driving on a flat terrain (7). The battery pack weighs 440lb and contains 48 laminated lithium-ion modules connected in series (7). Each module contains 4 lithium-ion cells connected in parallel where each cell has a minimum operating voltage of 3.0V, a max operating voltage of 4.2V, and a nominal operating voltage of 4.0V. This gives the vehicle a minimum operating voltage of 144V and a max operating voltage of 202V. The LEAF is designed to only use 80% of its battery, or 19.2kWH; the battery will not charge over 90% capacity and will reach a zero charge at 10% capacity. Also, when the vehicle reaches 30% capacity or 20% charge it goes into “Turtle Mode,” which governs the BEV to a max speed of 50mph as well as locate nearby charging locations (8).

             Nissan is releasing 4700 of its BEV to qualifying customers in 11 markets to participate in eTec’s EV Project in the 4th quarter of 2010. They also plan to sell an additional 11,000 models nationwide (United States) in 2011, 20,000 in 2012, and 50,000 in 2013 (8). Nissan is in the process of building a LEAF manufacturing plant in Smyrna, TN which when complete in 2012 will have the capacity to produce 150,000 LEAF BEVs annually (9).

 EV Charging

The charging system for an EV is consists of an AC power source, a connection coupler, an AC to DC converter device, and a battery pack to store the charge. The Nissan LEAF carries an on-board smart charging system that can be plugged into a single phase AC line that provides power at 120 or 240V through specially designed connectors that can sense the line voltage and adjust the charging rate accordingly. These have been designated as Level I and Level II EVSE.

 Level I EVSE is a power source of 120VAC at currents up to 15A (12A continuous) which is equivalent to a typical phase I home electrical outlet. Level I equipment will fully charge electric vehicle batteries in approximately 8 hours. Level II EVSE (shown in Figure 1) is an electricity source of 240VAC currents from 12A to 80A which is similar to a typical phase II home electrical outlet. The J1772 (shown in Figure 40) approved connector allows for current as high as 80A (100 amp rated circuit) (10). However, current levels that high are rare and a more typical rating would be 40 amps AC which allows a maximum current of 32A (10). Level II EVSE will fully charge electric vehicle batteries in approximately 5 hours. The obvious advantage is faster charging time.


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Figure 1: Level II EVSE Diagram (on-board charging)

 DC fast charger (shown in Figure 2) is a high voltage electricity source of 480V AC which the equipment rectifies, or converts, to DC at a current of 400A (10). Since fast chargers have an AC to DC converter built in, they are considered “off-board” or “real” chargers. Fast charging equipment will fully charge electric vehicle batteries in approximately 30 minutes (10).

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Figure 2: DC Fast Charger Diagram (off-board charging)

 

Figure 3 shows the charge connection points of the Nissan LEAF. The left connection is designated for dc fast chargers while the smaller hookup on the right is designated for Level I and II EVSE.

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 Figure 3: Connection Points of the Nissan LEAF

 Electric Vehicle Supply Equipment (EVSE)

Nissan recently announced the selection of AeroVironment to supply Level II EVSE and installation services (3). This company is recommended by Nissan to provide and install home-based Level II equipment for the LEAF. For the national project, eTec will provide a Level II EVSE to the 4700 participants of the project at no cost to the participant. The eTec brand EVSE will have a web-based interface and connection. So, when the Nissan LEAF and EVSE are connected, this entitles the user to view instantaneous charging levels from any computer (2). Also, users can set charging times from the web portal to avoid charging at peak hours which might spike the power grid. In some cities, utility companies offer Time-of-Use rates to encourage off-peak electricity use. The web-based control feature permits addressing the pricing fluctuations. The data (distance traveled between charges, state of charge before recharge, length of charging time, and time of day charge takes place) that is collected from every web-based EVSE will be analyzed to study vehicle operations and infrastructure in order to support future release of electric vehicles (2).

 For the national project, eTec has announced that there will be 11,210 EVSE provided to the participating markets. Of those, 10,950 will be eTec brand Level II EVSE and 260 will be eTec brand DC Fast Chargers. Since the exact number of EVSE being deployed to each market is not known, it is assumed that all markets will receive approximately equal amounts of each type of EVSE. So, Tennessee will receive 2,190 Level II EVSE and 52 DC fast chargers (2).

EVSE Smart Features

The public charging sites will not require a full-time attendant worker as typical gas stations do. Instead, a remote monitoring system will be used for security and a smart billing system will be used to charge users for their electricity. The current national average (peak and off-peak) of residential use is 11.3 cents per kilowatt-hour. The billing system will use a subscription service where the energy used is automatically debited from the user’s checking account. An additional feature of the chargers being web-based is that when a charger breaks or needs servicing, the network will identify the problem immediately and send for a maintenance assistant. The electric vehicle associated with this project has an on board navigation system that can show and tell the user where a nearby charging site is located (2).

 Since the eTec brand EVSE will require an internet connection, implementing a Wi-Fi network to a public charging site would be an inexpensive way of providing users who do not have an internet capable phone a way of passing time by browsing the web from a Wi-Fi accessible laptop or PDA. A full charge in the Nissan LEAF with a “fast charging” EVSE will take thirty minutes which is approximately five times longer than a full fill-up at the gas pump.

 Future Power Grid Integration

Utilities providers are always looking for new, innovative ways to provide clean energy at a low cost to their customers. Many of these providers have started implementing “Smart-Grid” technologies. These technologies in conjunction with EVs can have a major role in controlling the use of electricity. Although the United States power grid has the capability to provide energy to a national fleet of EVs, it may not be capable of charging all of them at the same time for example from 5-6pm weekdays when the demand for power is the greatest.

EV drivers should schedule their vehicle to be charged during off-peak hours which generally take place at night and early morning. Utility providers are starting to implement real time pricing, especially across the west coast, so an EV can be set to charge only when the power grid is low. By employing these two methods, an EV can be fully charged over night while only charging during the most cost effective times. During times when utility companies are having an excessive amount energy usage, they can send signals to their customers including EV users to make cuts on their electric usage. This demand response method can offer compensation to those who volunteer to make energy reductions.

Another option for providing electricity to the grid is the Vehicle-to-Grid (V2G) concept. This allows the EVSE’s bi-directional capabilities to provide energy back to the power grid or to provide energy to an individual’s home. An EV can charge during off-peak hours and then be used to provide energy back to a home during peak hours and actually save the home owner money on their electric bill (12). This is a smart, futuristic concept that would allow the energy stored in electric cars to be used to improve the stability of the electric grid during peak periods while providing much needed energy storage capability. This is needed to fully utilize renewable sources of energy such as wind and solar generators which often are most productive when demand is low

Geographical Ranges        

Chattanooga, Tennessee, which has a downtown elevation of approximately 680 feet, lies at the transition between the ridge-and-valley  portion of the Appalachian Mountains and the Cumberland Plateau. The city is surrounded by various mountains and ridges; Lookout Mountain being the tallest at 2,391 feet. Driving on this mountainous terrain requires more power from the vehicle compared to driving on flat terrains. Therefore, Chattanooga’s role in the national EV Project is extremely significiant in assesing how EVs with an expected 100 mile range will perform in a mountainous city.

Figure 4 is a satellite image of Chattanooga with a 100 mile radius circle surrounding it. The Nissan LEAF EV has an expected range of 100 miles per charge, so this represents the straight line path that the vehicle could make in a single charge. After completing simulated driving trips on Google, all starting from Chattanooga and ending in Knoxville, Nashville and Atlanta; the calculations revealed that the car was attaining about 90% of the straight line path. For example, a straight line from Chattanooga to Knoxville extended 97 miles while the same trip done on actual roads accumulated to 108 miles (13). There is a 10% difference between these two distances.

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Figure 4: 100 mile radius circle surrounding Chattanooga 

Figure 5 is similar to Figure 4 in that it is a satellite image of Chattanooga, but the radius shown is 50 miles. This map focuses on the average Chattanoogan commuter’s round trip. Driving simulations of typical routes in Chattanooga were performed with Google and showed many differences from the simulations performed in the map area of Figure 4. Due to additional non-highway driving, the vehicle must make more turns compared to highway driving, resulting in a 20% difference of straight line paths and actual paths. For example, the trip from the bottom of Signal Mountain to the center of Taft Highway (a popular highway flowing through the center of Signal Mountain) totaled 10.7 miles, while the straight line path was only 7.3 miles (13). This is a 30% difference. Also, the mountain’s drastically changing elevation would greatly impact vehicle mileage.

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Figure 5: 50 mile radius circle surrounding Chattanooga

Figure 6 is a combination of both Figure 4 and 5. This map has a 100 mile radius (teal) circle and 50 mile radius (blue) circle around Chattanooga, Knoxville and Nashvile because these are three of the cities that are partners and sites for The EV Project. This map demonstrtates the ability  a vehicle has to travel from city to city, while only stopping to charge once. Note: The Nissan LEAF’s 100 mile range is based on LA-4 or “in-city” driving profile and highway. 

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Figure 6: 100 and 50 mile radius circles around Chattanooga, Knoxville, and Nashville

Figure 7 shows the EV infrastructure on a national level. This map has a 100 mile radius (blue) circles that have been centered at all the cities that will be implementing an EV infrasture in the Fall 2010. This map shows that if more cities continually recieve EVs and expand the EV infrastructure, then eventually there will not be need for vehicles to run on gasoline.

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Figure 7: 100 mile radius circles centered at all cities implementing the EV infrastructure.

 Demographics

Figure 8 is a a demographic map that geographically defines Chattanooga’s 15 zip codes. A demographic analysis focused on population, land mass, and finanacial statuses (EVs have steep prices compared to internal combustion vehicles) of each zip codes can help determine where to place charging stations. Chattanooga has a population of 170,000 people. Approximately a quarter of those people live in East Brainerd, zip code 37421, while another quarter lives in Red Bank, 37415, and East Ridge, 37412 (14).  Looking over the map, it is clear that Lookout Mountain, 37405 / 37419, and East Brainerd, 37421, cover a substantial portion of Chattanooga’s land (14).  The highest priced median homes occur in 37403 at $216,000, 37405 at $183,000 and 37421 at $156,000. 

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Figure 8: Chattanooga divided by zip codes

The demographics being researched are the current inventory, or fleet which is the percentage of different types of registered vehicles in Chattanooga and where these residents live, the number of vehicles per house by income level in Chattanooga, and recent past sales of hybrids/plug-in hybrids in Chattanooga as well as the nation. Also, driver profiles, or driving habits of an individual (narrow scope), and driving profiles, or driving habits of a defined group (broad scope), are being developed. This information will help justify the team’s DC fast charger placement.

Annual Average Daily Traffic

Annual average daily traffic, AADT, is a measure used primarily in transportation planning and transportation engineering. It is defined as the total volume of vehicle traffic of a highway or road for a year divided by 365 days. AADT is a useful and simple measurement of how busy the road is.

The AADT for the Hamilton County area allowed the highest traffic volumes to be found. These volumes provided the best possible solutions as to where to put fast chargers in the Hamilton County area. The AADT for Hamilton County is provided by TDOT, and the way that the charts are read is by reference numbers. Figure 9 is an exert from the TDOT website of the downtown and north Chattanooga areas. The numbers shown are reference numbers that correspond to a table that contains the AADT for that particular spot on the road (15). 

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Figure 9: Exert of AADT site map

Power Utilities Area Diagrams

When assessing the quality of a proposed charging station site, it is imperative that adequate power utilities are identified and accessible. Availability of utilities can be compared for each proposed site, respectively. This adds to the already long list of criteria when comparing and contrasting the quality of proposed sites. If adequate utilities are not present for a proposed site, the utilities may be constructed with proper funding, or incentives and appropriate consent.

 Utilities area diagrams can be accessed using GTViewer Graphic Technologies software.  The EVI team has been authorized by Electric Power Board (EPB) to use GTViewer Graphic Technologies software in conjunction with the current ENGR 485 project. GTViewer provides geospatial viewing and analysis capabilities, including but not limited to spatial analysis, redlining and markup, GPS integration and scale backdrop imagery support.  This software provides a means through which utilities and power source analysis can be performed per site. Figures 10 and 11 illustrate area diagrams for primary and secondary utilities for a proposed charging station site.

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Figure 10: Primary utilities (470 Manufacturer’s Rd., Chattanooga, TN).

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Figure 11: Secondary utilities (470 Manufacturer’s Rd., Chattanooga, TN).

 Planning Considerations

            EV owners will be required to have a dedicated branch circuit hardwired to a permanently mounted EVSE with a 240VAC/Single Phase and a 40Amp breaker. For existing homes, the expense for installing an internet network throughout the house will be dependant on the area. Installing this network as well as the dedicated branch for future EVSE in new construction should be relatively inexpensive.

Fleet use will require multiple charging locations which may cause spacing issues to existing businesses. Also, they will most likely be used during business hours so utility companies and the businesses with fleets will have to take the extra energy use into consideration. The internet network will be able to communicate with the grid to lessen the energy provided to the chargers. As for commercial EVSE, they have many variants to take into consideration. Safety will be paramount, so proper signage, lighting, and shelter must be placed correctly. Public chargers must be accessible to all users. Also, any of the fast chargers that require more than 30kW will require 480VAC/3-Phase (16). Internet capabilities will be crucial on these chargers as they will help design future placement of EVSE determined from the demand feedback.

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