Direct Charging a BEV

Problem Statement:
Our group will determine how to charge a Nissan Leaf from a 1750 Watt photo voltaic panel. Our group will also determine the feasibility of replacing SLO’s mail and garbage trucks, maintenance vehicles, and buses with clean energy drivetrains through an environmental and economic analysis.

Figure 1: Per capita CO2 emissions Vs. Cars, trucks, buses per 1000 people by country in 2007 [7]

The US has among the highest per capita CO2 emissions in the world as well as having the second largest transportation system, per capita, in the world [7]. While looking at the Gapminder graph of CO2 per capita Vs. Cars, trucks buses per 1000 people, decreasing vehicles per 1000 people is an effective method to reducing green house gas emissions. However, between 2003 and 2007, the United States has increased the number of vehicles per 1000 people, and the CO2 emissions per capita have largely stayed the same [7]. This is likely due to higher efficiency vehicles being used. Ultimately, a combination of improved vehicle efficiency and decrease in the number of vehicles would be the most effective means to reduce CO2 emissions.

This project explores clean transportation technology on the consumer level by investigating feasibility of direct charging of a BEV via photo voltaic panels from a performance, economic, and environmental perspective. This project also investigates clean transportation technology on the government level by determining the feasibility of clean energy mail and garbage trucks as well as buses from a performance, economic, environmental, and political standpoint.

Part 1: Direct Charging of a Nissan Leaf from 1750 Watt Photo Voltaic Panel

This section of the project explores how to charge a Nissan Leaf from a 1750 Watt photo voltaic panel.

Nissan Leaf Specs 2014 [1]:

Starting MSRP ~ $30,000 ($6000 used)
Horsepower 107
Battery Pack Size 24 kWh
Battery Chemistry Li-ion
Range 84 mile
Onboard Charger Power 6.6 kW

EV Stats [2][3]:

Total Cars on US Roads 263.6 million
Total EVs on US roads 535000 (2% of total cars on US roads)
Average New Car Price $33560
New Electric Vehicle Price $46228

Figure 2: total number of EVs sold in the United States in 2016 by model [2]

As of May 2015, the average price for a new car in the United States is $33560.00, which was 2.6% higher than the average price of a new vehicle in the USA at that the same time year before [11]. The average price for a new electric vehicle in 2016 was $46228. This was calculated by finding the total sales in dollars for each car in figure 2 (excluding hybrids), summing these dollar amounts together, and then dividing this dollar amount by the total number of EVs sold. Each individual EV price is based off of the vehicles base MSRP price. The consumer could end up paying more than this price as he or she adds options, or could pay less than this price by negotiation.
While the average price of EVs are higher than the average price a consumer pays for a new car in the US, there are still several factors playing in the favor of electric vehicles. First, two of the top five selling EVs in the US are luxury EVs, the Tesla Model S and Tesla Model X. These cars’ MSRP is over twice the average US vehicle price. With these two vehicles removed from the average electric vehicle price calculation, the new electric vehicle price is $34,241 which, after considering vehicle price after negotiations, is a negligible difference between new EV price and new average car price. Additionally, while average vehicle price in the US increased 2.6% average last between May 2015 and May 2016, lithium battery cost has decreased by 80% between 2010 and 2016 as show in figure 3, and is project to continue decreasing [12]. Lithium battery price is a major driving factor for the price of EVs. In addition to lower lithium battery costs, people can determine the cost of their vehicle based on their driving habits. People who do not drive very far distances each day can by a car with a small battery pack and low range, opposed to people who drive far distances each day and can pay for a larger battery pack. Finally, while comparing the cost of fuel per mile between the bestselling Sedan in the US, the Toyota Camry, and the bestselling EV in the US, the Tesla Model S, the cost per mile for the Toyota Camry is 1.75 times greater than that for the Model S [13][2]. This calculation assumes an average electricity cost of 15 cents per kWh, an average fuel price of $2.40 per gallon, and highway speeds [14]. This project explores charging EVs directly from a photovoltaic panel, which will further reduce the energy cost of electric vehicles.

Figure 3: Battery pack price Vs. time [12]

This charging solution is targeted towards United States Customers due to variance in EV charging regulations. However, this same solution can be applied elsewhere if adapted to satisfy local regulations.

US, Rooftop Solar and EV Demographics [4][5][6]:

Average New Car Buyer Age 51.7 years old
Average Income of New Car Buyer $80000
Average Age New Solar Customer 45
Average Income New Rooftop Solar Customer $100000
Average US Population Age 36.8 years old
US Median Income $50000

Setting up a PV charging system involves a high capital cost with a low operating cost. The customers of direct charging of BEVs is the cross section between those who can afford a car, those who would buy an electric vehicle, and those that can afford rooftop solar, and those who are willing to install rooftop solar. While the average new car owner age is 51.7 years old, and the average age of a new rooftop solar customer is 45 years old, the target age group for direct charging of BEVs through rooftop solar is around 50 years old. Furthermore, the target demographic is a bit wealthier than the average American. The average US income is $50000 while the average car buyer’s income is $80000 and the average rooftop solar customer income is over $100000. As solar panels have become more affordable, approximately half of the installations have been for people earning $62500 per year. While electric vehicles such as the Nissan Leaf are in the proximity of the average new car price in the US, the issue is not with the price of the vehicles, but a question of the performance. Business Insider found that driving range is the second most cited barrier to purchase an electric vehicle, directly behind purchase price. As a result, only 2% of all vehicles currently on the road are electric. The range anxiety issue further shrinks the demographic that would be benefiting from the direct solar charging of BEV project because the customer would encompass people who either do not drive long distances each day, people who have another vehicle, or people who would invest in higher priced electric vehicles that have longer ranges.

With that being said, the decreasing cost of solar, the decreasing cost of lithium batteries, and the increasing energy density of lithium batteries, the issues of cost and range anxiety may no longer be a barrier to purchasing an EV and charging through photovoltaic cells. Figure 4 shows that the cost of residential solar dropped approximately 43% between 2010 and 2015, and is project to continue dropping in price. This will allow solar power to be available to much larger demographic in the coming years. Figure 5 shows that between 1990 and 2010, the price per kWh for lithium batteries decreased by approximately 85%, and the energy density of lithium ion cells increased by approximately 150%. Since 2010 the cost of Li-ion batteries have continued to decrease, and the energy density has continued to increase. Furthermore, lithium ion batteries are only half as energy dense as the theoretical limit, so energy density will continue to improve significantly over the coming years. With improvements in lithium ion cell power density, and decreasing lithium ion cell cost, the consumer is alleviated of financial concerns as well a “range anxiety” concerns.

Figure 4: Cost of roof top solar over time [15]

Figure 5: Cost and power density of Li-ion batteries Vs. Time [16]

The overall system is intended to go from the solar panels directly to an EV, such as a Nissan Leaf. The four 425 W solar panels will typically output voltages around 72 V at 6 A. The Nissan Leaf has a DC charging port installed on it. Therefore, the system requires a DC-DC converter to stabilize the output for the varying input voltages from the solar panel. The output of the DC-DC converter would need a connection to the charging cord of the Nissan Leaf. For convenience, the system should have voltage and current sensors connected to the output of the DC-DC converter to determine the power distributed to the vehicle. This should be interconnected with a micro-controller and LCD display to show valuable information to the consumer.

The average sun hours in Santa Maria are 5.94 kWh/m2/day [8]. The four, 425 W solar panels, have an area of 8 m2. Assuming the solar panels are of high quality, the conversion efficiency is 20%. Therefore, 5.94 x 8 x 0.20 = 9.504 kWh per day. On average, the total energy output of the installed solar panels creates 9.5 kWh per day.

The Nissan Leaf has a maximum charging current of 32A and the solar panels max current output is 24 A. Therefore, a wire with a cross-sectional area of 5.3 mm2 would suffice. The wire is made of copper and has a resistance of 3.277 mΩ/m. The wire travels 10 m. The resistance of the line is 0.003277 x 10 = 32.7mΩ. The voltage drop across the wire is 24 A x 0.0327 Ω = 0.786 V. The voltage produced by the solar panel is 72 V. Therefore, the line losses are equivalent to 1.1 %. The Dc-DC buck converter is 95% efficient. The microcontroller, LCD, and sensors consume a total of 6.6Wh. Therefore, after the system losses, the user has, on average, 8.92 kWh/day of total energy output.

The cost of a 2014 Nissan Leaf is $6,000. The embodied carbon dioxide emissions from producing a Nissan Leaf is 4,600 kg. This is 15% higher than a similarly sized internal combustion engine vehicle. The average miles traveled over its lifetime of a 2014 Nissan Leaf is 34,000. A lithium-ion battery, if only charged between 20% to 80%, has a life cycle of 1000 charges. The Nissan Leaf’s 24 kWh battery averages 84 miles of travel. This translates into 3.5 miles/kWh. If you are charging 60% of a 24 kWh battery, each charge is 14.4 kWh. The Li-ion battery charges 14.4 kWh 1000 times; this results in a life cycle of 50,400 miles. Thus, the car had 34,000 miles driven when you bought it, in turn, the remaining life of the vehicle is 16,400 miles. Over the next 16,400 miles, the car costs $0.37/mile.

The carbon dioxide reduction from each battery life cycle is 18,330 kg. If used as much as an average licensed Californian, the Nissan Leaf reduces carbon dioxide emission by 5,237 kg per year. This assumes that both cars would travel a total of 50,400 miles, that each gallon of gas burned results in 8,887 grams of carbon dioxide, that the ICE gets 30 mpg, and that the embodied carbon dioxide of the ICE is 4,000 kg and the Leaf is 4,600 kg.

The 8.92 kWh/day resulting from the solar panels translates into 31.22 miles of driving per day. The averaged licensed Californian driver drives 14,435 miles per year, or 40 miles per day [9].

The biggest concern of this project is the fact that solar power is generated during the day. Most Californians drive to work in the morning. Therefore, the car will not be connected to the solar panel while it is generating power. Therefore, the solution would be to invest in a battery. However, a 10 kWh battery, the amount needed for a day’s power generation capabilities, costs roughly $4,000; the battery would need to be replaced after 5 to 10 years. This changes the previous value of $0.37/mile to $0.61/mile, but without increasing the range of the vehicle.

The second solution looked at is a flexible solar panel cover for your car that can be used while at work. The area of the Nissan Leaf is 7.9 m^2. Thus, you could fit 10 flex solar panels over this area. Ten flexible solar panels result in a 1.2 kW system and costs $2,160. However, due to the inability to control the solar panels always facing the sun, the conversion efficiency would be, at most, 5%. Therefore, assuming the same sun hours per day as your home, this new technology would result in 2.38 kWh/day or 8.33 miles more per day, on average. However, this option would require the use of the battery at home. The total of this solution comes to $6,160 total, or $0.74/mile and still only allows 39.55 miles of range.

Another solution is covering a parking lot with solar panels. Let’s assume it is a 100 car lot with an area of 1,700 meters squared, the solar panels have 16% conversion efficiency and that it receives 5.95 kWh/m^2/day of sun coverage. This massive solar project would result in 1,600 kWh/day. This massive amount of energy lends itself to the ability to fully charge 65 24kWh Li-ion batteries per day. This project utilizes 850 solar panels at 425 W each. The cost of non-residential large scale solar is $2.5/W. Therefore, the system would cost a total of $903,125. Let’s assume that this parking lot is owned by the company you work for and they will pay for half of the cost. The rest of the cost would be paid by all 24 kWh EV users. This means each EV driver would pay $7,000, or $0.79/mile. However, this increases your range from 32 miles/day to essentially 84 miles/day.

In comparison, a 2014 Nissan Altima with, roughly, 34000 miles gets about 30 mpg at a price of $15,000. Let’s assume you drive this vehicle 16,400 miles before any major problem arises. This means you need to buy 547 gallons of gasoline. The average price of gas in California is $2.50 per gallon. Therefore, in gas alone, you spend $1,368. The total of the car is now $16,368 for the first 16,400 miles, or $1/mile. In all likelihood, the Altima will last longer than 16,400 miles, the ICE would need to drive 52,264 miles without any maintenance costs to be $0.37/mile, the cost of driving a rooftop solar powered Nissan Leaf.

Part 2: City of SLO Clean Energy Vehicles


Various Fuels have a known energy density given by Pf=E/Mf
A vehicle requires a certain amount of energy in order to perform its tasks during each duty cycle. We have defined a duty cycle to be the typical actions taken by the vehicle over the course of a single working day. For example, a single duty cycle for a mail truck would be delivering the mail along its standard route. We are choosing to count duty cycles instead of days of operation as certain utility vehicles such garbage trucks do not operate daily.
If we were to consider the minimum effective energy density of the vehicle required for 1 duty cycle, it would be given as P=E/(M+Md)

where Md represents the mass of the drivetrain, and E represents the energy needed to preform 1 duty cycle.
This can be simplified by letting, E=nPfMf where n is the vehicle efficiency and PfMf represents the amount of energy released by consuming the fuel.
So the effective energy density of the vehicle is Pe=(nPf)/(1+Md/Mf)
The effective energy density can be solved for given the usage information of existing utility vehicles, and then be treated as a constant. When evaluating alternative fuels, a reasonable assumption to guide selection is that the utility vehicle must maintain the same effective energy density regardless of fuel type. This ensures that the switching over does not have any adverse performance effects which would limit practicality.
As the effective energy density, the energy density of the fuel, the drivetrain mass, and vehicle efficiencies are all well known, the only unknown variable is the required mass of the alternative fuel.
Once the quantity of fuel is known, a comparison of economics and emission reduction can be preformed.

Garbage Truck:

Type of Fuel Used Diesel Electric B20 B100 LNG
Number of Trucks 14
Daily Distance Traveled (miles) 70
Miles Per Gallon 2.7 0.29mi/kWh 2.73 2.63 1.62
Gallons of Fuel / Month 102 7020kWh 102.6 106.2 173.2
Lbs of CO2 Released / Month 17300 0 13800 13200 13100
Monthly Savings (Over Diesel) $0 $124 $6.96 -$65.9 $3.17

Mail Truck:

Type of Fuel Used Gasoline Electric E85 LNG
Number of Trucks
Daily Distance Traveled (miles)
Miles Per Gallon 10 2mi/kWh 3.03 3.59
Gallons of Fuel / Month 102 450kWh 199 141
Lbs of CO2 Released / Month 2126 0 2140 1743
Monthly Savings (Over Gasoline) 0 $75 -$233 -$97


Type of Fuel Used Diesel Electric B20 B100 LNG
Number of Trucks 16
Daily Distance Traveled (miles) 110
Miles Per Gallon 2.7 0.38mi/kWh 2.69 2.6 1.6
Gallons of Fuel / Month 1210 8615kWh 1225 1250 2040
Lbs of CO2 Released / Month 27100 0 22000 20720 20600
Monthly Savings (Over Diesel) 0 $1369 $38.63 -$780.61 $42.02

For each vehicle type switching to electricity would save money on fuel. Liquefied natural gas and B20 resulted in similar overall fueling costs to the original fuel type. Switching fuels would be slightly cheaper for garbage trucks but slightly more expensive for the mail trucks and buses. Pure biodiesel appears to be the least cost efficient based on national fuel prices. Biodiesel is preferable to diesel in regards to emissions though; lifecycle CO2 emissions of biodiesel are about 74% less than the emissions of diesel [17]. While an electric motor has no regular CO2 emissions from use, there would be some amount of CO2 from the creation of the motor, so lifecycle emissions would be non-zero but still clearly better than any other fuel choice. This information should ideally be passed to SLO city so that they can consider alternative fuels for their vehicle fleets moving forward.

National Average Prices of
Alternative Fuels between
April 1 and April 17, 2017
Fuel Type Fuel Price
Biodiesel (B20) $2.49/gallon
Biodiesel (B99-B100) $3.09/gallon
Electricity $0.12/kWh
Ethanol (E85) $2.11/gallon
Natural Gas (CNG) $2.15/GGE
Liquefied Natural Gas $2.52/DGE
Gasoline $2.38/gallon
Diesel $2.55/gallon

Note: calculations used the price of electricity to be $0.15/kWh which is the standard price for the SLO area.

Suggestions for future project objectives:

This project was a good investigation into comparing Electric and ICE vehicles. Using this project as a starting point, there are several directions in which this project can go. Future recommended objectives for this project are:

1) Construct a direct solar panel to EV charger.
2) Work closely with the city of SLO and use the information on this webpage to help achieve the city’s goals of clean energy vehicles and reduced emissions.
3) Investigate the infrastructure demand for electric vehicles, how much it will cost to install, and where the infrastructure should be installed strategically.

Group members: Roger Dorris, Daniel Baron, Nate DeBruno, Sarah Stephens

Personal Introductions:
Roger Dorris is a 2nd year Physics Major
Daniel Baron is a 4th year Electrical Engineering Student.
Nate DeBruno is a 4th year Electrical Engineering Student.
Sarah Stephens is a 3rd year Computer Engineering major.